Non-octahedral deformation activity in cold rolled 70:30 brass and its influence on the development of brass texture

A structure of elongated, wavy bands develops at high strains in both fine grained and normal 70:30 brass. Recovery twins and evidence of non-octahedral slip activity are observed in the wavy bands after further deformation. The non-octahedral process generally operates on several sets of closely spaced (0.002–0.004 μm) planes, producing substructure comprised of intersecting trace lines. The occurrence of this process cannot be explained by slip on only a single system but combined activation of {110} and {112} planes accounts for most of the traces observed. Texture changes that can be attributed to the non-octahedral process are also evident and orientations around {110}〈112〉 develop in the regions where the activity has operated. The results are in good agreement with recent simulations of rolling textures based on non-octahedral slip in which a strong brass texture is produced bythe operation of {110} + {112} slip systems.     

High strain plane-strain deformation of 70-30 brass in a channel die

Parallel-piped samples of 90 and 4 μm grain size 70-30 brass have been deformed in plane-strain in a channel die up to a true strain of 2.3. Optical and electron metallography and X-ray diffraction have been used to determine the development of microstructure and texture with strain. The stress-strain data have been obtained by measuring the specimen dimensions and the load after each increment of 0.1 true strain. At low strains 70-30 brass deforms mainly by slip and at slightly higher strains by a combination of slip and twinning. At medium strains shear bands form. The average angle which they make with the compression plane and also their density increases with strain. The strain at which they form and their angle is different for the two grain sizes examined. The stress-strain curves show three distinct hardening stages. At low and high strains the rate of work hardening is high, while at medium strains the rate is low. Shear bands form when the rate of work hardening is low but positive and continue to form at high strains under a high rate of work hardening.     

Experimental deformation textures of OFE copper and 70:30 brass from wire drawing,compression, and torsion

Inverse pole figures have been made from OFE copper and 70:30 brass samples which were deformed to a von Mises equivalent strain of 1.5 in wiredrawing, compression, and torsion. Measurements were taken from the plane normal to the axis of maximum or minimum principal strain for the cases of tension and compression, respectively. We studied three sections for the specimens deformed in torsion, namely the planes normal to the three cylindrical coordinate axes (Z, R, and π). Our results were consistent with the literature data for both wiredwaring and compression. In wiredrawing we found a duplex fiber texture of [001] and [111] orientations. The amount of the [001] texture was much less for the 70:30 brass. A [011] fiber texture developed in both materials in compression. For the OFE copper, the [011] texture spread toward [113]. In the case of the 70:30 brass there was a spread toward [111]. The inverse pole figures we obtained from the torsion samples had similar trends for both copper and brass. Data from the section taken normal to theR axis showed no distinct preferred orientation. For both materials the Z-section had an increased concentration of [111] poles and a distinct absence of [011] poles. In the case of the copper there was also a slight [001] component. Finally, we found the [011] component in the π-section. This section was also characterized by a lack of [001] or [111] orientations.     

Transient tensile behavior of interstitial-free steel and 70/30 brass following plane-strain deformation

The transient behavior of interstitial-free (IF) steel and 70/30 brass which results from an abrupt change in strain state has been investigated experimentally and modeled analytically. After a plane-strain prestrain, reloading in uniaxial tension results in a negative stress transient for brass and a positive stress transient for IF steel. The strain behavior during the stress transient was studied by measuring the local axial and transverse strains using resistance strain gages. The monotonic data exhibited a constant plastic strain ratio, whereas the prestrain data showed decreasing plastic strain ratios with increasing axial strain for both IF steel and brass. A simple analysis of the transient was performed by modifying Hill's nonquadratic yield surface to allow variable plastic anisotropy (via r) during the transient. By choosing an appropriate variation ofr, the stress transient could be reproduced. The predicted variations in strain ratios by the model agreed qualitatively with measurements for brass but were of the opposite sign to measurements for steel. Although not conclusive, this result suggests that the normality condition is violated during a stress transient induced by an abrupt change in strain path. A.B. DOUCET, formerly A.E. Browning, Graduate Research Associate, Department of Materials Science and Engineering, The Ohio State University     

Shear band formation in heavily cold rolled 70-30 brass

Blocks of 70 μm grain size 70-30 brass have been cold rolled up to a strain of 2.4. Polished parallelepiped samples have been prepared from the cold rolled strips and deformed in plane strain in a well-lubricated channel die. Three specimen orientations have been studied. Optical metallography has been used to determine the critical strain for the onset of shear banding and the angle which the shear bands make with the compression plane in the channel die. The strain at which shear bands form and the angle which they make with the compression plane depend upon the specimen orientation. The stress-strain curves show two distinct work hardening stages. Shear bands form under a positive rate of work hardening.     

