Characteristics and Thermal Shock Resistance of HVOF-Sprayed TiAlNb Coatings
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Characteristics and Thermal Shock Resistance of HVOF-Sprayed TiAlNb Coatings Lei Wang1 • Laiqi Zhang1 • Qian Huang1 • Changlei Zhang1 • Lichun Zhang2
Submitted: 15 January 2020 / in revised form: 3 June 2020 Ó ASM International 2020
Abstract Two Ti-63.39Al-8.26Nb-0.2Y powders (powder 1 and powder 2) were fabricated by rapid in situ reaction and arc melting, respectively, then deposited on 316L stainless-steel substrate by the high-velocity oxygen fuel (HVOF) process. The phase composition, microstructure, porosity, microhardness, and adhesive strength of the two kinds of coating (DC1 and DC2) were characterized. DC1 had lower porosity, higher microhardness, and higher adhesive strength than DC2, which can be attributed to the difference in particle size distribution and mean particle size; a narrow particle size distribution and suitable mean particle size favor the formation of a HVOF coating with denser and more uniform microstructure. The thermal shock behavior was investigated by heating and water quenching from 600 °C to room temperature. The results showed that the failure of both TiAlNb coatings occurred due to spallation of the top coat, but the thermal shock resistance of DC2 was better than that of DC1. Thermal stress concentration caused by thermal expansion mismatch between the top coat and substrate was recognized as the major reason for TiAlNb coating failure. Keywords TiAlNb adhesive strength microhardness porosity thermal shock resistance
& Laiqi Zhang [email protected] 1
State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, People’s Republic of China
2
Department of Materials Science and Engineering, Institute of Materials Science, University of Connecticut, Storrs, CT 06269-3136, USA
Introduction Hot dipping galvanization is one of the best and most effective methods employed to protect steel materials from corrosion in atmospheric environments (Ref 1-4). However, serious corrosion of equipment (e.g., sink rolls, supporting bearings, stabilizer, and supporting roll arms) remains a major problem in continuous galvanizing lines (CGLs) (Ref 5). The degradation and frequent failure of these equipment components result in severe production downtime and high maintenance costs. HVOF-sprayed WC-Co coatings are usually applied to 316L stainless-steel components used in CGLs, but their lifetime in liquid zinc is too short (about 1-2 weeks in duration) (Ref 2, 6-9). Therefore, the key to solve this problem is to identify a material that offers excellent corrosion resistance. Numerous materials, such as ceramics (Ref 8-11), alloys (Ref 12-14), intermetallics (Ref 15-19), and other composite materials, have been selected and studied to improve the corrosion resistance of CGL components in molten zinc. However, almost none of these can satisfy the rigorous working conditions on CGLs. In previous study, we found that TiAlNb alloys exhibit excellent resistance to corrosion by molten zinc (Ref 20). The lifetime of TiAlN
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