Patent Application
20140202596
The present disclosure is directed to a method of overheating the melt of an alloy capable of forming metallic glass prior to quenching the melt in order to improve the glass-forming ability of the alloy and/or the toughness of the metallic glass.
Overheating the melt of alloys capable of forming metallic glass to temperatures sufficiently higher than the melting temperature is shown to influence certain kinetic properties of the liquid. Specifically, Lin et al. (U.S. Pat. No. 5,797,443) demonstrated that by overheating the melt of a bulk-solidifying Zr-based amorphous metal above a threshold temperature, which is sufficiently higher than the melting temperature, the degree to which the alloy can be undercooled to below the melting temperature by quenching increases. Lin et al. conjectured that by overheating the melt, certain oxide inclusions were dissolved into the melt and therefore could not serve as sites for heterogeneous nucleation of crystalline phases. The implication of a larger degree of undercooling is that the glass-forming ability of the alloy is enhanced. As such, the critical cooling rate (i.e. lowest cooling rate required to bypass crystallization of the alloy and form the amorphous phase) is decreased, while the critical casting thickness (i.e. largest lateral dimension of parts that can be formed with an amorphous phase) is increased. Lin et al. did not directly demonstrate that the critical casting thickness of the alloy increases with melt overheating, but concluded so by interpreting the undercooling results in the context of crystallization kinetics.
Lin et al. also discloses that after processing the melt at a temperature higher than TGFA, it is possible to cool and isothermally hold to an intermediate temperature between TGFA and Tliquidus prior to quenching without substantially losing the gains in glass-forming ability attained by initially overheating to above TGFA. In other words, once the melt is heated to a temperature higher than TGFA, its capacity undergo deeper undercooling is maintained even if it is subsequently annealed at temperatures between TGFA and Tliquidus prior to undercooling.
However, Lin et al. did not demonstrate, suggest, or imply that overheating the melt above some threshold temperature would have any influence on the mechanical properties of the amorphous metal, such as the fracture toughness.
The present disclosure provides methods of forming bulk metallic glasses or shaped metallic glass articles having higher toughness by overheating the alloy melt.
The disclosure is directed to a method of processing alloys into metallic glasses or metallic glass articles. The method includes melting an alloy by heating to a temperature above the liquidus temperature of the alloy, Tliquidus. The method also includes overheating the alloy melt to a temperature above a threshold temperature, Ttough, associated with the metallic glass (i.e. the alloy in an amorphous phase) demonstrating increased toughness compared to the toughness demonstrated by heating the alloy melt just above Tliquidus. The method further includes quenching the alloy melt at a high enough rate to form metallic glasses or shaped metallic glass articles.
In another embodiment, the temperature of the overheated alloy melt is also above another threshold temperature, TGFA, associated with the alloy demonstrating increased glass-forming ability compared to the glass-forming ability demonstrated by heating the alloy melt just above Tliquidus.
In yet another embodiment, Ttough is greater than TGFA.
In yet another embodiment, both Ttough and TGFA are greater than Tliquidus.
In yet another embodiment, the method also includes cooling the alloy melt following overheating to above Ttough and TGFA to an intermediate temperature below Ttough and TGFA but above Tliquidus and equilibrating the alloy melt at the intermediate temperature, and subsequently quenching the alloy melt at a high enough rate to form a metallic glass article.
In yet another embodiment, a method of forming a shaped metallic glass article is provided. The method includes melting a metallic glass forming alloy by heating the alloy to a temperature above the liquidus temperature of the alloy, Tliquidus. The method also includes overheating the alloy melt to a temperature above both a threshold temperature, Ttough, associated with the metallic glass demonstrating substantial improvement in toughness compared to the toughness demonstrated by heating the melt just above Tliquidus, and another threshold temperature, TGFA, associated with the alloy demonstrating substantial improvement in glass-forming ability compared to the glass-forming ability demonstrated by heating the melt just above Tliquidus. The method further includes simultaneously or subsequently quenching the alloy melt at a high enough rate to form a shaped metallic glass article.
