Patent Grant
12043888
The present disclosure relates to hardened case-nitrided metal articles and methods of forming the same.
Many metals and metal alloys require a hardening treatment to possess adequate hardness for use in a variety of mechanical applications such as wear parts. Nitriding is an example of a common hardening technique that is utilized in various industries to case-harden metal or metal alloy components. Generally speaking, the nitriding process diffuses nitrogen through the surface of a metal or metal alloy component to produce a thin nitrided case layer that surrounds and is hardened relative to a core of the component. While some metals and metal alloys are rendered to be adequately wear resistant by nitriding to be utilized as mechanical components, other metals and metal alloys are less responsive to nitriding and remain overly prone to wear mechanisms associated with inadequate hardness or case depth for use in many mechanical applications.
Examples of such metals and metal alloys include titanium and titanium alloys. While the nitriding of titanium has been described in literature for over 50 years, current processes for nitriding titanium and titanium alloys produce very thin case depths. Particularly for wear parts such as gears or bearings, the nitrided case depth should be deeper than the stresses experienced by the component during operation to avoid failure. Typically, titanium and titanium alloys that are nitrided by existing techniques do not possess a sufficient case depth to support the subsurface stresses experienced by many wear parts, and thus are not suitable for these applications. Owing to the otherwise excellent material properties of titanium and titanium alloys, including a high strength to weight ratio, many industries have long sought to form various mechanical components from these materials but have been unable to effectively do so because of the inability of existing techniques to achieve adequate effective case depths. Thus, a need exists for improved methods of increasing the hardness of case-nitrided metal or metal alloy articles, methods for increasing the effective case depth of metal or metal alloy articles, as well as case-nitrided metal or metal alloy articles with increased hardness and/or increased effective case depth.
Methods of hardening a case-nitrided metal article, methods of producing a hardened case-nitrided metal article, and hardened case-nitrided metal articles are disclosed herein. The methods of hardening a case-nitrided metal article include heat-aging the case-nitrided metal article, which comprises heating the case-nitrided metal article to an aging temperature, maintaining the case-nitrided metal article at the aging temperature for an aging time, and cooling the case-nitrided metal article from the aging temperature. The methods of producing a hardened case-nitrided metal article include case-nitriding a metal article to produce a case-nitrided metal article and subsequently hardening the case-nitrided metal article, which includes heating the case-nitrided metal article to an aging temperature, maintaining the case-nitrided metal article at the aging temperature for an aging time, and cooling the case-nitrided metal article from the aging temperature. The hardened case-nitrided metal articles comprise a body formed of a metal or a metal alloy, a surface surrounding the body, and a nitrided case layer formed in the body and extending inwardly from the surface of the body toward the core. The hardened case-nitrided metal articles are nitrided by a nitriding process and subsequently hardened by a hardening process. The nitrided case layer of the hardened case-nitrided metal articles comprises a hardness that is greater than an otherwise equivalent case-nitrided metal article that has not been hardened by the heat aging process.
Generally, in the figures, elements that are likely to be included in a given example are illustrated in solid lines, while elements that are optional to a given example are illustrated in dashed lines. However, elements that are illustrated in solid lines are not essential to all examples of the present disclosure, and an element shown in solid lines may be omitted from a particular example without departing from the scope of the present disclosure. In
As shown in
The particular type(s), total amount, relative amount(s), and/or distribution(s) of the nitrogen-containing phase(s) 120 within the nitrided case layer 106 may vary based on the type of metal 108 or metal alloy 110 and the parameters of the nitriding process. In some examples, the heat-aging process alters the type(s), the phase(s), the form(s), the relative amount(s), and/or the distribution(s) of the nitrogen-containing phase(s) 120 within the nitrided case layer 106. Thus, in such examples, the particular type(s), relative amount(s), and/or distribution(s) of the nitrogen-containing phase(s) 120 within the nitrided case layer 106 additionally or alternatively are determined by the heat-aging process. Stated differently, the type(s), the phase(s), the form(s), the relative amount(s), and/or the distribution(s) of the nitrogen-containing phase(s) 120 within the nitrided case layer 106 of hardened case-nitrided metal article 100 may be different from that present in an otherwise equivalent case-nitrided metal article.
As referred to herein, a case-nitrided metal article that is “otherwise equivalent” to a hardened case-nitrided metal article 100 is formed of the same metal or metal alloy, includes the same dimensions, and has been case-nitrided via the same case-nitriding process as the hardened case-nitrided metal article 100 but has not been hardened via the heat-aging process subsequent to the case-nitriding process. Thus, in a more specific example where a single metal article is nitrided and subsequently heat aged, the “otherwise equivalent” case-nitrided metal article describes the material properties subsequent to the nitriding process and prior to the heat-aging process.
As further shown in
Hardened case-nitrided metal article 100 is formed from any suitable metal 108 or metal alloy 110. As utilized herein, a metal 108 refers to a pure or elemental metal that may include incidental impurities, and a metal alloy 110 includes a mixture of at least one metal and at least one other metal and/or one or more non-metallic elements. As used to herein, the hardened case-nitrided metal article 100 being formed of a metal 108 or metal alloy 110 means that the metal article from which the hardened case-nitrided metal article 100 is formed, consists of, or consists essentially of, the metal 108 or metal alloy 110. As such, even when core 112 of hardened case-nitrided metal article 100 is formed of a metal 108, nitrided case layer 106 may be regarded as being a metal alloy 110 owing to the diffused nitrogen content.
In some examples, the metal 108 or metal alloy 110 that forms hardened case-nitrided metal article 100 is selected to further harden via a heat-aging process subsequent to being nitrided. As discussed in more detail herein, in some examples, the heat-aging process comprises precipitation-hardening the nitrided case layer 106. As such, in some examples, hardened case-nitrided metal article 100 is formed of a precipitation-hardening metal or a precipitation-hardening metal alloy. In some examples, the metal 108 or metal alloy 110 that forms hardened case-nitrided metal article 100 is selected to be compatible with solution treatment and heat-aging. In some examples, the metal 108 or metal alloy 110 that forms hardened case-nitrided metal article 100 is selected to be compatible with nitriding. As more specific examples, hardened case-nitrided metal article 100 may be formed of an iron alloy, a steel, stainless steel, and/or a titanium alloy. More specific examples of suitable titanium alloys include a Ti—Al—V—Mo—Cr alloy, Ti-5Al-5V-5Mo-3Cr (Ti-5553), a Ti—Al—V alloy, and/or Ti-6Al-4V (Ti-64).
