This work investigates the effect of feedstock size on the hardness and wear resistance of metal-matrix composite coatings produced by cold spraying. Feedstocks consisting of Al and Al 2 O 3 powders were prepared for the study. The feedstocks, which differ in regard to Al 2 O 3 particle size (100, 50, 10 µm) and composition (25-50 vol%), were accelerated by compressed air through a Delaval-type nozzle positioned 10 mm from the target substrate. The morphology of the coating resembled that of an Al matrix with embedded Al 2 O 3 particles. Optical microscopy showed that large Al 2 O 3 particles (> 50 µm) fractured into small pieces and embedded in the matrix. It is likely that some of the fragmented particles bounced off, rather than adhering. These collisions (tamping effect) increase coating hardness and density. In the case of the feedstock with 10 µm Al 2 O 3 , particle sizes were unchanged during spraying and the benefits of work hardening were not achieved.

This study investigates the effects of various reinforcement materials and solid lubricants on cold spray aluminum composite coatings. The wear resistance and friction coefficient of the coatings were very different with and without a reinforcement and solid lubricant. It was found that Al 2 O 3 greatly improves wear properties, Mo results in better dispersion hardening, and MoS 2 reduces the friction coefficient.

Comparative studies on the intermetallic compound (IMC) formations of nano- and micro-size Sn with Ni and Cu in cold gas dynamic sprayed (CGDS, or Cold Spray) coatings were carried out. High purity pure nano (average 150 nm) and micro (under 45 μm) Sn were selected and prepared as raw materials mixture in order to be sprayed onto Ni and Cu plate-shape substrates. Nano particles of Sn were successfully coated under conventional coating parameters when they are mixed with microsize materials. And thermodynamic predictions regards to compound formation similarly worked out for both nano and micro Sn mixture. However, the kinetics of formation reaction were turned out to be different. In all case, nano particle showed more sluggish behavior. After post-annealing, microsize Sn formed larger amount of IMC with Ni than nanosize Sn although, owing to larger interfacial area, more intensive reactivities were expected. Also, there were significant differences in the size and distribution of eutectic pores as well.

The Al-Ti, Al-Ni mixed powders were successfully coated by cold gas dynamic spray process (CDSP) and alloying behaviors of films after post-annealing were investigated. The particles were accelerated through a standard de Laval type of nozzle with 120psi (prior to enter). Instead of conventional He gas, the air was used as particle carrying gas. The as-purchased power size of Al, Ti, Ni, was 77, 44, and 3, respectively. The composition of Ti and Ni was varied from 10 and 30 wt%. The coated films were annealed at 600~630. in air or N 2 atmosphere for 3 hrs. It was observed that Ni and Ti particles were finely dispersed and imbedded densely in Al matrix. After post annealing of Al-Ti and Al-Ni films, alloy phases such as the Al 3 Ti and Al 3 Ni phase were formed in the films. In case of Al-Ni films after annealing in air, the oxidation process seemed to retard the alloying of Al 3 Ni. However, after annealing in N 2 , the limitless alloying was proceeded until Ni particles were all consumed. In case of Al-Ti films, it was found that oxidation were virtually nonexistent even in air atmosphere. The formation of Al 3 Ti seemed to be limited by Al or Ti diffusion via preformed Al 3 Ti phase encapsulating Ti powder. In bond strength test, Al-Ti and Al- Ni composite films have higher adhesive bond strength up to 2~ 3 times more than pure Al coating due to massive crater formation of hard Ni or Ti particles. In conclusion, CDSP of Al-metal composite powder source can be a practical and economical way to prepare hard and adhesive Al-alloy thick films owing to stable and finely dispersed inter metallic compound formed in low Temperature annealing. Abstract only; no full-text paper available.