Effect Of Heat Treatment Process On Properties Of High Speed Arc Sprayed FeCrAl/Al Composite Coatings

The coating is prepared by high-speed arc spraying technology.The powder-cored wire is very rapid from melting to cooling and solidification.The coating has a large residual stress and an unstable internal structure,making it susceptible to stress concentration and microcracks due to external influences.During the layering process,the particles did not completely overlap and pores were formed between the flattened particles,the pores affect the mechanical properties and corrosion resistance of the coating.In existing studies,proper heat treatment of coatings prepared by high speed arc spray improves their structure,reduces internal residual stress,reduces porosity,improves mechanical and corrosion resistance,and improves the overall coating.Quality has been shown to improve.Based on the existing experiments,this paper selects the optimal parameters of high-velocity arc spraying to prepare FeCrAl/Al coatings,and study its structure and performance;using a box-type resistance furnace,the FeCrAl/Al coatings prepared by high-velocity arc spraying are applied in an atmospheric environment Heat treatments with different lengths and different temperatures were carried out,and the effects of heat treatment temperature and time on the structure,mechanical properties and corrosion resistance of FeCrAl/Al coatings were systematically studied.The main research contents and conclusions of this paper are as follows:1.Select the optimal high-velocity arc spraying parameters to prepare FeCrAl/Al coating,and study its structure and performance.The coating has a typical layered structure with compact microstructure.The main phases are Fe-Cr solid solution,Al,Fe Al,and Fe O,Al₂O₃phases;the porosity of the coating is 4.68%,which is a low-porosity coating with an average microstructure The hardness value is 494.11 Hv_0.1,which is about 2.8 times that of the base Q235 steel.The self-corrosion potential of the coating is higher than the base and the self-corrosion current density is lower than the base.It has excellent corrosion resistance and can be adapted to the working environment in seawater.2.Study the effect of heat treatment temperature on the structure and properties of FeCrAl/Al coating（holding time 1h）.（1）When the heat treatment temperature is below 600℃,the microscopic morphology of the coating does not change significantly and the porosity and hardness are lower than those of a normal sprayed coating.When the temperature rises,the intensity of the Al phase diffraction peak decreases,and the Fe-Al intermetallic compound increases.The porosity becomes larger;when the heat treatment temperature rises to 600℃or higher,the dark gray areas,white particles,and metallurgical bonding areas of the coating become more,the pores become larger,and the Al diffraction peak disappears.（2）As the temperature rises,the self-corrosion potential of the coating shifts positively,increasing the self-corrosion current density and increasing the rate of corrosion.After heat treatment at 300℃,the FeCrAl/Al coating has the lowest self-corrosion current density,the highest passivation region and the best corrosion resistance.After heat treatment at 700℃,the coating has the highest self-corrosion potential and the best thermodynamic stability.3.Study the effect of heat treatment time on the structure and properties of FeCrAl/Al coatings.（1）When the heat treatment temperature is lower than 500℃,the heat preservation time is prolonged,and the micro morphology and phase composition of the coating do not change significantly;when the temperature rises to 500℃or higher,the heat preservation time is prolonged,and the diffraction peak of Al is enhanced,and the coating The layer has more dark gray areas and more particles,and the higher the temperature,the more metallurgical bonding areas between the coating and the substrate.（2）The porosity of the coating is lowest at a heat treatment temperature of 300℃and a retention time of 7 hours.When the temperature drops below 600℃,the heat treatment time increases and the porosity of the coating decreases.Coatings with a heat treatment temperature of 600℃and a retention time of 7 hours have the highest average microhardness.When the temperature reaches 600℃,the porosity of the coating increases and the hardness increases as the retention time increases.（3）In 3.5%Na Cl solution,the FeCrAl/Al coating treated at 300℃for 1h has the smallest self-etching current density and the largest reactance arc radius.At the same temperature,the self-etching current density and corrosion rate of the coating increase when the temperature is the same and the insulation time is prolonged.It indicates that the coating’s insulation time is prolonged at the same temperature,the corrosion resistance of FeCrAl/Al coating is not improved.