Development of a synthesis route for high-entropy alloy feedstock particles for cold spray following conventional and sequential mechanical milling regimes

Manufacturability of a single-phased solid solution of an equiatomic AlCoCrFeNi high-entropy alloy (HEA) feedstock particle in high-energy mechanical alloying (HE-MA) method was investigated in this research. The transient alloy particles were developed using a planetary mill at a constant 580 rpm with milling time varying between 4 and 24 hours. Stearic acid of 3wt.% of the precursor composition was used as a process controlling agent (PCA). Two HE-MA manufacturing regimes were used: conventional (milling constituent elements simultaneously) and sequential (progressive milling while adding elements in certain order). Medium entropy AlCoCrFe alloy was analyzed as a reference material in terms of microstructures and compared to those of the AlCoCrFeNi system, evaluating both the effect of Ni and elemental interaction in the conventional regime. Sequential regime was employed to develop FeNiCoCrAl wherein individual elements were added every 4 hours to the starting/milled Fe + Ni mixture. Inherent thermodynamic factors of the latter two systems were calculated to predict phase formation and compared with the experimental results. The HE-MA FeNiCoCrAl showed a single-phase formation and no intermetallic traceability was recorded. Furthermore, milled powder characteristics such as particle size distribution, morphology, apparent density, flowability, grain size and phase transformation were investigated.