Showing papers in "Journal of Materials Engineering and Performance in 2007"

Superplastic Forming 40 Years and Still Growing

Abstract: In late 1964 Backofen, Turner & Avery, at MIT, published a paper in which they described the “extraordinary formability” exhibited when fine-grain zinc-aluminum eutectoid (Zn 22 Al) was subjected to bulge testing under appropriate conditions. They concluded their research findings with the following insightful comment “even more appealing is the thought of applying to superplastic metals forming techniques borrowed from polymer and glass processing.” Since then their insightful thought has become a substantial reality with thousands of tons of metallic sheet materials now being superplastically formed each year. This paper reviews the significant advances that have taken place over the past 40 years including alloy developments, improved forming techniques and equipment, and an ever increasing number of commercial applications. Current and likely future trends are discussed including; applications in the aerospace and automotive markets, faster-forming techniques to improve productivity, the increasing importance of computer modeling and simulation in tool design and process optimization and new alloy developments including superplastic magnesium alloys.

Effect of Cement on Emulsified Asphalt Mixtures

Abstract: Emulsified asphalt mixtures have environmental, economical, and logistical advantages over hot mixtures. However, they have attracted little attention as structural layers due to their inadequate performance and susceptibility to early life damage by rainfall. The objective of this article is to provide an improved insight into how the mechanical properties of emulsion mixtures may be improved and to determine the influence of cement on emulsified asphalt mixtures. Laboratory tests on strength, temperature susceptibility, water damage, creep and permanent deformation were implemented to evaluate the mechanical properties of emulsified asphalt mixtures. The test results showed that mechanical properties of emulsified asphalt mixtures have significantly improved with Portland cement addition. This experimental study suggested that cement modified asphalt emulsion mixtures might be an alternate way of a structural layer material in pavement.

Material Formability and Coil Design in Electromagnetic Forming

Abstract: Pulsed electromagnetic forming is based on high-voltage discharge of capacitors through a coil. An intense transient magnetic field is generated in the coil and through interaction with the metal work-piece; pressure in the form of a magnetic pulse is built up to do the work. Data on formability of two aluminum alloys employed for exterior (6111-T4) and interior (5754) automotive body panels will be shown. Comparison of traditional Forming Limit Diagrams obtained by stretching of aluminum sheet with hemispherical punch to the results on formability, where hemispherical punch is replaced by a coil will be provided. It will be shown that material formability in high-rate forming conditions can significantly depend upon interaction with the forming die: electromagnetic forming into an open round window provides only slight improvement in formability, while forming in a V-shape die or into a conical die indicates a significant improvement. An important part of the electromagnetic forming technology is the design of the coil. The coil failure modes and measures preventing them are discussed.

Slurry Erosion Studies on Surface Modified 13Cr-4Ni Steels: Effect of Angle of Impingement and Particle Size

Abstract: Hydroturbine steels, such as 13Cr-4Ni martensitic steels, are generally subjected to heavy-erosive wear and loss of efficiency due to solid particulate entrainment in the water. Surface-modified steels have proven to give better performance in terms of erosive wear resistance. In the present study, an attempt is made to investigate the effect of angle of impingement and particle size on slurry-jet erosion behavior of pulsed plasma nitrided and laser hardened 13Cr-4Ni steels. Laser hardening process has shown good performance at all angles of impingement due to martensitic transformation of retained austenite. Plastic deformation mode of material removal was also an evident feature of all laser-hardened surface damage locations. However, pulsed-plasma nitrided steels have exhibited chip formation and micro-cutting mode of erosive wear. Erosion with 150-300 μm size was twice compared to 150 μm size slurry particulates.

Investigation of the Friction Stir Lap Welding of Aluminum Alloys AA 5182 and AA 6022

Abstract: Friction stir lap welding of the similar and dissimilar aluminum alloys is investigated. AA 5182 and AA 6022 aluminum alloys (the widely used aluminum alloys for automobile applications) are selected for the feasibility studies. The friction stir lap welding shows that the placement of the aluminum alloys in the different orders over each other affect the final weld quality and its mechanical properties. The welding parameters such as rotational and traverse speeds and the penetration depth are key factors to affect the micro-structure soundness. The mechanical and the micro-structural characterization is performed on the joints formed with varying welding parameters and from the different order of placement of the AA 6022 and the AA 5182 sheets. The weld failure occurs on the advancing side during the peel tests indicating that the retreating side is relatively stronger. Measured temperatures indicate that the advancing side has higher developed temperature during the course of welding compared to the retreating side.

