US20040247479A1

US20040247479A1 - Method of liquid phase sintering a two-phase alloy

Info

Publication number: US20040247479A1
Application number: US10/453,542
Authority: US
Inventors: William Spencer
Original assignee: Lockheed Martin Corp
Current assignee: Lockheed Martin Corp
Priority date: 2003-06-04
Filing date: 2003-06-04
Publication date: 2004-12-09

Abstract

Liquid phase sintering method for a two-phase alloy includes forming a green body billet of a two-phase alloy, solid state sintering the green body billet, surrounding the solid state sintered billet with a refractory barrier medium within a refractory container to form a charge, optionally flowing wet hydrogen through at least a portion of the charge, equilibrating a charge temperature below a solidus temperature of the two-phase alloy, changing the charge temperature to a liquid phase sintering temperature of the two-phase alloy, maintaining the liquid phase sintering temperature for a period of time of ≦four hours, reducing the charge temperature to less than the solidus temperature of the two-phase alloy, and optionally holding the charge stationary as the charge temperature passes through the solidus temperature. Optionally, the charge can be rotated about an axis of symmetry during liquid phase sintering and a portion of the charge can be zone heated.

Description

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0001] At least some aspects of this invention were made with Government support under contract no. F08630-96-C-0042 DMCPW. The Government may have certain rights in this invention.

BACKGROUND

The present invention relates to liquid phase sintering of a two-phase metal alloy. More particularly, the present invention relates to a method to liquid phase sinter a tungsten heavy alloy.

Large size and/or geometrically complex two-phase alloy materials, such as tungsten heavy alloy (WHA), are difficult to produce as a single piece.

Liquid phase sintering (LPS) can be used to produce WHA parts. However, LPS can be limited by, for example, maximum furnace size, severe slumping of parts, liquid matrix runout of WHA material, and substantial compositional variation due to alloying elements, such as tungsten in WHA, settling under gravity. Further, long process times at temperatures where liquid matrix is present can exacerbate the limitations. For example, LPS processes can include up to 14 to 20 hours at greater than 1475° C., resulting in settling of the tungsten grains toward the bottom of the part and/or the formation of a portion of the part that is matrix rich.

Current methods of producing large pieces include liquid phase sintering in a pusher furnace. A pusher furnace LPS process can include pushing a WHA billet at a given rate through a hot zone of a long furnace with an essentially fixed temperature profile along the length. However, part size in a typical pusher furnace LPS consolidation process can be limited by the furnace opening, which is approximately 20 inches wide and 4 inches high. Further, tungsten particle settling can occur in a WHA billet higher than four inches when processed in a pusher furnace due to gravity during the time when the matrix of the material is liquid. This can be especially pronounced in thicker WHA parts, which can show compositional variations of up to 10 weight percent (wt. %) or more in the part.

