Structure, castability and mechanical properties of commercially pure and alloyed titanium cast in graphite mould.

This report is a study of structure, castability, mechanical properties as well as corrosion behaviour of titanium doped with up to 5 weight percentage (wt%) of a series of alloy elements, including Ta, Mo, Nb, Hf, Zr, Sn, Bi and Ag. The results indicate that, with addition of 1 wt% alloy element, Bi and Mo were most effective in enhancing the castability of titanium. With more alloy elements added, the castability values of most alloys more or less decreased. Except Ti-Mo system, all Ti alloys with a fine acicular morphology had the same crystal structure (hcp) as that of c.p. Ti with a typical lath type morphology. When 3 wt% or more Mo was added, a finer orthorhombic alpha'' phase was formed. The microhardness and bending strength values of Ti alloys were all higher than those of c.p. Ti. Among all alloys, Ti-Mo system exhibited the highest hardness and strength level. For a certain alloy, the bending strength did not necessarily increase with its alloy content. Except Ti-5Zr and Ti-Mo alloys, the bending moduli of most alloy systems were not much different from that of c.p. Ti. All alloys showed an excellent resistance to corrosion in Hanks' solution at 37 degrees C.