UC San Diego

Owing to superior mechanical properties such as high fatigue life and high yield strength of many non-equiatomic high entropy alloys (HEA), a novel division of non-equiatomic FeNiCoAlTaB (NCATB) HEAs has been introduced. The novel NCTAB HEAs exhibit a very high yield stress which is around 1.1~1.2 GPa with appreciable ductility under quasi-static compression. The strengthening mechanisms in NCATB-HEA system are strongly dependent on the grain precipitates, solid solution and martensite transformation under dynamic loading. Martensitic transformation can commonly be attributed to athermal induction and deformation induction. In respect of athermal induced martensitic transformation, temperature of bulk materials needs to be lowered below Ms temperature rapidly. Whereas, martensitic transformation can commence above Ms temperature. The chemical driving force for phase transition can be balanced through drastic cooling or external loading. Different shape of martensite (lath, butterfly, lenticular, thin plate) can be formed depending on the temperature while the lath-like martensite tends to appear at highest forming temperature and thin plate tends to appear at lowest forming temperature. Due to its superior mechanical properties including higher strengthen and strain hardening rate and high endurance limit, this novel HEA system is considered to be conducted into wider application including high damping materials and aviation application. The strain rate effect on martensitic transformation is also studied in current research. Microband is a very common phenomenon in high stacking fault energy material, whereas its formation mechanism remains unclear. Microband formation and its effect on martensitic transformation are also dedicated to study in this research.