Effect of laser additive repair on high cycle fatigue properties of TC17 titanium alloy

Abstract

This paper investigates the influence of laser cladding (LC) on the phase distribution, microstructure, residual stress, microhardness, and high-cycle fatigue performance of TC17 titanium alloy. The experimental results are analyzed through microscopic characterization and fatigue tests, and the fatigue fracture mechanism is discussed. The LC process transforms the dual-phase α + β material containing stable β phase into a microstructure composed entirely of β phases. The β phases exhibit a coarse grain size up to 200 μm and numerous epitaxial columnar crystals in the additive direction. Near the laser cladding zone (LCZ), residual stress is in a tensile state, while the stress in the additive region relaxes to almost 0 after 106 cycles under a load of 300 MPa, without any change in the substrate's stress. Microhardness in the substrate, heat affected zone (HAZ), and LCZ shows a slight decrease trend, with only a 5 % drop. The fatigue limit of the TC17 repaired sample (309 MPa) decreases by approximately 45 % compared to the forging material (557 MPa) after 106 cycles at a stress ratio of 0.1. However, this result (309 MPa) is over 70 % higher than that of samples damaged by foreign objects (180 MPa), indicating a significant repair effect. Fatigue fracture observations reveal that cracks originate from additive manufacturing pores, and the crack propagation rate in the LCZ is significantly higher than that in the substrate. The characteristics of dimples in the final fracture region indicate a decrease in the plasticity of TC17 titanium alloy due to the additive repair.