Effect of laser surface remelting and low temperature aging treatments on microstructures and surface properties of Ti-55511 alloy.

The near-β titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) was firstly remelted on the surface by laser and a series of subsequent low temperatures aging treatments were carried out to obtain ultrafine microstructures in the remelted layer. Microhardness and wear resistance of each treated sample were then tested to evaluate the effects of ω-assisted α phase on the surface properties. Microstructure evolution of the whole process was observed by optical and electron microscopes. Results showed that nano-scaled athermal ω phase uniformly precipitated in β matrix of Ti-55511 after rapid solidification, and it had a little reinforcement effects in the remelted layer due to the low contents. After low temperatures aging, ultrafine α lamellas could form in the remelted layer by ω-assisted nucleation. By increasing the aging temperatures, the sizes and volume fractions of α lamellas increase, resulting in an improvement of surface hardness and wear resistance. However, the high surface hardness did not effectively enhance the wear resistance of Ti-55511 due to the ductility deterioration caused by nano-sized α phase of the aged samples. The remelted samples can achieve the highest surface microhardness over 520HV and relatively best wear resistance after aging at 500 °C for 5 h. [ABSTRACT FROM AUTHOR]