Showing papers in "Transactions of The Indian Institute of Metals in 2018"

Mechanical Properties and Tribological Behavior of Al6061–SiC–Gr Self-Lubricating Hybrid Nanocomposites

Abstract: In the present investigation, a newly fabricated Al6061 reinforced with various quantity (0.4–1.6 wt%) of nano SiC in steps of 0.4 and fixed quantity (0.5 wt%) of micro graphite particle’s hybrid nanocomposites were prepared by ultrasonic assisted stir casting method. The influence of nano SiC and graphite content on the mechanical and tribological properties of Al6061 hybrid nanocomposites were studied. The pin-on-disc equipment was used to carry out experiment at 10–40 N applied load, 0.5 m/s sliding speed and 1000 m sliding distance. The Al/SiC/Gr hybrid nano-composite and matrix alloy wear surfaces were characterized by FESEM equipped with an EDS, 3D profilometer to understand the wear mechanisms. The results of Al/SiC/Gr self-lubricating hybrid nano-composites showed improved wear resistance than the Al6061 matrix alloy. The co-efficient of friction of Al/SiC/Gr hybrid nano-composites were lower than those of the unreinforced alloy at various applied load. Compared to matrix alloy, the surface roughness of Al/SiC/Gr hybrid nano-composites had significantly reduced to 66% at low load and 75% at high load. Self-lubricating Al/SiC/Gr hybrid nanocomposites showed superior surface smoothness compared to matrix alloy.

Review of Nickel-Based Electrodeposited Tribo-Coatings

Abstract: Among various methods used for protecting the industrial components from wear/abrasion failures, electrodeposition has attracted considerable attention in recent years because of its advantages such as being efficient, accurate, affordable, and easy to perform. In this regard, electrodeposition of nickel-based composite and alloy coatings is an inexpensive method compared with other coating methods such as chemical vapor deposition and physical vapor deposition. Furthermore, nickel-based composite electrodeposition is an eco-friendly substitute for conventional toxic coatings such as hard chrome. Embedding hard particles within the metallic matrix improves the wear resistance by increasing the ductility of the matrix in the contact area, changing the preferred grain growth direction to close-packed directions, and boosting dispersion and grain-refinement strength. In addition, lubricant particles provide superior anti-abrasive behavior because of their non-sticky nature. Several factors affect the incorporation of the particles into the electrodeposited coating and therefore the wear behavior of these coatings is related to different parameters such as current density, bath composition, pH, amount and size of the embedded particles. This review paper provides an overview of the wear behavior of nickel-based electrodeposited coatings including their composites and alloys with the focus on the parameters affecting wear rate, coefficient of friction, hardness, and roughness.

Synthesis, Characterization and Mechanical Properties of AA7075 Based MMCs Reinforced with TiB 2 Particles Processed Through Ultrasound Assisted In-Situ Casting Technique

Abstract: AA7075/TiB2 composites have been synthesized through both in situ salt-melt reaction method and ultrasound assisted in situ process. Microstructural studies reveals that ultrasound assisted in situ method improves the dispersion of TiB2 particles and reduces the porosity level. Moreover, the ultrasonic treatment refines the reinforcement particle size along with improvement in particle dispersion. The mechanical property assessment confirms that ultrasonic treatment improves the mechanical properties of composite. The hardness of the AA7075 alloy is increased from 55 HV to 74 HV by the addition of 5% TiB2 particles and it further increased to 82 HV by ultrasonic treatment. A similar trend is also observed when weight percentage of particles increases to 7.5%. Addition of 5% in situ TiB2 particles increases the ultimate tensile strength of AA7075 alloy by 60 MPa and it is further enhanced by 80 MPa upon ultrasound assisted process. Composites have shown a small reduction in ductility when compared to un-reinforced alloy, though 81% ductility of matrix alloy has been retained. Similar trend has been observed in composites fabricated using ultrasonic assisted casting.

Investigation of Microstructure, Mechanical and Wear Behaviour of B 4 C Particulate Reinforced Magnesium Matrix Composites by Powder Metallurgy

Abstract: In the present study, magnesium and magnesium matrix composites reinforced with 10, 20 and 30 wt% B4C particulates were fabricated by powder metallurgy using hot pressing technique. The microstructure, mechanical properties and wear behaviour of the samples were investigated. Microstructure characterization showed generally uniform distribution of B4C particulates. XRD investigations revealed the presence of Mg, B4C and MgO phases. The mechanical properties of the investigated samples were determined by hardness and compression tests. Hardness and compressive yield strength significantly increased with increasing B4C content. The reciprocating wear tests was applied under loads of 5, 10 and 20 N. Wear volume losses decreased with increasing B4C content. Abrasive and oxidative wear mechanisms were observed.

