Showing papers in "Journal of Materials Engineering and Performance in 2011"
TL;DR: In this article, microstructural analyses of thermal or mechanical fatigued Nitinol show remarkable similarities and are characterized by an increase in dislocation density with increasing number of cycles.
Abstract: Microstructural analyses of thermal or mechanical fatigued Nitinol show remarkable similarities and are characterized by an increase in dislocation density with increasing number of cycles. Dislocation bands, which are thought to be due to the effects of moving martensite interfaces, align with the martensite lattice invariant plane. These microstructural effects result in modification of transformation temperatures, strain (under stress-control) and stress (under strain-control). Processing has a major effect on fatigue properties, whereby optimized thermomechanically treated microstructures provide more stable (and predictable) behavior than the annealed microstructures.
197 citations
TL;DR: In this article, the room temperature tensile properties of Ti-6Al-4V alloy prepared under two different processing routes were evaluated and compared, one group of samples was prepared by conventional casting-forging-rolling into flat plates, and the other group were prepared by using Triton's Laser Free-Form Fabrication (LF3)™ processes, i.e., a laser was used to melt pre-alloyed powders of the required metallic composition as they were dropped onto a moveable substrate programmed to move in such a manner as to form a solid
Abstract: The room temperature tensile properties of Ti-6Al-4V alloy prepared under two different processing routes were evaluated and compared. One group of samples was prepared by conventional casting-forging-rolling into flat plates. The other group was prepared by using Triton’s Laser Free-Form Fabrication (LF3)™ processes, i.e., a laser was used to melt pre-alloyed powders of the required metallic composition as they were dropped onto a moveable substrate programmed to move in such a manner as to form a solid alloy plate. Five populations of Ti-6Al-4V were evaluated: a standard wrought form, an as-deposited form, a machined as-deposited form, a heat-treated as-deposited form, and a machined as-deposited and heat-treated form. The poorest mechanical properties occurred with the rough surfaces, likely due to existing microcracks and stress concentrations. The LF3™ as-deposited material had mechanical properties comparable to, if not higher than, the mechanical properties of the wrought material. Further evaluations of the laser-formed material for complex spacecraft piece parts were warranted, specifically in regards to improving the surface finish of the materials.
182 citations
TL;DR: In this paper, the effect of layer orientation on the mechanical strength and toughness of a polymer was evaluated using tensile testing and three-point bend testing, and the toughness was evaluated by Izod impact testing.
Abstract: Rapid Prototyping (RP) is a method used everywhere from the entertainment industry to healthcare. Layer orientation is an important aspect of the final product. The objective of this research was to evaluate the effect of layer orientation on the mechanical strength and toughness of a polymer. The polymer used was a combination of two materials, ZP 130 and ZB 58, fused together in the Z Corporation Spectrum Z510 Rapid Prototyping Machine. ZP 130 is a powder composed of vinyl polymer (2-20%), sulfate salt (0-5%), and plaster that contains <1% crystalline silica (50-95%). ZB 58 is a liquid composed of glycerol (1-10%), preservative (sorbic acid salt) (0-2%), surfactant (<1%), pigment (<1%), and water (85-95%). After removal from the machine the samples were sealed with Z bond 101 which is Beta-methoxyethyl cyanoacrylate (60-100%). The layer orientations studied were the crack arrestor, crack divider, and short transverse with various combinations of the three, for a total of seven orientations. The mechanical strength was evaluated using tensile testing and three-point bend testing. The toughness was evaluated by Izod impact testing. Five samples for tensile testing and three-point bend testing as well as 15 samples for the Izod impact test for each of the seven orientations were made. The total number of samples was 175. The crack arrestor orientation was the strongest main orientation for the tensile and three-point bend test. Weibull analysis was done on the Izod impact testing due to high variation in the results for the crack arrestor and short transverse directions. It was found that the layer orientation and surface roughness played a significant role in the penetration of the Z bond 101 coating and in the overall strength of the samples.
120 citations
TL;DR: P-GMAW as discussed by the authors uses a higher peak current to allow one molten droplet per pulse, and a lower background current to maintain the arc stability, which can reduce the weld service life in continuous mode gas metal arc welding.
