Improved structural integrity of cold-sprayed aluminum alloy-quasicrystal composite coatings assessed by cavitation erosion testing

Abstract

Metal matrix composite coatings (MMCs) offer functionalities beyond those of single-phase alloys due to the favorable properties of their constituent phases combined. This work investigated how reinforcing AA6061 aluminum alloy (AA) with hard Al-based quasicrystal particles (QC) influences the integrity of the final composite. Coatings were deposited using solid-state high pressure cold spray (CS) using mixture of AA particles and 0, 50, or 90 vol.% QC particles as the feedstock, sprayed with identical process parameters to isolate the reinforcement effect. QC particles, dispersed as reinforcements in the final composite coating, reduces porosity, and drive microstructural refinement such as elongated and refined grains (≈ 30–200 nm). Consequently, localized strengthening occurred within the matrix, increasing local nano-hardness by over 50% (from 2.21 to 3.43 GPa), as revealed by dense in-situ nanoindentation and corresponding mapping of hardness/elastic modulus. Cavitation erosion was repurposed as a probe for assessing coating integrity. The average cumulative volume loss was significantly reduced relative to AA6061 at 30 min of exposure, from 34.7 mm3 dropping down to ∼20% (7.4 mm3) and ∼5% (1.7 mm3) for the composites with 50 and 90 vol.% QC in starting feedstock, respectively, due to matrix strengthening and improved cohesion between bonded particles. Microstructural investigation of eroded surfaces revealed transition in the damage mechanism, from particle chunk detachment along AA particle boundaries in the non-reinforced coating, to gradual and uniform removal of matrix and reinforcement as fine debris in the composite structures. Our findings suggest improved coating durability, enhanced interparticle cohesion and matrix strengthening.