Preparation Of FeMnSi Memory Alloy Layer By Laser Alloying On 304 Stainless Steel Surface

In order to improve the physical and mechanical properties of 304 stainless steel surface,the FeMnSi memory alloy layer was in situ prepared on 304 stainless steel surface by using coaxial powder feeding laser alloying process through additional powder design and optimization of laser process parameters.The phase composition,corrosion resistance,microhardness and wear resistance of the alloying layer were tested and analyzed,and the temperature field distribution in the laser alloying process was simulated and analyzed by ANSYS finite element software.Laser power,laser scanning speed,laser defocusing,carrier gas flow and powder feeding speed were selected as the main process parameters,and the range of each parameter was preliminarily determined by analyzing the macroscopic morphology and the cross-section micromorphology of each single channel alloying layer.Then,the regression equation and response surface atlas of all parameters were obtained by response surface method with dilution rate as the response value.The regression equation analysis showed that the laser power has the greatest influence on the dilution rate,followed by the carrier gas flow rate,which is consistent with the influence of the parameter changes on the macroscopic morphology and the cross-section micromorphology in the actual experiment.It proved that the response surface method could provide reference for the reasonable selection and optimization of process parameters in the actual experiment.Fe17Mn5Si10Cr5Ni memory alloy was used as the target component of the alloying layer,and the alloying powder was prepared based on the content of Cr element in the substrate.Through multiple experiments,the element component of the alloying layer that close to the target was prepared with powder added to the alloying layer in the ratio of Mn:Si:Cr:Ni=42.591:14.916:0:0.166(Fe being the margin),and the optimal laser process parameters matched was the power,defocusing,canning speed,powder feeding speed and carrier gas flow rate of 800W,0mm,400mm/min,16.5g/min and 9L/min respectively.The overlap rate was also determined as 30%to get a better surface quality of the alloying layer.FeMnSi alloying layers were obtained by multichannel laser alloying under optimal process parameters and powder ratio.The results showed that the sample layer had the microstructure characteristics of stress induced ??? martpnsitic phase transition in the FeMnSi memory alloy;The Nyquist atlas showed that the electrochemical impedance of the alloying layer was greater than 304 stainless steel,and the absolute corrosion potential was less than 304 stainless steel,both indicating that the corrosion resistance of the alloying layer was better than 304 stainless steel;The average microhardness of the alloying layer was 240HV,while that of 304 stainless steel was 185HV,indicating that the microhardness of the alloying layer surface was higher;The friction coefficient of the alloy layer was 0.5014 and that of the substrate was 0.6425,and the wear mechanism of the both were adhesive wear and abrasive wear.Based on the actual experiment parameter settings and test conditions,the temperature field in the experiment process was solved and analyzed by ANSYS finite element analysis software,and the formation of alloying layer was simulated by life-death element method,so as to obtain the temperature change curve of different nodes over time and the temperature distribution cloud diagram of the specimen at different times.The analysis showed that when the laser spot passes through a node,the temperature of the node rises rapidly,and when it is far away from the node,the temperature drops rapidly,which is consistent with the characteristics of rapid heating and cooling of the actual laser processing;In the process of laser processing,the energy was mainly concentrated in the laser spot,which leads to the highest central temperature,temperature reduction in the radial direction and higher material temperature in a smaller range around the spot,besides,the farther away from the spot,the less thermal influence the material had,which was consistent with the small thermal influence area in the actual laser processing;In the cooling process,the temperature in the alloying region gradually decreased,while the temperature of the substrate far from the alloying region slowly went up and then down,and the overall temperature gradient of the material showed a decreasing trend,which was consistent with the actual cooling situation.