Abstract: The weld quality comprises bead geometry and its microstructure, which influence the mechanical properties of the weld. The coarse-grained weld microstructure, higher heat-affected zone, and lower penetration together with higher reinforcement reduce the weld service life in continuous mode gas metal arc welding (GMAW). Pulsed GMAW (P-GMAW) is an alternative method providing a better way for overcoming these afore mentioned problems. It uses a higher peak current to allow one molten droplet per pulse, and a lower background current to maintain the arc stability. Current pulsing refines the grains in weld fusion zone with increasing depth of penetration due to arc oscillations. Optimum weld joint characteristics can be achieved by controlling the pulse parameters. The process is versatile and easily automated. This brief review illustrates the effect of pulse parameters on weld quality.
105 citations
TL;DR: In this article, the authors investigated the blast impact mitigation performance of an advanced combat helmet (ACH) head protection system equipped with polyurea suspension pads and subjected to two different blast peak pressure loadings.
Abstract: To combat the problem of traumatic brain injury (TBI), a signature injury of the current military conflicts, there is an urgent need to design head protection systems with superior blast/ballistic impact mitigation capabilities. Toward that end, the blast impact mitigation performance of an advanced combat helmet (ACH) head protection system equipped with polyurea suspension pads and subjected to two different blast peak pressure loadings has been investigated computationally. A fairly detailed (Lagrangian) finite-element model of a helmet/skull/brain assembly is first constructed and placed into an Eulerian air domain through which a single planar blast wave propagates. A combined Eulerian/Lagrangian transient nonlinear dynamics computational fluid/solid interaction analysis is next conducted in order to assess the extent of reduction in intra-cranial shock-wave ingress (responsible for TBI). This was done by comparing temporal evolutions of intra-cranial normal and shear stresses for the cases of an unprotected head and the helmet-protected head and by correlating these quantities with the three most common types of mild traumatic brain injury (mTBI), i.e., axonal damage, contusion, and subdural hemorrhage. The results obtained show that the ACH provides some level of protection against all investigated types of mTBI and that the level of protection increases somewhat with an increase in blast peak pressure. In order to rationalize the aforementioned findings, a shockwave propagation/reflection analysis is carried out for the unprotected head and helmet-protected head cases. The analysis qualitatively corroborated the results pertaining to the blast-mitigation efficacy of an ACH, but also suggested that there are additional shockwave energy dissipation phenomena which play an important role in the mechanical response of the unprotected/protected head to blast impact.
103 citations
TL;DR: In this paper, the effects of particle size and extrusion on the microstructures and mechanical properties of SiC particle-reinforced pure aluminum composites produced by powder metallurgy method were examined.
Abstract: This article examined the effects of particle size and extrusion on the microstructures and mechanical properties of SiC particle-reinforced pure aluminum composites produced by powder metallurgy method. It has been shown that both particle size and extrusion have important effects on the microstructures and mechanical properties of the composites. The SiC particles distribute more uniformly when the ratio of the matrix powder size and SiC particle size approaches unity, and the smaller-sized SiC particles tend to cluster easily. The voids are found to coexist with the clustered and large-sized SiC particles, and they significantly decrease the density and mechanical properties of the composites. Extrusion can redistribute the SiC particles in the matrix and decrease the number of pores, thus make the SiC particles distribute more uniformly in the matrix, and enhance the interfacial bonding strength. The decrease in the SiC particle size improves the tensile strength and yield strength, but decreases the ductility of the composites.
97 citations
TL;DR: In this paper, the authors examined NiTi shape memory alloy (SMA) wires that were annealed into springs to develop an active, soft orthotic (ASO) for the knee, which provided variable assistances depending on factors such as when, during the gait cycle, the springs are activated; ongoing muscle activity level; and needs of the wearer.
Abstract: Current treatments for gait pathologies associated with neuromuscular disorders may employ a passive, rigid brace. While these provide certain benefits, they can also cause muscle atrophy. In this study, we examined NiTi shape memory alloy (SMA) wires that were annealed into springs to develop an active, soft orthotic (ASO) for the knee. Actively controlled SMA springs may provide variable assistances depending on factors such as when, during the gait cycle, the springs are activated; ongoing muscle activity level; and needs of the wearer. Unlike a passive brace, an active orthotic may provide individualized control, assisting the muscles so that they may be used more appropriately, and possibly leading to a re-education of the neuro-motor system and eventual independence from the orthotic system. A prototype was tested on a suspended, robotic leg to simulate the swing phase of a typical gait. The total deflection generated by the orthotic depended on the knee angle and the total number of actuators triggered, with a max deflection of 35°. While SMA wires have a high energy density, they require a significant amount of power. Furthermore, the loaded SMA spring response times were much longer than the natural frequency of an average gait for the power conditions tested. While the SMA wires are not appropriate for correction of gait pathologies as currently implemented, the ability to have a soft, actuated material could be appropriate for slower timescale applications.
