硅表面上电荷分布的晶向关系

本文分别用Si_(16)H_(21)模拟Si(113),Si_(35)H_(30)模拟Si(112)高密勒指数表面,用Si_(37)H_(39)模拟Si(111)及Si_(19)H_(18)模拟Si(100)表面.通过SCF-LCAC-CNDO理论计算,研究了各种表面上的净电荷分布.发现,各种表面上存在不同程度且不同分布的净电荷,表面原子sp^3轨道中的电荷做了重新分布,净电荷较多地局域在悬键方向上.表面上台阶的存在强烈地影响着表面净电荷转移的性质.此现象在Si(112)面上尤其突出.本文据此解释了不同晶面上附加表面电偶极子及态密度等实验结果.

A new rhombohedral phase and its 48 variants inβtitanium alloy

A new rhombohedral phase(termed R′)in a solution-aging-treated titanium alloy(Ti-4.5Al-6.5Mo-2Cr-2Nb-1V-1Sn-1Zr,wt.%)was identified.Its accurate Bravais lattice parameters were determined by a novel unit cell reconstruction method based on conventional selected-area electron diffraction(SAED)technique.The orientation relationship between R'phase and BCC phase was revealed.The results show that the R′phase is found to have 48crystallographically equivalent variants,resulting in rather complicated SAED patterns with high-order reflections.A series of in-situ SAED patterns were taken along both low-and high-index zone axes,and all weak and strong reflections arising from the 48 variants were properly explained and directly assigned with self-consistent Miller indices,confirming the presence of the rhombohedral phase.Additionally,some criteria were also proposed for evaluating the indexed results,which together with the Bravais lattice reconstruction method shed light on the microstructure characterization of even unknown phases in other alloys.

Microstructures of TiN,TiAlN and TiAlVN coatings on AISI M2 steel deposited by magnetron reactive sputtering

In order to study the effect of the microstructure with Al and V added TiN coatings, TiN, TiAlN and TiAlVN coatings were deposited on AISI M2 high-speed steels by magnetron reactive sputtering. The microstructures of all the coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that the addition of Al into TiN coatings reduces their lattice constant, but a further addition of V into TiAlN coatings increases their lattice constant. Moreover, the growth morphologies for TiN, TiAlN, and TiAlVN indicate that adding Al and V has a tendency to improve the columnar structure. The (111) and (200) orientations of TiN, TiAlN, and TiAlVN are identified. Theε(Fe3N-Fe2N) phase occurs because a small amount of Fe is present in the coatings. The interlayers of TiAlN and TiAlVN have the preferred (01 1 0) orientation. The texture (columnar) structure of the (111) and (200) orientations is observed in the TiAlN and TiAlVN coatings. An orientation relationship of (01 1 0)α-Ti//(110)T.M occurs between the interlayer and tempered martensite (T.M) in TiAlVN.

Evolution of coordination between α and β phases for two-phase titanium alloy during hot working

The evolution of coordination betweenαandβphases for a two-phase titanium alloy was investigated.For this purpose,hot compression and heat treatment under different conditions were carried out.The results show that the ability of coordinated deformation betweenαandβphases can influence uniformity of microstructure evolution.Specifically,αphase maintains the lamellar structure andβphase has a low degree of recrystallization when the ability of coordinated deformation is good.In this case,αandβphases still maintain the BOR(Burgers orientation relationship),and their interface relationship is not destroyed even at large deformation.Both of the deformation extent ofαlamellae and recrystallization degree ofβphase increase with the decline of ability of coordinated deformation.Theαphase only maintains the BOR withβphase on one side,while the uncoordinated rotation with theβphase on the other side occurs within 10°.Theαandβphases rotate asynchronously when ability of coordinated deformation is poor.The degree of interface dislocation increases,andαandβphases deviate from the BOR.

Nucleation potency prediction of LaB_6 with E2EM model and its influence on microstructure and tensile properties of Al-7Si-0.3Mg alloy

The edge-to-edge matching(E2EM)crystallographic model was used to predict the orientation relationships(ORs)between LaB6 and Al.Three different possible ORs can be predicted between LaB6 and Al,which are(100)Al||(100)LaB6,[001]Al||[001]LaB6;(110)Al||(110)LaB6,[001]Al||[001]LaB6;and(111)Al||(111)LaB6,[011]Al||[011]LaB6.The prediction results are perfectly confirmed through TEM analysis and prove the nucleation potency of LaB6.The refining efficacy of Al-2La-1B refiner and its influence on the tensile properties were investigated in the as-cast Al-7Si-0.3Mg alloy.According to the results,LaB6 has higher nucleation potency than TiB2,leading to better grain refining efficacy of Al-2La-1B refiner in the as-cast Al-7Si-0.3Mg alloy.Regarding the mechanical performances,tensile properties of the as-cast Al-7Si-0.3Mg casting alloy are prominently improved after addition of Al-2La-1B refiner,due to the refined microstructures.

Multiple eutectic orientation relationships in undercooled Ni-38wt.%Si eutectic alloy

Eutectic orientation relationships(EORs) in an undercooled Ni-38 wt.%Si alloy were analyzed by electron backscatter diffraction. A total of seven EORs were identified, and three of them were found at the under-cooling degree ?T≈31 K. It is found that their orientations of the primary NiSi phase are same but the misorientation between the neighboring NiSi2 grains can be either 50° or 60°. The multiple EORs were ascribed to a possible change in the growth direction of the primary phase, the change of the primary phase from the NiSi phase to the NiSi2 phase, and the transition from coupled to uncoupled eutectic growth. The current work shows that epitaxial growth of the second eutectic phase on the primary eutectic phase can obey either a single EOR or multiple EORs, which is a unique phenomenon.