Thin Film Combinatorial Sputtering of TaTiHfZr Compositionally Complex Alloys for Rapid Materials Discovery

Combinatorially sputtered thin films can be leveraged as a rapid, materials discovery process in mechanical alloy design. Ta_wTi_xHf_yZr_zthin films were synthesized via combinatorial sputtering from pure Ta, Ti, Hf, and Zr targets. The substrate was not rotated to generate compositional gradients where 12.4<w<71.6, 6.40<x<55.6, 4.22<y<58.8, 7.25<z<48.9 over a 100 mm diameter substrate. The crystal structure, phase fraction, film morphology, mechanical (i.e. modulus and hardness), optical (i.e. n and k), thermal (i.e. phase stability, CTE, and thermal conductivities), and corrosion properties (i.e. corrosion current and rates) are all correlated to the Ta_wTi_xHf_yZr_zcomposition. Temperature dependent x-ray diffraction (TDXRD) reveals the thermal stability of the material system. TDXRD has shown the as-deposited material library is primarily stable in a single HCP phase below 60 at. % Ta at room temperature but will form increasing amounts of a BCC phase at elevated temperatures. Nanoindentation of as-deposited films shows good agreement between experimental, solid solution estimations of hardness via a simple rule of mixtures from bulk elements, and correlated to a few up-scaled bulk samples. Thin film modulus shows good agreement with bulk rule of mixture estimations after accounting for thin film substrate effects via King’s correction. As-deposited and annealed film properties are compared. Compositions with an optimal combinations of the aforementioned properties were then upscaled to bulk materials for further investigation.