Showing papers in "Journal of Materials Engineering and Performance in 2019"
TL;DR: In this paper, the authors proposed to combine acoustic emission and reinforcement learning for in situ and real-time quality monitoring of additive manufacturing (AM) processes in commercial equipment and demonstrated that each level of quality produced unique acoustic signatures during the build that were recognized by the classifier.
Abstract: Additive manufacturing (AM) has attracted considerable attention in recent years. This technology overcomes the geometrical limits of workpieces produced with the traditional subtractive methods and so gives the opportunity to manufacture highly complex shapes. Unfortunately, the repeatability of the manufacturing process and the monitoring of quality are not reliable enough to be utilized in mass production. The quality monitoring of AM processes in commercial equipment has been largely based on temperature measurements of the process zone or high-resolution imaging of the layers. However, both techniques lack information about the physical phenomena taking place in the depth of the materials medium and this limits their reliability in real-life applications. To overcome those restrictions, we propose to combine acoustic emission and reinforcement learning. The former captures the information about the subsurface dynamics of the process. The latter is a branch of machine learning that allows interpreting the received data in terms of quality. The combination of both is an original method for in situ and real-time quality monitoring. Acoustic data were collected during a real process using a commercial AM machine. The process parameters were selected to achieve three levels of quality in terms of porosity concentration while manufacturing a stainless steel 316L cuboid shape. Using our method, we demonstrated that each level of quality produced unique acoustic signatures during the build that were recognized by the classifier. The classification accuracy reached in this work proves that the proposed method has high potential to be used as in situ and real-time monitoring of AM quality.
76 citations
TL;DR: In this paper, the authors focused on the optimization of the parameters to achieve higher tensile strength and lower surface roughness with less build time during the FDM process based on central composite design for the tensile specimen forming process.
Abstract: Fused deposition modeling (FDM) has become one of the most extensively used additive manufacturing technologies in recent years because of its wide adaptability, simple mechanism and low cost. It is difficult, however, to achieve an equitable trade-off among mechanical properties, surface finish quality and production time, which is an area seldom explored. This paper concentrates on the optimization of the parameters to achieve higher tensile strength and lower surface roughness with less build time during the FDM process based on central composite design for the tensile specimen forming process. The effects of five extrusion parameters (nozzle diameter, liquefier temperature, extrusion velocity, filling velocity and layer thickness) on the three outputs of tensile strength (TS), surface roughness (SR) and build time (BT) are investigated. Response surface methodology combined with nondominated sorting genetic algorithm II is developed to optimize the process parameters to achieve the maximum TS, minimum SR and BT, as verified by subsequent experiments. The predicted results are found to be very close to the experimental data, illustrating that the presented approach in this paper is effective for improving mechanical properties, surface finish and efficiency of the FDM process.
75 citations
TL;DR: In this article, high-cycle fatigue (HCF) tests were conducted on samples fabricated by two powder-bed additive manufacturing techniques, including electron beam melting (EBM) and selective laser melting (SLM).
Abstract: High-cycle fatigue (HCF) tests were conducted on samples fabricated by two powder-bed additive manufacturing techniques. Samples were tested with as-produced surfaces and after various non-contact surface improvement treatments. Ti-6Al-4V samples were made using both electron beam melting (EBM) and selective laser melting (SLM), while Inconel 625 was fabricated using SLM. Ti-6Al-4V was treated with a commercial chemically accelerated vibratory polishing process, with target material removal of approximately 200 µm from each surface for EBM samples and 100 µm for SLM samples. This technique led to increases in both the number of cycles before failure at a given loading condition and endurance limit (at 107 cycles) compared to samples with as-produced surfaces. The results are interpreted as the reduction in elastic stress concentration factor associated with surface defects where fatigue cracks initiate. SLM 625 was treated with both an abrasive polishing method and laser surface remelting. Both methods led to improvements in surface roughness, but these did not lead to improvements in fatigue properties of SLM 625. For abrasive polished samples, the combination of improved measured surface roughness without fatigue property enhancement suggests that surface material is removed, but the roots of surface defects, where fatigue cracks initiate, were left intact. For laser treatment, the remelted surface layer retained a rapidly solidified microstructure that did not increase the number of cycles before crack initiation even though the surface was smoother compared to the surface prior to polishing.
74 citations
TL;DR: In this article, a multi-scale model combining finite element method (FEM) and phase-field model (PFM) is applied to simulate the evolution of solidification microstructures at different locations within a molten pool of an additively manufactured IN718 alloy.