In yet another embodiment, following overheating to above Ttough and TGFA, the method of forming a shaped metallic glass article includes cooling and equilibrating the alloy melt to an intermediate temperature below Ttough and TGFA but above Tliquidus. The method further includes simultaneously or subsequently quenching the alloy melt at a high enough rate to form a shaped metallic glass article.
In yet another embodiment, the metallic glass article having a lateral dimension of at least 0.5 mm made according to the present method is capable of undergoing macroscopic plastic deformation without fracturing catastrophically under a bending load.
In yet another embodiment, the alloy or metallic glass is Zr-based, Ti-based, Al-based, Mg-based, Ce-based, La-based, Y-based, Fe-based, Ni-based, Co-based, Cu-based, Au-based, Pd-based, or Pt-based.
In yet another embodiment, the alloy or metallic glass is represented by the following formula:
X100-a-bYaZb Eq. (1)
wherein:
X is Ni, Fe, Co, Pd, Pt, Au, Cu or combinations thereof;
Y is Cr, Mo, Mn, Nb, Ta, Ni, Cu, Co, Fe, Pd, Pt, Ag or combinations thereof;
Z is P, B, Si, Ge, C or combinations thereof;
a is between 2 and 45 at %; and
b is between 15 and 25 at %.
In yet another embodiment, the alloy or metallic glass is represented by the following formula:
X100-a-bYaZb, Eq. (2)
where:
X is Ni, Fe, Co or combinations thereof
Y is Cr, Mo, Mn, Nb, Ta or combinations thereof
Z is P, B, Si, Ge or combinations thereof
a is between 5 and 15 at %
b is between 15 and 25 at %.
In yet another embodiment, the alloy melt is heated by a process that may include inductive heating, resistively heating (in a furnace), a plasma arc heating, or joule heating, where the melt is held in a crucible made of fused or crystalline silica, a ceramic such as alumina or zirconia, graphite, or a water-cooled hearth made of copper or silver.
In yet another embodiment, the alloy melt is quenched by a process that may include quenching the crucible containing the melt in a bath of room temperature water, iced water, or oil. The crucible is made of any of the aforementioned materials. Alternatively, the method includes quenching the melt by driving the melt under pressure or pouring the melt into a metal mold. In some embodiments, the mold is made of copper, brass, or steel.
Additional embodiments and features are set forth in part in the description that follows, and will become apparent to those skilled in the art upon examination of the specification or may be learned by the practice of the disclosed subject matter. A further understanding of the nature and advantages of the present disclosure may be realized by reference to the remaining portions of the specification and the drawings, which forms a part of this disclosure.
The description will be more fully understood with reference to the following figures and data graphs, which are presented as various embodiments of the disclosure and should not be construed as a complete recitation of the scope of the disclosure, wherein:
The present disclosure may be understood by reference to the following detailed description, taken in conjunction with the drawings as described below. It is noted that, for purposes of illustrative clarity, certain elements in various drawings may not be drawn to scale.
The present disclosure provides methods of forming bulk metallic glasses or shaped metallic glass articles of improved toughness and glass forming ability by overheating the alloy melt to a temperature higher than Ttough and TGFA, which are both above Tliquidus, prior to quenching. The present disclosure also provides an alternative method, whereas after overheating the alloy melt to above Ttough and TGFA, the melt is cooled and equilibrated to an intermediate temperature below both Ttough and TGFA but above Tliquidus, and subsequently quenched at a high enough rate to form a bulk metallic glass.
In the context of the present disclosure, glass-forming ability is understood as measured by the “critical rod diameter” as defined herein. Where the disclosure refers to improved or increased glass-forming ability, it will be understood to be as measured by the “critical rod diameter.” In the context of the present disclosure, toughness is measured by “notch toughness” as defined herein. Where the disclosure refers to improved or increased toughness, it will be understood to be as measured by the “notch toughness.”
