Mechanism and microstructure/property control of inclined water-jet guided laser machining of Ti-6Al-4V alloy

Water-jet guided laser machining is characterized by cold cutting, low kerfs of taper, smooth machined surfaces, large depth-to-width ratio and environmental friendliness. Although water-jet guided laser machining with vertical incidence has been extensively studied, there has been no systematic investigation into the effects of oblique incidence on groove geometry, and microstructure evolution in Ti-6Al-4V material. Existing studies have not investigated the direct relationship between angle-dependent thermal effects and local material properties. To address this problem, this study explores the mechanism of inclination angle (0-50°) on the geometric morphology, microstructure and mechanical properties of the machined channel. The findings demonstrate that the inclination angle significantly affects material removal and microstructural evolution by regulating thermo-mechanical coupling behavior. Finite element simulation further confirms that the inclined heat source produces an asymmetric temperature-gradient distribution across the groove, which is consistent with the observed EBSD microstructure and microhardness variation. Increasing inclination angle redistributes effective heat input and produces asymmetric thermal histories across the groove. This suppresses the formation of acicular α′ martensite, promotes the generation of (α+β) dual-phase structure, and induces the formation of an ultra-fine grained remelted layer. An optimal balance of geometric and mechanical properties was obtained at 40°, with an aspect ratio of 0.96, an average microhardness of 429.62 ± 6.90 HV within the measured near-surface region, and a residual compressive stress of approximately −167 MPa. The findings provide both theoretical and practical support for low-stress manufacturing of high-precision water-jet guided laser machining of titanium alloy components.