Nonlinear ultrasonic Rayleigh wave detection of wear characteristics in TC4 titanium alloy: Correlation with residual stress

TC4 titanium alloy, widely utilized in mechanical systems due to its exceptional performance characteristics, faces inevitable challenges from frictional wear that results in volume loss and residual stresses, ultimately compromising system performance and reliability. This investigation systematically detects the dry friction wear behavior of TC4 titanium alloy under different conditions of normal load (0–100 N), wear cycles (0–6000 cycle), and displacement amplitudes (0–4 mm) by nonlinear ultrasonic Rayleigh wave technology in combination with white light interferometric detection and X-ray diffraction detection. Results demonstrate that surface morphology characteristics, wear volume, wear depth, and residual stress exhibit proportional increases with normal load, wear cycles, and displacement amplitude by white light interferometric detection and X-ray diffraction detection. These parameters correlate with enhanced nonlinear Rayleigh effects, manifesting in second/third harmonic (4 MHz/6 MHz) and zero frequency components with fundamental wave of 2 MHz. The ultrasonic nonlinear coefficients of the second and third harmonics increase monotonically with the increase of the wear parameter. And second/third harmonic components demonstrate superior sensitivity compared to zero frequency measurements. Significantly, the nonlinear coefficient is predominantly influenced by residual stress rather than wear depth or volume. Numerical simulations of nonlinear ultrasonics with indentation depth parameters (0/40/55/65/80 μm) and the 2–5 times material nonlinearity as the different wear residual stress state corroborate these experimental findings. The study establishes that ultrasonic nonlinear coefficients serve as effective indicators of residual stress during wear processes, thereby enabling quantitative wear severity assessment and facilitating in-situ nondestructive evaluation through nonlinear ultrasonic techniques.