Research On The Technology Of Plasma Spraying For Locomotive Cylinder

Based on the failure mechanism of the inner wall of locomotive diesel cylinder, the nano-intermixed WC-Co coating, common WC-Co coating and common NiCr-Cr₃C₂ coating have been developed by plasma spraying. The morphology, phase structure and chemical element have been studied by SEM, XRD and XPS. The porosity, microhardness and bond strength have been tested in this paper. And the wear property of the three coatings have been compared. The shock property have also been investigated. The results show:The coatings have typical by layer structure, the layer have mechanical bond with substrate and each other. The structure of nano-intermixed WC-Co coating is more denser the coating composition is distributed more even and have the minimum porosity rate . The common WC-Co coating is more coarse, and there existed a large amount of pieces of layer by layer structure. The layer structure and microcrackles are obvious in the common NiCr-Cr₃C₂ coatings.The phase of the WC-Co coatings are mainly WC, W₂C and Co₃W₃C, The phase of NiCr-Cr₃C₂ coating is Cr₂₃C₆ Cr₇C₃ Cr₃C₃ and Cr₂O₃,and there are still existed NiC rand NiCrO₃ phase The transformation of phase structure and chemical composition are complicated during the plasma spraying process . It play a important influence on coating performance.The nano-intermixed WC-Co coating has the highest microhardness and the best bond strength.The wear resistance of the three coatings are all better than T8 tool steel. The wear resistance of nano-intermixed WC-Co coating, common coating and NiCr-Cr3C2 coating are respectively 41 times ,14times and 9times of that of T8.Based on the coatings properties and economy , the common NiCr-Cr₃C₂ coating has been put into practical application to protect the inner wall of locomotive diesel.The micro-cracks are presented in the NiCr-Cr₃C₂ coating after 32 times thermal shock tests and the coatings strip off partly after 40times quenching from 800℃ room temperature .The Ni-Al transition coating highen the bond strength of coatingwith substrate. The NiCr-Cr^ coating has good ability at high temperature.The cylinder has runned for 89,000 kilometers, the MO-O3C2 coating is still integrated and the 300,000-500,000 kilometers testing are still going on. The NiCr-Cr^Cz coating shows successful performance.