79 citations
TL;DR: In this article, the effects of rotational and traverse speeds and the FSP pass number on the microstructure and microhardness of the friction stir processed (FSPed) layer with and without SiC particles were investigated using optical microscopy and scanning electron microscopy (SEM).
Abstract: In this study, friction stir processing (FSP) was employed to develop a composite layer on the surface of as-cast AZ91 magnesium alloy using SiC particles (5 μm and 30 nm) The effects of the rotational and traverse speeds and the FSP pass number on the microstructure and microhardness of the friction stir processed (FSPed) layer with and without SiC particles were investigated Optical microscopy and scanning electron microscopy (SEM) were employed for microstructural analysis FSP produces a homogeneous microstructure by eliminating the precipitates near the grain boundaries The analyses showed that the effects of the rotational and traverse speeds on the microstructure of specimens produced without nano-sized SiC particles are considerable; however, they are negligible in the specimens with particles While the second FSP pass enhances the microstructure and microhardness of the samples with SiC particles, it has no significant effect on such properties in the samples without SiC particles
71 citations
TL;DR: In this article, the influence of surface preparation on the cold roll bonding (CRB) process was investigated and it was found that higher surface roughness values and shorter delay times improved the bond strength.
Abstract: It is the objective of this article to investigate the influence of surface preparation on the cold roll bonding (CRB) process. In this context, the effects of surface preparation parameters consisting of surface preparation method, surface roughness, scratch-brushing parameters, and the delay time between surface preparation and rolling are investigated on the bond strength of aluminum strips. The bond strength of two adjacent aluminum strips produced by the CRB process is evaluated by the peeling test. Furthermore, the interface region is investigated by metallographic observations. Our findings indicate that higher surface roughness values and shorter delay times improve the bond strength. It is also found that degreasing followed by scratch-brushing yield the best bonding properties.
70 citations
TL;DR: In this paper, the effects of three different sizes of Al2O3 particles in the friction stir processing on grain size, cluster size, microstructure, and micro-hardness of as-cast magnesium alloy AZ91 were investigated.
Abstract: In this article, the effects of three different sizes of Al2O3 particles in the friction stir processing on grain size, cluster size, microstructure, and micro-hardness of as-cast magnesium alloy AZ91 were investigated. Moreover, the effects of two types of tool geometries and number of passes on the mentioned parameters were considered. Effect of mentioned parameters on microstructure, grain refinement, and micro-hardness profile in the friction stirred zone of the specimens was compared by as-cast received form and also friction stir processed (FSPed) specimens without particles. Microstructural characterization of the materials revealed reasonably uniform distribution of Al2O3 reinforcement and significant grain refinement. Hardness studies revealed that the incorporation of nano- and micro-size Al2O3 particulates in magnesium matrix led to a simultaneous increase in hardness.
70 citations
TL;DR: In order to improve titanium corrosion behavior, the authors in this article increased the thickness of oxide layer on titanium surface during anodizing process and by electrochemistry in self-color anodising of Ti in sulfuric acid.
Abstract: In order to improve titanium corrosion behavior, we can increase the thickness of oxide layer on titanium surface during anodizing process and by electrochemistry In this research, self-color anodizing of Ti in sulfuric acid was done, and anodizing layers were created in different colors The highest value of chromaticity was 378 for the anodized sample in 10 V, and the lowest value was 86 at 15 V The oxide layer thickness was calculated by optical method (light refraction) The anodic film thickness increased by increasing the anodizing voltage The highest thickness of anodic film was 190 nm in sulfuric acid solution for the anodized sample in 80 V Corrosion resistance of anodized Ti was studied by potentiodynamic polarization curves in biological solution of Ringer’s at 37 °C On increasing the anodizing voltage further, corrosion rate of the alloy increased from its lowest rate The lowest rate of corrosion was for the sample anodized in 10 V, which was 096 × 10−3 mpy
TL;DR: In this paper, the effects of varying seven different machining parameters in addition to varying the material thickness on the machining responses such as material removal rate, kerf, and surface roughness of tungsten carbide samples machined by wire electrical discharge machining (WEDM) were investigated.
