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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。
X-ray diffraction analysis and differential thermal analysis showed that the Ni-P brush coating crystallized from about 300 ℃, crystallized at about 400 ℃, and finally transformed into a mixture of Ni and dispersed Ni_3P phase. The crystallization kinetics curve and TTT diagram of Ni-9.3% P brush coating were obtained by the isothermal analysis method with Johnsoa-Mehl-Avrami equation. The obtained crystallization activation energy was 192 kJ / mol, Avrami equation transformation index n is 2.7. Extrapolation of the instantaneous crystallization temperature of about 440-450 ℃. After heat treatment at different temperatures, the peak hardness of Ni-P coating appears at about 400 ℃, which corresponds to the optimum dispersion state of the hardened phase after crystallization. Therefore, the improvement of life of hot die, amorphous Ni-P coating occurs under the conditions of crystallization and precipitation hardening, the red hardness of the mold surface results.