Abnormal ductility increase of commercial purity Al during accumulative roll bonding

In this paper, sheets of commercial purity Al were fabricated by the accumulative roll-bonding (ARB) method up to six cycles. To increase the shear deformation, no lubricant was used during the ARB processing and the samples were carried out for ARB processing without any preheat treatment. One interesting finding is that the ductility and strength both increased during the first several cycles of ARB processing. It is proposed that the initial rolling texture might play an important part in the subsequent ARB processing since the original Al sheets for ARB processing have not been subjected to any annealing. The microstructures of the specimens after each ARB cycle were investigated by transmission electron microscopy and correlated with the mechanical properties

Response of the al Σ5 〈001〉 left {310} symmetric tilt grain boundary to the shear deformation simulated by molecular dynamics

In the present study, shear response of the Al [001] symmetrical tilting Σ5 (310) grain boundary (GB) was investigated by a three dimensional bicrystal at 500~750 K. It was found that the GB gradually rotated around the [001] tilt axis during the shear deformation due to the combination of surface strain, GB sliding and GB coupled motion. These rotated grain boundaries were Σ5 asymmetrical or symmetrical tilt grain boundaries and led to the normal stress σxx in the bicrystal system. It was also found that the response of the grain boundary to the shear deformation was closely related to the temperatures. At lower temperature (500~650 K), further shear deformation was mediated by crack initiation or dislocation release which is closely related to the local stress condition and temperature etc. The lattice dislocations emitted from GB were identified as pure edge dislocations with Burgers vectors of 〈110〉/2. Interestingly, they have the [001] line direction and glide on the left curly bracket110right curly bracket planes. The reaction between grain boundary and lattice dislocations has been carefully discussed with its role in the shear deformation. At higher temperatures (above 700 K), after a short while of perfect coupling at the early stage the grain boundary quickly rotated and the two grains smoothly slid away from each other in the way of viscous grain boundary sliding under the shear deformation. 2014 by American Scientific Publishers

A dual deformation mechanism of grain boundary at different stress stages

Molecular dynamics (MD) simulation with embedded-atom method (EAM) potential was carried out to study the structure and shear response of an asymmetric tilt grain boundary in copper bicrystal. A non-planar structure with dissociated intrinsic stacking faults was observed in the grain boundary. Simulation results show that this type of structure can significantly increase the ductility of the simulation sample under shear deformation. A dual deformation mechanism of the grain boundary was observed; the grain boundary can be a source of dislocation emission and migrate itself at different stress stages. The result of this study can provide further information to understand the grain boundary mediated plasticity in nanocrystalline materials

Surface film adsorption and lubricity of soybean oil in-water emulsion and triblock copolymer aqueous solution: A comparative study

This paper investigates the surface film adsorption and lubricity of two different types of potential environmentally friendly cold metal forming lubricants: soybean vegetable oil in water VO/W emulsions and triblock copolymer aqueous solutions. The lubricants have different visual appearance, surface film adsorption characteristic, lubricity and surface cleaning behaviour. The effects of concentration, temperature and emulsification ultrasonic energy (for VO/W emulsion) are studied. The result shows that the soybean VO/W emulsions have stronger adsorption, superior lubricity and anti-wear property compared to the copolymer solutions. The effect of temperature is investigated at 30 °C and 65 °C which are below and above cloud point of the aqueous copolymer solutions. Both lubricants show improved friction and anti-wear property at 65 °C. However, tenacious residual film remained on the discs surface after surface cleaning indicates lower cleanability of the soybean VO/W emulsions compared to the copolymer solutions, postulating the need for extra post-processing cleaning operations after cold forming process with VO/W emulsion lubricant

Microstructure and mechanical properties of AA5005/AA6061 laminated composite processed by accumulative roll bonding

ULTRAFINE-GRAINED (UFG) materials have been gathering much interest for the last two decades as the materials have extraordinary mechanical properties such as high strength, low temperature superplastisity, and high corrosion resistance. Severe plastic deformation (SPD) is the most widely used method to produce UFG materials. Accumulative roll bonding (ARB) has become one of the most important SPD techniques since it was first introduced by Saito et al.[1] As the same equipment as in conventional rolling is used, ARB is considered to be one of the most promising methods for manufacturing UFG sheet materials

Integrated Condition Monitoring and Prognosis Method for Incipient Defect Detection and Remaining Life Prediction of Low Speed Slew Bearings

