Research On Forming Mechanism And Properties Of Gradient Interface Ni Based Composite Fabricated By Laser Additive Manufacturing

In present research,the SLM technology was applied to fabricate the WC/Inconel 718 composite parts.The effects of laser energy linear density ???=P/v?on the microstructure,densification behavior and mechanical properties of the WC/Inconel 718 composite parts were investigated.It found that with the increase of the applied ?,the microstructure of the Inconel 718 matrix underwent a series changes from inadequately grown microstructures to fully grown and refined microstructure and finally to coarsened columnar crystal.A gradient interfacial layer with a composition of?W,M?C₃?M = Ni,Cr,Fe?was formatted between the WC particles and the Incoenl 718 matrix.With the increase of applied ?,the mean thickness of the gradient interfacial layer increased and the morphology became clearer until the coarsening.Due to the atomic diffusion,a diffusion layer with a composition of?W,M?C₂?M = Ni,Cr,Fe,Nb?was formed between the interfacial layer and the matrix.When the applied ?increased from 173J/mto 303J/m,the densification rate of the SLM-processed WC/Inconel 718 composite parts enhanced from 86.3% to 98.3% and the distribution state of the WC reinforcing particles became more uniform.At the ?=242J/m,the microhardness of the samples reached as high as 389.4HV0.1with an even distribution.At the same time,the COF and wear rate of the samples were as low as 0.39 and 2.3×10^-4mm³N-1m^-1,respectively.Further refine the processing parameters and the effects of laser scanning speed v on the interfacial microstructure and the wear properties of WC/Inconel 718 block,and the influence mechanism of the gradient interface on the friction and wear properties were discussed.When the laser power was set as 110 W,the used vdecreased from 650mm/s to 350mm/s,the changes of interfacial microstructure between the WC and matrix were: no gradient interface ?thin gradient interface ? regular gradient interface with certain thickness ?Coarsened gradient interface.When the used v was 450mm/s,a regular gradient interface was formed in WC/Inconel 718 composite part.At this circumstance,an excellent wear performance was obtained,in which the COF was as low as 0.35 with little fluctuation and the wear rate was decreased to 2.5×10^-4mm³N-1m^-1,and the wear mechanism was also changed from serious abrasive wear to mild adhesive wear.It was because of the existence of gradient interface that can prevent the the crack propagation and enhance the bonding between particles and matrix in the process of wear that the friction and wear properties of WC/Inconel 718 composites were significantly improved.It can conclude that the gradient interface formed between WC particles and matrix was W₂C,while the diffusion layer between W₂C and matrix was M₂₃C₆ through the TEM analysis of the gradient interface.The formation mechanism of the gradient interface and diffusion layer were also revealed.The nano hardness of the gradient interface was between that of WC particles and Inconel 718 matrix,which can effectively balance the hardness difference between them,thus reducing the impacts on performance caused by the hardness difference,and eventually improving the comprehensive performance of WC/Inconel 718 composite parts.