In support of the former method, the present disclosure demonstrates that once the melt is heated to a temperature higher than TGFA, the glass forming ability of the alloy is considerably higher as compared to heating the melt just above Tliquidus. The disclosure further demonstrates that once the melt is heated to a temperature higher than Ttough, the toughness of the metallic glass is considerably higher as compared to heating the melt just above Tliquidus.
In some embodiments, “heating the melt just above Tliquidus” or “in the absence of overheating” is intended to imply that the melt is overheated by less than 50° C. above the alloy liquidus temperature. In other embodiments, “just above Tliquidus” or “in the absence of overheating” is intended to imply that the melt is overheated by less than 5% of the alloy liquidus temperature (where Tliquidus is expressed in units of Kelvin).
In support of the latter method, the present disclosure demonstrates that once the melt is heated to a temperature higher than TGFA and then annealed below TGFA prior to quenching to form a glass, its higher glass-forming ability is actually retained. More surprisingly, the present disclosure reveals that once the melt is heated to a temperature higher than Ttough and then annealed at an intermediate temperature below Ttough prior to quenching to form a glass, its higher toughness is also retained.
The behavior of amorphous metals that are processed in the high-temperature melt state is complex. Quite unexpectedly, an independent threshold temperature above the liquidus temperature Tliquidus is identified to be associated with enhanced toughness, and is referred to as a first threshold temperature Ltough hereafter. Specifically, the metallic glasses processed by overheating the alloy melt above this threshold temperature, Ttough, have an improved toughness at room temperature over the metallic glasses processed by heating the alloy melt above Tliquidus but below Ttough.
Specifically, Ttough is defined as the melt overheating temperature associated with a substantial improvement in toughness, as measured by notch toughness, of the metallic glass at room temperature as compared to the toughness demonstrated in the absence of overheating above Tliquidus, More specifically, Ttough may be identified as the temperature following the steepest increase in toughness with increasing melt overheating temperature (i.e. the temperature following the largest slope of the toughness function against temperature above Tliquidus).
Another threshold temperature, TGFA, is defined as the melt overheating temperature associated with substantial improvement in glass-forming ability, as measured by critical rod diameter, as compared to the glass-forming ability demonstrated in the absence of overheating above Tliquidus. More specifically, TGFA may be identified as the temperature following the steepest increase in glass forming ability with increasing melt overheating temperature (i.e. the temperature following the largest slope of the glass forming ability function against temperature above Tliquidus).
In some embodiments, “significant improvement” in toughness and glass-forming ability may be interpreted as an improvement of at least 10% compared to the respective values obtained in the absence of overheating above Tliquidus. In some embodiments, “substantial improvement” in toughness and glass-forming ability may be interpreted as an improvement of at least 25% compared to the respective values obtained in the absence of overheating above Tliquidus. In some embodiments, “substantial improvement” is interpreted as an improvement of at least 50% compared to the respective values obtained in the absence of overheating above Tliquidus. In some embodiments, “substantial improvement” is interpreted as an improvement of at least 75% compared to the respective values obtained in the absence of overheating above Tliquidus.
In some embodiments, “substantial improvement” in toughness and glass-forming ability may be interpreted as an improvement of at least 50% compared to the respective values obtained in the absence of overheating above Tliquidus attained by overheating the melt by at least 100° C. above Tliquidus. In some embodiments, “substantial improvement” is interpreted as an improvement of at least 50% compared to the respective values obtained in the absence of overheating above Tliquidus attained by overheating the melt by at least 50° C. above Tliquidus. In some embodiments, “substantial improvement” is interpreted as an improvement of at least 50% compared to the respective values obtained in the absence of overheating above Tliquidus attained by overheating the melt by at least 25° C. above Tliquidus.
