| LI Xu-qiang,LI Wen-sheng,ZHAI Hai-min1，MA Xu.Effect of Coating Thickness on Fe-based Amorphous Detonation Spraying Deposition Characteristics and Properties[J],52(5):140-148, 162 |
| Effect of Coating Thickness on Fe-based Amorphous Detonation Spraying Deposition Characteristics and Properties |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.05.014 |
| KeyWord:invar alloy Fe-based amorphous coatings detonation spray cooling stress bonding strength corrosion resistance |
| Author | Institution |
| LI Xu-qiang |
School of Materials Science and Engineering, Lanzhou University of Technology, Lanzhou , China |
| LI Wen-sheng |
School of Materials Science and Engineering, Lanzhou University of Technology, Lanzhou , China ;School of Materials Science and Engineering, Shandong University of Science and Technology, Shandong Qingdao , China |
| ZHAI Hai-min1，MA Xu |
School of Materials Science and Engineering, Lanzhou University of Technology, Lanzhou , China |
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| Abstract: |
| Fe-based amorphous coatings with various thicknesses (dAC1≈50 μm, dAC2≈150 μm, dAC3≈250 μm, dAC4≈500 μm) were successfully deposited on the invar alloy substrate by detonation spray to evaluate the effect of the coating thickness on its service performance. The microstructure, phase composition, microhardness, elastic modulus, residual stress, bonding strength and electrochemical corrosion properties of each coating sample were studied. The results showed that the XRD patterns of each coating showed a typical broad and diffuse peak between 30° to 55° of 2θ range, suggesting an amorphous nature of the coatings. By contrast, AC1 had the highest porosity of 2.8%, and then rapidly decreased to 1.4%, 1.0%, and 1.1% for AC2, AC3, and AC4, respectively, due to the shot peening of the subsequently sprayed particles. AC1 and AC2 were well bonded on the substrate with no cracks at the interface between the coating and the substrate, while when it came to AC3, obvious cracks could be observed, and the cracks further expanded when the coating thickness increased to AC4. Since the thermal expansion coefficient of the invar substrate (3.4×10–6 ℃–1) was smaller than that of the coating (12.5×10–6 ℃–1), the cooling stress of the coating was tensile stress, and decreased with the increase of the coating thickness, and the comprehensive residual stress of the coating therefore tended to decrease in tensile stress or increase in compressive stress, which was beneficial to the bonding between coating layers. However, the increase of coating thickness weakened the adaptability of the coating/substrate interface stress, promoted the generation of interface cracks, and reduced the bonding strength of the coating, from AC1/32.0 MPa to AC2/29.6 MPa, AC3/21.0 MPa and AC4/16.6 MPa. Moreover, AC1 had the worst corrosion resistance, and the corresponding corrosion current density (26.6×10–6 A/cm2) was even much higher than that of the uncoated substrate (3.401×10–6 A/cm2), which was due to the penetrating pores in this coating that allowed the electrolyte to pass through the pores and directly contact the substrate, resulting in galvanic corrosion between the coating and the substrate. And the coating acted as a cathode to accelerate the corrosion rate of the substrate. When the coating thickness increased to the grade of AC3, the corrosion current density of the coating was lower than that of the substrate, and the corrosion potential and polarization resistance were both higher, and the corrosion current density continued to decrease with the increase of thickness, indicating that AC3 and thicker Fe-based amorphous coatings could play an effective corrosion protection role. Overall, under different thickness grades, the bonding performance of Fe-based amorphous coatings is negatively correlated with corrosion resistance, hence, the deposition thickness of the coating should be determined according to the service conditions of the coating. And under the condition of corrosion resistance, the coating thickness shall reach AC3 level or thicker. If there are penetrating pores in the coating, galvanic corrosion of the large cathode and the small anode will be formed, resulting in the rapid failure of the protected substrate. |
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