化学镀Ni-Mo-P/Ni-P梯度合金镀层退火晶化及磨损机理

Annealing crystallization and wear mechanism of Ni-Mo-P/Ni-P gradient coatings by electroless plating

通过化学沉积法制备了Ni-Mo-P/Ni-P梯度合金镀层。采用XRD定量分析、SEM/EDS扫描电镜观察及光学干涉法,并通过显微硬度测试、摩擦磨损试验,研究了退火前后梯度合金的晶化组织特征、硬度、耐磨性及磨损机理。结果表明,从镀态到300℃退火后,梯度合金外层Ni-Mo-P仅发生Ni相晶化,内层Ni-P还伴有Ni3P析出。从400℃到800℃退火后,外层开始发生Ni3P晶化反应,同时Ni-Mo固溶体形成,800℃晶化程度约为97.13%,而内层完全晶化。无论内层还是外层,在Ni3P刚开始析出时,Ni相的晶粒尺寸总是小于Ni3P相。梯度合金400℃热处理后的显微硬度出现峰值,但相应的耐磨性最低;600℃热处理后表现出优异的耐磨性,这一性能特征可为在高温条件下工作、且要求保持高耐磨性的工件的工业应用提供潜在的可能性。梯度合金的磨损机制主要取决于外层磨屑中含有的Ni/Ni-Mo、Ni3P相尺寸大小对内层摩擦磨损过程的影响以及内层的组织状态。

Ni-Mo-P / Ni-P gradient coatings were prepared by electroless plating. The microstructural characteristics,microhardness and wear resistance as well as wear mechanism of the gradient coatings before and after annealing were investigated by means of XRD,SEM /EDS observation,interferometry,measurement of microhardness,friction and wear tests. The results indicate that annealing at 300 ℃,crystallization of only Ni phase occurs for the outer layer Ni-Mo-P,and the Ni phase crystallization and precipitation of Ni3 P phase are observed for the inner layer Ni-P. After annealing at 400 ℃ to 800 ℃,precipitation of Ni3 P phase and formation of Ni-Mo solid solution are detected in outer layer. When annealing at 800 ℃,the degree of crystallization of the outer layer is about 97. 13%,but the inner layer is completely crystallized. The grain size of Ni phase for both inner and outer layer is always smaller than that of Ni3 P phase at the crystallization reaction temperature of Ni3 P phase. The maximum microhardness of the gradient coatings appears at annealing temperature of 400 ℃,but corresponding wear resistance is the lowest. The gradient coatings after annealing at 600 ℃ exhibits excellent wear resistance,which can provide a possibility of engineering applications for components required to keep high wear resistance at high temperature. The wear mechanism of the gradient coatings mainly depends on the effect of grain size of Ni / Ni-Mo,Ni3 P phases in wear debris of the outer layer on the friction and wear process of the inner layer,and microstructure of the inner layer.