Both Ttough and TGFA may be higher than the solidus and liquidus temperatures Tsolidus and Tliquidus, respectively. In some embodiments, Ttough may be higher than TGFA, as shown in
Regardless of the order of Ttough versus TGFA, it is observed that Ttough is independent of and different from TGFA. Accordingly, attempts to achieve high glass-forming ability by overheating the melt above a certain TGFA would not necessarily lead to a tougher metallic glass.
As shown in
An alloy would not only have improved glass-forming ability, i.e. being capable of forming a metallic glass in larger lateral dimensions, but would also form a metallic glass article or hardware having an improved toughness according to the present overheating method. One of the benefits of the improved toughness is to enable the metallic glass article or hardware formed from the alloy to evade catastrophic fracture upon loading initiating from structural flaws, particularly in bending loading. Specifically, an amorphous metal article having a lateral dimension of at least 0.5 mm made according to the present method would be able to undergo macroscopic plastic bending when overloaded, evading catastrophic fracture. This improved toughness, together with the improved glass-forming ability, can result in an improved overall engineering applicability and performance.
The present disclosure also provides a method for the melt to retain “memory” of its high temperature state at intermediate temperatures. Specifically, after heating the melt to a temperature higher than both TGFA and Ttough, the melt may be cooled to an intermediate temperature below TGFA and Ttough but above Tliquidus prior to quenching, and may be held isothermally at the intermediate temperature without substantially losing the gains in both the glass-forming ability and toughness attained by initially overheating to above TGFA and Ttough.
One of the benefits of the alternative path is to limit the degradation of a metal mold tool by avoiding injecting the melt into the mold tool from very high temperatures. For processes that utilize pressure to drive the processed melt into a metal mold in order to shape the melt and simultaneously quench the melt to form an amorphous metal article or hardware, such as die casting, the ability of the melt to retain “memory” of its high temperature state is very important. This is because the tool life of the mold depends strongly on the temperature of the alloy melt. To achieve the high toughness and high glass-forming ability, the alloy is overheated to be above TGFA and Ttough which may be much higher than Tliquidus. With such high temperatures, the tool life of mold may be dramatically shortened using the present method at a temperature above TGFA and Ttough, like for example at TH, as shown in processing path 102. However, injecting the melt into the mold at a lower intermediate temperature below TGFA and Trough but above Tliquidus, like for example at TL, according to the alternative processing path 104, would diminish any adverse effects on the tool life. Other potential benefits include lower power requirements for heating the melt, less thermal shrinkage of the part, and potentially better melt flow control with higher viscosity at lower temperature.
The present method is applicable to any processing that produces an amorphous metal article or part by melting and quenching a metallic alloy.
The method is also applicable, without limitation, to any heating process that involve melting the alloy. Heating processes may include, without limitation, inductive heating, resistive heating (e.g. in a furnace), plasma arc heating, or joule heating, where the alloy melt is held in a crucible. The crucible material may include, without limitation, fused or crystalline silica, a ceramic such as alumina or zirconia, graphite, or a water-cooled hearth made of copper or silver.
The method is also applicable, without limitation, to any quenching processes that involve quenching the crucible containing the melt in a bath of room temperature water, iced water, or oil, or quenching the melt by driving it under pressure or pouring it into a metal mold made of copper, brass, or steel. The crucible may be made of any of the aforementioned materials.
The disclosed methods are applicable to all metal alloys capable of forming a metallic glass by quenching the alloy melt form high temperature. A “critical cooling rate”, which is defined as the cooling rate required to avoid crystallization and form the amorphous phase of the alloy (i.e. the metallic glass) determines the critical rod diameter. The lower the critical cooling rate of an alloy, the larger its critical rod diameter. The critical cooling rate Rc in K/s and critical rod diameter dc in mm are related via the following approximate empirical formula:
R
c=1000/dc2 Eq. (2)
According to Eq. (2), the critical cooling rate for an alloy having a critical rod diameter of about 1 mm, as in the case of the alloys according to embodiments of the present disclosure, is only about 103 K/s.
