Processing of aluminides by sintering of intermetallic powders

Abstract

A sintering process for producing an aluminide by reacting a first powder with a second powder, the first powder comprising M x Al y wherein M is Fe, Ni or Ti, x≧1, y≧1 and x>y or y>x and the second powder comprises pure M or M alloy powder. Iron aluminides such as Fe 3 Al, FeAl or alloys thereof can be made by reacting powders of one or more of Fe 3 Al, FeAl 3 , FeAl 2 , Fe 2 Al 5 or alloys thereof with pure iron or an iron alloy. Nickel aluminides such as Ni 3 Al or NiAl or alloys thereof can be made by reacting powders of one or more of NiAl 3 , Ni 2 Al 3 , Ni 3 Al 2 , Ni 5 Al 3 or alloys thereof with pure Ni or a Ni alloy powder. Titanium aluminides such as Ti 3 Al, TiAl or alloys thereof can be made by reacting one or more of TiAl 3 , TiAl 2 or alloys thereof with pure Ti or Ti alloy powder. The process provides a more dense product by solid state reaction of an intermediate intermetallic compound with a component of the final aluminide compact. As a result of the process, the final density can be increased to at least 98% of the theoretical density. Products which can be made by the process include worked products such as rolled sheet, extruded shapes such as tube, drawn products such as wire or bar, or molded/forged products such as fuel injection nozzles.

What is claimed is:  
     
         1 . A method of manufacturing a non-porous aluminide compact by a powder metallurgical technique, comprising steps of: 
 forming a powder mixture comprising a first powder comprising M x Al y  wherein M is Fe, Ti or Ni, x≧1, y≧2, x>y or y>x, and a second powder comprising M or M alloy;    heating the powder mixture so as to react the first powder with the second powder to form the non-porous aluminide compact.    
     
     
         2 . The method of  claim 1 , wherein the heating step is carried out in a vacuum environment and the non-porous aluminide compact produced during the heating step has a porosity of less than 1%.  
     
     
         3 . The method of  claim 1 , wherein the aluminide is FeAl, Fe 3 Al or alloy thereof, the first powder is one or more of Fe 2 Al 5 , FeAl 3 , FeAl 2 , Fe 3 Al and the second powder is pure Fe or iron base alloy powder.  
     
     
         4 . The method of  claim 1 , wherein the aluminide is NiAl, Ni 3 Al or alloy thereof, the first powder is one or more of Ni 2 Al 3 , Ni 3 Al 2 , Ni 5 Al 3 , NiAl 3  and the second powder is pure Ni or Ni base alloy powder.  
     
     
         5 . The method of  claim 1 , wherein the aluminide is TiAl, Ti 3 Al or alloy thereof, the first powder is one or more of TiAl 2  or TiAl 3  and the second powder is pure Ti or Ti base alloy powder.  
     
     
         6 . The method of  claim 1 , wherein the first powder is Fe 2 Al 5 , FeAl 2 , FeAl 3 , Fe 3 Al or alloy thereof and the second powder is pure Fe or Fe base alloy.  
     
     
         7 . The method of  claim 1 , wherein the first powder is Ni 2 Al 3 , Ni 3 Al 2 , Ni 5 Al 3 , NiAl 3  or alloy thereof and the second powder is pure Ni or an Ni base alloy.  
     
     
         8 . The method of  claim 1 , wherein the first powder is TiAl 2  or TiAl 3  or alloy thereof and the second powder is pure Ti or Ti base alloy.  
     
     
         9 . The method of  claim 1 , wherein the powder mixture is free of pure aluminum powder.  
     
     
         10 . The method of  claim 1 , wherein the aluminide is FeAl, Fe 3 Al, NiAl, Ni 3 Al, TiAl, Ti 3 Al or alloy thereof.  
     
     
         11 . The method of  claim 1 , wherein the iron aluminide is iron aluminide or an iron aluminide alloy, the first powder is Fe 2 Al 5  and the second powder comprises pure iron or an iron base alloy, FeAl or Fe 3 Al being initially formed as a layer between the pure iron or iron base alloy and the Fe 2 Al 5  during the heating step.  
     
