Influence of crystallography upon critical nucleus shapes and kinetics of homogeneous F.C.C.-F.C.C. nucleation—II. The non-classical regime

In a previous paper, the shape of the critical nucleus and its influence upon nucleation kinetics were studied at near zero supersaturation, i.e. in the classical nucleation regime, using a discrete lattice plane model of the coherent interphase boundary energy. In order to extend these studies to higher supersaturations, a discrete lattice point model, based on a formalism developed by Cook, de Fontaine and Hilliard, is employed in the present paper and applied to homogeneous nucleation of coherent f.c.c. precipitates in an f.c.c. matrix. Concentration profiles and free energies of formation of critical nuclei are calculated from this model as a function of temperature and supersaturation and compared with results obtained from the Cahn-Hilliard continuum non-classical model and the previously used discrete lattice plane classical model. As predicted in effect by Cahn and Hilliard, the three models converge at very low supersaturations, and the continuum and the discrete lattice point (but not the classical discrete lattice plane) models also do so near the spinodal. Thus the most important differences between the continuum and the discrete lattice point models develop at intermediate supersaturations. The main advantages of the discrete lattice point model are that it allows the influence of crystalline anisotropy to be taken into account, permits treatment of arbitrarily steep variations in composition and provides a more convenient milieu for the incorporation of volume strain energy, as is done in the next paper in this series.     

A discrete lattice plane analysis of the interfacial energy of coherent F.C.C.: H.C.P. interfaces and its application to the nucleation of γ in AlAg alloys

The discrete lattice plane (DLP) model is used to calculate the chemical interfacial energy (γ) of coherent f.c.c.:h.c.p. interfaces of arbitrary orientation in AlAg alloys. The compositional diffuseness of the interface is neglected. The results of these calculations are used to develop polar γ-plots of an h.c.p. crystal within an f.c.c. matrix, obtained as a function of alloy composition. The Wulff construction on the γ-plot yield the equilibrium shapes taken to correspond to that of homogeneously formed h.c.p. γ′ critical nuclei in an f.c.c. α AlAg matrix. These shapes are then used to calculate the steady state homogeneous nucleation rate of γ′ as a function of alloy composition and reaction temperature. Although these calculations indicated that homogeneous nucleation of coherent γ′ should be feasible in the temperature region between the GP zone solvus and the metastable equilibrium (α/(α+γ′)) solvus, a concurrent TEM investigation showed that the only γ′ present was nucleated on dislocations. While competition with such heterogeneous nucleation may have inhibited homogeneous nucleation, it is probable that the nearest neighbor version of the discrete lattice plane model used significantly underestimated the energy of coherent α:γ′ boundaries in AlAg alloys.     

C.C.C.轧机的工艺及结构特点

介绍了唐钢高速线材厂从美国birdsboro公司的紧凑式粗轧机的主要工艺参数和工艺、结构特点，提出了堆钢事故解决办法，展望了C．C．C．轧机的发展前景。     

The role of structural ledges at phase boundaries—III. F.C.C.-B.C.C. interfaces in Kurdjumov-Sachs orientation

The ledge mode of misfit accommodation is extended to {111} f.c.c.∥{110} b.c.c. interfaces with the Kurdjumov-Sachs (KS) orientation relationship. As with the Nishiyama-Wassermann (NW) relationship the geometric quantities are uniquely related by the misfit ratio r of atomic diameters. A rigid lattice analysis shows that the driving forces for a KS orientation relationship are significantly larger than those for the NW-x and even more so than those for the NW-y relationships. The rigid analysis also predicts that the terrace width which satisfies the periodicity conditions for a stepped interface are well within the terrace widths which allow significant energy gains. The models developed for the NW analysis are modified for KS configurations and employed to sum energies for the terrace patches, tilt misfit dislocations and the riser interface energy. Comparing this energy with that of a planar interphase boundary comprised of only misfit compensating dislocations shows that a stepped interphase boundary is energetically favored at r values near and greater than r_KS but less than r_NW-y.     

The slip character and low cycle fatigue behaviour: The influence of F.C.C. twinning and strain-induced F.C.C. → H.C.P. martensitic transformation

The influence of slip character on the low cycle fatigue behaviour was investigated in the CoNi system at room temperature. Three alloys of increasing stacking fault energy (SFE) were used: Co31Ni (SFE ∼- 12 mJm⁻²) which deforms by slip and f.c.c. → h.c.p. strain-induced martensitic transformation, Co33Ni (SFE = 15 mJm⁻²) which exhibits slip and twinning and Co45Ni (SFE = 45mJm⁻²) which deforms only by slip with easy cross-slip. Push-pull low cycle fatigue tests were conducted under plastic strain control up to a few 10⁴ cycles. The number of cycles to fracture was found to increase with decreasing SFE which promotes planar deformation mechanisms: the life obtained in Co31 Ni and Co33Ni alloys is respectively about 6 and 3 times higher than that of Co45Ni alloy.Measurements of striation spacings on the fracture surfaces have enabled to show that the influence of twinning on fatigue life is mainly due to a large increase of the initiation period before stage II crack propagation. This behaviour was associated with a difference in crack initiation sites along twin or h.c.p. platelets where there is a strain localization in low SFE alloys or along grain boundaries in the high SFE alloy. The increase of crack initiation period was explained on the basis of a reduced stage I crack propagation rate in the alloys exhibiting planar deformation mechanisms.     

