Nanostructured Titanium Alloy And Method For Thermomechanically Processing The Same

Abstract

A nanostructured titanium alloy article is provided. The nanostructured alloy includes a developed structure that has been processed from a combination of severe plastic deformation and non-severe plastic deformation type thermomechanical processing steps, with at least 80% of grains in the developed structure having a grain size≦1.0 microns.

What is claimed is: 
     
         1 . A nanostructured titanium alloy article, comprising:
 a developed α-titanium structure processed from a combination of a severe plastic deformation process type and non-severe plastic deformation type thermomechanical processing steps and having ≧80% of grains in the developed a-titanium structure have a size≦1.0 micron.   
     
     
         2 . The nanostructured titanium alloy article according to  claim 1 , wherein the developed structure has a dislocation density≧10 15  m −2 . 
     
     
         3 . The nanostructured titanium alloy article according to  claim 1 , wherein 20-40% of the grains in the α-titanium matrix have high angle grain boundaries with a misorientation angle≧15°. 
     
     
         4 . The nanostructured titanium alloy article according to  claim 1 , wherein ≧80% of all grains in the α-titanium matrix have a grain shape aspect ratio that is in a range of 0.3 to 0.7. 
     
     
         5 . The nanostructured titanium alloy article according to  claim 1 , wherein the severe plastic deformation process type is equal-channel angular pressing-conform. 
     
     
         6 . The nanostructured titanium alloy article according to  claim 1 , wherein an average crystallite size is ≦100 nanometers. 
     
     
         7 . The nanostructured titanium alloy article according to  claim 6 , wherein a dislocation density is ≧10 15  m −2 . 
     
     
         8 . The nanostructured titanium alloy article according to  claim 7 , wherein 20-40% of the grains have high angle grain boundaries with a misorientation angle≧15°. 
     
     
         9 . The nanostructured titanium alloy article according to  claim 8 , wherein ≧80% of all grains have a grain shape aspect ratio in a range from 0.3 to 0.7. 
     
     
         10 . The nanostructured titanium alloy article according to  claim 9 , wherein the developed structure has an ultimate tensile strength≧1200 MPa. 
     
     
         11 . The nanostructured titanium alloy article according to  claim 10 , wherein the developed structure has a total tensile elongation≧10%. 
     
     
         12 . The nanostructured titanium alloy article according to  claim 11 , wherein the developed structure has an area reduction≧25%. 
     
     
         13 . The nanostructured titanium alloy article according to  claim 12 , wherein the developed structure has an ultimate shear strength≧650 MPa. 
     
     
         14 . The nanostructured titanium alloy article according to  claim 13 , wherein the developed structure has an axial fatigue endurance limit≧700 MPa measured at 10 7  cycles. 
     
     
         15 . The nanostructured titanium alloy article according to  claim 14 , wherein the developed structure has a cantilever-rotating beam fatigue endurance limit≧650 MPa measured at 10 7  cycles. 
     
     
         16 . The nanostructured titanium alloy article according to  claim 1 , wherein the developed structure consists of commercially pure titanium. 
     
     
         17 . The nanostructured titanium alloy article according to  claim 16 , wherein the developed structure is α-titanium matrix having retained β-titanium particles. 
     
     
         18 . The nanostructured titanium alloy article according to  claim 1 , wherein the developed structure consists of Ti-6Al-4V. 
     
     
         19 . The nanostructured titanium alloy article according to  claim 1 , wherein the developed structure consists of Ti-6Al-4V ELI. 
     
     
         20 . The nanostructured titanium alloy article according to  claim 1 , wherein the developed structure consists of Ti—Zr. 
     
     
         21 . The nanostructured titanium alloy article according to  claim 1 , wherein the developed structure consists of Ti-6Al-7Nb. 
     
     
         22 . The nanostructured titanium alloy article according to  claim 1 , wherein the developed structure has a composition by weight percent:
 nitrogen (N) 0.05% maximum;   carbon (C) 0.08% maximum;   hydrogen (H) 0.015% maximum;   iron (Fe) 0.50% maximum;   oxygen (O) 0.40% maximum; and   a balance of titanium (Ti) and trace impurities.   
     
     
         23 . A method for making a nanostructured titanium alloy, comprising the steps of:
 providing a workpiece of commercially pure titanium alloy;   inducing severe plastic deformation to the workpiece using an equal-channel angular pressing-conform machine at temperatures≦450° C. and having a die set at a channel angle of intersection between ψ=75° and ψ=135°; and   subjecting the workpiece to thermomechanical processing at temperatures≦450° C. to prepare an article having a cross-sectional area reduction≧35%.