Two-phase Brass Research Articles

ВОССТАНОВЛЕНИЕ ИЗНОШЕННЫХ ПОВЕРХНОСТЕЙ ТРЕНИЯ СКОЛЬЖЕНИЯ ГАЗОДИНАМИЧЕСКИМ НАПЫЛЕНИЕМ МЕДНО-ЦИНКОВЫХ ПОКРЫТИЙ

Preliminary studies of copper and copper-zinc coatings obtained by gas-dynamic spraying have shown high mechanical and tribological properties of the formed functional surfaces. The influence of the modes of spraying and subsequent heat treatment on copper-zinc gas dynamic coatings has been little studied. (Research purpose) The research purpose is investigating the effect of technological modes of spraying, as well as subsequent heat treatment of the coating on its phase composition, structure and properties. (Materials and methods) The coating was applied using a Dimet gas dynamic installation with different overlap of the sprayed layers and subsequent heat treatment of the resulting coating at different temperatures and exposure times. The structure of the coating was studied using an X-ray diffractometer and a spectrometer. Cohesive properties were determined on a bursting testing machine by the "ring separation" method, tribological properties were determined on the MT-8 stand during reciprocating sliding of flat mating bodies. (Results and discussion) It was determined that the chemical and phase composition of the copper-zinc coating applied with a displacement of the nozzle by two millimeters and an air flow temperature of 450 degrees Celsius, after heat treatment in the temperature range of 420-430 degrees Celsius and a holding time of 180 minutes corresponds to two-phase brass type L65. The study of the parameters of the copper lattice shows that after exposure in the furnace for 60 minutes, a two-phase structure is formed based on solid solutions of zinc in copper with different copper content and an electronic-type solid solution based on CuZn. (Conclusions) Tribological tests of the copper-zinc coating in the I-20A industrial oil medium revealed the presence of mutual mass transfer of copper and zinc from the coating to the counterbody and vice versa, which is accompanied by a wear-free effect at a load of up to 10 megapascals. The cohesive strength of the copper-zinc coating depends on the time of heat treatment (phase composition) and after 60 minutes of exposure exceeds the initial values (approximately 78 megapascals) and reaches approximately 93 megapascals.

Self-equilibrated backstresses induce compensation between hardening and softening: Micromechanical and microstructural features

For crystal plasticity formulation neglecting the strain gradients at the dislocation scale, backstresses are necessary to satisfy the mesoscopic stress equilibrium and strain compatibility requirements. Backstresses in a material point and those between neighboring points are treated separately. Physically backstresses can dynamically induce either hardening or softening effects to adjust the dislocation hardening of slip systems, whereas the sum of the stresses resulting in backstresses in the representative volume element (RVE) is zero. Backstress hardening suppresses certain slip activities, while backstress softening triggers excess dislocations.A two-phase brass is studied. Backstresses make the hard phase deform smaller and the soft phase deform more than those without employing backstresses in a model. In the former, more homogeneous lattice strain and higher yield stress are obtained. Backstress has limited effects on the evolution of the critical resolved shear stress and crystallographic texture. However, it is a major cause of the banded structures featuring sharp crystallographic contrasts which are not parallel to the slip planes. Tests indicate that backstress induces a serrated behavior at the early stages of deformation and induces the geometrically necessary bands (GNBs), which are parallel to the macroscopic axes.

Effect of brass composition and phases on stress corrosion mitigation by laser shock peening

While laser shock peening (LSP) is meant to mitigate stress corrosion cracking (SCC) by inducing compressive residual stress, it is also known to produce dense dislocation tangles in the treated surface. The impact of such microstructure changes on SCC resistance is material-dependent and not well-understood. In this study single-phase brass 260 and two-phase brass 280 with different zinc content were LSP treated and subjected to SCC. Besides the competing effects of compressive stress and dislocation generation, dezincification was identified as a contributor to SCC specifically in brasses. Reduction of dezincification from LSP was evaluated using energy dispersive spectroscopy (EDS).