Abstract: In this article, the effects of varying seven different machining parameters in addition to varying the material thickness on the machining responses such as material removal rate, kerf, and surface roughness of tungsten carbide samples machined by wire electrical discharge machining (WEDM) were investigated. The design of experiments was based on a Taguchi orthogonal design with 8 control factors with three levels each, requiring a set of 27 experiments that were repeated three times. ANOVA was carried out after obtaining the responses to determine the significant factors. The work piece thickness was expected to have a major effect on the material removal rate but showed to be significant in the case of surface roughness only. Finally, optimization of the machining responses was carried out and models for the material removal rate, kerf, and surface roughness were created. The models were validated through confirmation experiments that showed significant improvements in machining performance for all investigated machining outcomes.
TL;DR: In this paper, a fully coupled thermo-mechanical finite-element analysis of the friction-stir welding (FSW) process developed in previous work is combined with the basic physical metallurgy of two wrought aluminum alloys to predict/assess their FSW behaviors.
Abstract: A fully coupled thermo-mechanical finite-element analysis of the friction-stir welding (FSW) process developed in our previous work is combined with the basic physical metallurgy of two wrought aluminum alloys to predict/assess their FSW behaviors. The two alloys selected are AA5083 (a solid-solution strengthened and strain-hardened/stabilized Al-Mg-Mn alloy) and AA2139 (a precipitation hardened quaternary Al-Cu-Mg-Ag alloy). Both of these alloys are currently being used in military-vehicle hull structural and armor systems. In the case of non-age-hardenable AA5083, the dominant microstructure-evolution processes taking place during FSW are extensive plastic deformation and dynamic re-crystallization of highly deformed material subjected to elevated temperatures approaching the melting temperature. In the case of AA2139, in addition to plastic deformation and dynamic recrystallization, precipitates coarsening, over-aging, dissolution, and re-precipitation had to be also considered. Limited data available in the open literature pertaining to the kinetics of the aforementioned microstructure-evolution processes are used to predict variation in the material hardness throughout the various FSW zones of the two alloys. The computed results are found to be in reasonably good agreement with their experimental counterparts.
TL;DR: In this article, the optimization of dry sliding performances on the aluminum hybrid metal matrix composites using gray relational analysis in the Taguchi method was investigated, where different loads, sliding speeds and varying percentage of molybdenum disulfide are selected as control factors.
Abstract: This article investigates the optimization of dry sliding performances on the aluminum hybrid metal matrix composites using gray relational analysis in the Taguchi method. Different loads, sliding speeds and varying percentage of molybdenum disulfide are selected as control factors. The multiple responses to evaluate the dry sliding performances are specific wear rate and coefficient of friction. Using a pin-on-disk apparatus, the volume loss and frictional force are measured. Based on gray relational analysis, the optimum level parameters for specific wear rate and coefficient of friction have been identified. An L27 orthogonal array was employed for the experimental design. Analysis of Variance (ANOVA) had given the impact of individual factors and interactions on the specific wear rate as well as the coefficient of friction. The results indicated that the three test parameters had a significant role in controlling the friction and wear behavior of composites. Interaction of the control factors showed the sizable influence on tribological performance. Using Scanning Electron Microscopy (SEM) the wear surface morphology and wear mechanism of the composites have been investigated.
TL;DR: In this article, a simulation-based approach to optimize five-axis micro-milling processes with respect to the special material properties of NiTi SMA is presented, where the influence of the various tool inclination angles is considered for introducing an intelligent tool inclination optimization algorithm.
Abstract: Micro-sized applications are gaining more and more relevance for NiTi-based shape memory alloys (SMA). Different types of micro-machining offer unique possibilities for the manufacturing of NiTi components. The advantage of machining is the low thermal influence on the workpiece. This is important, because the phase transformation temperatures of NiTi SMAs can be changed and the components may need extensive post manufacturing. The article offers a simulation-based approach to optimize five-axis micro-milling processes with respect to the special material properties of NiTi SMA. Especially, the influence of the various tool inclination angles is considered for introducing an intelligent tool inclination optimization algorithm. Furthermore, aspects of micro deep-hole drilling of SMAs are discussed. Tools with diameters as small as 0.5 mm are used. The possible length-to-diameter ratio reaches up to 50. This process offers new possibilities in the manufacturing of microstents. The study concentrates on the influence of the cutting speed, the feed and the tool design on the tool wear and the quality of the drilled holes.
