厚度主导铝合金表面304不锈钢涂层组织结构及性能的演变行为

Microstructure and Properties of 304 Stainless Steel Coating with Different Thickness on Aluminum Alloy Surface

目的 评价不同沉积厚度对铝合金基体上304不锈钢涂层综合性能的影响。方法 采用超音速火焰喷涂在铝合金表面制备3种不同厚度(200、600、1 000μm)的304不锈钢涂层。利用附带能谱的扫描电镜(SEM)、X射线衍射仪(XRD)、维氏显微硬度计、纳米压痕仪、液压式万能试验机以及摩擦磨损试验机,研究涂层的微观结构、物相组成、残余应力、硬度分布、弹性模量、结合强度、弯曲性能和摩擦学行为。结果 304不锈钢涂层组织均匀、无裂纹,与基体结合良好。涂层主要由奥氏体相组成,其余为少量铁素体相和氧化物,且涂层中奥氏体晶粒相比粉末中发生晶粒细化。随着涂层厚度的增加,涂层孔隙率(C200≈0.5%、C600≈2.5%、C1000≈4.3%)、氧含量(C200≈2.4%、C600≈3.1%、C1000≈4.2%)增加,涂层残余压应力减小,显微硬度、弹性模量和结合强度均呈下降趋势;但涂层断裂刚度与其厚度成正比,断裂时裂纹主要沿未熔颗粒边界和氧化物聚集区域萌生和扩展。在干摩擦条件下,304不锈钢涂层的摩擦系数约为0.6,与铝合金相比,摩擦过程更加稳定,耐磨性提高3倍。随着涂层厚度的增加,涂层摩擦系数稳定性降低,磨损率增大,磨损机制以疲劳磨损和犁沟磨损为主。结论 与304不锈钢粉末相比,晶粒细化和残余压应力的存在致使涂层整体硬度提升。然而,随着涂层厚度增加,涂层中缺陷的增多以及残余压应力的减小又降低了涂层的综合性能。涂层断裂刚度与其断裂能有关,厚涂层体系具有更大的等效抗弯刚度。

304 stainless steel coatings with different thickness(≈200μm,≈600μm,≈1000μm)were successfully deposited on the surface of aluminum alloy by High Velocity Oxygen-fuel(HVOF)spraying technology to improve the surface properties.Meanwhile,the effect of the coating thickness on the service performance was evaluated.The microstructure,phase composition residual stress,micro-hardness distribution,elastic modulus,bonding strength,bending strength and tribology properties of each 304 stainless steel coating were studied.Then the relationship between microstructure,mechanical and tribology properties of coatings with different thickness was systematically discussed.The results showed that the microstructure of each coating was uniform and crack-free,and it was well combined with the aluminum alloy substrate.The XRD patterns showed that each coating was mainly composed of austenite phases,the rest were a small number of ferrite phases and oxides,which were caused by temperature change.At the same time,the austenite grains in the coating were refined significantly compared with those in the original powder.It was caused by the plastic deformation of un-melted particles and the rapid cooling of molten particles.Porosity(C200≈0.5%,C600≈2.5%,C1000≈4.3%)and oxygen content(C200≈2.4%,C600≈3.1%,C1000≈4.2%)increased with the increase of coating thickness.The comprehensive residual stress in each coating was compressive stress by curvature method,and decreased with the increase of the coating thickness,which was beneficial for various properties of the coating.In terms of mechanical properties,the micro-hardness and elastic modulus were obviously higher than that of the substrate,but they all decreased with the increase of coating thickness.And the bonding strength of the coating also decreased from C200/50.4 MPa to C600/43.6 MPa and C1000/39.6 MPa.Moreover,the fracture stiffness of the coating was positively correlated with the thickness of the coating,which was related to the increase of fracture energy with the increase of coating thickness.In all coatings,the crack initiation and propagation occurred through un-melted particles and the area of oxide accumulation when the coating was fractured,so that the amount and location of un-melted particles and oxides in the coating was the most important characteristic in their fracture behaviors.In the end,under dry friction conditions,the friction coefficient of the 304 stainless steel coating was about 0.6,the friction process was more stable and the wear resistance was up to 3 times that of the aluminum alloy substrate(5.53×10–4 mmN–1m–1).The wear rate of C200(1.48×10–4 mmN–1m–1)was significantly lower than that of C600(1.88×10–4 mmN–1m–1)and C1000(2.08×10–4 mmN–1m–1).Therefore,with the increase of coating thickness,the stability of coating friction coefficient decreased,the wear mark deepened,and the wear rate increased.The wear mechanism was mainly fatigue wear and furrow wear.In addition,it was accompanied by oxidation wear,in which Fe2O3 produced in the friction process aggravated the wear process of 304 stainless steel coating.Overall,grain refinement,residual compressive stress and oxide increase the micro-hardness of the coating.However,with the increase of coating thickness,the increase of defects and the decrease of residual compressive stress reduce the overall performance of the coating.