Powder metal process for producing multiphase NI-AL-TI intermetallic alloys

• US 5,098,469 A
• Filed: 09/12/1991
• Issued: 03/24/1992
• Est. Priority Date: 09/12/1991
• Status: Expired due to Fees

• Current Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Rezhets, Vadim
• Primary Examiner(s): Lechert, Jr., Stephen J.
• Application Number:
  US07/758,138
• Time in Patent Office: 194 Days
• Field of Search: 75/249, 419/32, 419/38, 419/54, 419/60, 419/47
• US Class Current: 75/249
• CPC Class Codes: B22F 1/09 Mixtures of metallic powders
• CPC Class Codes: B22F 2999/00 Aspects linked to processes or compositions used in powder metallurgy
• CPC Class Codes: C22C 1/0433 Nickel- or cobalt-based alloys
• CPC Class Codes: C22C 19/03 based on nickel
• CPC Class Codes: C22C 21/00 Alloys based on aluminium

Abstract

A powder metallurgy process for producing near-net shape, near-theoretical density structures of multiphase nickel, aluminum and/or titanium intermetallic alloys is provided by employing pressureless sintering techniques. The process consists of blending a brittle aluminide master alloy powder with ductile nickel powder, so as to achieve the desired composition. Then, after cold compaction of the powdered mixture, the compact is liquid phase sintered. The four step liquid phase sintering process is intended to ensure maximum degassing, eliminate surface nickel oxide, homogenize the alloy, and complete densification of the alloy by liquid phase sintering.

Claims

1. A method for producing sintered articles of multiphase intermetallic alloys which are characterized by near-theoretical density and near-net shape, comprising the following steps:

blending a powdered mixture, said powdered mixture comprising nickel powder and a prealloyed powder containing aluminum and at least one metal chosen from the group consisting of nickel and titanium, wherein the ratio of said nickel powder to said prealloyed aluminum-containing powder is at least 1.5 but not greater than about 3.5;

compacting said powdered mixture at a pressure sufficient to form a compact of said powdered mixture;

degassing said compact by heating in a vacuum to a first temperature and for a duration sufficient to diffuse internal gases from said compact, said first temperature and duration being insufficient to cause substantial diffusion of the elements within said compact;

heating said compact to a second temperature within said vacuum, wherein said second temperature is greater than said first temperature, and wherein said duration and said vacuum pressure are sufficient to permit the chemical decomposition of nickel oxide within said compact to nickel and oxygen gas;

homogenizing said compact at a third temperature within said vacuum, wherein said third temperature is greater than said second temperature but not greater than the solidus temperature of said powdered mixture, and wherein said duration at said third temperature is sufficient to uniformly diffuse said elements within said compact while substantially increasing the density of said compact; and

sintering said homogenized compact at a fourth temperature within said vacuum, wherein said fourth temperature is greater than said third temperature, and wherein the duration at said fourth temperature is sufficient for said aluminum to react with said other metals so as to form at least one aluminide phase, and sufficient to liquify a portion of said aluminide phases, thereby resulting in a sintered article containing a uniform distribution of fine particles of said intermetallic aluminide phases, and said sintered article being characterized by less than about two percent porosity.

2. A method for producing sintered articles of multiphase intermetallic alloys as recited in claim 1 wherein said degassing step occurs at a temperature ranging from about 950°

C. to about 1050°

C.

3. A method for producing sintered articles of multiphase intermetallic alloys as recited in claim 1 wherein said second temperature ranges from about 1100°

C. to about 1200°

C.

4. A method for producing sintered articles of multiphase intermetallic alloys as recited in claim 1 wherein said homogenizing step occurs at a temperature ranging from about 1250°

C. to about 1300°

C.

5. A method for producing sintered articles of multiphase intermetallic alloys as recited in claim 1 wherein said sintering step occurs at a temperature ranging from about 1300°

C. to about 1350°

C.

6. A method for producing sintered articles of multiphase intermetallic alloys as recited in claim 1 wherein said liquified portion during said sintering step is approximately 30 to 35 volume percent of said aluminide phases.

