High oxygen-content titanium and titanium alloys made from powder

Abstract

Oxygen remains to be a central issue in the manufacture of titanium (Ti) and its alloys from powder. The strong and short-range repulsion between interstitial oxygen and screw dislocation core strengthens titanium but compromises its resistance to cracking. It is therefore challenging to produce strong and ductile (tensile) Ti materials from high oxygen-content powder. This article reviews the tensile properties of high oxygen-content α-Ti, (α+β)-Ti alloys, and β-Ti alloys made from powder. A minimum tensile ductility value of 6% is used to define ductile Ti according to existing technical specifications for Ti-6Al-4V and other powder metallurgy materials. Two post-processing methods, solution heat treatment and thermomechanical processing, are identified to be effective remedies to convert non-ductile high oxygen-content Ti alloys into ductile ones. The underlying ductility-improvement mechanisms are discussed, which vary with alloy system. In particular, redistribution of oxygen between α and β phases by solution heat treatment offers a practical remedy to substantially improve tensile ductility, e.g., from 6% to 19% for the Ti-0.94 wt%O alloy. It is shown that appropriate post processing can enable a wide variety of Ti alloys made from powder to tolerate ≥0.5 wt%O for ≥6% tensile ductility for structural applications. • Redistribution of oxygen by solution heat treatment can reverse the detrimental effect of oxygen for Ti. • Thermomechanical processing can enable high oxygen-content Ti alloys to offer high tensile ductility (>15%). • Alloy composition affects exploitation of high oxygen Ti powder by PM, MIM and AM. • Alloy design plus post processing allows fabrication of strong and ductile Ti alloys from high oxygen Ti powder.