Effect of precipitates on plastic anisotropy for polycrystalline aluminum alloys

The effects of crystallographic texture and precipitate distribution on macroscopic anisotropy in aluminum alloys were investigated. In order to simultaneously consider the effects of crystallographic texture and precipitate distribution on macroscopic anisotropy, predictions of plastic properties were carried out using an anisotropic yield function based on the material texture and a combined isotropic-kinematic hardening rule. The input to the model was a single stress-strain curve, the crystallographic texture, and the precipitate volume fraction, shape, and habit planes. It was shown that the kinematic hardening rule, which expresses a translation of the yield surface in stress space, was a function of all the parameters describing the precipitate distribution. The model was applied to the case of an extruded and recrystallized binary Al-3 wt pct Cu alloy deformed in uniaxial compression in different directions. Excellent agreement was observed between the experimental and predicted yield stress anisotropy and the specimen cross section shape anisotropy. Gaussian distributions of grain orientations around ideal texture components typical of aluminum alloys were generated using computer simulations. These textures were combined with the isotropic-kinematic hardening rule determined for the Al-3 wt pct Cu binary alloy to theoretically assess the influence of precipitates on the r-value (the width-to-thickness plastic strain ratio in uniaxial tension) and yield stress anisotropy for aluminum sheets. It was shown that, for these textures, the precipitate distribution had the effect of reducing plastic anisotropy, in agreement with the trends generally observed in practice.     

Morphology transition of deformation-induced lenticular martensite in FeNiC alloys

The morphology and habit planes of deformation-induced lenticular martensite were investigated by optical and transmission electron microscopy in Fe30Ni and Fe30Ni0.11C alloys. Transitions in morphology were observed with progressive deformation levels going from lenticular to butterfly and to compact martensite for the Fe30Ni alloy and lenticular to butterfly and to small butterfly martensite for the Fe30Ni0.11C alloy. The habit planes changed from {225}_f or {259}_f for the thermal lenticular martensite to {111}_f for the strain-induced martensite. The morphology and crystallography of the small butterfly martensites was also investigated. A change in the orientation relationships from K-S to N-W relations was also observed. These changes were attributed to the contribution of mobile dislocations which modified the shear mode from twinning to slip, and to a plastic accomodation of transformation strains.     

锆合金的织构及其对性能的影响

锆合金被广泛应用于核反应堆中，作为燃料元件的包壳材料或堆内结构部件，织构会影响其众多的应用性能，因此织构的研究及控制在锆合金的开发利用中具有重要作用。综述了，锆合金塑性变形的滑移和孪生系统；锆合金管板材的织构特点及控制方法；热轧温度对锆合金板材织构的影响以及退火处理锆合金织构的演化；并分别总结了织构与锆合金屈服强度、蠕变强度、碘致应力腐蚀开裂、氢化物取向分布以及辐照生长等性能的相互关系。     

Phase composition,texture, and anisotropy of the properties of Al–Cu–Li–Mg alloy sheets

The formation of the anisotropy of the mechanical properties, the texture, and the phase composition of thin-sheet Al–4.3Cu–1.4Li–0.4Mg and Al–1.8Li–1.8Cu–0.9 Mg alloys have been studied by X-ray diffraction and tensile tests. Various types of anisotropy of the strength properties of the alloys have been revealed: normal anisotropy (strength in the longitudinal direction is higher than that in the transverse direction) in the Al–4.3Cu–1.4Li–0.4Mg alloy and inverse anisotropy in the Al–1.8Li–1.8Cu–0.9Mg alloy. It is shown that the anisotropy of the strength properties is dependent not only on the texture of a solid solution, but also on the content and the texture of the δ' (Al₃Li) and T1 (Al₂CuLi) phases and their coherency and compatibility of deformation with the matrix.     

SPD技术对锆及锆合金力学行为影响研究现状

综述了锆及锆合金剧烈塑性变形(SPD)后性能变化的研究进展,系统阐述了锆及锆合金经剧烈塑性变形后显微硬度、拉伸/压缩性能、高低周疲劳性能,重点介绍了SPD技术在纯锆、Zr-Nb系合金中的应用.经过剧烈塑性变形后,锆及锆合金的抗拉强度及屈服强度均显著提升,但依据剧烈塑性成形轨迹、合金成分、第二相分布、热处理制度不同,其提...     

