| 摘 要： | Al and Y modified silicide coatings on the Nb-15Si-22Ti-(2,14)Cr-2Al-2Hf-2V alloys(where the alloy with 2 at%Cr or 14 at%Cr is hereafter referred to as 2Cr and 14 Cr alloy,respectively) was prepared by pack cementation.The microstructural evolution and the oxidation behaviours of the coating 2Cr and 14 Cr samples at 1250 ℃ were studied.The 2Cr alloy consists of Nb solid solution(Nb_(SS)) and α-Nb_5Si_3 silicide,while the Laves C15-Cr_2Nb phase arised in the 14 Cr alloy.The coating structure of the coating 2Cr sample contained the outer(Nb,X)Si_2+(Nb,X)_5Si_3 layer,the middle(Nb,X)_5Si_3 layer and the inner undeveloped intermetallic(Nb,Ti)_3(Al,X) layer,the structure of the coating 14 Cr sample consisted of the outer single(Nb,X)Si_2 layer,the middle(Nb,X)_5Si_3 layer,the transition(Nb,Ti)(Cr,Al) layer and the inner(Cr,Al)_2(Nb,Ti) layer.The coating 14 Cr sample exhibited better oxidation resistance than the coating 2Cr sample.With an outer single(Nb,X)Si_2 layer,a compact oxide scale consisting of SiO_2 and TiO_2 formed on the coating14 Cr sample,which can efficiently prevent the substrate from oxidising.For the coating 2Cr sample with an outer(Nb,X)Si_2 +(Nb,X)_5Si_3 layer,the oxide scale of the SiO_2,TiO_2,Nb_2O_5 and CrNbO_4 mixture generated,and the scale spalled out from the surface of the sample,resulting in disastrous failure.
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