Decision science-driven selection of conventional high-temperature titanium alloys for aeroengine applications and future directions

High-temperature near α titanium alloys find themselves in advanced aero engines for applications up to the temperatures of 600°C mainly as compressor components, namely blades, discs, shafts, cases, etc., owing to their superior combination of room temperature and elevated-temperature mechanical properties and oxidation resistance. We adopted a decision science-driven approach to analyze the mechanical properties of several grades and variants of high-temperature Ti alloys (both commercial and research alloys), viz., IMI829, IMI 834, Ti-1100, TA 29, and so on, reported in the literature to date. We applied a novel methodology that combines multiple-attribute decision-making (MADM) methods, principal component analysis (PCA), and hierarchical cluster analysis (HCA). Weights of the properties (or attributes) were evaluated by objective (Shannon's entropy method) and subjective methods. The rank assigned by several MADMs, viz., Simple additive weighting (SAW), Combined compromise solution (CoCoSo), Operational competitive ratio (OCRA), Range of value methods (ROVM), and Measurement of alternatives and ranking according to compromise solution (MARCOS), and Technique of order preference by similarity to ideal solution (TOPSIS), were consistent. PCA and HCA not only consolidated the MADM ranks but also grouped similar alloys. The investigation highlights similarities across several grades/variants of the alloys, suggest potential replacement or substitute for existing alloys, and provides directions for improvement and/or development of titanium alloys over the current ones to push out some of the heavier alloys and thus help in reducing the weight of the engine to advantage. This methodology further demonstrates that it is possible to explore different weightage scenarios and decide the optimum alloy(s) for the specific intended application(s).