Effect of Ni-Al intermetallic sublayers on tribological properties of crystallised Ni-P coatings on aluminium substrates

摘要

The effect of Ni-Al intermetallic sublayers on thetribological properties of Ni-P coated aluminium substrates hasbeen investigated. For this purpose an Ni-P coating was diRECtlydeposited on to an 1100 aluminium substrate and Al-Ni diffusionsublayers were produced by subsequent vacuum heat treatment.The diffusion layers were characterised by optical and scanningelectron microscopy (SEM), X-ray diffraction, microanalysis, andtribological testing. The results show that after annealing for 10 hat 520℃, three layers are formed with a total thickness of 3-4times during diffusion annealing are the intermediate phases of theNi-Al system where their formation is controlled by processkinetics. The outermost layer was identified as a crystallised Ni-Presidue along with two distinct layers of Ni2Al3 and NiAl3intermetallic compounds formed beneath it. The results of weartesting indicate much improved wear resistance after diffusiontreatment, believed to result from a smooth hardness gradient andthe formation of intermetallic phases at the interface, which acts asa firm substrate beneath the hard crystallised Ni-P surface layer.From SEM studied of the wear debris and the worn specimens itcan be concluded that delamination is the predominant wearechanism of the surface layer.