In this study, an equiatomic Al20Co20Cr20Fe20Ni20 high entropy alloy was fabricated using mechanical alloying (MA) by ball milling and field assisted sintering technique/spark plasma sintering (FAST/SPS). The elements were chosen because of their high catalytic activity in hydrogen evolution reactions for water electrolysis.

Firstly, the influence of different wet-milling parameters (time, rotation speed, ball-to-powder weight ratio) on the powder macro- and microstructure was investigated. The characterization of the powder comprised particle measurements, phase analysis by XRD, morphology and chemical composition by SEM and EDS. The HEA powder with suitable ball milling parameters (48 h, 300 rpm, BPR 10:1) were homogeneously distributed in particle size (50 µm), consisted of a single face centered cubic phase (FCC) and confirmed the same alloy composition of the initial elements.

Additionally, a new approach and helpful tool to predict suitable sintering temperatures for the alloy were in-situ powder XRD measurements. Within the ascertained temperature range, the milled powder was sintered in FAST/SPS with different pressure values to achieve high-density and single-phased samples. The relative density of sintered samples was more than 99 %, making them suitable for sputtering applications. The crystal structure and chemical composition compared between powder and sintered samples showed the evidence of a HEA or the necessity of an additional annealing step to achieve a single phase.

Finally, FAST/SPS tooling was examined for upsizing sample size diameters from 20 to 100 mm. Two different tool designs were used to withstand high pressure at elevated temperatures and ensure an uniform temperature distribution in the sintered part. Numerical evaluations and microstructure investigations confirmed the need of special tool designs for an increase in size of sintered samples.