This study developed microstructure-based finite element (FE) models to investigate the behavior of cold-sprayed aluminum-alumina (Al-Al2O3) metal matrix composite (MMCs) coatings subject to indentation and quasi-static compression. Based on microstructural features (i.e., particle weight fraction, particle size, and porosity) of the MMC coatings, representative volume elements (RVEs) were generated by using Digimat software and then imported into ABAQUS/Explicit. State-of-the-art physics-based modelling approaches were incorporated into the model to account for particle cracking, interface debonding, and ductile failure of the matrix. This allowed for analysis and informing on the deformation and failure responses. The model was validated with experimental results for cold-sprayed Al-18 wt.% Al2O3, Al-34 wt.% Al2O3, and Al-46 wt.% Al2O3 metal matrix composite coatings under quasi-static compression by comparing the stress versus strain histories and observed failure mechanisms (e.g., matrix ductile failure). The results showed that the computational framework is able to capture the response of this cold-sprayed material system under compression and indentation, both qualitatively and quantitatively. The outcomes of this work have implications for extending the model to materials design and under different types of loading (e.g., erosion and fatigue).

In this work, Al and Al-Al 2 O 3 coatings up to 8 mm thick were cold sprayed on AZ91D magnesium alloy substrates. Microstructure, microhardness, bond strength, and corrosion and wear resistance were studied to assess the viability of using these coatings to restore dimensionally degraded parts and protect them from further corrosion and wear.

Cold gas dynamic spraying (“cold spraying”) at low pressure (150 psig) was used to fabricate Al-Al 2 O 3 metal-matrix composite (MMC) coatings onto 6061 Al alloy. The powder contained -45 µm Al stock powder admixed with -10 Al 2 O 3 in fractions ranging from 0-90 wt%. Scanning electron microscopy (SEM), Vickers microhardness testing, and image analysis were conducted on the as-sprayed coatings. The coatings were then friction-stir processed (FSP) using a milling machine and a 12 mm diameter cylindrical tool. Microhardness testing, SEM, and image analysis were then repeated to study the effect that FSP had on the MMC coating hardness. Hardness increased with increasing fraction of Al 2 O 3 in the feedstock powder, resulting in a maximum as-sprayed coating hardness of 85 HV when 90 wt% Al 2 O 3 is used. After FSP, the hardness of the MMC fabricated from a 90 wt% Al 2 O 3 powder blend increased to a maximum of 140 HV. SEM micrographs showed that the as-sprayed MMC coatings contained Al 2 O 3 particles that had been trapped between the larger Al particles. FSP succeeded in redistributing the Al 2 O 3 particles, decreasing the mean free interparticle distance and increasing the probability of load sharing between the reinforcing particles. It was suggested that this redistribution may be the primary reason for hardness improvement in the MMC coatings.

This work assesses the potential of using an ultrasonic probe attached to the back of the substrate to monitor the cold spraying process. While this is only a preliminary study, focusing more on presenting the results than analyzing them, a few conclusions may be drawn. With acoustic sensing, not only can the final value of thickness be estimated, it is also possible to see the dynamics of how the buildup takes place in real time. As shown in the data plots, the buildup process for aluminum-alumina composites is fairly universal across the spray with slower buildup at the outer edges of the coating. More importantly, it is shown that nozzle speed, spray diameter, and thickness estimates fit well with measured values.

In this study, low-pressure cold spraying was used to deposit Al and Al-Al 2 O 3 composite powders on different substrate materials, including steel, aluminum, and magnesium alloy. Corrosion performance was evaluated by electrochemical testing in 1M NaCl electrolyte and microstructure was examined by means of SEM analysis. The results show that the corrosion potential of Al-Al 2 O 3 coatings depends on the content of alumina and that its presence does not appear to accelerate dissolution and failure of passivation oxide films. The investigation also revealed that pure aluminum coatings on aluminum alloy substrates can act as sacrificial anodes, thus providing corrosion protection.

In the present work, pure Al and Al-Al 2 O 3 composite coatings are deposited by cold spraying while measuring in-flight particle velocities. Residual stresses, evaluated using the Almen curvature method, X-day diffraction, and modified layer removal, are correlated with particle velocity, coating thickness, and alumina content. Peening stresses due to plastic deformation were estimated to be less than 100 MPa and are shown to be nearly constant through the thickness of the coatings.

Coating build-up mechanisms and properties of cold sprayed aluminum-alumina cermets were investigated. Two spherical aluminum powders having average diameters of 36 and 81 microns were compared. Those powders were blended with alumina at several concentrations. Coatings were produced using a commercial low pressure cold spray system. Powders and coatings were characterized by electronic microscopy and microhardness measurements. In-flight particle velocities were monitored for all powders. The deposition efficiency was measured for all experimental conditions. Coating performance and properties were investigated by performing bond strength test, abrasion test and corrosion tests, namely, salt spray and alternated immersion in salt water tests. These coating properties were correlated to the alumina fraction either in the starting powder or in the coating.

Dual-wire arc sprayed Al/Al2O3 MMC coatings have been successfully applied to shipboard and other steel structures. However, the feed wire used is difficult to produce, restricting the application potential of the method. To avoid this difficulty, arc sprayable cored wire was developed, with Al2O3 powder as the filling material and commercial aluminum strip as the retaining sheath. Arc sprayed coatings made from cored Al/Al2O3 wire have been characterized based on bond strength, Al2O3 content, microstructure, microhardness, and wear resistance, and the results are compared with those of pure aluminium coatings.