Evolution characteristics of residual stress in metastable Ni-B alloy coatings identified by nanoindentation

Residual stress has a strong effect on the mechanical performance of coatings. To understand the mechanism of its generation and evolution in metastable alloy coatings, Ni-B alloy coatings with different degrees of crystallinity were prepared on 0.45% carbon steel substrate by an electro-brush plating technique. The amorphous proportion and grain size were investigated by X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). With the help of the Lee model and Suresh model, residual stress in metastable state Ni-B alloy coating was determined from the load-displacement curves obtained by nanoindentation. From XRD and TEM results, the deposition was composed of amorphous and nanocrystalline phases, which contained compressive stress in the as-plated coatings. The compressive level decreased with the increase of annealing temperature. Compared with the Suresh model, Lee model is more suitable to evaluate residual stress in the metastable state materials. The experimental results also revealed that the compressive residual stress level was directly related to the total area of grain boundary.