SUMMARY

An exemplary liquid phase sintering method for a two-phase alloy comprises forming a green body billet of a two-phase alloy, solid state sintering (SSS) the green body billet, forming a charge by surrounding the solid state sintered billet by a refractory barrier medium within a refractory container, wherein the refractory barrier medium prevents contact between the solid state sintered billet and the refractory container, equilibrating a temperature of the charge below a solidus temperature of the two-phase alloy, changing the temperature of the charge to a liquid phase sintering temperature of the two-phase alloy, maintaining the liquid phase sintering temperature for a period of time of less than or equal to four hours, and reducing the temperature of the charge to less than the solidus temperature of the two-phase alloy.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The following detailed description makes reference to the accompanying drawings in which like numerals designate like elements and in which: [0007]
FIG. 1 schematically illustrates an exemplary liquid phase sintering method. [0008]
FIG. 2 shows a cross section of an exemplary charge used in the liquid phase sintering method of FIG. 1. [0009]
FIG. 3 shows an exemplary temperature versus time plot for a charge indicating the temperature profile in the charge during the liquid phase sintering method of FIG. 1. [0010]
FIG. 4 shows a cross section of an exemplary rotating apparatus used in the liquid phase sintering method of FIG. 1. [0011]
FIG. 5 shows an exemplary embodiment of a charge and a heating element for a liquid phase sintering method with zone heating. [0012]
FIGS. 6[0013] a and 6 b show micrographs of a tungsten heavy alloy after (a) solid state sintering and (b) rapid liquid phase sintering according to the exemplary method, respectively.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates an exemplary liquid phase sintering method for a two-phase alloy. The method [0014] 100 comprises forming a green body billet of a two-phase alloy 102, solid state sintering (SSS) the green body billet 104, forming a charge 106 by surrounding the solid state sintered billet by a refractory barrier medium within a refractory container, wherein the refractory barrier medium prevents contact between the solid state sintered billet and the refractory container, optionally flowing wet hydrogen through at least a portion of the charge 108, equilibrating a temperature of the charge below a solidus temperature of the two-phase alloy 110, changing the temperature of the charge to a liquid phase sintering temperature of the two-phase alloy 112, maintaining the liquid phase sintering temperature for a period of time of less than or equal to four hours 114, optionally rotating the charge about an axis of symmetry 116, optionally zone heating 118 a portion of the charge to liquid phase sinter the two-phase alloy, reducing the temperature of the charge to less than the solidus temperature of the two-phase alloy 120, and optionally holding the charge stationary as the temperature passes through the solidus temperature 122.
Forming the green body billet can be by any suitable method. For example, a green body billet can be cold pressed to about 50-60%, or higher, theoretical density. The shape of the green body billet can be any suitable shape such as a solid shape, a hollow shape, or a shape containing both solid and hollow sections. For example, the shape of the green body billet can be a solid geometric form, both regular and irregular, or the shape can have one or more hollows open to an outer surface of the green body billet. [0015]
Solid state sintering of the green body billet can occur at any suitable temperature for the materials used. For example, WHA sintering can occur in a multistep process with a final step at approximately 1400° C. for several hours, e.g., 8 hours. Theoretical densities of the solid state sintered billet can be from 50 to 95% theoretical density or higher, preferably greater than 80% theoretical density and most preferably greater than 90% theoretical density. [0016]
FIG. 2 shows an exemplary embodiment of a [0017] charge 200. The charge 200 includes a refractory container 202 in which the solid state sintered (SSS) billet 204 of a two-phase alloy is placed. The SSS billet 204 is surrounded by a refractory barrier medium 206, such that the SSS billet 204 does not touch the refractory container 202.
The [0018] refractory container 202 can take any suitable form and can be made of any suitable material. For example, the refractory container 202 can be formed of a metallic materials. Exemplary metallic materials include molybdenum (Mo) based alloys and tungsten (W) based alloys. Ceramic materials can also be used for the refractory container.