Superplastic deformation behaviour of aluminium containing brasses

Superplastic behaviour of binary two-phase brass and brasses with aluminium addition are compared. Indicators of the superplasticity are considered at a temperature range of 525–600°C and at constant strain rates of 5·10−4s−1 and 1·10−3s−1. The effect of aluminium addition on the superplastic deformation indicators is studied. Improvement of superplasticity and significant decreasing of cavitation are identified due to alloying by aluminium. Surface relief of the samples after superplastic deformation, and grain boundary sliding contribution are analysed, and deformation mechanisms are discussed.

The Influence of Temperature on the Frictional Behavior of Duplex-Coated Die Steel Rubbing Against Forging Brass

Improvement of die life under hot forging of brass alloys is considered vital from both economical and technical points of view. One of the best methods for improving die life is duplex coatings. In this research, the influence of temperature on the tribological behavior of duplex-coated die steel rubbing against forging brass was investigated. The wear tests were performed on a pin-on-disk machine from room temperature to 700 °C; the pins were made in H13 hot work tool steel treated by plasma nitriding and by PVD coatings of TiN-TiAlN-CrAlN. The disks were machined from a two-phase brass alloy too. The results revealed that the friction coefficient of this tribosystem went through a maximum at 550 °C and decreased largely at 700 °C. Furthermore, the formation of Cr2O3 caused the reduction of friction coefficient at 700 °C. PVD coatings proved their wear resistance up to 550 °C, well above the working temperature of the brass forging dies.

A comparative study of surface deformation and quality of brass workpiece in contact with coated dies by pin-on-disc testing

Manufacturing technology must ensure the production of parts with required characteristics: dimensional accuracy, overall strength, and surface quality. The surface layers in metal forming generally remain at the surface. The quality of the deformed surface is therefore determined by the initial surface and the history of the various forming processes undergone. Surface roughness influences surface quality and wear of metal forming products. Pin-on-disc tests at a range of temperatures were employed to study the influence of die coatings on the surface quality of a two-phase brass alloy during forging operation. The pins were made in H13 hot work tool steel and given duplex surface treatments including plasma nitriding and physical vapor deposition (PVD) coatings. The discs were machined from CuZn38Pb2 forging brass. Mechanical properties, surface roughness, and compositional properties of pins were determined by nanoindentaion, two-dimensional profilometer, and scanning electron microscopy equipped with energy-dispersive X-ray detector, respectively. At 25 °C, wear track parameters were more affected by the changes in Young’s modulus and the surface roughness of the pins. At 250 °C, the highest tendency to adhesion was observed in H13 steel pin. At 700 °C, oxidation of the pins influenced the wear track parameters on the discs. R a parameters inside the wear tracks were constant at 25 and 250 °C, but R ku parameters were maximum for the wear tracks of disc in contact with plasma nitriding and H13 pins at 25 and 250 °C, respectively. At 700 °C, the lowest surface quality was for the disc in contact with H13 steel pin. It was concluded that in forging process of brass alloys, the surface quality and deformation behavior of workpiece were improved by applied PVD coating on the surface of the die.

Evolution of texture and grain boundary microstructure in two-phase (α + β) brass during recrystallization

The evolution of texture and microstructure during recrystallization is studied for two-phase copper alloy (Cu–40Zn) with a variation of the initial texture and microstructure (hot rolled and solution treated) as well as the mode of rolling (deformation path: uni-directional rolling and cross rolling). The results of bulk texture have been supported by micro-texture and microstructure studies carried out using electron back scatter diffraction (EBSD). The initial microstructural condition as well as the mode of rolling has been found to alter the recrystallization texture and microstructure. The uni-directionally rolled samples showed a strong Goss and BR {236}⟨385⟩ component while a weaker texture similar to that of rolling evolved for the cross-rolled samples in the α phase on recrystallization. The recrystallization texture of the β phase was similar to that of the rolling texture with discontinuous ⟨101⟩ α and {111} γ fiber with high intensity at {111}⟨101⟩. For a given microstructure, the cross-rolled samples showed a higher fraction of coincident site lattice Σ3 twin boundaries in the α phase. The higher fraction of Σ3 boundaries is explained on the basis of the higher propensity of growth accidents during annealing of the cross-rolled samples. The present investigation demonstrates that change in strain path, as introduced during cross-rolling, could be a viable tool for grain boundary engineering of low SFE fcc materials.

