Mechanical Properties Control in High Entropy Alloys

Developing new BCC Alloys that delay and minimize plastic localization and accumulation: Toward High Yield and Fatigue strength materials.

The weakening of the metals caused by cyclic loading ultimately results in fracture of the part under stresses that are lower than necessary to cause fracture under monotonic loading. It is observed linear relations between the fatigue strength and intrinsic mechanical properties of metals as yield strength and ultimate tensile strength. The fatigue strength of metals is increasing with increasing yield strength or ultimate tensile strength. However, it is also observed that high-strength materials displayed poor fatigue strengths in relation to their yield strengths. While very low-strength materials generally display fatigue strengths above their yield strengths, high-strength materials can display fatigue strengths as low as 20% of their yield strengths. For this reason, fatigue properties are of high interest for the engineering design of structural parts with high-strength metals. Can we develop high-strength metals with high fatigue strength efficiency? The recent statistical investigations of the plastic localization during monotonic and reverse loading demonstrate the relation of the fatigue strength with the amplitude of the localization that occurs during the first cycle. The aptitude of the materials to localize the deformation is controlling their fatigue strengths. It is also observed linear relation between yield strength and plastic localization amplitude in FCC, HCP, and BCC metals that elucidate the surprising relation between yield strengths and fatigues strengths. High-strength materials systematically display high plastic localization amplitude. While the average plastic localization in FCC and HCP is systematically high for high-strength materials inducing poor efficiency in fatigue, the average plastic localization is observed to be significantly lower for bcc alloys. However, the highest localization for the BCC materials is observed as intense than the FCC and HCP metals. This is related to few microstructural configurations that display high plastic localization during deformation. By metallurgical processing (control of the texture, chemistry, segregation, etc…), these microstructural configurations can be prevented. Consequently, it is expected to produce high-strength metals that produce low plastic localization and, therefore, high fatigue strength efficiency. It is expected to obtain for the first time a high-strength alloy with very high fatigue strength efficiency.