Jun ZHANG
材料科学技术（英）
An ideal method has been established for calculating the precipitation ofα2 ordered phase in near-α titanium alloys based on the theory on the critical electron concentration for the precipitation of α2 ordered phase in near-α titanium alloys. With complete precipitation of α2 phase in near-α titanium alloys, the alloys can be considered to be composed of two parts: (1) the ®2 ordered phase with the stoichiometric atomic ratio of Ti3X; (2) the disorder solid solution with the critical composition in which the α2 ordered phase is just unable to precipitate. By using this method, the volume fractions of α2 ordered phase precipitated in Ti-Al, Ti-Sn, Ti-Al-Sn-Zr alloys with various Al, Sn and/or Zr contents have been calculated. The influences of Al and Sn on the precipitation of α2 ordered phase are discussed. The calculating results show substantial agreement with the experimental ones.
关键词:
Ordered α2 phase
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2
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phase
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precipitation
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electron
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
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null
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null
Jun ZHANG
材料科学技术（英）
An empirical formula for composition demixing analysis in cathodic arc ion plating using alloy target is established based on the concepts of average charged state and relative demixing parameter. The level of composition demixing effect is presented by demixing degree of one element. For binary constituent alloy target, the composition change trend in coating is discussed and the limit of demixing degree for each element is determined. The content of one element with higher average charged state gets larger in coating than in alloy target, at meantime, the content of one element with lower average charged state gets less. For each one of the two constituents, the less the atom percent in alloy target, the larger the difference of its contents between the coating and the target. For triple constituent alloy target, the content change of one element with moderate average charged state is discussed in detail. Its content in coating getting larger or less is determined by the combination result of the contents of the other two elements in alloy target. For a given content of the element with moderate average charged state in triple alloy target, the content deviation level of that element from coating to alloy target will be not larger than that using binary alloy target containing only that element and one of the two others. According to the wanted coating composition, the composition design of alloy target is easily deduced from the formula.
关键词:
Cathodic arc ion plating
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arc
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ion
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plating
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alloy
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coating
,
a
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:
Jun ZHANG
材料科学技术（英）
The composition from alloy cathode target to alloy coating generally changes to some extent in multi-are ion plating. This demixing effect leads to the difficulties in the control of alloy composition of coating and in the design of composition of alloy cathode target. A new simple formula, a(n) = [(a(n)(o) . f(n))/Sigma(i)(a(i)(o) . f(i))].100%, is proposed in present work to deal with the problem. According to this formula, the composition of alloy coating can be calculated by means of the degrees of ionization of alloy elements. The results of calculation agree with the experimental ones within very limited error range. Modifying the formula into another form, a(n)(o) = [(a(n)/f(n))/Sigma(i)(a(i)/f(i))].100%, the design for alloy composition of cathode target can be conveniently carried out, and the ideal composition of alloy coating can be obtained.
关键词:
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
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null
,
null
Jun ZHANG
,
Qian LIU
,
Lin WANG
材料科学技术（英）
Fine and coarse aggregates play an important role in the fracture of concrete. However, quantitative information available on the effect of the coarse aggregate size on the fracture properties of concrete is still limited. In the present paper, the effect of coarse aggregate size (single grade of 5～10, 10～16, 16～20 and 20～25 mm) on stress-crack opening (σ-ω) relation in normal and high strength concretes (compressive strength of 40 and 80 MPa, respectively) was studied. The investigation was based on three-point bending tests implemented by fictitious crack analysis. The result shows that coarse aggregate size and cement matrix strength significantly influence the shape ofσ-ω curve. For a given total aggregate content, in normal strength concrete, smaller size of aggregate leads to a high tensile strength and a sharp stress drop after the peak stress. The smaller the coarse aggregate, the steeper the σ-ωcurve. By contrast, in high strength concrete, the effect of aggregate size on σ-ω relation almost vanishes. A similar σ-ω relation is obtained for the concrete except for the case of 20～25 mm coarse aggregate size. The stress drop after the peak stress is more significant for high strength concrete than that for normal strength concrete. Meanwhile, the smaller the coarse aggregate size, the higher the flexural strength. Fracture energy and characteristic length increase with increasing coarse aggregate size in both normal and high strength concretes.
关键词:
Aggregate size
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null
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null
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null
