Patent Grant
9845523
The present disclosure is directed to methods and metallic glass alloy feedstock that are capable of being shaped into high aspect ratio articles using rapid capacitive discharge forming.
U.S. Patent Publication No. 2009/0236017 is directed to a method of rapidly heating and shaping a metallic glass using a rapid discharge of electrical current. A quantum of electrical energy is discharged with near uniformity through a metallic glass feedstock having a substantially uniform cross-section. The sample is rapidly heated substantially uniformly to a processing temperature between the glass transition temperature of the amorphous phase and the equilibrium melting temperature of the alloy. Either simultaneously or subsequently, the sample is shaped and cooled to form an amorphous article. U.S. Patent Publication No. 2012/0103478 is directed to a metallic glass article having a high aspect ratio that is fabricated by this rapid capacitive discharge forming (RCDF) method.
Both U.S. Patent Publication No. 2009/0236017 and U.S. Patent Publication No. 20120103478 are incorporated herein by reference in their entirety. While both publications disclose a wide-range of materials that may be used with the described methods, neither publication discloses specific ranges of properties of metallic glass alloys for the RCDF method such that the alloys are capable of being shaped into high aspect ratio metallic glass articles.
In one aspect, the disclosure is directed to a method of shaping high-aspect ratio articles. A feedstock is formed of a metallic glass alloy that has a uniform cross-section capable of resisting crystallization for at least 100 ms at a temperature above the glass transition of the alloy where the viscosity of the metallic glass is between 100-104 Pa-s. In some variations, the viscosity of the metallic glass is between 101-103 Pa-s. In other variations, the viscosity of the metallic glass is between 102-104 Pa-s. In some embodiments, the feedstock is capable of resisting crystallization for at least 100 ms at a temperature above the glass transition of the alloy where the viscosity of the metallic glass is between 100-104 Pa-s. Likewise, in some embodiments the viscosity of the metallic glass is between 101-103 Pa-s, while in other embodiments the viscosity of the metallic glass is between 102-104 Pa-s. A quantum of electrical energy is applied to the feedstock, thereby heating the feedstock to a processing window at a temperature within the viscosity range. At such temperature, the heated feedstock is shaped into a high-aspect-ratio article. The shaped article is cooled to a temperature below the glass transition temperature of the metallic glass sufficiently fast to avoid crystallization of the metallic glass. In some variations, the shaped amorphous article has a high aspect ratio of at least 10.
In other variations, the shaped amorphous article has thickness of 2 mm or less. In some further embodiments, the thickness is in the range of 0.5 to 2 mm.
In additional aspects, the present disclosure is directed to methods of screening metallic glass forming alloys for use in making a high aspect ratio metallic glass article. A quantum of electric energy is applied to a sample of metallic glass alloy to heat the sample to a temperature above the glass transition temperature of the alloy, where the viscosity of the metallic glass is between 100 and 104 Pa-s, or alternatively between 102 and 104 Pa-s, or alternatively between 102 and 104 Pa-s. The temperature of the sample is measured. Once the quantum of electric energy has been applied, the sample maintains a roughly constant temperature until crystallization starts. Crystallization of the alloy results in the release of energy and corresponding sharp rise in temperature. The difference between the end of the capacitive discharge and the release of energy due to crystallization defines the crystallization time window. A metallic glass is suitable to make high aspect ratio parts if the crystallization time window is at least 100 ms. In some embodiments the viscosity of the metallic glass is between 102-104 Pa-s.
In further aspects, the disclosure is directed to a metallic glass alloy feedstock. The metallic glass feedstock comprises metallic glass capable of resisting crystallization for at least 100 ms at a temperature where the viscosity is in the range of 100 and 104 Pa-s. In some embodiments, the metallic glass is capable of resisting crystallization for at least 100 ms at a temperature where the viscosity is in the range of 102 and 104 Pa-s. In certain variations, the feedstock has a substantially uniform cross section. The metallic glass alloy feedstock can be used in the methods described herein.
In additional aspects, the disclosure is directed to a shaped amorphous article formed from said feedstock using the methods described herein having features with aspect ratio of at least 10. In other aspects, the shaped amorphous article has features with a thickness of 2 mm or less. In some embodiments, the shaped amorphous article has features where the thickness is in the range of 0.5 to 2 mm.