Investigation of Mechanical Properties and Dry Sliding Wear Behaviour of Squeeze Cast LM6 Aluminium Alloy Reinforced with Copper Coated Short Steel Fibers

Abstract: LM6 aluminium alloy with 2.5–10 wt% of copper coated short steel fiber reinforced composites were prepared using squeeze casting process. Microstructure and mechanical properties viz., hardness, tensile strength and ductility were investigated. Dry sliding wear behaviour was tested by considering sliding distance and load. Fracture surface and worn surface were examined using field emission scanning electron microscope (FESEM). Hardness of composites increased with increasing wt% of fiber. Tensile strength of composites increased up to 19% for 5 wt% fiber composites. Further addition of fibers decreased the tensile strength of composites. Ductility of the composites decreased with the addition of fibers into the matrix. Wt% of fibers significantly decreased the weight loss, coefficient of friction and wear rate. Also the cumulative weight loss decreased up to 57% for 10 wt% of composites compared to LM6 aluminium alloy. Fracture surface of composite tensile specimen showed dimple formation and fiber pullout. Worn surface of matrix showed long continuous grooves due to local delamination on the surface. However, worn surface of composites showed fine and smooth grooves due to ploughing rather than local delamination. Copper coated steel fiber reinforcement in LM6 aluminium alloy exhibited better mechanical properties and wear resistance compared to matrix.

60NiTi: A Review of Recent Research Findings, Potential for Structural and Mechanical Applications, and Areas of Continued Investigations

Abstract: Recent advances in the manufacture and processing of high purity NiTinol 60 (60 wt% Ni–40 wt% Ti) has spurred a renewed interest in the use of this alloy for structural and mechanical component applications. NiTinol 60 (60NiTi) exhibits excellent corrosion resistance, can be hardened to high levels, has a low elastic modulus and extensive elastic range that imparts high mechanical contact load resilience. It is dimensionally stable, has good bio-compatibility, can be machined into precision components and is non-magnetic. This unique set of characteristics make the intermetallic 60NiTi suitable for a wide variety of applications in the marine, medical, aerospace and food processing industries. This article surveys and reviews a broad range of historic and recent publications on 60NiTi to highlight what is known and areas that require further study. In particular, recent results indicate a dichotomy in friction and wear behavior. Under good lubrication (liquid or solid) both friction and wear are low but in dry un-lubricated sliding, wear exceeds that of other materials such as steel that have comparable hardness. This unexpected behavior is proposed as an important topic for future investigations before any of widespread adoption in engineering applications.

Effect of Copper Coating and Reinforcement Orientation on Mechanical Properties of LM6 Aluminium Alloy Composites Reinforced with Steel Mesh by Squeeze Casting

Abstract: Uncoated and copper coated steel wire mesh reinforcing LM6 aluminium alloy composites have been produced using squeeze casting process by varying reinforcement orientation viz., 0°, 45° and 90° respectively. Microstructure of the castings has been examined and mechanical properties such as hardness, tensile strength and ductility have been investigated. Fracture surface of tensile specimens has been analysed using field emission scanning electron microscope. Microstructure of samples reveals that copper coating on steel wires improves the interface bonding between matrix and reinforcement. Average hardness values of 259 and 90 Hv have been observed in steel wire and matrix respectively. Tensile strength of composites increases with increasing angle of reinforcement orientation from 0° to 90°. Tensile strength increases up to 11% by reinforcing copper coated steel wire mesh at 90° orientation as compared to LM6 aluminium alloy. Fracture surface of composites shows pullout of steel wires in uncoated steel wire mesh composites and broken wires in copper coated steel wire mesh composites respectively. Dimples have been observed on the fracture surface of LM6 aluminium alloy. In general, copper coated steel wire mesh composites offer better hardness and tensile strength compared to uncoated steel wire mesh composites and LM6 aluminium alloy. This may be attributed to the copper coating on steel wires which results better interface bonding between matrix and reinforcement.

