Guangye ZHANG
,
Xinghao DU
,
Jianting GUO
,
Hengqiang YE
材料科学技术（英文）
Brittle-to-ductile transition (BDT) behavior and creep behavior of extruded NiAl-25Cr alloy at elevated temperatures were investigated. The results reveal that the alloy exhibits obvious BDT behavior with the increase in temperature and BDT temperature (BDTT) is sensitive to initial strain rate. When the initial strain rate increases by two orders of magnitude, BDTT has an increase of approximate 80 K. The creep data in the temperature range of 1073～1123 K reveal two distinct regions of creep behavior in this material. At lower temperature, the creep characteristics are consistent with structural controlled creep process where creep deformation is controlled by dislocation climb. At higher temperature, the creep characteristics are consistent with mobility-controlled deformation where viscous glide of dislocations controls creep. The apparent activation energy determined by creep in both regions exceeds the value for lattice self-diffusion in NiAl by a considerable amount. This can be explained in terms of the simultaneous deformation of second phase particles (γ'-Ni3Al and α-Cr phase) along NiAl matrix during creep.
关键词:
NiAl
,
null
,
null
,
null
,
null
Limin LIU
,
Shaoqing WANG
,
Hengqiang YE
材料科学技术（英文）
The interface structure, work of adhesion, and bonding character of the polar TiC/Ti interface have been examined by the first-principles density functional plane-wave pseudopotential calculations. Both Ti- and C-terminated interfaces including six different interface structures were calculated, which present quite different features. For the Ti-terminated interface, the interfacial Ti-Ti bond has a strong metallic and weak covalent character; while for the C-terminated interface, the interfacial bond is a strong polar covalent interaction between the Ti-3d and C-2p orbital. The work of adhesion of C-terminated interface is nearly 9 J/m2 stronger than that of the Ti-terminated. It is found that each termination has relatively large work of adhesion, which is consistent with other polar interfaces.
关键词:
First-principles
,
null
,
null
,
null
Jiuzhou ZHAO
,
Dongming LIU
,
Hengqiang YE
材料科学技术（英文）
In order to understand the solidification process of an atomized droplet and predict the fraction solidification of droplets with flight distance during spray forming, a numerical model based on the population dynamics approach is developed to describe the microstructure evolution under the common action of the nucleation and growth of grains. The model is coupled with droplets heat transfer controlling equations and solved for Al-4.5~wt~pct Cu alloy. It is demonstrated that the numerical results describe the solidification process well.
关键词:
Rapid solidification
,
null
,
null
,
null
Chiwei LUNG
,
Enke TIAN
,
Hengqiang YE
材料科学技术（英文）
Introducing the stress distribution near grain boundaries to improve the dislocation pileup model for the Halt-Petch (H-P) relation, the continuous distribution of dislocations in the pileup could be solved by means of Tschebysheff polynomials for the Hilbert transformation. An analytical formula of the stress intensity factor for the dislocation pileup is obtained. The reverse H-P relation may be explained by the modified dislocation-pileup-model.
关键词:
Shouliang BU
,
Shaoqing WANG
,
Hengqiang YE
材料科学技术（英文）
It is shown that synchronization, in a weak sense, can be achieved between two-parameter non-matching systems by using the adaptive control method. In essence, this requires just a scalar signal transmitted from the drive to the response system. Two typical chaotic systems, i.e., Lorenz and Rőssler system, are taken as examples of applications in this paper.
关键词:
Chaotic systems
,
null
,
null
赵显武
,
褚武扬
,
宿彦京
,
高克玮
,
乔利杰
金属学报
doi:10.3321/j.issn:0412-1961.2005.07.007
研究了不同极化状态下PZT-5H铁电陶瓷压痕裂纹在应力和电场单独作用以及耦合作用下的扩展行为.结果表明,压痕裂纹残余应力引起的应力场强度因子近似等于断裂韧性.对沿长度方向极化的试样,正、负电场均能引起压痕裂纹的扩展,但正电场的作用更大.电场和应力的耦合作用表现为对应力的线性叠加.电场引起的内应力σin=(φ)YE/[1.16(1-v2)EC],式中(4)=(2.75-5.71)×10-4,与PZT的极化状态有关.
关键词:
PZT铁电陶瓷
,
压痕裂纹
,
应力和电场耦合
陈嘉良
,
李万捷
高分子材料科学与工程
单体丙烯酰胺(AM)和甲基丙烯酰氧乙基三甲基氯化铵(DMC)通过2,2'-偶氮(2-脒基丙烷)二氢氯化物(V-50)引发,在紫外光的作用下合成P(AM-co-DMC)共聚物.通过毛细管膨胀计法测定了其反应动力学.随着单体浓度、引发剂浓度、反应温度的升高,反应速率也随之增加.在控制低转化率的条件下,以Fineman-Ross、Kelen-Tudos及Ye2rielevBrokhina-Roskin法计算了单体竞聚率.得出了在紫外光与引发剂共同作用下,AM和DMC共聚单体的反应级数为2.2502,引发剂的反应级数为0.5032,反应活化能为38.1920kJ/mol,AM和DMC的竞聚率分别为2.3398和0.2849.