In various embodiments, the metallic glass alloy composition 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 other embodiments, the metallic glass alloy composition is Ta—based, Hf-based, Pr-based, Nd-based, Gd-based, or Ca-based.
In still other embodiments, the metallic glass alloy composition has the following formula:
X100-a-bYaZb EQ. 1
wherein:
X is Ni, Fe, Co or combinations thereof
Y is Cr, Mo, Mn, Nb, Ta or combinations thereof
Z is P, B, Si, C, Ge or combinations thereof
a is between 5 and 15 atomic %
b is between 15 and 25 atomic %.
In various embodiments, the metallic glass alloy composition is any Ni—based glass-forming alloy, including but not limited to, Ni—Cr—Nb—P—B, Ni—Cr—Ta—P—B, Ni—Cr—Mn—P—B, Ni—Mo—Nb—Mn—P—B, Ni—Mn—Nb—P—B, Ni—Cr—Mo—Si—B—P, and Ni—Fe—Si—B—P metallic glass alloy compositions.
In still other embodiments, the metallic glass alloy composition has the following formula:
Ni100-a-b-c-dXaYbPcZd EQ. 2
wherein:
X is Cr, Mo, Mn or combinations thereof
Y is Nb, Ta, Mn or combinations thereof
Z is B, Si or combinations thereof
a is between 3 and 15 atomic %
b is between 1 and 6 atomic %
c is between 12 and 20 atomic %
d is between 0.5 and 6 atomic %
In still yet other embodiments, the metallic glass alloy is selected from Ni68.17Cr8.65Nb2.98P16.42B3.28Si0.5, Ni68.17Cr8.65Nb2.98P15.92B3.28Si1, Ni69Cr10Nb1.5P18B1.5, Ni69Cr9.5Nb2P17.5B2, Ni69Cr9Nb2.5P17B2.5, Ni69Cr8Nb3.5P16B3.5, Ni69Cr7.5Nb4P15.5B4, Ni69Cr7Nb4.5P15B4.5, Ni69Cr8.75Nb2.75P16B3.5, Ni69Cr9Nb2.5P15.5B4, Ni69Cr9.25Nb2.25P15B4.5, Ni69Cr9.5Nb2P14.5B5, Ni69Cr9.75Nb1.75P14B5.5, Ni69Cr10Nb1.5P13.5B6, Ni67.5Co1.5Cr8.5Nb3P16.5B3, Ni66Co3Cr8.5Nb3P16.5B3, Ni64Co5Cr8.5Nb3P16.5B3, Ni59Co10Cr8.5Nb3P16.5B3, Ni54Co15Cr8.5Nb3P16.5B3, Ni49Co20Cr8.5Nb3P16.5B3, Ni44Co25Cr8.5Nb3P16.5B3, Ni61.4Co10Cr5.52Nb3.38P16.67B3.03, Ni56.4Co15Cr5.52Nb3.38P16.67B3.03, Ni51.4Co20Cr5.52Nb3.38P16.67B3.03, Ni46.4Co25Cr5.52Nb3.38P16.67B3.03, Ni67.1Cr10Nb3.4P18Si1.5, Ni66.1Cr11Nb3.4P18Si1.5, Ni64.1Cr13Nb3.4P18Si1.5, Ni62.1Cr15Nb3.4P18Si1.5, Ni68.5Cr8.5Mn3P17B3, Ni68.5Cr7.5Mn3Mo1P16.5B3, Ni68.5Cr9Ta3P16.5B3, Ni68.5Cr9Ta3P16.25B3.25, Ni68.5Cr9Ta3P16B3.5, Ni68.5Cr9Ta3P15.5B4, Ni68.5Cr9Ta3P15B4.5, Ni69.5Cr8Ta3P16.25B3.25, Ni68.5Cr9Ta3P16.25B3.25, Ni67.5Cr10Ta3P16.25B3.25, Ni68.5Cr10Ta2P16.25B3.25, Ni68.5Cr9.5Ta2.5P16.25B3.25, and Ni68.5Cr8.5Ta3.5P16.25B3.25.
In still yet other embodiments, the metallic glass alloy crystallizes at a temperature Tx that is at least 45° C. higher than its glass transition temperature Tg when heated by a constant heating rate of 0.67° C./s.
