WANG Yan, LI Kexian, HONG Xin, WANG Zhongyu, LI Wenbo, ZENG Liang, CHU Xin, XIE Yingchun, DENG Chunming
Titanium alloys have become core structural materials for aero-engines due to their low density，high specific strength，and excellent corrosion resistance. However，they exhibit low surface hardness and poor wear resistance. Surface micro-damage often occurs under fretting wear，inducing the initiation and propagation of fatigue cracks. Meanwhile，titanium alloys show high crack sensitivity，strong chemical activity，and low thermal conductivity，and their fatigue performance can be easily degraded during processing. For titanium alloy components characterized by large size and irregular geometry，traditional surface strengthening processes are limited by temperature，structural adaptability，and coating uniformity，making it difficult to meet the requirements of high-performance surface strengthening for components with complex morphologies. Cold Spray (CS)，as a solid-state deposition technology，has the advantages of low deposition temperature，small heat-affected zone on the substrate，controllable coating residual stress，and strong adaptability to large and special-shaped components. It enables efficient and high-quality coating preparation while avoiding high-temperature oxidation and thermal distortion of titanium alloys.In this study，IN718 and IN718＋WC10Co4Cr nickel-based wear-resistant coatings were prepared on Ti55531 titanium alloy by cold spraying. The microstructure，hardness，bonding strength，fretting wear performance，and high-cycle bending fatigue performance of the coatings were systematically characterized，and the action mechanism of the coatings on substrate wear and fatigue behavior was revealed. The results showed that the cold-sprayed nickel-based coatings had uniform and dense microstructure with good bonding to the substrate. The porosities of the two coatings were 0.21％ and 0.17％，respectively，and the bonding strengths were both higher than 70 MPa. The addition of WC10Co4Cr hard phase increased the hardness of the IN718＋WC10Co4Cr coating by 29 HV compared with the IN718 coating.The Ti55531 titanium alloy substrate suffered the most severe wear，with a wear rate of 9.81×102 μm3/(N·m). Deep and wide plowing grooves were observed on its worn surface，with significant material spalling and delamination，accompanied by a large amount of wear debris. The wear mechanisms of the two cold-sprayed nickel-based coatings were both mild adhesive wear and abrasive wear. Among them，the IN718＋WC10Co4Cr coating exhibited the best wear resistance，with a wear rate of (55±28) μm3/(N·m) and a wear volume of (14540±7428) μm3，increasing the wear resistance by a factor of44.39 compared with the substrate. Its worn surface presented a typical tribo-layer morphology，which could partially fill the plowing grooves，inhibit crack initiation and propagation，and exert significant buffering and protective effects on the substrate.After deposition of the IN718＋WC10Co4Cr nickel-based coating，the high-cycle fatigue strength of the titanium alloy substrate decreased.Analysis of fatigue fracture，substrate hardness，and grain size variation indicated that interface defects，work hardening，and grain coarsening were not the main causes of fatigue degradation. Residual stress was identified as the primary factor reducing fatigue performance. The residual stress on the coating surface was compressive under both single-pass and multi-pass spraying，with the compressive stress in multi-pass coatings significantly higher. At a depth of50 μm within the coating，the residual stress transformed into tensile stress along the RD direction，and the residual tensile stress in single-pass coatings was significantly higher than that in multi-pass coatings. The fatigue strength of multi-pass coated specimens (560 MPa) was significantly higher than that of single-pass coated specimens (400 MPa). The lower internal tensile stress reduced the initiation and propagation of fatigue cracks at the substrate interface，which was consistent with the better high-cycle rotating-bending fatigue performance of multi-pass specimens.