Generally, three categories are known in the art for identifying the ability of a metal alloy to form glass (i.e. to bypass the stable crystal phase and form an amorphous phase). Metal alloys having critical cooling rates in excess of 1012 K/s are typically referred to as non-glass formers, as it is physically impossible to achieve such cooling rates over a meaningful thickness. Metal alloys having critical cooling rates in the range of 105 to 1012 K/s are typically referred to as marginal glass formers, as they are able to form glass over thicknesses ranging from 1 to 100 micrometers according to Eq. (2). Metal alloys having critical cooling rates on the order of 103 or less, and as low as 1 or 0.1 K/s, are typically referred to as bulk glass formers, as they are able to form glass over thicknesses ranging from 1 millimeter to several centimeters. The glass-forming ability of a metallic alloy is, to a very large extent, dependent on the combination and composition of the alloy. It is important to state that the combinational and compositional ranges for alloys capable of forming marginal glass formers are considerably broader than those for forming bulk glass formers.
The present method is applicable to any metallic glass-forming alloy, including but not limited to, Zr-based, Ti-based, Al-based, Mg-based, Ce-based, La-based, Ca-based, Y-based, Fe-based, Ni-based, Co-based, Cu-based, Au-based, Pd-based, and Pt-based.
Without limitation, Zr-based glass-forming alloys may include elements selected from the group consisting of Ti, Ni, Cu, Be, Hf, Nb, V, Al, Sn, Ag, Pd, Fe, Co, and Cr.
Without limitation, Fe-based glass-forming alloys may include elements selected from the group consisting of Co, Ni, Mo, Cr, P, C, B, Si, Al, Zr, W, Mn, Y, and Er.
Without limitation, Ni-based glass-forming alloys may include elements selected from the group consisting of Co, Fe, Cu, Mo, Cr, P, B, Si, Sn, Nb, Ta, V, and Mn.
Without limitation, Cu-based glass-forming alloys may include elements selected from the group consisting of Zr, Ti, Ni, Au, Ag, Hf, Nb, V, Si, Sn, and P.
Without limitation, Au-based glass-forming alloys may include elements selected from the group consisting of Cu, Si, Ag, Pd, Pt, Ge, Y, and Al.
Without limitation, Pd-based glass-forming alloys may include elements selected from the group consisting of Pt, Ni, Cu, P, Si, Ge, Ag, Au, Fe, and Co.
Without limitation, Pt-based glass-forming alloys may include elements selected from the group consisting of Pd, Ni, Cu, P, Si, Ge, Ag, Au, Fe, and Co.
In some embodiments, for certain alloys whose melt can be fluxed to increase glass-forming ability, fluxing can also help achieve both high toughness and high glass-forming ability without the need for melt overheating. A fluxing method is disclosed in a recent patent application U.S. Patent No. 61/913,732, filed on Dec. 9, 2013, entitled “Melt fluxing method for improved toughness and glass-forming ability of metallic glasses and glass forming alloys”, which is incorporated herein by reference in its entirety. Fluxing the alloy melt may help avoid overheating to very high temperatures in order to achieve high toughness and high glass-forming ability.
The following non-limiting examples are illustrative of aspects of the present disclosure.
To demonstrate the effects of the method of melt overheating at TH on glass-forming ability (GFA) and toughness, Ni-based glass-forming alloys from the Ni—Cr—Nb—P—B family, disclosed in a recent application (U.S. Patent Application No. 61/720,015, entitled “Bulk Nickel-Based Chromium and Phosphorous Bearing Metallic Glasses with High Toughness”, filed on Oct. 30, 2012, which is incorporated herein by reference), and the Fe-based glass forming alloy Fe67Mo6Ni3.5Cr3.5P12C5.5B2.5 are used here as example systems.
The glass-forming ability of each alloy was assessed by determining the “critical” rod diameter”, defined as the maximum rod diameter at which the amorphous phase can be formed when processed by the method of water quenching the molten alloy in quartz tubes having 0.5 mm wall thickness.