In still yet other embodiments the disclosure is directed to a high-aspect-ratio article. The article has at least one featuring with an aspect ratio of at least 10. In some embodiments, the article has at least one feature with a thickness of 2 mm or less. In further embodiments, the article has at least one feature with a thickness in the range of 0.5 to 2 mm shaped from a metallic glass as described herein.
In still yet other embodiments, the high-aspect-ratio article is a component of a consumer electronics device, a watch component, a medical implant, a dental prosthetic, a ferromagnetic core, a sporting good, or a luxury good.
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.
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, may be represented schematically or conceptually, or otherwise may not correspond exactly to certain physical configurations of embodiments.
The present disclosure is directed to methods and materials that allow for the use of RCDF to shape high aspect ratio articles. The articles prepared in this manner exhibit finished surfaces that are substantially free from cosmetic defects and/or flaws.
As used herein, “high aspect ratio articles” refer to articles having aspect ratios (defined as the longest dimension of a 3D object article divided over the shortest dimension of a 3D object) of at least 10. In some embodiments, the article has a thickness (the shortest dimension of a 3D object) on the order of 2 mm or less. In other embodiments, the article has at least one feature with a thickness of 2 mm or less. In further embodiments, the article has at least one feature with a thickness in the range of 0.5 to 2 mm. It will be understood to those in the art that high aspect ratios articles refer to articles having at least one feature with a high aspect ratio. A feature can be any portion of an article, and is not limited to the total size of the article. In various embodiments, the crystallization time of an amorphous alloy is sufficiently long to allow the amorphous alloy to occupy the high aspect ratio feature without defects or incongruities.
RCDF Process
In RCDF, a quantum of electrical energy is discharged through a metallic glass sample having a uniform cross-section. The sample is rapidly and uniformly heated to a processing temperature between the glass transition temperature of the metallic glass and the equilibrium melting temperature of the metallic glass alloy. A deformational force is applied to the heated and softened feedstock either during or after the rapid uniform heating. The sample is shaped and cooled to form a metallic glass article.
As used herein, a “uniform cross-section” includes minor surface inconsistencies (e.g. <5% of a cross-sectional diameter) in the cross-section. As used herein, “uniformly heated” refers to heating the feedstock core to substantially the same temperature (e.g. within 10% of the temperature in Kelvin). It is contemplated that uniform heating refers to the feedstock core, and very small regions in the feedstock sufficiently close to the contact points with the electrodes (i.e. in some embodiments within 5 mm, and in other embodiments within 1 mm) may have temperatures above or below the mean temperature of the core of the feedstock.
The article can be shaped by any shaping method known in the art. For example, any deformational force can be applied simultaneously or subsequently to heating in order to shape the heated sample into an article. Non-limiting examples of different shaping techniques may include molding, forging, casting, and blow molding, among others.
The RCDF process involves rapidly discharging electrical current across a metallic glass feedstock via electrodes in contact with feedstock in order to rapidly and uniformly heat the feedstock to a temperature conducive for viscous flow. The RCDF process has certain internal time scales, the first of which is the duration of the heating pulse, th, which is the time to heat a metallic glass feedstock to a desired process temperature above the glass transition. The second time scale is the duration of the shaping process, ts. This is the available time during which the heated feedstock may be shaped to the desired final shape without crystallizing the metallic glass. Another time scale, tc, is the amount of time to cool the fully shaped part to below Tg. Adding these time scales together gives the duration of the RCDF process as tRCDF=th+ts+tc. It is critical for the heating and shaping of the initial unprocessed metallic glass (“feedstock”) to be completed before the amorphous feedstock crystallizes. Therefore, the crystallization time tcryst must be longer than tRCDF the time it takes for the RCDF process to heat, shape and cool the feedstock sample (i.e. tcryst>tRCDF).
For high aspect ratio articles, the duration of the RCDF process is dominated by the duration of the shaping process. The target process temperature range in RCDF is the range of temperatures associated with a viscosity in the range of 100 to 104 Pa-s, or alternatively in the range of 101 to 103 Pa-s, or in the range of 102 to 104 Pa-s. As disclosed in U.S. Patent Publications 2012/0103478 and 2009/0236017, each of which is incorporated herein by reference in its entirety, if the viscosity is higher than about 104 Pa-s, the metallic glass alloy may not fill a mold by injection molding, or the injection pressure required to enable complete filling may be too high causing damage to the mold. On the other hand, if the viscosity is substantially lower than 100 Pa-s, it may be too low to sustain stable flow such that flow instabilities would develop causing voids or defects in the final article.
