Study On Crack And Porosity Control Methods Of Laser Cladding Ni60A Alloy Coating

NiCrBSi alloys materials with excellent corrosion resistance,high-temperature resistance,wear resistance and relatively low cost are widely used in the remanufacturing industry to repair high-value tools and extend tools life.However,crack and porosity are easily generated during laser cladding NiCrBSi alloys,which hinder the promotion of laser cladding NiCrBSi alloys.Aiming at the current situation that the crack control process is single and the relationship between the porosity and the laser processing parameters is not clear,this paper conducts a comprehensive investigation on the formation of crack and porosity of the laser cladding Ni60A alloy.The specific work profiles are as follows:Firstly,based on material and stress analysis,it is revealed that the crack of Ni60A alloy cladding layer is closely related to the properties of the cladding layer and the temperature gradient.Both the preheating process and the thermal insulation process can effectively reduce the temperature gradient of the cladding layer.However,the crack cannot be completely eliminated utilizing the low substrate preheating temperature or cladding with the insulated plank.The crack can only be effectively eliminated by the composite process(the combination of preheating up to 300℃and placing insulated plank under the substrate).Secondly,it is found that the bubble motion is closely related to the laser energy input by analyzing the bubble motion in the molten pool.The experiment investigates the influence of laser linear energy E_l on the porosity area A_p of the cladding layer.The results show that when the powder feed rate is fixed at 15 r/min,the cladding layers with low A_p can be obtained when E_l is equal or greater to 200 J/mm;When E_l exceeds 300 J/mm,the dilution of the cladding layer is greater than 50%,indicating that the laser energy input is excessive.A statistical model between the process parameters(laser power,scanning speed,and powder feeding rate)and the porosity area of the cladding layer was built using DoE(Design of Experiment).The analysis of variance(ANOVA)shows that the effect of powder feeding rate on the porosity area is the most significant factor.In the case of low powder feeding rate,cladding with the high laser energy density could obtain the cladding layers with low porosity area.Finally,two sets of response surface method(RSM)optimized process parameters were selected for crack and porosity control methods of laser cladding experiment.The result shows one crack-free and low porosity rate(0.01%)coating(No.1)is prepared successfully without preheating and its average microhardness is about 1.8 times as much as that of the substrate.The other crack-free coating with low porosity rate(0.027%)coating(No.2)is obtained successfully when utilizing the composite process and its average microhardness is about 2.7times as much as that of the substrate.Then,setting several experiments investigates the effect of composite process and optimal parameters process on microstructures,compositions and microhardness of the cladding layers.