A study on coherency strain and precipitate morphologyvia a discrete atom method

Morphological evolution of coherent precipitates is studied by means of a discrete atom method under a plane strain condition with a purely dilatational misfit. The method is predicated upon Hookean atomic interactions and Monte Carlo diffusion and makes no assumption of a specific precipitate shape. Precipitates having elastic constants different from those of the matrix phase are treated in both isotropic and anisotropic elastic systems. Shape evolution is examined under the condition of a constant precipitate size and an isotropic interfacial energy. The results show that in general, an elastically soft precipitate tends to have an equilibrium morphology of low symmetry such as a plate, whereas a hard particle tends to take up a shape of high symmetry such as a circle. Morphological evolution proceeds through dynamic activities of coherency-induced interfacial waves whose wavelength depends upon the difference in elastic constants, precipitate geometry, anisotropy, and diffusion temperature. Coherency-induced interfacial waves seem to be responsible for the protrusions often observed along elastically hard directions in γ′ particles of Ni-base superalloys and also to be a source for fresh ledges for growthvia the ledge mechanism. For a highly nonequilibrium precipitate, first splitting followed by coalescence appears to be a common feature in achieving its equilibrium morphology. This article is based on a presentation made during TMS/ASM Materials Week in the symposium entitled “Atomistic Mechanisms of Nucleation and Growth in Solids,” organized in honor of H.I. Aaronson’s 70th Anniversary and given October 3–5, 1994, in Rosemont, Illinois.     

The influence of coherency strain on the elevated temperature tensile behavior of Ni-15Cr-AI-Ti-Mo alloys

The effect of coherency strain on elevated temperature tensile strength was examined in a model, two-phase y’-strengthened Ni-15Cr-Al-Ti-Mo alloy series. The temperature dependence of coherency strain as represented by the γ-γ’ mismatch was determined over the temperature range 25 to 800 °C. The flow stress incrementAσ _γ, due to precipitation of γ’, was found to correlate well to the magnitude of the γ-γ’ mismatch over the same temperature interval. The correlation was strongest for high misfit alloys regardless of the Antiphase Boundary Energy (APBE). The predominance of by-pass type dislocation-particle interactions in high coherency alloys confirms that strengthening is primarily due to coherency strains. Conversely, alloys with low misfit exhibit two distinct particle shear mechanisms believed to be dependent upon the relative APBE and matrix stacking fault energy of the alloy.     

不同矿物对硅酸盐细菌JXF菌株生长的抑制作用

硅酸盐细菌在不同的固体培养基和液体培养基中培养2～3d后,菌种繁殖产生的细菌数、细菌及荚膜直径、发酵液中黏度的大小顺序为:硅酸盐矿物培养基＞铝土矿培养基＞赤铁矿培养基＞阿什比基质培养基,菌种在不同的硅酸盐矿物培养基中生长特性差别不大.菌种驯化培养试验表明,不同类型矿物对细菌的生长抑制作用表现为:赤铁矿＞铝土矿＞硅酸盐矿物.摇瓶脱硅试验表明,驯化菌种的脱硅率要比未驯化菌种的平均高15%左右,不同来源的硅酸盐细菌均具有较好的脱硅能力.     

The strain effect of dam on intrauterine incisal growth in mouse fetuses

The embryo transfer technique was carried out to examine the strain effect of dams on the intrauterine incisal growth of mouse fetuses. A mean of nine DDD/Qdj embryos was transferred to each female recipient of the four strains (DDD/Qdj, C3H/Qdjl C57BL/Qdj, and DBA/IJ Sea). The dam's weight, the litter size, the gestation period and the newborn offspring weight were recorded. The mandibular incisal size of the newborn offspring was measured two-dimensionally by means of an image analyzing system. Statistical analyses of the incisal size of the DDD/Qdj newborn offspring delivered from the four strains of recipients showed the following results: 1) There were significant interstrain differences in the dam's weight and the newborn offspring weight, but not in the litter size and the gestation period among the four strains of recipients. 2) There was an inverse relation between the litter size and the mandibular incisal size while there were direct relations between the dam's weight and the mandibular incisal size, and between the newborn offspring weight and the mandibular incisal size. 3) There was a significant strain effect of the dam on the mandibular incisal size of the newborn offspring. 4) After eliminating the effects of the litter size, the gestation period, and the newborn offspring weight on the mandibular incisal size of the DDD/Qdj newborn offspring developed in the four strains of dams, a significant interstrain difference in the adjusted mandibular incisal size was found (C3H/Qdj > DBA/IJ Sea > C57BL/Qdj > DDD/Qdj), suggesting that the uteri of the C3H/Qdj strain of dams provided a more suitable environment for the intrauterine incisal growth than those of the other three strains of dams. Thus, it is concluded that the strain effect of dam played an important role in the intrauterine incisal growth of mouse fetuses.     

