Engineering new metallic alloys is vital for the development of the new materials required for the enhancement of numerous industrial applications. Alloying has been used, certainly since the bronze age, to confer required mechanical properties on new materials. Classically, it meant adding comparatively minor quantities of secondary elements to a main element. However, In the last two decades a novel strategy has been developed, of mixing multiple principal elements in high concentrations to produce new materials. It has been shown that these highly concentrated alloys, also known as High Entropy Alloys (HEAs) can show exceptional properties, superior to conventional alloys, including a high resistance to corrosion. This thesis reports the fabrication and testing of three HEAs: AlFeMnNi in equimolar composition and AlFeMnNiC10 in close to equimolar composition produced as bulk by vacuum arc melting and as thin films by ion beam sputtering deposition onto silicon and mild steel substrates. The third alloy was AlFeNbNiC in close to equimolar composition but produced only as a thin film. The elemental chemical compositions were determined by Energy Dispersive X-Ray (EDX) analysis and atomic structures by X-Ray Diffraction (XRD). A crystalline single-phase material was observed with FeMnNiAl, and amorphous single-phase materials with FeMnNiAlC10 and AlFeNBNiC. The corrosion resistance of the materials was evaluated by potentiodynamic polarization in sodium chloride and sulphuric acid solutions and sweet crude oil and compared to a reference material, stainless steel 304 which has good corrosion resistance. The sintered alloys showed better corrosion resistance than SS 304 and nanoindentation test showed that the thin films had higher hardness than M4 steel.
|Date of Award||11 Apr 2023|
|Supervisor||Vladimir Vishnyakov (Main Supervisor) & Karl Walton (Co-Supervisor)|