Thermoplastic casting of amorphous alloys

• US 7,017,645 B2
• Filed: 01/31/2003
• Issued: 03/28/2006
• Est. Priority Date: 02/01/2002
• Status: Expired due to Term

• Current Assignee: Crucible Intellectual Property LLC
• Original Assignee: Liquidmetal Technologies
• Inventors: Johnson, William L., Peker, Atakan, Kim, Choongnyun
• Primary Examiner(s): Lin, Kuang Y.
• Application Number:
  US10/355,490
• Publication Number:
  US 20030222122A1
• Time in Patent Office: 1,152 Days
• Field of Search: 164/113, 164/312, 164/463, 164/423
• US Class Current: 164/113
• CPC Class Codes: B22D 11/001 of specific alloys
• CPC Class Codes: B22D 27/04 Influencing the temperature of the metal, e.g. by heating or cooling the mould
• CPC Class Codes: C22C 1/11 Making amorphous alloys
• CPC Class Codes: C22C 30/00 Alloys containing less than 50% by weight of each constituent
• CPC Class Codes: C22C 45/008 with Fe, Co or Ni as the major constituent C22C45/02, C22C45/04 take precedence
• CPC Class Codes: C22C 45/10 with molybdenum, tungsten, niobium, tantalum, titanium, or zirconium or Hf as the major constituent
• CPC Class Codes: C22F 1/183 of titanium or alloys based thereon
• CPC Class Codes: C22F 1/186 of zirconium or alloys based thereon

Abstract

A process and apparatus for thermoplastic casting of a suitable glass forming alloy is provided. The method and apparatus comprising thermoplastically casting the alloy in either a continuous or batch process by maintaining the alloy at a temperature in a thermoplastic zone, which is below a temperature, T_nose, (where, the resistance to crystallization is minimum) and above the glass transition temperature, Tg, during the shaping or moulding step, followed by a quenching step where the item is cooled to the ambient temperature. A product formed according to the thermoplastic casting process is also provided.

Claims

1. A method of thermoplastically casting an amorphous alloy comprising the steps of:

providing a quantity of an amorphous alloy in a molten state above the melting temperature of the amorphous alloy (Tm);

cooling said molten amorphous alloy directly to an intermediate thermoplastic forming temperature range above the glass transition temperature of the amorphous alloy and below the crystallization nose temperature, where the crystallization nose temperature (T_NOSE) is defined as the temperature at which crystallization of the amorphous alloy occurs on the shortest time scale, wherein said cooling happens at a rate sufficiently fast to avoid crystallization of the amorphous alloy;

stabilizing the temperature of the amorphous alloy within the intermediate thermoplastic forming temperature range;

shaping the amorphous alloy under a shaping pressure low enough to maintain the amorphous alloy in a Newtonian viscous flow regime and within the intermediate thermoplastic forming temperature for a period of time sufficiently short to avoid crystalization of the amorphous alloy to form a molded part; and

cooling the molded part to ambient temperature.

2. The method as described in claim 1, wherein the intermediate thermoplastic forming temperature is sufficiently high to avoid melt flow instabilities in the cooled alloy.

3. The method as described in claim 1, wherein the shaping pressure is from about 1 to about 100 MPa.

4. The method as described in claim 1, wherein a heated shaping apparatus is selected from the group consisting of a mould, a die tool, a closed die, and an open-cavity die.

5. The method as described in claim 4, wherein the heated shaping apparatus is kept at a temperature within about 150°

C. of the glass transition temperature of the amorphous alloy.

6. The method as described in claim 4, wherein the heated shaping apparatus is kept at a temperature within about 50°

C. of the glass transition temperature of the amorphous alloy.

7. The method as described in claim 4, wherein the temperature of the heated shaping apparatus is controlled through a temperature feedback controller.

8. The method as described in claim 4, wherein the temperature of the heated shaping apparatus is increased during the forming step.

9. The method as described in claim 4, wherein the amorphous alloy is maintained in the heated shaping apparatus for a time suitable for the amorphous alloy to reach a nearly uniform temperature substantially equal to that of the heated shaping apparatus.

10. The method as described in claim 4, wherein the amorphous alloy is introduced into the heated shaping apparatus at a specified flow rate, and wherein the rate of flow of liquid alloy through the heated shaping apparatus is maintained at one of either a constant velocity or a constant strain rate.

