Band 64, Heft 8

The electrical and mechanical properties of a Cu–2.50Ni–0.50Si–0.45Cr–0.25Co–0.25Zr (wt%) cast alloy were investigated. The alloy produced as billet material by arc melting technique was solution annealed at 900 °C for 2 h, quenched in water, and aged at 350–500 °C for 2–192 h. The electrical conductivity of the heat-treated alloy was measured using an Eddy current apparatus, and the mechanical properties were determined using hardness measurements and compression tests applied between room temperature and 600 °C. Microstructural characterization of the cast and aged alloys was carried using light optical and scanning electron microscopy to characterize the precipitated phases within the Cu solid solution matrix. It is found that (i) very fine δ -Ni 2 Si precipitates in the matrix of cast alloy aged at 400 °C for 72 h give an optimal combination of hardness and conductivity and (ii) the aged alloy has a higher yield strength than the cast one at all temperatures investigated.

The effect of isothermal heat treatment temperatures under martensite start (M s ) temperature on the microstructure and mechanical properties of high-silicon commercial spring steel has been investigated. For this purpose, tensile specimens are prepared from AISI 9254 steel isothermally heat-treated under M s temperatures (225 °C, 250 °C, and 275 °C) for 168 h after austenitizing at 870 °C for 30 min. Optical microscopy, scanning electron microscopy and X-ray diffraction analysis were used to characterize the microstructures of the specimens. Mechanical properties were determined by the tensile and hardness tests. Experimental results revealed that microstructure consists of carbide-free bainite, carbon enriched retained austenite, and martensite in high-silicon spring steel by the isothermal treatment under M s temperature. The yield and tensile strength were increased by decreasing the isothermal temperature. However, uniform elongation and breaking energy were decreased by decreasing the isothermal temperature. The specimen which was isothermally heat-treated at 250 °C under M s temperature showed a very good combination of tensile strength and total elongation as 2046 MPa and 8.5%, respectively. Dimples along with cap and cone formation which are evidence of a ductile fracture were observed in fractured surfaces of all isothermally heat-treated specimens.

The effect of different austenitizing temperatures on the type, morphology, distribution of carbides and martensite content in cobalt high-speed steel is characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and energy dispersive spectrometry. The results show that the eutectic MC carbides hardly dissolve during austenitizing process, and the lamellar M 2 C carbides decompose into MC and M 6 C carbides at 1100 °C. A large amount of M 23 C 6 carbides uniformly distributed on the matrix are dissolved into austenite at 1100 °C. With the increase of austenitizing temperature, alloy element dissolves into matrix and the effect of solid solution strengthening of martensite enhances, which increases the hardness of cobalt high-speed steel. However, when the austenitizing temperature exceeds 1050 °C, the excess alloying elements in the matrix reduce the Ms point and increase the volume fraction of retained austenite, resulting in decrease of hardness of cobalt high-speed steel. The peak hardness with 66.4 HRC appears when the austenitizing temperature reaches 1050 °C.

In this work, high-strength low-alloy (HSLA) steel with 0.22 wt% carbon was produced in laboratory scale and hot rolled with a total deformation of 42% via 4, 5, or 6 passes. After multipass hot rolling process, samples were examined either in as-rolled (AR) or as-rolled and heat-treated (ARH) conditions. The results indicated that microstructural and mechanical properties of HSLA steels are influenced by hot rolling conditions for both cases. It was observed that strength values in AR samples have a tendency to increase with increment in rolling pass number. In contrast to AR samples, it was seen that the mechanical properties were slightly decreased in ARH samples that were austenitized at 1150 °C for 45 min and then cooled in still air. Microstructural investigations showed that finer precipitates in AR samples are obviously more than that of ARH samples, as an evidence for higher strength results by precipitation hardening. In addition to precipitation strengthening, refinement of lath bainite and amount of blocky martensite/austenite in AR samples favor the increase in strength.

