Powder Technology, Vol.340, 362-369, 2018
Oxygen scavenging, grain refinement and mechanical properties improvement in powder metallurgy titanium and titanium alloys with CaB6
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 alpha grain in CP-Ti and a fine and homogeneous basket-weave structure in Ti-6Al-4 V. Compared to CP-Ti, the a phase of Ti-1CaB(6) reduces from 178 mu m to 36 mu m. With respect to Ti-6Al-4 V, the alpha + beta lamellae length reduces from 203 to 38 mu m. The sintered relative density is also improved with O scavenging. The relatively density increases to 99.3% in Ti-0.2CaB(6) and 98.8% in Ti-6Al-4 V-0.1CaB(6). 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-0.2CaB(6); UTS = 944 MPa, YS = 903 MPa, EL. = 9% for Ti-6Al-4 V-0.1CaB(6)). (C) 2018 Elsevier B.V. All rights reserved.