Deformation mechanisms of Ti-6Al-4V during tensile behavior at low strain rate

Abstract: A superplastic Ti-6Al-4V grade has been deformed at a strain rate of 5 × 10−4 s−1 and at temperatures up to 1050 °C. Structural mechanisms like grain boundary sliding, dynamic recrystallization, and dynamic grain growth, occurring during deformation, have been investigated and mechanical properties such as flow stress, strain hardening, and strain at rupture have been determined. Dynamic recrystallization (DRX) brings on a decrease in the grain size. This could be of great interest because a smaller grain size allows a decrease in temperature for superplastic forming. For DRX, the driving force present in the deformed microstructure must be high enough. This means the temperature must be sufficiently low to ensure storing of enough dislocation energy but must also be high enough to provide the activation energy needed for DRX and to allow superplastic deformation. The best compromise for the temperature was found to be situated at about 800 °C; this is quite a bit lower than the 925 °C referenced in the literature as the optimum for the superplastic deformation. At this medium temperature the engineering strain that could be reached exceeds 400%, a value high enough to ensure the industrial production of complex parts by the way of the superplastic forming. Microstructural, EBSD, and mechanical investigations were used to describe the observed mechanisms, some of which are concurrent.

Application of a Uniform Pressure Actuator for Electromagnetic Processing of Sheet Metal

Abstract: High-velocity electromagnetic sheet-metal forming and processing has many potential advantages over more conventional techniques, including: higher-forming limits, resistance to wrinkling and springback, one-sided tooling, and physical contact to only one side of the work piece. Traditional electromagnetic actuators are flat spirals that produce a nonuniform pressure distribution, limiting the types of parts that can be formed. A new type of electromagnetic actuator, the uniform pressure (UP) actuator, has been developed. The UP actuator can uniformly and efficiently accelerate conductive sheet metal to velocities on the order of 200 m/s or greater over distances of a few millimeters. When the material is arrested by impact with a tool, high-forming pressures can be imparted to it. The utility of the UP actuator is illustrated here by demonstrating its ability to form sheet metal components with intricate shape, to shock harden, and also to pick up nearly arbitrarily small details from a die surface. Thus, electromagnetic processing with the use of the UP actuator offers the unprecedented ability to simultaneously form and engineer the surface morphology and microstructure of sheet metal samples.

Metallurgical Evaluation of AZ31B-H24 Magnesium Alloy Friction Stir Welds

Abstract: Friction Stir welding of 3.175 mm (0.125 in.) thick plates of AZ31-H24 magnesium alloy was performed using several travel velocities and tool-rotation speeds. After production the welds were cross-sectioned and a metallurgical characterization was performed using optical microscopy, and scanning electron microscopy. Assessment of the weld nugget or “stirred zone” shows evidence of dynamic recrystallization and the start of grain growth in some spots of this region compared to the parent metal. Recrystallization was identified in the thermomechanically affected zone (TAZ) as well. The mechanical properties of the weld are correlated with the corresponding microstructures present in the weld nugget and TMAZ. Corrosion resistance of the weld was assessed using Electrochemical Impedance Spectroscopy (EIS) techniques and immersion tests in a corrosive environment; it showed better corrosion resistance than the base metal.

Dendritic Growth in an Aluminum-Silicon Alloy

Abstract: Unidirectional solidification experiments have been carried out on an Al-3 wt.% Si alloy as a function of temperature gradient, G and growth rate, V. The samples were solidified under steady-state conditions with a constant growth rate of 8.20 μm/s at different temperature gradients (1.97-6.84 K/mm) and with a constant temperature gradient (6.84 K/mm) at different growth rates (8.20-492.76 μm/s). Microstructure parameters (primary dendrite arm spacing, λ1, secondary dendrite arm spacing, λ2, dendrite tip radius, R and mushy zone depth, d) were measured as a function of temperature gradient and growth rate. The experimental results have been compared with the current theoretical models and similar experimental works.

