Modification of High Speed Steel Surface with Laser Cladded AlTiN/NiCoCr Bilayers

The porous AlTiN ceramic layer and compact NiCoCr alloy layer were consecutively synthesized by laser cladding on substrate of high speed steel.The influence of the adhesive transition AlTiN-layer on the microstructures,interfacial adhesion and residual stress was investigated with X-ray diffraction and scanning electron microscopy.The preliminary results show that the AlTiN transition layer makes the difference.For example,the 146 μm thick AlTiN layer,comprising the randomly oriented equiaxed grains,in α-Al₂O₃/Al₂Ti₅N/Rutile-TiN phases,and quite a few Co and Ni diffused into and deposited on the pore surfaces,significantly increased the mechanical-strength/interfacial-adhesion and considerably decreased the pore-sizes and residual stress,possibly because the interfacial diffusion/segregation/reaction/reconstruction greatly increased the compactness/density/bonding of the 200 μm thick adhesive layer.In addition,the stepped fracture was observed.