The [0019] refractory barrier medium 206 can function to provide a barrier between the refractory container 202 and the SSS billet 204, such that the SSS billet 204 does not contact the refractory container 202. In addition, the refractory barrier medium 206 can be permeable to hydrogen, especially wet hydrogen, which can reduce oxides. Further, the refractory barrier medium 206 can function to constrain and/or mold the SSS billet when the two-phase alloy is above the solidus temperature. For example, the restraining function of the refractory medium can assist in maintaining the shape of the two-phase alloy during the liquid phase sintering portion of the method. If freestanding when heated above the solidus temperature, the two-phase alloy can undergo severe slumping and ejection of liquid matrix from the bulk. In an exemplary embodiment, the refractory barrier medium can be a ceramic liner, a ceramic sand, an open cell ceramic foam, or any suitable form that can meet one or more of the functions of the barrier medium.
For example, the ceramic of the refractory barrier medium can be Al[0020] ₂O₃, ZrO₂, MgO, or any other suitable oxide or combinations thereof. In a preferred embodiment, the refractory barrier medium is a ceramic sand formed of Al₂O₃. Al₂O₃sand can be easier to remove from the charge at the end of the liquid phase sintering method, and also allows wet hydrogen atmosphere to permeate through and contact at least a portion of the SSS billet, preferably the entire surface of the SSS billet. Additionally, Al₂O₃sand has a suitable grain size such that seepage of liquid matrix during the liquid phase sintering process does not seep into the sand. For example, a preferred Al₂O₃sand has a grain size of between −325 and 80 mesh. However, a uniform grain size is not required and a suitable distribution of grain sizes may be used.
The charge can be configured to allow wet hydrogen to contact at least a portion of the SSS billet. The contact can be for any suitable time, such as, for example, up to 12 hours or longer, depending on the size of the SSS billet, the type and/or permeability to wet hydrogen of the refractory barrier medium, and/or the manner in which the wet hydrogen is supplied to the charge. [0021]
For example, the refractory barrier material can be permeable to a wet hydrogen atmosphere. The refractory barrier medium can either be diffusively permeable, i.e., a blanket of wet hydrogen atmosphere in contact with the refractory barrier medium will defuse through and to at least a portion of the SSS billet, and/or the wet hydrogen atmosphere can be forced to flow through the refractory barrier medium to contact the SSS billet, such as wet hydrogen having a pressure of 3 to 4 psi. [0022]
The wet hydrogen atmosphere can be supplied to the charge by any suitable means. For example, the refractory container can have one or more inlets, connections, or other suitable openings or fixtures to port weight hydrogen atmosphere diffusively and/or at a specified pressure into the interior of the refractory container. FIG. 2 shows the [0023] charge 200 with a hydrogen inlet 208. Optionally, the hydrogen inlet 208 can be located on the closure 210.
In the exemplary embodiment shown in FIG. 2, the [0024] refractory barrier medium 206 completely fills the interior space of the refractory container 202 and completely surrounds the SSS billet 204. Further, in embodiments in which the shape has one or more hollow sections, the hollow sections contain the refractory barrier medium to assist in obtaining a uniform temperature profile across a cross section of the SSS billet during the liquid sintering process, e.g., the refractory barrier medium can be packed around the SSS billet and into any hollows, such as troughs, holes, cut-outs, and so forth, so that the refractory barrier medium contacts all exterior surfaces of the SSS billet and/or is tightly packed about the SSS billet. Optionally, the refractory barrier medium can surround only a portion of the SSS billet that is to be liquid phase sintered and/or the refractory barrier medium can also only partially fill the refractory container. However, partially surrounding the SSS billet or partially filling the refractory container can result in voids which can allow seepage of matrix and/or slumping of the two-phase alloy during liquid phase sintering. The restraining function of the refractory medium assists in maintaining the shape of the two-phase alloy during the process. For example, if freestanding when heated above the solidus temperature, the two-phase alloy can undergo severe slumping and ejection of liquid matrix from the bulk. The refractory medium, such as an aluminum oxide sand, can serve to protect the container as well as allowing hydrogen gas to contact the surfaces of the SSS billet and prevent the SSS billet contacting the refractory container because liquid billet material can alloy with select materials, such as molybdenum alloys of the refractory container.
