Abstract
As one of the most effective mechanisms,precipitation-hardening is widely used to strengthen high-entropy alloys.Yet,heavy precipitation-hardened high-entropy alloys usually exhibit serious embrittlement.How to effectively achieve ultra-high strength and maintain reliable ductility remains a challenge.Here,we report a study of doping extremely little boron to meet this target.We found that adding of 30 ppm boron into the heavy Ti and Al alloyed FCC FeCoNiCr high-entropy,(FeCoNiCr)88Ti6Al6 HEA(at.％)which is strengthened mainly by both coarse BCC-based(Ni,Co)2TiAl Heusler and fine L12-type FCC-based(Ni,Co)3TiAl precipitates and shows ultrahigh strength but poor ductility,could significantly change the original microstructure and consequently improve mechanical performance,owing to the well-known effect of boron on reducing the energy of grain boundaries.The boron addition can(1)eliminate microcavities formed at Heusler precipitate-matrix interfaces;(2)suppress the formation and segregation of coarse BCC Heusler precipitates;(3)promote the formation of L12 nanoparticles.This changes of microstructure substantially improve the tensile ductility more than by～86％and retain comparable or even better ultimate tensile strength.These findings may provide a simple and cost-less solution to produce heavy precipitation-strengthened HEAs with ultrahigh strength and prevent accidental brittleness.
NETL
NSTL
维普
万方数据