Modeling of Process Parameters for Surface Roughness and Analysis of Machined Surface in WEDM of Al/SiC-MMC

Abstract: Wire electric discharge machining (WEDM) is a newly emerging non-traditional technology for machining MMCs. In the present study, an attempt has been made to investigate the effect of WEDM parameters such as pulse on time, pulse off time, peak current, spark gap voltage, wire feed rate and wire tension on the surface roughness height (Ra) during WEDM of particulate silicon carbide aluminum metal matrix composites (Al/SiC-MMC). The RSM based Box–Behnken design is employed for experimental investigation. Utilized the acquired results, a quadratic regression model for surface roughness height (Ra) has been developed. An attempt has been made to optimize the process parameters for surface roughness height (Ra). To validate, confirmation experiments have been carried out and predicted results have been found to be in good agreement with experimental findings. The surface morphology of machined surfaces has also been studied using scanning electron microscope. Various surface defects and their possible reasons have been discussed.

Investigation on microstructure and tensile behaviour of stir cast LM13 aluminium alloy reinforced with copper coated short steel fibers using response surface methodology

Abstract: Copper coated steel fibers reinforced LM13 aluminium alloy composites have been prepared using stir casting process. Experiments have been designed using response surface methodology by varying wt% of reinforcement (0–10), stirrer speed (350–800 rpm) and pouring temperature (700–800 °C). Microstructure, tensile strength and fracture surface of composites have been investigated. Analysis of variance, significance test and confirmation tests have been performed and regressions models have been developed to predict the tensile strength of composites. Response surface plots reveal that tensile strength of composites increases with increasing wt% of copper coated steel fibers reinforcement up to 6 wt%. Further increase in wt% of steel fibers decreases the tensile strength of composites. However tensile strength of composites increases with increasing stirrer speed due to the uniform and homogeneous dispersion of steel fibers in matrix. Optimum stir cast process parameters for obtaining higher tensile strength are found to be 5.9 wt% of reinforcement, 753 °C pouring temperature and stirrer speed of 633 rpm. Fracture mechanism is dominated by steel fiber pullouts in composites with higher wt% of reinforcement and dimples are observed in the surface of composites containing lower levels of wt% of reinforcement.

Statistical Analysis and Mathematical Modeling of Dry Sliding Wear Parameters of 2024 Aluminium Hybrid Composites Reinforced with Fly Ash and SiC Particles

Abstract: The present studies are focused to analyze mathematically the dry sliding wear of 2024 aluminium alloy reinforced with fly ash (FA) and silicon carbide (SiC) particles with weight percentages of 5, 10 and 15. Both FA and SiC reinforcements are combined equally in weight proportion. Dry sliding wear values are computed using the pin-on-disc wear testing machine. The process parameters or factors like applied load, the weight percentage of FA and SiC, sliding time are identified, which are going to affect the wear of the sample under investigation. The experiments are designed based on Taguchi L27 orthogonal array. Mathematical/statistical methods such as Taguchi’s signal-to-noise ratio and Analysis of Variance (ANOVA) are the best tools, which are used to find out the influence of factors/parameters on the wear of composite. The analysis of experimental data using such methods is done using MINITAB 18 software considering smaller is better as a quality characteristic. Multiple linear regression and response surface methodology (RSM) mathematical models are used to develop the relation between wear with process factors. The results obtained from multiple linear regression model and RSM are compared. 2D contour plots are drawn for evaluation of wear at different set of process conditions. The wear mechanisms are studied using SEM pictures.

Studies on Tribological Characteristics of Centrifugally Cast SiCp-Reinforced Functionally Graded A319 Aluminium Matrix Composites

Abstract: The concept of functionally graded materials is effectively applied to design and fabricate engineering components with location-specific wear resistance suited to the particular application. The present study describes the wear behaviour of centrifugally cast A319 aluminium functionally graded metal matrix composites (FGMMC) formed from 20 wt% SiCp-reinforced composite. Liquid stir casting method is used for homogeneous metal matrix composite preparation followed by vertical centrifugal casting for FGMMC rings production. Microstructure analysis of specimen reveals a homogeneous distribution of SiCp reinforcements for the gravity and a gradient particle distribution, in the radial direction forming different zones, for the centrifugal castings. The dry sliding wear behaviour is studied on a DUCOM pin-on-disc tribometer with steel disc and by using FGMMC pins produced from different zones. Wear studies show gradient tribological properties, within a component, with a maximum wear resistance at the particle rich region, lesser in transition zone and the minimum wear resistance at the inner zones. SEM observation confirms abrasive wear predominance by revealing the microgrooves and ploughing on the worn-out surfaces.