The viscosity of the metallic glass depends strongly on temperature. Most metallic glasses have a predictable dependence between temperature and viscosity. Specifically, the viscosity of the BMG drops by about 15 orders of magnitude when the temperature rises from the glass transition to above the melting point of the alloy following a predictable function. This means that the forming conditions (pressure and time) required to shape a metallic glass depends critically on the temperature under which shaping is being performed.
To successfully shape high-aspect-ratio articles that are free of structural and cosmetic defects, shaping should be performed at a strain rate low enough to keep the flow inertia force low compared to the flow front surface tension and avoid flow-front breakup (Weber instabilities), which leads to surface defects such as cellularization, roughening, and flow lines. Generally, when shaping high aspect ratio articles, processing strain rates should not exceed 100 s−1.
Based on these processing parameters, the lower limit for ts may be estimated as the ratio between the lower limit of total strain, which is essentially the aspect ratio, and the higher limit of strain rate. For example, in the current disclosure, the lowest limit in aspect ratio is about 10 and the highest limit in strain rate is about 100 s−1, thus the lower bound for the shaping time may be 0.1 s or 100 ms. As shown below, such shaping time is significantly larger than both th and tc.
The heating time may be estimated as follows. In the RCDF process, the circuit capacitance typically ranges between 0.1 and 2 F, and a total resistance (metallic glass feedstock resistance plus system resistance) between 1 and 5 mΩ, is typical. Therefore, the heating time th, which is essentially equivalent to the rise time for the current discharge and may be roughly approximated by the product between capacitance and resistance, may be on the order of few ms and not significantly more than 10 ms. Hence, th<<ts.
The cooling time may be estimated as follows. The time to cool the centerline of an article with a lateral dimension 2L by about 63% of the temperature difference (difference between process temperature and mold temperature) may be approximated by the thermal relaxation (Fourier) time τth=L2/a, where L is the article half-thickness, and may be on the order of 0.5 mm, and a is the metallic glass thermal diffusivity, which ranges between 1×10−6 and 5×10−6 m2/s for most metallic glasses. Therefore typical thermal relaxation times for such metallic glass articles may be on the order of τth about 100 ms. But these relaxation times represent cooling times to about 63% of the total temperature difference. The total temperature difference in RCDF is typically on the order of 500-600 degrees when cooling from a process temperature where the viscosity is between 100 and 104 Pa-s (or alternatively in the range of 101 and 103 Pa-s or in the range of 102 and 104 Pa-s) to the temperature of the mold, which is typically held at room temperature. The requirement for bypassing crystallization in the RCDF process is to cool the melt to just below the process temperature, but not necessarily below Tg, i.e. only by about 100-200 degrees, so the cooling time is only a small fraction of τth, that is, only a small fraction of about 100 ms. For example, the cooling time may be 20 ms, which is much smaller than the minimum shaping time, i.e. 100 ms.
Accordingly, some embodiments are directed to a process for shaping high-aspect ratio articles using RCDF. A metallic glass is selected wherein tcryst>ts>100 ms at a temperature where the viscosity of the metallic glass is between 100 and 104 Pa-s, or alternatively in the range of 101 and 103 Pa-s, or in the range of 102 and 104 Pa-s. A feedstock of the metallic glass having a substantially uniform cross-section is formed. A quantum of electrical energy is applied to the feedstock using an RCDF system to heat the feedstock to a processing window at a temperature where the viscosity is between 100 and 104 Pa-s, or alternatively in the range of 101 and 103 Pa-s, or in the range of 102 and 104 Pa-s. The heated feedstock is shaped into a high-aspect-ratio article. The shaped article is cooled to a temperature below the glass transition temperature of the metallic glass sufficiently fast to avoid crystallization of the metallic glass.
In some embodiments the shaped amorphous article has features with aspect ratio of at least 10. In other embodiments, the shaped amorphous article has features with a thickness of 2 mm or less. In yet other embodiments, the shaped amorphous article has features with a thickness in the range of 0.5 to 2 mm. The shaping step may take the form of any application of deformational force applied simultaneously or subsequently to shape the heated sample into an article. Examples of such shaping techniques may include molding, forging, casting, and blow molding, among others.
In some embodiments, the shaped article is a component of a consumer electronics device, a watch component, a medical implant, a dental prosthetic, a ferromagnetic core, a sporting good, or a luxury good.
