Influence of deposition time and surface roughness on microstructure and corrosion behavior of sputter-deposited pure Al coating on 4130 chromalloy steel

Abstract

In the present investigation, a comparison of three sputter-deposited pure Al coatings on 4130-grade steel with different process parameters has been explored based on surface morphology and corrosion behaviour. In a natural environment, Al coatings are happened to be more corrosion resistant than Zn ccoatings owing to the formation of impervious Al2O3 layer on top of the substrate. Even at a temperature up to 180 °C, Al coatings are not corroded by distilled water. Al-coated steel can, therefore, be used for many applications like distilled water storage and handling, oven, heaters, car exhaust system, etc. Magnetron sputtering (MS) nowadays has gained a great deal of importance in developing different coatings. Al coatings with MS technique have emerged with uniform and contamination-free quality coating exhibiting high deposition rateandintensebonding with the substrate compared to other popular deposition processes. The influence of surface condition and deposition time on microstructure, thickness, corrosion behavior, adhesion and final surface roughness of the coated surfacehas been the topic of discussion in the current research. The surface morphology and composition were examined by Field Emission Scanning Electron Microscope (FESEM) and Energy Dispersive X-Ray Analysis (EDX), phase constitution by X-Ray Diffraction (XRD) and surface roughness by Optical Laser Spectroscopy (OLS spectroscopy). The effect of surface roughness on pitting potential was also discussed. Corrosion properties were evaluated by Electro-Chemical Impedance Spectroscopy (EIS), which revealed that the sample with 10 h of deposition time (sand blasted) has exhibited the bestcorrosion resistance property compared to the other two samples sand blasted for 5 h and without sand blasted for 10 h deposition time, respectively. This fact has been further corroborated by contact angle measurement tests. Glow discharge optical emission spectroscopy (GDOES) established the depth to depth profile of the coatings. The adhesion property for all three coatings was found good without any trace of pilling off in the bend test. Sand blasting operation before coatings also has a great effect on materials property basically roughness means smooth surface after coating with high resistance property.