Effects of solution treating on microstructural and mechanical properties of a heavily deformed new biocompatible Ti-Nb-Zr-Fe alloy

Abstract

The effects of heavy cold plastic deformation by rolling on microstructural features and mechanical properties of Ti-25Nb-6Zr-1.7Fe (wt %) biocompatible alloy (TNZF) were studied. After a preliminary alloy processing, a heavy plastic deformation by cold-rolling (CR) with a total relative degree of plastic deformation of 90% (equivalent plastic strain, ε = 2.42) and a subsequent solution heat treatment (CR+ST) at 900 °C for 0.6 ks/water quenching were applied and then investigated. The CR and CR+ST states have microstructures consisting of mixtures of β''-Ti phases and α''-Ti. The alloy in CR state shows a pronounced deformation texture, with highly deformed and elongated β-Ti grains, exhibiting internal highly fragmented areas, with shear lines at about 45° and a sub-micron/nanocrystalline fine dispersed α''-Ti phase. The alloy in CR+ST state has completely recrystallized equiaxed polyhedral β''-Ti grains, with average grain size close to 52 µm and a sub-micron/nanocrystalline fine dispersed α''-Ti phase. Recorded mechanical properties, for both CR and CR+ST states, show quite similar values for the yield strength (σ0.2), ultimate tensile strength (σUTS) and Vickers microhardness (HV0.1) for CR state (σ0.2 = 603 MPa, σUTS = 1282 MPa and 287 HV0.1) in comparison with CR+ST state (σ0.2 = 598 MPa, σUTS = 1256 MPa and 256 HV0.1). Values for the modulus of elasticity (E) are lower (E = 72 GPa for CR state and E = 61 GPa for CR+ST state) than those for conventional biocompatible alloys (E ~ 110 GPa).