Effect of equal-channel angular pressing and annealing conditions on the texture,microstructure, and deformability of an MA2-1 alloy

Equal-channel angular pressing (ECAP) of am MA2-1 alloy according to routes A and Bc is used to study the possibility of increasing the low-temperature deformability of the alloy due to grain refinement and a change in its texture. To separate the grain refinement effect from the effect of texture on the deformability of the alloy, samples after ECAP are subjected to recrystallization annealing that provides grain growth to the grain size characteristic of the initial state (IS) of the alloy. Upon ECAP, the average grain size is found to decrease to 2–2.4 μm and the initial sharp axial texture changes substantially (it decomposes into several scattered orientations). The type of orientations and the degree of their scattering depend on the type of ECAP routes. The detected change in the texture is accompanied by an increase in the deformability parameters (normal plastic anisotropy coefficient R, strain-hardening exponent n, relative uniform elongation δ_u) determined upon tensile tests at 20°C for the states of the alloy formed in the IS-4A-4Bc and IS-4Ao-4B_cO sequences. The experimental values of R agree with the values calculated in terms of the Taylor model of plastic deformation in the Bishop-Hill approximation using quantitative texture data in the form of orientation distribution function coefficients with allowance for the activation of prismatic slip, especially for ECAP routes 4B_c and 4B_cO. When the simulation results, the Hall-Petch relation, and the generalized Schmid factors are taken into account, a correlation is detected between the deformability parameter, the Hall-Petch coefficient, and the ratio of the critical shear stresses on prismatic and basal planes.     

X-ray diffraction analysis by Rietveld refinement of FeAl alloys doped with terbium and its correlation with magnetostriction

Fe₈₁Al₁₉ polycrystalline alloys doped with Tb(0-0.25 at%) were obtained by arc melting.The introduction of Tb favors the formation of columnar grains in the micro structure of the alloys,which develops a texture in the [100]crystal direction.Microstructural examination shows that the alloys are composed in great proportion by the disordered body-centered cubic(bcc),A2 phase and by a small proportion of the ordered bcc,B2 phase.As a consequence of doping with Tb,the lattice ...     

The Mode of Deformation in a Cold-Swaged Multifunctional Ti-Nb-Ta-Zr-O Alloy

Multifunctional titanium alloys, termed Gum Metal?, are β-phase Ti alloys first developed in 2003. These alloys exhibit many interesting properties including, for example, low rate of work-hardening and superplasticity during cold deformation. The original report described a new plastic deformation mechanism not involving major dislocation activity to explain such deformation behavior. In the current study, a comparable Ti-36.8Nb-2.7Zr-2.0Ta-0.44O (wt pct) alloy to the original investigators was produced by powder sintering, hot forging, solution treatment, and cold swaging with the aim at investigating the microstructural development during swaging. XRD and TEM showed that the forged/solution-treated alloy was β-phase with a small amount of ω-phase. After cold swaging by up to 96 pct area reduction, TEM/HRTEM revealed the existence of dislocations, deformation twins, ω-phase, nanodisturbances, and lattice bending, with EBSD showing the grains to be highly elongated in the swaging direction, fragmented, and distorted. Most notably, swaging also generated a strong 〈110〉 fiber texture, even after moderate strains. The foregoing structural analysis provides substantial evidence that dislocations are present in the alloy after cold swaging. The major support of dislocation glide processes acting as the dominant plastic deformation mode in the swaged alloy is the strong 〈110〉 fiber texture that develops, which is a characteristic feature of all cold-drawn/swaged body centered cubic metals and alloys.     

Bimodal size distributions of γ′ precipitates in Ni-Al-Mo—I. Small-angle neutron scattering

The evolution of the microstructure during the decomposition of two Ni-Al-Mo alloys with a bimodal size distribution of precipitates was studied using small-angle neutron scattering. Precipitate size distributions and space correlations of the bimodal precipitate ensemble were determined by model fitting of the scattering curves. The correlation effects between the precipitates were taken into account by the locally-monodisperse (LMD) hard-sphere model. This model assumes that the ensemble of precipitates have their positions correlated with their sizes, being locally monodisperse. The form factors were used according to the shape of the precipitates, spherical in the case of alloy I, Ni-8.8Al-9.6Mo (at.%) (isotropic system), and cuboidal for alloy II, Ni-9.5Al-5.4Mo (anistropic system). To characterize the microstructure of the two alloys a set of characteristic parameters (e.g. volume fraction, average radii, precipitate number density, etc.) were obtained using relations between the moments r^¯n of the size distribution N(r). The model proved particularly suited to characterize the isotropic system. In the case of the anisotropic system it was insensitive to changes of the size distribution N(r) during aging.     

