Effect of Annealing Treatment on Microstructure and Properties of Cr-Coatings Deposited on AISI 5140 Steel by Brush-Plating

Cr-coating was deposited on AISI 5140 steel by electro brush-plating, followed by annealing treatment at different temperatures, from 300 to 1100 degrees C. The microstructure evolution of the Cr-coating was characterized by backscattered electron imaging (BSEI) and energy dispersive spectrometry (EDS). The results show that the brush-plated sample has a nodular shaped microstructure, which is very stable at 300 degrees C of annealing. At 500 degrees C of annealing, the constitution of the microstructure changes from nodules to grains. As the annealing temperature further increases, the grains grow significantly. When the temperature reaches 1100 degrees C, a Cr-Fe solid-solution layer is formed within the original pure Cr-coatings. With increasing annealing temperature, the number of micro-cracks in the coating increases first and then decreases, reaching a maximum at 500 degrees C. The hardness and wear-resistance of the coating are improved when the annealing temperature increases to 1100 degrees C, owing to the decrease of micro-cracks that formed during brush-plating.