The [0025] charge 200 can be an open vessel, i.e., open at one end, or can be closed. As shown in the exemplary embodiment of FIG. 2, the charge 200 has a closure 210 at one end. The closure 210 can include threads 212 for cooperating with threads 214 on the refractory container 202 to form a closed refractory container. Further, the closure 210 at an outer surface 216 can have a connection 218, such as a socket, threaded connection, bolt, and so forth, for connecting to a mechanical device (not shown), such as a motor, for moving or imparting motion, rotation, or other motive force to the charge 200.
FIG. 3 shows an exemplary temperature versus time plot for a charge indicating the temperature profile in the charge during the liquid phase sintering method of FIG. 1. Temperature in the charge at a starting time is initially at a starting temperature (point A), which is changed at a reasonable rate (Δ[0026] ₁) to a first temperature T₁(point B). A reasonable rate can be any suitable rate that does not unnecessarily prolong the process, for example, the heating rate can be 50 to 60° C. per hour to a temperature of 750° C. and 30 to 40° C. thereafter. Temperature T₁can be any suitable temperature below the solidus temperature (T_solidus) of the two-phase alloy. For example, T₁can be 20-40° C. below the solidus temperature. The temperature of the charge is equilibrated at T₁for a period of time, the equilibration period (t_eq). For example, the equilibration period can be approximately 6 to 8 hours, depending on the size of the charge and the furnace. At the end of the equilibration period (point C), the temperature of the charge is increased to a liquid phase sintering temperature (T_LPS) at a suitable rate (Δ₂). The rate of change (Δ₂) from the end of the equilibration period to T_LPScan be, for example, 40-400° C. per hour or can occur over approximately 0.1-2 hours.
Liquid phase sintering (starting at point D) continues for a liquid phase sintering period (t[0027] _LPS) of less than or equal to four hours. The liquid phase sintering period can vary depending on the medium of the two-phase alloy and on the size of the SSS billet and/or the charge. For example, a larger SSS billet or charge can require additional time at the liquid phase sintering temperature to liquid phase sinter the two-phase alloy. Preferably, the liquid phase sintering period is from 0.3-1.5 hours.
At the end of the liquid phase sintering period (point E), the temperature of the charge is reduced to less than the solidus temperature of the two-phase alloy. A suitable rate of change (Δ[0028] ₃) for the reduction of temperature is 20-100° C. per hour or can occur over approximately 0.2-4 hours. If the rate of change (Δ₃) is too fast, the two-phase alloy can have increased porosity. However, if the rate of change (Δ₃) is too slow, the two-phase alloy can have increased settling of tungsten particles within liquid metal matrix. Further, the rate of change (Δ₃) to a temperature below the solidus temperature of the two-phase alloy can occur by suitable cooling methods including ambient cooling and/or forced cooling.
At the end of the process (point F), the two-phase alloy can be removed from the charge for subsequent processing and/or use. [0029]
Tungsten heavy alloy (WHA) is a two-phase alloy or metal-matrix composite consisting of almost pure tungsten (W) grains surrounded by a matrix that consists of an alloy of tungsten with secondary elements, e.g., nickel (Ni), iron (Fe), and/or cobalt (Co). WHA can vary in composition from at least 80-90 wt. % W to about 95 wt. % W and the balance Ni, Fe and/or Co. In an exemplary embodiment, the two-phase alloy is a tungsten heavy alloy including ≦93 wt. % W. Further, the WHA can optionally include a balance of at least one secondary element selected from the group consisting of Ni, Fe, and Co. An exemplary WHA comprises 90 wt. % W, 8 wt. % Ni, and 2 wt. % Co. [0030]
An exemplary WHA, such as tungsten heavy alloy formed of 93 wt. % W and the balance Ni, Fe, and Co that has been solid state sintered to about 95% theoretical density, e.g., greater than 90%, can have a solidus temperature of 1475° C.±20° C. and a liquid phase sintering temperature of 1535° C.±20° C. The solidus temperature is the temperature at which the components of the matrix, such as nickel, begin to melt. For a tungsten heavy alloy solid state sintered to 90% theoretical density, the solidus temperature is 1455° C.±20° C. [0031]
As depicted in FIG. 2, the [0032] charge 200 has a cylindrical shape with an axis X-X′ in the height dimension. However, the charge can have any form with an axis of symmetry about which the charge can be rotated during an optional rotation step of the method. For example, when the charge is cylindrical shaped, the charge can be rotated about the axis of symmetry X-X′ by a suitable rotating apparatus. Alternatively, the charge can be rotated about the axis of symmetry Y-Y′ by a suitable rotating apparatus. Other suitable forms for the charge include a sphere, a cone, a box, or other suitable form that has an axis of symmetry about which rotation can occur in a suitable rotating apparatus.
