Titanium aluminide alloy material for hot forging, forging method for titanium aluminide alloy material, and forged body

Abstract

A titanium aluminide alloy material for hot forging has a chemical composition including, by atom, aluminum of 43.0% or greater and 45.0% or less, niobium of 4.0% or greater and 6.0% or less, chromium of 1.5% or greater and 3.5% or less, and titanium and an inevitable impurity as a residue.

What is claimed is: 
     
         1 . A titanium aluminide alloy material for hot forging having a chemical composition including, by atom, aluminum of 43.0% or greater and 45.0% or less, niobium of 4.0% or greater and 6.0% or less, chromium of 1.5% or greater and 3.5% or less, and titanium and an inevitable impurity as a residue. 
     
     
         2 . A titanium aluminide alloy material for hot forging having a chemical composition including, by atom, aluminum of 43.0% or greater and 45.0% or less, niobium of 4.0% or greater and 6.0% or less, chromium of 1.5% or greater and 3.5% or less, boron of greater than 0% and 0.25% or less, and titanium and an inevitable impurity as a residue. 
     
     
         3 . A hot forging method for a titanium aluminide alloy material, the method comprising:
 preparing the titanium aluminide alloy material for hot forging according to  claim 1 ; and   executing hot forging by setting a forging temperature within a range of a phase equilibrium temperature of any of a β-phase, a (β+α) phase, and a (β+α+γ) phase in a phase diagram of the titanium aluminide alloy material, and forging the titanium aluminide alloy material while keeping the set forging temperature in a non-oxidizing atmosphere.   
     
     
         4 . The hot forging method for the titanium aluminide alloy material according to  claim 3 , wherein the forging temperature in the hot forging is set to 1200° C. or higher and 1300° C. or lower. 
     
     
         5 . The hot forging method for the titanium aluminide alloy material according to  claim 3 , further comprising:
 executing a first heat treatment of heating a titanium aluminide alloy forged body obtained by the hot forging to a temperature of 1240° C. or higher and 1290° C. or lower; and   executing a second heat treatment of keeping the titanium aluminide alloy forged body through the first heat treatment at a temperature of 900° C. or higher and 1100° C. or lower for one hour or longer.   
     
     
         6 . The hot forging method for the titanium aluminide alloy material according to  claim 5 , wherein the temperature of the titanium aluminide alloy forged body after the first heat treatment is temporarily decreased before the second heat treatment step. 
     
     
         7 . A titanium aluminide alloy forged body having a chemical composition including, by atom, aluminum of 43.0% or greater and 45.0% or less, niobium of 4.0% or greater and 6.0% or less, chromium of 1.5% or greater and 3.5% or less, and titanium and an inevitable impurity as a residue,
 the titanium aluminide alloy forged body having a metallographic structure including a crystalline grain of a lamellar structure, a crystalline grain of a γ-phase, and a crystalline grain of a β-phase, the metallographic structure having a volume proportion of the γ-phase set to 80% or greater.   
     
     
         8 . A titanium aluminide alloy forged body having a chemical composition including, by atom, aluminum of 43.0% or greater and 45.0% or less, niobium of 4.0% or greater and 6.0% or less, chromium of 1.5% or greater and 3.5% or less, boron of greater than 0% and 0.25% or less, and titanium and an inevitable impurity as a residue,
 the titanium aluminide alloy forged body having a metallographic structure including a crystalline grain of a lamellar structure, a crystalline grain of a γ-phase, a crystalline grain of a β-phase, and a boride grain, the metallographic structure having a volume proportion of the γ-phase set to 80% or greater.