Role of oxygen on the precipitation and deformation behavior of an aged β Ti-15Mo alloy

Abstract

The mechanical behavior of aged metastable β titanium alloys is directly influenced by the formation and stability of metastable ω and stable α phases during thermomechanical processing. Interstitial oxygen, which is known to cause embrittlement in Ti alloys, affects phase stability in these alloys and also impacts their structural properties. The present study investigated the role of interstitial oxygen on ω and α precipitation in an aged metastable β Ti-15Mo alloy and the subsequent effect of these microstructural changes on the alloy’s compressive mechanical properties. High oxygen levels reduced the ω growth rate and induced a shape change for ω precipitates with oxygen partitioning to ω precipitates during ageing. Oxygen-containing specimens displayed higher compressive yield strengths than in oxygen-free specimens during micropillar compression testing. However, in both cases, ω precipitates were ultimately sheared leading to slip band formation and plastic flow localization. Elevated oxygen also refined the α precipitate distribution whether α nucleation happened homogeneously or heterogeneously. The finer α precipitates with oxygen led to increased compressive yield strength during micropillar compression compared to specimens without oxygen. Oxygen plays a key role in the evolution of ω and α precipitate distributions and associated mechanical properties, which is another example of how oxygen may be a useful alloying element in β titanium alloys.