Microstructure of hard biocompatible Ti1−xAux alloys

Ti1−xAux binary alloys are biocompatible materials. We studied the hardness and the microstructures of six casted Ti1−xAux alloys with Au molar fraction x = 0.22, 0.25, 0.335, 0.5, 0.6 and 0.8 by transmission electron microscopy down to atomic level. Ti1−xAux alloys with x from 0.2 to 0.40 have high hardness, in which the β-Ti3Au is the dominating phase. This reveals that intermetallic β-Ti3Au is the hardest of all intermetallic Ti1−xAux alloys. Alloys with x from 0.4 to 0.8 are softer, and their hardness is similar to that of casted pure Ti. Very high density nanotwins are observed in phases, such as fcc Ti, β-TiAu, TiAu2, and Au(Ti). An interesting checker board pattern of defects consisting of orthogonal three dimensional bands of extremely high density nanotwins with a width of 2 to 3 {111} atomic planes is observed in Au(Ti). The high density defects may explain the relatively high hardness comparable to pure casted Ti for samples with high Au content. The hard β-Ti3Au or the nanotwinned Au might be a promising candidate for hard coating.