Initial Observation of Grain Orientation Dependent Nanoindentation Hardness of Al 6061 Gas-atomized Powder

Abstract

The dependence-based relationship between the hardness of a small volume of polycrystalline metallic material and the material's crystallographic orientations has been established for systems. Typically, these systems are comprised of hexagonal close packed orientation, such as β-Ti alloys, dual-phase steels, and FeCrAl alloys. Recently, advances in nanoscale-instrumented indentation testing of materials via nanoindentation have shown that the grain orientation dependence of a measured hardness also holds for cubic structured polycrystalline metal systems. In order to contribute to this debate, this work takes a precursory look at the effect of grain orientation on nanoindentation hardness in gas-atomized metallic powders. Grain orientation was measured using electron backscatter diffraction and hardness using nanoindentation. These powders offer the unique challenge of having much smaller grains than those typically researched. It was found that even in face centered cubic gas-atomized Al 6061 powder there is a noteworthy difference in hardness as a function of grain orientation. Though this work demonstrates the influence of grain orientation upon measured nanomechanical properties for a gas-atomized alloyed aluminum powder, additional work will be required to explore and develop an explicit relation between grain orientation and cold spray processing. However, discussion surrounding potential implications for cold spray materials consolidation were provided herein.