# Study on the microstructure and properties of a laser cladding Fe–Ni–Al coating based on the invar effect

## TL;DR

This study explores how adding aluminum affects the structure and performance of laser-clad Fe–Ni–Al coatings, finding optimal properties at 4% Al.

## Contribution

The study identifies the optimal Al content (4%) that balances low thermal expansion and improved wear resistance in Fe–Ni–Al coatings.

## Key findings

- Low Al content results in γ-[Fe,Ni] austenite microstructure with the Invar effect.
- Increasing Al leads to α phase formation and coating defects.
- At 4% Al, the coating shows minimal cracks and best wear resistance.

## Abstract

The purpose of this study was to investigate the effect of Al content on Fe–Ni–Al coatings. A Fe–Ni–Al coating was prepared using a semiconductor laser, and the influence of the Al content on the microstructure and properties of the coating was examined. The microstructure of the coating was characterized using scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. The coefficient of thermal expansion of the coating was measured using a static thermomechanical analyzer. The microhardness and wear performance of the coating were analyzed using a microhardness tester and a wear testing machine. The results were as follows. The addition of Al to the Fe–Ni ferroalloy powder resulted in the in situ formation of an AlNi/Fe–Ni laser cladding layer. When the Al content was low, the coating mainly consisted of γ-[Fe,Ni] austenite. As the Al content increased, the matrix phase structure of the cladding layer transformed into the α phase. Consequently, the Invar effect was gradually compromised, leading to the generation of defects in the coating. When the Al content was 4%, the coating performance improved while maintaining a low coefficient of thermal expansion. At this point, there were relatively few cracks in the cladding layer, and it exhibited the best wear resistance.