Effects of oxygen concentration and phase stability on nano-domain structure and thermal expansion behavior of Ti–Nb–Zr–Ta–O alloys

Abstract In this study, in order to fully elucidate the origin of nano-domain structure and abnormal thermal expansion behavior of Gum metals, the effects of oxygen concentration, β phase stability and cold rolling on the microstructure and thermal expansion properties were investigated in (Ti– x Nb–2Zr–0.7Ta)– y O (at.%) ( x  = 21–25; y  = 0.3–1.8) alloys. Normal thermal expansion behaviors with positive linear thermal expansion coefficients were observed in all the annealed alloys irrespective of oxygen and Nb concentrations. The thermal expansion behavior of as-rolled alloys was strongly affected by the concentration of oxygen and Nb. A negative thermal expansion coefficient was observed in the as-rolled alloys with lower oxygen and Nb concentrations. The thermal expansion coefficient increased with increasing oxygen and Nb concentrations. The amount of nano-domains increased with increasing oxygen concentration while decreased with increasing Nb concentration. The growth of a preferential nano-domain variant was observed in as-rolled alloys and became more prominent with decreasing oxygen and Nb concentrations. The reverse transformation from the nano-domain structure to the β phase occurred with increasing temperature. Thermal expansion behavior of as-rolled alloys resulted from a competing relationship between the contribution of lattice distortion of nano-domain structure and the contribution of lattice vibration of the β phase.