High speed titanium alloy microstructural conversion method

Abstract

A high speed titanium alloy microstructural conversion method from lamellar to equiaxed is disclosed. The method includes identification and estimation of process parameters such that the average strain rate is between about 1-100 s −1 and the deformation temperature of the material is in the range of about 975°-1010° C.

1. A method of converting a Ti—6 Al—4V alloy material microstructure from lamellar to equiaxed, comprising the steps of:
 providing a lamellar microstruure Ti—6Al—4V alloy material;  
 processing said material in such manner to convert the microstructure thereof from lamellar to equiaxed, said processing step including the step of; 
 estimating an average high strain rate for said material;  
 estimating an adiabatic temperature rise within said material as a result of deformation at said strain rate;  
 
 determining the effect of chemical composition of said material upon the β transus temperature;  
 estimating a deformation temperature by incorporating said adiabatic temperature rise from said adiabatic temperature rise estimating step above and incorporating the effect of chemical composition from said determining step above such that the temperature of the material is within the range of about 975-1010° C., said deformation temperature further being chosen such that the β transus temperature is not exceeded at any location within said material;  
 heating said material to the temperature obtained from said deformation temperature estimating step above; and, 
 extruding said material at a rate obtained from said strain rate estimating step above.  
 
 
     
     
       2. A method of converting a Ti—6Al—4V alloy material microstructure from lamellar to equiaxed, comprising the steps of:
 providing a lamellar microstructure Ti—6Al—4V alloy material;  
 processing said material in such manner to convert the microstructure thereof from lamellar to equiaxed, said processing step including the steps of; 
 estimating an average high strain rate for said material, said strain rate being in the range of about 1-100 s −1 ;  
 estimating an adiabatic temperature rise within said material as a result of deformation at said strain rate;  
 determining the effect of chemical composition of said material upon the β transus temperature;  
 estimating a deformation temperature by incorporating said adiabatic temperature rise from said adiabatic temperature estimating step above and incorporating the effect of chemical oomposition from said determining step above such that the temperature of the material is proximate the (α+β)→β transformation temperature, said deformation temperature further being chosen such that the β transus temperature is not exceeded at any location within said material;  
 heating said material to the temperature obtained from said deformation temperature estimating step above; and,  
 extruding said material at a rate obtained from said stain rate extimating step above.  
 
 
     
     
       3. A method of converting a Ti—6Al—4V alloy material microstructure from lamellar to equiaxed comprising the steps of:
 providing a lamellar microstructure Ti—6Al—4V alloy material;  
 processing said material in such manner to convert the microstructure of thereof from lamellar to equiaxed, said processing step including the steps of; 
 estimating an average strain rate for said material using the relation 
           ɛ   _     .     =         6   ⁢     v   0     ⁢     D   b   2           D   b   3     -     D   p   3         ⁢     ln   ⁡     (   Γ   )             
 
 
 
       wherein V o is ram speed, D b  is billet diameter, D p  is product diameter, and Γ is extrusion ratio;
   estimating an adiabatic temperature rise within said material as a result of deformation at said strain rate;    determining the effect of chemical composition of said material upon the β transus temperature;    estimating a deformation temperature by incorporating said adiabatic temperature rise from said adiabatic temperature rise estimating step above and incorporating the effect of chemical composition from said determining step above such that the temperature of the material is within the range of about 975-1010° C., said deformation temperature further being chosen such that the β transus temperature is not exceeding at any location within said material;    heating said material to the temperature obtained from said deformation temperature estimating step above; and,    extruding said material at a rate obtained from said strain rate estimating step above.