Surface hardening behavior of titanium alloys in carburization

Surface hardening of titanium alloys has been attracting a lot of interest in recent years because of their increasing use in machine components and orthopedic implants requiring improved tribological properties. The present paper describes the surface hardening behavior of two commercial titanium alloys in pack carburization. Carburization of IMI 318 and IMI 325 was carried out in a packed bed containing 50% charcoal, 35% coke, 10% barium carbonate, 3% calcium carbonate and 2% sodium carbonate. Carburization was done in the temperature range of 800 degrees C to 900 degrees C for 1 to 3 hours. The carburized samples were investigated by optical microscopy, microhardness measurements and X-ray diffraction(XRD). Surface hardness as high as 900 KHN was achieved in the carburized samples. Development of hardness profiles on the samples was found to be dependent on the alloy type, carburizing temperature and time. The hardness profiles on each of the alloys are discussed in terms of the phases formed and microstructure developed during the carburization process.