Manipulating Stacking Fault Energy to Achieve Crack Inhibition and Superior Strength-Ductility Synergy in an Additively Manufactured High-Entropy Alloy.

Additive manufacturing (AM) is a revolutionary technology that heralds a new era in metal processing, yet the quality of AM-produced parts is inevitably compromised by cracking induced by severe residual stress. In this study, a novel approach is presented to inhibit cracks and enhance the mechanical performances of AM-produced alloys by manipulating stacking fault energy (SFE). A high-entropy alloy (HEA) based on an equimolar FeCoCrNi composition is selected as the prototype material due to the presence of microcracks during laser powder bed fusion (LPBF) AM process. Introducing a small amount (≈2.4 at%) of Al doping can effectively lower SFE and yield the formation of multiscale microstructures that efficiently dissipate thermal stress during LPBF processing. Distinct from the Al-free HEA containing visible microcracks, the Al-doped HEA (Al0.1CoCrFeNi) is crack free and demonstrates ≈55% improvement in elongation without compromising tensile strength. Additionally, the lowered SFE enhances the resistance to crack propagation, thereby improving the durability of AM-printed products. By manipulating SFE, the thermal cycle-induced stress during the printing process can be effectively consumed via stacking faults formation, and the proposed strategy offers novel insights into the development of crack-free alloys with superior strength-ductility synergy for intricate structural applications.

Superhard bulk high-entropy carbides with enhanced toughness via metastable in-situ particles.

Despite the extremely high hardness of recently proposed high-entropy carbides (HECs), the low fracture toughness limits their applications in harsh mechanical environment. Here, we introduce a metastability engineering strategy to achieve superhard HECs with enhanced toughness via in-situ metastable particles. This is realized by developing a (WTaNbZrTi)C HEC showing a solid solution matrix with uniformly dispersed in-situ tetragonal and monoclinic ZrO2 particles. Apart from a high hardness of 21.0 GPa, the HEC can obtain an enhanced fracture toughness of 5.89 MPa·m1/2, significantly exceeding the value predicted by rule of mixture and that of other reported HECs. The toughening effect is primarily attributed to the transformation of the metastable tetragonal ZrO2 particles under mechanical loading, which promotes crack tip shielding mechanisms including crack deflection, crack bridging and crack branching. The work demonstrates the concept of using in-situ metastable particles for toughening bulk high-entropy ceramics by taking advantage of their compositional flexibility.