Inhibited coarsening of solid-liquid microstructures in spray casting at high volume fractions of solid

Experimental studies on coarsening in fine grained solid-liquid microstructures at high volume fractions of solid (f_s) have been carried out to determine if inhibited coarsening under these circumstances could account for the anomalous fine cell sizes observed in spray castings. The materials investigated included a chill-cast dendritic binary alloy of Al-Cu, two spray cast alloys—AA2014 and Cu-Ti, whose grain size was the segregate spacing, and a d.c.-cast alloy Al-4.5 wt% Cu-1.5 wt% Mg in both coarse-grain and grain-refined conditions. The observed segregate spacings after coarsening were smaller than that predicted by empirical correlations of dendrite arm spacing and freezing time. In all cases, the coarsening was found to become slower as the temperature was reduced and f_s increased. Conventional coarsening theories and experiments predict the opposite, i.e. faster coarsening at higher volume fractions of solid. Two additional coarsening models were developed for the grain growth at high volume fractions of solid by processes whose rates are limited by migration of liquid at grain boundaries as liquid films on 2-grain surfaces or liquid rods on 3-grain triple points. In both models, the conventional diffusion-limitedt¹³ coarsening law was reproduced, but the rate constant K contained the term 11−f_s and so also predicted accelerated coarsening asf_s → 1 . Three possible explanations for the observed lower K values at increasing f_s are proposed. The first is the effect of the increasing difference between the solute contents of solid and liquid as the temperature is reduced. This produces a1/X₁ dependence of the coarsening rate constant K. The second inhibiting effect, specific to dendritic structures, is in-grain coalescence of dendrite arms at high f_s which produces isolated liquid particles within the grains. The final possibility is particle-inhibition of grain boundary migration by minority (impurity) particles at the grain boundaries. Such particles were seen, however, for only two of the alloys, viz. the grain defined d.c. cast Al-4.5 wt% Cu-1.5 wt% Mg and the spray case AA2014, but they or gas-filled pores are proposed as strong possibilities to account for the fine grain sizes observed in all spray cast microstructures.     

Effect of manganese on annealing texture,plastic anisotropy,and mechanical properties of low-carbon steels containing 0.067 Pct phosphorus

To establish the range of manganese content in phosphorus-containing low-carbon steels that will provide superiorr _m andAr values in cold-rolled sheets, the effects of manganese on annealing texture, plastic anisotropy, and mechanical properties of steels containing 0.067 pct P were studied. Both vacuum and air-melted laboratory heats were investigated. Results show that highr _m and low Ar values, a desirable combination for deepdrawing applications, can be obtained with manganese contents up to 0.25 pct, when the hot-rolled band is cold-rolled 80 pct, and annealed at 710 or 780° (1310 or 1435∮F) for 20 h. Annealing at the higher temperature developed better plastic anisotropy than did annealing at the lower temperature. Ther _m values of the air-melted steels were superior to those of the vacuum-melted steels. It is believed that complex interactions of manganese with other elements in the steel, such as sulfur and oxygen, and possibly carbon, influenced the annealing behavior of the steels.     

Effects of Cerium on Texture and Mechanical Property of 2090 Aluminium-Lithium Alloys

Conventional processing of Al-Li alloys asstructural materials used in aerospace industries such as rolling, prestretching, solutioningand aging will produce various textures such asrolling texture, recrystallization texture whichcan lead to mechanical anisotropy. Adding Ceto Al-Li alloys by means of rare earth microalloying and purification, the mechanical properties will be improved[' ~3). It is significant tostudy the actions of Ce on Al-Li alloys from theviewpoint of texture, hilt resea…     

Texture and anisotropy of zirconium in relation to plastic deformation

Abstract

Possible modes of plastic deformation of tubular materials are analyzed generally. Based on symmetry considerations applied to known textures of zirconium wire and strip, textures of zirconium tubes are predicted as resulting from a wide range of deformation modes. This is made possible by focusing on the main feature of texture, Le., the orientation distribution of basal poles. A relation between texture and the mechanical anisotropy of zirconium is developed, and rules are suggested for softening and hardening caused by texture change. Experimentally, Zircaloy tubes were deformed by various techniques. The resulting textures were determined by X-ray diffraction and the mechanical anisotropy by Knoop-hardness measurement. Each determination is condensed into two representative figures, one describing the type of texture or anisotropy and the other describing the sharpness of texture or the degree of deviation from isotropy.

