| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 105 === In this experiment, the study of microstructures and wear behaviors on Cobalt Hardfacing alloys was designed by various vibration frequencies welding. The frequencies were chosen 0Hz (no vibration), 419 Hz, 744 Hz, 750 Hz, 1257 Hz, 1499 Hz and 1593 Hz, then the Stellite 1 powder was deposited on a substrate of SS400 low carbon steel by transfer plasma arc welding (PTA). The structure of the cladding layer was identified by WDS analysis, X-ray diffraction and microstructural analysis. The mechanical properties of the cladding layer were evaluated by residual stress analysis, hardness test and ring-on-disk wear test. The wear surface was observed by scanning electron microscopy (SEM) to understand the abrasion behavior. The results of WDS analysis and X-ray diffraction showed that the microstructures of M7C3, M12C and α-Co after PTA welding. It was found that the morphology of the longitudinal M7C3 carbides was changed to the transverse M7C3 carbide and special eutectic-phase with the increase of the frequency. The results of X-ray diffraction showed that the residual stress decreases with the increase of frequency, and the frequency 1499 Hz was the best elimination rate of residual stress. The hardness measurement results caused by Microstructure refinement, and the result showed that synchronous vibration welding will enhance the overall hardness of the weld, which the frequency of 1593 Hz weld the hardness of the best performance (872HV1). Adhesive wear test results show that the anti-wear rate is proportional to the hardness value, where the lowest frequency 744Hz hardness (718HV1), the best anti-adhesion wear rate(3.3×10-3mg/m). The wear surface observation indicated that the cladding layer was special eutectic-phase and shortened M7C3 carbide, the wear mechanism was controlled by the abrasive wear, therefore the wear resistance of specimen became worse. When the coating structure was special eutectic-phase structure and the longitudinal M7C3 carbides, the wear mechanism was controlled by the oxidative layers, therefore the wear resistance of specimen became better.
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