电沉积纳米晶Ni-Co-Fe合金镀层的热稳定性

摘要

用脉冲电沉积方法制备表面平整光亮的纳米晶Ni-Co-Fe合金镀层.采用XRD、TEM、EDS、DSC和显微硬度计分别研究纳米晶Ni-Co-Fe合金镀层的微观结构、化学成分、热稳定性及其硬度.结果表明:纳米晶Ni-Co-Fe合金镀层的晶体结构为单相的面心立方结构,其晶粒尺寸随镀层Co含量的增加而减小;合金镀层的显微硬度随退火温度的升高而提高,在300～375℃时达最大值,存在明显的退火再强化,之后,随着退火温度的继续升高明显下降;当镀层在低于375℃退火时,晶粒长大速度较慢;而当镀层在高于450℃退火时,晶粒迅速长大,并呈现较强的(111)织构.升温速率为20℃/min时,纳米晶Ni-Co-Fe合金镀层的DSC结果显示,晶粒长大的峰值温度随镀层Co含量的增加而升高.由Kissinger方程求得纳米晶Ni-Co-Fe合金的晶粒长大激活能随镀层Co含量的增加而增大.%Nanocrystalline Ni-Co-Fe alloy coatings with smooth and bright surface were synthesized by pulsed electrodeposition. The microstructure, chemical composition, thermal stability and hardness of the coatings were studied by XRD, TEM, EDS, DSC and microhardness tester, respectively. The results reveal that the grain size of the nanocrystalline Ni-Co-Fe alloy coatings with FCC structure decreases with increasing the content of Co in the coatings.The microhardness of Ni-Co-Fe alloys increases with the increase of the annealing temperature after annealed at low temperatures, and reaches the peak value at 300-375 ℃, showing a significant hardening during annealing, and the hardness decreases with increasing the annealing temperature further. The grain grows slowly when the annealing temperature is lower than 375 ℃, while the rapid grain growth occurs during annealing above 450℃, showing a strong (111 ) texture. The DSC results obtained at the heating rate of 20 ℃/min show that the peak temperature value for the grain growth in nanocrystalline Ni-Co-Fe alloy coatings increases with increasing the content of Co in the coatings. The activation energy obtained from the Kissinger equation for the grain growth of Ni-Co-Fe alloy coatings increases with increasing content of Co in alloy coatings.