11. The method as described in claim 10, wherein the strain rate is between about 0.1 and 100 s⁻

1.

12. The method as described in claim 4, wherein an applied pressure is used to move the amorphous alloy through the heated shaping apparatus.

13. The method as described in claim 12, wherein the applied pressure is less than about 100 Epa.

14. The method as described in claim 12, wherein the applied pressure is less than about 10 EPa.

15. The method as described in claim 1, wherein the shaping step takes about 10 to 100 times longer than the cooling step.

16. The method as described in claim 1, wherein the shaping step takes about 5 to 15 times longer than the cooling step.

17. The method as described in claim 1, wherein the shaping time is between about 3 and 200 seconds.

18. The method as described in claim 1, wherein the shaping time is between about 10 and 100 seconds.

19. The method as described in claim 1, wherein the shaping pressure is about 5 to 15 times more than the pressure applied to the molten amorphous alloy in the cooling step.

20. The method as described in claim 1, wherein the shaping pressure is about 10 to 100 times more than the pressure applied to the molten amorphous alloy in the cooling step.

21. The method as described in claim 1, wherein the shaping pressure is about 50 to 500 times more than the pressure applied to the molten amorphous alloy in the cooling step.

22. The method as described in claim 1, wherein the step of shaping the amorphous alloy further comprises extracting the molded part continuously.

23. The method as described in claim 1, wherein the amorphous alloy is a Zr—

Ti alloy, where the sum of the Ti and Zr content is at least about 20 atomic percent of the composition of the amorphous alloy.

24. The method as described in claim 1, wherein the amorphous alloy is a Zr—

Ti—

Nb—

Ni—

Cu—

He alloy, where sum of the Ti and Zr content is at least about 40 atomic percent of the composition of amorphous alloy.

25. The method as described in claim 1, wherein the amorphous alloy is a Zr—

Ti—

Nb—

Ni—

Cu—

Al alloy, where sum of the Ti and Zr content is at least about 40 atomic percent of the composition of the amorphous alloy.

26. The method as described in claim 1, wherein the amorphous alloy is an Fe-base alloy, where the Fe content is at least about 40 atomic percent of the composition of the amorphous alloy.

27. The method as described in claim 1, wherein the amorphous alloy may be described in general terms by the formula (Zr,Ti)_a(Ni,Cu, Fe)_b(Be,Al,si,B)_c, where a is in the range of from about 30% to 75% of the total composition in atomic percentage, b is in the range of from about 5% to 60% of the total composition in atomic percentage, and c is in the range of from about 0% to 50% in total composition in atomic percentage.

28. The method as described in claim 1, wherein the amorphous alloy is Zr₄₇Ti₈Ni₁₀cu_7.5Be_27.5.

29. The method as described in claim 1, wherein the amorphous alloy has a supercooled liquid region (Δ

Tsc) of about 30°

C. or more, where Δ

Tsc is defined as the difference of the onset of crystallization of the amorphous alloy (T_x) and the onset of glass transition of the amorphous alloy (T_g), as determined from standard differential scanning calorimetry scans at 20°

C./min.

30. The method as described in claim 29, wherein the supercooled liquid region (Δ

Tsc) is about 60°

C. or more.

31. The method as described in claim 29, wherein the supercooled liquid region (Δ

Tsc) is about 90°

C. or more.

32. The method as described in claim 1, wherein the amorphous alloy has a critical cooling rate of about 1,000°

C./sec or less.

33. A method of thermoplastically casting an amorphous alloy comprising the steps of:

providing a quantity of an amorphous alloy at a melt temperature above the melting temperature of the amorphous alloy.

pouring the amorphous alloy into a shaping apparatus at a flow rate and under a pressure to ensure Newtonian flow of the amorphous alloy, and simultaneously directly cooling said amorphous alloy to within an intermediate thermoplastic forming temperature range above the glass transition temperature of the amorphous alloy at a rate sufficiently fast to avoid crystallization of the amorphous alloy;

stabilizing the temperature of the amorphous alloy within the intermediate thermoplastic forming temperature range;

shaping the amorphous alloy to form a molded part, wherein the shaping occurs under a shaping pressure sufficiently low to avoid melt instabilities and wear on the shaping apparatus, within the intermediate thermoplastic forming temperature range for a period of time sufficiently short to avoid crystallization of the amorphous alloy; and

cooling the molded part to ambient temperature.