Quantitative Nondestructive Evaluation of Cold Spray Manufactured Aluminum Alloy 6061 and Copper Samples

Abstract

Cold spray (CS) is a solid-state process for depositing thick layers of material via the successive high-velocity impact of powder particles onto a solid surface, which leads to high rates of deformation, interparticle bonding, and coating build-up. Although CS is finding commercial utilization in non-load-bearing repair and coating applications, clear nondestructive characterization procedures are necessary to realize its potential in load-bearing structural applications. In this study, the viability of electrical conductivity and through thickness ultrasound wave velocity measurement methods was studied to serve as a means for nondestructive quantitative measurement for quality control in CS and potentially other additive manufacturing (AM) methods. Eddy current, ultrasound, porosity, hardness, and uniaxial tensile strength tests were conducted on CS deposited layers of aluminum alloy 6061 and copper on aluminum alloy 6061 and commercially pure copper substrates, respectively. CS gas dynamic parameters were intentionally and systematically varied to result in corresponding discrete differences in mechanical properties of deposits. Ultrasound measurements of longitudinal wave velocity and eddy current electrical conductivity measurements showed good correlation with process conditions, microstructural characterization results, and destructive mechanical tests (hardness, tensile). The results of this work show that ultrasound wave velocity and electrical conductivity correlate well with increased particle impact velocity in CS deposited aluminum and copper blocks, which evidently show an incremental decrease in porosity, increase in hardness, and increase in tensile strength. The outlined ultrasound and eddy current nondestructive testing methods present effective means for quantitative assessment of cold spray deposited structures while intact with the substrate.