Effect of mode of rolling on development of texture and microstructure in two-phase (α + β) brass

The evolution of microstructure and texture during deformation of two-phase (α+β) brass was studied for different initial microstructure and texture. The deformation processing involved unidirectional and multi-step cross-rolling. The bulk textures were determined by measuring the pole figures and calculating the orientation distribution function ODF for both α (fcc) and β (bcc) phases, while the microstructure and other microstructural parameters were measured through optical microscopy and scanning electron microscopy with electron back scatter diffraction (SEM-EBSD). Results indicate that textures developed after unidirectional rolling and multi-step cross-rolling are significantly different. The variation in initial texture had a pronounced effect on the development of texture in the α phase during subsequent deformation.

Dezincification of Epoxy Coated Brass in Cochin Estuary, India

Inhibited α brasses are largely immune to dezincification in most water, but the effect of tin and arsenic addition to α/β brasses is not so reliable or predictable in controlling the problem. There have been many cases of dezincification in duplex brasses in both fresh water and seawater. There is no reliable method of inhibiting the dezincification of two-phase brass despite there are some protection methods such as inhibitors, electro deposition and electro polymerization. Organic coatings are effectively used for the protection of metals due to their capacity to act as a physical barrier between the metal surface and corrosive environment. Hence, epoxy coating on brass was applied and effect of this against dezincification in Cochin estuarine water over a period of one year was studied and reported in this paper.

Effect of thermomechanical processing on grain boundary characteristics in two-phase brass

Commercial 60Cu–40Zn two-phase α–β′ alloy was thermomechanically processed to enhance the special low CSL boundaries. Repeated cycles of cold rolling (20%) and heat treatment (680°C/20min) resulted in an increase in Σ3 boundaries in the α phase that were identified as the annealing twins in the Electron Backscattered Diffraction analysis. The identical processing, however, produced a high frequency of low angle boundaries within the β′ phase. Formation of annealing twins in the α phase was accompanied by randomization of the texture of the starting material. The present result demonstrates the effectiveness of this thermomechanical processing in promoting annealing twins in the fcc α phase compared to the bcc β′ phase of commercial brass.

The Orientation Dependence of Crystallite Stresses in a Deformed Alloyed Steel and a Rolled Two-Phase Brass

The proposed evaluation of strain data measured by diffraction methods allows to determine the dependence of crystallite stress tensors on their orientation within the polycrystal, i.e. the stress-orientation-functions (SOF). The procedure is shortly reviewed. It is applicable even if the texture and the microstresses strongly influence the measured strains and the usual sin 2 ψ-method of stress evaluation can not be used any more. This appears especially after uniaxial deformation. The SOF has been determined from the strains measured on a rolled brass material and an alloyed steel each after two different grades of deformation.

Determination of the Interaction Strains in Two-Phase Brass with X-Ray Diffraction

AbstractDeformation in polycrystalline materials is highly inhomogeneous on a micro scale. This inhomogeneity arises from the anisotropy of the constituent grains, coupled with local configurational parameters such as texture, gram size or proximity to a free surface. In a recent paper, we had outlined a new method that extended the traditional x-ray stress analysis to yield quantitative measures of such inhomogeneous deformation. In this paper, this method is used to study the partitioning of inhomogeneous deformation between the phases of 60-40 brass tensile specimens subjected to applied loads.

