Effect of quenching on the matrix microstructure of SiCf/Ti-6Al-4V composites

Heat treatment can change the matrix microstructure of metal based composites, which leads to the change of mechanical properties of the composites. In the present work, the variation of microstructure and hardness of the matrix of SiCf/Ti-6Al-4V composites prepared by foil-fiber-foil (FFF) method were investigated after quenching from 950, 980 and 990 A degrees C. The results indicated that the beta transus temperature of the matrix was close to 990 A degrees C, which is slightly higher than that of the Ti-6Al-4V alloy, which is between 950 and 970 A degrees C. This increase was attributed to the diffusion effect of carbon atoms. Some carbide particles were precipitated at the prior beta grain boundaries when full martensite was obtained. Transmission electron microscopy examination observed three alpha' variants that obeyed the Burgers orientation relationship with the beta phase in the sample quenched from 950 A degrees C. The hardness of the matrix increased with the increase in quenching temperature, and the highest hardness of 420 HV was obtained after quenching from 990 A degrees C, which is much higher than that of the Ti-6Al-4V alloy. The high hardness was resulted from phase transformation strengthening by martensite, solid solution strengthening of carbon atoms and the dispersion strengthening of TiC precipitates.