FeNiCoTiNb低膨胀激光熔覆涂层的组织特征及摩擦学行为

Microstructure Characteristics and Tribological Behaviour of Low Thermal Expansion FeNiCoTiNb Coating by Laser Cladding

目的借助低膨胀合金的因瓦效应,降低熔覆技术产生的热应力,在保证涂层具有低膨胀性的前提下,同时具有优良的机械性能。方法采用激光熔覆技术在316L不锈钢体表面制备了具有低膨胀系数的FeNiCoTiNb涂层。采用SEM、EDS、热膨胀分析仪、摩擦磨损试验机等对涂层的显微组织、残余应力、热膨胀系数、硬度及耐磨性能进行了分析。结果涂层主要由具有FCC结构的γ-(Fe,Ni)固溶体相构成,涂层底部组织主要为胞状晶和柱状晶,局部区域观察到了胞状晶与柱状晶组织向等轴晶组织转变的行为,涂层顶部组织主要由等轴晶组成。涂层的残余应力与热膨胀系数均处于较低水平,其中残余应力平均值为(43±15)MPa,在30~600℃间热膨胀系数的平均值为8.5×10^-6℃^-1,显著低于FeCrNi及NiCrBSi熔覆层。涂层的显微硬度可达到400HV0.5。涂层的磨损机制为磨粒磨损及氧化磨损,316L的磨损机制主要为粘着磨损及氧化磨损。结论通过在316L不锈钢表面进行激光熔覆,得到了兼具低膨胀系数、高硬度、高耐磨性的FeNiCoTiNb涂层,涂层在一定程度上降低了熔覆产生的热应力。

The work aims to reduce thermal stress of laser cladding with invar effect of low thermal expansion alloy, and ensure the coating having excellent mechanical properties on the premise of low expansion. A low thermal expansion FeNiCoTiNb coating was successfully fabricated on 316L stainless steel via laser cladding technique. Microstructure, residual stress, CTE, microhardness and wear-resisting property of the coating were analyzed by SEM, EDS, thermal expansion analyzer, friction wear testing machine, etc. The coating was mainly composed of γ-(Fe,Ni) solid solution matrix phase with FCC structure. Cellular or columnar dendritic structure was observed at the coating bottom and equiaxed dendritic structure transformed by cellular or columnar dendritic structure also appeared at the bottom and upper region, respectively. The residual stresses and thermal expansion coefficient of coating all remained at a low level with an average value of (43±15) MPa and 8.5×10^-6 ℃^-1 at 30~600 ℃, respectively. The CTE of FeNiCoTiNb coating was lower than that of FeCrNi and NiCrBSi coatings significantly. The hardness of the coatings could reach 400HV0.5. The wear mechanism of coating was abrasive wear and oxidation wear. The wear mechanism of substrate was adhesive wear and oxidation wear. In the end, low thermal expansion FeNiCoTiNb coating is produced by laser cladding on 316L stainless steel, which has low thermal expansion coefficient, high microhardness and high tribological resistance, and reduces thermal stress of laser cladding to some extent.