Deformation behaviour in α/β two-phase super-plastic brass

Deformation behaviour in α/β two-phase super-plastic brass

Positron lifetimes in deformed two-phase brass

Positron lifetimes in deformed two-phase brass

X-ray diffraction study of changes in stress-strain distributions during the fatigue of a two-phase alloy

In annealed two-phase brass, push-pull fatigue at loads near the endurance limit produces residual stresses only in the softer majority α phase and not in the β phase. These stresses are balanced between undeformed α phase regions and a small fraction of deformed α; the β phase is not involved in this balance. The uniform deformation produced by peening becomes inhomogeneous during fatigue, especially in the softer α phase. This inhomogeneity of deformation is greater after fatigue of the peened specimens than after fatigue of annealed material.

An X-ray diffraction study of the residual stress-strain distributions in shot-peened two-phase brass

X-ray residual stress determination and line-broadening analysis were used to study the deformation distributions existing in the surface layers of a shot-peened two-phase brass specimen. The results indicate inhomogeneous partitioning of the plastic strains between the α and β grains, as well as between the surface layers and the bulk. The residual microstresses, which occur because of the differential deformation between the α and β grains, have a maximum in the β grains at the material surface, while the residual macro-stresses, which arise because of the differential plastic deformation between the surface and the bulk, exhibit a maximum deeper in the material. A qualitative model (describing these residual stress profiles in terms of the plastic strains caused by the peening operation) is presented.

Phase transformation in two-phase α+β′ brasses

The influence of lead, tin, and manganese on the low-temperature transformations of two-phase brasses was studied. Heat treatment was applied in one and in two stages: quenching from the β-phase temperature range, and quenching followed by annealing in the temperature range 100°–400°C. Hardness measurements, tensile tests, diltometric studies, and electron and optical microscopy were used to study the changes in physical and mechanical properties following these two heat treatments. It was shown that lead, tin, and manganese have a significant influence on the structure and properties of two-phase brass.

Acoustic emission of two-phase brass

The acoustic emission occurring during the deformation of two-phase β′ + γ brass was analysed. A fundamental difference between the acoustic signal arising during flow of the plastic β′ phase and that originating during cracking of the brittle γ phase was established. Measurements of the acoustic emission of single-phase β′ brass were also carried out in order to isolate the acoustic signal caused by cracking of the γ phase. A good correspondence was established between the intensity of the acoustic signal and the number of cracked grains at particular stages of deformation.

黄銅の脱亜鉛腐食

The observation with an optical microscope and an electron probe microanalyzer (EPMA) has been made on copper-zinc alloys electrochemically dezincified in a 3% NaCl aqueous solution and the Admiralty and Munty metal dezincified in practical use, respectively. In a groupe of α-brasses, the alloys of low zinc content are easily dezincified at the less noble potentials. In a two-phase brass, β-phase were dezincified more rapidly than α-brass, but the depth and morphology of the dezincified layer were independent of the potentiostatically applied potential. Measuring with EPMA, the Zn Kα radiation was not detected in the dezincified α-brass. On the other hand, in the two-phase brass the dezincified β phase grains emitted the Zn Kα radiation. The dezincification seems to start from the grain boundary and propagate into the inside of the grain. The Zn Kα radiation appears to be emitted from accumulated corrosion products of zinc near dissolution sites. Because of the presence of a surface films, the potential at the metal-solution interface may be less noble than the applied potential. At that potential, brass dissolve in the solution and the copper ions in the solution deposit on the brass surface.

銅合金ばね材料の改良に関する研究（第3報）黄銅系ばね材料の経年変化現象とその防止

One of the most unfavorable defects of a spring sheet of brass is that the spring properties change with time at room temperature after working or low-temperature annealing. The authors have researched the phenomenon and could find the possibility to suppress the secular change after low-temperature annealing. The secular change after final low-temperature annealing was considered to be related with the change after cold-rolling. The secular change after cold-rolling had a tendency to stabilize the spring properties and, if the brass plate as rolled was low-temperature annealed after being left at room temperature long enough to stabilize its properties of cold-rolled condition, the change after low-temperature annealing could be decreased. The secular change of two-phase brass, namely, of 60/40 brass, could be considered as the combined effect of α- and β-brass, though β-brass showed more complicate change than α-brass. All the experiments were carried out atroom temperature and the constat temperatures of 25° or 40°.