When hardened case-nitrided metal article 100 is formed of a titanium alloy, hardened case-nitrided metal article 100 may be referred to herein as hardened case-nitrided titanium alloy article 100. Likewise, when hardened case-nitrided metal article 100 is formed of Ti-5553, hardened case-nitrided metal article 100 may be referred to herein as hardened case-nitrided Ti-5553 article 100.
In addition to the hardening process, the nominal hardness of nitrided case layer 106 of hardened case-nitrided metal article 100 may depend upon the type of metal 108 or metal alloy 110 that forms hardened case-nitrided metal article 100, the depth from the surface 104, and the parameters or type of nitriding process that is utilized for the case-nitriding. Generally speaking, case-nitriding is performed to harden the surface or outermost layer of a metal article. Thus, the nitrided case layer 106 of a case-nitrided metal article and of hardened case-nitrided metal article 100 typically possesses a hardness that is greater than the hardness of the core 112. Typically, the hardness of the nitrided case layer 106 decreases at greater depths towards the core 112.
As mentioned, the hardening process increases the hardness of the nitrided case layer 106. Thus, the nitrided case layer 106 of hardened case-nitrided metal article 100 has a hardness that is greater than the hardness of the nitrided case layer 106 of an otherwise equivalent case-nitrided metal article. In particular, at least a portion of, and in some examples, the entirety of, the nitrided case layer 106 of hardened case-nitrided metal article 100 is harder than the nitrided case layer 106 of an otherwise equivalent case-nitrided metal article. More specifically, the hardness of the hardened case-nitrided metal article at a given depth may be greater than a hardness of the nitrided case layer of the otherwise equivalent case-nitrided metal article at the given depth.
As a more specific example, the hardened case-nitrided metal article 100 has a second hardness measured at a given depth within the nitrided case layer 106, the otherwise equivalent case-nitrided metal article has a first hardness measured at the given depth within its respective nitrided case layer, and the second hardness of the hardened case-nitrided metal article 100 is greater than the first hardness of the otherwise equivalent case-nitrided metal article. In some examples, the second hardness of the hardened case-nitrided metal article is a threshold fraction of the first hardness of the otherwise equivalent case-nitrided metal article, with examples of the threshold fraction of the first hardness to the second hardness including at least 1.1, at least 1.2, at least 1.3, at least 1.4, at least 1.5, at least 1.6, at least 1.7, at least 2, at most 1.2, at most 1.3, at most 1.4, at most 1.5, at most 1.6, at most 1.7, at most 1.8, at most 1.9, at most 2, and/or at most 3.
In some examples, an age hardening process also hardens the core 112 of body 102. In some examples, hardened case-nitrided metal article 100 includes a core hardness that is greater than a core hardness of an otherwise equivalent case-nitrided metal article. As referred to herein, a core hardness refers to the hardness of core 112, the hardness of interior region of body 102 that is not nitrided, or the hardness of body 102 at a depth that is beyond the nitrogen diffusion boundary 118. In some examples the core hardness is measured at the geometric center of a metallurgical cross-section of body 102. In some examples, the core hardness of hardened case-nitrided metal article 100 is a threshold fraction of the core hardness of an otherwise equivalent case-nitrided metal article, with examples of the threshold fraction including at least 1.2, at least 1.3, at least 1.4, at least 1.5, at least 1.6, at least 1.7, at least 1.8, at most 1.5, at most 1.6, at most 1.7, at most 1.8, at most 1.9, and at most 2.0.
In the present disclosure, hardness may be measured and/or reported in any suitable manner. As examples, the harnesses discussed herein may include Rockwell hardness, Rockwell C hardness (HRC), Rockwell 15N hardness (HRN 15), Vickers hardness (VH), and/or Brinell hardness (BH). Effective case depth 114 is another metric that may be utilized herein for discussing the hardness of nitrided case layer 106, hardened case-nitrided metal article 100, and a case-nitrided metal article. Effective case depth 114 is defined herein as the depth from surface 104 that the hardness of body 102 is greater than or equal to HRC 50. As shown in
In some examples, hardened case-nitrided metal article 100 includes an effective case depth 114 that is greater than the effective case depth 114 of an otherwise equivalent case-nitrided metal article. As examples, the effective case depth 114 of hardened case-nitrided metal article 100 may be at least 0.25 millimeters (mm), at least 0.45 mm, at least 0.5 mm, at least 0.55 mm, at least 0.6 mm, at least 0.65 mm, at least 0.7 mm, at most 0.8 mm, at most 0.9 mm, and at most 1 mm. As more examples, the effective case depth 114 of hardened case-nitrided metal article 100 may be greater than the effective case depth 114 of an otherwise equivalent case-nitrided metal article by at least 0.25 mm, at least 0.45 mm, at least 0.5 mm, at least 0.55 mm, at least 0.6 mm, at least 0.65 mm, at least 0.7 mm, at most 0.8 mm, at most 0.9 mm, at most 1 mm, and/or at most 1.5 mm. In some examples, the otherwise equivalent case-nitrided metal article does not achieve an effective case depth 114 as defined herein, in which case the entirety of the effective case depth 114 of the hardened case-nitrided metal article 100 is taken to be an increase over the otherwise equivalent case-nitrided metal article. As a more specific example, when hardened case-nitrided metal article 100 is formed of Ti-5553, hardened case-nitrided metal article 100 may include an effective case depth 114 of at least 0.25 mm, at least 0.45 mm, at least 0.5 mm, at least 0.55 mm, at least 0.6 mm, at least 0.65 mm, at least 0.7 mm, at most 0.8 mm, at most 0.9 mm, and at most 1 mm.