Abstract: In this work, we apply a multi-scale model combining finite-element method (FEM) and phase-field model (PFM) to simulate the evolution of solidification microstructures at different locations within a molten pool of an additively manufactured IN718 alloy. Specifically, the FEM is used to calculate the shape of molten pool and the relative thermal gradient G at the macroscale. Then, the calculated thermal information is input into PFM for microstructure simulation. Finally, the morphology of solidification structures and formation of Laves phase at different sites are studied and compared. We found that the solidification site with a large angle between the temperature gradient and the preferred crystalline orientation could build up a high niobium (Nb) concentration in the liquid during solidification but has less possibility of forming continuous long chain morphology of Laves phase particles. This finding provides an understanding of the microstructure evolution inside the molten pool of IN718 alloy during solidification. Further, the finding indicates that the site with a large misorientation angle will have a good hot cracking resistance after solidification.
67 citations
TL;DR: In this article, the variation in tensile properties of Inconel 718 at varying angles with respect to build direction was investigated, and it was found that a preferred grain texture and twinning orientation that aligns with the build direction may contribute to the anisotropic enhancement in ductility.
Abstract: The production of components via selective laser melting (SLM) metal additive manufacturing results in microstructures unique to the process that are highly dependent on laser processing parameters and orientation of part geometry relative to the build direction. This study investigates the variation in tensile properties of SLM Inconel 718 at varying angles with respect to build direction. ASTM E8 tensile specimens were built in XY, Z, and B+45 from Z orientations to near-net shape, HIP and heat treated, and tensile tested at room temperature. Orientation dependence of mechanical properties was observed; Z samples had the lowest strength and highest elongation, while XY samples had the highest strength and lowest elongation. Optical, SEM, and EBSD analysis were conducted to probe for microstructure variation that could be the cause of the difference in mechanical properties. Analysis of pole figures and grain maps suggests a preferred grain texture and twinning orientation that aligns with the build direction, which may contribute to the anisotropic enhancement in ductility.
67 citations
TL;DR: The additive friction stir (MELD) process is an emerging solid-state process that enables additive manufacturing of a broad range of metals and metal matrix composites as mentioned in this paper, such as Al-SiC, Al 6061-Mo, and Al 60 61-W composites.
Abstract: MELD, previously known as additive friction stir, is an emerging solid-state process that enables additive manufacturing of a broad range of metals and metal matrix composites. Here, we discuss its potential for fabricating aluminum matrix composites by showing examples of Al-SiC, Al 6061-Mo, and Al 6061-W composites. Thanks to its solid-state nature, MELD is uniquely suited for the use of high-strength aluminum alloys as matrix material, which would suffer from hot cracking problems in liquid-state processes. Using complementary characterization tools, we show that this process results in aluminum matrix composites with no observed porosity and homogeneous particle distribution. These properties stem from the extensive material flow and mixing during the deposition process. In addition to the high quality of produced composites, its ease of use, versatility of feed materials, and scalability all make MELD an attractive tool for additive manufacturing of aluminum matrix composites. We also discuss the limitations of MELD for composite fabrication, with issues related to maximum reinforcement loading, tool wear, and in-plane resolution. Finally, we compare the benefits and limitations of MELD with other composite fabrication processes such as powder bed fusion, friction stir processing, stir casting, and powder processing.
61 citations
TL;DR: In this article, the authors report results obtained during an investigation of the processing and properties of aluminum-cerium alloys produced via casting, extrusion and additive manufacturing, and show complete recovery of mechanical properties at room temperature when exposed to elevated temperatures as high as 500 h for 1000 h.
Abstract: A common rare earth (cerium) when added to aluminum in compositions up to the eutectic compositions of around 10 wt.% improves the high-temperature performance of aluminum alloys. In the early 1980s, some promising research and development efforts focused on powder metallurgy revealed that aluminum alloys containing 4 wt.% cerium exhibit high-temperature mechanical properties exceeding those of the best commercial aluminum casting alloys then in production. Those compositions, which also included high levels of iron, were difficult to process. Recently, magnesium replaces iron to reduce density and improve processing. Cerium oxide is an abundant rare earth oxide that is often discarded during the refining of more valuable rare earths such as Nd and Dy. Therefore, the economics are compelling for cerium as an alloy additive. In this review, we report results obtained during an investigation of the processing and properties of aluminum-cerium alloys produced via casting, extrusion and additive manufacturing. The results show mechanical properties are retained at higher temperatures than other aluminum alloys and show complete recovery of mechanical properties at room temperature when exposed to elevated temperatures as high as 500 °C for 1000 h. Alloys containing cerium also have superior corrosion properties when compared to most aluminum alloys.
