Microstructure and Wear Behavior of HVOF 410 Stainless Steel Coating

Low density and excellent mechanical properties of aluminium alloy make it widely used as a lightweight structural material in automobile manufacturing, but its lack of surface protection properties as a working part, especially low surface strength, hardness and poor wear resistance, limits its application as a heavy truck and tracked vehicle wheel in harsh working conditions such as gobi beach and sand field. Therefore, it is necessary to strengthen the surface of aluminium alloys to improve their comprehensive surface properties, which is important to improve their service life and expand their applications. 410 stainless steel has been widely used in surface engineering due to its high toughness, good hardness and wear resistance, and low material cost. In this study, 410 stainless steel coatings with oxygen-fuel ratios (OF) of 4.36, 4.91, and 5.51 were prepared on 6061 aluminum alloy surface using high-velocity oxygen-fuel (HVOF) spraying. The microstructure and mechanical properties of the 410 stainless steel coatings were characterized by XRD, SEM, and microhardness analysis. The effects of microstructure and powder deposition characteristics on the dry sliding friction and wear properties of the coatings at room temperature and atmosphere were studied. The results showed that both martensitic and ferrite structures were formed in the 410 stainless steel coatings sprayed with different OFs. As the OF increased from 4.36 to 5.51, the number of unmelted and semi-melted particles in the coating decreased, the structure became homogeneous and dense, the porosity of the coating decreased from 0.71% to 0.38%, the microhardness decreased from 592 HV_0.1 to 586 HV_0.1, and the surface roughness in the sprayed state decreased from 11.35 μm to approximately 7.05 μm. Under the conditions of dry sliding friction between the 410 stainless steel coating and the Si₃N₄ ball, the coefficient of friction changed with the surface state of the 410 stainless steel coating and exhibited different wear mechanisms at different run-in stages. In the pre-run-in stage (Stage I), the fraction coefficient tended to be 0.2 and remained stable, with the main wear mechanism being micro-contact high stress sliding wear; in the second run-in stage (Stage II), the fraction coefficient rised rapidly, with the wear mechanisms being micro-cutting, brittle peeling and three-body abrasive wear; in the third run-in stage (Stage III), the fraction coefficient falled slightly and then rised to around 0.7, with the main wear mechanisms being three-body abrasive wear and delamination wear. The deposition characteristics (porosity, hardness, etc.) and microstructure of the spray coating directly influenced the frictional run-in characteristics of the coating. The decrease in porosity and hardness of the coating caused a lag in its second run-in phase, while the increase in ferrite prolonged its second and third run-in phases. As OF increased, the wear resistance of the coating increased and the wear rate of the coating decreased from 17.96×10⁻⁶ mm³/(N·m) to 9.35×10⁻⁶ mm³/(N·m). The wear rate of the coating is 89%~94% lower than the aluminium alloy substrate wear rate of 164.27×10⁻⁶ mm³/(N·m). As the OF increased, the main wear mechanism in the stable wear phase of the coating changed from delamination wear to oxidation wear. At a low OF of 4.36, the coating induced delamination due to high porosity and frictional stress cracking of unfused deposited particles, and the main wear mechanisms were delamination, oxidation and abrasive wear; at a high OF of 5.51, delamination and abrasive wear were reduced due to low porosity and a more homogeneous microstructure, and the main wear mechanisms were oxidation and slight abrasive wear.