Preparation-remelting Of Plasma-sprayed Nano Coating On Mild Steel And Its Evaluation Of Pitting

In this paper, Cu, Fe Cr, Ni Al, Fe Si four nano powder were used as raw material, the Cu, Fe Cr, Ni Al, Fe Si four nano plasma-sprayed nano coating were manufactured and remelted processing,and the plasma-sprayed nano coating with a dense structure, excellent performance were manufactured. In this paper, A series of works have been carried out as follows: firstly, through the spray granulation method and plasma spraying technology, Cu, Fe Cr, Ni Al, Fe Si four plasma-sprayed nano coating were preparated, and these microstructure and performance were test and analysis. In order to further improve the four plasma-sprayednano coating microstructure, corrosion resistance and mechanical properties, the Cu, Fe Cr,Ni Al, Fe Si four plasma-sprayed nano coating were remelted processing under hydrogen in 850 ℃, 900 ℃, 950 ℃, 950 ℃; 1050 ℃, 1100 ℃, 1150 ℃, 1200 ℃; 650 ℃, 700 ℃, 750 ℃, 800 ℃; 1100 ℃, 1150 ℃, 1200 ℃, 1250 ℃,respectively,and these microstructure and performance were tested and analyzed. In addition, in order to further study the corrosion mechanism of plasma-sprayed coatings in 3.5% Na Cl solution, the pitting behavior were tested and analyzed by Scanning electrochemical microscopy(SECM) so as to further unfold the corrosion process and mechanism of the plasma-sprayed coating in corrosion solution.In addition, the passivation phenomenon and passive film of the four plasma-sprayed coatings in borate buffer were studied. Finally,the relationship between the surface energy and heat treatment temperature of four plasma-sprayed nano coating were simulated by materials studio software.Four nano powder were agglomerating processing Through the spray granulation method, the agglomerated powder has good quality and liquidity. the agglomerated powder were sprayed under mild steel, and the four nano plasma-sprayed coating were manufactured. The plasma-sprayed nano coating showed bimodal structure consisting of unmelted nanoscale particles and the other part that had melted, the structure led to the existence of pores and cracks in the coating.The Cu, Fe Cr, Ni Al, Fe Si four plasma-sprayed nano coating were remelted processing under hydrogen in 850 ℃, 900 ℃, 950 ℃, 950 ℃; 1050 ℃, 1100 ℃,1150 ℃, 1200 ℃; 650 ℃, 700 ℃, 750 ℃, 800 ℃; 1100 ℃, 1150 ℃, 1200 ℃, 1250 ℃, respectively, and finding that nanoscale particles disappear when Cu, Fe Cr,Ni Al, Fe Si four plasma-sprayed nano coating were remelted processing in 950 ℃, 1150 ℃, 700 ℃,1200℃, respectively,and the pores and cracks decreased significantly of the coating,and corrosion resistance and mechanical performance ofthe coating were significantly improved.The pitting behavior was tested in 3.5% Na Cl solution, and finding that Cu, Fe Cr, Ni Al, Fe Si four plasma-sprayed coating that were remeltedin 950 ℃, 1150 ℃, 700 ℃,1200 ℃,respectively,had no obvious pitting phenomenon after immersing 3 h, 2 h, 3 h, 4 h in 3.5% Na Cl solution,while obvious pitting occuredunder other samples.SECM data showed that the corrosion behavior of plasma-sprayednano coating in 3.5% Na Cl solution including the uniform corrosion and pitting. The uniform corrosion had no obvious variation while pitting had obvious variation in in 3.5% Na Cl solution. The pitting were gradually enhanced in the large pores and cracks while the pitting gradually weakened in small pores and cracks, it because small pores and cracks were blocked by the corrosion products.Mild steel substrate and Cu, Fe Cr, Ni Al, Fe Si four plasma-sprayed nano coating remelted under 950 ℃, 1150 ℃, 700 ℃, 1200℃, respectively, had passivation phenomenon in borate buffer, and the passive current of four four plasma-sprayed nano coating smaller than mild steel. And the passive film of Cu, Fe Cr, Ni Al, Fe Si four plasma-sprayed nano coating were p type semiconductor,and coating were compact while the passive film of mild steel was n type semiconductor, and coating was loose.There were the minimum surface energy when Cu, Fe Cr, Ni Al, Fe Si four plasma-sprayed nano coating were remelted under 950 ℃, 1150 ℃, 700 ℃, 1200℃, respectively by materials studio software simulate. It showed when Cu, Fe Cr, Ni Al, Fe Si four plasma-sprayed nano coating were remelted under 950 ℃, 1150 ℃, 700 ℃, 1200℃, respectively, these coating were stable, and had fewer defects.