Study On Microstructure And High Temperature Oxidation Performance Of Laser Cladding MCrAlY Coating On 304 Stainless Steel

NiCoCrAlY coatings are widely used in high temperature protective coatings and thermal barrier coating bonding layers because of their excellent high temperature oxidation resistance and thermal corrosion resistance.The technical methods for preparing NiCoCrAlY coating mainly include plasma spraying,electron beam-physical vapor deposition,etc.,and the coating prepared by laser cladding technology has the advantages of compact and fine tissue,low dilution rate,and metallurgical combination with the substrate.Based on this,this article uses laser cladding technology to prepare NiCoCrAlY coating on the 304 stainless steel substrate,focusing on the structure and performance of the coating under different process conditions,and on this basis,further study of NiCoCrAlY coating at 750?,850 Oxidation kinetic behavior at?,950?,the high temperature oxidation mechanism and failure mechanism of NiCoCrAlY coating were analyzed.The main research contents are as follows:The effect of different process parameters on the macro-morphology of NiCoCrAlY cladding layer was studied.The research results show that under the conditions of laser power and powder feed rate,with the increase of scanning speed,the height of the cladding layer decreases,the depth of the cladding layer becomes shallower,the width of the cladding layer becomes narrower,the dilution rate is affected by the high melting and melting The common effect of widening becomes larger.When the scanning speed and powder feed rate are constant,with the increase of laser power,the height of the cladding layer increases first and then decreases,the depth of the cladding layer becomes deeper,and the width of the cladding layer becomes wider.The dilution rate decreases first and then increases;as the Al content in the coating increases,the melt width and depth of the coating decrease,and the dilution rate decreases significantly.The effects of process parameters on the phase composition and microstructure of NiCoCrAlY cladding layer were studied.The results show that when the laser power and powder feed rate are constant,as the scanning speed increases,the?phase content in the coating decreases,and the porosity and inclusions in the coating are obvious;when the scan speed and powder feed rate are constant,with the As the laser power increases,the?'phase content in the coating increases,and the?phase content decreases,and the columnar crystal dendrites in the coating gradually grow thicker;in the cladding layer with Al added.The?phase is distributed on the surface of the?phase in the form of columns,fish scales,nets,and dendrites,and the increase of Al content increases the?phase content in the coating.The effect of process parameters on the hardness and wear resistance of NiCoCrAlY cladding layer was studied.The research results show that the hardness of the coating is better than the substrate under different process parameters.When the laser power is 1500W,the scanning speed is 10mm/s,and the powder feed rate is 450mg/min,the maximum hardness of the coating is 375HV_0.5,the wear resistance is good,the minimum friction coefficient is 0.46,and the minimum volume wear is 0.2359mm³.,Determined as the optimal process parameters.Oxidation weight gain curves of laser cladding NiCoCrAlY coating at 750?,850?and 950?were drawn,and the kinetic behavior of NiCoCrAlY coating at high temperature was studied.Fitting the relationship between the weight gain of oxidation and the square root of time,the oxidation rate constant at 750?is 0.09157,the correlation coefficient R2=0.99719;the oxidation rate constant at 850?is 0.10687,the correlation coefficient R2=0.98056;the oxidation rate constant at 950?is 0.13023,the correlation coefficient R2=0.97604.The microstructure of the oxidation products after laser cladding NiCoCrAlY coating at 750?,850?and 950?at 20h,60h,80h and 100h were studied,and the oxidation mechanism and failure mechanism were analyzed.The research results show that the mixed oxides of Cr,Fe,and Al are mainly dominated at the initial stage of oxidation at 750°C and850°C.As the oxidation time prolongs,the initial oxide layer blisters and falls off.After100 hours of oxidation,Cr₂O₃ is formed Oxide layer,in which spinel phase is also found in the oxide layer at 850°C;a denser Cr₂O₃ oxide film is formed after oxidizing at 950°C for20h.There is a spinel phase in the local area.After 100h of oxidation,the tissue in the oxide layer grows,And the content of spinel phase increased significantly.