| In recent years,high entropy alloys(HEA)have attracted the attention of researchers both at home and abroad because of their unique four effects and excellent high-temperature properties.The research on high-temperature oxidation behaviors of high entropy alloys has great significance in both theory and practice.The study shows that the microstructure of CrMnFeCoNi system high entropy alloy is single FCC solid solution phase,and has excellent comprehensive performance.The addition of Nb elements enhances the hardness and yield strength of the alloy,and the CrMnFeCoNiNbx high entropy alloy has good thermal stability.High temperature oxidation behavior in the air of CrMnFeCoNiNbx(x=0,0.1,0.25,0.5)high entropy alloy is studied under 700?,800? and 900? based on the methods such as discontinuous weighing method,XRD,SEM and EDS.In addition,the influence of oxidative temperature and Nb content on the high temperature oxidation resistance of CrMnFeCoNiNbx high entropy alloy is analyzed,and the influence of high temperature heat treatment for 100h on the matrix micro structure is investigated.The main conclusions are as follows.With the increase of Nb content in the alloy,the CrMnFeCoNiNbx high entropy alloy has rich Nb phase precipitation,and its phase composition is converted by the FCC to the FCC and Laves phase,and Nb promotes the generation of Laves precipitating phase.Phase composition and chemical composition of alloy matrix and the as-cast alloy were similar after the 100 hours of high temperature oxidation at 700?,800? and 900? respectively.However,the precipitation phase will converge and grow up in a certain area.With the increase of temperature,the phase volume fraction of Laves phase in the same alloy gradually increased and the precipitated phase accumulated.At the same temperature,with the content of Nb increases,the phase volume fraction of Laves phase increases gradually,and the influence of Nb content on the volume fraction of Laves is greater than temperature.In the air,Mn,Cr and Nb of CrMnFeCoNiNbx(x=0,0.1,0.25,0.5)are mainly oxidized and with a small amount of spinel oxides such as NiCr2O4 at 700?,800? and 900? temperature.The outermost layer oxide are rich manganese oxide layer,manganese oxide is mainly Mn2O3 at 700? and 800?,and is mainly Mn3O4 at 900?.From the outer layer of the oxide layer to the inner layer,the content of manganese decreases gradually,and the chromium content increases gradually.And in the innermost chromic content is the most.The results show that after high temperature oxidation,in the middle and near the base of the rich Cr layer and the rich Mn layer,a rich Nb oxide laye can be found in the o Nb alloy.At 900?,Nb alloy will have obvious internal oxidation phenomenon,and which occurs near the rich Nb precipitated phase.Arter the 100 hours of high temperature oxidation at 700?,800? and 900?respectively,the oxidative weight gain of CrMnFeCoNiNbx(x=0,0.1,0.25,0.5)high entropy alloy and time are parabolic.The oxidation rate constant and apparent activation energy of each alloy are calculated according to the Wagner theory.Study shows that Nb0 alloy has the worst antioxidant properties.Under the 700? and 800?,the alloy is belong to the level of antioxidant.However,the oxide layer on the surface of the alloy has fallen off and oxidation resistance decrease sharply at 900?.A moderate amount of Nb elements can significantly improve the high temperature antioxidant performance of CrMnFeCoNiNbx system,while excessive Nb elements will weaken the antioxidant properties of the alloy.The results show that the oxidation resistance of the alloys from strong to weak is CrMnFeCoNiNb0.1,CrMnFeCoNiNb0.25,CrMnFeCoNiNb0.5 and CrMnFeCoNi. |
PDF Full Text Request