Commercial Airplane Applications of Superplastically Formed AA5083 Aluminum Sheet

Abstract: This article discusses some of the advances that have been made at Boeing Commercial Airplanes during the manufacture of superplastically formed (SPF) AA5083 aluminum components for aircraft applications This specially processed material is the lowest cost aluminum alloy that exhibits superplastic properties Therefore, the use of 5083 would be beneficial to aircraft in forming complicated configurations Since this aluminum alloy is non-heat treatable and therefore low strength, it is not typically considered a material for use on commercial airplanes However, applications have been found on the Boeing Commercial fleet that provide lower cost hardware which, in some cases, is lighter weight Design Engineers have been able to take advantage of the benefits of using SPF sheet metal hardware fabricated from AA5083 in areas where failure of the component during flight would not cause loss of the aircraft SPF AA5083 components have replaced aluminum castings, fiberglass assemblies, and components fabricated by SPF from other aluminum alloys Since this alloy is non-heat treatable, the cost of heat treating, quenching, and aging is avoided Also, there is no contour distortion to straighten due to the solution heat treating and quenching process Therefore, the quality of the hardware being delivered to the customer is greatly improved

Mechanical Characteristics of Superplastic Deformation of AZ31Magnesium Alloy

Abstract: As the lightest constructional metal on earth, magnesium (and its alloys) offers a great potential for weight reduction in the transportation industry. Many automotive components have been already produced from different magnesium alloys, but they are mainly cast components. Production of magnesium outer body components is still hindered by the material’s inferior ductility at room temperature. Magnesium alloys are usually warm-formed to overcome this problem; however, it was observed that some magnesium alloys exhibits superior ductility and superplastic behavior at higher temperatures. More comprehensive investigation of magnesium’s high temperature behavior is needed for broader utilization of the metal and its alloys. In this work, the high temperature deformation aspects of the AZ31B-H24 commercial magnesium alloy are investigated through a set of uniaxial tensile tests that cover forming temperatures ranging between 23 and 500 °C, and constant true strain rates between 2 × 10−5 and 2.5 × 10−2 s−1. The study targets mainly the superplastic behavior of the alloy, by characterizing flow stress, elongation-to-fracture, and strain rate sensitivity under various conditions. In addition, the initial anisotropy is also investigated at different forming temperatures. The results of these and other mechanical and microstructural tests will be used to develop a microstructure-based constitutive model that can capture the superplastic behavior of the material.

New methods for severe plastic deformation processing

Abstract: Several new concepts for possible methods of severe plastic deformation (SPD) of bulk quantities of materials are presented. The first of these are variations of equal channel angular extrusion (ECAE) in which the conventional fixed die is replaced by rotating tools, for the inner die corner, the outer die corner, or both corners. Other methods share some characteristics of ECAE in that they use shearing strains to deform the material; these are reversed shear spinning and transverse rolling. Deformation sequences for a cylindrical or annular workpiece that deform the workpiece while eventually restoring the initial workpiece geometry can be performed by numerous processes. These techniques can be used to accumulate high strains by repeated deformation cycles. These methods offer possible alternatives to ECAE and high-pressure torsion, with potential benefits that include different and larger workpiece geometries, simplified tooling design, lower tooling loads, ease of lubrication, automated or reduced part handling, and, in some cases, potentially continuous operation. It is hoped that these suggestions will prompt new examination of alternative methods for SPD.

Tensile, Compression and Fracture Properties of Thick-Walled Ductile Cast Iron Components

Abstract: The article presents the outcome of a comprehensive program of tensile, compression and fracture toughness experiments, addressing thick-walled ductile cast iron inserts used for the production of three nuclear waste canisters. The resulting data are required as input to the assessment of the failure probability of the canisters. Moreover, these data are useful for the improvement of the casting technique as such. Although the same material specification is always used, material properties are found to show significant variation. Considerable attention is paid to linking the scatter in tensile properties to fractographic and microstructural observations. The main finding is that low ductility tensile test results can be primarily connected to the presence of specific casting defects, from which oxide films have the most detrimental effect. Another important observation is that compression experiments do not result in low ductility failure. During fracture testing, stable ductile crack propagation is observed. Basic fracture analysis of a tensile test is performed in order to better understand the effect of defect size, stress-strain behavior and fracture toughness on the ductility measured through tensile testing. Two opposing specimen size effects are observed.

