摘要
X 射线衍射分析和差热分析结果表明,Ni-P 电刷镀层自约300℃开始晶化,于约400℃晶化结束,最后转变为 Ni 与弥散分布的 Ni_3P 相的混合物组织。采用等温热分析法,利用 Johnsoa-Mehl-Avrami 方程,作出了 Ni-9.3%P 电刷镀层的晶化动力学曲线和 TTT 图;得到的晶化激活能为192kJ/mol,Johnson-Mehl-Avrami 方程转变方式指数 n为2.7。外推的瞬时晶化温度约为440—450℃。经不同温度热处理后,Ni-P 镀层的峰值硬度出现在400℃左右,对应于晶化后硬化相的最佳弥散分布状态。所以,热模具寿命的提高,是非晶态Ni-P 镀层在工作条件下发生晶化和沉淀硬化,使模具表面红硬性提高的结果。
The results of X-ray structural and differential thermal analysesshow that the crystallization of Ni-P coatings starts from about 300℃ andfinishes near 400℃,and the stable structure obtained consists of Ni anddisperse Ni_3 P phases.Using the isothermal analysis,on the basis of the Johnson-Mehl-Avrami'sequation,the kinetic curves and TTT-diagram of crystallizaticn of Ni-9.3%Pbrush-plated coatings are constructed.The value of activation energy forcrystallization is 192kJ/mol;the exponent of conversion tpyes in the Johnson-Mehl-Avrami's equation n is 2.7.The instaneous crystallization temperatureobtained by extrapolation is in the interval 440—450℃.After heat-treatmentat various temperatures,the maximum hardness of Ni-P coatings appears in thevicinity of 400℃,that corresponds to the optimum distribution of the harden-ing phase Ni_3P in crystallized coatings.Therefore,the appreciable increase in life of industrial hot-working dieswill be attributed to that,under the conditions of operation in the amorphouscoatings take place the crystallization and preeipitation hardening,whichresult in a higher red hardness in the surface layer of dies.
基金
国家自然科学基金
5860265
关键词
非昌态
电刷
镀层
晶化
动力学
amorphous brush-plated coating
crystallization prccess
kinetics of crystallization
red hardness
