Microstructures and Mechanical Properties of Ti-4mass%Cr Alloy Compact Prepared by the Technique of Elemental Powder Mixing

The sintering behavior of TI-4mass%Cr alloy compact prepared by the technique of elemental powder mixing was investigated by means of EPMA analysis and optical microscopy. Mechanical properties of sintered compacts, in which the microstructure of (α+β) two phases was controlled by varying the cooling rate from sintering temperature, were also examined In relation to the fracture behavior. Addition of 4mass%Cr gives no effect on compactibility and sintering densification of titanium powder. However, the diffusion of chromium Into titanium matrix is greatly dependent on temperature, so that the sintering above 1373K is required for the 3.6ks sintering in order to obtain homogenlous materials in the chemical composition. In the case of 1473K-3.6ks sintering, the density of Ti-4mass%Cr alloy compacts increases to more than 95% in relative density in addition to the homogeneity of chemical composition. The structure of compacts is of β(bcc) phase at 1473K, but a platelet a(hcp) phase precipitates during cooling from the sintering temperature. When the cooling rate after sintering is over 1K/s, a fine mixed structure of α and β is obtained at room temperature, and this results in excellent mechanical properties. When the cooling rate is not so fast, the a phase grows large. Specimens with coarse structure of α and β undergo a quasi-cleavage fracture, In which cracks propagate in the β phase along a plates and then connect retained pores. Such a fracture mode affects harmfully to mechanical properties, especially to bending strength.