FIG. 4 shows an exemplary [0033] rotating apparatus 400 for use in the method of FIG. 1. As shown, the rotating apparatus 400 places the charge 402 (shown in cross section corresponding to section A-A in FIG. 2) in contact with rotating bars 404 seated in notches 406 of support blocks 408. A motor or other means of imparting motive force (not shown) can be attached to the charge 402 by way of the connection on the closure (shown in FIG. 2 as connection 218). For example, a bar can connect the motor and the charge via the socket in the closure. In other respects, the charge can include a SSS billet 410, a refractory barrier medium 412, a refractory container 414, and a hydrogen connection (not shown).
Rotation (ω) of the charge [0034] 402 can occur in any direction around any axis of symmetry, such as clockwise or counter clockwise around axis X-X′. Rotation can be from one to several cycles per minute to limit centrifugal forces acting on the particles and to limit the settling due to gravity. The exemplary method of FIG. 1 can optionally include rotating the charge during at least a portion of the method during which the temperature of the charge is above the solidus temperature, e.g., during the portion of the temperature-time profile represented in FIG. 3 between points D and E. Such rotation can limit settling of the tungsten which is surround by liquid matrix alloy and also can assist in compositional uniformity. However, the charge can also be maintained in a fixed position during the period of time the charge is above solidus temperature.
Further, when the charge has been rotated during at least a portion of the method during which the temperature of the charge is above the solidus temperature, the charge can be held stationary as the temperature passes through the solidus temperature. For example, during the reduction of temperature from the liquid phase temperature to the end of the process, e.g., during the portion of the temperature-time profile represented in FIG. 3 between points E and F, the charge can be held stationary during the time when the temperature passes through the solidus temperature (T[0035] _solidus). The period of time during which the charge is held stationary can be any suitable time, for example, the charge can be held stationary within a temperature range of ±5° preferably ±2°, about the solidus temperature.
The temperature of the charge during any point of the exemplary process, can be equilibrated, changed, or maintained by suitable methods such as radiative heating, resistive heating, or electromagnetic heating. Exemplary electromagnetic heating methods include radio frequency (RF) heating or microwave (MW) heating. [0036]
The charge can be heated in any suitable environment. For example, the charge or the charge in the rotating apparatus can be placed within a furnace to achieve the desired temperature profile during the method. Suitable furnaces include partial vacuum furnaces and atmospheric furnaces. [0037]
An exemplary method of liquid phase sintering can optionally include zone heating a charge or a portion of a charge to liquid phase sinter the two-phase alloy. Zone heating can include heating the portion of the charge to the liquid phase sintering temperature to form a heating zone and traversing the heating zone from a first end of the charge to a second end of the charge by relative motion between the charge and a heating element. The temperature profile produced in the portion of a charge is sufficient to liquid phase sinter a two-phase alloy. For example, the temperature profile presented and described with reference to FIG. 3 can be applied to a charge or portions of a charge with a WHA SSS billet and the heating element can traverse the geometry of the charge. Zone heating can occur both alternative to and in combination with rotating the charge about an axis of symmetry. [0038]
FIG. 5 shows an exemplary embodiment of a charge and a heating element for a liquid phase sintering method with zone heating. As shown in FIG. 5, a [0039] zone heating apparatus 500 includes a heating element 502 positioned about a charge 504. Examples of heating elements include an inductively, resistively, radiatively or electromagnetically heated ring, jacket, coupling, sleeve, or other heating element that can be placed around or approximate to a portion of the outer surface of the charge and that can produce a suitably constrained heating zone projected toward the charge to achieve, within a two-phase alloy located in a charge, at least the liquid phase sintering temperature of the two-phase alloy. Preferably, the heating element is heated by an electric resistance furnace or an induction furnace. In the exemplary embodiment, the charge 504 is cylindrical and the heating element 502 is an inductive ring about the circumference of the cylindrical charge 504.