With continued reference to
As shown in
As further shown in
Traditionally, some metals and metal alloys have been excluded from use in certain wear parts owing to their inadequate hardness and thereby inability to adequately resist the various mechanisms of wear, such as those discussed above. As a more specific example, titanium and certain titanium alloys, including Ti-5553, typically cannot be utilized as or in many wear parts such as gears as a result of inadequate hardness. Even when case-nitrided, some metals and metal alloys, such as case-nitrided titanium, case-nitrided titanium alloys, and case-nitrided Ti-5553 typically possess inadequate hardness or inadequate case depth to be utilized as or in many wear parts, and more specifically gears.
By contrast, hardened case-nitrided metal articles 100, hardened case-nitrided titanium alloy articles 100, and/or hardened case-nitrided Ti-5553 articles 100 may possess sufficient hardness or effective case depth 114 to be utilized as or in such wear parts, and specifically gears. More generally, hardened case-nitrided metal articles 100, according to the present disclosure, may allow wear parts to be formed of metals and metal alloys that were not previously possible with traditional hardening techniques, such as nitriding alone. In particular, hardened case-nitrided metal articles 100, hardened case-nitrided titanium alloy articles 100, and/or hardened case-nitrided Ti-5553 articles according to the present disclosure may possess adequate hardness and/or adequate effective case depth to be sufficiently resistant to the above-discussed wear mechanisms and as such, to be utilized as or in wear parts. As a more specific example, hardened case-nitrided metal articles 100, hardened case-nitrided titanium alloy articles 100, and/or hardened case-nitrided Ti-5553 articles 100 may possess sufficient hardness and/or effective case depth 114 to be utilized in various aerospace applications that previously were not possible with components formed of corresponding metals or metal alloys and/or case-nitrided analogues thereof.
In some examples, the increased effective case depth 114 of hardened case-nitrided metal articles 100, hardened case-nitrided titanium alloy articles 100, and/or hardened case-nitrided Ti-5553 articles 100 prevents failures, such as via pitting, galling, etc., that otherwise would occur due to shallow case depths. In this way, hardened case-nitrided metal articles 100, hardened case-nitrided titanium alloy articles 100, and/or hardened case-nitrided Ti-5553 articles 100 may not fail, or fail as readily, via pitting, galling, etc. as would an otherwise equivalent case-nitrided metal article having a shallower case depth. In a more specific example, the effective case depth 114 of hardened case-nitrided metal articles 100, hardened case-nitrided titanium alloy articles 100, and/or hardened case-nitrided Ti-5553 articles 100 is greater than the spalling depth of the corresponding wear part 200, such as a gear. In such an example, a hardened case-nitrided gear 202, a hardened case-nitrided titanium alloy gear 202, and/or a hardened case-nitrided Ti-5553 gear 202, according to the present disclosure, may not fail via spalling as would an otherwise equivalent case-nitrided gear, an otherwise equivalent case-nitrided titanium alloy gear, and/or an otherwise equivalent case-nitrided Ti-5553 gear respectively.
In some examples, hardened case-nitrided metal articles 100, hardened case-nitrided wear parts 200, and/or hardened case-nitrided gears 202 illustrated and discussed herein with reference to
Methods 500 may include hardening case-nitrided metal articles 90, case-nitrided wear parts 201, and/or case-nitrided gears 203 to produce the hardened case-nitrided metal articles 100, the hardened case-nitrided wear parts 200, and/or the hardened case-nitrided gears 202 that are illustrated and discussed herein with reference to
As shown in
Methods 500 are performed on any suitable case-nitrided metal article 90, such as one formed of any of the metals 108 or metal alloys 110 discussed herein. In some examples, the metal 108 or metal alloy 110 that forms the case-nitrided metal article is selected to be compatible with precipitation hardening. In some examples, the metal 108 or metal alloy 110 that forms the case-nitrided metal article is selected to be compatible with solution treatment and heat-aging. In some examples, the case-nitrided metal article is formed from a metal 108 or a metal alloy 110 that is compatible with case-nitriding.
In some examples, the case-nitrided metal article is a case-nitrided wear part and/or a case-nitrided gear. In some examples, the case-nitrided metal article is case-nitrided and/or formed by performing one or more of the steps of methods 600 as discussed in more detail herein. As referred to herein, a “case-nitrided” metal article refers to a metal article that has been case-nitrided, that has been taken through a case-nitriding process, and not necessarily a metal article that includes metal nitrides.
In some examples, methods 500 are performed utilizing a heat-aging system 400, illustrative non-exclusive examples of which are shown in
In some examples, heat-aging chamber 402 is configured to receive a plurality of case-nitrided metal articles 90. In some examples, heat-aging chamber 402 is sealable such as to prevent unwanted gasses from entering heat-aging chamber 402 during the heat-aging at 515. Heat-aging system 400 further includes a heating system 404 configured to heat the at least one case-nitrided metal article 90 positioned within the heat-aging chamber 402. Examples of suitable heat-aging systems 400 include resistive heating systems and/or inductive heating systems. In some examples, heat-aging system 400 includes a vacuum system 406 configured to evacuate, remove gas from, and/or reduce the pressure in heat-aging chamber 402. In some examples, heat-aging system 400 further includes an atmosphere supply system 408 configured to supply a heat-aging atmosphere to the heat-aging chamber, such as one or more inert gasses. Thus, in some examples, heat-aging system 400 is referred to as vacuum furnace.
