Effects Of Laser Annealing Processes On Crystallization And Properties Of Electroless Ni-Mo-P Coating

Electroless plating has been widely applied in practical because of its simple process,easy to operate and excellent properties.For as-depositedcoating,its properties have some limitation,Therefore,extensive use of furnace annealing for heat treatment to improve its hardness,wear resistance,corrosion resistance on the basis of plating.However,there are relatively few studies on the effect of laser heat treatment on the change of coating performance,and the studies of the change of laser process parameters is less.Therefore,Ni-4.63Mo-12.39P?wt%?alloy coating was prepared by chemical deposition,and the use of two laser technology?line spot without overlapping scanning,round spot with overlapping scanning?on the coating heat treatment.The microscopic characteristics of the composition,microstructure and surface morphology of the coating were analyzed with XRD,SEM and EDS.The hardness of the coating under different laser processes was studied by hardness test;The corrosion resistance of the coating was studied by EIS test and surface roughness test;Through the comparison of the two laser scanning processes,find the optimal laser process parameters,the main conclusion are as below:?1?Effect of Laser Process on Microstructure of Ni-Mo-P CoatingThe results show that Ni-4.63Mo-12.39P?wt%?alloy coating belongs to high phosphorus coating and its structures is amorphous.The crystallization reaction of the Ni₃P phase occurs at the line light spot scanning velocity of less than 12mm/s and round light spot scanning velocity of less than 10mm/s,and accompanies by the formation of Ni-Mo solid solution at the same time;Two coating are not both fully crystallized at the scanning velocity of 6mm/s.At the same scanning speed,line light spotscanningwith large energy density is beneficial to the precipitation of Ni₃P phase,and its crystallization degree and Ni₃P mass fraction are larger.At low speed?6,8mm/s?scanning,the round light spot with overlapping scanning is more conducive to Ni₃P phase size growth.?2?Effect of Laser Process on Hardness of Ni-Mo-P CoatingWith the decrease of the scanning speed,the hardness of the line and the round light spot scanning coating both showed a tendency to increase first and then decrease,and the hardness of the coating reached the maximum at 8mm/s,the hardness of the line light spot coating is12.6GPa higher;The round light spot has a smaller change in the hardness of the coating using the lap scanning method.At the same scanning speed,the hardness of the line light spot coating with larger energy density is higher under the low speed scanning?6,8mm/s?,while the hardness of the round light spot with overlapping scanning is higher at 10mm/s.?3?Effect of Laser Process on Corrosion Resistance of Ni-Mo-P CoatingThe electrochemical impedance spectroscopy of Ni-Mo-P alloy coating in 3.5wt%NaCl solution is composed of only one of the capacitive arc.The radius of the capacitive arc is largest when the line lightspot coating is 12mm/s,the round light spot scanning coating is8mm/s,means that two coatings obtain the best corrosionresistance.Under the same scanning speed of low speed scanning?6,8mm/s?,the round light spot with overlapping scanning can reduce the surface roughness of coating value,so,it obtain the best corrosion resistance;In the 10mm/s,the line light spot with large energy density smaller roughness and better resistance.