In the exemplary embodiment depicted in FIG. 5, the [0040] charge 504 includes a 90% dense SSS billet 506 constrained vertically within a refractory container 508 and surround by a refractory medium 510. The charge 504 is heated by the heating element 502, which is depicted as an inductive coil, so as to melt a heating zone 512 at a first end 514 of the charge 502. As shown, the heating zone 512 is disc-like and is approximately 10 centimeters or less in height. The heating zone 512 is then moved up the charge 504 toward a second end 516 by movement of the charge 504 and/or the heating element 502.
Relative motion can occur between the [0041] charge 504 and the heating element 502 such that a temperature profile in the charge 504 is controlled and the solidifying front of the liquid phase sintered material is moved uniformly toward a free surface of the two-phase alloy, e.g., toward an end of the two-phase alloy. Movement of the heating zone 512 can be coordinated with achieving a desired peak temperature within the charge and relative motion can occur either step wise or continuously. Once the heating zone 512 at any one portion of the charge completes the liquid phase sintering time period, the heating element is moved relative to the charge by either moving the heating element, the charge, or both. For example, the heating zone can be moved from a first end 514 of the charge 504 to a second end 516 of the charge 504 by any suitable means, such as by a mechanical arm, a conveyor system, a stepper motor, and so forth. Further, the charge can be stationary or can also be moved through the heating zone by a suitable elevating or conveying system.
The rate of movement of the heating zone, and thus of the temperature profile, can depend upon the size of the part and the heating system. Traverse rates in the range of about 1-5 centimeters per hour can be used to achieve melting and solidification gradients in the heating zone to achieve the desired compositional and mechanical results. Solidification gradients in the range of 50-200° per hour are preferred in order to avoid generation of porosity defects in the material. [0042]
The moving heating zone can eliminate both defects caused by conventional methods, e.g., leakage and settling. For example, movement of the temperature profile toward a free surface can avoid shrinkage defects within the two-phase alloy, e.g., an ingot of tungsten heavy alloy, formed by the liquid phase sintering process. Further, the size of the heating zone, e.g., cylindrical with less than 10 centimeters in height depending on the thickness of the charge and/or solid state sintered billet in the transverse direction, and the rapid movement of the solidifying front, e.g., 1 to 5 centimeters per hour, can result in insufficient time for any significant tungsten green settling. Also, the directional solidification of the moving zone can sweep shrinkage or evolved gas porosity up the ingot to the free surface of the top, thereby reducing porosity to less than or equal to 5%, preferably less than or equal to 2%. [0043]
FIGS. 6[0044] a and 6 b show micrographs of a tungsten heavy alloy after (a) solid state sintering and (b) rapid liquid phase sintering according to the exemplary method, respectively. The photomicrograph in FIG. 6a shows porosity distributed throughout the image. This porosity is approximately 5%. Further, the tungsten phase (the light shaded phase) is contiguous and the matrix material (the dark gray phase) is not contiguous. The contiguous tungsten phase, which has low ductility, can negatively impact crack propagation within the material.
The photomicrograph in FIG. 6[0045] b shows that the tungsten phase has ripened into substantially spherical phase regions. Further, the matrix material, e.g., nickel, iron and/or cobalt, has an increased contiguous character, e.g., a larger proportion of the matrix material is contiguous than in the solid state sintered sample of FIG. 6a, and the porosity is not evident. Accordingly, the increase in proportion matrix material that is contiguous improves the ductility of the liquid phase sintered two-phase alloy. As shown, the tungsten phase is approximately 50 microns in diameter. Also, FIG. 6b shows that at least a portion of the tungsten phase is not contiguous or is completely surround by matrix phase, e.g., does not contact a neighboring tungsten phase.
While the present invention has been described by reference to the above-mentioned embodiments, certain modifications and variations will be evident to those of ordinary skill in the art. Therefore, the present invention is to be limited only by the scope and spirit of the appended claims. [0046]