The experiments verify the predicted relation between type of texture and mechanical anisotropy, and also indicate how degree of anisotropy depends on sharpness of texture. Changes in texture are investigated in relation to plastic deformation, and further refined rules are derived for the direction and rate of these changes. The initially predicted textures are concluded to be stable, i.e., they are reached only after a certain degree of deformation. Zircaloy tubes of three different textures were subjected to tensile testing, closed-end burst testing and open-end burst testing. The observed texture-softening phenomenon corroborates the rules suggested and is considered to commonly occur, as opposed to texture hardening, which requires special combinations of texture and testing method.

Résumé

Les différents modes de déformation plastique possibles dans les tubes ont été analysés d'une façon générale. En se basant sur des considérations de symétrie appliquées aux textures connues pour le zirconium en fil et en bandes, la texture des tubes de zirconium resultant de divers modes de déformation a été prédite. Ceci est possible si l'on tient surtout compte des principes de la texture, c'est à dire, la distribution des orientations des poles de base. Une relation entre la texture et l'anisotropie du zirconium est développée, et des règles sont suggérées pour l'adoucissement et la consolidation dûs à un changement de texture. Dans les expériences, les tubes de zirconium ont été déformés par plusieurs modes. Les textures résultantes ont été déterminées par la diffraction des rayons-X. et l'anisotropie par des mesures de dureté Knoop. Chacune de ces déterminations est représentée dans deux figures, l'une décrivant le genre de texture ou anisotropie, l'autre décrivant la netteté de la texture ou l'écart du caractère isotrope. Les expériences vérifient la relation prévue entre la texture et l'anisotropie. Les changements de texture sont examinés en fonction de la déformation plastique, et d'autres règles plus rigoureuses sont dérivées pour la direction et la vitesse de ces changements. On conc1ut que les textures prévues initialement sont stables, c'est à dire qu'elles ont lieu apres une certaine déformation. Des tubes de Zircalloy de trois textures différentes ont été soumis à des essais detraction, des essais d'éc1atement à extrémités ouvertes ou fermées.

Le phénomène d'adoucissement observé, causé par la texture, est en accord avec les règles suggérées et est généralement présent, ce qui n'est pas le cas du durcissement causé par la texture, durcissement nécessitant des combinaisons spéciales de texture et de méthodes d'essai.     

锆合金变形机理及其板材织构演化规律

锆是核工业的重要结构材料,又是优秀的化工耐蚀结构材料。锆合金的织构会对它的屈服强度、蠕变和疲劳强度、应力腐蚀开裂行为以及辐照尺寸变化等产生很大影响,因此变形机理的研究和织构控制在锆合金的开发利用中有十分重要的地位。综述了锆合金的变形机理,介绍了锆合金板材在不同轧制温度下的织构演化规律,以及退火温度对锆合金板材织构的影响,并总结了织构对锆合金板材力学性能的影响。最后指出,目前对锆合金板材加工后的织构进行精确预测还十分困难,需进行详细深入的研究,同时在加工中产生的织构对加_丁过程的影响以及与温度、应力分布、合金成分和组织的关系还需进一步认识。     

Interrelations between fracture toughness and other mechanical properties in titanium alloys

Critical stress intensity factors and general tensile properties were measured for a class of metastable beta and alpha-beta titanium alloys with a limited number of compositions but processed to have a wide variety of strength levels and microstructures. These data were used to test thirteen theoretical relations between the fracture toughness and tensile parameters. Many of the theoretical relations had been proposed previously, but several new forms were derived in the present work. The correlation showed that for alloys exhibiting a limited range of microstructures, the simpler correlations gave the better fits withK _Ic α γ⁻¹specifically being the best one. For correlations of alloys with a wide range of microstructures, more complex correlations which included microstructural parameters were found to be superior.     

织构对先进锆合金蠕变性能各向异性的影响

研究了两种组织形貌相似的先进锆合金M5TM和N36锆合金核燃料包壳管材的单轴拉伸和内压蠕变性能.利用x射线衍射仪分析了它们的织构.试验发现两种先进锆合金包壳材料的蠕变性能表现出明显的各向异性.根据试验条件下的蠕变机理,结合弹性粘塑性自洽模型定性地分析了织构对锆合金管材蠕变各向异性的影响,解释了先进锫合金各向异性随应力指数变化的共性规律.揭示了织构与先进锆合金管材蠕变各向异性的定性关系.由于成分和织构因素的共同作用,在研究的试验条件下,N36合金的初始蠕变应变、稳态蠕变速率低于M5合金.织构是合金蠕变行为产生各向异性的主要原因,对于再结晶状态的先进锆合金包壳管,具有(0002)织构特征时,应力指数越高(即施加的应力水平越高),其蠕变的各向异性值越大.     

