To investigate the effects of homogenizing and aging treatments on the microstructure of an Nb-Ti-Cr-Si based ultrahigh temperature alloy,coupons were homogenized at 1 200-1 500 °C for 24 h,and then aged at 1 000...To investigate the effects of homogenizing and aging treatments on the microstructure of an Nb-Ti-Cr-Si based ultrahigh temperature alloy,coupons were homogenized at 1 200-1 500 °C for 24 h,and then aged at 1 000 °C for 24 h.The results show that the heat-treated alloy is composed of Nb solid solution（Nbss）,（Nb,X）5Si3 and Cr2Nb phases.With the increase of heat-treatment temperature,previous Nbss dendrites transformed into equiaxed grains,and petal-like Nbss/（Nb,X）5Si3 eutectic colonies gradually changed into small（Nb,X）5Si3 particles distributed in Nbss matrix.A drastic change occurred in the morphology of the Laves phase after homogenizing treatment.Previously coarse Cr2Nb blocks dissolved during homogenizing at temperature above 1 300 °C,and then much finer and crowded Cr2Nb flakes precipitated in the Nbss matrix in cooling.Aging treatment at 1 000 °C for 24 h led to further precipitation of fine particles of Laves phase in Nbss matrix and made the difference in concentrations of Ti,Hf and Al in Nbss,（Nb,X）5Si3 and Cr2Nb phases reduced.展开更多
Zr-Y jointly modified silicide coatings were prepared on an Nb-Ti-Si-Cr based ultrahigh temperature alloy by pack cementation process. The wear behaviors of both the base alloy and coatings were comparatively studied ...Zr-Y jointly modified silicide coatings were prepared on an Nb-Ti-Si-Cr based ultrahigh temperature alloy by pack cementation process. The wear behaviors of both the base alloy and coatings were comparatively studied at room temperature and 800 ℃ using SiC balls as the counterpart. The Zr-Y jointly modified silicide coating is mainly composed of a thick （Nb,X）Si2 outer layer and a thin （Ti,Nb）5Si4 inner layer. The coatings possess much higher microhardness than the base alloy. The wear rates of both the base alloy and coatings increase with increasing the sliding loads. However, the coatings have much lower wear rates than the base alloy under the same sliding conditions. The coatings have superior anti-friction property, and can provide effective protection for the base alloy at both room temperature and 800 ℃ in air.展开更多
基金Project (51071124) supported by the National Natural Science Foundation of ChinaProject (20096102110012) supported by the Ministry of Education, China Project (07-TP-2008) supported by the State Key Laboratory of Solidification Processing in Northwestern Polytechnical University,China
文摘To investigate the effects of homogenizing and aging treatments on the microstructure of an Nb-Ti-Cr-Si based ultrahigh temperature alloy,coupons were homogenized at 1 200-1 500 °C for 24 h,and then aged at 1 000 °C for 24 h.The results show that the heat-treated alloy is composed of Nb solid solution（Nbss）,（Nb,X）5Si3 and Cr2Nb phases.With the increase of heat-treatment temperature,previous Nbss dendrites transformed into equiaxed grains,and petal-like Nbss/（Nb,X）5Si3 eutectic colonies gradually changed into small（Nb,X）5Si3 particles distributed in Nbss matrix.A drastic change occurred in the morphology of the Laves phase after homogenizing treatment.Previously coarse Cr2Nb blocks dissolved during homogenizing at temperature above 1 300 °C,and then much finer and crowded Cr2Nb flakes precipitated in the Nbss matrix in cooling.Aging treatment at 1 000 °C for 24 h led to further precipitation of fine particles of Laves phase in Nbss matrix and made the difference in concentrations of Ti,Hf and Al in Nbss,（Nb,X）5Si3 and Cr2Nb phases reduced.
基金Projects(51371145,51431003,U1435201,51401166)supported by the National Natural Science Foundation of ChinaProject(B080401)supported by the Programme of Introducing Talents of Discipline to Universities,China
文摘Zr-Y jointly modified silicide coatings were prepared on an Nb-Ti-Si-Cr based ultrahigh temperature alloy by pack cementation process. The wear behaviors of both the base alloy and coatings were comparatively studied at room temperature and 800 ℃ using SiC balls as the counterpart. The Zr-Y jointly modified silicide coating is mainly composed of a thick （Nb,X）Si2 outer layer and a thin （Ti,Nb）5Si4 inner layer. The coatings possess much higher microhardness than the base alloy. The wear rates of both the base alloy and coatings increase with increasing the sliding loads. However, the coatings have much lower wear rates than the base alloy under the same sliding conditions. The coatings have superior anti-friction property, and can provide effective protection for the base alloy at both room temperature and 800 ℃ in air.