TL;DR: In this article, the effect of burnishing parameters (i.e., burnishing speed, burnishing force, and feed rate) on surface roughness, surface hardness, and microstructure of burnished surfaces was investigated.
Abstract: A newly developed ball burnishing tool was designed and tested for surface finishing of large flat surfaces in a shortest possible time. Optimization and analysis of the burnishing process were carried on AISI 1010 steel hot-rolled plates using the Taguchi technique and response surface methodology (RSM) to identify the effect of burnishing parameters (i.e., burnishing speed, burnishing force, and feed rate) on surface roughness, surface hardness, and microstructure of burnished surfaces. The optimal burnishing parameters were found after conducting the Taguchi’s L25 matrix experiments and obtaining the response models for the surface roughness and the hardness. It was found that the burnishing force has the most influential effect on the surface roughness and hardness, followed by the burnishing speed, and least influence by the feed rate. In addition, microstructural examinations of the burnished surface indicate that burnishing force more than 400 N causes flaking of the burnished surfaces. The optimal burnishing parameters for the steel plates were a combination of a burnishing speed of 235 rpm, a burnishing force of 400 N, and a feed rate of 0.18 mm/rev. Using these parameters, the mean surface roughness has been improved from Ra = 2.48 to 1.75 μm, while the hardness increases from 59 to 65.5 HRB.
TL;DR: In this paper, the effects of various microstructural and topological defects (e.g., chain ends, axial chain misalignment, inorganic solvent impurities, and sheet stacking faults) on the strength, ductility, and stiffness of p-phenylene terephthalamide (PPTA) fibers/filaments were investigated.
Abstract: Molecular statics and molecular dynamics are employed to study the effects of various microstructural and topological defects (e.g., chain ends, axial chain misalignment, inorganic solvent impurities, and sheet stacking faults) on the strength, ductility, and stiffness of p-phenylene terephthalamide (PPTA) fibers/filaments. These fibers can be considered as prototypes for advanced high strength/high-stiffness fibers like Kevlar®, Twaron®, New Star®, etc. While modeling these fibers, it was taken into account that they are essentially crystalline materials consisting of stacks of sheets, with each sheet containing an array of nearly parallel hydrogen-bonded molecules/chains. The inter-sheet bonding, on the other hand, was considered as mainly being of van der Waals or p-electron character. The effects of various deviations of the PPTA fiber structure from that of the perfectly crystalline structure (i.e., microstructural/topological defects) on the material’s mechanical properties are then considered. The results obtained show that while the presence of these defects decreases all the mechanical properties of PPTA fibers, specific properties display an increased level of sensitivity to the presence of certain defects. For example, longitudinal tensile properties are found to be most sensitive to the presence of chain ends, in-sheet transverse properties to the presence of chain misalignments, while cross-sheet transverse properties are found to be most affected by the presence of sheet stacking faults.
TL;DR: In this paper, the influence of tool-sheet contact conditions on features such as surface roughness, forming force, and formability was evaluated for components produced by incremental forming, a highly flexible innovative sheet metal-forming process.
Abstract: The influence of tool-sheet contact conditions on features such as surface roughness, forming force, and formability was evaluated for components produced by incremental forming, a highly flexible innovative sheet metal-forming process. Experimental tests were carried out on sheets of AA7075T0 to create two types of component: pyramid frusta (for the evaluation of roughness and force) and cone frusta (for the evaluation of formability). Four different types of tool-sheet contact were analyzed, using two types of tool. From the experimental tests, the influence on the surface finishing and on the trend of the forming forces depending on contact type was revealed. Contact types do not, however, influence sheet formability.
TL;DR: In this paper, the authors used the stir casting method to achieve uniform distribution of SiC particles in the 7075 aluminum alloy matrix, characterization, and analysis of composite formed at stirring speeds of 500, 650, 750, and stirring period of 10 min.
Abstract: The stir casting method was used for fabrication of 7075 aluminum alloy with 10 wt.% SiC particles of size 20-40 μm. The research objective of this paper are to achieve uniform distribution of SiC particles in the 7075 aluminum alloy matrix, characterization, and analysis of mechanical properties of composite formed. Experiments were carried out at stirring speeds of 500, 650, 750 rpm, and stirring period of 10 min. Microstructures of aluminum alloy and composites with 5, 10 wt.% SiC reinforcements were examined. The results reveal that composite produced at stirring speed of 650 rpm and stirring time of 10 min has uniform distribution of SiC particles. XRD and EDAX analysis were carried out for 7075 Al alloy and composite with 10 wt.% SiC reinforcement. No adverse reaction was observed in XRD and EDAX of composite with 10 wt.% SiC reinforcement. Tensile strength and hardness increased by 12.74% and 10.48%, respectively, with the increase in percentage of SiC reinforcement from 5 to 15 wt.%.