Claims

What is claimed is:

1. A method to liquid phase sinter a two-phase alloy, the method comprising:

forming a green body billet of a two-phase alloy;

solid state sintering the green body billet;

forming a charge by surrounding the solid state sintered billet by a refractory barrier medium within a refractory container, wherein the refractory barrier medium prevents contact between the solid state sintered billet and the refractory container;

equilibrating a temperature of the charge below a solidus temperature of the two-phase alloy;

changing the temperature of the charge to a liquid phase sintering temperature of the two-phase alloy;

maintaining the liquid phase sintering temperature for a period of time of less than or equal to four hours; and

reducing the temperature of the charge to less than the solidus temperature of the two-phase alloy.

2. The method of claim 1, wherein solid state sintering the green body billet results in at least 80% theoretical density.

3. The method of claim 1, wherein the refractory barrier medium is a ceramic liner, a ceramic sand, or an open cell ceramic foam.

4. The method of claim 3, wherein the ceramic sand is Al₂O₃, ZrO₂, or MgO.

5. The method of claim 3, wherein the ceramic sand has a grain size of −325 to 80 mesh

6. The method of claim 1, wherein the refractory container is formed of a metallic material.

7. The method of claim 6, wherein the metallic material is a Mo-based alloy or a W-based alloy.

8. The method of claim 1, wherein the refractory barrier medium is permeable to a wet hydrogen atmosphere and the method comprises flowing wet hydrogen through at least a portion of the charge.

9. The method of claim 8, wherein the wet hydrogen atmosphere contacts at least a portion of the two-phase alloy.

10. The method of claim 8, wherein the wet hydrogen has a pressure of 3 to 4 psi.

11. The method of claim 1, wherein equilibrating a temperature of the charge below a solidus temperature of the two-phase alloy is equilibrating at less than 20° C. below the solidus temperature.

12. The method of claim 1, wherein changing the temperature of the charge to a liquid phase sintering temperature of the two-phase alloy is changing the temperature at a rate of from 40° C./hr to 400° C./hr.

13. The method of claim 1, wherein the period of time for maintaining the liquid phase sintering temperature is from 0.3 hours to 1.5 hours.

14. The method of claim 1, wherein reducing the temperature of the charge to less than the solidus temperature of the two-phase alloy is reducing the temperature at a rate of from 20° C./hr to 100° C./hr.

15. The method of claim 1, wherein the two-phase alloy is a tungsten heavy alloy.

16. The method of claim 15, wherein the tungsten heavy alloy includes less than or equal to 93 wt. % tungsten.

17. The method of claim 15, wherein the tungsten heavy alloy includes less than or equal to 93 wt. % tungsten and the balance at least one secondary element selected from the group consisting of Ni, Fe and Co.

18. The method of claim 15, wherein the solidus temperature is 1475±20° C.

19. The method of claim 15, wherein the liquid phase sintering temperature is 1535±20° C.

20. The method of claim 1, wherein the charge has an axis of symmetry and the method comprises rotating the charge about the axis of symmetry during at least a portion of the method during which the temperature of the charge is above the solidus temperature.

21. The method of claim 20, wherein a rotation rate of the rotating charge is from 1 to several cycles per minute.

22. The method of claim 1, wherein the charge has a cylindrical shape with an axis in a height dimension and the method comprises rotating the charge about the axis of symmetry during at least a portion of the method during which the temperature of the charge is above the solidus temperature.

23. The method of claim 22, wherein a rotation rate of the rotating charge is from 1 to several cycles per minute.

24. The method of claim 1, comprising holding the charge stationary as the temperature passes through the solidus temperature during the step of reducing the temperature of the charge to less than the solidus temperature.

25. The method of claim 1, wherein the charge is placed in a partial vacuum or an atmospheric furnace.

26. The method of claim 1, wherein the temperature of the charge is equilibrated, changed, or maintained by radiative heating, resistive heating, or electromagnetic heating.

27. The method of claim 26, wherein electromagnetic heating includes RF heating or MW heating.

28. The method of claim 1, comprising zone heating a portion of the charge to liquid phase sinter the two-phase alloy.

29. The method of claim 28, wherein zone heating comprises heating the portion of the charge to the liquid phase sintering temperature to form a heating zone and traversing the heating zone from a first end of the charge to a second end of the charge by relative motion between the charge and a heating element.

30. The method of claim 29, wherein the relative motion is step-wise or continuous.

31. The method of claim 29, wherein the relative motion is at a rate of 1 to 5 cm per hour.

32. The method of claim 28, wherein zone heating occurs during the step of changing the temperature of the charge to a liquid phase sintering temperature of the two-phase alloy.

33. The method of claim 28, wherein the charge has an axis of symmetry and the method comprises rotating the charge about the axis of symmetry during at least a portion of the method during which the temperature of the charge is above the solidus temperature.

34. The method of claim 33, wherein a rotation rate of the rotating charge is from 1 to several cycles per minute.

35. The method of claim 28, wherein the charge has a cylindrical shape with an axis in a height dimension and the method comprises rotating the charge about the axis of symmetry during at least a portion of the method during which the temperature of the charge is above the solidus temperature.

36. The method of claim 35, wherein a rotation rate of the rotating charge is from 1 to several cycles per minute.