Thermally sprayed WC-based coating systems are generally used to increase engineering components’ wear resistance. This research presents the results of a comparative study conducted to examine the tribological characteristics of a new brake disc created with thermal sprayed WC-10Co4Cr coating. This study implemented braking tests on the WC-10Co4Cr coated brake disc against commercial friction material on a laboratory scale disc-pad tester and compared the findings with the reference disc. The coating system was created with a high velocity oxygen-fuel spraying on a cast iron disc. The braking tests followed the sections of the SAE-J2430 test procedure. The microstructure, phase composition and properties of the coating were characterized by SEM/EDS, XRD and Vickers microstructure. The effect of carbide coating on the friction and wear behaviour of the tribological system was examined. The WC-10Co4Cr coating has increased the hardness by 3 times with a thickness of 300 μm compared to the cast iron surface. The amount of wear in the coated disc (CD) was reduced by about 85% compared to the reference disc (BD). The coefficient of frictions of BD and CD was found to be in the range of 0.43–0.61 and 0.47–0.62, respectively. The inclusion of hard phases (WC and W 2 C) in the disc coating played an important role in improving the sliding wear resistance by maintaining the coefficient of friction of the brake disc at an acceptable level. In brief, carbide coating could be claimed to be promising for challenging braking implementations.

In this study, AISI 304 stainless steel and DUROSTAT 500 steel are combined using TIG double-sided arc welding. Microstructural differences of welded joints were researched by using a scanning electron microscope (SEM), an optical microscope, and electron backscattered diffraction. Mechanical properties of welded joints were investigated by microhardness, notch impact, and tensile tests. In addition, fracture surface morphology was evaluated using a SEM. The current power had a major impress on bead and hourglass shape. Maximum tensile resistance (677 MPa) was achieved at a welding time of 0.21 (m·min −1 ) at 460 (A) current, and the impact energy (116 J) was obtained. The weld metal consisted 41 wt% cementite, 25 wt% chromium carbide, 20 wt% martensite, and 14 wt% tetrataenite phases. With the increase in the current voltage, both bead and penetration sizes increased.

Nature-inspired metaheuristic algorithms have wide applications that have greater emphasis over the classical optimization techniques. The INFO algorithm is developed on the basis of the weighted mean of the vectors, which enhances the superior vector position that enables to get the global optimal solution. Moreover, it evaluates the fitness function within the updating stage, vectors combining, and local search stage. Accordingly, in the present article, a population-based algorithm named weighted mean of vectors (INFO) is hybridized with the Nelder–Mead algorithm (HINFO-NM) and adapted to optimize the standard benchmark function structural optimization of the vehicle suspension arm. This provides a superior convergence rate, prevention of trapping in the local search domain, and class balance between the exploration and exploitation phase. The pursued results suggest that the HINFO-NM algorithm is the robust optimizer that provides the best results compared to the rest of the algorithms. Moreover, the scalability of this algorithm can be realized by having the least standard deviation in the results. The HINFO-NM algorithm can be adopted in a wide range of optimization challenges by assuring superior results obtained in the present article.

In this research, the compressive behavior of structures consisting of two types of cells were studied (honeycombs and re-entrant), in order to know the effect of the ratios of these cells on the mechanical properties of the structures. In addition, by controlling the Poisson’s ratio with a constant Young’s modulus, three types of structures (traditional honeycomb, auxetic and zero Poisson’s ratio (ZPR)) were obtained together with the ability to control their mechanical properties without changing the geometric properties of the cell. Numerical models were created and compared with the results obtained from the structures manufactured by the 3D printer experimentally, and where the Young’s modulus, Poisson factor and compressive deformation were close to the experimental results. In this current research, new structures have been proposed by incorporating traditional honeycomb cells with auxiliary honeycomb cells into a single structure without changing the cell geometry. The aim was to control the Poisson’s ratio in order to obtain all types of structures mentioned above without changing the geometric properties of the cell.

Evaluation of directly bonded single-lap joint (SLJ) obtained using Al5754 alloy and 20 wt% long glass fiber-reinforced polypropylene (PP) is performed via the lap-shear testing at various temperatures. A fiber laser is used to form a multi-groove microstructure on the aluminum (Al) surface. The bonding regions are investigated microscopically before and after the mechanical testing. Dissimilar joint is manufactured under a 100 kN force at 200 °C for 60 min through hot-pressing technique without using any adhesives. Afterward, lap-shear strength of the joints is determined under elevated working temperatures (25, 75 and 125 °C). Damaged surfaces are also scrutinized for studying the failure mechanism of the joints. According to the experimental results, mechanical anchoring between the Al alloy substrate and thermoplastic composite (TPC) is formed at the interface through the applied laser treatment. Strength exhibits a significant decrease with the test temperature increasing from 25 to 125 °C. Fiber/matrix debonding is the dominant failure mode in the composite adherend. The SEM observations also highlight the pulled-out fibers in the PP composite at the elevated temperatures.