TL;DR: In this article, the effects of different processing parameters, such as isothermal temperature and holding time on the semi-solid microstructures (the liquid volume fraction, average grain size, and degree of spheroidization of the solid particles) during partial remelting have been investigated on 7075 Al alloy manufactured by strain-induced melt activation (SIMA) process.
Abstract: Microstructural evolution of semi-solid 7075 Al alloy manufactured by strain-induced melt activation (SIMA) process was investigated The effects of different processing parameters, such as isothermal temperature and holding time on the semi-solid microstructures (the liquid volume fraction, average grain size, and degree of spheroidization of the solid particles) during partial remelting have been investigated on 7075 Al alloy that was extruded by an extrusion ratio of 20 before remelting Experiments of remelting were carried out in the range of 560-610 °C for 10, 20, and 30 min holding time and then the specimens were quenched in cold water Microstructure of quenched samples were observed under optical microscope and then analyzed via image analysis The results showed that high semi-solid isothermal temperature would increase the liquid volume fraction and accelerate the spherical processing of the solid particles Furthermore at long holding time, the globular grains coarsened slightly and the average grains size are increased The experimental results showed that the optimum process parameters, should be chosen at isothermal temperature of 580 °C with the holding time, <30 min
TL;DR: In this paper, a 2219 aluminum alloy was underwater friction stir welded and the homogeneity of mechanical properties of the joint was investigated by dividing the joint into three layers, and the results indicated that the tensile strength of the three layers was improved by underwater FSW.
Abstract: Underwater friction stir welding (FSW) has been demonstrated to be available for the improvement in tensile strength of normal FSW joints. In order to illuminate the intrinsic reason for strength improvement through underwater FSW, a 2219 aluminum alloy was underwater friction stir welded and the homogeneity of mechanical properties of the joint was investigated by dividing the joint into three layers. The results indicate that the tensile strength of the three layers of the joint is all improved by underwater FSW, furthermore, the middle and lower layers have larger extent of strength improvement than the upper layer, leading to an increase in the homogeneity of mechanical properties of the joint. The minimum hardness value of each layer, especially the middle and lower layers, is improved under the integral water cooling effect, which is the intrinsic reason for the strength improvement of underwater joint.
TL;DR: In this article, rare earth oxide (CeO2) has been incorporated in NiCrAlY alloy and hot corrosion resistance of detonation-gun-sprayed NiCAlY + 0.4 Wt.% CeO2 coatings on superalloys, namely, superni 75, Superni 718, and superfer 800H in molten 40% Na2SO4-60% V2O5 salt environment were investigated at 900°C for 100 cycles.
Abstract: Rare earth oxide (CeO2) has been incorporated in NiCrAlY alloy and hot corrosion resistance of detonation-gun-sprayed NiCrAlY + 0.4 wt.% CeO2 coatings on superalloys, namely, superni 75, superni 718, and superfer 800H in molten 40% Na2SO4-60% V2O5 salt environment were investigated at 900 °C for 100 cycles. The coatings exhibited characteristic splat globular dendritic structure with diameter similar to the original powder particles. The weight change technique was used to establish corrosion kinetics. X-ray diffraction (XRD), field emission scanning electron microscopy/energy-dispersive analysis (FE-SEM/EDAX), and x-ray mapping techniques were used to analyze the corrosion products. Coated superfer 800H alloy showed the highest corrosion resistance among the examined superalloys. CeO2 was found to be distributed in the coating along the splat boundaries, whereas Al streaks distributed non-uniformly. The main phases observed for the coated superalloys are oxides of Ni, Cr, Al, and spinels, which are suggested to be responsible for developing corrosion resistance.
TL;DR: In this article, the effect of cobalt (Co) alloying additions on the stiffness and plateau stresses of a superelastic nickel-titanium alloy was studied. And the results showed Co to be an interesting alloying addition that should be considered for future medical devices in applications, where stiffness is of concern.
