Study on the microstructure evolution performance improvement of Invar alloy repaired by laser cladding Aermet100 ultra-high strength steel

Abstract

Invar alloy is prone to surface wear and cracking during service. To repair damaged areas of Invar alloy and enhance its service performance, this study laser cladding three layers of AerMet100 alloy onto an Invar alloy substrate. The microstructural evolution and property enhancement mechanisms of AerMet100/Invar alloy were investigated, and the mechanical properties and wear resistance were compared to verify the feasibility of the repair method. The thermal cycling during the repair process led to microstructural diversity across the repairing layer, which mainly consisted of tempered martensite, quenched martensite, acicular lower bainite, and retained austenite. The diversity of microstructures and significant grain refinement result in higher hardness, tensile strength, and wear resistance of the cladding layer compared to the Invar substrate. Specifically, the hardness and tensile strength of the repair layer were approximately 278 % and 321 % higher than those of the Invar substrate, respectively, while the mass loss of the repair layer is 48.02 % lower than that of the substrate. Although the tensile strength of the repair layer has been significantly improved, the presence of lower bainite and retained austenite reduced its ductility. The M₂C particles and martensite above the repair interface hindered dislocation glide, contributing to the high tensile strength of the repaired specimen. Meanwhile, the single-phase FCC structure at the lower part of the interface significantly diminisheed the resistance to dislocation slip, facilitating coordinated deformation. Consequently, the repaired specimen exhibited an enhanced tensile strength-to-ductility balance. The experimental results indicated that laser cladding of AerMet100 alloy for repairing Invar alloy is a competitive method.