常规超音速和低温超音速火焰喷涂WC-10Co-4Cr涂层的断裂韧性

Fracture Toughness of Normal High Velocity Oxygen-fuel Flame and Low Temperature High Velocity Oxygen-fuel Sprayed WC-10Co-4Cr Coating

以5～15扯m的超细WC-10Co-4Cr粉末为材料，分别采用常规超音速火焰喷涂（HVOF）和低温超音速火焰喷涂（LT_HVOF）技术制备WC-10Co-4Cr涂层。借助于扫描电子显微镜、粗糙度测试仪、显微硬度仪和3D形貌仪对涂层的显微结构、粗糙度和显微硬度进行了表征。结果表明：LT-HVOF下WC-10Co-4Cr粒子为微熔化状态，HVOF下WC-10Co-4Cr粒子为半熔化状态；HVOF涂层的主晶相为W2C，LT-HVOF涂层的主晶相为WC；LT-HVOF涂层的粗糙度（兄约为1．22μm）远低于HVOF涂层的，而显微硬度[Hv0．3=1316±85]和断裂韧性（Kc=3．23MPa·m1/2）均高于HVOF涂层的。HVOF涂层的裂纹沿富cr带扩展，LT-HVOF涂层的裂纹扩展到WC硬质相时偏转至CoCr黏结相，富cr带的存在对涂层的韧性有明显降低作用。

WC-10Co-4Cr splats and coatings were prepared with the ultrafine powder as a feed material by high velocity oxygen- fuel flame （HVOF） and low temperature high velocity oxygen-fuel （LT-HVOF） techniques, respectively. The microstruture, roughness, micro-hardness and fracture toughness were characterized by scanning electron microscope, micro-hardness tester, roughness tester and 3D topography tester, respectively. The results show that the LT-HVOF WC-10Co-4Cr splats are in a slightly-melted state, and the HVOF WC-10Co-4Cr splats are in a partially-melted state. The main crystal phases for the HVOF and LT-HVOF coatings are W2C and WC, respectively. Compared to the HVOF coating, the LT-HVOF coating has a lower surface roughness （i. e. , Kc =1.22μm）, a higher micro-hardness （i. e. , Hv0.3 =1 316±85） and a higher fracture tough- ness （i. e. , Kc=3.23 MPa.m1/2 ）. The cracks in the HVOF coating propagate along the Cr-rich strip, and the cracks in the LT-HVOF coating deflect to the CoCr adhesive phase when propagated to the WC particles. In addition, it is also indicated that the fracture toughness of the coating could be decreased due to the presence of the Cr-rich strip.