Application of GRA and TOPSIS Optimization Techniques in GTA Welding of 15CDV6 Aerospace Material

Abstract: In this article, an attempt was made to optimize the welding parameters of gas tungsten arc welding of 15CDV6 steel. Experiments based on Taguchi’s L9 orthogonal array were carried out in this research paper. The input parameters such as current, voltage, travel speed were considered for joining 15CDV6 plates of thickness 3.7 mm. Aftermath, the welds were subjected to post weld heat treatment. The performance characteristics such as bead width, reinforcement, tensile strength, hardness and depth of penetration of the welds were also measured. Grey relational analysis (GRA) and technique for order preference by similarity to ideal solution method (TOPSIS) were used for identifying the optimised input parameters. Analysis of variance was used to identify the influence of each individual parameter on the multi-objective function. The metallurgical characterisations of the optimised weld were compared with the microstructures obtained using optical microscope. It was made clear that both GRA and TOPSIS produced different set of optimized parameters. But on experimentation, it was found that optimized parameters obtained from TOPSIS produced weld with better properties. At the initial stage, the base metal reflected inferior properties to weldments but there was a significant improvement in the properties of base metal after post weld heat treatment.

Machining Characteristics and Corrosion Behavior of Grain Refined AZ91 Mg Alloy Produced by Friction Stir Processing: Role of Tool Pin Profile

Abstract: In the present study, influence of friction stir processing (FSP) tool pin profile on the microstructure evolution, corrosion and machining characteristics of the AZ91 magnesium alloy was investigated. Three different pin profiles namely simple taper, threaded taper and square taper were selected and FSP was carried out at 1400 rpm and 25 mm/min tool travel speed. Microstructural observations indicated grain refinement from a starting grain size of 166.5–7.9, 22.1 and 4.08 µm for FSPed samples processed by simple taper, threaded taper and square taper pins, respectively. In all the FSPed samples, decreased amount of secondary phase (Mg17Al12) was observed compared with that of the unprocessed sample. From the X-ray diffraction analysis, it was observed that the square taper pin tool had induced higher texture effect compared with the other two FSP tools. From the electrochemical studies, the corrosion resistance of the sample processed with square taper pin tool was observed to be more in comparison to that of the other samples; which could be attributed to the texture effect and decreased fraction of secondary phase. Machining behavior assessed by conducting drilling experiments showed a significant influence of grain refinement on the cutting forces.

Performance of ANFIS Coupled with PSO in Manufacturing Superior Wear Resistant Aluminum Matrix Nano Composites

Abstract: In this study, ANFIS was combined with PSO in order to optimize the parameters in pressure assisted semi solid processing of A360 aluminum matrix nano composites. ANFIS was utilized to calculate the objective function, which was later minimized using PSO. Combination of EMS semi solid processing and pressure assistance during solidification resulted in improvement of microstructural features and tribological properties. Globular grain structure was formed in the pressure assisted EMS parts. Tribological properties were investigated using pin on disk. It was noted that wear properties of EMS parts were benefited from the refinement of the primary α-Al phase and uniform distribution of the particles. EMS composites showed higher hardness than conventional cast parts, consequently there was a lower real area of contact and therefore lower wear rate. Moreover, hard dispersoid made the virgin alloy plastically constrained and improved their wear resistance.

Characterization, Tribological and Mechanical Properties of Plasma Paste Borided AISI 316 Steel

