Volume 62, Issue 2

Manufacturing wheel rims in the automobile industry demands high quality, high production, cost-effective and flawless wheels. At present, JIS G3138 SPFH 590 steel is widely used for manufacturing wheel rims for light and medium commercial vehicles. For high productivity, Flash butt welding is used for joining the edges of hot rolled strips. Cracking in wheel rims is a significant problem encountered in the production sectors. The present study is aimed at evaluating failure types in wheel rims by factors governing flash butt weld and subsequent cold forming processes. The microstructure of fractured specimens was examined by field emission scanning electron microscopy (FESEM) and an optical microscope. The mechanical characterization was analysed by tensile tests and crack tip opening displaced testing. The outcome of the results obtained was correlated with metallurgical concepts in order to find the cause of cracking failure.

Fatigue testing experiments and computer-simulations have been conducted for notched specimens of two cutting-tool materials: high speed steel (M42 HSS) and cemented carbide composite (WC-10Co). The effects of varying loads and notches on the fatigue lives of M42 HSS and WC-10Co, including a comparative study of the fatigue behavior of the two cutting-tool materials, have been reported. The fatigue behavior of the two cutting-tool materials has been investigated by developing their S-N curves as well as by examinations of the fracture surfaces of the materials. A fatigue life of 10 7 cycles corresponding to a fatigue limit of 430 × 10 6 Nm −2 was determined for M42 HSS. It has been found that a reduction of stress amplitude by 60 × 10 6 Nm −2 results in an increase of fatigue life by around 175 percent for the notched specimens of cemented carbide. The computer simulation studies involved the use of ANSYS finite element analysis (FEA) as well as SolidWorks software packages. Both experimental and simulation results were found to be in agreement. The research findings should enable engineers to select a suitable cutting tool material with a notch for application under cyclic stressed machining.

The early corrosion stage of carbon steel welded joints in water occurring in a CO 2 -saturated oilfield was investigated. Electron backscatter diffraction (EBSD) and energy dispersive X-ray spectrometry (EDS) were used to characterize the microstructure and chemical composition distribution of the different zones in the welded joint. Atomic force microscopy (AFM) and a VEECO optical profiler were used to observe the sample surface corrosion morphology at different immersion times. The results show that the early stage corrosion characteristics of each zone in the welded joint are related to grain orientation and not related to grain size, grain boundary type, or to the second phase. Additionally, it was found that chemical composition distribution is the primary reason for the differences in the early stage corrosion characteristics observed for each zone in the welded joints.

The effect of quenching and tempering temperature on the tensile properties and the yield strength ratio of 30MnB5, 27MnCrB5, and 34MnB5 boron steel have been investigated. Quenching (Q) and tempering (T) temperatures varied in the range of 850 to 950 °C and 150 to 450 °C, respectively. The mechanical properties of quenched and tempered steel were examined with the application of the tensile test and hardness testing. The microstructure was characterized using optical microscopy and X-ray diffraction. The increase in Q & T temperatures resulted in a decrease in the ultimate tensile strength (UTS), yield strength (YS) and break strength (BS) values and an increase in the yield strength ratio. The tempering temperature was found to be more effective on the UTS, YS and BS values than was the austenitizing temperature. It was noted that the effect of tempering temperature is greater on the ultimate tensile than on the yield strength for the investigated low alloyed boron steel. The effect of the tempering temperature on the elongation to fracture is also greater than the effect on the uniform elongation. The yield strength ratio showed a tendency to increase with increasing tempering temperatures. It was raised considerably by increasing the tempering temperatures from 300 to 450 °C, while it remained at a similar level between 150 and 300 °C. The ratio of ultimate tensile strength and mean hardness decreased with increasing tempering temperatures for the tested varieties of steel. Increasing tempering temperature leads to an increase in yield strength ratio and a total elongation and a decrease in the strength of the tempered martensite.

