Thermal stability of High entropy alloys

Thermal Stability of High Entropy Alloys

Garlapati Mohan Muralikrishna

Properties of materials play a major role in any application. The properties of a material depend on the structure. The ability of retaining those properties depends on the stability of that structure in different environments like high/low temperature, corrosive environment, heavy loads and high speed applications. High entropy alloys(HEAs) are the one with equi / near equi atomic multicomponent alloys containing high configurational entropy which makes the alloy to be more stable in simple BCC and FCC structures. In literature HEAs are said to have very good properties (high hardness, high creep strength, good thermal conductivity, corrosion resistance etc.) all these properties mainly depends on the structure of the alloy and it’s stability in extreme conditions. In this context we have started enquiring about the stability of structure at high temperatures and long annealing periods.

AlCoCrFeNi HEA is known to be well studied alloy. Our research on this alloy includes studies on phase formation with varying Al content and it’s stability at high temperatures. Mechanical alloying through planetary ball milling and spark plasma sintering (SPS) are chosen as the synthesis root to gain the benefits of nano size grains. Fig. 1 represents the phases that are present in AlxCoCrFeNi in as milled condition with grain size of <10 nm. Tools like X-ray diffraction, scanning electron microscopy and transmission electron microscopy are used to characterize the samples. Main objective of this work is to identify the exact mechanism that makes these alloys to be more stable at high temperatures or identify the mechanism that causing the phase transformations in these materials.

Fig 1. Structure of AlxCoCrFeNi (x-0, 0.3, 0.6, 1 mole) synthesized through mechanical alloying