Mechanical Behavior of Additively Manufactured GRCop-84 Copper Alloy Lattice Structures

This study investigates the interplay between microstructure, topology and their combined effect on the quasi static and dynamic behavior of additively manufactured Copper-Chromium-Niobium alloy (GRCop-84) lattice structures. Lattice structures made of GRCop-84 alloys are beneficial for wide range of applications due to the combination of the high strength and thermal conductivity imparted by GRCop-84 while minimizing weight and increasing the energy absorption through the use of the lattice structure. X-ray computed tomography (XCT) and optical microscopy were used to characterize the porosity and grain structure, respectively. Quasi static and dynamic testing was performed on the as-built (AB) samples at strain rates of 10(-1)s(-1) and 10(3)s(-1), respectively. The observations indicated that reducing the unit cell size from 4 mm to 2 mm led to a 66% reduction in porosity. Depending on the topology of the tested sample, the reduced porosity within the 2 mm unit cell samples resulted in a 35% to 60% increase in the compressive yield strength. To understand whether topology is the only driving mechanism that influence the mechanical properties e.g., yield strength, the microstructure was altered through hot isostatic pressing (HIP) heat treatment while the topology was kept constant. It was noted that the 4 mm unit cell size was more responsive to HIPing with a 40% reduction in porosity, while the 2 mm unit cell size only experienced a 28% reduction in porosity. It was also noticed that there was a 48% reduction in porosity by minimizing the unit cell size from 4 mm to 2 mm in the case of the HIPed samples. Using this data, a correlation was recognized between microstructure and topology. It was found that HIPed samples experienced more plastic deformation and exhibited stress plateau that is common in cellular solids, indicating improved energy absorbing abilities compared to AB. AB Samples demonstrated higher compressive strength and failed due to the brittle nature of the AB microstructure. Lattice Structures with unit cell sizes of 4 mm and 2 mm experienced different collapse mechanisms, with 2 mm unit cell lattices being topology dependent and 4 mm unit cell lattices dependent on microstructure.