【作者】 曹亚男；

【导师】 张艳梅；

【作者基本信息】 广东工业大学 ， 材料加工工程， 2012， 硕士

【摘要】 激光熔覆技术是高能量密度表面处理技术的一种,具有许多其它表面处理方法无法比拟的优点。镍基白熔性合金粉末具有优良的耐腐蚀、抗氧化、耐磨损等综合性能。超声波对金属凝固组织细化有很好的改善作用。本文研究了超声波对激光熔覆Ni60B及WC/Ni60B涂层的影响,通过扫描电镜及附带的能谱仪、X射线衍射仪、显微硬度测试系统和多功能表面综合性能测试仪对熔覆层的显微组织结构、裂纹情况、显微硬度和摩擦磨损性能进行了系统分析。研究结果及主要结论如下：(1)本文研究中,主要熔覆工艺参数对熔覆层宏观形貌和熔覆裂纹影响程度大小依次为：扫描速度>电流、脉宽(即功率)>送粉量>频率。(2)添加超声振动后Ni60B熔覆组织变得均匀细小,枝晶数量减少,等轴晶数量增加。Ni60B+10％WC涂层中WC基本上全部溶解,超声波促进了WC在熔覆层中的均匀分布和组织细化；Ni60B+20％WC熔覆层底部出现充分溶解的WC相,熔覆层中部有大量溶解再析出的WC,WC的团聚被削弱。WC集中分布在熔覆层中上部的特点使熔覆层既可获得更高硬度和更好耐磨性,同时又保证了与基体的良好冶金结合。超声波对Ni60B+10％WC涂层组织的改善更显著。(3)Ni60B熔覆层的裂纹为垂直熔覆方向的横向裂纹,熔覆层上部的裂纹以冷裂纹为主,横贯熔覆截面的裂纹以热裂纹为主,添加超声振动后,裂纹数显著减少,但仍有少量微裂纹,添加1%Y2O3后制得无裂纹质量良好的熔覆层；WC/Ni60B熔覆层中有很多垂直和沿熔覆方向的宏微观裂纹,添加超声振动后裂纹数量明显减少、开裂程度减弱,超声波对含20%WC熔覆层的裂纹抑制作用更为明显。(4)未加超声振动时,Ni60B和WC/Ni60B熔覆层的显微硬度波动性较大；添加超声振动后,熔覆层显微硬度的均匀性和硬度值均有提高。Ni60B+1％Y203涂层的显微硬度可达1100HV0.2,Ni60B+10％WC涂层表层硬度高达1750HV0.2。(5)超声振动可提高Ni60B和WC/Ni60B熔覆层的耐磨性,摩擦系数稳定性变好,磨损机理前者主要为疲劳磨损,后者主要为疲劳磨损和磨粒磨损。经超声振动的Ni60B+10％WC涂层耐磨性最好,摩擦系数最小。更多还原

【Abstract】 Laser cladding is a kind of high energy density surface treatment technology, it has many advantages which other surface treatment methods cannot compare with. Ni-based self-fluxing alloy powder has excellent properties, such as corrosion resistance, anti-oxidation, wear resistance. Ultrasonic has good refine effect on metal solidification. The influence of ultrasonic to laser cladding Ni60B and WC/Ni60B coatings were researched in this paper. The microstructure, crack, micro-hardness and wear resistance were systematically analyzed by scanning electron microscope with energy disperse spectroscopy, X-ray diffractomer, micro-hardness test system and multi-function surface compositive test instrument. Research results and main conclusions were summarized as follow:(1) In this study, the influence degree of main laser cladding processing parameters to the laser cladding coating and crack were ranked as follow:scanning velocity>current and impulse width (namely laser power)>powder feeding velocity>frequency.(2) With the aid of ultrasonic, the Ni60B laser cladding coating microstructure got well-distributed and fine, dentrite reduced and isometric crystal increased. In the Ni60B+10%WC coating, WC dissolved mostly and ultrasonic vibration improved the WC distribution in the whole coating and the microstructure became fine. Fully dissolved WC was found at the bottom of the Ni60B+20%WC coating, and there were more dissolved WC re-precipitation in the middle of the coating. WC particles aggregation was weakened by ultrasonic vibration. The WC distribution character which was concentrated in the middle and at the top of the coating kept the laser cladding coating with high hardness and excellent wear resistance, meanwhile ensured the metallurgical bonding with the substrate. Ultrasonic had a great influence to the microstructure of laser cladding Ni60B+10%WC coating.(3) There were many transverse cracks which were perpendicular to the direction of laser scanning speed in the Ni60B coating. Cracks on the upper layer of the coating were mainly cold cracks, and cracks propagated throughout the cross-section of the coating were mainly hot cracks. After adding ultrasonic vibration, the cracks reduced, but there were still several micro-cracks. Crack-free and good qualified laser cladding Ni60B coating by adding1%Y2O3was obtained with the aid of ultrasonic. In the WC/Ni60B coating, there were many transverse and longitudinal macro micro cracks. The crack number and crack gap in extent obviously decreased after ultrasonic vibration, meanwhile ultrasonic had a prominent effect to the crack inhibition of the Ni60B+20%WC coating.(4) The micro-hardness of the laser cladding Ni60B+1%Y2O3coating was HOOHVo.2, and the surface layer micro-hardness of the laser cladding Ni60B+10%WC coating could reached1750HV0.2both with the aid of ultrasonic.(5) The micro-hardness of the laser cladding Ni60B coating and WC/Ni60B coating without the aid of ultrasonic fluctuated violently, the homogenization and numerical value were improved after ultrasonic vibration.(6) Wear resistance of the laser cladding Ni60B and WC/Ni60B coating were improved with the aid of ultrasonic vibration, and the stability of the friction coefficients got better. To the laser cladding Ni60B coating, the wear mechanism was endurance failure and abrasive wear compared with endurance failure to the laser cladding WC/Ni60B coating. The laser cladding Ni60B+10%WC coating with the aid of ultrasonic had the best wear resistance and the smallest friction coefficient compared with other coatincs.更多还原