Effects of cutting depth on the surface microstructure of a Zn-Al alloy during ultra-precision machining

The microstructural changes and phase decomposition at the surface of an ultra-precision machined Zn-Al based alloy were studied using optical microscopy, back-scattered electron microscopy, electron back-scattered diffraction and X-ray diffraction techniques. It was found that with increasing DoC the phase decomposition was accelerated and further increasing DoC might cause a microstructural recovery on the surface of the UPM specimen. UPM induced phase decomposition was discussed in relation to the structural evolution of the chips.     

光学非球曲面器件的超精密磨削加工技术研究

为磨削加工出高精度、高质量的光学非球曲面器件。详尽分析了砂轮的安装及半径等误差对零件加工精度的影响。设计研制出了一套非球曲面磨削系统 ,并用它进行了实验研究。实验结果表明 :要获得高精度的非球曲面器件 ,只有当金刚石砂轮的平均磨粒尺寸低于 10 μm ,并在采用较高的砂轮线速度和较小的进给量的情况下 ,才能实现光学非球曲面的超精密磨削加工 ,经过各种磨削参数的优化选择 ,其非球曲面最终的零件轮廓精度为 0 4 μm ,表面粗糙度Ra优于 0 0 1μm。     

基于误差递减修正法的非球面超精密加工

误差滤波和分离技术是超精密加工中的关键技术之一。采用误差递减法修正加工路径,利用修正的高斯权函数对测量表面进行滤波处理,设计并完成了整个误差递减系统,实现非球面的超精密车削加工,并在很大程度上提高其表面精度(P-V值)。通过实验验证,利用该加工方法,提高了加工效率,可明显地提高非球面的表面精度,最终达到面形精度小于200nm。     

Simulation of the early stage of binary alloy decomposition,based on the free energy density functional method

Based on the free energy density functional method, the early stage of decomposition of a onedimensional binary alloy corresponding to the approximation of regular solutions has been simulated. In the simulation, Gaussian composition fluctuations caused by the initial alloy state are taken into account. The calculation is performed using the block approach implying discretization of the extensive solution volume into independent fragments for each of which the decomposition process is calculated, and then a joint analysis of the formed second phase segregations is performed. It was possible to trace all stages of solid solution decomposition: nucleation, growth, and coalescence (initial stage). The time dependences of the main phase distribution characteristics are calculated: the average size and concentration of the second phase particles, their size distribution function, and the nucleation rate of the second phase particles (clusters). Cluster trajectories in the size–composition space are constructed for the cases of growth and dissolution.     

Features of the ordered phase formation in Au4V alloy

The kinetics of ordering in Au₄V alloy has been studied by X-ray diffraction. The features of ordering, coexisting with the ordered phase decomposition, have been investigated. Coexistence of these processes leads to a nonmonotonic change in the volume fraction of the ordered phase. Possible models of realization of ordering and decomposition processes are considered.     

Micromechanisms of deformation and fracture in a VT6 titanium laminate under impact load

The paper studies the phase composition, microstructure, and mechanisms of plastic deformation and fracture under impact load in a laminate obtained by pressure welding of VT6 titanium alloy sheets. Under impact loading at 20 and -196°C, the material is delaminated into sheet piles with attendant changes in their fracture rate. At fracture surfaces, the initial crystal structure experiences structural phase decomposition which results in dynamic rotations. In fracture and delamination sublayers, the material is fragmented. The effects are more pronounced at T _def = -196°C.     

An Investigation of Phase Diagrams of Decomposing Magnetic Alloys

The interaction of phase decomposition and magnetic ordering processes in an A–B alloy of an arbitrary structure is studied theoretically. The decomposition and magnetization temperatures are calculated. The phase diagrams are constructed and compared with experiment on Fe–Cr, Fe–Co, and Pt–Co alloys.     

Compositionally modulated ripples induced by sputtering of alloy surfaces

Sputtering of an amorphous or crystalline material by an ion beam often results in the formation of periodic nanoscale ripple patterns on the surface. In this Letter, we show that, in the case of alloy surfaces, the differences in the sputter yields and surface diffusivities of the alloy components will also lead to spontaneous modulations in composition that can be in or out of phase with the ripple topography. The degree of this kinetic alloy decomposition can be altered by varying the flux of the ion beam. In the high-temperature and low-flux regime, the degree of decomposition scales linearly with the ion flux, but it scales inversely with the ion flux in the low-temperature, high-flux regime.     

