H13钢激光熔覆Co基涂层组织及热疲劳性能

针对热作模具用H13钢工况下易产生热疲劳失效的问题,采用Nd:YAG激光器在H13钢表面制备Co基合金涂层。利用光学显微镜、扫描电镜、能谱仪和X射线衍射仪,对涂层组织、合金元素分布及物相组成进行检测。利用显微硬度计和热震实验法,测试热疲劳对Co基合金涂层和淬火回火态H13钢硬度影响。结果表明,Co基合金涂层从底部到表层,依次为平面晶、胞状晶、树枝晶和等轴晶。Co基合金涂层物相主要由-Co和M23C6相组成,热疲劳后涂层表面形成M2O3和M3O4(M=Fe,Co,Cr)氧化物。Co基合金涂层硬度最高可达706HV0.2且呈梯度降低；热循环1000次后,Co基合金涂层表面硬度降低24.4%,H13钢表面硬度降低37.7%,Co基合金涂层硬度下降幅度低于H13钢。热循环1000次后,Co基合金涂层表面未发现明显热裂纹,H13钢表面形成大量网状热裂纹。Co基合金涂层中,Cr元素形成致密Cr2O3氧化膜使其热疲劳性能优于H13钢。

Microstructure and thermal fatigue resistance of Co-based alloy coating on H13 steel by laser cladding

Thermal fatigue failure is easy to occur on H13 steel surface under working condition, the Co-based coating was fabricated by Nd:YAG laser on H13 steel. Microstructure, distribution of elements and composition of phases were investigated by means of optical microscope(OM), scanning electron microscope(SEM), energy dispersive spectrometer(EDS) and X-ray diffraction(XRD).The effect of thermal fatigue on microhardness of Co-based coating and quenching-tempering H13 steel was tested by microhardness tester. The results show that: From bottom to the surface of Co-based coating, planar crystal, cellular crystal, dendrite crystal and equiaxed crystal were observed; Co-based alloy coating is mainly composed of -Co and M23C6, M2O3 and M3O4(M=Fe, Co, Cr)are produced on the surface of coating after thermal cycling; Microhardness of Co-based coating which could reach 706HV0.2, decreased gradually. After 1000 thermal cycles, the microhardness decreases of Co-based alloy coating and H13 steel are 24.4% and 37.7%, respectively; The surface of the Co-based coating has no thermal cracks, while that of H13 steel has a large number of thermal cracks; Cr2O3 oxide film is formed on Co-based alloy coating, which makes thermal fatigue resistance of coating better than that of H13 steel.