Indentation behavior and Youngʹs modulus evaluation in electroless Ni modified CrN coating on mild steel

The acid hypophosphite-reduced bath is applied to deposit electroless Ni–P(EN) on the mild steel (MS) substrate and the CrN film is coated on the NiP modified substrate by reactive r.f. sputtering. A coating configuration of Ni/Ni3P/MS is fabricated as the precipitation Ni3P phase is formed due to the elevated substrate annealing during r.f. sputtering. Microhardness, Youngʹs modulus and indentation behavior of the EN/MS and CrN/NiNi3P/MS are investigated. The measured microhardness of the complex coating assembly is increased due to the employment of electroless Ni as the interlayer in the CrN/MS system. The indentation and cracking tester (ICT) is further employed to investigate the indentation behavior of the coating assembly. The loading–unloading curves of as-plated and heat-treated electroless Ni–P layers with different thickness are evaluated. In addition, the Youngʹs modulus of the coating can be derived with appropriate load applied.