Screening for RCDF Alloys Satisfying the Criterion Set Forth Herein
The present disclosure is also directed to methods of screening metallic glass-forming alloy systems to assess the suitability of specific alloys for being shaped into high-aspect ratio articles substantially free of cosmetic defects and flaws using RCDF.
In some such embodiments, the tcryst time window is measured by heating a sample of the metallic glass by capacitive discharge using the RCDF method while concurrently measuring the temperature of the sample. Once the capacitive discharge is completed, the sample attains and maintains a roughly constant temperature (which also can be referred to as the “process temperature”) until crystallization of the feedstock occurs, marked by releasing energy and causing the temperature to rise sharply, thereby designating tcryst. Knowledge of the viscosity function of temperature for the specific alloy (or for an alloy of very similar composition), would enable those skilled in the art to determine whether the viscosity at the process temperature is within the range of viscosities described herein.
RCDF Alloy Systems
The present disclosure is also directed to metallic glass-forming alloy systems possessing specific stability criteria such that they are capable of being shaped into high-aspect ratio articles substantially free of cosmetic defects and flaws using RCDF. More particularly, in many variations the disclosure is directed to a metallic glass alloy capable of resisting crystallization for at least 100 ms at a temperature above the glass transition where the viscosity is in the range of 100 and 104 Pa-s, or alternatively in the range of 101 and 103 Pa-s, or alternatively in the range of 102 and 104 Pa-s.
The metallic glass alloy composition is Zr—based, Ti—based, Ta—based, Y-based, Hf-based, Ni—based, Pd-based, Pt-based, Fe-based, Ni—based, Co-based, Cu-based, Au-based, Al-based, La-based, Ce-based, Pr-based, Ng-based, Gd-based, Mg-based, or Ca-based.
In certain embodiments, the metallic glass alloy composition is a Zr—based metallic glass alloy composition that may include elements selected from the group consisting of Ti, Ni, Cu, Be, Hf, Nb, V, Al, Sn, Ag, Pd, Fe, Co, and Cr.
In certain embodiments, the metallic glass alloy composition is Fe-based metallic glass alloy composition that may include elements selected from the group consisting of Co, Ni, Mo, Cr, P, C, B, Si, Al, Zr, W, Mn, Y, and Er.
In certain embodiments, the metallic glass alloy composition is Ni—based metallic glass alloy composition that may include elements selected from the group consisting of Co, Fe, Cu, Mo, Cr, P, B, Si, Sn, Nb, Ta, V, and Mn.
In certain embodiments, the metallic glass alloy composition is Cu-based metallic glass alloy composition that may include elements selected from the group consisting of Zr, Ti, Ni, Au, Ag, Hf, Nb, V, Si, Sn, and P.
In certain embodiments, the metallic glass alloy composition is Au-based metallic glass alloy composition that may include elements selected from the group consisting of Cu, Si, Ag, Pd, Pt, Ge, Y, and Al.
In certain embodiments, the metallic glass alloy composition is Pd-based metallic glass alloy composition that may include elements selected from the group consisting of Pt, Ni, Cu, P, Si, Ge, Ag, Au, Fe, and Co.
In certain embodiments, the metallic glass alloy composition is Pt-based metallic glass alloy composition that may include elements selected from the group consisting of Pd, Ni, Cu, P, Si, Ge, Ag, Au, Fe, and Co.
In still other embodiments, the metallic glass alloy composition has the following formula:
X100-a-bYaZb EQ. 1
wherein:
X is Ni, Fe, Co or combinations thereof
Y is Cr, Mo, Mn, Nb, Ta or combinations thereof
Z is P, B, Si, C, Ge or combinations thereof
a is between 5 and 15 atomic %
b is between 15 and 25 atomic %.
In various embodiments, the metallic glass alloy composition is any Ni—based glass-forming alloy, including but not limited to, Ni—Cr—Nb—P—B, Ni—Cr—Ta—P—B, Ni—Cr—Mn—P—B, Ni—Mo—Nb—Mn—P—B, Ni—Mn—Nb—P—B, Ni—Cr—Mo—Si—B—P, and Ni—Fe—Si—B—P metallic glass alloy compositions.
