Effect of serrated grain boundary on tensile and creep properties of a precipitation strengthened high entropy alloy

Abstract

In this study, tensile and creep deformation of a high-entropy alloy processed by selective laser melting (SLM) has been investigated; hot ductility drop was identified at first, and the loss of ductility at elevated temperature was associated with intergranular fracture. By modifying the grain boundary morphology from straight to serration, the hot ductility drop issue has been resolved successfully. The serrated grain boundary could be achieved by reducing the cooling rate of solution heat treatment, which allowed the coarsening of L1 2 structured γ′ precipitates to interfere with mobile grain boundaries, resulting in undulation of the grain boundary morphology. Tensile and creep tests at 650°C were conducted, and serrated grain boundary could render a significant increase in tensile fracture strain and creep rupture life by a factor of 3.5 and 400, respectively. Detailed microstructure analysis has indicated that serrated grain boundary could distribute strains more evenly than that of straight morphology. The underlying mechanism of deformation with grain boundary serration was further demonstrated by molecular dynamic simulation, which has indicated that serrated grain boundaries could reduce local strain concentration and provide resistance against intergranular cracking. This is the first study to tackle the hot ductility drop issue in a high-entropy alloy fabricated by SLM; it can provide a guideline to develop future high-entropy alloys and design post heat treatment for elevated temperature applications.

Molecular Dynamics Study of Temperature Dependence of Grain Boundaries (100) in Pure Aluminum with Application of Machine Learning

“…Grain boundaries can be sources of crystal structure defects such as dislocations [4][5][6][7], and GBs are also able to interact with mobile dislocations from crystal grains [8]. In addition, GBs can be initiators of cracks, the propagation of which leads to the subsequent fracture of materials [9,10]. At the same time, GBs affect the strength and mechanical properties of metals and alloys of various types, whether they are samples with FCC [10] or BCC [11] lattices or more complex materials, namely high-entropy alloys, where the lattice type may depend on the concentration of certain alloy elements [9].…”

“…In addition, GBs can be initiators of cracks, the propagation of which leads to the subsequent fracture of materials [9,10]. At the same time, GBs affect the strength and mechanical properties of metals and alloys of various types, whether they are samples with FCC [10] or BCC [11] lattices or more complex materials, namely high-entropy alloys, where the lattice type may depend on the concentration of certain alloy elements [9]. The GBs are generally determined through 5 degrees of freedom: Three are related to grain misorientation, and two determine the boundary plane.…”