| Selective laser melting(SLM)uses high-energy laser beam to scan and melt the powder in the predefined area point by point,line by line and layer by layer,which can form complex structure parts from bottom to top.In order to improve the performance of AISI420 mould steel formed by SLM and apply it to the mould industry.In this paper,the micron TiC and nano TiC were used as reinforcing phase materials to prepare 5 wt.%micron TiC/AISI420 and 5 wt.%nano TiC/AISI420 mixed powder by mechanical ball milling,and they were formed by SLM technology.Starting from SLM forming process parameters and TiC enhancement of different particle size scales,the effects of processes and materials on the microstructure,mechanical and friction properties of formed parts were studied.Specifically,on the one hand,the effects of different laser volumetric energy density on the phase composition,density,microstructure,microhardness,tensile strength and friction properties of micron 5 wt.%TiC/AISI420composites samples formed by SLM were discussed;On the other,the effects of TiC with different particle size scales on the microstructure and properties of TiC/AISI420composites samples formed by SLM were investigated.According to the results of this paper,the following conclusions are as follows:(1)SLM was used to fabricate 5 wt.%micron TiC/AISI420 composites samples under different process parameters.The optimized process parameters were obtained,scanning speed?=850 mm/s,laser power P=320 W,layer thickness h=0.04 mm,sacnning pitch d=0.11 mm and the corresponding laser volumetric energy density?=85.6 J/mm3.It?s found that the?performed an important influence on the density,microstructure,mechanical and friction properties of micron TiC/AISI420 samples by SLM.When?was too low,the porosity and cracks on the surface of the sample were increased and the density was low,resulting in poor mechanical and friction properties.As?increased,the density of the sample increased,the microstructure was more uniform and refined,the mechanical and friction properties were improved.When?=85.6 J/mm3,the density was the highest,the grain size was the smallest,and the TiC ring-structure was uniformly and continuously distributed in the AISI420 matrix.What's more,its hardness was 592.2±53.6 HV,its ultimate tensile strength was 1452.4±28.3 MPa,its elongation was 8.64±1.18%.The minimum wear depth,wear width and wear rate were 3.59?m,0.4475 mm and 2.385×10-5mm3/(N·m),respectively.(2)The effects of different loads(50 N,100 N,150 N)on the friction properties of SLM formed 5 wt.%micron TiC/AISI420 samples were investigated.When the load was 50/100/150(N),the wear mechanism was adhesive wear,the friction coefficient was 0.59/0.60/0.65,and the wear rate was 2.385/3.584/2.018(×10-5mm3/(N·m)).The decrease of wear rate was attributed to the increase of load that promoted the formation of stress hardening layer and the lubrication effect of TiC particles.When the load was150 N,the wear resistance of the sample was the best.(3)Pure AISI420 and 5 wt.%nano TiC/AISI420 samples were formed under the optimal SLM process parameters.The results showed that nano TiC particles were easy to agglomerate,resulting in bad metallurgical bonding with the AISI420 matrix.Plenty of defects appeared on the forming surface,leading to a sharp drop in density and inhomogeneous and discontinuous TiC ring-structure.The further experimental results showed that the microhardness,tensile and friction properties showed the same rule:micron TiC/AISI420>pure AISI420>nano TiC/AISI420.Therefore,the milling process parameters and SLM forming process parameters will be further optimized to achieve the uniform dispersion of nano reinforced phase in the matrix,in order to further improve the properties of nano TiC/AISI420 composites by SLM.This study provides technological and theoretical reference for the application of SLM formed TiC/AISI420 composites in the field of mould. |
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