In still other embodiments, the metallic glass alloy composition has the following formula:
Ni100-a-b-c-dXaYbPcZd EQ. 2
wherein:
X is Cr, Mo, Mn or combinations thereof
Y is Nb, Ta, Mn or combinations thereof
Z is B, Si or combinations thereof
a is between 3 and 15 atomic %
b is between 1 and 6 atomic %
c is between 12 and 20 atomic %
d is between 0.5 and 6 atomic %.
In various additional embodiments, the metallic glass alloy composition is selected from Ni68.17Cr8.65Nb2.98P16.42B3.28Si0.5Ni68.17Cr8.65Nb2.98P15.92B3.28Si1, Ni69Cr10Nb1.5P18B1.5, Ni69Cr9.5Nb2P17.5B2, Ni69Cr9Nb2.5P17B2.5, Ni69Cr8Nb3.5P16B3.5, Ni69Cr7.5Nb4P15.5B4, Ni69Cr7Nb4.5P15B4.5, Ni69Cr8.75Nb2.75P16B3.5, Ni69Cr8Nb2.5P15.5B4, Ni69Cr9.25Nb2.25P15B4.5, Ni69Cr9.5Nb2P14.5 B3, Ni69Cr9.75Nb1.75P14B5.5. Ni69Cr10NbL5P13.5B6, Ni67.5Co1.5Cr8.5Nb3P16.5B3 Ni66Co3Cr8.5Nb3P16.5B3, Ni64Co5Cr8.5Nb3P16.5B3, Ni59Co10Cr8.5Nb3P16.5B3, Ni54Co15Cr8.5Nb3P16.5B3, Ni49Co20Cr8.5Nb3P16.5B3, Ni44Co25Cr8.5Nb3P16.5B3, N61.4Co10Cr5.52Nb3.38P16.67 Ni56.4Co15Cr5.52Nb3.38P16.67B3.03, Ni51.4Co20Cr5.52 Nb3.38P16.67 B3.03, Ni46.4Co25Cr5.52Nb3.38P16.67B3.03, Ni67.1Cr10Nb3.4P18Si1.5, Ni66.1Cr11Nb3.4P18Si1.5, Ni64.1Cr13Nb3.4P18Si1.5, Ni62.1 Cr15Nb3.4P18Si1.5, Ni68.5Cr8.5Mn3P17B3, Ni68.5Cr7.5Mn3Mo1P16.5B3, Ni68.5Cr9Ta3P16.5B3, Ni68.5Cr9Ta3P16.25B3.25, Ni68.5Cr9Ta3P16.25B3.5, Ni68.5Cr9Ta3P15.5 B4, Ni68.5Cr8Ta3P15B4.5, Ni69.5Cr8Ta3P16.25 B3.25, Ni68.5Cr9Ta3P16.25B3.25, Ni67.5Cr10Ta3P16.25 B3.25, Ni68.5Cr10Ta2P16.25B3.25, Ni68.5Cr9.5Ta2.5P16.25 B3.25, and Ni68.5Cr8.5Ta3.5P16.25B3.25.
Correlation with ΔT
The metallic glass alloys that satisfy the criterion tcryst>ts>100 ms within the temperature range associated with a viscosity range of 100 and 104 Pa-s, or alternatively in the range of 101 and 103 Pa-s, or alternatively in the range of 102 and 104 Pa-s, generally demonstrate a relatively high stability against crystallization. The present disclosure provides metallic glass alloys that are stable against crystallization when held at temperatures associated with viscosities in the range of 100 and 104 Pa-s, or alternatively in the range of 101 and 103 Pa-s, or alternatively in the range of 102 and 104 Pa-s, such that tcryst>100 ms at those temperatures, and are also stable against crystallization when heated at a constant rate above Tg, such that ΔT=Tx−Tg, where Tx is the crystallization temperature, is relatively large. Likewise, metallic glass alloys demonstrating insufficient stability against crystallization at the disclosed temperatures also demonstrate limited ΔT when heated at constant rate above Tg. Accordingly, in yet other embodiments, metallic glasses capable of being shaped into high-aspect ratio articles using RCDF may crystallize at a temperature Tx that is at least 45° C. higher than their glass transition temperature Tg when heated by a constant heating rate of 0.67° C./s.
The following examples describe in detail preparation and characterization of alloys and methods disclosed herein. It will be apparent to those of ordinary skill in the art that many modifications, to both materials and methods, may be practiced.