In the present investigation, an aluminum alloy AA7178 was reinforced with three different weight fractions (3, 6 and 9 wt.-%) of titanium diboride (TiB 2 ) particles which were efficaciously synthesized through exothermic reaction of halide salts such as potassium hexafluoro-titanate (K 2 TiF 6 ) and potassium tetrafluoro-borate (KBF 4 ), with molten aluminum melt to bring out unique properties. In-situ reaction between the halide salts, e. g., K 2 TiF 6 and KBF 4 in molten aluminum leads to the formation of TiB 2 particles. The synthesized final composites were characterized using X-ray diffraction (XRD) and a scanning electron microscope (SEM). The SEM micrographs indicated the even dispersion of the TiB 2 filler particle in the composites. Tensile strength, compression strength and micro-hardness of the prepared composites is measured and compared to plain matrix alloy. The manufactured composites are mechanically characterized as per the American Society for Testing and Materials (ASTM) standards, employing a computerized universal testing machine. The mechanical properties of the composite were discovered to be obviously superior to those of the basic matrix alloy owing to augmented particle content.

The minor deformation in a material is an important factor which influences the failure of component. Monitoring the deformation accurately is the basis for rationally evaluating the residual life of components. However, the existing technical means remain limited by complex environment. In this work, a method for evaluating material strain is established based on potential drop technology, and the accurate prediction of experimental results is conducted by the finite element technique. Both results are in accordance with the theoretical mathematical model. Through the experiment carried out on 304 stainless steel tensile specimens, the relationship between potential drop and strain based on this method is established. The experimental results basically comply with the finite element results and the theoretical derivation.

In this work, the MAF set-up is fixed on a vertical milling machine, and experiments are performed for optimizing the process parameters using central composite design (CCD) based on response surface methodology (RSM). From these experiments, output responses like percentage improvement in surface roughness (%ΔRa) and the material removal rate (MRR) are measured. An airgap is maintained in the range of 1.5-2 mm at a voltage of 10-20 V. A series of 62 experiments are conducted using selected process parameters at different levels. A grey based fuzzy algorithm is used to optimize the multi-response characteristics. The grey fuzzy reasoning grade (GFRG) is used to identify the optimal process parameters. From the results, the highest GFRG value is obtained at a voltage of 15 V with a corresponding rotational speed, machining gap, mesh number and mixing ratio of 750 rpm, 1.75 mm, 800 and 1: 2, respectively. In addition, analysis of variance (ANOVA) is used to identify the percentage contribution of each parameter in the MAF process, and the same is verified through experimentation. Optical microscopic images confirm that the surface finish of SS310s has been improved using the MAF process.

In this study, the boronizing method was applied to a crankshaft of a diesel engine, and exposed to bending and torsional stress and pressure, and the material characterization was examined. The boronizing method was applied to the crankshaft at 950 °C for 4 hours. Optical microscope, microhardness, SEM, EDAX, XRD, wear, TGA and corrosion analyses were performed to determine the material characterization. According to the results obtained, the optical and SEM images showed the presence of FeB and Fe 2 B layers, and EDAX and XRD analyses showed the presence of boron and its compounds. A 6.7-fold increase in hardness was observed in the microhardness analysis and 4-fold wear resistance was observed in the wear analysis. Resistance of 85 % was observed in the corrosion analysis and oxidation delay of 300 °C were observed in the TGA test. After wear analysis, SEM and XRD analyses were performed and the surfaces were examined.

A YLS-6000 fiber laser was used to weld high strength steel E36 with a thickness of 6 mm. The main composition (wt.-%) of high strength steel E36 is 0.15C, 1.40Mn, 0.31Si, 0.04Al, and 0.08Ni. The morphology, tensile strength and microhardness of butt joints were studied by using scanning electron microscopy (SEM), a tensile tester and a microhardness tester. The results showed that butt joints of high strength steel E36 consist of a weld seam (WS), a heat affected zone (HAZ) and a base metal (BM). The microstructure of the WS is mainly composed of lath martensite, and the microstructure of the HAZ is mainly composed of martensite, bainite and ferrite. The hardness of the WS increases with an increase in laser power, and the maximum hardness of the butt joint appears in the transition zone between WS and HAZ. When laser power reaches 3500 W, the maximum microhardness is 450 HV. The laser power has little effect on the tensile strength of the butt joint. All tensile specimens were broken at the base material. There is many dimples on the fracture, and the butt joint displays a ductile fracture.