Abstract: Development of a superelastic material with higher stiffness and plateau stresses than binary nitinol is of interest to the medical device industry because it may allow for lower profile, less intrusive devices without compromising the material’s characteristics. This project studied the effect of cobalt (Co) alloying additions on the stiffness and plateau stresses of a superelastic nickel-titanium alloy. In addition, the general physical, mechanical, corrosion, and biocompatibility properties of the alloy were compared to binary nitinol. The results of this study showed Co to be an interesting alloying addition that should be considered for future medical devices in applications, where stiffness is of concern.
TL;DR: In this article, the effect of forming start temperature and the contact state between blank and die on the microstructure evolution of UHSS sheet metal for channel components using water cooling is investigated on a laboratory scale.
Abstract: Hot forming of ultra high strength steel (UHSS) sheet metal grade 22MnB5 boron for channel components using water cooling is studied on a laboratory scale. After hot forming, the different microstructures such as martensite, bainite, and pearlite in formed component are produced, which are closely related with mechanical properties of formed component. The effect of forming start temperature and the contact state between blank and die on the microstructure evolution is investigated. In addition, the effect of processing parameters, such as forming start temperature and blank holder force (BHF), on the final quality of component, i.e., springback, that happens after hot forming of UHSS is investigated. It can be concluded that the forming start temperature has a significant effect on the final mechanical properties of formed components. The effect of forming start temperature on springback is examined in detail under a wide range of operating conditions. The higher the BHF and the forming start temperature, the lower is the springback after hot forming. Furthermore, thermo-mechanically coupled finite element analysis model encompassing heating of sheet blank, forming and quenching are developed for hot forming process. The stress distributions on sheet blank under different conditions during hot forming are compared to gain a fundamental understanding of the mechanism of springback. Comparisons show that numerical simulation results have good agreement with experimental results.
TL;DR: In this article, an attempt was made to model input-output relationships of an electrical discharge machining process based on the experimental data (collected according to a central composite design) using multiple regression analysis.
Abstract: An attempt was made to model input-output relationships of an electrical discharge machining process based on the experimental data (collected according to a central composite design) using multiple regression analysis. Three input parameters, such as peak current, pulse-on-time and pulse-duty-factor, and two outputs, namely, material removal rate (MRR) and surface roughness (SR) had been considered for the said modeling. The value of regression coefficient was determined for each model. The performances of the developed models were tested with the help of some test cases collected through the real experiments and were found to be satisfactory. It had been posed as an optimization problem and solved using a genetic algorithm to determine the set(s) of optimal parameters for ensuring the maximum MRR and minimum SR. It was also formulated as a multi-objective optimization problem and a Pareto-optimal front of solutions had been obtained.
TL;DR: In this article, the authors developed a three-step approach to determine the optimal tool design and the optimal FSW process parameters which result in maximal productivity of the joining process and the highest quality of the weld.
Abstract: To respond to the advent of more lethal threats, recently designed aluminum-armor-based military-vehicle systems have resorted to an increasing use of higher strength aluminum alloys (with superior ballistic resistance against armor piercing (AP) threats and with high vehicle-light weighing potential). Unfortunately, these alloys are not very amenable to conventional fusion-based welding technologies and in-order to obtain high-quality welds, solid-state joining technologies such as Friction stir welding (FSW) have to be employed. However, since FSW is a relatively new and fairly complex joining technology, its introduction into advanced military vehicle structures is not straight forward and entails a comprehensive multi-step approach. One such (three-step) approach is developed in the present work. Within the first step, experimental and computational techniques are utilized to determine the optimal tool design and the optimal FSW process parameters which result in maximal productivity of the joining process and the highest quality of the weld. Within the second step, techniques are developed for the identification and qualification of the optimal weld joint designs in different sections of a prototypical military vehicle structure. In the third step, problems associated with the fabrication of a sub-scale military vehicle test structure and the blast survivability of the structure are assessed. The results obtained and the lessons learned are used to judge the potential of the current approach in shortening the development time and in enhancing reliability and blast survivability of military vehicle structures.
TL;DR: In this article, the effect of strain-rate sensitivity on formability of AA 5754-O alloy sheet at a test temperature range of −60 to 250 °C by duplicate tensile test at different strain rates.
