Method for heat treating titanium aluminide alloys

Abstract

A heat treatment method for producing moderate α grain size (50-250 μm) fully lamellar, microstructures in thin cross section near-γ titanium aluminide alloy products is described, wherein a wrought, fine y grain starting microstructure is heated at a temperature high in the two-phase α+γ phase field and 30-60° C. below the α transus temperature to produce a structure of small equiaxed α grains (about 25 μm dim) and fine γ phase grains, which is then briefly heated to a temperature in the single-phase α field in order to complete dissolution of remnant γ grains and to minimize growth of α grains. The material is then cooled to transform the microstructure to fully lamellar α 2 +γ.

We claim: 
     
       1. A method for heat treating titanium aluminide ahoy, comprising the steps of: (a) providing titanium aluminide alloy material having a recrystallized microstructure of gamma phase grains in a matrix of alpha-2 phase or lamellar alpha-2 plus gamma phase;   (b) heating said material at a temperature 30 to 60 centigrade degrees below the alpha transus temperature of said alloy whereby a microstructure having equiaxed alpha phase grains surrounded by fine gamma phase grains is produced within said alloy;   (c) thereafter heating said alloy at a temperature 20 to 50 centigrade degrees above the alpha transus temperature of said alloy to dissolve said fine gamma phase grains to produce in said alloy substantially single phase equiaxed alpha grain structure of grain size in the range of 50 to 250 μm; and   (d) thereafter cooling said alloy to transform the microstructure of said alloy to fully lamellar alpha-2 plus gamma phase.   
     
     
       2. The method of claim 1 wherein said alloy has a composition in the ranges Ti-(42-49)A1-(0-10)X, where X is one or more alloying elements selected from the group consisting of chromium, manganese, vanadium, niobium, tantalum, tungsten, molybdenum, silicon, boron, and zirconium. 
     
     
       3. The method of claim 1 wherein said alloy is an alpha-beta titanium alloy. 
     
     
       4. A method for heat treating titanium aluminide alloy, comprising the steps of: (a) providing titanium aluminide alloy;   (b) hot working said material to produce therein a recrystallized microstructure of gamma phase grains in a matrix of alpha-2 phase or lamellar alpha 2 plus gamma phase;   (c) thereafter heating said alloy at a temperature 30 to 60 centigrade degrees below the alpha transus temperature of said alloy whereby a microstructure having equiaxed alpha phase grains surrounded by fine gamma phase grains is produced within said alloy;   (d) thereafter heating said alloy at a temperature 20 to 50 centigrade degrees above the alpha transus temperature of said alloy to dissolve said fine gamma phase grains to produce in said alloy a substantially single phase equiaxed alpha grain structure of grain size in the range of 50 to 250 μm; and   (e) thereafter cooling said alloy to transform the microstructure of said alloy to fully lamellar alpha-2 plus gamma phase.   
     
     
       5. The method of claim 4 wherein said alloy has a composition in the ranges Ti-(42-49(A1-(0-10)X, where X is one or more alloying elements selected from the group consisting of chromium, manganese, vanadium, niobium, tantalum, tungsten, molybdenum, silicon, boron, and zirconium. 
     
     
       6. The method of claim 4 wherein said alloy is previously cast or previously cast and hot isostatically pressed. 
     
     
       7. The method of claim 4 wherein said alloy is an alpha-beta titanium alloy.