Cryogenic assisted abrasive waterjet machining of Ti-6Al-4V alloy: Thermo-mechanical optimization and AI-based surface integrity prediction

Abstract

This study investigates the optimization of surface integrity in Ti-6Al-4V alloy through cryogenically assisted abrasive waterjet machining (CAAWJM), focusing on the regulation of thermo-mechanical mediated performance using liquid nitrogen (LN₂) deep cooling. While conventional abrasive waterjet machining (AWJM) offers distinct advantages for difficult-to-machine materials, such as titanium alloys, its inherent transient high-temperature effects can induce microstructural damage and thermal instability. Results demonstrated that LN₂ integration effectively reduces peak temperatures by 42 % while enhancing cooling rates, thereby substantially mitigating thermal degradation. Microstructural analyses reveal that CAAWJM promotes grain refinement (58 % reduction in α-Ti grain size), increases high-angle grain boundaries (up to 60.2 %), and stabilizes the β-phase (28 % higher retention compared to AWJM). Mechanical testing shows a 42 % improvement in microhardness near the jet impact zone, accompanied by a substantial reduction in surface roughness due to suppressed abrasive embedding and oxidation (TiO₂ content decreased by 42.48 %). A novel deep learning model (Bootstrap + TabPFN) is developed to predict surface integrity, achieving an R² of 0.955. These findings establish CAAWJM as a promising strategy for high-integrity machining of Ti-6Al-4V alloy, with implications for aerospace and biomedical applications.