Laser shock peening combined with temperature-increasing ion implantation improves fretting fatigue performance of TC6 titanium alloy

To address the challenge that a single surface strengthening technique is unable to simultaneously tackle the issues of crack initiation and propagation in the fretting fatigue failure of titanium alloys, a composite treatment involving initial laser shock peening followed by nitrogen ion implantation at 300 ℃ is employed to enhance the properties of TC6 titanium alloy. The residual stress distributions of four types of specimens, namely the untreated ones, those subjected to nitrogen ion implantation at 300 ℃, those treated with laser shock peening, and those receiving the composite treatment, are measured using an X-ray diffraction stress analyzer. The fretting fatigue life of the titanium alloy specimens is assessed on a self-designed surface-contact fretting fatigue testing rig. The fracture surfaces and wear scars at the crack initiation zones are characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results demonstrate that the composite treatment creates both a high-hardness nitrided layer and a deep gradient residual compressive stress field, with the residual compressive stress extending to a depth of approximately 1.4 mm. The average fretting fatigue life of the specimens subjected to the composite treatment reaches 2.98×10⁵ cycles, which is 161.4%, 108.4%, and 30.1% higher than that of the untreated specimens, those implanted with nitrogen ions at 300 ℃, and those treated with laser shock peening, respectively. Fracture analysis reveals that the composite strengthening transforms the damage mechanism in the fretting contact area from severe adhesive wear to predominantly abrasive wear, significantly postponing crack initiation. Meanwhile, the deep residual compressive stress effectively reduces the crack propagation rate.