Abstract: The AISI 316 steel was treated by the plasma paste boriding by using a gas mixture of 70%H2–30%Ar with a boron source of 100% B2O3 in the temperature range of 700–800 °C for 3, 5 and 7 h. The boride layers formed on the samples were observed by scanning electron microscope. The iron borides were also identified by the use of an X-ray microanalyzer, equipped with energy dispersive X-ray spectroscopy. The XRD analysis was carried out to identify the iron and metallic borides present inside the boride layer. Based on the kinetic data, the value of boron activation energy for the AISI 316 steel was estimated as 118.12 kJ mol−1 and compared with the data available in the literature. A regression model based on ANOVA analysis was used to predict the boride layers’ thicknesses depending on the boriding parameters: the treatment time and the boriding temperature. A good correspondence was obtained between the experimental values and those predicted by the regression model. Furthermore, the wear behavior of the sample borided at 750 °C for 5 h was investigated. The significant increase in wear resistance of plasma borided layer was observed in comparison with the untreated AISI 316 steel. The nanomechanical properties of the sample, plasma paste borided at 700 °C for 7 h, were examined using the nanoindenter with a Vickers diamond tip. The load–displacement curves, as well as, Young’s moduli and hardness were shown for the selected measurements. The obtained results depended on the phase composition of the tested area.

Microstructure, Mechanical and Sliding Wear Behavior of AA5083–B 4 C/SiC/TiC Surface Composites Fabricated Using Friction Stir Processing

Abstract: In this research, friction stir processing (FSP) was used to produce three different surface composites of AA5083 reinforced with B4C, SiC, and TiC particles. The effects of reinforced particles and three consecutive FSP passes on particle distribution, microstructure, mechanical and wear properties were studied. The microstructure reveals significant grain refinement with a dense distribution of particulates towards the retreating side and advancing side of stir zone, some region at the centre of stir zone shows particle free bands and excellent bonding between particle and matrix. FSP induces severe plastic deformation promoting mixing and refining the constituent phase in the materials. Mechanical properties and wear resistance of the FSPed samples were evaluated and compared with the matrix alloy. The results show that the incorporation of B4C, SiC and TiC particles into the matrix improves the hardness, tensile and wear properties. TiC and SiC particulates reinforced surface composites reveals a ductile mode of fracture whereas B4C reinforced surface composite shows a bimodal type of fracture. The investigation on wear mechanism was performed using a pin-on-disc tribometer. The results show that the wear mode changes from abrasive to delamination wear.

Experimental Study of Surface Hardening of AISI 420 Martensitic Stainless Steel Using High Power Diode Laser

Abstract: In this paper laser surface hardening of martensitic stainless steel AISI 420 was conducted using a 1600 W semiconductor diode laser. Focal plane position, laser power and scanning speed were considered as process variables. Microhardness was measured in depth and surface of the hardened layer and metallography of samples were conducted in order to study the microstructure of the hardened zone. Macrography was also performed to measure the geometrical dimensions of hardened zone (width and depth). Microstructure evaluation was investigated through optical microscopy and field emission scanning electron microscopy. Microstructure observation of laser treated zone indicated that the higher surface hardness created the finer and more uniform martensitic phase. Results showed that by increasing the laser power and decreasing the focal plane position, depth of penetration and microhardness of hardened zone increased. By increasing the scanning speed and focal plane position, penetration depth decreased while width of hardened zone increased. Under desired conditions resulting from this research (laser power 1400 W, scanning speed 5 mm/s and focal plane position 65 mm), surface hardness of AISI 420 martensitic steel increased to 720 from 210 Vickers. The dimension of hardened layer was 1.2 mm in depth and 6.1 mm in width. Comparing the results with the furnace hardening heat treatment showed that the laser hardening process was more effective and precise than conventional processes.

Identification of Constitutive Model Parameters for Nimonic 80A Superalloy

Abstract: Nimonic 80A is a nickel-chrome superalloy, commonly used due to its high resistance against creep, oxidation, and temperature corrosion. This paper presents the material constitutive models of Nimonic 80A superalloy. Johnson–Cook (JC) and modified JC model is preferred among the different material constitutive equations (Zerill Armstrong, Bodner Partom, Arrhenius type) due to its accuracy in the literature. Three different types of compression tests were applied to determine the equation parameters. Firstly, quasi-static tests were performed at room temperature. These tests were conducted at 10−3, 10−2, and 10−1 s−1 strain rates. Secondly, compression tests were performed at room temperature at high strain rates (370–954 s−1) using the Split-Hopkinson pressure bar. Finally, compression tests were performed at a temperature level from 24 to 200 °C at the reference strain rate (10−3 s−1). Johnson–Cook and modified JC model parameters of Nimonic 80A were determined with the data obtained from these tests, and they were finally verified statistically.

