【作者】 王一博；

【导师】 龚凡；

【作者基本信息】 哈尔滨工程大学 ， 应用化学， 2009， 硕士

【摘要】 本文采用横流式CO2激光器在40Cr钢基体表面上进行了不同质量百分比的Co包WC+Ni60A混合粉末的激光熔覆实验,优选出最佳的WC添加量,在此基础上添加不同质量百分比的纳米Ce02,从而优化出最佳配比。利用SEM、XRD等手段进行了熔覆层的相组成和显微组织结构分析,并阐述了激光熔覆过程中WC和纳米CeO2对熔覆层的影响。并利用显微硬度仪、摩擦磨损试验机对熔覆层进行硬度、耐磨性进行表征；利用极化曲线和浸泡试验对熔覆层的耐腐蚀性能分析。对比WC和纳米CeO2添加量对涂层各性能的影响,优化出最合适的熔覆材料配比。微观组织分析表明,熔覆试样由表层至基体分为三个不同的组织区域：熔覆层、熔覆层与基体之间的结合带、热影响区。熔覆层组织为树枝状晶和块状物,并且随着WC加入量的增加,枝晶迅速变小；而加入少量稀土氧化物后,使得激光熔覆层组织生长的方向性减弱,针状组织数量增加。涂层主要是由γ-Ni、WC、W2C、CrB2、Cr23C6、Cr7C3等相组成,加入纳米CeO2后,激光熔覆层中除有上述相组成外,还形成了CeNi3, Ce3BO6等化合物相。在未加入纳米CeO2时,随着WC加入量的增加,熔覆层的硬度呈现先升后降的趋势,而磨损率则呈现先降后增的趋势,这说明熔覆层的力学性能在WC加入量较小时随着WC加入量的增加而逐渐提高,在WC加入量过大时,随着WC加入量的增加而逐渐下降。在本实验条件下,存在一个WC加入量最佳值使得熔覆层的力学性能达到最佳,即为30%。浸泡试验结果显示,WC加入量对熔覆层的耐腐蚀性能同样有影响,随着WC加入量的增加,熔覆层在1mol/L硫酸腐蚀介质中的腐蚀速率先减后增,在WC加入量为30%时达到最小,仅为0.32 mg/cm2·h,说明在WC加入量为30%时熔覆层的综合性能达到最佳。在加入纳米CeO2时,熔覆层的硬度、耐磨性极耐腐蚀性较未加入纳米CeO2的有所提高,随着纳米CeO2加入量的增加,熔覆层综合性能也存在着一个最佳值,纳米CeO2的最佳加入量为1.5%。在本文的实验条件下,配比为30%WC+1.5%纳米CeO2+ Ni基合金可使熔覆层达到最优综合性能。更多还原

【Abstract】 In this study, through a series of laser cladding experiments, CO/WC+Ni60A powders of different weight percentage were prepared on the surface of 40 Cr steel substrate, with a HJ-3kW crosscurrent typed CO2 laser apparatus, and the additive amount of WC was optimized. Then different content of nano CeO2 was added to the optimal CO/WC+Ni60A powder, and the best ratio was obtained.SEM and XRD measurments were employed to analyse the phase constitution and microstructure of the cladding layer, the impact of WC and nano CeO2 on the layer in the process of laser cladding was discussed. The hardness and wear resistance of the cladding layer were characterized by Micro hard-ness tester and wear testing machine, respectively, and the corrosion resistance was analyzed by polarization curves and immersion tests. The most suitable ratio of cladding material was optimized.The microstructure analysis results indicated that the cladding layer could be divided into three distinct areas:the suture zone, the substrate and the heat-affected zone. Cladding layer were dendritic crystal and the lump structure, and with the addition of WC, dendrites become fine rapidly. The direction character of laser cladding becomes weak, and the needle structure increased after the addition of a small amount of rare earth oxides. The cladding was mainly composed of y-Ni, WC, W2C, CrB2, Cr23C6, and Cr7C3. Besides the materials above, the compounds such as CeNi3 and Ce3BO6 were formed in the laser cladding layer by adding nano CeO2.The hardness of the cladding layer first increased and then decreased, and the wear resistance first increased and then decreased with the increase of WC befor the addition of nano CeO2. It indicated that the mechanical property of the cladding layer improved as the increase of the WC when the amount of WC added was small, and descended when the WC amount was lage. Under the experimental conditions, the best value of the WC amount was 30%, which made the mechanical properties of the cladding layer achieve the best. The results in the soaking experiments showed that, the addition of WC can impact the corrosion resistance of the cladding layer. The corrosion rate of the cladding layer in lmol/L sulfuric acid first decreased and then increased, and achieve the best when the amount of added WC was 30%, only 0.32 mg/cm2·h.The hardness, wear-resistance and corrosion resistant of cladding layer all increased after the addition of nano CeO2. The optimum value appeared when the best amount of nano-CeO2 was 1.5%. Therefore, under the experimental conditions, the best ratio was 30% WC,1.5% CeO2 and Ni-based alloys.更多还原