Mechanical and Fatigue Properties of Diamond-Reinforced Cu and Al Metal Matrix Composites Prepared by Cold Spray

Diamond-reinforced metal matrix composites (DMMC) prepared by cold spray are emerging materials simultaneously featuring outstanding thermal conductivity and wear resistance. In our paper, their mechanical and fatigue properties relevant to perspective engineering applications were investigated using miniature bending specimens. Two different diamond mass concentrations (20 and 50%) embedded in two metal matrices (Al-lighter than diamond, Cu-heavier than diamond) were compared with the respective cold-sprayed pure metals, as well as bulk Al and Cu references. The pure Al, Cu coatings showed properties typical for cold spray deposits, i.e., decreased elastic moduli (50 GPa for Al, 80 GPa for Cu), limited ductility (< 1 × 10-3) and low fracture toughness (3.8 MPa·m0.5 for Al, 5.6 MPa·m0.5 for Cu) when compared to the bulks. Significantly improved properties (strain at fracture, ultimate strength, fatigue crack growth resistance, fracture toughness) were then observed for the produced DMMC. The improvement can be explained by a combination of two factors: changes in the properties of the metallic matrix triggered by the reinforcement particles peening effect and stress redistribution due to the particles presence.

Increasing Fatigue Endurance of Hydroxyapatite and Rutile Plasma Sprayed Biocomponents by Controlling Deposition In-Flight Properties

Three sets of hydroxyapatite and rutile-TiO₂ coatings were plasma sprayed onto metallic substrates. The spray parameters of the sets were modified so as to obtain different in-flight temperatures and velocities of the powder particles within the plasma jet (ranging from 1778 to 2385 K and 128 to 199 m s^-1, respectively). Fatigue endurance of the coated specimens was then tested. The samples were subjected to a symmetric cyclical bend loading, and the crack propagation was monitored until it reached a predefined cross-section damage. The influence of the coating deposition was evaluated with respect to a noncoated reference set and the in-flight characteristics. Attributed to favorable residual stress development in the sprayed samples, it was found that the deposition of the coatings generally led to a prolongation of the fatigue lives. The highest lifetime increase (up to 46% as compared to the noncoated set) was recorded for the coatings deposited under high in-flight temperature and velocity. Importantly, this was achieved without significantly compromising the microstructure or phase composition of the deposited HA and TiO₂ layers.