Numerical and Experimental Evaluation of Springback in Advanced High Strength Steel

Abstract: The automotive industry is using more and more of Advanced High Strength Steel in order to reduce the weight of the car. Since this will generate more springback, it is of vital importance to be able to predict the amount of springback in the parts. Otherwise, many late changes have to be made in order to fit the parts in their position. In order to increase the ability to understand and test the behavior of the springback in sheet-metal parts, a new semi-industrial experimental tool, the flex-rail, has been developed. This is a very flexible tool, which can be used for various kinds of materials, from mild steel and aluminum to advanced high strength steel such as TRIP-steel and CP-steel by using different insert. The tool is designed for experimental analysis of 3D-springback, which is the case in the more complicated automotive parts, such as b-pillars and side members. The scope of this work is to analyze the springback behavior and prediction for Advanced High Strength Steel both numerically and experimentally. Sheet-metal-forming simulations were made in LS-DYNA. The results proved that the new geometry, flex-rail, gave a complex springback behavior for all tested materials. Furthermore, the prediction of springback showed good correlation in sections with small amounts of twist but that LS-DYNA under-predicts the springback for sections with large amounts of twist for all materials except DP600.

The Effect of Surface Engineering Treatments on the Fatigue Behavior of 2024-T351 Aluminum Alloy

Abstract: The work examines the effect of controlled shot peening (CSP), laser shock peening (LSP) and ultrasonic impact treatment (UIT) on the fatigue behavior of 2024-T351 aluminum alloy. The testing methodology has been designed to extract information regarding specific products of the treatments and their individual affect on fatigue damage. The work concludes that all three surface treatments improve the fatigue resistance of the material with the LSP covering the areas of safe-life and damage tolerance, the control shot peening can only benefit the area of short crack growth while the UIT proved to benefit both the short and long crack growth.

Physical and Magnetic Properties of Calcium-Substituted Li-Zn Ferrite

Abstract: The effect of Ca-substitution on the physical and magnetic properties of Li0.3-0.5x Zn0.4Ca x Fe2.3-0.5x O4 ferrites (x = 0.0, 0.01, 0.02, 0.03, and 0.05), prepared by the standard ceramic method, has been studied. It is found that the saturation magnetization increases up to x = 0.01 and then it decreases. On the other hand, the initial permeability decreased while the Curie temperature remained almost constant with increasing x. The coercivity and remanence ratio increased with increasing x.

Modeling Microstructural Evolution During Dynamic Recrystallization of Alloy D9 Using Artificial Neural Network

Abstract: An artificial neural network (ANN) model was developed to predict the microstructural evolution of a 15Cr-15Ni-2.2Mo-Ti modified austenitic stainless steel (Alloy D9) during dynamic recrystallization (DRX). The input parameters were strain, strain rate, and temperature whereas microstructural features namely, %DRX and average grain size were the output parameters. The ANN was trained with the database obtained from various industrial scale metal-forming operations like forge hammer, hydraulic press, and rolling carried out in the temperature range 1173-1473 K to various strain levels. The performance of the model was evaluated using a wide variety of statistical indices and the predictability of the model was found to be good. The combined influence of temperature and strain on microstructural features has been simulated employing the developed model. The results were found to be consistent with the relevant fundamental metallurgical phenomena.

Experimental Validation of Two-dimensional Finite Element Method for Simulating Constitutive Response of Polycrystals During High Temperature Plastic Deformation

Abstract: A finite element method was recently designed to model the mechanisms that cause superplastic deformation (A.F. Bower and E. Wininger, A Two-Dimensional Finite Element Method for Simulating the Constitutive Response and Microstructure of Polycrystals during High-Temperature Plastic Deformation, J. Mech. Phys. Solids, 2004, 52, p 1289–1317). The computations idealize the solid as a collection of two-dimensional grains, separated by sharp grain boundaries. The grains may deform plastically by thermally activated dislocation motion, which is modeled using a conventional crystal plasticity law. The solid may also deform by sliding on the grain boundaries, or by stress-driven diffusion of atoms along grain boundaries. The governing equations are solved using a finite element method, which includes a front-tracking procedure to monitor the evolution of the grain boundaries and surfaces in the solid. The goal of this article is to validate these computations by systematically comparing numerical predictions to experimental measurements of the elevated-temperature response of aluminum alloy AA5083 (M.-A. Kulas, W.P. Green, E.M. Taleff, P.E. Krajewski, and T.R. McNelley, Deformation Mechanisms in Superplastic AA5083 materials. Metall. Mater. Trans. A, 2005, 36(5), p 1249–1261). The experimental work revealed that a transition occurs from grain-boundary sliding to dislocation (solute-drag) creep at approximately 0.001/s for temperatures between 425 and 500 °C. In addition, increasing the grain size from 7 to 10 μm decreased the transition to significantly lower strain rates. Predictions from the finite element method accurately predict the effect of grain size on the transition in deformation mechanisms.