54 citations
TL;DR: In this article, the use of cold metal transfer-based additive manufacturing (WAAM) process for the production of maraging steel bulk material is reported, and the effect of building strategies including oscillation, parallel and weaving on bead shape is investigated.
Abstract: Wire + arc additive manufacture (WAAM) is a new process for fabricating large-scale metallic components. In this paper, the use of cold metal transfer-based WAAM process for the production of maraging steel bulk material is reported. Process parameters were studied, and the effect of building strategies including oscillation, parallel and weaving on bead shape was investigated. The structural integrity of the WAAM bulk material regarding the surface finish, lack-of-fusion issue and microstructure was characterized. Results proved the feasibility of applying WAAM to producing maraging steel bulk material, and weaving was identified to be most recommended building strategy.
49 citations
TL;DR: In this article, the compressive mechanical behavior of four different types of cellular solids with topologies based on the mathematically known triply periodic minimal surfaces (TPMS) was investigated.
Abstract: Lightweight materials with complex structures such as cellular solids (or foams) have proven to possess desirable properties, specifically in terms of its stiffness, strength, and thermal conductivity, among other mechanical and thermal performance aspects while the density is reduced. The fabrication of such attractive yet complex materials has become possible due to the witnessed advancements in fabrication techniques. However, a major challenge in adapting cellular solids in mechanical design is choosing the appropriate lattice design. Therefore, this paper focuses on studying the compressive mechanical behavior of four different types of cellular solids with topologies based on the mathematically known triply periodic minimal surfaces (TPMS); namely, Diamond (D), I-WP (IWP), Gyroid (G), and Fisher-Koch C(Y) (CY). These cellular materials are 3D printed using the powder bed fusion selective laser sintering technique out of Nylon thermoplastic polymer at various relative densities. The effects of the number of unit cells, type of the ligament-based TPMS architecture, and relative density on the stiffness, yield strength, ultimate strength, and toughness are thoroughly investigated. The results indicated that the effect of the architecture is stronger when the relative density is decreased. Also, the analyses showed that all the tested architectures were bending dominated implying that it could be best applied in shock absorbing and vibration mitigation applications.
47 citations
TL;DR: In this article, the AlCoCrFeNiTi high-entropy alloy (HEA) coatings were prepared on the AISI1045 steel to improve its surface properties.
Abstract: AISI1045 steel is widely used in mechanical engineering. In spite of the favorable toughness and strength, the surface properties of AISI1045 steel, such as hardness, wear resistance and corrosion resistance, are not ideal. Therefore, surface modification of AISI1045 is necessary, especially for the parts suffering severe work condition. Laser cladding is a promising surface modification technology. In this work, the AlCoCrFeNiTi high-entropy alloy (HEA) coatings were prepared on the AISI1045 steel to improve its surface properties. Metallurgical bonding is obtained between the coating and the substrate. The microstructure and surface properties of the coating were characterized by scanning electron microscope, energy-dispersive spectrometry, x-ray diffraction, electrochemical workstation, microhardness tester and pin-on-ring wear tester. The microstructure of the coating produced by laser cladding is dendritic. The AlCoCrFeNiTi HEA coating is mainly composed of disordered body-centered cubic phase (Fe-Cr), ordered B2 phase (AlNi) and intermetallic phase (Ti-rich). The coating shows excellent abrasion resistance and corrosion resistance in comparison with the substrate. The maximum microhardness of the coating reaches approximately 865 HV, which is 4.5 times of AISI1045 steel.
37 citations
TL;DR: In this paper, the manufacturing of metallic composite coatings of Al-Al2O3 on organic composite substrates with thermoplastic PLA matrix and hemp fibers was studied using a low-pressure cold spray equipment.
Abstract: In this work, the manufacturing through cold gas dynamic spray (cold spray or CS) of metallic composite coatings of Al-Al2O3 on organic composite substrates with thermoplastic PLA matrix and hemp fibers was studied. Alumina powders, with a mean diameter of 50 μm, were used blended with aluminum powders in three different weight concentration percentages (0, 15, 20, and 45%) as feedstock material in order to highlight and discuss the variations of the coating surface properties depending on the alumina percentage. The coatings were produced by using a low-pressure cold spray equipment. A detailed experimental campaign, including microstructural observations and confocal microscopy, was carried out to study the structure of the coatings. Moreover, the tribological behavior of the coatings was studied through both scratch test and pin-on-disk test. The experiments showed that a small addition of alumina improves the compactness of the coating and its resistance to scratch and wear behavior.