Plastic behavior of 70/30 brass sheet

The plastic yield behavior of strip annealed 70/30 brass sheet has been investigated using several experimental techniques. Proportional path, stress-strain relations were measured in two strain states using a recently devised plane-strain test and a standard sheet tensile test. Based on these data, 70/30 brass exhibits a dramatic departure from Hill's plasticity models. Particularly notable is the lower work-hardening rate in plane strain. A second series of tests was carried out by deforming first in plane-strain tension and subsequently in uniaxial tension. The relative orientation of the principal strain directions in the two strain paths strongly affected the transient yielding behavior, but the original work-hardening pattern and plastic anisotropy were approached after an additional effective strain of ∼0.04. These observations are consistent with a two yield-surface model;i.e., one an underlying, proportional path yield surface and one an instantaneous, transient yield surface.     

Slip observations in 70–30 alpha brass

Observations have been made on slip nucleation in 70–30 alpha brass for plastic strains ranging from 0.05 pct to 0.7 pct in four grain sizes: 33, 84, 126, and 163 μm. Slip was seen to start primarily at grain and twin boundaries and occasionally within grains. In grains in which slip commenced first, slip tended to traverse the entire grain and multiple slip tended to develop as well. The average length of the longest slip band, compared to the available slip path, was longer in large than in small grains. The volume fraction of grains covered by slip was greater at a given strain the larger the grain size. However, when the volume fraction of multiple slip was separated from single slip the volume fraction of multiple slip increased more slowly with increasing strain for the 33, 84, and 126 μm grain sizes than for the 163 μm grain size. Evidence was adduced to indicate that slip nucleation caused by elastic interaction is more significant than slip nucleation by slip impingement.     

Comparison of temper-rolled and temper-annealed 70/30 brass strip

Abstract

The possibility of using temper annealing of heavily rolled strip, as an alternative to temper rolling has been investigated in 70/30 brass.

It has been found that temper annealing is an attractive alternative because (a) the combination of mechanical properties obtained is better at virtually any desired strength level, and (b) temper annealing lends itself easily to continuous annealing as well as to batch annealing. Normal mill variations in composition were found to have negligible effects on the annealing behaviour and on the properties of the finished material.

Résumé

Les auteurs ont étudié la possibilité d'effectuer un recuit ménagé sur de la tôle fortement laminée de laiton 70/30 pour obtenir les mêmes propriétés qu'après laminage superficiel.

Les essais ont montré que le recuit ménagé est une alternative intéressante parce que (a) il en résulte une meilleure combinaison de propriétés mécaniques pour presque tous les niveaux désirés de résistance à la traction, et (b) le recuit ménagé peut être réalisé facilement par recuit en continu tout aussi bien que par recuit en lots. Les variations de composition normalement acceptées en usine exercent une influence négligeable sur le comportement au recuit et sur les propriétés du produit fini.     

The effect of grain size and plastic strain on slip length in 70-30 brass

Polycrystalline 70−30 brass of varying grain size has been studied. Measurements were made of slip line lengths on the polished surface of specimens which had undergone different plastic strains. A relation between the slip line length and the grain size and plastic strain was found based on experimental data using a multiple regression technique. Qualitative agreement was found between the observed slip lengths and slip lengths calculated from a published work-hardening model. The effect of the boundary on slip behavior was observed, and both passive and active types of obstruction to slip by boundaries are suggested. H. DONG, formerly with Carnegie-Mellon University, is now with Jilin Institute of Engineering, Changchun, China. A. W. THOMPSON     

Yielding behavior of prestrained interstitial-free steel and 70/30 brass

The yielding behavior of interstitial-free (IF) steel and 70/30 brass prestrained in plane strain tension and subsequently strained in uniaxial tension has been investigated experimentally. Upon reloading in uniaxial tension, brass exhibited a negative transient (decrease in flow stress) and steel exhibited a positive transient (increase in flow stress). When the yield stress is defined by the offset method, the positive transient is difficult to model using conventional yield theories as elastic deformation is thought to occur outside the original yield or loading surface. In this work, the yield point was defined using the axial strainvs transverse strain curve as measured with biaxial resistance strain gages. The curve has an initially linear elastic portion; the slope then gradually changes until the linear plastic slope is reached. The intersection of the elastic and plastic slopes is defined as the yield point. Using this alternate definition, the yielding behavior of the prestrained metals was investigated. The yield stress for both prestrained brass and steel was found to be lower than the expected monotonic stress. Compared to previous research based on a traditional definition of yield point, this result is unexpected in prestrained steel and shows that yielding does occur inside the loading surface. The positive transient may, therefore, be modeled using conventional yield theories provided that the yield surface is defined using this alternate technique.     

