Geping LI
,
Dong LI
,
Yuyin LIU and Zhuangqi HU (Institute of Metal Research
,
Chinese Academy of Sciences
,
Shenyang
,
110015
,
China)
材料科学技术（英）
The morphology of the melt-equenched Ti-5Al-4Sn-2Zr-1Mo-9.25Si-1Nd alloy is uniformly distributed Nd-rich phase particles in matrix. The particles within grains are spherical, and the particles at grain boundaries are elliptical. The Nd-rich phase particle calculated is 6.6 nm in diameter, which is within the 6-15 nm range of average particle diameter experimentally ob served in the alloy The practical interfsce velocity (0.5 m/s) is much greater than the critical velocity (0.15 m/s), hence the Nd-rich phase particles are trapped by the liquid-solid interface
关键词:
Wenbin SHENG
,
Dong LI
,
Rui YANG
,
Yuyin LIU
,
Jingjie GUO
,
Jun JIA
材料科学技术（英）
Ti-48Al-2Cr-2Nb automobile exhaust valves were formed with permanent mold centrifugal cast method and their surface layer structure, microstructure, elements distribution and mechanical properties were analyzed by SEM, XRD and EMPA etc. Furthermore, the HIPped valves were tested on 483Q diesel engine. Results showed that the element distribution of TiAl based alloy exhaust valves was uniform and their microstructure was refined. The typical mechanical properties of HiPped exhaust valves were sigma (b)=670 MPa, sigma (0.2)=527.5 MPa and delta =3%. Engine test showed that the valves had excellent airtightness and wear resistance properties and satisfied the requirements of engine successfully.
关键词:
Yulin HAO
,
Rui YANG
,
Yuyou CUI
,
Dong LI
,
Wanfu GAO
材料科学技术（英）
Room temperature compression properties of Ti-51Al-(1-2)X and Ti-26Al-(1-2)X alloys (X = V, Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, Ta, Ga or Sn) were measured in oder to examine how the compression deformability correlates with the site occupancies of the alloying elements in γ-TiAl and α2-Ti3Al. The results showed that, for the γ phase, the compression ratio is not related to the site preference of the alloying elements in a simple way. For the α2 phase, the following correlation was observed between the compression ratio and the site occupancies of the investigated elements, those which occupy Al sites decrease the deformability, while those occupying Ti sites (except V) improve the deformability of the α2 phase. Compression properties of dual-phase TiAl alloys based on Ti-46Al-(1, 3, 5)X were also measured at room temperature to test a hypothetical mechanism of ductilization based on mechanical compatibility at phase interface. It was concluded that no simple relationship exists between the deformability of the dual-phase alloys and the properties of their constituent phases.
关键词:
Jun ZHANG
,
Qingjiang WANG
,
Yuyin LIU
,
Li LI
,
Dong LI
材料科学技术（英）
The characteristic of the precipitation and growth of α2 ordered phase during aging treatment in near αTi alloys have been investigated in terms of the influences of aging temperature, aging time and aging manner. The results exhibit that aging temperatures influence the distribution ofα2 phase precipitated and cause the changes in growth speed ofα2 phase. For various aging temperatures, the time to finish precipitation ofα2 phase is different. The facts that various distribution characteristics and growth speed ofα2 ordered phase are caused by changed aging condition imply optimal selection and control for precipitation ofα2 ordered phase reachable. Some discussions on adoptable aging steps are presented.
关键词:
α2 ordered phase
,
null
,
null
Jun ZHANG
,
Dong LI
材料科学技术（英）
A series of Ti-Al-Sn-Zr-Mo-Si-Nd alloys with various content of Al were solution treated in alpha+beta phase field and air-cooled. The precipitation of α(2) phase in cooling was investigated by transmission electron microscopic analysis. The precipitation characteristic of α(2) phase was discussed. The precipitation of α(2) phase would proceed by the nucleation and growth of α(2) phase dependent on the diffusion of Al atoms. And a comparison on the difference of precipitation of α(2) phase was carried out under the conditions of air-cooling and quenching in water. The investigation showed that the air-cooling and even quenching could supply enough time for the precipitation and growth of α(2) phase when Al content reached a certain value even though far away from the stoichiometric composition of Ti3Al.
关键词:
Weimin MAO
,
Dong LI
材料科学技术（英）
The image stress of straight screw dislocations parallel to the medium surface covered by thin heterogeneous films was analyzed and deduced, in order to calculate the image shear stress. The relationship between image stress and distance from the screw dislocation to the interface of pure aluminum and its oxide covering was calculated based on the analysis. It was shown quantitatively that a sign conversion of the image stress appears in the case of thin oxide covering, while dislocation would pile up near the interface because of the possible slips of the screw dislocations induced by the image stress, which might break down the very thin oxide covering. Further investigation on edge dislocations or other dislocation configurations need to be done.
关键词:
Dislocation
,
null
,
null
,
null
,
null
,
null
,
null
Jun ZHANG
,
Dong LI
材料科学技术（英）
The precipitation characteristics of the a2 ordered phase in Ti-Al-Sn-Zr-Mo-Si-Nd alloys with various content of Al, under different aging conditions, were investigated. The distribution and size of the a2 ordered phase changed with temperature and Al content. The dislocations were the only places where the a2 ordered phase could precipitate at higher temperature near the critical transformation temperature for each alloy experimented. With the addition of Al content, the critical transformation temperature of a2 ordered phase increased. When the aging temperature was relatively low (650ºC), the precedent precipitation of a2 ordered phase took place in primary a phase at the early stage of aging, in the duplex microstructure (the primary a with the transformed b) of the alloys with lower Al content. But after certain aging time (50h), the size of a2 particles was almost equal in both the primary a and the transformed b. And no obvious growth of a2 particles could be observed after 50 h.
关键词:
Ti-Al-Sn-Zr-Mo-Si-Nd alloys
,
null
,
null
Guoxing ZHANG
,
Qiang KANG
,
Nanlin SHI
,
Geping LI
,
Dong LI
材料科学技术（英）
In order to evaluate the interfacial reaction, a SiCf/Ti (TA1) composite was fabricated by a vacuum hot pressing method and then heat-treated in vacuum at 800℃ for up to 100 h. The elemental distributions of C, Si and Ti at the interfacial reaction zone were investigated. It was found that the reaction zone occurs during the fabrication process and continuously grows at high temperature because the Si and C atoms diffuse from SiC fibers to the matrix and Ti atoms diffuse in the opposite direction. The growth of the reaction zone is diffusion controlled and the mechanism of the reaction can be described by a reactive diffusion model of solid-state growth of an AmBn layer between two elementary substances A and B.
关键词:
SiCf/Ti (TA1) composite
,
null
,
null
Dongsheng XU
,
Dong LI
,
Zhuangqi HU
材料科学技术（英）
The substitution behavior of some alloying elements in CoZr is investigated using the discrete variational Xa cluster method. The method proposed by the author to predict the substitution behavior is amended to consider the local lattice relaxation. A diagram is drawn based on the binding energies of clusters with alloying elements taking either Co or Zr site. Two straight lines on the diagram separate the alloying elements into three groups with different substitution behavior. The elements above the upper line will take Zr sites and those below the lower line will take Co sites regardless of the composition. The substitution behavior of elements in between the two lines will be affected by the alloy composition. The concept of site competition and step ordering is proposed.
关键词:
