Showing papers in "Transactions of The Indian Institute of Metals in 2019"

Metals Extraction from Sulfide Ores with Microorganisms: The Bioleaching Technology and Recent Developments

Abstract: Nowadays, due to fast global industrial progress and near diminution of high-grade ore reserves, there has been massive call to cost-effectively process the resources of low-grade ores and industrial effluents for metal extraction. However, conventional approaches cannot be used to process such resources due to high capital cost and energy, also causing environmental pollution. Alternatively, bioleaching is highly environmental friendly and economic method to process such resources. Metal recovery from metal sulfide ore is carried out by chemolithotrophic bacteria like Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. The same is done by heterotrophic microorganisms in non-sulfide ores. Additionally, for gold and copper extractions, bioleaching is used to extract cobalt, zinc, nickel, and uranium from low-grade ores and industrial effluents. In this review, the fundamental process of bioleaching from low-grade metal sulfide ores are discussed with emphasis on mechanism, types, pathways, techniques, and bioleaching development.

Characterization of Microstructure and Interface Reactions in Friction Welded Bimetallic Joints of Titanium to 304 Stainless Steel Using Nickel Interlayer

Abstract: Direct joining of 304 stainless steel to titanium poses many challenges because of a lack of metallurgical compatibility and the formation of FeTi and CrTi types of brittle intermetallic compounds. The use of a low thermal heat input process of friction welding allows to obtain good microstructure properties through the improvement of metallurgical compatibility between two metals. In the present investigation, a novel approach of nickel interlayer was applied to explore a new bimetallic structure of titanium to stainless steel. Microstructure characterization, interface formation and its reactions were analysed via scanning electron microscope, X-ray diffraction and electron probe microanalyser analyses. The results exhibited that the intermetallic phases were successfully avoided through the use of Ni interlayer. Microhardness values demonstrated the absence of brittle FeTi and CrTi phases in the weld interface. The weld interface was found to be within two intermetallic layers situated at Ti/Ni interface.

Experimental and Taguchi-Based Grey Approach of Laser Metal Deposition Technique on Nickel-Based Superalloy

Abstract: Thin sections of Inconel 718 sample was treated with laser-based metal deposition using a CW CO2 laser. The Taguchi-based grey relational approach was incorporated for determining the optimized process characteristics of the laser treatment. Laser scan speed was varied at a constant laser power in order to analyze the effect of cooling rate and the subsequent thermal gradient on the microstructure and other properties of the base alloy. The presence of γ′-(Ni3Al, Ni3Ti) and γ″-Ni3Nb precipitates in the interdendritic boundaries was evidenced in the deposition zone. The increase in laser scan speed to 600 m/min changed the microstructure from coarse to fine grains, and a further increase to maximum laser power of 1.75 kW showed the transformation to still finer dendritic structure. Even though the fine dendritic structure, it also resulted in delamination of bonding layers which could be deleterious. X-ray diffraction spectrum revealed the precipitation of γ-NiCr, γ′-Ni3Al and γ″-Ni3Nb in the γ-Ni matrix and there was no evidence for the transformation of γ″-Ni3Nb to δ-Ni3Nb. It indicated that the selected laser parameter had the least possibility of influence in the formation of intermetallics after treatment. The significant effect of grain refinement improved the hardness by 15–20%. The tensile test on Inconel 718 showed the Ni3Nb precipitate particles initiated the interfacial failure and was encountered with ductile mode of fracture.

Effect of Power Input on Metallurgical and Mechanical Characteristics of Inconel-625 Welded Joints Processed Through Microwave Hybrid Heating

Abstract: In the present study, welding of Inconel-625 through the use of microwave hybrid heating (MHH) has been achieved at two power levels 600 W and 900 W in a low-cost home microwave oven. Nickel-based powder EWAC was used as filler interface between faying surfaces. Effect of power variation on the metallurgical and mechanical characteristics of the microwave welded joints has been investigated. Developed joints were characterized through XRD, optical microscope, SEM, universal testing machine and Vickers microhardness tester. XRD study of the weld zone indicated the formation of various carbides and intermetallics. Joint microstructures witnessed a completely fused weld interface without any interfacial cracks. EDS analysis of the joint microstructure revealed lesser amount of segregation of niobium and molybdenum with the specimens developed at 600 W which could be attributed to the lower heat input associated with 600 W power that also resulted in fine grain structure. Further, the specimens processed at 600 W exhibited better tensile and flexural properties when compared to their counterparts produced at 900 W power. Fractography study of the specimens revealed a combined ductile and brittle fracture.

Sustainable Primary Aluminium Production: Technology Status and Future Opportunities

Abstract: Energy and greenhouse gas emission remain the major technological challenges to the aluminium production. Over the last few decades, aluminium industries have been aiming for higher production volumes through capacity creep in the existing smelters with reasonable additional investment. However, a strong focus on specific energy consumption has always been part of technology considerations, and this aspect is even more critical today from the point of view of long-term sustainability. Through research and innovations in design, control and operations of Hall–Heroult cell, modern smelters are achieving a benchmark performance as low as 13 kWh/kg of Al at commercial scale and 12 kWh/kg of Al at pilot scale. There is also significant research effort put on alternate technology platforms like drained cathode cell and inert anode. Although there are many pilot-scale demonstrations, many critical issues like operating cost and stability problems in drained cell and higher specific energy in inert anode need to be addressed for commercial consideration of these technologies. Industry 4.0 platform technologies like internet of things, cloud computing, machine learning and artificial intelligence, etc., are opening up further opportunities for benchmark performance to the modern smelters. Digital twin is such an emerging technology for predictive control and operation and will be a key driver for low-energy cells. Based on a discussion on the status of present technology, this article presents a comprehensive review of the technological progress of aluminium smelting and emerging new technology like Industry 4.0, towards reduction of energy and making aluminium production sustainable.

Friction Welding of Titanium to Stainless Steel Using Al Interlayer

Abstract: Dissimilar friction welding between titanium and 304 austenitic stainless steel with aluminum as insert layer was examined to amend the joint properties and interface characteristics. To insert the interlayer into the joint, a two-step method was used. The resultant of the joint interfaces was characterized to reveal the reactions between interlayer and parent metals using scanning electron microscope, X-ray diffraction and electron probe micro-analyzer. Microhardness and tensile tests were used to evaluate the mechanical properties of the joints. It was observed that the development of brittle phases of FeTi and CrTi in the welded joint was successfully precluded using aluminum interlayer, whereas the presence of other phases which were in ductile nature compared to the FeTi- and CrTi-type phases of AlTi and FeAl was identified. The absence of reaction compounds and brittle phases ensued improvement in the mechanical and microstructural properties of the aluminum insert layer joints.

Strengthening and Mechanical Properties of SiC and Graphite Reinforced Al6061 Hybrid Nanocomposites Processed Through Ultrasonically Assisted Casting Technique

Abstract: Al6061 alloy-based hybrid nanocomposites reinforced with 2wt% SiC and x wt% of graphite (x = 0, 0.5, 1, 1.5, 2 and 3) nanoparticles are fabricated through ultrasonically assisted casting technique. Microstructure, phases, grain size and fracture surfaces of the hybrid nanocomposites are studied to understand the mechanical properties. Microstructural studies revealed the uniform distribution of SiC and graphite nano-reinforcements in the matrix. The small-scale clusters appeared in the microstructure with the increase in graphite nanoparticles. The grain size, density, hardness and ultimate tensile strength of hybrid nanocomposites decreased with the rise of graphite in the composite material. The yield strength of the hybrid nanocomposites increased with increase in graphite up to 2 wt% and then decreased. SiC and graphite dual phase nanoparticles’ strengthening effect on yield strength was theoretically evaluated using various strengthening mechanisms including porosity effect. Enhancement of yield strength in hybrid nanocomposite due to strengthening mechanisms followed the trend $$\Delta \sigma_{{\Delta {\text{CTE}}}} > \Delta \sigma_{\text{Orowan}} > \Delta \sigma_{\text{HP}} > \Delta \sigma_{\text{load}}$$ . The predicted yield strength of hybrid nanocomposites obtained using the modified Clyne model and quadratic summation model were close to the experimental values. Fracture surfaces of hybrid nanocomposites exhibited brittle fracture with interdendritic cracking, stepwise facets and particle pull out with the increase in graphite content in the matrix.

Effect of Hybrid Machining Techniques on Machining Performance of In-House Developed Mg-PMMC

Abstract: High demand of lightweight material makes magnesium alloys and composites more suitable to aerospace and automotive industries. However, poor corrosion resistance and fatigue resistance make its applications limited. Due to inherent capability of machining processes, the surface characteristics of the component can be improved. Many articles reported improvement in machinability of different difficult-to-machine materials while using ultrasonic-assisted turning (UAT) process and cryogenic-assisted turning individually. In this paper, the newly developed cryogenic–ultrasonic-assisted turning (CUAT) technique is used for the machining of in-house developed magnesium AZ91/SiC particulate metal matrix composite (PMMC). In this study, surface roughness and chip breakability index are measured under different machining methods, i.e. conventional turning (CT), UAT and CUAT. The full factorial method is used to design the experiments. A regression model of surface roughness is developed for CT and UAT processes and optimized using Jaya algorithm. Our results provide evidence of improvement in surface finish for UAT of magnesium AZ91/SiC PMMC in comparison with CT. An improvement up to 36.50% and 15% has been observed in surface roughness and chip breakability index, respectively, with CUAT process as compared to UAT process at optimized cutting parameters of the UAT process.

Optimization of Electrochemical Micromachining Process Parameters for Machining of AMCs with Different % Compositions of GGBS Using Taguchi and TOPSIS Methods

Abstract: In recent years, the application of aluminum metal matrix composites is expanding to various fields like aerospace, automobile and other industrial machineries. This paper presents the machinability of ground-granulated blast furnace slag (GGBS)-reinforced aluminum 6061 metal matrix composites using electrochemical micromachining for material removal rate (MRR) and radial overcut (ROC). Input voltage, duty cycle, electrolyte concentration and % of composition are selected as the input process parameters. Experiments have been investigated using the L18 mixed-level orthogonal array, and process parameters are optimized using Taguchi technique. The model equation for MRR and ROC is developed using regression analysis. Analysis of variance is performed, and the most significant factor is found to be percentage (%) composition of GGBS. Additionally, the multi-criteria decision-making technique has been used to find optimal machining parameters for higher MRR and lower ROC. The optimal combination for higher MRR and lower ROC is 10 V, 50%, 35 g/l and 12% of GGBS composition. The confirmation test has been carried out to validate the results, and the obtained optimal parameter levels are very close to an ideal solution.

Fabrication and Characterization of Cu–B 4 C Metal Matrix Composite by Powder Metallurgy: Effect of B 4 C on Microstructure, Mechanical Properties and Electrical Conductivity

Abstract: Boron carbide-reinforced copper metal matrix composites have been the subject of broad research because of their good mechanical, electrical and tribological properties. In the present research, Cu–B4C composites containing 5, 10 and 15 wt% of B4C have been fabricated by cold powder compaction followed by conventional sintering at 900 °C for 1 h under argon atmosphere. The fabricated composites are characterized by X-ray diffraction, optical microscopy and field emission scanning electron microscopy (FESEM). From microscopic study, we have found that B4C particles are homogeneously distributed in the copper matrix and there is good compatibility between B4C and Cu. The microstructure analyzed by FESEM shows that the interface between Cu matrix and B4C is clean and no interfacial product is formed. The effect of B4C particles and their weight fraction on microstructure, mechanical properties and electrical conductivity is also studied. The Vickers hardness value increases with increasing weight percentage of boron carbide in Cu matrix. The hardness value increases from 38 VHN for pure copper to 79 VHN for Cu-15 wt% B4C metal matrix composite (MMC). A maximum relative density of 82% is achieved for Cu-5 wt% B4C MMC. The maximum compressive strength of 315 MPa is achieved for Cu-15 wt% B4C MMC. The electrical conductivity of pure Cu is found to be 4.5 × 106 S/m, and it decreases to 1.92 × 106, 0.75 × 106 and 0.32 × 106 S/m for Cu-5 wt% B4C, Cu-10 wt% B4C and Cu-15 wt% B4C MMCs, respectively.

Effect of Grain Refinement on Corrosion Rate, Mechanical and Machining Behavior of Friction Stir Processed ZE41 Mg Alloy

Abstract: The aim of the present work is to modify the microstructure of ZE41 Mg alloy by friction stir processing (FSP) and to study the influence of microstructure on the corrosion, mechanical and machining behavior. Microstructural observations revealed the prevalence of grain refinement from ≈ 100 to 3.5 µm. The compound present at the grain boundary was observed to have decreased to a great extent after FSP suggesting the formation of supersaturated grains. Hardness measurements indicated increased hardness after FSP which was attributed to grain refinement effect. Tensile tests showed increased yield strength after FSP without altering the percentage of elongation which was due to the grain boundary strengthening. Corrosion performance of FSPed ZE41 was found to be similar compared with ZE41 due to the synergy of grain refinement, decreased amount of secondary phase and development of supersaturated grains. Grain size was observed as significant factor on machining characteristics as observed from improved machinability for FSPed ZE41 during drilling experiments. It was learnt from the current work that the grain-refined supersaturated ZE41 Mg alloy could be produced through FSP with better mechanical and machining behavior without deteriorating the corrosion performance.

Effect of Mechanical Mixing in Dissimilar Friction Stir Welding of Aluminum to Titanium with Zinc Interlayer

Abstract: Welding of aluminum (Al) and titanium (Ti) is difficult and challenging due to their differences in chemical and physical properties, and the evolution of brittle intermetallic compounds. Formation of critical intermetallics can be minimized by using an interlayer material, which leads to ternary mechanical mixing in the weld nugget. In the present investigation, a zinc (Zn) interlayer has been used during friction stir welding (FSW) of Al–Ti. It has been found that tool offset position is one of the important parameters in controlling the amount of ternary mechanical mixing of materials. The mechanical mixing of Zn with Al and Ti alters the phase evolution and restricts the formation of the brittle Al3Ti intermetallic compound. The optimum tool offset exhibits a homogeneous mechanical mixing and inhibits the formation of brittle intermetallic compounds, which leads to a substantial increment in the mechanical properties of the weld.

Advanced High-Temperature Structural Materials for Aerospace and Power Sectors: A Critical Review

Abstract: Advanced high-temperature structural materials are expected to play an important role in realizing the aspirations related to the next-generation aerospace propulsion devices, thermal protection system of reusable launch vehicles and thermal/nuclear power reactors. Despite considerable amount of research conducted for developing new and more efficient high-temperature structural materials, the advancement is inadequate and warrants continued efforts to address several unresolved issues concerning synthesis and processing of new materials, related characterization and testing to evaluate and ensure desired performance, durability, reproducibility and reliability in simulated experiments and real-life condition and finally, upscaling the operation for large-scale commercially viable production. In this article, an attempt has been made to review the latest status and trend in developing high-temperature structural materials for aerospace and thermal/nuclear sectors and highlight the challenges associated with development and processing of such advanced structural materials.

Synthesis of Aluminium Composites Using Squeeze Casting and Investigating the Effect of Reinforcements on Their Mechanical and Wear Properties

Abstract: The research aims to fabricate LM25 alloy and composites reinforced with 15 wt% TiB2, 15 wt% ZrO2 and 15 wt% WC using squeeze casting technique. The fabricated cylindrical castings were of dimensions 50 mm diameter and 150 mm length. Microstructural analysis revealed better distribution of reinforcement particles for each composite, which provided better hardness and tensile properties. Physical and wear properties were studied comparatively to understand the influence of reinforcements, and tungsten carbide (WC)-reinforced composites showed better performance. Fractographic analysis revealed ductile mode of failure for LM25 and a combination of ductile and brittle mode for its composites. Dry sliding performance of both alloy and composites was analysed under different sliding conditions of applied load (10–50 N), slide distance (500–2500 m) and slide velocity (1–5 m/s) using pin-on-disc tribometer. WC-reinforced composite improved resistance to wear by 70% compared to alloy. Wear analysis of composite using scanning electron microscope showed change in wear features from mild to severe at high loads. The developed LM25/WC composite was found to be most suitable for non-lubricated slide applications.

Characterization of NbC-Reinforced AA7075 Alloy Composites Produced Using Friction Stir Processing

Abstract: Aluminium alloy AA7075 matrix composites reinforced with varying vol% (5, 10 and 15 vol%) of niobium carbide (NbC) were fabricated by friction stir processing. Micrographs revealed that a homogeneous dispersion of NbC in the AA7075 matrix had no interfacial reaction. Significant degree of grain refinement was observed in the composites due to dynamic recrystallization and pinning effect of NbC particles. Hardness and tensile strength of AA7075 matrix were found to be enhanced by the addition of NbC particles. The fracture surface of the tensile-tested samples revealed deep dimples indicating a good ductility.

Finite Element-Based Parametric Studies of Nugget Diameter and Temperature Distribution in the Resistance Spot Welding of AISI 304 and AISI 316L Sheets

Abstract: Resistance spot welding (RSW) of dissimilar metals is prominent in automobile industries to utilize the material properties of both the metals. RSW of dissimilar austenitic stainless steel sheets (AISI 304/316L) is investigated in this paper by varying the process parameters such as welding current and weld time at three different levels. Tensile shear test and macrostructural examinations are carried out to analyze the performance of spot welds. A three-dimensional model is also developed using commercial finite element analysis software ABAQUS FEA to predict the nugget diameter and thermal distribution profile through simultaneous structural electrothermal analysis with temperature-dependent material properties. The generated model is validated by comparing the predicted nugget diameter with experimental nugget diameter. Experimental results show good coherence with the simulation results, and the macrostructure of the spot-welded joints indicates successful welding of dissimilar sheets with defect-free fusion zone.

Recovery of Valuable Metals from Copper Smelter Slag by Sulfation Roasting

Abstract: In the present paper, recovery of valuable metals from copper smelter slag of Balkhash copper plant (Kazakhstan) was investigated. To recover Fe, Zn and Cu to water-soluble form, the mixture of 150 g of copper slag and 60 g of 85% sulfuric acid was granulated and then roasted in the temperature range of 473–643 K (200–370 °C) followed by sulfuric acid leaching. Once the roasting temperature and duration are, respectively, 643 K (370 °C) and 150 min, the recovery% values of metals to water-soluble form reaches, accordingly: Fe—80.6, Zn—88.7, Cu—81.8. The resulting calcine was subjected to sulfuric acid leaching; after solid: liquid separation, a filtrate was obtained with the following composition, g/L: Fe2+—0.60; Zn2+—3.58; Cu2+—1.03. On adding ammonia water into the filtrate, 98% of iron was selectively precipitated, thereby separating from zinc and copper.

Temperature Distribution During Friction Stir Welding of AA2014 Aluminum Alloy: Experimental and Statistical Analysis

Abstract: FSW has shown great potential to weld AA2014 heat-treatable aluminum alloy. But the effectiveness of joint in FSW depends on the temperature distribution across the length and width of weld zone. The present study aims to investigate the temperature distribution during FSW of AA2014 alloy. The temperatures were recorded at eight different positions by inserting K-type thermocouples on pre-drilled AA2014 alloy under different process parameters like tool rotation (N), welding speed (v) and tilt angle. These temperatures were recorded using two thermocouple layouts: First layout was “equal distance and same depth” on advancing side (AS) whereas second layout was “equal distance and varying depth” on retreating side (RS). Experimental results showed that by increasing the N/v ratio, the peak temperature increased whereas the peak temperature decreased by decreasing the N/v ratio. On the other hand, effect of tool tilt angle on peak temperature was also found to be significant and confirmed by experimental as well as statistical analysis. Furthermore, it was concluded that temperature was higher on AS compared to the RS. The conclusion drawn from statistical analysis was in good agreement with experimental results.

End-point Prediction of BOF Steelmaking Based on KNNWTSVR and LWOA

Abstract: Basic oxygen furnace (BOF) steelmaking plays an important role in steelmaking process. Therefore, research on BOF steelmaking modeling is very necessary. In this paper, a novel combination prediction model has been proposed, which consists of a time series prediction model and a compensation prediction model. Both models are established by k-nearest neighbor-based weighted twin support vector regression (KNNWTSVR) algorithm. By introducing Levy flight algorithm and inertia weight, an improved algorithm of whale optimization algorithm (WOA) called Levy flight WOA has been initially proposed to solve the optimization problem in the objective function of KNNWTSVR. The simulation results show that the proposed models are effective and feasible. Within different error bounds (0.005% for carbon content model and 10 °C for temperature model), the strike rates of carbon content and temperature both achieve 93%, and a double strike rate of 86% is obtained, which can provide a significant reference for real BOF applications, and the proposed method is also appropriate for the prediction models of other metallurgical applications.

Effect of Ternary Addition of Cobalt on Shape Memory Characteristics of Ni–Ti Alloys

Abstract: Shape memory alloys (SMAs) are a class of metallic materials that exhibit two unique characteristics: shape memory effect and superelasticity. These alloys are capable of responding to stimuli like heat when they are subjected to thermo-mechanical treatment. Therefore, these alloys have proven their utility in many areas and are very common in applications such as sensors and actuators, various life-saving medical devices and stents. Ni–Ti alloys are in the forefront with respect to shape memory materials and have been employed in many practical applications. In recent times, there have been attempts to improve their shape memory characteristics, mechanical properties and corrosion resistance through alloying addition, thermo-mechanical processing, severe plastic deformation, etc. Among these methods, ternary alloying addition seems to have a greater effect in comparison with other methods. In this work, cobalt was added to a binary Ni–Ti alloy and its influence on transformation temperatures and microstructure was studied. Ternary NiTiCo alloys with varying cobalt contents (1, 2, 3 at.%) were prepared by vacuum induction melting, and the alloys were then hot-rolled and homogenized. Various characterization techniques such as differential scanning calorimetry, transmission electron microscopy and X-ray diffraction were employed to study the transformation temperatures, the microstructure and the phase structure of the ternary SMAs. It was seen that cobalt addition decreased the phase transformation temperatures and influenced the functional properties of the binary Ni–Ti alloy. Elaborate results have been discussed in this paper.

Influence of Cobalt on the Hot Deformation Characteristics of an NiTi Shape Memory Alloy

Abstract: Among shape memory alloys (SMAs), Ni–Ti alloys are more widely used in multifarious sectors because of their functional properties of shape memory effect and superelastic effect. With an emphasis on miniaturization and higher performance of actuators and biomedical devices these days, there is a necessity to develop SMAs with high stiffness, i.e., high upper/lower plateau stress, and high modulus. In recent times, there have been attempts to improve their shape memory characteristics, mechanical properties and corrosion resistance through alloying, thermal treatment, etc. In this context, addition of Co has been made to binary Ni–Ti alloys. But till date, there has been a dearth of literature on hot deformation characteristics of NiTiCo SMAs. This work therefore investigates the role of cobalt on hot deformation characteristics of an Ni–Ti SMA. The addition of cobalt results in raising the yield strength and reducing the Ms temperature of the alloys. In this study, elemental forms of high-purity nickel, titanium and cobalt were melted together in a vacuum induction melting furnace to produce cylindrical rods. These rods were homogenized at 900 °C for 3 h and quenched to room temperature in water and subsequently machined so as to obtain a length-to-diameter ratio of 1.5, which was ideal to carry out hot deformation studies on a Gleeble thermomechanical simulator. The samples were deformed at different strain rates (0.01, 0.1, 1 and 10 s−1) at temperatures of 800, 900, 1000 and 1100 °C, respectively. Elaborate results on the deformation characteristics of an NiTiCo SMA have been discussed in this paper.

Effect of Oxide Fluxes in Activated TIG Welding of Stainless Steel 316LN to Low Activation Ferritic/Martensitic Steel (LAFM) Dissimilar Combination

Abstract: The aim of current work is to study the effect of different oxide fluxes in activated TIG welding process of dissimilar welding between LAFM and 316LN on weld dimensions, macro- and microexamination, and microhardness. Different oxide fluxes, namely TiO2, Fe2O3, CuO, Co3O4, and HgO, were used for the experiment, and its results were compared with convention TIG welding. Flux paste was applied over the area to be welded using a paint brush at the middle portion of the specimen. All welding experiments were carried out on a bead on a plate and under the same welding conditions and parameters. The experimental result reveals that full-length penetration was achieved with the use of Co3O4 and TiO2 fluxes. This enhancement in depth of penetration is attributed to the reverse Marangoni effect and arc constriction mechanism. In this study, insight was also revealed pertaining to the depth-enhancing mechanism present during ATIG welding of LAFM and SS316LN joints.

Dislocation Interaction and V-Shaped Growth of the Distorted Structure During Nanoindentation of Cu 20 Ni 20 Al 20 Co 20 Fe 20 (high-entropy alloy)-Coated Copper: A Molecular Dynamics Simulation-Based Study

Abstract: In this paper, the deformation behavior of Cu20Ni20Al20Co20Fe20 high-entropy alloy-coated single-crystal Cu substrate which undergoes nanoindentation has been investigated under molecular dynamic simulation with embedded-atom method potential. The dynamic structural evolutions under nanoindentation are presented using centrosymmetry parameter analysis, common neighbor analysis and radial distribution function plots. In the initial level of nanoindentation, the interface deformation is greatly confronted by the confined V-shaped growth of the distorted structure. But the sudden discrete dislocation burst account for avalanche break-down in the interface layer, which further get influenced by the evolution of multiple dislocation nodes that is significantly governed by core spreading, extended misfit dislocation generation and relative rotation. In the meanwhile, the subsequent generation of dislocation locks, complicated multiple dislocation loops, dislocation junctions and limited cross-slip in wide stacking faults (SFs) hasten the work hardening and in turn slows down the deformation progress. On the other hand, the intermediate appearance of narrow SFs and slip bands significantly reduces the work hardening rate that increases the optimum fracture strain value of the specimen. Moreover, the overall increase in dislocation density and dislocation length leads to a significant growth in dislocation sources which leads to forest hardening in the later stage.

Wear Study of Chicken Eggshell-Reinforced Al6061 Matrix Composites

Abstract: The present work deals with conduction of wear test on Al6061/eggshell composites with load, reinforcement and sliding distance as control factors and its regression analysis. Chicken eggshell is one of the most abundant natural waste products generated in large amount by food processing industry due to its everyday consumption. This material is simply disposed in nature thus constituting environmental hazards. Commercial use of eggshells can produce lightweight materials at low cost. Therefore, being complemented with less dense calcium carbonate, it can be used as reinforcement to develop metal matrix composite using stir casting process. Reinforcement is added in the range of 2–10 wt% at an interval of 2%. Optical microstructural characterization indicated fair distribution of particles in the matrix, and 4 wt% composite exhibited best properties among all. Further addition of particles proved to be detrimental due to increase in porosity and agglomeration of particles. Wear track and debris were examined with scanning electron microscope to explain the wear process. Regression analysis helped in establishing the relationship between the control factors. Reinforcement of eggshell particles improved the wear resistance of matrix significantly as suggested by analysis of variance.

Constitutive Modeling of 2024 Aluminum Alloy Based on the Johnson–Cook Model

Abstract: In this paper, hot compression behavior of Al2024 in the temperatures range of 573–723 K and strain rate range of 0.001–0.6 s−1 was studied based on standard tests. The prediction of flow stress was performed using constitutive equations based on the basic and modified Johnson–Cook model, and the accuracy of the proposed models was estimated by statistical error analysis method. Based on the experimental results, flow stress got changed significantly with changes in the strain rate and temperature. Since the basic model could not examine the correlated effects of the parameters, it had inadequate exactness to estimate the flow stress especially at high temperatures. During calculation, the constants in the modified model, effects of hardening and softening behavior were included in addition to considering the correlated effects of the parameters, so the accuracy of the modified model was increased significantly.

Friction Stir Welding of Copper: Numerical Modeling and Validation

Abstract: High thermal and electrical conductivities, corrosion resistance and relatively good strength lead to use of copper and its alloys for several engineering applications. Copper alloys also find application in the nuclear industry for manufacturing storage canisters for spent nuclear fuel. Conventional fusion welding of copper and its alloys is difficult due to high-energy input requirement and various weld defects such as porosity, solidification cracks and distortion. Friction stir welding (FSW) has been proposed as an alternative way of joining copper as it is a solid-state joining process avoiding most of the fusion welding defects. Numerical models are very useful in understanding a welding process, and various models have been developed for FSW of steels, aluminum and titanium alloys. However, such models are not available for copper and its alloys. Here we present a three-dimensional heat transfer numerical model for FSW of copper. The model uses finite element method to calculate the three-dimensional distribution of temperature due to frictional heat generation at the tool and workpiece interface. The computed results are validated with the measured temperatures using a thermocouple near the tool shoulder. The experimentally welded samples are found to be defect free and acceptable based on radiographic testing. The tensile strength of these samples is measured and compared with strength of the base material. The variation in the peak temperature and weld joint strength is studied as a function of the rotation speed. This validated numerical model can be developed further by including material flow calculation for joining of copper.

Microstructural, Tribological and Mechanical Properties Evolution of ZrSiO4/A4047 Surface Composite Fabricated through Friction Stir Processing

Abstract: In this study, zircon sand (ZrSiO4)-reinforced aluminum surface composite up to 15 vol % of microparticles with an average diameter of 3 µm was prepared through multi-pass FSP. The microstructural, mechanical and tribological characterizations of the friction stir-processed ZrSiO4/A4047 surface composite were evaluated. The effects of FSP passes (2, 4 and 6) were evaluated, and it suggests that the surface composite after 6-pass reveals better homogeneous distribution of reinforcement (ZrSiO4) particle in the matrix. The tensile test showed 16, 24 and 44% with increase in FSP passes, respectively, compared to the base metal. Similarly, the microhardness of the surface composite produced through 6-pass FSP was increased to 112 HV while that produced through base metal increased to 74 HV. Also, it was observed that erosion–corrosion resistance and abrasion wear performance were significantly improved with increase in FSP passes.

Dissimilar Welding of Maraging Steel (250) and 13-8 Mo Stainless Steel by GTCAW, LBW and EBW Processes

Abstract: The frequently used aerospace materials, i.e., ultra-high-strength maraging steel (250) and corrosion-resistant 13-8 Mo stainless steel in the solution-annealed and cold-worked condition, have been joined by three fusion welding processes, namely interpulse TIG welding, and high energy density fusion processes like electron beam welding (EBW) and laser beam welding (LBW). The interpulse TIG welding process was carried out by using W2 grade maraging steel filler wire. The dissimilar joints were welded by EBW and LBW processes without any filler wire. All the dissimilar welded joints were characterized by microstructural observations and validated by mechanical properties in the as-welded as well as precipitation-hardened conditions after welding. The weld microstructures and microhardness profiles were correlated to the tensile strength of weld. Electron beam welded joint with precipitation hardening after welding, i.e., soaking at 510 °C and subsequent air cooling, demonstrated the superior mechanical properties among all the welds.

Effect of Sintering Parameters on the Microstructure and Mechanical Properties of Medical Mg–3Mn and Mg–3Zn Prepared by Powder Metallurgy

Abstract: Magnesium alloys as the lightest commercial structural materials have wide application prospects such as in the medical application. However, it is difficult to sinter Mg alloys dense when powder metallurgy was used because of the oxide layers covered by the surface of Mg powders. To solve this problem, Mg–3Zn and Mg–3Mn alloys were sintered under vacuum system in this study. Mg–3Zn and Mg–3Mn compactions were sintered at different temperatures for 2 h based on their phase diagrams in the vacuum furnace. The results show that when sintered at 560 °C, the highest microhardness and relative density of Mg–3Zn alloy are 74.3 HV and 98.4%, respectively. For Mg–3Mn alloy, its highest corresponding value is 46.08 HV and 86.6%, respectively, when sintered at 600 °C. Mg–3Mn is more difficult to be sintered because it is denser than Mg–3Zn. The microstructure of sintered Mg–3Zn and Mg–3Mn mainly is composed of α-Mg and MgZn2, and α-Mn, α-Mg and MnO2, respectively.

Hard Anodizing of Aerospace AA7075-T6 Aluminum Alloy for Improving Surface Properties

Abstract: In the current research work undertaken, an oxide film was grown by performing hard anodizing process on a pure aluminum layer deposited by PVD magnetron sputtering process on AA7075-T6 alloy. The corresponding tribo-mechanical properties were evaluated and compared with those of the base alloy. The dry sliding wear experiments were carried out to investigate wear resistance of anodized AA7075-T6 against the AISI SS316 counter-body by means of a reciprocating tribo-testing setup. The hardness of AA7075-T6 after the anodizing process exhibited an enhancement of about 1.94 times. Results revealed that the wear of anodized coating was exceptionally less when compared with the substrate. Based on morphology and chemistry changes of worn-out surfaces and debris, it was determined that severe abrasive and oxidative wear was the primary wear mechanism for AA7075-T6. The anodizing process increased the friction coefficient from 0.33 to 0.46 but reduced the wear severity by altering the wear mechanism into mild polishing and abrasion. Anodizing enhanced the wear resistance of AA7075-T6 to about three times, and the wear rate decreased to around 4.3 times.