Combinatorial design of Nickel-Chromium alloys by physical vapor deposition and electron beam welding

by 1979- Frafjord, Jaret James

Combinatorial methods, which include high efficiency and high throughput methods to create a large compositional range of materials, have proven to be highly effective and efficient in research and development in the chemical and pharmaceutical industries. In this thesis, similar methods for the development and optimization of metals and alloy systems are explored. Combinatorial Ni-Cr alloy samples were developed by physical vapor deposition (PVD) of a wedged film on a bulk material, and then locally melting the two by electron beam welding (EBW). A combinatorial alloy gradient was thus created along the length of the weld. The samples were rapidly characterized for chemical properties by energy dispersive x-ray spectrometry (EDS) and for mechanical properties, namely modulus and hardness, by nanoindentation. All measurements were compared with similar tests on melted and cast Ni-Cr alloy standards, and the microstructures were compared by scanning electron microscopy (SEM). The entire Ni-Cr composition range was established and reproduced with several welded samples of both nickel films on chromium substrates and chromium films on nickel substrates. There were no strong tendencies in the elastic modulus measurements compared to composition, though all values were within reasonable deviation of the modulus of the cast standards. On the other hand, there were strong trends in the hardness measurements that followed similar tendencies of the standard cast Ni-Cr alloys. The hardness values also showed trends that coincided with the composition and phases associated with the Ni-Cr phase diagram. The hardness results obeyed a more definite trend in the nickel rich ?-phase, where the hardness increased linearly from 1.2 GPa at pure nickel to about 3.5 GPa at 40 at% Cr. The hardness of the chromium rich ?-phase approached nearly 13 GPa when the alloy was between 70 and 85 at% Cr, and then dropped toward the hardness of pure chromium at 3.7 GPa. v