Compositional Design and Microstructural Control of Ultrastrong-yet-ductile Chemically Complex Intermetallic Alloys for Advanced High-temperature Structural Applications

Description

Intermetallic alloys (IMAs) with long-range ordered crystalline structures represent a unique class of materials that are highly attractive for advanced structural applications at elevated temperatures. However, most high-strength IMAs usually suffer severe embrittlement behavior at room temperature, in particular the early crack and failure along grain boundaries. Such a serious problem significantly limits their large-scale practical applications and has stumped materials scientists for decades. Unfortunately, most conventional IMAs in earlier studies were designed mainly based on the chemically simple systems, such as the Ni3A1 and NiA1 alloys, which fails to breakthrough this thorny dilemma due to the limited abilities for further optimization of alloys’ chemistries and microstructures. In this proposal, we innovatively depart from the conventional wisdom and preliminarily designed a novel L12-type chemically complex IMA (CCIMA) based on the multicomponent CoNiA1TiTaNbB system. Strikingly, this new-type CCIMA exhibits unexpected, excellent strength-ductility synergy at room temperature, i.e., an ultrahigh tensile strength of ~1.7 GPa and a large ductility over 30%, which outperforms most conventional IMAs in previous studies. Initial results show that the grain-boundary disordered nanolayer and unique type of deformable nano-twinned boride may play important roles in the superb mechanical properties. However, the alloying effects and underlying micro-mechanisms remain elusive without a comprehensive understanding. More strikingly, as the test temperatures increase to 700oC, we can find that its strength increases rather than decreases, indicating a prominent yielding anomaly. Inspired by these results, superior softening resistance can be anticipated at higher temperatures, which however, remain unexplored now. Moreover, the creep behavior, which is usually of major concern when evaluating components that operate under high stresses at elevated temperatures, have not been well evaluated. The structural origins governing the creep resistance also remains poorly understood.  As a result, we propose to conduct systematical studies on the compositional design, microstructural control, and deformation behavior of this new kind of CCIMAs. By successfully implementing this project, we will provide unique insights into the “composition-microstructure– property” correlations of these newly designed CCIMAs in a quantitative manner. Based on these achievements, the well-targeted compositional design and microstructural control of CCIMAs can be effectively realized, which will significantly facilitate the innovative design and controllable fabrication of new-type structural materials with remarkable thermal-mechanical properties at elevated temperatures. More significantly, we believe that the knowledge gained from this proposed work will benefit a variety of modern industries, especially for those rely heavily on advanced high-temperature structural alloys.