Abstract: Aluminum-magnesium (Al-Mg) alloys have been widely used in diverse applications ranging from automotive bodies to food processing industries because of their excellent high-strength-to-weight ratio, corrosion resistance, and recyclability potential. The formability of these alloys is decreased at room temperature (RT) and is related with the strain-rate sensitivity. This study presents the effect of strain-rate sensitivity on formability of AA 5754-O alloy sheet at a test temperature range of −60 to 250 °C by duplicate tensile test at different strain rates. The test results indicated that the formability change with positive or negative strain-rate sensitivity values. It was observed that the strain-rate sensitivity values increased at negative temperatures with respect to RT. The best formability condition for this alloy in the test ranges was observed at 250 °C and 0.0016 s−1.
TL;DR: In this article, the microstructural evolution of Inconel alloy 740 during solution treatment and aging was characterized using optical and scanning electron microscopy, and the main source of micro-structural instability observed during exposure at 760°C was the coarsening of the γ′ phase.
Abstract: In this study, the microstructural evolution of Inconel alloy 740 during solution treatment and aging was characterized using optical and scanning electron microscopy. During double solution heat treatment, carbon is liberated from the dissolution of MC carbides during the first solution treatment at 1150 °C, and fine MC carbides are precipitated on gamma grain boundaries during the second solution treatment at 1120 °C. Due to the concurrent decrease in carbon solubility and the increase in the contribution of grain boundary diffusion at lower temperatures, the MC carbides on the gamma grain boundaries provide a localized carbon reservoir that aids in M23C6 carbide precipitation on gamma grain boundaries during exposure at 760 °C. The γ′ phase, which is the key strengthening phase in alloy 740, is incorporated into the alloy microstructure during aging at 850 °C. The main source of microstructural instability observed during exposure at 760 °C was the coarsening of the γ′ phase.
TL;DR: In this article, induction dilatometry was performed on 5150 steel with ferrite-pearlite and tempered martensite initial microstructures to assess effects of experimentally controlled prior microstructure and heating rate on austenitization kinetics.
Abstract: Induction heating has permitted great progress in the surface hardening of a wide variety of steels, but results in a wide range of local thermal cycles. The metallurgical changes during rapid heating and cooling have not been sufficiently studied with respect to heating rate and prior microstructure. In the present investigation, induction dilatometry was performed on 5150 steel with ferrite-pearlite and tempered martensite initial microstructures to assess effects of experimentally controlled prior microstructure and heating rate on austenitization kinetics. Heating rates were varied from 0.3 to 300 °C/s to simulate industrial processes, and post-hardening metallography and hardness testing were performed. Results show that the transformation kinetics for prior ferrite-pearlite microstructures are significantly slower than for prior tempered martensite microstructures, although hardness is equivalent for a given thermal cycle. Metallographic evidence suggests significant remnant segregation of chromium in regions of pearlitic cementite (enriched); evidence of segregation was not observed metallographically for prior tempered martensite. Diffusion-based transformation simulations support observed ferrite-pearlite alloy segregation, suggest residual alloy segregation is possible for prior tempered martensite, and can be used to tailor austenitization thermal cycles to process requirements. Detailed time and temperature-dependent local microstructure development results from this study are directly applicable to practical induction hardening simulations.
TL;DR: An active orthosis powered by two rotary actuators containing NiTi wire was designed to obtain ankle dorsiflexion and proved that it can produce strokes up to 36° against resisting torques exceeding 180 Ncm.
Abstract: The capacity of flexing one’s ankle is an indispensible segment of gait re-learning, as imbalance, wrong compensatory use of other joints and risk of falling may depend on the so-called drop-foot. The rehabilitation of ankle dorsiflexion may be achieved through active exercising of the relevant musculature (especially tibialis anterior, TA). This can be troublesome for patients affected by weakness and flaccid paresis. Thus, as needs evolve during patient’s improvements, a therapeutic device should be able to guide and sustain gradual recovery by providing commensurate aid. This includes exploiting even initial attempts at voluntary motion and turns those into effective workout. An active orthosis powered by two rotary actuators containing NiTi wire was designed to obtain ankle dorsiflexion. A computer routine that analyzes the electromyographic (sEMG) signal from TA muscle is used to control the orthosis and trigger its activation. The software also provides instructions and feed-back for the patient. Tests on the orthosis proved that it can produce strokes up to 36° against resisting torques exceeding 180 Ncm. Three healthy subjects were able to control the orthosis by modulating their TA sEMG activity. The movement produced in the preliminary tests is interesting for lower limb rehabilitation, and will be further improved by optimizing body-orthosis interface. It is hoped that this device will enhance early rehabilitation and recovery of ankle mobility in stroke patients.