The strain dependence of the flow stress-grain size relation for 70:30 brass

The grain size dependence of the stress-strain behavior of annealed 70:30 brass was evaluated using room temperature tensile tests. The resulting data, which covered × 10^-5 to 4 × 10^-1, were analyzed in terms of the conventional Hall-Petch stress-grain size equation, σ_∈ = σ_O∈ +k∈l-1/2, and, also, in terms of the extended Hall-Petch equation previously proposed for 70:30 brass, σ_є = σ0y+ A Є _p + β(є _p /l ^1/2 +kl ^−1/2 The lattice friction stress, σ0_∈, increased linearly with plastic strain over nearly the full strain range. The lattice friction stress for the initiation of plastic flow, σ0_y, was evaluated using two alternative double extrapolation procedures. Both extrapolation techniques, which involved the macrostrain behavior, gave the same σ0_y value of 3.4 kg/mm², which agreed with the σ0_∈ value determined directly in the microstrain region (∈ <-10^-3). Large grain size specimens, which yielded homogeneously, exhibited a kx2208; value of only 0.2 kg/mm^3/2 at a plastic strain of 1 × 10^-5; however this small kx2208; increased rapidly with increasing microstrain. For the small grain size specimens, which yielded via a Luders extension,kε was essentially constant at 0.8 kg/mm^3/2 for all microstrains; however, kx03B5; did increase in the macrostrain region to a maximum value of 1.6 kg/mm^3/2. When consideration was given to a grain size dependent increase in dislocation density, an intrinsic grain boundary resistance to plastic flow of approximately 0.7 kg/mm^3/2 was obtained. This paper is based upon a thesis submitted by W. L. Phillips in partial fulfillment of the requirements of the degree of Doctor of Philosophy at University of Maryland.     

Existence of the coaxing effect and effects of small artificial holes on fatigue strength of an aluminum alloy and 70-30 brass

In order to study the existence of the coaxing effect and the effects of small defects on the fatigue strength of an aluminum alloy and 70-30 brass, plain specimens and special holed specimens containing one or more very small drilled holes with diameters of 40,50,100,200, and 500 ώm were prepared. Contrary to commonly accepted knowledge, the existence of a distinct coaxing effect was confirmed in the fatigue test on 2017-T4 aluminum alloy. However, the coaxing effect was not confirmed in the fatigue test on 70-30 brass, though specimens with small artificial holes could contain non-propagating cracks at the fatigue limit. It was found that the appearance of the coaxing effect depends on the endurance at a higher stress level of small cracks initiated at a lower stress level. The very small drilled holes with diameters of 40 and 50 ώm had no harmful effect on the fatigue strength of both the aluminum alloy and 70-30 brass; that is, the fatigue limits of specimens containing one or more drilled holes with diameters of 40 and 50 ώm were identical with those of the plain specimens.     

Effect of dissolved tungsten on the deformation of 70Ni-30Fe alloys

A series of Ni-Fe alloys containing various levels of tungsten in solid solution have been prepared as a means to assess the influence of solid solution strengthening on the mechanical behavior of monolithic 70Ni-30Fe. In particular, 70Ni-30Fe alloys plus equilibrium concentrations of tungsten in solid solution nominally correspond to the compositions associated with the matrix-only portion of certain tungsten heavy alloys, that is, alloys comprised of a high volume fraction of nominally pure tungsten particles embedded within a minority Ni-Fe-W based matrix. The study shows that the working solubility of tungsten within the 70Ni-30Fe base composition increases slightly with temperature, from approximately 21 wt pct at room temperature to approximately 23 wt pct at 1400 °C. Increasing the level of tungsten in solid solution leads to increases in room-temperature yield strength, tensile strength, and ductility. In contrast, the deformation characteristics of the alloys, as quantified by the power-law work-hardening exponent, n, and the strain-rate-sensitivity exponent, m, show little variation with tungsten solute concentration.     

6005A与6082铝合金热变形流变行为

利用Gleeble-1500热模拟试验机对6005A和6082铝合金进行高温等温压缩试验,研究了在变形温度为450~550℃和应变速率为0.005~10 s^-1条件下两种铝合金的热变形流变行为.6005A铝合金在低应变速率条件下,不同变形温度时的流变曲线均呈现波浪形特征,随着应变速率的增加,硬化和软化接近平衡,表现为稳态流变特征;在高应变速率条件下,硬化过程占据主导地位,回复和硬化过程的竞争使流变曲线呈现波浪形上升的趋势.6082铝合金在低应变速率情况下,不同变形温度时的流变曲线未出现周期性波动;在中等应变速率条件下也表现为稳态流变特征;在高应变速率条件下出现波浪形特征.两种铝合金均为正应变速率敏感材料,其热变形是受热激活控制.最后给出了铝合金热变形条件下流变应力、应变速率和变形温度三者之间的关系式.     

Dislocation structures in the strain localized region in fatigued 70/30 brass and the interaction with grain boundary

Long-term fatigue tests of polycrystalline 70/30 brass were carried out under low strain amplitudes in vacuum, and dislocation structures of the strain localized regions developed were examined by means of transmission electron microscopy In the planar dislocation structures, the strain localized regions (SLRs) bounded by a pair of parallel active glide layers were frequently observed in favorably oriented grains. Where the SLRs impinge on grain boundaries (GBs), extrusion-type deformations were sometimes formed notwithstanding the restraints of the neighboring grains. On the basis of observations, the mechanism of crack initiation at the GB is discussed.