RSM models approach for optimization of the mechanical properties of electroless Ni-B-nanodiamond coating: An experimental and molecular dynamic simulation study

Abstract

This report explores the effects of electroless Ni-B-nanodiamond plating bath parameters for optimization of the hardness and deposition rate based on response surface method (RSM). Quadratic models were developed and found to be mathematically appropriate for the optimization. The nanodiamonds (ND) and optimized coating were characterized using XPS, DLS, FIB-SEM, GDOES, microhardness, and nanoindentation. The results of the molecular dynamic simulation show low adsorption energy of borohydride on nanodiamonds surface is not favourable for borohydride dehydrogenation, therefore the boron content of the coating decreases when ND are added. Raman spectroscopy, SEM, and EDS analysis carried out on different zones of the surface after scratch test show nanodiamonds undergo graphitization and micro-cracking which block crack propagation at lower load. In addition, ND improves formation of the tribolayer at higher loads. The Raman spectroscopy results after indentation tests show the possibility of SP3 to SP2 phase transformation for nanodiamonds. The molecular dynamic simulation results confirm that phase transformation through monitoring the changes in nanodiamonds interatomic potential and interatomic distances. It is believed that the volume expansion caused by this phase transformation increases the toughness of coating.