Global constraint-insensitive fracture in SiC particulate-reinforced AA 2009

Experimental results prove this hypothesis:The effective plastic fracture strain (∈_f ^{ˉ p}) for a discontinuously reinforced metal matrix composite (MMC) is insensitive to globally imposed triaxial tensile stress, because the elastic reinforcement independently produces high local matrix constraint during plastic deformation. The value∈ _f ^{ˉ p} is measured for SiC particulate-reinforced AA 2009-T6, with cylindrical circumferentially notched (global constraint ratio, (σ_m/ˉσ, of 1.0) and smooth tensile specimens (σ_m/ˉσ of 0.3), as a function of temperature. The MMC fractures by microvoid-based processes associated with the SiC at all temperatures. The ratio (r) of smooth to notched specimen ∈ _f ^ˉp equals unity from 25 °C to 200 °C and is less than values of 2 or higher typical of monolithic Al alloys at similar global constraint. This result establishes that global constraint does not degrade MMC fracture resistance because of the unique effect of local matrix constraint. The ratior for the MMC increases from near 1 at 200 °C to a maximum of 3.3 at 250 °C, indicating a loss of local matrix constraint, possibly due to reduced matrix-particleload transfer or microvoid nucleation at low strains. Uncertainties hinder precise definition of ∈ _f ^{ˉp vs} global σ_m/σ-σ. Global constraint-insensitive fracture for the MMC suggests that plane strain fracture toughness differences between the composite and unreinforced matrix are not well defined by smooth specimen ductilities. Further, MMC fracture toughness should be insensitive to global constraint and associated cracked specimen dimensions.     

Effects of Different Modes of Hot Cross-Rolling in 7010 Aluminum Alloy: Part II. Mechanical Properties Anisotropy

The influence of microstructure and texture developed by different modes of hot cross-rolling on in-plane anisotropy (A _IP) of yield strength, work hardening behavior, and anisotropy of Knoop hardness (KHN) yield locus has been investigated. The A _IP and work hardening behavior are evaluated by tensile testing at 0 deg, 45 deg, and 90 deg to the rolling direction, while yield loci have been generated by directional KHN measurements. It has been observed that specimens especially in the peak-aged temper, in spite of having a strong, rotated Brass texture, show low A _IP. The results are discussed on the basis of Schmid factor analyses in conjunction with microstructural features, namely grain morphology and precipitation effects. For the specimen having a single-component texture, the yield strength variation as a function of orientation can be rationalized by the Schmid factor analysis of a perfectly textured material behaving as a quasi-single crystal. The work hardening behavior is significantly affected by the presence of solute in the matrix and the state of precipitation rather than texture, while yield loci derived from KHN measurements reiterate the low anisotropy of the materials. Theoretic yield loci calculated from the texture data using the visco-plastic self-consistent model and Hill’s anisotropic equation are compared with that obtained experimentally.     

Characterization of formability in cold-rolled steel sheets using electromagnetic acoustic tranducers

An ultrasonic technique for evaluating the formability of cold-rolled steel sheets is developed. The technique is based on the generalized dispersion relation, which correlates the velocity anisotropy of ultrasonic plate modes guided in the sheet plane to the texture defined by orientation distribution coefficients. Electromagnetic acoustic transducers (EMAT’s), constructed of permanent magnets and meander-line coils, allow the accurate and easy measurement of transit times of theS _o (fundamental symmetric) mode. The planar average of the transit times shows a close correlation with both the planar average of plastic strain ratios (r value), obtained through tensile tests and the pole intensities, measured with the X-ray diffraction method. These favorable comparisons with the destructive tests indicate a good possibility of texture monitoring with the noncontacting EMAT’s.     

The relation between preferred orientation and the Lankford parameter r of plastic anisotropy

Calculation of the r-value of plastic anisotropy from experimentally determined texture data on the basis of the Taylor theory with different assumptions about the glide systems. Experimental determination of the r-value at different angles to the rolling direction in a steel RSt 14. Comparison of the experimental results with the theory on the basis of texture and cell formation.