A Comparison of Aging Kinetics of New and Rejuvenated Conventionally Cast GTD-111 Gas Turbine Blades

Abstract: Two industrial gas turbine blades made from a conventionally cast Ni-base superalloy GTD-111, one new and the other rejuvenated, were removed from the same machine after a particular operational cycle for an examination in order to determine the effect of rejuvenation on the material’s behavior during service. It was found that service-induced changes in the microstructure, such as γ′-phase coarsening and coalescence, excessive grain-boundary secondary M23C6 carbides formation, and primary MC carbides decomposition, were noticeably more advanced in the rejuvenated blade. The stress-rupture life of the rejuvenated blade decreased significantly compared to that of the new blade after the same number of hours in service. The cause of this decrease appears to be related to a release of additional amounts of carbon and carbide-forming elements into the matrix during rejuvenating heat treatment as a result of the primary MC carbide decomposition.

A Microstructure Study on an AZ31 Magnesium Alloy Tube after Hot Metal Gas Forming Process

Abstract: An AZ31 magnesium alloy tube has been deformed by the hot metal gas forming (HMGF) technique. Microstructures before and after deformation have been investigated by using Electron Backscattered Diffraction (EBSD) and Electron Microscopy. Due to the inhomogeneous distribution by induction heating, there is a temperature gradient distribution along the tube axis. Accordingly, the deformation mechanism is also different. In the middle area of deformation zone where the temperature is ∼410 °C, almost no twinning has been found, whereas at the edge areas of deformation zone where the temperature is ∼200 °C, a high density of twins has been found. EBSD experiments show a weak (0001) fiber texture along the radial direction of the tube before and after deformation in the high-temperature zone. EBSD experiments on the low temperature deformation region were not successful due to the high stored energy. Schmid factor analysis on the EBSD data shows that, despite the (0001) fiber texture, there are still many grains favoring basal slip along both the axis direction and hoop direction.

Residual Stress Evaluation of AA2024-T3 Friction Stir Welded Joints

Abstract: The main aim of this study was to evaluate the residual stress field in friction stir welded joints of 2024-T3 aluminum alloy plates using the slitting method. This is based on the fact that when a cut, simulating a growing crack, is incrementally introduced into a part, residual stresses are relieved on the slot surfaces created, causing the part to deform. Such deformation can be measured by strain gages attached to specific regions of the part and the residual stress profile that originally existed can be evaluated. Cuts were introduced by wire electro discharge machining (WEDM), in finishing mode, either perpendicularly or longitudinally to the weld nugget, in 3.2 · 60 · 120 mm 3 rectangular testpieces. For the longitudinal testpieces, the slot was introduced in two different positions: on the center of the weld nugget and 5 mm distant from the weld center line, in order to sample the thermomechanically/heat affected zone. The residual stress intensity factor, Kr, was calculated using a fracture mechanics approach and the inverse weight function method was employed to obtain the initial residual stress profile. Residual stress redistribution profiles ahead of the slot tip could also be derived using the inverse weight function method. However, for cracked components subjected to compressive residual stress fields, when the crack faces are in contact, a non-linear problem arises and the zero displacement condition has to be taken into account in order to provide a more accurate solution of the residual stress field.

Effect of Mg Content on the Performance of Al-Zn-Mg Sacrificial Anodes

Abstract: Aluminum sacrificial anodes are widely used in cathodic protection of steel structures in sea water. In the present work, samples of Al-5.3 at.% Zn-x at.% Mg (x = 5.5-8.5) alloys were microstructurally and electrochemically characterized to evaluate their performance as Al-sacrificial anodes for cathodic protection of structures exposed to marine environments. The experiments focussed on the influence of Mg content on electrochemical behavior and efficiency. Mg was used in different concentrations ranging from 5.5 to 8.5 at.%. Short-term electrochemical tests, DNV RP B401, as well as polarization curves and electrochemical impedance spectroscopy were performed to obtain electrochemical behavior and efficiency and to reveal any tendencies to passivation. It is shown that by increasing Mg content an improvement of electrochemical properties of Al-alloy such as current capacity and then electrochemical efficiency can be obtained.

