College of Engineering
Materials Engineering Department
BS in Materials Engineering
Rocket engines have always relied on high-conductivity copper liners to protect structural components from extreme thermal loads produced by combustion. Forged NARloy-Z has been the material of choice for decades but increasing cost of its constituent silver and high waste in the machining process has reduced the alloy’s cost effectiveness. Aerojet Rocketdyne wants to determine the viability of cold-spray additively manufactured GRCop-42 as a replacement alloy to reduce liner cost. Screening tests were performed to observe the microstructural development and microhardness changes of cold-sprayed GRCop-42 after being subjected to multiple stages of the typical heat treatment of a combustion chamber liner. Two batches of samples with different cold-spray parameters were given one of four treatments: as-sprayed, HIPed, HIPed and annealed at 1700℉, and HIPed and annealed at 1800℉. Statistical analysis of hardness data concluded a reduction in mean hardness from 197HV to 119HV after HIPing and an additional reduction to 86HV after the annealing treatment. The temperature of the annealing was statistically insignificant. Optical microscopy revealed ‘healing’ of former powder boundaries after annealing treatment, indicated by the boundaries no longer being preferentially etched. These heat treatment effects suggest an increase in yield strength and low-cycle fatigue life, with fewer crack propagating, high-energy boundaries present. No reliable data could be collected on particle coarsening due to natural particle size variance.