However, the alloy with improved glass-forming ability still lacks good toughness when heated to 1250° C., showing a room-temperature notch toughness of just 30 MPa m1/2. Surprisingly, when heating the alloy to 1350° C., which is above its Ttough of 1300° C., and subsequently quenching, the alloy forms a metallic glass that has a substantially improved toughness of about 80 MPa m1/2.
The same effect is shown for four more alloys. For each alloy, one can define values for TGFA and Ttough.
The alloy and metallic glass compositions along with the associated Tliquidus, TGFA, and Ttough values in degrees Celcius (° C.) are presented in Table 1. As shown, for this alloy family Ttough is higher than TGFA in all four compositions in Table 1, and both Ttough and TGFA are substantially higher than Tliquidus. The degree of overheating to achieve the high glass-forming ability and toughness, respectively defined as ΔTGFA=TGFA−Tliquidus and ΔTtough=Ttough−Tliquidus, are also presented for each composition in Table 1.
Table 2 presents values for Tliquidus, TGFA, Ttough, ratios of ΔTGFA/Tliquidus and ΔTtough/Tliquidus for sample alloys and metallic glasses (in degrees Kelvin).
The effects of overheating the melt to a temperature above Ttough and TGFA and subsequently cooling to an intermediate temperature below Ttough and TGFA but above Tliquidus on glass-forming ability and toughness is investigated for alloy Ni71.4Cr5.64Nb3.46P16.5B3. The alloy is melted and the melt is overheated to a temperature at least as high as Ttough and TGFA, followed by cooling to an intermediate temperature below Ttough and TGFA but above Tliquidus for a fixed period of time, and then quenched to form a metallic glass.
As shown in
Also, when the melt is heated to 1250° C., subsequently annealed at an intermediate temperature of 1100° C., which is slightly below its TGFA of 1125° C. and well below its Ttough of 1250° C., and then quenched, the critical rod diameter drops slightly to about 9 mm and the toughness drops slightly to about 70 MPa m1/2.
Furthermore, when the melt is heated to 1250° C., subsequently annealed at a lower intermediate temperature of 950° C., which is substantially below both its TGFA and Ttough, and then quenched, the critical rod diameter remains high at about 9 mm but the toughness drops sharply to about 30 MPa m1/2.
When the melt is annealed at lower intermediate temperatures below 950° C. (e.g. 900° C.) and above Tliquidus after first being heated to 1250° C., both the toughness and the critical rod diameter appear to also drop sharply to about 30 MPa m1/2 and 7 mm, respectively.
Hence, these results suggest that although the threshold temperatures TGFA and Ttough are quite high, one does not have to quench from such high temperature and encounter the associated adverse effects (e.g. low tool life in the case of die casting) in order to improve or enhance glass-forming ability and toughness. Rather, one can cool the melt to an intermediate temperature (e.g. by transferring it to another cooler reservoir), such as 1100° C. for Ni71.4Cr5.64Nb3.64P16.5B3 rather than 1250° C., and then quench from that intermediate temperature, thus avoiding the adverse high-temperature effects while retaining significant glass-forming ability and toughness.
The effect of time on holding the melt isothermally at an intermediate temperature below TGFA and Ttough but above Tliquidus following overheating above TGFA and Ttough is also investigated for alloy Ni71.4Cr5.64Nb3.46P16.5B3. The alloy is melted and the melt is overheated to a temperature of at least as high as Ttough and TGFA, followed by cooling to an intermediate temperature below TGFA and Ttough but above Tliquidus where it is held for various periods of time, and then quenched to form the metallic glass.
As shown in
When the alloy melt is held for about 450 seconds and also for about 900 seconds at 1150° C. in addition to the time required to equilibrate to that temperature and then subsequently quenched, the critical rod diameter and toughness remain essentially unchanged.
This result reveals that no transient processes take place during isothermal holding at the intermediate temperature. This result suggests that after the melt is heated to above TGFA and Ttough, the melt can be cooled to an intermediate temperature below TGFA and Ttough but above Tliquidus and held there for a long period of time without affecting the enhanced glass-forming ability and toughness.
