Reaction of titanium alloys with different mould shell materials

The aim of this study was to research the surface reaction layer between Ti, Titanium alloys and different investment shells prepared by the low-cost binder. As the stucco zirconia and alumina powder mixed separately with the low-cost binder to making up two kinds of slurries. The refractory material was alumina. The titanium alloys were cast into investment shells prepared with two kinds of slurries. A centrifugal vacuum pressure machine (LZ5, Luo Yang Common Machine Factory, China) was used to cast titanium alloys sample. The microstructure of the titanium alloys were observed by optical microscope (OM), the distribution of elements of topping investment on the surfaces of titanium alloys castings was analyzed by electron probe micro-analysis (EPMA). The microstructure of titanium alloys that be cast into zirconia-as-stucco investment shell was finer and evener than alumina-as-stucco, especially the difference was distinct for Ti-6Al-4V (TC4) alloy and Ti-(6-6.5)Al-2Zr-1Mo-1V (BT20) alloy. The EPMA results show that to the same titanium alloys the stability of zirconia-as-stucco investment shell was better than that of alumina. The reactive diffusion distance of Al element between titanium alloys and alumina as-stucco investment shell was about 30~40 μm and the thickness of reactive diffusion layer was uniform; the reactive diffusion distance of Zr element was about 1/3 of that of Al, and the thickness was narrow and discontinuous.