Understanding the Influence of Copper Nanoparticles on Thermal Characteristics and Microstructural Development of a Tin-Silver Solder

Abstract: This paper presents and discusses issues relevant to solidification of a chosen lead-free solder, the eutectic Sn-3.5%Ag, and its composite counterparts. Direct temperature recordings for the no-clean solder paste during the simulated reflow process revealed a significant amount of undercooling to occur prior to the initiation of solidification of the eutectic Sn-3.5%Ag solder, which is 6.5 °C, and for the composite counterparts, it is dependent on the percentage of copper nanopowder. Temperature recordings revealed the same temperature level of 221 °C for both melting (from solid to liquid) and final solidification (after recalescence) of the Sn-3.5%Ag solder. Addition of copper nanoparticles was observed to have no appreciable influence on melting temperature of the composite solder. However, it does influence solidification of the composite solder. The addition of 0.5 wt.% copper nanoparticles lowered the solidification temperature to 219.5 °C, while addition of 1.0 wt.% copper nanoparticles lowered the solidification temperature to 217.5 °C, which is close to the melting point of the ternary eutectic Sn-Ag-Cu solder alloy, Sn-3.7Ag-0.9Cu. This indicates the copper nanoparticles are completely dissolved in the eutectic Sn-3.5%Ag solder and precipitate as the Cu6Sn5, which reinforces the eutectic solder. Optical microscopy observations revealed the addition of 1.0 wt.% of copper nanoparticles to the Sn-3.5%Ag solder results in the formation and presence of the intermetallic compound Cu6Sn5. These particles are polygonal in morphology and dispersed randomly through the solder matrix. Addition of microsized copper particles cannot completely dissolve in the eutectic solder and projects a sunflower morphology with the solid copper particle surrounded by the Cu6Sn5 intermetallic compound coupled with residual porosity present in the solder sample. Microhardness measurements revealed the addition of copper nanopowder to the eutectic Sn-3.5%Ag solder resulted in higher hardness.

Optimization of Injection Molding Processing Parameters for LCD Light-Guide Plates

Abstract: Liquid crystal display (LCD) light-guide plate injection molding has always had the unexpected deformation issue which results in variations in the quality of the resulting products. The main cause for this lies in the setting of the processing parameters. The objective of this paper is to combine grey relational analysis (GRA) with the Taguchi method to optimize multiple-quality injection molding processing parameter combination. First, a L18(21 × 37) orthogonal array was used to plan out the processing parameters that would affect the injection molding process. Then GRA was applied to resolve the drawback of single quality characteristics in the Taguchi method, and then the optimized processing parameter combination was obtained for multiple quality characteristics from the response table and the response graph from GRA. The quality characteristics of this experiment were the depth and angle of the light-guide plate V-cut microstructure. Signal-to-noise ratio (SN ratio) calculation and analysis of variance (ANOVA) would be performed to look into the results obtained from the experiment. From ANOVA the significant factors could be obtained which had the greatest effect on the light-guide plate quality characteristics, in other words, by controlling these factors, the quality characteristics of the LCD light-guide plate could be effectively controlled. Finally, the reliability and reproducibility of the experiment was verified by confirming a confidence interval (CI) of 95%.

Analysis of Tempering Treatment on Material Properties of DIN 41Cr4 and DIN 42CrMo4 Steels

Abstract: DIN 41Cr4 and DIN 42CrMo4 materials have been widely used in automotive driving elements. Although 42CrMo4 is more expensive than 41Cr4, it is more preferable in terms of material properties. In this study, these two materials were heat treated by austenitizing in a continuous furnace at 850 °C and quenched in oil at 90 °C. After they were tempered at various temperatures, mechanical properties were determined for each tempering temperature. The material properties for both materials were compared with each other. Results indicated that same mechanical properties for 41Cr4 and 42CrMo4 can be achieved by tempering 41Cr4 about 50 °C lower temperature than for 42CrMo4. In addition to the mechanical tests, fatigue tests were performed for both materials. Weibull distributions were plotted. Results indicated that 42CrMo4 had a longer life than 41Cr4 material.