Fatigue crack nucleation based on a random slip process—I. Computer model

A computer model of fatigue crack nucleation, based on the concept of random slip, has been developed with guidance from surface observations of slip behavior within a persistent slip band (PSB), using bright field viewing and interferometry. The observations provide direct experimental determination of the parameters needed in the model. The computer simulations show that crack nucleation, defined as an intrusion of 4 μm depth, occurs in good agreement with the observed number of cycles, and that the generated PSB profiles agree well in appearance with those of real PSB's. The model also can account (indirectly) for crack nucleation at PSB edges, as is often observed, when local strain variations within actual PSB's are considered; the local strain tends to be higher at the edges of PSB's. It is shown that earlier model of crack nucleation based on random slip can be rehabilitated if up-to-date understanding on slip behavior is taken into consideration.     

H.C.斯塔克集团概况

Ｈ．Ｃ．斯塔克集团为世界著名的难熔、硬质合金制品公司。本文对该公司的基本情况和发展现状作了简要介绍。     

Heterogeneous nucleation and growth of δ′ in Al at.% Li

The nucleation of δ′ at dislocations at small undercooling is investigated. The primary site for heterogeneous nucleation is matrix dislocations with strong edge components. The edge dislocation half-plane and the development of a δ′ anti-phase boundary is considered. The morphological development of the δ′ precipitate is that of a “kidney” shape with a consistent relationship with the edge dislocation half-plabe. A model is developed based on the energetics of loss of coherency of a spherical precipitate and is employed to predict coherency loss of the δ′ precipitate and to compare it to the experimentally determined diameter of 400 nm. The loss of coherency is shown to be assisted by the growth of the equilibrium precipitate, δ.     

Creep rupture by diffusive growth of randomly distributed cavities—I. Instantaneous cavity nucleation

To treat many cavities of varying size randomly distributed on the grain boundary, cylindrically long (1-D) cavities are assumed and their growth rates are analytically solved within the framework of diffusive growth mode and rigid grain separation. Cavity growth rates are presented for the three cases when all the cavities grow exclusively in the quasi-equilibrium or crack-like mode, and when the two types of the limiting growth mode coexist. The analyses are applied to the rupture time estimation when all the cavities are nucleated simultaneously at loading. A case study of a 316 stainless steel used by Gandhi and Raj [Acta metall.30, 505 (1982)] shows that the predicted rupture times based on the instantaneous nucleation fall far short of the experimental data for all the cases and exhibit much weaker stress dependence, which provides a basis for further work on the continual cavity nucleation which is pursued in the accompanying paper. A statistical analysis of quasi-equilibrium cavities shows that the effect of non-uniform cavity spacing is to increase rupture time 6 times which exceeds that of non-uniform cavity size or that of cavity sintering and coalescence.     

Creep rupture by diffusive growth of randomly distributed cavities—II. continual cavity nucleation

Based on the 1-D cavity formulas developed in the accompanying paper [Acta metall. mater.38, 1423 (1990)] and the empirical cavity nucleation formula deduced from experiments, rupture times are estimated for a 316 stainless steel, α-Fe, Nimonic 80A, and proposed as functions of the steady state cavity nucleation rate (I_s) and the remotely applied stress (σ_∞). Despite possible differences in micromechanisms of creep cavitation among different materials, predicted rupture times agree with experimental data within a factor of 3 for all the materials studied under various stress and temperature ranges, which renders support to the validity of the present approach. The present analysis shows that the cavity nucleation rate is the most crucial factor determining the rupture time under diffusive cavity growth and continual cavity nucleation, and that whether cavities grow in a quasi-equilibrium or crack-like mode is not so important as usually assumed. Between the two limiting cavity growth modes, the cavity sintering and coalescence are very active in the quasi-equilibrium mode, and the cavity size distribution diagrams, generally bell-shaped, are skewed toward smaller cavity diameter in the crack-like growth. The effect of non-uniformities in cavity size and spacing is to increase rupture time by a factor of 2–3 under the continual cavity nucleation.     