TL;DR: In this paper, the effect of nitrogen pressure on the properties of CrAlN coatings formed from Al80Cr20 cathode, such as chemical and phase composition of the coatings, surface morphology, deposition rate, hardness and adhesion to the substrate, and friction and wear were investigated.
Abstract: AlCrN coatings were deposited on steel substrates (HS6-5-2) using cathodic arc evaporation. The effect of nitrogen pressure on the properties of CrAlN coatings formed from Al80Cr20 cathode, such as chemical and phase composition of the coatings, surface morphology, deposition rate, hardness and adhesion to the substrate, and friction and wear were investigated. The coating deposited at nitrogen pressure of 3 Pa shows the highest deposition rate. The roughness parameter Ra of the coating surface decreases with increasing nitrogen pressure during its formation. The test results showed that the AlCrN coatings deposited under nitrogen pressure in the range from 1 to 5 Pa show similar hardness for all the coatings, which is around 17 GPa. The increase in the negative bias voltage of the substrate during the formation of the coating deteriorates its adhesion to the substrate, although the wear rate is rather good, about 1.4 × 10−7 mm3/Nm. The coatings deposited at nitrogen pressure of 3-4 Pa are characterized by the highest critical load, 95 N. Despite worse adhesion, these coatings are characterized by high resistance to wear, the wear rate is about 1.4 × 10−7 mm3/Nm.
TL;DR: In this article, the effect of various solution treatment processes on the characteristics and microstructural evolution of powder aluminum alloy 6061 was studied using light microscopy, scanning electron microscopy and hardness.
Abstract: Gas-atomized metallic powders are commonly used in additive manufacturing processes. Research has shown that, for certain AM techniques, the chemistry and microstructural properties of the feedstock powders significantly affect the properties of the consolidated material. Understanding the powder characteristics before use in additive manufacturing can lead to optimizing properties of additively manufactured materials as well as determining the recyclability of feedstock powders. This research studies the effect of various solution treatment processes on the characteristics and microstructural evolution of powder aluminum alloy 6061. Solution treatment times and temperatures were guided by thermodynamic and kinetic modeling. Light microscopy, scanning electron microscopy, and hardness were used to evaluate each condition in both two and three dimensions. Results indicate that the Mg2Si present in the untreated condition dissolves after 60 min of solution treatment, while there are competing effects from the dissolution and concurrent growth of various Fe-containing phases. Additionally, it is shown that both granular and sub-granular structures exist in these rapidly solidified powders, and the sub-grains reorient themselves during solution treatment.
TL;DR: In this article, the authors investigated the inhibition effect of gum arabic (GA) using weight loss measurements and electrochemical techniques and found that the inhibition efficiency of GA increased with an increase in the concentration of the inhibitor but decreased with the temperature.
Abstract: The inhibition effect of gum arabic (GA) was investigated using weight loss measurements and electrochemical techniques. The results show that the inhibition efficiency of GA increased with an increase in the concentration of the inhibitor but decreased with the temperature. Immersion time was found to have a profound effect on the corrosion inhibition performance of the inhibitor. Polarization measurements revealed that GA was a mixed-type inhibitor, with higher influence on the anodic reaction. The inhibitor followed the Temkin’s adsorption isotherm, and the values of the standard free adsorption energy indicate a mixed-type adsorption, with the physical adsorption being more dominant. SEM–EDS and FT-IR measurements were also employed to support the findings.
TL;DR: In this article, the effect of channel angles on material properties was investigated during equal channel angular pressing of AZ80 magnesium alloy using processing route R at 325°C processing temperature, and it has been revealed that the channel angle has a significant influence on deformation homogeneity, microhardness, ultimate tensile strength, ductility and corrosion behavior of Mg alloys.
Abstract: In this article, the effect of channel angles on material properties was investigated during equal channel angular pressing of AZ80 magnesium alloy using processing route R at 325 °C processing temperature. Channel angles of 90° and 110° and common corner angle 30° have been considered for this study. It has been revealed that the channel angle has a significant influence on deformation homogeneity, microhardness, ultimate tensile strength, ductility and corrosion behavior of Mg alloys. Investigation with reference to as-received AZ80 Mg alloy indicates 18.47% improvement in UTS and 76.07% enhancement in ductility after processing through 3P-90° and 2P-110° ECAP, respectively. Also, the corrosion rate reduces to 89.47% after processing the sample with 3P-110° ECAP die.
