Cold spray deformation and deposition of blended feedstock powders not necessarily obey the rule of mixture

Abstract

Cold spray additive manufacturing has the potential to be used in repair and manufacturing of a wide variety of parts and coatings including composite coatings . Understanding materials' fundamental behaviour during deposition is essential for the process development which was not addressed enough for mixed powders. One objective of this study is to explore the process-structure relation of mixed Ni-Ti powders in cold spray to provide a methodology to achieve a coating with the composition of interest. Single/multi-particle impact experiments and FEM modelling were employed to investigate the particle deformation and microstructure evolution using SEM, EBSD and EDS. The sprays of mixed powders were performed using a wide process parameter window and the deposition characteristics and composition variation as a function of process parameters were explored. The experiments and modelling showed that splats in dissimilar multi-particle impacts experience more deformation than those of similar materials, which in microstructural scale translates to variation of deformation mechanism from single-component coatings. This results in higher degree of grain refinement, specifically for Ti in the composite coating with an average grain size of 500 nm. Experiments showed that the DE of mixed powder deviates from the rule of mixture, which means the critical velocity of Ni-Ti powder is different from the single-component Ni and Ti coatings due to material interactions. Findings showed there is a process parameter criteria for which relative DEs of components, and thereby composition of composite coatings, remain at almost constant ratios. η (impact velocity/critical velocity ratio) is used as a measure to predict qualitative composition variation as a function of spraying parameters and powder characteristics. • Process-structure relation of cold sprayed mixed powders is explored experimentally & numerically. • Process criteria are proposed to predict composition variation using V and V cr . • A methodology is proposed to achieve a composite with the composition of interest. • Materials interaction & intrinsic materials properties result in change of V cr & DE deviation from mixing rule.