Excellent thermal shock resistance of NiCrAlY coatings on copper substrate via laser cladding

Abstract

• NiCrAlY layers were prepared on copper substrate via laser cladding technology. • Metallurgical bonding and excellent thermal shock resistance are obtained. • Lifetime of this NiCrAlY layers is much longer than NiCrAlY by other methods. Coatings are widely used to protect substrates in extreme thermal environments (e.g., arc heaters), and thermal shock resistance is a crucial parameter for the coatings, which requires tight interlayer bonding between coatings and substrates. In this work, NiCrAlY coatings were highly required for the pure copper substrate to restrict the electric arc in arc heaters. To overcome the bonding difficulty of coating on the copper surface, the NiCrAlY coatings were prepared by two laser cladding methods: conventional laser cladding (CLC) and high-speed laser cladding (HSLC). The microstructure, composition, and thermal shock resistance of NiCrAlY cladding layers prepared by both methods were investigated. Benefitting from the high cooling rate and high energy density, the HSLC-layer has better composition uniformity and tighter interlayer bonding than the CLC-layer, achieving a 30%–45% improvement in thermal cycling lifetime. Besides, the NiCrAlY layers prepared on copper substrate by both laser cladding methods exhibit 3–10 times better thermal shock resistance than those NiCrAlY layers prepared by conventional spraying methods. It further confirms the great effects of metallurgical bonding and composition uniformity on the thermal shock resistance of coatings. The NiCrAlY layers fail in the form of internal cracking and interface peeling, and the corresponding failure mechanism is discussed.