Effect of Heat Input on Microstructure and Corrosion Behavior of Duplex Stainless Steel Shielded Metal Arc Welds

Abstract: In the present work, UNS S32750 super duplex stainless steel sheets were welded by shielded metal arc welding process with E2595 electrode using two different heat inputs, 0.54 and 1.10 kJ/mm. Microstructural investigations (optical and scanning electron microscopy) showed very small differences in the heat affected zone for both the heat inputs. The weld metals showed presence of three different morphologies of austenite—Widmanstatten, intra-granular and grain boundary austenite along with ferrite. Ferrite content in the weld region was also nearly same and did not change significantly with the increase in heat input. Both the weldments showed similar mechanical properties (ultimate tensile strength, impact strength and hardness) and failed in a ductile manner. Electrochemical studies in 3.5% NaCl solution showed the degree of sensitization to less than 1% and nearly same pitting potential for both heat inputs. Since the effect of heat input on the weld behavior was negligible, low heat input may be preffered for welding UNS S32750 super duplex stainless steel.

Nano-/Ultrafine Eutectic in CoCrFeNi(Nb/Ta) High-Entropy Alloys

Abstract: The development of single-phase high-entropy alloys (HEAs) emerges as a new paradigm shift in material research society during the last decade A strong rise in the demand for structural and functional applications leads to the design and fabrication of super-strong eutectic HEAs through solidification processing We report on the evolution of eutectic microstructure in CoCrFeNiNb05 and CoCrFeNiTa04 HEAs synthesized by arc melting The evolved microstructure consists of nanolamellae of FCC γ-Ni and hexagonal β (Fe2Nb or Co2Ta type) Laves phases of 150 nm lamellae thickness These alloys exhibit high yield strength of 2 GPa, ultimate compressive strength up to 22 GPa and 20% plastic strain The strain rate jump test and transmission electron microscopic studies of deformed specimens have been performed to explore the microscopic mechanism of deformation in these high-strength advanced eutectic alloys

Effect of Centrifugal Speed in Abrasive Wear Behavior of Al-Si5Cu3/SiC Functionally Graded Composite Fabricated by Centrifugal Casting

Abstract: Centrifugal casting was adopted for fabricating AlSi5Cu3/10 wt% SiC functionally graded metal matrix composite under three different centrifugal speeds of 800, 1000 and 1200 rpm, and hollow cylindrical components (φout 150 × φin 132 × 150 mm) were obtained. Microstructures of outer and inner periphery of all composites were observed through optical microscope and micro hardness of outer, intermediate and inner region of composite was tested using Vicker’s hardness tester. Results revealed that outer region of the composites centrifuged at all speeds have particle rich region with higher hardness. Abrasive wear experiments were conducted only on surface of particle rich region based on Taguchi’s technique by varying parameters such as centrifugal speed of casting process, rotating speed and applied load of abrasive wear tester. Analysis of variance results revealed that, centrifugal speed had highest significance on wear rate. Abraded surfaces were examined using scanning electron microscope and the maximum wear resistance was observed on particle rich zone of composite centrifuged at 1200 rpm.

Influence of Two-Stage Stir Casting Process on Mechanical Characterization and Wear Behavior of AA2014-ZrO 2 Nano-composites

Abstract: In the current research work synthesis, characterization, mechanical and wear behavior of 2, 4 and 6 wt% of nano-ZrO2 particulate-reinforced AA2014 alloy composites have been investigated. The matrix phase of AA2014 alloy containing nano-ZrO2 particulates composites was geared up by two-stage melt stir system. After the preparation, the organized composites were studied by SEM and EDS for analyzing the microstructures and chemical elements. Further, mechanical characterization and wear studies of as-cast AA2014 alloy and AA2014-nano-ZrO2 composites were studied. From the investigation, it was observed that the tensile behavior of composites was enhanced due to addition of nano-sized ZrO2 particles in the AA2014 alloy matrix. In nano-ZrO2-reinforced composites, the percentage elongation decreased. Further, the wear loss increased with respect to the load for all the prepared materials. To study the fractography and different wear mechanisms for various test conditions of different compositions, tensile fractured surfaces and the worn surfaces were observed by SEM.