As shown in
In some examples, methods 500 further include applying a heat-aging atmosphere to the heat-aging chamber at 510. In some examples, the applying at 510 comprises removing air, oxygen gas, and/or other potential contaminants from the heat-aging chamber 402. In some examples, the applying at 510 comprises evacuating or reducing the pressure of the heat-aging chamber 402, such as by utilizing vacuum system 406. Additionally or alternatively, in some examples, the applying at 510 comprises supplying one or more inert gasses, such as nitrogen gas and/or argon gas, to the heat-aging chamber 402, such as by utilizing the atmosphere supply system 408. In some examples, the applying at 510 includes pump-purging the heat-aging chamber or repeatedly evacuating and supplying the one or more inert gasses to the heat-aging chamber to thoroughly remove any air, oxygen, and/or other potential contaminants from the heat-aging chamber 402. In some examples, the applying at 510 includes applying a negative pressure to the heat-aging chamber 402 such as to seal the heat-aging pressure. As referred to herein, a negative pressure refers to a pressure that is less than a standard pressure, and/or less than an ambient pressure or the pressure of the atmosphere surrounding the heat-aging chamber. In a more specific example, the applying at 510 comprises evacuating the heat-aging chamber to a pressure of that is at least 80%, at least 90%, at most 90%, at most 95%, and/or at most 99% of the standard pressure.
In some examples, the applying at 510 comprises maintaining the heat-aging atmosphere during at least a portion of the heat-aging at 515 such as to prevent oxygen and/or other contaminates from entering the heat-aging chamber 402 during the heat-aging at 515. More specifically, in some examples, the maintaining is performed during the heating at 520, during the maintaining at 525, and optionally during the cooling at 530. In some examples, the applying at 510 comprises maintaining, during at least a portion of the heat-aging at 515, the heat-aging chamber 402 at the negative pressure and/or continually supplying the heat-aging atmosphere to the heat-aging chamber during the heat-aging 515.
When included, the applying at 510 is performed with any suitable sequence or timing within methods 500, such as subsequent to the positioning at 505, prior to the heat-aging at 515, and/or at least substantially simultaneously with the heat-aging at 515.
With continued reference to
In some examples, the heating at 520 comprises directly heating the case-nitrided metal article 90 (e.g., via induction). Additionally or alternatively, in some examples, the heating at 520 comprises heating the atmosphere surrounding the case-nitrided metal article 90 to heat the case-nitrided metal article 90 to the heat-aging temperature. For some examples in which methods 500 include the positioning at 505, the heating at 520 comprises heating the case-nitrided metal article 90 with the heating system 404, such as directly or indirectly. In some such examples, the heating at 520 comprises heating the heat-aging atmosphere to heat the case-nitrided metal article to the heat-aging temperature.
The heat-aging temperature may be selected based upon the type of metal 108 or metal alloy 110 from which the case-nitrided metal article is formed. The heat-aging temperature is selected to be less than the melting point of the metal 108 or metal alloy 110 from which the case-nitrided metal article 90 is formed. In some examples, the heat-aging temperature is selected to be less than a nitriding temperature that is discussed in more detail herein.
In some examples, the heat-aging temperature is selected to be at least a threshold minimum temperature that is required to facilitate or induce microstructural changes within the nitrided case layer 106, and optionally the core, 112 that increase the hardness thereof. In some examples, the heat-aging temperature is, or is at least substantially similar to, the age-hardening, precipitation hardening, or particle hardening temperature of the metal 108 or metal alloy 110 from which the case-nitrided metal article 90 is formed. In some examples, the heat-aging temperature is less than the solution treatment temperature of the metal 108 or metal alloy 110 from which the case-nitrided metal article 90 is formed. In some examples, the heat-aging temperature is at least a minimum activation temperature for inducing precipitation within the nitrided case layer 106. As more specific examples, when the case-nitrided metal article 90 is formed of Ti-5553, the heat-aging temperature may be at least 300 degrees Celsius (° C.), at least 400° C., at least 450° C., at least 475° C., at least 500° C., at least 525° C., at least 535° C., at least 540° C., at least 560° C., at least 580° C., at least 600° C., at least 650° C., at most 525° C., at most 535° C., at most 540° C., at most 560° C., at most 580° C., at most 600° C., at most 650° C., at most 700° C., and/or at most 800° C.
The heating at 520 is performed with any suitable sequence or timing within methods 500, such as prior to the maintaining at 525, prior to the cooling at 530, subsequent to the positioning at 505, subsequent to the applying at 510, and/or at least substantially simultaneously with the applying at 510.
With continued reference to
The maintaining at 520 is performed with any suitable sequence or timing within methods 500, such as subsequent to the positioning at 505, subsequent to and/or at least substantially simultaneously with the applying at 510, subsequent to the heating at 520, and/or prior to the cooling at 530.
The heat-aging at 515 further includes cooling the case-nitrided metal article from the heat-aging temperature at 530. In some examples, the cooling at 530 comprises cooling the case-nitrided metal article to an ambient temperature or to room temperature. In some examples, the cooling at 530 comprises passively cooling and/or air cooling the case-nitrided metal article. In some such examples, the cooling at 530 comprises removing the case-nitrided metal article from heat-aging chamber 402 and placing the case-nitrided metal article 90 in an atmosphere that is at room temperature. Thus, in some examples, the cooling at 530 is performed with the case-nitrided metal article removed from the heat-aging atmosphere and/or under air. Alternatively, in some examples, the cooling at 530 is performed while the case-nitrided metal article 90 is within the heat-aging chamber 402, such as by turning off ceasing heating with the heating system 404 and permitting the case-nitrided metal article 90 to cool within the heat-aging chamber. In some examples, the cooling at 530 comprises rapidly cooling the case-nitrided metal article 90, such as by placing the case-nitrided metal article 90 in water.
The cooling at 530 is performed with any suitable sequence or timing within methods 500, such as subsequent to the maintaining at 525, subsequent to the applying at 510, and/or at least substantially simultaneously with the applying at 510.
When methods 500 include the positioning at 505, at least the heating 520 and the maintaining at 525, and optionally the cooling at 530, of the heat-aging at 515 is performed with the case-nitrided metal article positioned within the heat-aging chamber. Likewise, for some examples in which methods 500 include the applying at 510, at the least the heating at 520 and the maintaining at 525, and optionally the cooling at 530, of the heat-aging at 515 are performed with the case-nitrided metal article 90 within the heat-aging atmosphere.