TL;DR: In this article, four constitutive models, namely modified Cowper-Symonds, modified Johnson Cook, modified Zerillie-Armstrong and integrated Johnson Cook-ZerillieArmstrong (JC-ZA) models have been investigated for flow stress prediction.
Abstract: An accurate constitutive model is essential for analyzing deformation behavior of material and reliable numerical simulations in metal forming processes. In this study, hot tensile tests of Inconel 718 alloy have been conducted over a wide range of temperatures (300-973 K at an interval of 100 K), strains (0.01-0.3 at an interval of 0.01) and quasi-static strain rates (0.0001, 0.001, 0.01 s−1). Flow stress behavior is significantly affected by test temperatures and strain rates. Microstructure characteristics of deformed test specimens have been examined using scanning electron microscope and electron backscatter diffraction (EBSD). The fractography study revealed that fracture is mix-mode type, i.e., ductile and brittle. Subsequently, EBSD analysis shown that dynamic recrystallization mechanism is more pronounced at a higher temperature. Furthermore, four constitutive models, namely modified Cowper–Symonds, modified Johnson Cook, modified Zerillie-Armstrong and integrated Johnson Cook–Zerillie-Armstrong (JC-ZA) models have been investigated for flow stress prediction. Capability of models has been evaluated based on the correlation coefficient (R), average absolute error (Δ) and its standard deviation (δ). Accurate prediction of flow stress behavior is found by integrated JC-ZA model with R = 0.9873, Δ = 2.44 and δ = 4.08%.
TL;DR: This article showed that LME cracks decreased strength from 7.8 to 42.2%, depending on location, between the coated (cracked) and uncoated (non-cracked).
Abstract: Advanced high-strength steels used in automotive structural components are commonly protected using zinc coatings. However, the steel/zinc system creates the potential for liquid metal embrittlement during welding. Although liquid metal embrittlement cracks are known to form, the current literature does not include crack location when assessing crack severity. In this work, TRIP1100 joints showed that LME cracks decreased strength from 7.8 to 42.2%, depending on location, between the coated (cracked) and uncoated (non-cracked) condition. Liquid metal embrittlement cracks in critical locations were observed to propagate until fracture from lap shear testing. However, cracks in non-critically loaded areas were not part of the fracture path and did not result in a significant loss in strength. This shows LME crack location can be controlled to improve joint performance and vehicle safety. In addition, a model of lap shear testing in a cracked sample showed how the presence of a crack can affect the internal stress field depending on its location.
TL;DR: In this paper, the effects of altering process parameters on microstructure, porosity, and mechanical performance of Inconel 718 were investigated, and the results showed that process parameter modifications that result in porosity formation can significantly reduce fatigue life, while micro-structure changes were minimal and had little effect on tensile properties.
Abstract: Additive manufacturing (AM) allows for the fabrication of complex parts via layer-by-layer melting of metal powder Laser powder-bed AM processes use a variety of process parameters including beam power, beam velocity, and hatch spacing to control melting Alterations to these parameters have often been attempted to reduce porosity, for example, but less work has been done to on comprehensive effects of process parameter modifications This study looks at the effects of altering these parameters on microstructure, porosity, and mechanical performance of Inconel 718 The results showed that process parameter modifications that result in porosity formation can significantly reduce fatigue life, while microstructure changes were minimal and had little effect on tensile properties The precipitate structure was not found to be changed significantly These results can inform future process parameter modifications, as well as heat treatments to optimize mechanical properties
TL;DR: In this article, the authors compared the mechanical properties of Hastelloy X alloys fabricated by selective laser melting with the wrought counterpart and found that the latter had better tensile strength.
Abstract: Mechanical properties of Hastelloy X alloys fabricated by selective laser melting were investigated and compared with the wrought counterpart. Nano-inclusions (Mo-rich carbides) distributed at the sub-grain boundaries in the selective laser-melted (SLMed) Hastelloy X alloy, whereas micron-scale precipitations existed in the wrought counterpart. The molten pool boundaries widely existed in the SLMed substrate, which acted as an initial site for crack and led to poor plasticity. However, the ultimate tensile strength values of the SLMed Hastelloy X alloys were around 910 MPa and much higher than the wrought counterpart (~ 750 MPa), which was mainly ascribed to the high-density dislocations enriched at the sub-grain boundaries. Process parameter effects on the mechanical properties were also delineated in this work, and the volumetric energy density for the best mechanical properties of the SLMed Hastelloy X alloy was in the range from 140 to 170 J/mm3.
TL;DR: HA-reinforced composites of Mg-based (Mg-3Zn) matrix are evaluated for their mechanical integrity in simulated in vitro condition and the effect of HA on mechanical integrity of M g-based composites in orthopedic application is established.