Slag waste generated during the metallurgical process in a ferrochromium plant in Elazig, Turkey, ferro alloys and other required ceramic based powders were mixed to obtain recycled powders produced by submerged arc welding using the agglomeration method. High carbon ferrochromium was also added to the recycled powder mixtures to improve the microstructure, hardness, and wear properties of SAE 1020 steel using a submerged arc welding technique for hardfacing. After the powder production and welding process, there were no crack and porosities on the surface of the hardfacings. As the amount of high carbon ferrochromium in the recycled powders increased, homogeneity and slag removal properties of the hardfacings decreased. Their microstructures changed, macrohardness values increased, and wear losses decreased. The highest macrohardness value 46 HRC and the lowest wear loss 4.8 g were observed in hardfacing obtained using the recycled powder with 16 wt.-% high carbon ferrochromium.

Alloys based on Sn and Bi are considered to be one of the best soft lead-free solders due to their low melting temperature and low price. In addition, Bi-Sn alloy with a eutectic composition represents a promising candidate as a metallic phase change material (PCM) for use in the field of thermal energy storage (TES). The accurate knowledge of microstructural and thermophysical properties such as the latent heat of melting, thermal conductivity, specific heat capacity is of crucial importance for PCM selection. Thus, the aim of the current study has been to determine the microstructure, latent heat of melting and thermal conductivity of a eutectic alloy from the binary Bi-Sn system.

In this study dry sliding wear behavior of AISI 4140 steel at given elevated temperatures was examined. The experiments were performed on a heat-modulated ball-on-disc wear device under 3, 5, 7 and 10 N loads at room temperature, 100, 200, 300 and 450 °C. 3D optical microscopy was performed for determining the volume loss of the worn samples. SEM (scanning electron microscopy) was used to determine the morphology of the worn surfaces of the samples while Raman spectrometry was used for determining oxide types occurring as a result of wear. Experimental applications showed that volume loses slightly increased as a function of indenter load elevation. The experiments performed at 300 °C, the volume loss ratios were found to be lower compared to all other samples. The highest volume loss was obtained in the experiments performed at 450 °C. Volume loss decreased in all samples under 10 N load. A tribological layer formed on the surface of samples subjected to a dry-sliding process. In the experiments performed at 100 °C and 200 °C, the delamination type was the dominant wear mechanism at all loads.

In the current environment, aluminum metal matrix composites are in enormous demand due to notable improvement in mechanical and wear characteristics. Several manufacturing techniques have been developed among which traditional stir casting is preferred due to simple processing techniques other than available methods like compocasting, in situ fabrication, powder metallurgy or friction stir processing. Nanoparticles seem appealing to researchers for manufacturing nanocomposites due to their improved microstructural, mechanical and tribological properties. Parameters like weight or volume fraction, stirrer design, number of blades, stirring speed, stirring time, reinforcement feed rate and melting temperature required to prepare a composite are discussed in great detail. The innovation of this assessment effort lie in the fact that few such review works have been published for the stircasting technique to prepare aluminum metal matrix composites/nano composites reinforced with SiC, TiO 2 , Al 2 O 3 , B 4 C and TiC.

A design and principle of silicon photodiodes (PD) operation in the frequency domain are presented. To further enhance the signal-to-noise ratio, a methodology is proposed regarding how to cut down the response in the frequency domain between the time constant and stability characteristics. An algebraic-analytic model is developed to obtain the frequency behavior of the PD which are used as semiconductor devices to capture optical modulated light. The proposed model consists of connecting the anode and cathode terminals of a PD, an operational amplifier (AOP) for performing a control over the frequency domain optical device. The basic idea consists in analyzing the response of the PD at different frequencies using Bode, Nyquist and Black diagrams which have been obtained by a transfer function in the frequency domain when the optical response is attenuated. Consequently, a cutoff frequency to be determined by a test signal, and thus allowing for a certain range of frequency capture for operation and application of the PD. This paper highlights several key issues in the measurement methods on frequency domain of the Si PD. In some cases, indirect signal metering of modulated light presents unwanted signals. Consequently, the RC filter responses they are frequency filtering effect. Therefore, for the improved PD measurements, might be necessary the solution in the frequency domain for transfer function and theoretical-experimental relationship on materials testing. The results show that this system has the capacity to acquire the operating range in the frequency domain and thereby calculate the cutoff frequency through the solution of the real and imaginary part of the PD-AOP transfer function model.