A particular method for producing the example alloys of the present disclosure involves inductive melting of the appropriate amounts of elemental constituents in a fused silica crucible under inert atmosphere to form alloy ingots. Alternatively, the crucible may also be crystalline silica, a ceramic such as alumina or zirconia, graphite, or a water-cooled hearth made of copper or silver. Particular purity levels of the constituent elements were as follows: Ni 99.995%, Cr 99.996% (crystalline), Nb 99.95%, B 99.5%, Si 99.9999, and P 99.9999%, Fe 99.95%, Mo 99.95%, and C 99.9995%.
A particular method for producing metallic glass rods from the alloys of the present disclosure involves re-melting the alloy ingots in quartz tubes having 0.5 mm thick walls in a furnace under high purity argon. After processing at specific temperatures, the melt is rapidly quenching in a room-temperature water bath.
In various experiments, the melt is heated to an overheating temperature above the liquidus temperature, followed by quenching to form metallic glass rods. The critical rod diameter of the alloys associated with the specific overheating temperature was determined. Another 3-mm diameter rod was produced for each overheating temperature following the same procedure, and the toughness of the 3-mm diameter metallic glass rod was measured. These data are presented in
In various experiments, the melt is first heated to an overheating temperature, followed by cooling to an intermediate temperature, and after equilibrating at the intermediate temperature then quenched. The critical rod diameter of the alloys associated with the specific overheating and intermediate temperature was determined. Another 3-mm diameter rod was produced for each overheating and intermediate temperature following the same procedure, and the toughness of the 3-mm diameter metallic glass rod was measured. These data are presented in
In various experiments, the melt is first heated to an overheating temperature, followed by cooling to an intermediate temperature, and after equilibrating at the intermediate temperature it was held there for a specific period of time, and then quenched. The critical rod diameter of the alloys associated with the specific overheating and intermediate temperatures and specific period of time was determined. Another 3-mm diameter rod was produced for each overheating and intermediate temperature and specific period of time following the same procedure, and the toughness of the 3-mm diameter metallic glass rod was measured. These data are presented in
The glass-forming ability of each alloy was assessed by determining the maximum rod diameter, i.e. “critical rod diameter”, in which the amorphous phase of the alloy (i.e. the metallic glass phase) could be formed when processed by the method of quenching the alloy melt contained in a quartz tube with 0.5 mm thick walls in a bath of room temperature water, as described above. X-ray diffraction with Cu-Kα radiation was performed to verify the amorphous structure of the alloys.
Measurement of notch toughness of the example alloys was performed on 3-mm diameter amorphous rods at room temperature. The rods were notched using a wire saw with a root radius of between 0.10 and 0.13 μm to a depth of approximately half the rod diameter. The notched specimens were placed on a 3-point bending fixture with span distance of 12.7 mm and carefully aligned with the notched side facing downward. The critical fracture load was measured by applying a monotonically increasing load at constant cross-head speed of 0.001 mm/s using a screw-driven testing frame. At least three tests were performed, and the variance between tests is included in the notch toughness plots. The stress intensity factor for the geometrical configuration employed here was evaluated using the analysis by Murakimi (Y. Murakami, Stress Intensity Factors Handbook, Vol. 2, Oxford: Pergamon Press, p. 666 (1987)).
Having described several embodiments, it will be recognized by those skilled in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Accordingly, the above description should not be taken as limiting the scope of the invention.
Those skilled in the art will appreciate that the presently disclosed embodiments teach by way of example and not by limitation. Therefore, the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall therebetween.
The present application claims the benefit of U.S. Provisional Patent Application No. 61/755,177, entitled “Melt Overheating Method For Improved Toughness and Glass-Forming Ability of Metallic Glasses” filed on Jan. 22, 2013, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61755177 | Jan 2013 | US |
