Nd:YAG laser cladding Ni base alloy/nano-h-BN self-lubricating composite coatings

Abstract

Ni base alloy/nano-hexagonal boron nitride (nano-h-BN) self-lubricating composite coatings were successfully produced on medium carbon steel substrate by means of Nd:YAG laser cladding. A novel high energy ball milling method was adopted to clad nano-Ni onto nano-h-BN with an aim to enhance the compatibility between the h-BN and the metal matrix during laser cladding process. The microhardness profile of the composite coatings along the depth direction was measured, while its cross-sectional microstructures and phase compositions were analysed by means of SEM incorporating EDX and XRD. The friction behaviour of the composite coatings sliding against GCr15 steel at room temperature was evaluated using a ball on disc friction and wear tester, and the worn surface morphologies of the composite coatings were observed using SEM. It was found that nano-h-BN was hardly to be composed into Ni45 matrix coating even if increasing the weight percentage of h-BN from 5 to 10 wt-% with a conventional mechanical mixing. The high energy ball milling of nano-Ni onto nano-h-BN significantly improved the interfacial compatibility between h-BN and Ni60 matrix. The friction coefficient of the laser clad Ni60/nano-Ni-clad h-BN coating was reduced obviously.