Abstract: Biodegradable metals are being frequently explored as a very potential replacement for bone implant and fixing accessories, owing to their superior mechanical and biological properties. In connection to this, biodegradable magnesium (Mg) and its alloys exhibit good biocompatibility for orthopedic applications. Nevertheless, the use of these biodegradable materials has been restricted due to their fast degradation rate in the physiological environment, even before the new tissue is adequately generated. So, it becomes necessary to bring down their corrosion rate to retain their mechanical integrity until the bone properly heals. A solution to this problem is found in hydroxyapatite (HA)-reinforced Mg-based composites. However, it is important to understand the mechanical behavior of these materials, after exposure to body environment. In this study, HA-reinforced composites of Mg-based (Mg-3Zn) matrix are evaluated for their mechanical integrity in simulated in vitro condition. Addition of 5 wt.% HA decreased the corrosion rate of Mg-3Zn, which in turn maintained the mechanical integrity of the structures even after 14 days of immersion. Mg-3Zn and Mg-3Zn-5HA composites have retained ~ 34 and 66% of ultimate compressive strength after 3 days of immersion. All these studies together establish the effect of HA on mechanical integrity of Mg-based composites in orthopedic application.
TL;DR: In this paper, the effect of postweld heat treatment (PWHT) on the mechanical properties and microstructural evolution of aluminum 7075 alloy processed via friction stir welding (FSW).
Abstract: This work focuses on the effect of postweld heat treatment (PWHT) on the mechanical properties and microstructural evolution of aluminum 7075 alloy processed via friction stir welding (FSW). FSW is known to be capable of grain refinement in the nugget zone (NZ). Two different quench media (water and air) were employed for PWHT. Regardless of the quench media, the PWHT led to the occurrence of grain growth in the NZ of the FSWed aluminum 7075 alloy. Abnormal grain growth occurred in the water quenched specimen. It is shown that ductility and strength of FSWed aluminum 7075 alloy are strongly dependent on the quenching rate. Changes in the mechanical properties and microstructure reveal that only at lower cooling rate this alloy is prone to the formation of precipitate-free zones (PFZs) in the vicinity of grain boundaries. Eventually, the PFZs deteriorate mechanical properties of this alloy.
TL;DR: In this article, the authors investigated the flow stress behavior and material properties of dual-phase (DP) 590 steel for different process parameters such as temperature (room temperature (RT) to 400 °C), strain rate (0.0001-0.01 ǫ s−1), and three different sheet orientations, viz., rolling direction (RD), transverse direction (TD), and normal direction (ND).
Abstract: In the present study, the flow stress behavior and material properties of dual-phase (DP) 590 steel have been investigated for different process parameters such as temperature (room temperature (RT) to 400 °C), strain rate (0.0001-0.01 s−1), and three different sheet orientations, viz., rolling direction (RD), transverse direction (TD), and normal direction (ND). The flow stress increases with an increase in temperature and strain rate. The yield and ultimate stress also decreased by approximately 13.85 and 13.45%, respectively, with an increase in temperature from RT to 400 °C; but no particular trend was observed for elongation. Subsequently, microstructural and fractographic studies were conducted using a scanning electron microscope. The volume fraction of the martensitic phase seems to decrease with an increase in temperature. In addition, from the electron backscattering diffraction studies, an increase in the ratio of high-angle grain boundaries was observed with an increase in the grain size of the material. The ductile type of failure was observed at all testing conditions. Furthermore, an investigation of strain hardening behavior using Swift and Voce modeling was carried out for DP590 steel. Three stages of hardening were observed in the case of both the applied strain hardening models. Predicted flow stress with the Voce model displayed a good agreement with the experimental data. The combined effect of temperature and strain rate was considered by formulating an Arrhenius-based Sellar model for the flow stress prediction.
TL;DR: In this paper, the pitting and intergranular corrosion properties of the welding joints have been tested using electrochemical testing and microstructure observations, and the volume fraction of the ferrite phase reached 70% in the weld zone of the laser beam welding joint of the SAF 2507 super duplex stainless steel.
Abstract: SAF 2507 super duplex stainless steel has been welded using laser beam (LB) welding and laser/gas metal arc hybrid (LGH) welding processes. The pitting and intergranular corrosion properties of the welding joints have been tested using electrochemical testing and microstructure observations. The volume fraction of the ferrite phase reaches 70% in the weld zone of the LB welding joint, while the volume fraction of the ferrite phase is 60% for the welding joint of LGH due to the introduction of Ni from welding wire. The pitting corrosion resistance of the welding joint for LB is better than that of LGH. The pitting corrosion is easily conceived in the heat-affected zone (HAZ) because of the formation of Cr2N in the HAZ during welding.