关键词:
共聚
,
动力学
,
竞聚率
,
紫外光
,
丙烯酰胺
Journal of Applied Physics
Using the full potential linearized augmented plane wave method based on the spin density functional theory, we investigate the ferromagnetic properties, the electronic structure, and the formation energy of Ga(0.9375)M(0.0625)N (M=vacancy, Ca). The calculations indicate that both cases prefer ferromagnetic ground state. The magnetic moments mainly come from the N atoms surrounding the defect centers, which are different from the conventional diluted magnetic semiconductor. High formation energy for the Ga vacancy Suggests that the defect concentration is too low to result in the ferromagnetic GaN. The formation energy for the two substitutional (Ca(Ga),Ca(N)) and two interstitial sites (tetrahedral T, Ca(i-T) and octahedral O, Ca(i-O)) doped configurations indicates that Ca prefers the substitutional Ga in GaN. The defect concentrations for the Ga(0.9375)Ca(0.0625)N under thermal equilibrium N-rich and N-realistic growth conditions are also discussed, respectively. The calculations show that defect concentration under N-rich condition can readily reach 7%, while under N-realistic growth condition, the maximum defect concentration is as low as 1.71% when the growth temperature increases to 1100 K (melting point of GaN). These results suggest that it would be a little difficult to achieve ferromagnetic state for Ga(0.9375)Ca(0.0625)N using the chemical-equilibrium fabrication method, such as chemical precipitation. Using the same method as that for Cu-doped ZnO [L. H. Ye et al., Phys. Rev. B 73, 033203 (2006)], the transition temperature of Ga(0.9375)Ca(0.0625)N may be close to room temperature. (C) 2008 American Institute of Physics.
关键词:
generalized gradient approximation;doped zno;gan;semiconductors;calcium;systems;origin
于红超
,
康海笑
,
焦正波
,
吕功煊
,
毕迎普
催化学报
doi:10.1016/S1872-2067(15)60938-X
半导体光催化材料既可以利用太阳能催化分解水制氢和降解各种有机污染物，同时还可以将温室气体CO2还原成有机低碳烷烃燃料，因此光催化是解决当今能源和环境问题最理想的途径之一.然而，目前所报道的可见光光催化材料大多具有较高的光生载流子复合率和较差的可见光吸收，导致其量子效率较低.因此，开发新型高效可见光光催化材料，拓展半导体材料光谱响应范围以及促进光生电子和空穴有效分离，成为目前光催化材料研究领域急需解决的科学问题.2010年Ye等首次报道了Ag3PO4在光催化中的应用，该材料表现出优异的光催化分解水制氧及降解有机污染物性能，在光吸收波长大于420 nm时的量子效率达到90%.然而，作为一种新型光催化材料，其组成、结构和晶面等对光催化性能的影响尚不清楚.因此，我们开展了Ag3PO4半导体纳米材料的表面微观结构调控研究，创制了一系列具有特殊形貌和选择暴露晶面的Ag3PO4基可见光催化材料，其表现出独特的光催化氧化性能.例如，利用金属络合法制备了具有(100)，(110)，(111)，(221)和(332)等晶面的Ag3PO4晶体，发现通过调控其暴露晶面可进一步提高光催化性能.利用Ag纳米材料所具有的独特表面等离子体共振效应以及良好的导电性，构建了Ag/Ag3PO4核壳型纳米线、项链状Ag/Ag3PO4纳米线、项链状及均匀分布的Ag3PO4/PAN纳米复合纤维等异质光催化材料，提高了光生电子-空穴的分离效率，实现了有机污染物的高效催化氧化消除.然而，由于Ag3PO4在光催化反应过程中的稳定性较差以及成本较高，严重限制了其实际应用.因此，设计和制备具有高稳定性、低成本的Ag3PO4光催化材料成为目前急需开展的研究领域.本文以Ba3(PO4)2纳米片为模板和磷酸离子源，通过阳离子置换法一步制备了具有中空结构的Ba离子掺杂Ag3PO4光催化材料. ；光催化结果表明， Ba离子的掺杂不但可以有效提高Ag3PO4光催化活性，并且可改变降解有机污染物甲基橙(MO)和罗丹明B(RhB)的选择性，实现优先降解MO.另外，此法制备的Ag3PO4材料经重复使用多次后仍表现出较高的光催化性能.进一步研究表明， Ba离子掺杂增强了Ag3PO4的表面电负性，因而吸附具有负电性的MO能力增加，使其光催化性能提高，此外，该法还可用于制备Ba3(PO4)2/Ag3PO4复合光催化材料，当Ag3PO4含量为40%时，该复合材料具有与纯相Ag3PO4相同的光催化剂活性.由此可见，通过合理掺杂金属离子及形成复合结构可以有效提高Ag3PO4光催化材料的活性和稳定性，降低Ag3PO4用量，这对Ag3PO4光催化材料的设计与改进具有一定指导意义.
关键词:
光催化
,
磷酸银
,
中空纳米片
,
钡掺杂