The high-strength aluminum alloy is the potential candidate to replace conventional materials. It has excellent corrosion-resistant, recyclable machinability. The joining of such a type of alloy using fusion welding is very difficult. Solid-state welding, friction stir welding (FSW) has been used. However, this process has attained a maximum joint of 90% of base material strength. The drop of remaining strength is due to the formation of the temperate region in the thermo-mechanically affected area. Most of the researchers have been reported that the failure has observed at the interface. Many techniques have been followed to improve the strength at the temperate region, namely, post-weld heat treatment, backing plate change, sheet position, tool offset, etc. In this study, the shot blasting technique has been used to improve the lost strength in the soft region. From the experimental result, the joint shot-peened with steel shot yielded higher strength than the classical friction stir welded (C-FSW) joints. Moreover, the stability of the shot-peened joint has been conceived 6.9% more than the C-FSW joint.

The single point incremental sheet forming process is a flexible manufacturing process to produce complex three-dimensional products. Unlike traditional forming processes, the single point incremental sheet forming process does not require unique tools or die. This method is constantly being improved to increase the uniform formability of the material. The fluid assisted single point incremental sheet metal forming process with a newly developed system was experimentally investigated in this research. A controlled pressure fluid was applied to the forming surface in the opposite direction during shaping. Shaping processes were carried out using different fluid pressure values. The effect of this pressurised system on the forming quality was investigated by considering material wall thickness changes, heat generation and surface roughness. The results were compared with the results obtained with the traditional single point incremental sheet forming method. It has been determined that our method increases the formability of the finished product and shows a homogeneous thickness distribution.

The main objective of this research paper is to investigate the nugget formation, microstructure and strength performance of DP 800 steel joints developed using resistance spot welding (RSW) process for automotive application. The influence of RSW parameters on nugget formation was studied using one variable at a time approach. The RSW joint showing optimum nugget area was further characterized for microstructural features and strength performance. The microstructural features of nugget were studied using optical and scanning electron microscopy (SEM). The lap tensile shear fractured specimens were analyzed using SEM for optimized condition. The microstructural features were correlated to the tensile shear strength and hardness of RSW joints. Results showed that welding current significantly influences the nugget formation than electrode force and welding time. The DP 800 RSW joints made using a welding current of 5.5 kA, an electrode pressure of 4.0 MPa and a welding time of 2.0 s disclosed defect free weld nugget of 7.28 mm diameter. It showed a higher tensile shear strength of 20 kN and microhardness of 564 HV thereby satisfying the requirement of automotive applications.

Nature-inspired optimization algorithms named meta-heuristics are found to be versatile in engineering design fields. Their adaptability is also used in various areas of the Internet of things, structural design, and thermal system design. With the very rapid progress in industrial modernization, waste heat recovery from the power generating and thermal engineering organization is an imperative key point to reduce the emission and support the government norms. However, the heat exchanger is the component applied in various heat recovery processes. Out of the available designs, shell and tube heat exchangers (SHTHEs) are the most commonly adopted for the heat recovery process. Hence, cost minimization is the major aspect while designing the heat exchanger confirming various constraints and optimized design variables. In this study, cost minimization of the SHTHE is performed by applying a novel metaheuristic algorithm which is the African vultures optimization algorithm (AVOA). Adopting the AVOA for the best-optimized value (least cost of heat exchanger) and the design parameters are realized, confirming all the constraints. It was found that the AVOA is able to pursue the best results among the rest of them and can be used for the cost optimization of the plate-fin and tube-fin heat exchanger case studies.

A comparative evaluation of the influence of welding current on Tungsten Inert Gas (TIG) welding and Activated Tungsten Inert Gas (ATIG) welding on the depth of penetration and microstructure properties was performed. Various super duplex stainless steel (SDSS) beads on plate weld joints were studied. Visual observation showed that lower welding current resulted in partial weld penetration in the case of both TIG and ATIG weldments. Weld joints obtained by the ATIG process have a higher depth of penetration and depth/width ratios than weld joints obtained in the conventional TIG process at comparatively lower welding currents. Further, microstructural characterizations were performed using optical microscopy. The weld zone microstructure consists of grain boundary austenite (GBA), widmanstätten austenite (WA) and intragranular austenite (IGA). Ferrite percentage in bulk material and each weldment was measured using ferrite scope. The TIG-welded heat affected zone (HAZ) joints showed higher ferrite content than activated flux TIG-welded HAZ joints for various welding current conditions. Ferrite content measured in the weld-zone, HAZ and base material was within the ranges of the standard values. The TIG weld zone showed higher hardness than that of the ATIG weld zone.