Microstructures and Mechanical Properties in a Sintered Ti-13mass%Cr Alloy

A Ti-13mass%Cr alloy, which is the eutectoid composition in Ti-Cr binary alloy, was prepared by the technique of elemental powder mixing and sintering in the temperature range of β(bcc) field. The microstructure of the sintered compacts was investigated by means of optical microscopy, EPMA analysis and thermal contraction test. Mechanical properties of sintered compacts were also examined in terms of the precipitation of ω phase which takes place during continuous cooling from sintering temperature. The structure of a compact at sintering temperature is of β phase, but during slow cooling after sintering, α phase precipitates on grain boundaries of β phase below β transus, and then ω phase precipitates in the β matrix below around 600K. As a result, a sintered compact is consisted of (β+ α+ω) three phases at room temperature. Sintered compacts cooled slowly from the β field undergo brittle fracture. This brittle fracture is attributed not to the precipitation of α phase at grain boundary, but to the precipitation of ω phase. The degree of the ω embrittlement was reduced when the cooling rate in the temperature below 600K was increased over 1K/s(Air cooling), and could be fully suppressed when it was over 50K/s(Oil quenching).