Effects of alloying and high-temperature heat treatment on the microstructure of Nb-Ti-Si based ultr

来源 :Progress in Natural Science:Materials International | 被引量 : 0次 | 上传用户:FlyingBird173
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The phase compositions,microstructure and especially phase interfaces in the as-cast and heat-treated Nb-Ti-Si based ultrahigh temperature alloys have been investigated.It is shown that b(Nb,X)5Si3 and g(Nb,X)5Si3 are the primary phases in the Nb-22Ti-16Si-5Cr-5Al(S1)(at%)and Nb-20Ti-16Si-6Cr-4Al-5Hf-2B-0.06Y(S2)(at%)alloys,respectively.The Nb solid solution(Nbss)is the primary phase in Nb-22Ti-14Si-5Hf-3Al-1.5B-0.06Y(S3)(at%)alloy.An orientation relationship between Nbss and g(Nb,X)5Si3 was determined to be(110)Nb//(1010)g and[111]Nb//[0001]g in the as-cast S2 and S3 alloys.Some original b(Nb,X)5Si3 transformed into a(Nb,X)5Si3 because Al and Cr diffused from the b(Nb,X)5Si3 to Nbss during heat treatment at 1500 1C for 50 h in the S1 alloy.Meanwhile,Ti diffused from Nbss to b(Nb,X)5Si3,which induced aTi to generate near the interface between Nbss and Ti-rich b(Nb,X)5Si3.The orientation relationship between the newly-formed aTi and previous Nbss was(110)Nb//(1101)aTi and[001]Nb//(1231)aTi.Among the(Nb,X)5Si3 phases,the contents of Cr and Al in b(Nb,X)5Si3 are nearly the same as those in g(Nb,X)5Si3 but obviously higher than those in the a(Nb,X)5Si3,whereas the content of Si in a(Nb,X)5Si3 is nearly the same as that in g(Nb,X)5Si3 but higher than that in the b(Nb,X)5Si3. The phase compositions, microstructure and especially phase interfaces in the as-cast and heat-treated Nb-Ti-Si based ultrahigh temperature alloys have been investigated. It is shown that b (Nb, X) 5Si3 and g (Nb, X) are the primary phases in the Nb-22Ti-16Si-5Cr-5Al (at) and Nb-20Ti-16Si-6Cr-4Al-5Hf-2B-0.06Y (S2) The Nb solid solution (Nbss) is the primary phase in Nb-22Ti-14Si-5Hf-3Al- 1.5B- 0.06Y (S3) (at%) alloy. An orientation relationship between Nbss and g (Nb, X) 5Si3 was determined to be (110) Nb // (1010) g and [111] Nb // [0001] g in the as-cast S2 and S3 alloys. Home original b (Nb, X) 5Si3 transformed into a (Nb, X ) 5Si3 because Al and Cr diffused from the b (Nb, X) 5Si3 to Nbss during heat treatment at 1500 1C for 50 h in the S1 alloy. While Ti diffused from Nbss to b (Nb, X) 5Si3, which induced aTi to generate near the interface between Nbss and Ti-rich b (Nb, X) 5Si3. The orientation relationship between the newly-formed aTi and previous Nbss was (110) Nb // (1101) aTi and [001] Nb // 1231) (Nb, X) 5Si3 phases, the contents of Cr and Al in b (Nb, X) 5Si3 are nearly the same as those in g (Nb, X) 5Si3 but obviously higher than those in the a , X) 5Si3, while the content of Si in a (Nb, X) 5Si3 is nearly the same as that in g (Nb, X) 5Si3 but higher than that in the b (Nb, X) 5Si3.
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