Microstructure and microhardness of Ti6246 linear friction weld

The microhardness and microstructure of linear friction welded Ti-6Al-2Sn-4Zr-6Mo (Ti6246) alloys were studied, in both as-welded and post-weld heat-treated conditions. It has been found that the as-welded Ti6246 has a lower microhardness value of about 360 HV in the central weld zone than that of the base material of about 420 HV. Post-weld heat-treatment of the Ti6246 weld at 600 °C for 1 h has led to the hardness increase of about 180 HV at the central weld zone. Transmission electron microscopy studies show that the microstructure at the central weld zone of the as-welded Ti6246 consists of fine grains with dense acicular orthorhombic α″ martensite. The soft α″ martensite is believed to account for the low hardness measured in the as-welded conditions. Phase transformation from orthorhombic α″ to hexagonal α occurred during the PWHT, resulting in the observed hardness increase.