Influence of crystallography upon critical nucleus shapes and kinetics of homogeneous f.c.c.-f.c.c. nucleation—III. The influence of elastic strain energy

The influence of crystallography upon critical nucleus shapes and kinetics of homogeneous f.c.c.-f.c.c. nucleation was studied by combining the discrete lattice point non-classical model utilized in paper II of this series with the microscopic theory of strain energy as applied by Cook and de Fontaine to compositional fluctuations in cubic lattices. This permits simultaneous consideration of the influence of anistropic interfacial energy and anisotropic strain energy upon nucleation. This is extremely difficult to do using other models of strain energy because of mathematical problems. The model is applied to f.c.c. nuclei in AlCu and CuCo alloys. Nuclei in AlCu are plates because coherency strain energy predominates in this system. In CuCo alloys, the misfit is smaller and the distortion tensor is cubic; thus the nuclei are essentially spherical. Despite this lesser effect, the influence of strain energy upon the nucleation kinetics of Co-rich precipitates in a Cu-rich CuCo alloy is found to be very important, reducing these kinetics by as much as five orders of magnitude.     

Structure-energy correlation for grain boundaries in F.C.C. metals—III. Symmetrical tilt boundaries

The correlation between the structure and zero-temperature energy of symmetrical tilt grain boundaries (STGBs) in f.c.c. metals is investigated using two embedded-atom-method potentials (for Cu and Au) and a Lennard-Jones potential fitted for Cu. Similar to free surfaces, misorientation phase space associated with these simple planar defects consists of only two degrees of freedom, namely those associated with the GB plane. The sampling of this two-dimensional phase space in terms of the stereographic triangle shows energy cusps as its corners and along its edges. These cusps are shown to arise from GB geometries with particularly small planar unit cells. Similar to free surfaces, a good correlation is found between the number of broken nearest-neighbor bonds per unit area and the GB energy. Also, as in our earlier study of twist boundaries, a practically linear relationship is found between the GB energy and volume expansion at the boundary. Finally, a comparison with twist boundaries shows that the STGBs represent the endpoints of the energy vs twist-angle curves. This enables a direct comparison of the properties of twist and tilt boundaries.     

Influence of crystallography upon critical nucleus shapes and kinetics of homogeneous f.c.c.-f.c.c. nucleation—IV. Comparisons between theory and experiment in CuCo alloys

A discrete lattice point model (Cook, de Fontaine and Hilliard) which incorporates strain energy (Cook and de Fontaine), described in earlier papers, has been used to determine the ranges of temperature and composition at which homogeneous nucleation kinetics of f.c.c. precipitates in CuCo alloys would be neither too fast nor too slow to be measured. These predictions proved successful and it was possible to measure experimentally nucleation kinetics in CuCo alloys containing from 0.5 to 1.0 at.% Co within 50°C temperature ranges. Experimental results were compared with theoretical values obtained from the discrete lattice point, the Cahn-Hilliard continuum and the classical theories of homogeneous nucleation. Very good agreement was obtained between the experiments and all three theories. Although surprising at first, the good matching between classical theory and experiments was explained by showing that the calculated concentration profiles of critical nuclei at the temperatures and alloy compositions experimentally studied did show distinct “volumes” and “interfaces” i.e. the solute concentration did not vary continuously throughout the nuclei. In this case, as pointed out in effect by Cahn and Hilliard, classical nucleation theory indeed applies. These findings provide the first strong support for the essential correctness of homogeneous nucleation theory.     

A.C.L顶燃式热风炉生产实践

A.C.L顶燃式热风炉通过冷铁半年来的工业试验,初步证实炉顶环形燃烧器具有燃烧均匀,安全、可靠,点火容易;炉体结构对称,炉内气流分布均匀,送风能力强等特性。文章肯定了该顶燃炉是一种高效、长寿、经济、合理的高风温热风炉。     

P.C.悬臂撞击式钢坯打印机

攀钢初轧厂为了加强钢坯的管理,确保产品质量,消除工人繁重的体力劳动,初步研制成功了P.C.悬臂撞击式钢坯打印机.这种打印机的打印程序是:由人工操纵按钮,使打印锤下落到最低位置.当大剪过来的钢坯以1～2米/秒的速度撞击带有字码的、具有一定重量的锤头时,钢坯就打上了印.同时,通过自动提升控制机构接通风阀电磁线圈并推动风缸,快速抬起锤头到原始位置,这就完成了一个打印程序.如果需打A段就落A锤,需打B段则落B锤,要打C段就将两锤同时落下.这种打印机简化了操作程序,实现了钢坯运动中的打印.     

V.C.R采矿法及工艺设计

V.C.R法是垂直深孔球形药包爆破后退式采矿法的简称。该方法的主要特点是:整个采场高度用潜孔钻机,按合理的孔网,从采场顶部凿岩硐室向下部水平拉底空间钻凿垂直或倾斜深孔(一般孔径为φ150～φ165毫米,普遍采用φ165毫米),然后采用高密度、高威力、高爆速、低感度的炸药,以球形药包(药包长度为直径的6倍以内),自下而上进行单分层或多分层爆破,并采用高效率的出矿设备(如铲运机),将爆下的矿石通