As discussed herein, the case-nitrided metal article 90 includes a nitrided case layer 106 extending inwardly from the surface 104 of case-nitrided metal article towards the core 112 of the case-nitrided metal article 90. The heat-aging at 515 comprises increasing the hardness of the nitrided case layer 106. In other words, the heat-aging at 515 comprises producing a hardened case-nitrided metal article 100 from the case-nitrided metal article 90. Thus, subsequent to the heat-aging at 515, the case-nitrided metal article 90 is a hardened case-nitrided metal article 100. In some examples, the heat-aging at 515 comprises facilitating microstructural changes within the nitrided case layer that increase the hardness thereof. In some examples, the heat-aging at 515 comprises precipitation hardening the nitrided case layer. More specifically, in some examples, the heat-aging at 515 comprises forming precipitates within the nitrided case layer 106 that increase the hardness and/or yield strength thereof. In some examples, the heat-aging at 515 comprises increasing a wear resistance of the case-nitrided metal article, such that the resulting hardened case-nitrided metal article 100 includes an increased resistance to any of the wear mechanisms discussed herein.
In some examples, the heat-aging at 515 includes increasing the effective case depth of the nitrided case layer 106. More specifically, in some examples the heat-aging at 515 includes increasing the effective depth of the nitrided case layer 106 by at least one of least 0.25 mm, at least 0.45 mm, at least 0.5 mm, at least 0.55 mm, at least 0.6 mm, at least 0.65 mm, at least 0.7 mm, at most 0.8 mm, at most 0.9 mm, and/or at most 1 mm.
In some examples, the nitrided case layer 106 comprises a first hardness at a given depth within the nitrided case layer prior to the heat-aging at 515 and comprises a second hardness at the given depth within the nitrided case layer 106 subsequent to the heat aging at 515, in which the second hardness is greater than the first hardness. In some examples, the second hardness is a threshold fraction of the first hardness. Examples of the threshold fraction of the first hardness to the second hardness include at least 1.1, at least 1.2, at least 1.3, at least 1.4, at least 1.5, at least 1.6, at least 1.7, at most 1.2, at most 1.3, at most 1.4, at most 1.5, at most 1.6, at most 1.7, at most 1.8, at most 1.9, and/or at most 2.
In some examples, the heat-aging at 515 comprises increasing a core hardness of the core 112 of the case-nitrided metal article 90. In some examples, the heat-aging at 515 comprises precipitation hardening the core 112 of the case-nitrided metal article 90. In particular, in some examples, the core 112 of the case-nitrided metal article 90 includes a first core hardness prior to the heat-aging at 515 and comprises a second core hardness subsequent to the heat-aging at 515, in which the second core hardness is greater than the first core hardness. In some examples, the second core hardness is a threshold fraction of the first core hardness, with examples of the threshold fraction including at least 1.2, at least 1.3, at least 1.4, at least 1.5, at least 1.6, at least 1.7, at least 1.8, at most 1.5, at most 1.6, at most 1.7, at most 1.8, at most 1.9, and/or at most 2.
With continued reference to
Methods 600 may include producing the hardened case-nitrided metal articles 100, the hardened case-nitrided wear parts 200, and/or the hardened case-nitrided gears 202 that are illustrated and discussed herein with reference to
As shown in
Methods 600 may be performed on any suitable metal article. More specifically, the metal 108 or metal alloy 110 which from the metal article is formed may be selected based upon the same factors as those discussed herein with reference to
As shown in
Methods 600 include case-nitriding the metal article to produce a case-nitrided metal article at 610. In some examples, the metal article is a wear part or a gear, such that the case-nitriding at 610 includes case-nitriding a wear part to produce a case-nitrided wear part 201 therefrom and/or case-nitriding a gear to produce a case-nitrided gear 203 therefrom.
The case-nitriding at 610 includes case-nitriding the metal article via any suitable process. In some examples, the case-nitriding at 610 includes gas-nitriding the metal article. Additionally or alternatively, in some examples, the case-nitriding at 610 includes plasma nitriding the metal article. Examples of suitable methods by which the case-nitriding at 610 may be carried out as well as suitable apparatuses with which the case-nitriding at 610 may be performed are disclosed in U.S. Pat. No. 8,496,872; the entirety of which is incorporated herein by reference.
As shown in
In some examples, methods 600 include providing a nitriding atmosphere to the nitriding chamber at 620. In some examples, the providing at 620 is performed subsequent to the positioning at 615. In some examples, the providing at 620 comprises providing a nitrogen-containing gas to the nitriding chamber, such as by utilizing the gas delivery system. Examples of suitable nitrogen-containing gasses include nitrogen gas and ammonia gas. In some examples, the providing at 620 includes evacuating the nitriding chamber, such as by utilizing the vacuum system, and subsequently providing a nitrogen-containing gas to the nitriding chamber. In some examples, the evacuating comprises reducing the pressure of the nitriding chamber to be at most at least 0.01 Torr, at most 0.02 Torr, at most 0.5 Torr, and/or at most 1 Torr. In some examples, the evacuating is performed to remove air, oxygen gas, and/or any other potential contaminants from the nitriding chamber.
In some examples, the providing at 620 comprises pump-purging or repeatedly evacuating the nitriding chamber and supplying the nitrogen-containing gas to the nitriding chamber, such as at least 2 times, at least 3 times, at least 4 times, at least 5 times and/or at most 10 times. In some examples, the nitriding chamber is filled with the nitrogen-containing gas at a pressure of at least 600 Torr, least 700 Torr, at most 700 Torr, at most 750 Torr, and/or at most 760 Torr subsequent to the providing at 620. However, higher or lower pressures of the nitrogen-containing gas may be utilized without departing from the scope of the present disclosure. In some examples, the providing at 620 comprises maintaining the pressure of the nitrogen-containing gas within the nitriding chamber during heating at 625, maintaining at 630, and optionally during cooling at 635.
