Oxygen scavenging, grain refinement and mechanical properties improvement in powder metallurgy titanium and titanium alloys with CaB6

Abstract

The effect of calcium hexa boride (CaB6) on microstructure and mechanical properties of powder metallurgy CP-Ti and Ti-6Al-4 V was studied. CaB6 can scavenge the solid solution O during sintering, producing Ca-Ti-O and TiB second phases. These Ca-containing particles precipitate in the grain boundary to inhibit grain growth, resulting in the formation of equiaxed α grain in CP-Ti and a fine and homogeneous basket-weave structure in Ti-6Al-4 V. Compared to CP-Ti, the α phase of Ti-1CaB6 reduces from 178 μm to 36 μm. With respect to Ti-6Al-4 V, the α + β lamellae length reduces from 203 to 38 μm. The sintered relative density is also improved with O scavenging. The relatively density increases to 99.3% in Ti-0.2CaB6 and 98.8% in Ti-6Al-4 V-0.1CaB6. The same reason may also account for the improved ductility. Overall, an addition of 0.2 wt% CaB6 in CP-Ti and 0.1 wt% CaB6 in Ti-6Al-4 V can obtain better comprehensive tensile properties (UTS = 665 MPa, YS = 604 MPa, EL. = 15% for Ti-0.2CaB6; UTS = 944 MPa, YS = 903 MPa, EL. = 9% for Ti-6Al-4 V-0.1CaB6).