On the Importance of Secondary Component Properties for Cold Spray Metallization of Carbon Fiber Reinforced Polymers.

In previous studies at McGill University, tin was successfully cold sprayed onto carbon fiber reinforced polymers (CFRPs). A "crack-filling" mechanism was described as the deposition mechanism that allowed deposition of tin onto the CFRP. Improving the coating conductivity for lightning strike protection (LSP) purposes was explored by adding other metal powders (aluminum, copper, zinc) to tin and cold spraying on the CFRP. At the same time, it was noticed that the addition of this secondary component (SC) provided an increase in deposition efficiency (DE); tamping was initially hypothesized to explain this improvement, thus prompting a study solely on the effect of SC hardness. However, it is recognized that other powder characteristics may also be influencing the DE. Thus, in this study, SCs with a wider variety of particle sizes, morphologies, densities and hardness values were mixed with tin and sprayed on CFRPs. The effect of SC properties on tin deposition is discussed and, while SC particle size, morphology and density individually do not notably influence the DE, the impact energy of the SC does. This opens a discussion on optimal parameters for deposition of metals on CFRP, based on results and observations from the literature.

Machinability of Rene 65 Superalloy.

Nickel-based superalloys are heavily used in the aerospace and power industries due to their excellent material and mechanical properties. They offer high strength at elevated temperatures, high hardness, corrosion resistance, thermal stability and improved fatigue properties. These superalloys were developed to address the demand for materials with the enhanced heat and stress capabilities needed to increase operational temperatures and speeds in jet and turbine engines. However, most of these properties come with machining difficulty, high wear rate, increased force and poor surface finish. Rene 65 is one of the next generation wrought nickel superalloys that addresses these demands at a reduced cost versus powder metallurgy superalloys. It is strengthened by the presence of gamma prime precipitates in its microstructure, which enhance its strength at high temperatures. Notwithstanding its advantages, Rene 65 must also deal with the reality of the poor workability and machinability generally associated with Ni-based superalloys. This study examines the machinability-using drilling tests-of Rene 65 and seeks to establish the influence of hardness (with varying microstructure) and cutting conditions on machinability indicators (surface finish, forces and chip formation). The experimental setup is based on a set of experimental drilling tests using three different heat-treated samples of varying hardness. The results indicate a negligible effect from material hardness, ranging from 41 HRC to 52 HRC, on generated cutting forces and a similarly low effect from cutting speeds. The feed rate was identified as the main factor of relevance in cutting force and chip morphology during the machining of this new superalloy.