Investigation of decomposition processes in alloy Cu-Ge-Ti

The process of the decomposition of alloy Cu-6 at.% Ge-2.8 at.% Ti in the 400–700°C temperature range was investigated by transmission electron microscopic methods and by a study of the kinetics of the change of electrical resistance. After quenching in water decomposition at 500–600° occurs in two stages. In the first stage the coherent phase precipitates as lamellae with habit plane 100. The second stage is associated with the occurrence of semicoherent lamellae of the same phase. The effect of hardening conditions of the character of decomposition is investigated.     

多晶凝固及后续调幅分解过程的晶体相场法模拟

采用晶体相场模型,模拟了二元合金多晶凝固及后续调幅分解全过程.结果表明,晶体相场模型可完整再现包括形核、生长、粗化、晶界形成等多晶生长过程以及圆满完成从凝固到调幅分解的多相变过程. 关键词： 晶体相场模型 多晶凝固 调幅分解 组织演化     

Modeling phase decomposition and patterning in binary alloy systems subjected to neutron irradiation

We study processes of phase decomposition and patterning in a model of a binary alloy system subjected to sustained irradiation. We exploit the reaction rate theory and generalize the Darken approach of vacancy diffusion to describe generation, recombination, annihilation and spatial interaction of point defects. It is shown that an increase in the defect production rate phase, decomposition processes are replaced by disordering and patterning with vacancy clusters' formation. At elevated damage rates, both phase separation and patterning are accompanied by pattern selection processes. In the framework of numerical simulations, dynamics of phase decomposition and vacancy clusters formation is studied in detail. A change in the morphology of vacancy clusters during irradiation and their statistical properties are discussed.     

Structural features of Ag-Cu alloy films produced by the codeposition of sputtered metals

Solid solutions in the form of alloy coatings are obtained in the entire concentration range of binary system using ion-plasma sputtering and the codeposition of Ag and Cu ultrafine particles. Sstudying the structure of solid solutions shows a change in the FCC-lattice parameters from silver to copper with a characteristic bend corresponding to the eutectic composition of the equilibrium phase diagram. Solid-solution decay begins at 100°C, and their complete decomposition occurs at 250°C. The surface structure of the initial solutions is presented by crystallites 20–30 nm in cross section; after decomposition, their size is less than 100 nm. For the latter, the distortions of the lattice parameters are 0.32% for a solution of Cu in Ag and 0.29% for a solution of Ag in Cu. The method of alloy production can be extended to the systems of metals immiscible in the solid phase.     

An X-ray absorption spectroscopy investigation of the local atomic structure in Cu–Ni–Si alloy after severe plastic deformation and ageing

The local atomic structure of Cu–Ni–Si alloy after severe plastic deformation (SPD) processing and the decomposition of supersaturated solid solution upon annealing were investigated by means of X-ray absorption spectroscopy. The coordination number and interatomic distances were obtained by analyzing experimental extend X-ray absorption fine structure data collected at the Ni K-edge. Results indicate that the environment of Ni atoms in Cu–Ni–Si alloy is strongly influenced by the deformation process. Moreover, ageing at 973 K affects strongly the atomic structure around the Ni atoms in Cu–Ni–Si deformed by equal channel angular pressing and high pressure torsion. This influence is discussed in terms of changes and decomposition features of the Cu–Ni–Si solid solution.     

High-pressure synthesis of A15 Nb3Si phase from amorphous NbSi alloys

An amorphous phase has been produced in a binary Nb-19 at .% Si alloy by rapidly quenching from the molten state. Primary decomposition of the amorphous phase by annealing resulted in the production of a small quantity of the A15 cubic Nb₃Si phase. However, long annealing treatments led to the complete transformation to the equilibrium phases. Application of high pressure of 10 GPa during decomposition of the amorphous phase resulted firstly in the improved stability of the amorphous phase and secondly, in the production of a much larger quantity of the A15 cubic Nb₃Si phase. The lattice parameter of this phase was calculated to be 0.515 nm, in conformity with the previous investigations.     

