student profile: Mr Naveed Aziz Khan


Thesis work

Thesis title: Microscopic Characterization of AlCoCrCuFeNi High Entropy Alloy (HEA) Thin Films

Supervisors: Zongwen LIU , Jun HUANG

Thesis abstract:

The high entropy alloys (HEAs) also known as the multi-principal element alloys (MPEAs) was first reported in the year 2004 which consist of at least five principal elements in equimolar or near equimolar ratios and the concentration of each principal elements can vary in between 35 and 5 at. %. In the recent years, it was found that HEAs are unique in nature and are different from the existing conventional alloys. The HEAs exhibit a surprising degree of intersolubility and has the possibility to influence solid solution phase stability by controlling the configurational entropy. Due to the high entropy of mixing, simple disordered solid solution structures like FCC and BCC are common for HEAs rather than the complex intermetallic phases. The HEAs has a wide range of microstructures including amorphous, nanocrystalline, single-phase and multi-phase structures which possess excellent mechanical, thermal, and electrical properties. The bulk HEAs are widely studied for their exceptional properties such as high corrosion resistance, good mechanical properties, and thermal stability. However, HEA thin films are also becoming popular and they also exhibit many potential properties and can be used as heat or wear resistant coatings, diffusion barriers, soft magnetic films, and coating materials for high temperature applications. Hence, an effort is being made in this work to understand the microstructural properties of HEA thin films which are essential for micro and nanoscale applications.
In this work, microscopic characterization will be performed on the HEA thin films of AlCoCrCu0.5FeNi which are deposited by pulsed laser deposition under various oxygen partial pressures and then subsequently annealed at high temperature. The thin films are deposited on silicon and glass substrates and their fundamental growth mechanism will be extensively studied at atomic resolution by transmission electron microscopy (TEM) and other sophisticated characterization methods like FESEM, EDX, EBSD, XRD, and TKD. The images and diffraction patterns from the TEM and XRD results will be carefully studied to obtain information about the growth mechanism, defect levels, and identify the structural phases. FESEM integrated with EDX, EBSD, and TKD system can provide the crucial information regarding the surface morphology, chemical composition, phase orientation, grain boundary and mapping information. Then the self-healing effect of the HEA films on different substrates will be observed by electron beam exposure and in-situ heating, monitoring the minute structural changes at an atomic resolution using the in-situ TEM analysis and simultaneously the compositional changes in the film will be recorded using the integrated EDX system with the TEM. Therefore, the outcome of this research is anticipated to reveal many fundamental properties of AlCoCrCu0.5FeNi HEA thin films exhibiting the self-healing effect which could have the potential to be a promising coating material for high temperature applications.

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