To explore the processing window and the RCDF shaping capabilities as a function of composition, the family of Ni—Cr—Nb—P—B glass-forming alloys disclosed in U.S. patent application Ser. No. 13/592,095, entitled “Bulk Nickel-Based Chromium and Phosphorus Bearing Metallic Glasses”, filed on Aug. 22, 2012, and Ser. No. 14/067,521, entitled “Bulk Nickel-Based Chromium and Phosphorus Bearing Metallic Glasses with High Toughness”, filed on Oct. 30, 2013, the disclosures of which are incorporated herein by reference in their entirety, was investigated. Experimental data and model fitting for the viscosity of Ni68.17Cr8.65Nb2.98P16.42B3.28Si0.5 metallic glass are presented in
The temperature vs. time curves following capacitive discharge heating of samples of metallic glasses Ni72.5Cr4.5Nb3.5P16.5B3 and Ni68.17Cr8.65Nb2.98P16.92B3.28 are presented in
Infrared images associated with the RCDF heating of metallic glass alloys Ni72.5Cr4.5Nb3.5P16.5B3 and Ni68.17Cr8.65Nb2.98P16.92B3.28 showing the spatial evolution of crystallization are presented in
The RCDF heating curves were produced for four metallic glass alloys heated to different temperatures, achieved by adjusting the energy discharge through various samples. The four metallic glass alloys are Ni68.17Cr8.65Nb2.98P16.92B3.28, Ni68.5Cr9Nb3P15.5B3Si1, Ni71.4Cr5.52Nb3.38P16.67B3.03, and Ni72.5Cr4.5Nb3.5P16.5B3. The crystallization times obtained for each alloy by RCDF heating to various plateau temperatures within the range of 525-675° C. are listed in Table 1. At each plateau temperature, the time to crystallization tcryst was recorded and plotted in Time-Temperature-Transformation (TTT) plot in
To further explore the processing window and the RCDF shaping capabilities, a Cu—Ti—Zr—Ni glass-forming alloy was also investigated. Experimental data and model fitting for the viscosity of Cu47Ti34Zr11Ni8 metallic glass is presented in
Differential scanning calorimetry was also performed for these alloys. The metallic glass alloys were scanned to above Tg at a constant heating rate of 0.67° C./s. The differential calorimetry scans for Ni68.17Cr8.65Nb2.98P16.92B3.28 and Ni72.5Cr4.5Nb3.5P16.5B3 metallic glasses are presented in
Differential scanning calorimetry was also performed for metallic glass alloys Ni68.5Cr9Nb3P15.5B3Si1, Ni71.4Cr5.52Nb3.38P16.67B3.03, whose TTT curves are also presented in
The method of differential scanning calorimetry can be used to identify the most suitable alloys for RCDF within a specific alloy family. Calorimetry is a more standard and simpler method than generating actual RCDF heating curves. Differential scanning calorimetry is therefore a useful tool in screening compositions within a specific metallic glass family for RCDF processing of high aspect ratio parts.
Methods
Experimental Procedure for Generating the RCDF Heating Curves
Ni—based metallic glass feedstock rods with a nominal diameter of 5 mm and Cu-based metallic glass feedstock strips 1 mm in thickness and 5 mm in width were verified to be amorphous by X-ray diffraction. The Ni—based metallic glass feedstock rods with diameters ranging between 4.83 to 4.91 mm were clamped on each end between two copper plates with a cylindrical hole slightly smaller than the diameter of the samples with exposed length between 7.28 mm and 36.96 mm. The exposed length was sheathed with a fused silica tube with nominal inner diameter of 5 mm and nominal outer diameter of 7 mm. Copper plates were clamped in a vise and attached to the leads of the capacitive discharge circuit. The fused silica sheath was supported so that when the sample heated and sagged under gravity, the sheath and sample would not shift. The Cu-based metallic glass feedstock strips were clamped on each end between two copper plates with exposed length of about 10 to 20 mm. A high-speed infrared pyrometer with a response time of 6 is and an Indium-Gallium-Arsenide sensor with a spectral range of 1.58-2.2 μm were used to measure the temperature at the midpoint of the exposed sample (for the rods, through the fused silica sleeve). A Rogowski coil current sensor and voltage probe were used to measure current and voltage, respectively, of the capacitive discharge pulse. Data from these sources were collected with an oscilloscope. Current and voltage data were used to verify that there were no anomalies in the shape of the current pulse. The temperature data shows a rapid heating during the current pulse, then a period of relatively constant temperature, then another period of increasing temperature due to the exothermic crystallization transition, and finally another period of relatively constant temperature before the data acquisition terminates. The time to crystallization tcryst was measured from the initiation of the current pulse to the onset of the temperature increase caused by crystallization.