TL;DR: In this article, the effect of two different post-treatments, namely hot isostatic pressing (HIP) and a combined HIP+heat treatment (HT) carried out inside the HIP vessel, have been studied and results from as-built and post-treated specimens were compared in terms of porosity/lack-of-fusion, microstructure, phase constitution (NbC content, δ-phase) and micro-hardness.
Abstract: Electron beam melting (EBM) of Alloy 718 is of rapidly growing interest as it allows cost-effective production of complex components. However, the inherent flaws in the component in as-built state are of concern in view of the severe working conditions in which Alloy 718 components typically operate. The present work entails an investigation of changes in microstructure that accompany some post-treatments that are being widely considered to address defects in EBM processed Alloy 718. The effect of two different post-treatments, namely hot isostatic pressing (HIP) and a combined HIP + heat treatment (HT) carried out inside the HIP vessel, have been studied and results from as-built and post-treated specimens were compared in terms of porosity/lack-of-fusion, microstructure, phase constitution (NbC content, δ-phase) and micro-hardness. Post-treatment resulted in reduction in defect content by more than an order of magnitude. HIPing led to complete dissolution of δ phase. In comparison to as-built material, HIPed specimens exhibited significant drop in hardness. However, a sharp ‘recovery’ of hardness to yield values higher than in as-built condition was observed after HIP + HT and can be attributed to precipitation of γ′′ phase.
TL;DR: In this paper, four annealed carbon steels with different carbon contents (0.002, 0.17 and 0.7% C) were selected to understand the corrosion behavior of carbon steel as a function of carbon content in freely aerated 3.5% NaCl solution.
Abstract: Four annealed carbon steels with different carbon contents (0.002, 0.17, 0.43, and 0.7% C), consisting of ferrite, ferrite-pearlite and fully pearlite microstructures, were selected to understand the corrosion behavior of carbon steel as a function of carbon content in freely aerated 3.5% NaCl solution. Dynamic polarization, electrochemical impedance and linear polarization methods were used. The corrosion rate obtained from the different carbon steels was found to increase greatly from ultra-low carbon steel (0.002%) to low carbon steel (0.17%) due to the presence of pearlite in the low carbon steel. However, the increase in corrosion rate was marginal with the increase in carbon content from low carbon (0.17%) to medium (0.43% C) and high carbon steels (0.7% C). The mirostrucural evolution of the steels before and after polarization test without etching as observed by scanning electron microscopy could show that the corrosion behavior of the steels with the presence of pearlite was due to the combined effect from % pearlite, interlamellar spacing and cementite/ferrite area ratio in pearlite. Pearlite morphology also led to the differential corrosion within the pearlite colony in all the steels except the steel with 0.002% C. Catalytic activity of cementite on enhancing oxygen reduction reaction attributes to the higher corrosion rates in case of the steels with the presence of pearlite.
TL;DR: In this article, the discharge performance of a Mg-air battery with 3N5 Mg, AZ31, AZ61, AZ91 alloys was investigated in a 0.6M NaCl electrolyte, with the aim of selecting a common commercial Mg alloy to decrease passivation and self-corrosion of Mg anode for Mg air battery.
Abstract: Electrochemical and discharge properties of Mg-air battery based on 3N5 Mg, AZ31, AZ61, AZ91 alloys were studied in a 0.6 M NaCl electrolyte, with the aim of selecting a common commercial Mg alloy to decrease passivation and self-corrosion of Mg anode for Mg-air battery. Results obtained indicate that self-corrosion and passivation decrease, and anodic utilization increases gradually with increasing Al content. This is associated with the double effect of Al on discharge performance of Mg anode. Al with high hydrogen overvoltage decreases self-corrosion of Mg anode and passivation of Mg anode by peeling off Mg(OH)2 discharge products. Results of electrochemical impedance spectroscopy and discharge morphology relate well with the results of electrochemical and discharge performances. It is concluded that solution-treated AZ91 alloy has a better discharge performance as anode of Mg-air battery in 0.6 M NaCl electrolyte.
TL;DR: In this article, a self-diagnosis approach was proposed to detect pure sensor failures without any structural dependence, but the results demonstrate that self-detection of the mixed mode of failures is challenging due to the opposite effect that different types of failure return.