Recrystallization and Precipitation Behavior of Cu-Cr-Zr Alloy

Abstract: Recrystallization and precipitation behaviors after cold rolling and aging are investigated for Cu-0.7Cr-0.13Zr alloy. The processed alloy was characterized using the measurement of Vickers hardness, scanning electron microscopy, and transmission electron microscopy. The resultant complex microstructures are interpreted in terms of the interactions between precipitation and recrystallization. Upon aging at 500 °C for 1 h, the 45% rolled alloy exhibits a retarded recrystallization process and therefore an efficient hardening response, which are attributed to the pinning effect of fine dispersed precipitates on the dislocation. When heavily deformed and aged at high temperature, the alloy shows an accelerated process of recrystallization, and precipitates are found to coarsen.

Effect of cold work on the tensile properties of 6061, 2024, and 7075 Al alloys

Abstract: Aluminum alloys 6061, 2024, and 7075 were heat treated to various tempers and then subjected to a range of plastic strain (stretching) in order to determine their strain limits. Tensile properties, conductivity, hardness, and grain size measurements were evaluated. The effects of the plastic strain on these properties are discussed and strain limits are suggested.

Interlocking Performances on Non-Oriented Electrical Steels

Abstract: Interlocking performance as fastened strength and magnetic deterioration by interlocking were investigated. The thickness of a surface insulation coating affected the interlocking fastened strength. Sheets with a thin coating resulted in a better interlocking performance than those with a thick coating due to the lubricating effect by resin as coating materials. Sheet gauge affected the interlocking fastened strength. The fastened strength of thin gauge sheet was less than that of a thick one, because of the reduction of the sticking area of interlocking protuberances. The protuberance shapes affected the fastening strength. The rectangular types are stronger than the circular ones, due to the ‘hooked by corners’ effect. Magnetic deteriorations by interlocking was caused by the core loss increased by the obstruction of magnetic flux flows and eddy current loss through the laminations. The core loss increased by the eddy current loss through the laminations was 78% of all deterioration by interlocking.

Use of Electrochemical Noise (EN) Technique to Study the Effect of sulfate and Chloride Ions on Passivation and Pitting Corrosion Behavior of 316 Stainless Steel

Abstract: In the present paper, studies were conducted on AISI Type 316 stainless steel (SS) in deaerated solutions of sodium sulfate as well as sodium chloride to establish the effect of sulfate and chloride ions on the electrochemical corrosion behavior of the material. The experiments were conducted in deaerated solutions of 0.5 M sodium sulfate as well as 0.5 M sodium chloride using electrochemical noise (EN) technique at open circuit potential (OCP) to collect the correlated current and potential signals. Visual records of the current and potential, analysis of data to arrive at the statistical parameters, spectral density estimation using the maximum entropy method (MEM) showed that sulfate ions were incorporated in the passive film to strengthen the same. However, the adsorption of chloride ions resulted in pitting corrosion thereby adversely affecting noise resistance (R N). Distinct current and potential signals were observed for metastable pitting, stable pitting and passive film build-up. Distinct changes in the values of the statistical parameters like R N and the spectral noise resistance at zero frequency (R°SN) revealed adsorption and incorporation of sulfate and chloride ions on the passive film/solution interface.

Aqueous Corrosion Behavior of Iron aluminide Intermetallics

Abstract: Iron aluminide intermetallics based on DO3 ordered structure are being developed for use as structural materials and cladding material for conventional engineering alloys. Aqueous corrosion behavior of iron aluminides has been studied extensively by electrochemical techniques. Studies were carried out on pure Fe (99.9%), Fe-28Al (at.%), Fe-28Al-3Cr (at.%), and AISI SS 304 so as to compare and contrast their behavior in same experimental condition. Polarization behavior under different pH conditions was examined to evaluate their performance in acidic, basic, and neutral solutions. Pitting behavior was also studied in solution containing Cl−1 ions. The stability of the passive film formed was studied by current time transients and potential decay profiles. The presence of 3 at.% Cr in iron aluminides was found to improve the aqueous corrosion resistance and makes it comparable to AISI SS 304.