Thermal stability of electrodeposition nanocrystalline Ni-Co-Fe alloy coatings

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.