Microstructural response and surface mechanical properties of TC6 titanium alloy subjected to laser peening with different laser energy

Abstract

In this paper, the main purpose was to investigate the effects of laser peening (LP) on the microstructural evolution and frictional wear resistance of TC6 titanium alloy. The surface topographic features, microhardness and residual stress distribution in the depth direction of differently treated specimens were measured using three-dimensional topography instrument, digital microhardness tester and residual stress instrument. The frictional wear test was carried out using a multifunctional friction wear tester. Meanwhile, X-ray diffraction (XRD), optical microscope (OM) and transmission electron microscopy (TEM) were utilized to investigate the effects of LP on the microstructural response of TC6 titanium alloy. The results indicated that the micro-pits induced by LP increased the surface roughness to a maximum of 6.94 μm. LP technique effectively improved the microhardness and frictional wear resistance of TC6 titanium alloy, and the wear form changed from abrasive wear, adhesive wear and fatigue spalling wear to abrasive wear at the laser energy of 8 J. Compared to the untreated specimens, the surface microhardness of the specimens treated by LP with 8 J increased from 356 HV to 442 HV, and the affected layer depth was approximately 500 μm. Moreover, the friction coefficient decreased from 1.2 to 0.5, the abrasion depth of the abrasion track was reduced by approximately 32 % compared to the untreated specimen. Additionally, the surface compressive residual stress induced by LP with 8 J reached about −510 MPa. The microstructural evolution of the specimens processed by LP was dominated by twin formation and dislocation slip, while the intercalation between multidirectional twins and the formation of sub-grain boundaries promoted grain refinement of TC6 titanium alloy. Refined grains, high density of dislocations, mechanical twins and the implantation of compressive residual stresses effectively improved the friction and wear resistance of TC6 titanium alloy.