Fabrication and microstrain evolution of al-tib₂ composite coating by cold spray deposition

This paper investigates the microstructure evolution of Al-TiB₂ coatings prepared by cold spraying. In situ Al-TiB₂ composite powders containing uniformly distributed titanium diboride (TiB₂) particles with a size range of 5–100 nm in the Al matrix and Al/Al-TiB₂ blended powders were used as the cold spray feedstock for coating fabrication on aluminium alloy substrates. The microstructures of the feedstock powders and as-deposited coatings were characterised using scanning electron microscopy with energy dispersive X-ray analysis and X-ray diffraction. Al/Al-TiB₂ blended powder coatings, compromising closely packed powder particles, were sprayed to an approximate thickness of 500 μm. Al-TiB₂ composite coatings (approximately 50 μm thick) were obtained retaining the microstructure of the composite powders being sprayed and no evidence of detrimental phase transformation was found. However, micro-cracks were found to exist in the Al-TiB₂ coating due to the hardly deformable powder particles. Little or no microstrain was revealed in the as-sprayed Al-TiB₂ coating, indicating that annealing may have occurred due to the localised adiabatic heating during the spraying process. It is demonstrated that it is possible to fabricate the Al-TiB₂ composite coating by cold spray deposition but further improvements to eliminate coating cracking are required.