Refill Friction Stir Spot Welding of 2198-T8 Aluminum Alloy

Abstract: Refill friction stir spot welding (RFSSW) technology was used to weld 2 mm-thick 2198-T8 aluminum alloy in this work As one of the most significant factors affecting the joint mechanical properties, effect of the tool rotating speeds on microstructure and mechanical properties of the RFSSW joint was mainly discussed Results showed that keyhole could be successfully refilled after the RFSSW process Due to the complicated movement of the tool components, different material flow behaviors could be obtained at the pin affected zone and sleeve affected zone, leading to different microstructures at the two regions By undergoing through different heat cycle during welding, the secondary phase particles (Al2Cu) showed different morphologies and sizes at different regions The lap shear failure load of the joint firstly increased and then decreased with increasing in the rotating speed The maximum failure load of 9298 N was obtained when using 1600 rpm All the joints showed lap-shear fracture mode

Effect of Al Addition on the Microstructural Evolution of Equiatomic CoCrFeMnNi Alloy

Abstract: The present investigation reports the effect of aluminum addition on the microstructural evolution in the equiatomic CoCrFeMnNi high-entropy alloy. Aluminum was added to the alloy in varying quantity (0 ≤ Al ≤ 10 at.%) using the vacuum arc melting technique, and phase formation was probed using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results indicate that the FCC phase in the alloy remains unaltered up to Al of 5 at.%. The higher amount of Al addition leads to the precipitation of B2 Al(Ni, Cr, Fe, Co, Mn) in the FCC matrix. For Al ≥ 7%, typical phase-separated microstructure consisting of FCC, and B2 phases have been observed. The microstructural changes lead to hardness variation from 1.3 to 2.2 GPa, mainly due to precipitation and solute solution hardening of FCC phase. For FCC phase, Al atoms being larger in size can lead to lattice distortion and improve yield strength. The results have been explained by detailed thermodynamic analysis using HEA3 database.

Microstructure and Wear Behavior of Zircon Reinforced Copper Based Surface Composite Synthesized by Friction Stir Processing Route

Abstract: Although copper has its use in many industrial and functional applications, but its low wear resistance limits its potential application. Hard particulates are generally reinforced in bulk copper to increase its wear resistance but it tend to decrease its toughness. Thus the present research focuses on synthesis of copper based surface composite by friction stir processing. Zircon sand was used as reinforcement in copper as it is hard and fairly inexpensive. To prepare the composites, a groove of defined dimension was machined in the copper plate for compaction of zircon sand (18 vol%) at the centre of the plate. After filling the zircon sand in grooves, friction stir processing technique was employed to reinforce it in copper. For microstructure analysis, XRD, microhardness and wear characterization, specimens were cut from the processed portion of the plate. The micrograph obtained by optical and scanning electron microscope revealed equiaxed and fine grain structure in stir zone with no sign of concentration gradient, aggregation and segregation of particles. XRD pattern revealed no peaks corresponding to intermetallics or interfacial reaction products. The microhardness and wear resistance of fabricated surface composite improved significantly as compared to pure copper. The micrograph of worn surface was also analysed to investigate the predominant wear mechanisms. Adhesion and delamination wear were predominant wear mechanisms in pure copper whereas these wear mechanism was not significant in Cu/Zircon composite.

Influence of Powder-Chip Based Reinforcement on Tensile Properties and Fracture Behaviors of LM6 Aluminum Alloy

Abstract: Tensile properties and fracture behaviors of silicon rich LM6 aluminum alloy were investigated in details for as cast alloy and modified by LM6 powdery-chip capsules. The obtained results showed that 20% modified LM6 cast composite ensured the excellent tensile properties (tensile strength of 203 MPa with 3.8% elongation). An impressive increase in the elongation (6.8%) was found for 25% modified cast composite with good ultimate tensile strength, 6.2% higher than unmodified (182 MPa). Characterization of the casts and fracture surfaces were carried out to study the effect of reinforcement particles. An influence of un-melted chip structure was observed inside the cavities and on fractured surfaces. The XRD results showed that cast consisted of inter-metallics of AlO2, Al2Si and Al4Si. It was attributed to micro-cracks prevalently propagated along the broken eutectic silicon particles and some rejected solid particles on the fractured surfaces with ductile and inter-granular fracture. Debonding and cracking of silicon particles were also detected on the fractured surface of the specimens.