With continued reference to
The nitriding temperature may be selected based upon the type of metal 108 or metal alloy 110 from which the metal article is formed. In some examples, the nitriding temperature is a threshold fraction of a melting point of the metal 108 or metal alloy 110 from which the metal article is formed, such as in the range of at least 60% to at most 99% of the melting point of the metal 108 or metal alloy 110. In some examples, the nitriding temperature is selected to be within a solution treatment temperature range of the metal 108 or metal alloy 110. In particular, for some examples in which the metal article is formed of ferrous metal alloys, the nitriding temperature is selected to be within the austenitizing or solution treatment temperature range for the particular ferrous metal alloy. Similarly, for some examples in which the metal article is formed of a titanium alloy, the nitriding temperature is selected to be within the solution treatment temperature of the particular titanium alloy.
As more specific examples, when the metal article is formed of titanium, the nitriding temperature is in the range of 1,000° C. to 1,600° C. For examples in which the metal article is formed of Ti-5553, the nitriding temperature is at least 1,000 degrees ° C., at least 1,100° C., at least 1,200° C., at least 1,300° C., at least 1,325° C., at least 1,350° C., at least 1,375° C., at least 1400° C., at least 1,425° C., at least 1,450° C., at least 1,475° C., at least 1,500° C., at least 1,525° C., at most 1,325° C., at most 1,350° C., at most 1,375° C., at most 1,400° C., at most 1,425° C., at most 1,450° C., at most 1,475° C., at most 1,500° C., at most 1,525° C., and/or at most 1,600° C.
In some examples, the case-nitriding at 610 further comprises maintaining the portion of the metal article at the nitriding temperature for a nitriding time. In some examples, the nitriding time is selected based upon the particular type of nitriding process, a desired total case depth of the nitrided case layer, and/or the type of metal 108 or metal alloy 110 from which the metal article is formed. Examples of suitable nitriding times include at least 3 minutes, at least 5 minutes, at least 8 minutes, at least 10 minutes, at least 15 minutes, at least 20 minutes, at most 8 minutes, at most 10 minutes, at most 15 minutes, at most 20 minutes, at most 30 minutes, and at most 40 minutes. As yet more specific examples, for some examples in which the metal article is formed of Ti-5553 and the heating at 625 and the maintaining at 630 is performed with an induction heater or via induction heating, the nitriding time is at least one of at least 4 minutes, at least 5 minutes, at least 8 minutes, at most 8 minutes, at most 10 minutes, and/or at most 12 minutes.
When included in the case-nitriding at 610, the maintaining at 630 is performed subsequent to the heating at 625 and prior to the cooling at 635.
With continued reference to
For some examples in which the heating at 625 and/or the maintaining at 630 are performed in the nitriding chamber, the cooling at 635 comprises removing the metal article from the nitriding chamber and/or at least a portion of the cooling at 635 is performed with the metal article removed from the nitriding chamber. In some examples, the cooling at 635 is performed at a rate that is selected based upon the metal 108 or metal alloy 110 from which the metal article is formed and/or based upon the nitriding temperature. In some examples, the cooling at 635 comprises cooling the portion of the metal article at a rate that is equivalent to or faster than air-cooling. In some such examples, the cooling at 635 includes air-cooling the metal article such as discussed herein. In other such examples, the cooling at 635 includes quenching in water or placing the metal article in a body of water. In such examples, the cooling at 635 comprises rapidly cooling the portion of the metal article at a rate that is faster than air-cooling.
Regardless of the particular type of nitriding performed and/or the particular combination of steps included in the case-nitriding at 610, the case-nitriding at 610 comprises diffusing nitrogen into the case of the metal article to form one or more nitrogen-containing phases therein. As such, in each example, the case-nitriding at 610 comprises forming the nitrided case layer 106 in the metal article. Additionally, the case-nitriding at 610 comprises hardening the case and the surface of the metal article. Thus, subsequent to the case-nitriding at 610, the metal article may be referred to herein as a case-nitrided metal article 90.
With continued reference to
The hardening at 500 is performed subsequent to the case-nitriding at 610. Thus, for examples in which the case-nitriding at 610 includes cooling at 635, the hardening at 500 is performed subsequent to the cooling at 635. In this way, the heating at 520 of the hardening at 500 includes heating the case-nitrided metal article from the reduced temperature.
As discussed herein, the hardening at 500 includes increasing the hardness of the nitrided case layer 106 of the case-nitrided metal article 90, and optionally increasing the hardness of the core 112 of the case-nitrided metal article 90. As such, the hardening at 500 may include hardening the case-nitrided metal article 90 produced during the case-nitriding at 610 in any manner to that discussed herein with reference to
In some examples, each step of methods 600 is performed by a single entity or party. In other examples, two or more steps of methods 500 are performed by two or more different entities or parties. For example, the case-nitriding at 610 and the hardening at 500 may be performed by the same entity or party, such as in the same factory, manufacturing environment and/or utilizing the same apparatus. In other examples, the case-nitriding at 610 and the hardening at 500 are performed by separate entities or parties, such as in separate factories, manufacturing environments, and/or apparatuses.
Further, it is within the scope of the present disclosure that methods 600 are performed with any suitable duration of time separating the case nitriding at 610 and the hardening at 500. In some examples, the hardening at 500 is performed immediately after, or as soon as possible after, the case-nitriding at 610, such as immediately after, or as soon as possible after, the case-nitrided metal article 90 is cooled to the reduced temperature. Alternatively, in some examples, the hardening at 500 is performed a significant time after the case-nitriding at 610. More specifically, in some examples, the hardening at 500 is performed hours, days, weeks, months, and/or even years after the case-nitriding at 610.
For examples in which the case-nitriding at 610 comprises case-nitriding the wear part to produce a case-nitrided wear part 201, the hardening at 500 comprises hardening the case-nitrided wear part 201 to produce a hardened case-nitrided wear part 200, such as discussed herein. Likewise, for examples in which the case-nitriding at 610 comprises case-nitriding the gear to produce a case-nitrided gear 203, the hardening at 500 comprises hardening the case-nitrided gear 203 to produce a hardened case-nitrided gear 202, such as discussed herein.
