Effects of LaB6 particle on microstructural evolution of PM Ti alloys

The use of cost-effective hydride-dehydride (HDH) titanium (Ti) powders is a key factor to reduce the cost of Ti parts. However, the contaminations of oxygen (O) and chlorine (Cl) from HDH Ti powder are the two challenges for powder metallurgy (PM) Ti performance. Herein, we designed a high strength and superior ductility Ti material by adding lanthanum hexaboride (LaB6) scavenger. The effects of additive content and particle size of LaB6 powder on the sintered density, O and Cl scavenging behaviour, microstructural evolution and mechanical properties are systematically investigated. Results reveal that a trace addition of small-sized LaB6 powder (<= 0.4 wt%) contributes to the high sintered density and the effective scavenging of O and Cl. In Ti matrix, the circular La2O3, rod-like LaOCl and TiB whiskers are in-situ formed, while the O-deficient clusters caused by large-sized powder are eliminated. These reinforcements can refine coarse rectangular grains into fine equiaxed grains. An addition of 0.4 wt% small-sized LaB6 provides an excellent elongation of 24.3%, almost 2.4 times as high as that of pure Ti (10.1%). Impurity scavenging, grain refinement and the elimination of clusters are responsible for the improved ductility. Furthermore, the multiple mechanisms of grain-boundary strengthening, load-bearing strengthening of LaOCl and TiB, Orowan strengthening of La2O3 nanoparticles work together to increase the tensile strength of Ti/LaB6 composites. This work provides an effective way to develop low-cost and highperformance Ti materials.