7. A method for producing sintered articles of multiphase Ni-Al-Ti intermetallic alloys which are characterized by near-theoretical density and near-net shape, comprising the following steps:

blending a powdered mixture, said powdered mixture comprising nickel powder in a ductile form and a prealloyed brittle powder containing aluminum and at least one metal chosen from the group consisting of nickel and titanium, wherein the ratio of said nickel powder to said prealloyed aluminum-containing powder is at least 1.5 but not greater than about 3.5;

compacting said powdered mixture at a pressure sufficient to form a compact of said powdered mixture, said compact having a density about 60% to 65% as compared to a theoretical density of a porosity-free compact of said powdered mixture;

degassing said compact by heating in a vacuum to a first temperature ranging from about 950°

C. to about 1050°

C. for a duration sufficient for any internal gases to diffuse from of said compact, said first temperature and duration being insufficient to cause substantial diffusion of the elements within said compact;

heating said compact to a second temperature and for a second duration within said vacuum, wherein said second temperature ranges from about 1100°

C. to about 1200°

C. and wherein said duration and said vacuum pressure are sufficient to permit the chemical decomposition of any nickel oxide within said compact to nickel and oxygen gas;

homogenizing said compact at a third temperature within said vacuum, wherein said third temperature ranges from about 1250°

C. to about 1300°

C. but is not higher than the solidus temperature of said powdered mixture, and wherein said duration at said third temperature is sufficient to uniformly diffuse said elements within said compact while substantially increasing the density of said compact; and

sintering said homogenized compact at a fourth temperature within said vacuum, wherein said fourth temperature ranges from about 1300°

C. to about 1350°

C., and wherein the duration at said fourth temperature is sufficient for said aluminum to react with said metals to form at least one aluminide phase, and sufficient to liquify a portion of said aluminide phases, thereby resulting in a sintered article containing a uniform distribution of said aluminide phases and said sintered article being characterized by less than about two percent porosity.

8. A method for producing sintered articles of multiphase intermetallic alloys as recited in claim 7 wherein said liquified portion during said sintering step is approximately 30 to 35 volume percent of said aluminide phases.

9. A sintered article formed of a multiphase Ni-Al-Ti intermetallic alloy which is suitable for use in high temperature applications, wherein said multiphase Ni-Al-Ti intermetallic alloy is formed by the method comprising the following steps:

blending a powdered mixture, said powdered mixture comprising nickel powder in a ductile form and a prealloyed brittle powder containing aluminum and at least one metal chosen from the group consisting of nickel and titanium, wherein the ratio of said nickel powder to said prealloyed aluminum-containing powder is at least 1.5 but not greater than about 3.5;

compacting said powdered mixture at a pressure sufficient to form a compact of said powdered mixture, said compact having a density about 60% to 65% as compared to a theoretical density of a porosity-free compact of said powdered mixture;

degassing said compact by heating in a vacuum to a first temperature ranging from about 950°

C. to about 1050°

C. for a duration sufficient for any internal gases to diffuse from of said compact, said first temperature and duration being insufficient to cause substantial diffusion of the elements within said compact;

heating said compact to a second temperature and for a second duration within said vacuum, wherein said second temperature ranges from about 1100°

C. to about 1200°

C. and wherein said duration and said vacuum pressure are sufficient to permit the chemical decomposition of any nickel oxide within said compact to nickel and oxygen gas;

homogenizing said compact at a third temperature within said vacuum, wherein said third temperature ranges from about 1250°

C. to about 1300°

C. but is not higher than the solidus temperature of said powdered mixture, and wherein said duration at said third temperature is sufficient to uniformly diffuse said elements within said compact while substantially increasing the density of said compact; and

sintering said homogenized compact at a fourth temperature within said vacuum, wherein said fourth temperature ranges from about 1300°

C. to about 1350°

C., and wherein the duration at said fourth temperature is sufficient for said aluminum to react with said metals to form at least one aluminide phase, and sufficient to liquify a portion of said aluminide phases;

thereby resulting in a sintered article containing a uniform distribution of said aluminide phases and said sintered article being characterized by less than about one percent porosity.

10. A sintered article formed of a multiphase Ni-Al-Ti intermetallic alloy which is suitable for use in high temperature applications as recited in claim 9 wherein said liquified portion during said sintering step is approximately 30 to 35 volume percent of said aluminide phases.