As shown in
As further shown in
Now with reference to
As depicted, Table 7 includes the Test results: Test 1, Test 2, Test 3, Test 4, Test 5, Test 6, Test 7, Test 8, Test 9, and Test 10. Each Test result was gathered from a 0.5-inch diameter cylindrical Ti-5553 Rod. Test 1, Test 3, Test 5, Test 7, and Test 9 include measurements of Ti-5553 Rods that were case-nitrided, while Test 2, Test 4, Test 6, Test 8, and Test 10 include the Test results of Ti-5553 Rods that were case-nitrided and subsequently hardened.
The Test results depicted in
During the case-nitriding, Rod 702 was heated to and maintained at a nitriding temperature of 1,325° C., Rod 704 was heated to and maintained at a nitriding temperature of 1,375° C., Rod 706 was heated to and maintained at a nitriding temperature of 1,425° C., Rod 708 was heated to and maintained at a nitriding temperature of 1,475° C., and Rod 710 was heated and maintained at a nitriding temperature of 1,500° C.
After cooling to room temperature, each Rod was mechanically sectioned radially at its longitudinal center for pre-hardening and post-hardening evaluation. In particular, one half of each Rod was saved for testing the effects of the nitriding process alone. The other half of each Rod subsequently was hardened according to the following procedure. The five Rod halves were placed in a vacuum furnace, and the vacuum furnace was closed. The pressure within the closed vacuum furnace then was reduced to just below atmospheric pressure to ensure that the vacuum furnace remained sealed during the hardening. The Rod halves then were heated to 593.3° C. within the vacuum furnace and maintained at 593.3° C. for 8.5 hours. The vacuum furnace and the Rods then were allowed to passively cool to room temperature and the Rods were removed for testing.
After the above-discussed treatment, metallographic cross-sections were taken through each Rod half for microhardness traverses (measured in HRC) and corresponding effective case depth (ECD) determination. Core hardness measurements (measured in HRC) were performed at the center of each Rod half, and surface hardness (measured in HRN 15N) were performed on the outer diameter of each Rod half. Metallurgical examination revealed a film of porous titanium nitride on the surface of each Rod half, which ranged from 0.001 inches in depth for Rod 702 to 0.0064 inches for Rod 710. To avoid the titanium nitride layer, all microhardness traverses were initiated approximately 0.003 inches from the bottom of the titanium nitride layer.
In Table 700, the Tests demonstrate the hardness measured for each Rod before and after hardening at a series of depths between 0.003-0.055 inches from the surface of the Rod. Table 7 also demonstrates the effective case depth as defined herein, the core hardness, the surface hardness, and the thickness of the porous titanium nitride layer of each Rod before and after hardening. In Table 7, all depths and thicknesses are reported in inches, surface hardness was measured and is reported in HRN 15N, and all other hardnesses were measured and are reported in HRC.
Test 1 includes these measurements for Rod 702 prior to hardening and Test 2 includes these measurements for Rod 702 subsequent to hardening. In other words, Test 1 includes measurements taken on the half of Rod 702 that was not hardened, and Test 2 includes measurements taken on the half of Rod 702 that was hardened. Test 3 includes these measurements for Rod 704 prior to hardening and Test 4 includes these measurements for Rod 704 subsequent to hardening. Test 5 includes these measurements for Rod 706 prior to hardening and Test 6 includes these measurements for Rod 706 subsequent to hardening. Test 7 includes these measurements for Rod 708 prior to hardening and Test 8 includes these measurements for Rod 708 subsequent to hardening. Test 9 includes these measurements for Rod 710 prior to hardening and Test 10 includes these measurements for Rod 710 subsequent to hardening.
As shown in Table 700, the hardening process increased the hardness of each Rod at depths between 0.003-0.055 inches from the surface by at least 5 HRC and as much as 18 HRC. All Rod halves that were not hardened subsequent to the case-nitriding process failed to reach the desired effective case depth, while the Rods halves that were hardened subsequent to the case-nitriding process demonstrated effective case depths in the range of 0.011 inches to 0.0274 inches, with the effective case depth increasing along with the nitriding temperature. The case-nitrided and hardened Rod halves also exhibited increased core hardness as compared to the non-hardened counterparts.
Turning to
Illustrative, non-exclusive examples of inventive subject matter according to the present disclosure are described in the following enumerated paragraphs:
E3. The hardened case-nitrided titanium alloy article (100) of any of paragraphs E-E2, wherein the hardened case-nitrided titanium alloy article (100) is, or is included in, a wear part (200).
As used herein, the phrase, “for example,” the phrase, “as an example,” and/or simply the term “example,” when used with reference to one or more components, features, details, structures, embodiments, and/or methods according to the present disclosure, are intended to convey that the described component, feature, detail, structure, embodiment, and/or method is an illustrative, non-exclusive example of components, features, details, structures, embodiments, and/or methods according to the present disclosure. Thus, the described component, feature, detail, structure, embodiment, and/or method is not intended to be limiting, required, or exclusive/exhaustive; and other components, features, details, structures, embodiments, and/or methods, including structurally and/or functionally similar and/or equivalent components, features, details, structures, embodiments, and/or methods, are also within the scope of the present disclosure.
As used herein, the terms “selective” and “selectively,” when modifying an action, movement, configuration, or other activity of one or more components or characteristics of an apparatus, mean that the specific action, movement, configuration, or other activity is a direct or indirect result of one or more dynamic processes, as described herein. The terms “selective” and “selectively” thus may characterize an activity that is a direct or indirect result of user manipulation of an aspect of, or one or more components of, the apparatus, or may characterize a process that occurs automatically, such as via the mechanisms disclosed herein.
As used herein, the terms “adapted” and “configured” mean that the element, component, or other subject matter is designed and/or intended to perform a given function. Thus, the use of the terms “adapted” and “configured” should not be construed to mean that a given element, component, or other subject matter is simply “capable of” performing a given function but that the element, component, and/or other subject matter is specifically selected, created, implemented, utilized, programmed, and/or designed for the purpose of performing the function. It is also within the scope of the present disclosure that elements, components, and/or other recited subject matter that is recited as being adapted to perform a particular function may additionally or alternatively be described as being configured to perform that function, and vice versa. Similarly, subject matter that is recited as being configured to perform a particular function may additionally or alternatively be described as being operative to perform that function.