     
         12 . The method of  claim 1 , wherein the powder mixture is binder-free.  
     
     
         13 . The method of  claim 1 , wherein the powder mixture is heated at a heating rate of less than 15° C./minute during the heating step.  
     
     
         14 . The method of  claim 1 , wherein the sintered compact is heated sufficiently to increase the density of the sintered compact to over 98% of the theoretical density.  
     
     
         15 . The method of  claim 1 , further comprising injection molding the powder mixture into a shaped article or working the powder mixture to form a continuous product.  
     
     
         16 . The method of  claim 1 , wherein the powders comprise reaction synthesized, water or gas atomized powder.  
     
     
         17 . The method of  claim 1 , wherein the powder mixture comprises an atomized powder and the method further comprises a step of sieving the powder and blending the powder without a binder prior to a consolidation step.  
     
     
         18 . The method of  claim 1 , wherein the heating step comprises heating the powder mixture at a temperature of 1200° C. to below the melting point of the powders in a vacuum atmosphere.  
     
     
         19 . The method of  claim 1 , wherein the sintered compact has a grain size of 10 to 50 μm.  
     
     
         20 . The method of  claim 1 , wherein the sintered product contains oxides in an amount sufficient to inhibit grain growth and/or enhance creep resistance of the sintered product.  
     
     
         21 . The method of  claim 1 , wherein the step of forming the powder mixture comprises mixing powders having an average particle size of 0.1 to 150 μm.  
     
     
         22 . The method of  claim 1 , wherein the powders include nanorized powders in an amount sufficient to enhance packing of the powders.  
     
     
         23 . The method of  claim 1 , wherein the aluminide comprises an iron aluminide alloy having, in weight %, ≦32% Al, ≦2% Mo, ≦1% Zr, ≦2% Si, ≦30% Ni, ≦10% Cr, ≦0.3% C, ≦0.5% Y, ≦0.1% B, ≦1% Nb and ≦1% Ta.  
     
     
         24 . The method of  claim 1 , wherein the aluminide comprises an iron aluminide alloy which includes, in weight %, 20-32% Al, 0.3-0.5% Mo, 0.05-0.3% Zr, 0.01-0.5% C, ≦0.1% B, ≦1% oxide particles, balance including Fe.  
     
     
         25 . The method of  claim 1 , wherein the sintering step provides a sintered product having an average grain size less than 40 μm.  
     
     
         26 . The method of  claim 1 , wherein the powder mixture consists essentially of Fe 2 Al 5  and pure Fe.  
     
     
         27 . The method of  claim 1 , wherein the aluminide comprises an alloy of Ni 3 Al containing, in weight %, 0.005 to 0.05% B, 6 to 12% Al, 4 to 8% Mo, 2 to 4% Ti, balance Ni.  
     
     
         28 . The method of  claim 1 , wherein the aluminide comprises an alloy of Ti 3 Al containing, in weight %, 2 to 20% Nb, 0.5 to 10% W, 0.5 to 10% Ta, 0.1 to 0.5% B, and/or up to 10% Mo.  
     
     
         29 . The method of  claim 1 , wherein the aluminide comprises an alloy of TiAl containing, in weight %, 2 to 20% Nb, 0.5 to 10% W, 0.5 to 10% Ta, 0.1 to 0.5% B, and/or up to 10% Mo.  
     
     
         30 . The method of  claim 1 , wherein the aluminide compact is forged into an automotive valve.  
     
     
         31 . The method of  claim 1 , wherein the aluminide compact is formed into a fuel injection nozzle for direct pressure fuel injection systems.  
     
     
         32 . The method of  claim 1 , wherein the aluminide compact is formed into a fuel injection nozzle for automobile, diesel or marine engines.  
     
     
         33 . The method of  claim 1 , wherein the aluminide compact includes sufficient tungsten carbide and/or oxide particles to provide improved wear resistance.  
     
     
         34 . The method of  claim 1 , wherein the first and second powders have a mean particle size of 2 to 20 μm.