Anomalous phase stability of surface and interior in a metastable Ti-Nb-Zr alloy

The structural stability of β phase is a key factor to determine the mechanical properties, such as strength and elastic modulus, of metastable β-type titanium alloys. In the present study, we reported an anomalous phenomenon that the surface and the interior of quenched Ti-22Nb-9Zr (wt%) alloy exhibit quite different phase constitutions. It is indicated that abundant α″ martensite phase forms in the surficial region of less than 200 µm in the specimen, while the interior consists of dominant β phase together with a few ω phase. This interesting result might be of great significance for research and development of metastable β titanium alloys with superior mechanical properties.