Abstract: Commercial aerospace vehicles have been increasingly demanding to withstand harsh conditions with low-weight material, i.e., composites. Unfortunately, low-velocity impacts strongly affect their performance. Structural health monitoring with permanently attached sensors allows achieving cost-effective maintenance and tearing down knockdown factors. However, the degradation of transducers adopted for online detection of damage negatively affects the diagnosis. That deterioration is addressed in this work with the electromechanical impedance approach employed at relatively low ultrasonic frequencies. Several degradation conditions are investigated with experimental and numerical simulations. The results demonstrate how the self-diagnosis approach detects pure sensor failures without any structural dependence. However, self-detection of the mixed mode of failures is challenging due to the opposite effect that different types of failure return. Numerical simulations provide a spectral response in compliance with measurements. On top of that, numerical results demonstrate that the combination of different types of damage may induce missed detection. That is where a multi-parameter self-diagnosis approach may further improve the overall monitoring system.
TL;DR: In this article, an experimental study of the efficiency of Arc-PVD and PACVD industrial technologies for the application of diamond-like carbon (DLC) coatings on ceramic cutting plates based on Al2O3+TiC to increase the wear resistance of the tool when turning of bearing hardened steel 102Cr6.
Abstract: The work is devoted to the experimental study of the efficiency of Arc-PVD and PACVD industrial technologies for the application of diamond-like carbon (DLC) coatings on ceramic cutting plates based on Al2O3 + TiC to increase the wear resistance of the tool when turning of bearing hardened steel 102Cr6. The authors conducted a set of studies and tests as the study of the structure of DLC coatings (correlation between sp3 and sp2 bonds) using photoelectron spectroscopy; evaluation of roughness, microhardness and adhesive bond strength of DLC coatings with the ceramic base; study of coated ceramics wear under fretting conditions; and experimental evaluation of the effect of DLC coatings on the resistance of ceramic plates during turning of hardened steel. The durability of ceramic plates was increased by 1.6 times by applying PACVD DLC coatings. A slightly smaller effect in 1.4 times was achieved by applying DLC coatings using Arc-PVD technology.
TL;DR: In this paper, dissimilar friction stir welding was carried out between stainless steel and mild steel plates of 4mm thickness using a tungsten carbide tool, and the influence of tool rotational speeds (600, 875, and tool offsets (0.6, 1.2) on mechanical properties, such as hardness, tensile strength, and impact toughness of welded joints was investigated.
Abstract: In the present study, dissimilar friction stir welding was carried out between stainless steel (UNS S30400) and mild steel (UNS G10080) plates of 4 mm thickness using a tungsten carbide tool. The influence of tool rotational speeds (600, 875 rpm) and tool offsets (0.6, 1.2 mm) on mechanical properties, i.e., hardness, tensile strength, and impact toughness of welded joints was investigated. Maximum tensile strength of the joint was about 107.6% of the mild steel under rotational speed of 875 rpm and tool offset of 1.2 mm. The maximum hardness reached in the stir zone was about 281 HV0.5 due to the phase transformations and grain refinement. Charpy’s notch toughness of the welded joints was observed lower than the base materials. The microstructural characterizations were carried by using an optical microscope, and FESEM–EDS analysis which revealed the complex material mixing and material movement during the welding. Tungsten-rich bands were observed in the weld micrograph especially toward the advancing side. During this study, various wear mechanisms like oxidation wear, abrasive wear, and adhesion wear were responsible for the degradation of tungsten carbide tool.
TL;DR: In this paper, the effect of applied multi-variant heat treatment on microstructure, phase composition and mechanical response of Haynes 282 nickel-based superalloy was investigated.
Abstract: In this paper, the effect of applied multi-variant heat treatment on microstructure, phase composition and mechanical response of Haynes 282 nickel-based superalloy was investigated. For this reason, temperatures of both stages of standard two-stage aging treatment (i.e., 1010 °C/2 h + 780 °C/8 h) were extended to 900-1100 °C/2 h and 680-880 °C/8 h ranges, respectively. Consequently, 30 different variants of heat treatment were applied. The microstructural features of heat-treated samples were investigated by means of light microscopy and SEM/EDS methods, while mechanical properties were examined via microhardness measurements. It was found that by using various combinations of temperatures of the first and second stage of aging, the room temperature hardness of Haynes 282 alloy can be decreased by ~ 100 HV units or increased by up to 25 HV units as compared to that of the alloy subjected to the standard heat treatment schedule. The mechanical response of the alloy is determined by a complex structural evolution involving the secondary precipitation of γ′, M23C6 and M6C phases, as well as their interaction with the fcc γ matrix.