Experimental Procedure for Molding High Aspect Ratio Parts Using RCDF
Metallic glass feedstock rods with a nominal diameter of 4 mm were verified to be amorphous by X-ray diffraction. The two ends of each rod were polished substantially parallel to each other and perpendicular to the axis of the rod, and subsequently ground to 180 grit surface finish. The rods were then confined within a fused silica sleeve with a copper electrode/plunger on each end. The fused silica was prepared so that two openings were ground into the sleeve and aligned with the gates of a stainless steel mold with a toroidal cavity having high aspect ratio features. Some of the cavity features had aspect ratio of about 10 and thickness of about 1 mm. This assembly of mold, sleeve, feedstock and electrodes was placed under compression along the axis of the feedstock and electrodes, and the electrodes were connected to the leads of the capacitor discharge circuit. The capacitors were discharged, and the material heated and flowed through the gates and into the toroidal mold cavity under the applied pressure. The injection molding of Ni68.17Cr8.65Nb2.98P16.92B3.28 was performed using a 23 mm long rod of feedstock. The successfully shaped high aspect ratio article is shown in
Experimental Procedure for Measuring Viscosity
The equilibrium (Newtonian) viscosity for Ni68.17Cr8.65Nb2.98P16.42B3.28Si0.5 metallic glass alloy was measured by performing three point beam bending of metallic glass rods 2 mm in diameter and 10 mm in length using a thermo-mechanical analyzer (PerkinElmer TMA 7), as described by Hagy (H. E. Hagy, “Experimental Evaluation of Beam Bending Method of Determining Glass Viscosities in the Range 108 to 1015 Poise”, J. Am. Ceram. Soc. 46, 93 (1963), the reference of which is incorporated herein in its entirety). Specifically, the isothermal viscosity at a given temperature is determined by the following equation:
where η is the apparent viscosity (Pa-s), g the gravitational constant (m/s2), L the support span length (m), Ic the cross sectional moment of inertia (m4), ν the midpoint deflection velocity (m/s), M the applied load (kg), ρ the density (kg/m3), and A is the cross sectional area (m2). Loads ranging from 20 to 1000 mN were applied.
Data for the equilibrium (Newtonian) viscosity for Ni68.17Cr8.65Nb2.98P16.42B3.28Si0.5 metallic glass alloy Cu47Ti34Zr11Ni8 were taken from Glade and Johnson (S. C. Glade and W. L. Johnson, “Viscous Flow of the Cu47Ti34Zr11Ni8 Glass-Forming Alloy”, J. Appl. Phys. 87, 7249 (2000), the reference of which is incorporated herein in its entirety).
Analytical Procedure for Fitting the Viscosity Data
To describe the temperature dependence of viscosity η(T), the cooperative shear model of Johnson et al. (W. L. Johnson, M. D. Demetriou, J. S. Harmon, M. L. Lind, and K. Samwer, “Rheology and Ultrasonic Properties of Metallic Glass Forming Liquids: a Potential Energy Landscape Perspective”, MRS Bulletin, 32, 644 (2007), the reference of which is incorporated herein in its entirety) is employed:
where η∞ the high-temperature limit of viscosity, Wg is the activation energy barrier at the glass transition, approximated by Wg≈kTgo log(ηg/η∞) (where ηg=1×1012 Pa-s, n is the effective fragility parameter, k the Boltzmann constant, T is temperature (in units of Kelvin), and Tgo the glass transition temperature associated with a the viscosity value of 1012 Pa-s (in units of Kelvin). The fitting parameters Ni68.17Cr8.65Nb2.98P16.42B3.28Sia5 and Cu47Ti34Zr11Ni8 metallic glass alloys are given in Table 4.
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 there between.
The present application claims the benefit of U.S. Provisional Patent Application No. 61/793,904, entitled “Methods for Shaping High Aspect Ratio Articles from Metallic Glass Alloys Using Rapid Capacitive Discharge and Metallic Glass Feedstock for Use in Such Methods”, filed on Mar. 15, 2013, which is incorporated herein by reference in its entirety.
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