Thermal analysis study for the phase determination and instable to metastable transformation of the Co–13Cu alloy

The differential thermal analysis (DTA) is utilized to determine the phase boundary and phase equilibria of Co–Cu alloy having a miscibility gap. Regions for various phase i.e., spinodal and coherent binodal, peritectic, magnetic and the transformation from the two phases to α phase transformations are distinctly determined for the Co–13 at%Cu alloy. The obtained results might indicate the continuity of the decomposition kinetics at the boundary between instable and the metastable regions but an activation barrier is needed. The activation energy for the magnetic transformation is determined to be 182.2 ± 2.1 kJ mol^?1.     

Decomposition of solid solution in an alloy under high plastic strain

The kinetics of impurity atmosphere formation and phase precipitation near the triple joints of deformation boundaries of the cellular structure is considered. The decomposition of solid solutions of substitutional impurities when an alloy is under high plastic strain is theoretically analyzed.     

Stability of bulk metastable Fe<Subscript>83</Subscript>B<Subscript>17</Subscript> eutectic alloy prepared by hypercooling method

The bulk metastable Fe₈₃B₁₇ eutectic alloy has been successfully prepared using hypercooling solidification. The bulk alloy consists of αFe and metastable Fe₃B phases, without the stable Fe₂B phase. Upon isothermal annealing, decomposition of the metastable Fe₃B phase (prepared by hypercooling) was investigated, as compared to the corresponding behaviour from amorphous Fe-B alloy. PACS 61.82.Bg; 64.60.-i; 64.60.My; 64.70.Kb; 68.60.Dv     

Mechanical properties of the alloy 36NKhTYu in relation to the mechanisms underlying the precipitation of the γ′ and η phases. III

The kinetic characteristics of the changes in elastic limit, ductility, and stress relaxation taking place in samples of the alloy 36NKhTYu on aging at 700°C are considered in relation to aging time, the measurements being made at 20 and 600°C. The samples are initially taken in five different states induced by various forms of preliminary treatment, being distinguished from one another with respect to grain size, mechanism of γ phase precipitation, and state of the grain boundaries. In order to obtain material with a high elastic limit, working at moderately low temperatures, the discontinuous precipitation of the strengthening phase has certain clear advantages over continuous precipitation. For high working temperatures, in which grain-boundary stress relaxation starts playing an appreciable role, however, it is undesirable that discontinuous decomposition should undergo any major development in the aging of the material.     

基于SVD的超精密工件自寻位加工算法能力评价

为进一步改善超精密表面修形的最终精度、效率与成本,优化超精密自寻位加工的工艺方向与工艺决策过程, 开展了对超精密工件的自寻位加工算法点云融合过程的定量评价研究,提出了基于SVD的自寻位加工算法能力评价方法。首先基于运动学方法建立了点云融合的矩阵表示,分别对平动、转动、复合运动等情况建立了自寻位结果的转换矩阵表示,获得自寻位点云融合转换矩阵;进而对转换矩阵进行奇异值分解得到转换矩阵的奇异值列表;最后将列表中最大奇异值用以表征自寻位加工算法的能力。通过对某型超精密叶片在平动、转动和复合运动、共计1078组自由放置状态进行分析,发现所提出的评价指标在独立平动和独立转动两种任意放置情况下能够正确地表征自寻位加工算法的工艺能力。对于独立平动情况,自寻位加工算法能够正常定位加工,其最大奇异值也与预设偏差较小;对于独立转动情况,当旋转角度小于45°时,均能够正确地进行自寻位加工,最大奇异值差值也趋近于零,旋转角度超过45°时,算法的自寻位加工能力恶化,这一特性能够被所提指标正确捕捉。对于由平动和转动构成的复合运动而言,所提指标显示约35%的情况能够正确进行自寻位加工,其余情况无法进行正确的自寻位加工。结果表明本文所提方法建立的指标能够正确表征自寻位加工算法能力。