As used herein, the term “and/or” placed between a first entity and a second entity means one of (1) the first entity, (2) the second entity, and (3) the first entity and the second entity. Multiple entries listed with “and/or” should be construed in the same manner, i.e., “one or more” of the entities so conjoined. Other entities optionally may be present other than the entities specifically identified by the “and/or” clause, whether related or unrelated to those entities specifically identified. Thus, as a non-limiting example, a reference to “A and/or B,” when used in conjunction with open-ended language such as “comprising,” may refer, in one example, to A only (optionally including entities other than B); in another example, to B only (optionally including entities other than A); in yet another example, to both A and B (optionally including other entities). These entities may refer to elements, actions, structures, steps, operations, values, and the like.
As used herein, the phrase “at least one,” in reference to a list of one or more entities should be understood to mean at least one entity selected from any one or more of the entities in the list of entities, but not necessarily including at least one of each and every entity specifically listed within the list of entities and not excluding any combinations of entities in the list of entities. This definition also allows that entities may optionally be present other than the entities specifically identified within the list of entities to which the phrase “at least one” refers, whether related or unrelated to those entities specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) may refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including entities other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including entities other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other entities). In other words, the phrases “at least one,” “one or more,” and “and/or” are open-ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions “at least one of A, B, and C,” “at least one of A, B, or C,” “one or more of A, B, and C,” “one or more of A, B, or C,” and “A, B, and/or C” may mean A alone, B alone, C alone, A and B together, A and C together, B and C together, A, B, and C together, and optionally any of the above in combination with at least one other entity.
As used herein, “at least substantially,” when modifying a degree or relationship, includes not only the recited “substantial” degree or relationship, but also the full extent of the recited degree or relationship. A substantial amount of a recited degree or relationship may include at least 75% of the recited degree or relationship. For example, an object that is at least substantially formed from a material includes an object for which at least 75% of the object is formed from the material and also includes an object that is completely formed from the material. As another example, a first direction that is at least substantially parallel to a second direction includes a first direction that forms an angle with respect to the second direction that is at most 22.5 degrees and also includes a first direction that is exactly parallel to the second direction. As another example, a first length that is substantially equal to a second length includes a first length that is at least 75% of the second length, a first length that is equal to the second length, and a first length that exceeds the second length such that the second length is at least 75% of the first length.
In the present disclosure, several of the illustrative, non-exclusive examples have been discussed and/or presented in the context of flow diagrams, or flow charts, in which the methods are shown and described as a series of blocks, or steps. Unless specifically set forth in the accompanying description, it is within the scope of the present disclosure that the order of the blocks may vary from the illustrated order in the flow diagram, including with two or more of the blocks (or steps) occurring in a different order, concurrently, and/or repeatedly. It is also within the scope of the present disclosure that the blocks, or steps, may be implemented as logic, which also may be described as implementing the blocks, or steps, as logics. In some applications, the blocks, or steps, may represent expressions and/or actions to be performed by functionally equivalent circuits or other logic devices. The illustrated blocks may, but are not required to, represent executable instructions that cause a computer, processor, and/or other logic device to respond, to perform an action, to change states, to generate an output or display, and/or to make decisions.
The various disclosed elements of apparatuses and steps of methods disclosed herein are not required to all apparatuses and methods according to the present disclosure, and the present disclosure includes all novel and non-obvious combinations and subcombinations of the various elements and steps disclosed herein. Moreover, one or more of the various elements and steps disclosed herein may define independent inventive subject matter that is separate and apart from the whole of a disclosed apparatus or method. Accordingly, such inventive subject matter is not required to be associated with the specific apparatuses and methods that are expressly disclosed herein, and such inventive subject matter may find utility in apparatuses and/or methods that are not expressly disclosed herein.
It is believed that the disclosure set forth above encompasses multiple distinct inventions with independent utility. While each of these inventions has been disclosed in its preferred form, the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense as numerous variations are possible. The subject matter of the inventions includes all novel and non-obvious combinations and subcombinations of the various elements, features, functions and/or properties disclosed herein. Similarly, where the claims recite “a” or “a first” element or the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements.
It is believed that the following claims particularly point out certain combinations and subcombinations that are directed to one of the disclosed inventions and are novel and non-obvious. Inventions embodied in other combinations and subcombinations of features, functions, elements, and/or properties may be claimed through amendment of the present claims or presentation of new claims in this or a related application. Such amended or new claims, whether they are directed to a different invention or directed to the same invention, whether different, broader, narrower, or equal in scope to the original claims, are also regarded as included within the subject matter of the inventions of the present disclosure.
The present application claims priority to U.S. patent application Ser. No. 17/528,996, filed on Nov. 17, 2021, now U.S. Pat. No. 11,634,806, and Provisional Patent Application No. 63/1459,145, filed on Mar. 10, 2021, both entitled “HARDENED CASE-NITRIDED METAL ARTICLES AND METHODS OF FORMING THE SAME,” the complete disclosures of which are incorporated by reference.
This invention was made with Government support under W911W6-16-2-0010 awarded by the Department of Defense. The government has certain rights in this invention.
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| 5173134 | Chakrabarti et al. | Dec 1992 | A |
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| Number | Date | Country |
|---|---|---|
| 2558320 | Jul 2015 | RU |
| 2736246 | Nov 2020 | RU |
| 2013140869 | Sep 2013 | WO |
| Entry |
|---|
| English Abstract and English Machine Translation of Gyotoku et al. (WO 2013/140869) (Sep. 26, 2013). |
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| Number | Date | Country | |
|---|---|---|---|
| 20230227955 A1 | Jul 2023 | US |
| Number | Date | Country | |
|---|---|---|---|
| 63159145 | Mar 2021 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17528996 | Nov 2021 | US |
| Child | 18183012 | US |