Computer simulation of microstructure

The microstructure that results from a martensitic transformation is largely determined by the elastic strain that develops as martensite particles grow and interact. To study the development of microstructure, it is useful to have computer simulation models that mimic the process. One such model is a finite-element model in which the transforming body is divided into elementary cells that transform when it is energetically favorable to do so. Using the linear elastic theory, the elastic energy of an arbitrary distribution of transformed cells can be calculated, and the elastic strain field can be monitored as the transformation proceeds. In the present article, a model of this type is developed and evaluated by testing its ability to generate the preferred configurations of isolated martensite particles, which can be predicted analytically from the linear elastic theory. Both two- and three-dimensional versions of the model are used. The computer model is in good agreement with analytic theory when the latter predicts single-variant martensite particles. The three-dimensional model also generates twinned martensite in reason- able agreement with the analytic predictions when the fractions of the two variants in the particle are near 0.5. It is less successful in reproducing twinned martensites when one variant is dom- inant; however, in this case, it does produce unusual morphologies, such as “butterfly mar- tensite,” that have been observed experimentally. Neither the analytic theory nor the computer simulation predicts twinned martensites in the two-dimensional transformations considered here, revealing an inherent limitation of studies that are restricted to two dimensions.     

Computer simulation of VC

A computer simulation technique was developed on the basis of the interaction between carbide precipitation and moving γ/α interfaces for predicting both the interphase precipitation kinetics and the microstructural evolution during austenite-to-ferrite transformation. Theoretical models for the calculation of the driving and pinning forces exerted on a moving interface boundary are described. The variations of the two forces lead to a phenomenon of periodic pinning and unpinning of the interface and, in turn, the characteristic microstructure of parallel sheet particles which is often associated with the interphase precipitation. The experimental data reported for a series of V-bearing steels were analyzed using the computer simulation technique. Three un- known physical parameters,i.e., the thickness of an incoherent interface or the height of the ledge of a coherent interface, the diffusion coefficient of V at the γ/α interface, and the co- herence loss parameter of a VC nucleus, were determined. The calculated intersheet spacing, precipitate size, and precipitation start time all show a good correlation with the experimental observations.     

Computer simulation of fatty acids

Fatty acids modified by sulfhydric collectors are investigated. Three-dimensional molecular models are constructed for these acids and the main computer parameters of the total steric energy are determined. Based on the computer design, new reagents are suggested and molecular models are constructed and the total steric energy is calculated for them.     

Computer simulation of thinking.

"The nub of the simulation problem involves the use of similar types of 'programs' of 'instructions' to the machine in order to reproduce the steps an individual goes through in thinking out the solution to a difficult problem." Simulation methods "have a tremendous role in sharpening our formulations concerning mental processes and phenomena." The "simulation of human responses has the same overwhelming advantages for our understanding of behavioral phenomena as similar methods in other sciences." Research "on simulation of complex psychological processes is yielding results of increasing importance." From Psyc Abstracts 36:02:2CM87H. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Computer simulation of movement-generating cross-bridges

A stochastic computational method was developed to study properties of cross-bridge models for muscle contraction, by following the time history of individual cross-bridge model of Andrew Huxley (1957) and a modified two-state model with more realistic behavior during steady stretching are used as examples. The method can readily compute steady-state force during shortening and stretching and force-transients following rapid changes in length. Computations of velocity with a steady load and of velocity transients are more sensitive to the randomness inherent in the stochastic method.     

Protective effect of a tetracycline-sensitive strain of Escherichia coli on the growth of a tetracyclic-resistant strain in the presence of tetracycline in a coculture

The addition of tetracycline to a culture of a tetracycline-sensitive strain of Escherichia coli leads to the appearance in the medium of a chemical compound (or compounds) that in part relieve the inhibition of growth of a tetracycline-resistant strain by a high concentration of the antibiotic. An increase in the growth rate can be as high as 50%.     

Effects of growth mechanism on solution kinetics

The solution kinetics of second phases were studied as a function of various initial conditions resulting from either diffusion-controlled growth or interface-reaction-controlled growth prior to solution treatment. Calculations of solution kinetics based upon a planar, finite-geometry model were carried out using numerical methods and computer techniques. It was shown that second-phase particles formed by diffusion-controlled growth and existing in a matrix containing concentration gradients exhibit dissolution kinetics that differ markedly from those of particles formed by interface-reaction-controlled growth. An experimental analysis designed to use solution kinetics measurements to obtain the mechanism of growth of second phases is discussed. The effects of linear-gradient assumptions that have been used in an existing, closed-form, infinite-geometry model are evaluated. Formerly, Graduate Student in the Department of Metallurgical Engineering, Drexel University, Philadelphia, Pa.     

Computer simulation of consumable melted slabs

A mathematical model has been developed to simulate two-dimensional heat flow for a slab ingot produced as a remelted product. Various heat flow parameters have been studied to determine the influence of changes in them on local solidification time. The parameters which show the greatest influence are the heat transfer coefficient and the thickness of the slab. The rate of addition of material changes the depth of the molten pool, but does not affect local solidification time.     

聚合射流氧枪射流特性的数值模拟及应用

利用Fluent软件对电炉炼钢中两种常用氧枪,聚合射流氧枪和普通超音速氧枪进行了射流特性的数值模拟,分析了保护气位置、射流角度及压强对聚合射流氧枪射流特性的影响,并在天津钢铁集团公司110t电炉进行了生产实践。结果表明,使用聚合射流氧枪后电炉冶炼效果改善,平均冶炼周期缩短10～15min,各项消耗指标改善。