AlCoCrFeNix (x = 0, 1, 2.1) high entropy alloy feedstock particle design and synthesis for cold spray application
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Date
2025-06
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University of New Brunswick
Abstract
Strength-ductility trade-off in high entropy alloys (HEAs) remains a critical area of research. BCC-structured HEAs typically exhibit high yield strength but limited plasticity, whereas FCC-structured HEAs display lower yield strength with enhanced ductility. This research investigated the properties of dual-phase HEAs where BCC is the predominant phase, aiming to optimize their performance in high-strength applications such as surface enhancement. This study is divided into two phases, (I) synthesis of equiatomic and non equiatomic AlCoCrFeNix (atomic ratio, x = 0, 1, 2.1) HEAs through mechanical alloying (MA) and (II) subsequent deposition of these particles using cold spray (CS) technique. Phase I analyzed the effect of milling parameters during the production of AlCoCrFeNix (x = 0, 1, 2.1) feedstock, the role Ni content in phase evolution of AlCoCrFeNix particles, and the effectiveness of MA in achieving the desired properties. Results indicate that the addition of Ni extends the milling time for producing AlCoCrFeNix HEAs and influences phase evolution, with increased FCC phase fractions. Phase I successfully synthesized dual-phase (BCC + FCC) AlCoCrFeNix HEAs, indicating the effectivity of MA to tailor desired properties of HEA particles.
Phase II then focused on the influence of substrate and spray parameters on AlCoCrFeNix deposition, and the resulting microstructure and mechanical properties of the deposits. The use of helium (He) as a propellant gas resulted in better deposition efficiency due to higher particle velocities compared to nitrogen (N2). While N2 led to metallurgical bonds accompanied by empty craters, He facilitated effective particle flattening and bonding. Key findings reveal that Ni content, substrate type, and CS conditions significantly affect deposition characteristics and the resulting properties of AlCoCrFeNix HEA particles. Higher Ni levels correlated with increased particle density and hardness but negatively impacted particle velocity and BCC phase presence.
Overall, this research successfully produced and deposited medium entropy alloy, AlCoCrFe, high entropy alloy, AlCoCrFeNi and eutectic high entropy alloy, AlCoCrFeNi2.1 using MA and CS, respectively. The presence of BCC and FCC phases in the HEA particles showed the strength and ductility balance in these materials. Consequently, the microstructure and mechanical properties of HEA particles influence the particle-substrate interaction during impact.