Characterization of Structure–Property Relationship of Incoloy 825 and SAF 2507 Dissimilar Welds

Abstract: This study was carried out to investigate the evaluation of dissimilar welding between Incoloy 825 Ni-based alloy and SAF 2507 super duplex stainless steel. Welding was conducted by pulsed current (PC) and continuous current (CC) gas tungsten arc welding (GTAW) methods using ERNiCrMo-3 filler wire. The microstructure of weld zones and base metal/weld interfaces as well as mechanical properties of weldments were characterized. The results detailed the formation of Nb, and Mo-rich phases in the inter-dendritic regions of weld metals leading to a decrease in impact resistance of weld zones in comparison to parent metals. Presence of more secondary phases at the CCGTA weld metal resulted in higher hardness and lower toughness than that of the PCGTAW sample. During tensile tests, fracture occurred at the Incoloy 825 base metal, and both weldments also underwent ductile mode of fracture. The research addressed the microstructure–property relationship for dissimilar weld joints.

Determination of Optimal Process Parameters of Friction Stir Welding to Join Dissimilar Aluminum Alloys Using Artificial Bee Colony Algorithm

Abstract: This paper presents the efforts of joining dissimilar aluminum alloys (AA6351-T6 and AA6061-T6) by friction stir welding (FSW) process. FSW experiments are conducted according to the three factors five level central composite rotatable design method, and the response surface methodology was used to establish the empirical relationship between FSW process parameters such as tool rotational speed (N), tool traverse speed (S) and axial force (F), and the response variables such as ultimate tensile strength, yield strength, and percentage of elongation. The developed empirical models’ adequacies are estimated using the analysis of variance technique. This paper also presents the application of the artificial bee colony algorithm to estimate the optimal process parameters to achieve good mechanical properties of FS weld joints. Results suggest that the estimations of the algorithm are in good agreement with the experimental findings.

Comparative Study on Microstructural Characteristics and Compression Deformation Behaviour of Alumina and Cenosphere Reinforced Aluminum Syntactic Foam Made Through Stir Casting Technique

Abstract: In order to examine the effect of microballoons type on microstructure and compressive deformation behaviour of aluminum syntactic foam, alumina reinforced and cenosphere reinforced aluminum syntactic foams have been made through stir-casting technique. Alumina microballoons reinforced aluminum syntactic foam (AMRASF) has been developed using stir casting technique. Volume fraction of alumina microballoons in AMRASF varies in the range of 0.39–0.74. The compressive deformation behavior of these AMRASF is compared with that of cenosphere reinforced aluminum syntactic foam (CPRASF). The AMRASF does not exhibit clear plastic collapse stage as observed in case of CPRSAF. It is further noted that AMRASF shows the existence of work hardening phenomena after yielding but CPRASF does not show any significant work hardening after yielding even at higher relative densities of foam. This is explained on the basis of characteristics of alumina microballoons and cenospheres and interface characteristics between matrix and respective microballoons used. Effect of individual microballoons’ characteristics on the foam properties has also been explained.

Investigation on Mechanical and Adhesive Wear Behavior of Centrifugally Cast Functionally Graded Copper/SiC Metal Matrix Composite

Abstract: The objective of this work is to fabricate functionally graded unreinforced copper alloy (Cu–10Sn) and a Cu–10Sn/SiC composite (Oout100 × Oin70 × 100 mm) by horizontal centrifugal casting process and to investigate its mechanical and tribological properties. The microstructure and hardness was analysed along the radial direction of the castings; tensile test was conducted at both inner and outer zones. Microstructural evaluation of composite indicated that the reinforcement particles formed a gradient structure across the radial direction and maximum reinforcement concentration was found at the inner periphery. Hence maximum hardness (205 HV) was observed at this surface. Tensile test results showed that, the tensile strength at inner zone of composite was observed to be higher (248 MPa) compared to that of the outer zone and unreinforced alloy. As mechanical properties showed better results at inner periphery, dry sliding wear experiments were carried out on the inner periphery of composite using pin-on-disc tribometer. Process parameters such as load (10–30 N), sliding distance (500–1500 m) and sliding velocity (1–3 m/s) were analyzed by Taguchi L27 orthogonal array. The influence of parameters on wear rate was analyzed by signal-to-noise ratio and analysis of variance. Analysis results revealed that load (54%) had the highest effect on wear rate followed by sliding distance (18.2%) and sliding velocity (3.7%). The wear rate of composite increased with load and sliding distance, but decreased with sliding velocity. Regression equation was developed and was validated by confirmatory experiment. Worn surface of composite was observed using scanning electron microscopy and transition of wear was observed at all extreme conditions.