Laser Cladding Molded Carbide Powder Layer And Finite Element Simulation

Hard alloy powder layer was formed by using hydraulic press and steel die. The precoated layer was melted and cladded on substrate surface by using continuious wave CO₂ laser of high power. Based on the caculation of temperature field by using APDL language attached to the commercial software ANSYS, the range of optimizing operation parameters of laser cladding was forcasted.Mixtures of iron alloy(25wt.%),cobalt(15wt.%),and tungsten carbide(60wt.%) powder were used as the coating material. The substrate of Q235 plain carbon steel was machined by milling to form some slots on its surface, 1.5mm deepth, used as cavity die during the pressing. The male die was machined according to the dimensions of cavity die. After investigating the basic theory of steel die pressing,a certain pressing process was brought forth,and the hard alloy powder is pressed into slot by using hydrulic press and steel die, and a high strengh and hardness precoated layer conbined with substrate mechanically was gotten. TJ-HL-T5000 continuious wave CO₂ laser was chosed,and during processing,the laser power was adjusted to 2600 kW,the beam width to 13 millimeter. The critical laser scanning speed was caculated according the theory of maximal depth of laser cladding,and several tentative speed parameters were chosed besides the critical speed. when using laser to cladding the procaoted layer,the optimal parameters were achieved by fixing laser power and the dimension of laser beam. Smooth coating which had high hardness and was conbined with substrate metallurgically with no cracks was gotten after laser processing under beam speed of 1 mm/s. The microstructure and mechanic performances of the coating were tested by SEM,EDAX and microhardness tester.The result showed that coating's microstructure was that various white carbides with high hardness were distributed in the matrix of martensite and austenite-based phase with low hardness,consisting of some eutectic,like fishbone.Hardness of gray substrate of layer was 200 HV while white phase's reached to 1145 HV.Macrohardness of laser coating was 56HRC.To forcast optimal parameters of laser cladding,temperature field in layer and substrate was caculated by using APDL parametic design language of ANSYS software . Transient temperature field under different parameters was simulated,based on second-development of the thermal analysis of ANSYS. After bringing forth a certain criterion which was used to estimate whether precoated layer were conbined with sustrate metallurgically, datas of temperature evolution atsome typical points along interface were abstracted from thermal analysis result. The result showed that ,to achieve metallurgical conbination , the beam scanning speed should be lower than 2 mm/s in melting the precoated layer of hard alloy powder(Fe,25wt.%;cobalt,15wt.%; tungsten carbide,60wt.%), 1.5mm in thickness, under the power of 2600kW and beam width of 13mm. The optimal range of beam scanning speed obtained from simulation was agreement with the optimal parameter obtained from actual laser cladding,which proved fully that the simulation of laser cladding was feasible and had a good instruction to parameter simulatiom.