This paper presents an application of multivariate state estimation technique (MSET), sequential probability ratio test (SPRT) and kernel regression for low speed slew bearing condition monitoring and prognosis. The method is applied in two steps. Step (1) is the detection of the incipient slew bearing defect. In this step, combined MSET and SPRT is used with circular-domain kurtosis, time-domain kurtosis, wavelet decomposition (WD) kurtosis, empirical mode decomposition (EMD) kurtosis and the largest Lyapunov exponent (LLE) feature. Step (2) is the prediction of the selected features\u27 trends and the estimation of the remaining useful life (RUL) of the slew bearing. In this step, kernel regression is used with time-domain kurtosis, WD kurtosis and the LLE feature. The application of the method is demonstrated with laboratory slew bearing acceleration data

Friction and anti-wear property of aqueous tri-block copolymer solutions in metal forming

Friction and anti-wear property of aqueous symmetrical tri-block normal PEOm-PPOn-PEOm and reverse PPOn-PEOm-PPOn copolymer solutions have been studied. The study focuses on the effect of the solution bulk temperatures and the copolymer block structures. It was found that the concentration and the length of the copolymer blocks affect the solution cloud points, friction and anti-wear property. When solution was supplied at bulk temperature above their cloud point, aqueous copolymer solutions were not able to develop effective adsorbed film resulting in high friction and severe wear. When the bulk temperatures were below the cloud point, the anti-wear property improved significantly and the dynamic friction is lower than that when the temperatures were above the cloud point. This demonstrates the importance of the supply temperature of this type of lubricant in metal forming. However by adding ethyl phosphate ester to the copolymer solutions further improved friction reducing property of the solutions was observed and the friction and anti-wear property of the lubricant become insensitive to bulk temperature. In the effort to understand the lubrication mechanism of the aqueous solutions, wear tracks were studied using scanning electron microscope (SEM) and atomic force microscope (AFM), and the surface wetting ability via contact angle measurements

Influence of loading conditions during tensile testing on acoustic emission

The Acoustic Emission (AE) monitoring technique is widely used in mechanical and material research for detection of plastic deformation, fracture initiation and crack growth. However, the influence of AE features (such as signal amplitude, frequency, rise time and duration) on the fracture parameters (such as brittle or ductile mode of propagation and fracture propagation speed) is not completely understood. In this paper, the effect of loading conditions on fracture behavior was studied using AE monitoring during tensile testing of an aluminum alloy specimen. The fracture development was observed using a high speed video camera and was analyzed using the finite element method. The hardware and software produced by Physical Acoustics Corporation (USA) was used. Variations in AE parameters were analyzed and correlated to the stress-Strain curves obtained during testing. It is shown that the strain rate and the presence of a crack (modeled by a notch on the sample), affect the fracture mode (brittle or ductile) and a relative amount of the mode dependent AE signatures

Lubricant as a sticking-scale inhibitor on high temperature sliding contact

Sticking oxide scale is one of the most serious concerns on moving steel surfaces at elevated temperature. However, there has been limited research dedicated to overcoming this issue. In the present work, pin-on-disc testing was carried out to reveal the effects of lubrication on wear characteristics of High Speed Steel sliding against Stainless Steel 316 at 700 °C. Apart from improved friction behavior, the use of inorganic lubricant significantly inhibits material transfer onto the HSS surface which otherwise suffers growing adhered scale during dry sliding contact. In addition, it was found that prolonged exposure to lubrication induces phase transformation of the subsurface iron oxides. The Hematite-to-Magnetite conversion is believed to be a result of complex oxidation and tribological reactions. Multiple characterization techniques were used to thoroughly analyze the worn surfaces, the underlying oxide microstructure and the chemical nature of lubricated interface

Coupled effects of initial orientation scatter and grain-interaction to texture evolution: a crystal plasticity FE study

Grain orientation and neighbourhood are two main factors that determine the in-grain and global texture. The coupled effects of them to texture evolution has not been well understood. In this work, initial orientations scattered from exact Cube at four different levels (2 ° , 5 ° , 20 ° and 45 ° ) were developed, running from near single crystal to polycrystal, which yielded grain-interaction at various grades. A crystal plasticity finite element model was developed and the predicted texture after a 50% and 75% reduction has been validated by experimental observations of both single crystals and polycrystals. When the deviation angles are small, the global texture is similar to that in exact Cube, where crystal rotation about transverse direction is dominant. Initial orientations of large scatter and grains of strong interaction led to high crystal rotations and the formation of rolling texture. To study the grain-interaction to specific grains, the orientations of neighbouring grains were replaced. It was found that texture evolution in the region close to grain boundaries is sensitive to grain-interaction, while crystal rotations in the inner region are basically determined by the initial orientation