Volume 65, Issue 6

The low cycle fatigue and creep-fatigue behavior of base material and similar welded joints of martensitic steel Grade 92 were examined in this work. Several low cycle fatigue tests with different loading scenarios: fatigue tests with strain-controlled hold time, fatigue tests with strain-controlled amplitudes, and load-controlled hold times, were performed at 873 K. The tests were evaluated with regard to fatigue lifetime, peak stress, the evolution of relaxation stress or creep strain, and failure location. The effect of amplitude level, hold time modus and hold time length on the lifetime of the specimens was investigated using lifetime and damage assessment methods based on strain energy approaches. The numerical simulations for the determination of the evolution of local strains and stresses were done using a viscoplastic material model of Chaboche type, including a strain energy based damage formulation. For the parameter identification, tests were carried out on the specimens made of base metal, welded joint, weld metal, and with microstructure simulated specimens aiming to obtain representative microstructures of the fine grain, intercritical, and coarse grain heat affected zone. The numerical assessment of the local stress, strain, and damage distribution explains the smaller lifetime of the welded joint specimens.

This study investigates the formability characteristics of dual phase steels (DP600 and DP800) under flange stretching conditions through hole expansion tests. The hole-splitting initiation was numerically predicted using ductile damage functions coupled with an orthotropic plasticity model. Therefore, a polynomial yield criterion coupled with three damage criteria, namely generalized plastic work, void growth model, and a shear ductile fracture model, is implemented into Marc software by the user defined material subroutine. Thus, the fracture stroke, hole expansion ratio, and fracture initiation location were estimated for both steels. The polynomial yield criterion could capture the anisotropic features of the dual phase steels. Furthermore, the stress triaxiality-based criteria were reasonably accurate in stretching limit predictions of both steels’ grades. Nevertheless, plastic work predicted the fracture strokes and hole expansion ratios noticeably lower than the experimental outcomes for both steels. In addition, all the numerical results captured the exact fracture initiation location for DP600, while a slight discrepancy was observed for DP800. All ductile fracture models pointed out the identical crack location, which shows the cruciality of the yield criterion for locating the fracture initiation in hole expansion test. Consequently, both void growth model and shear ductile fracture model showed accurate performances conforming to the stress triaxiality was found to be more dominant than the Lode parameter.

Electrical fire accidents occurred frequently all over the world in recent years, which had caused a large number of casualties and property losses. The main cause of electrical fire is electrical wire short circuit fault. Investigations of the characteristic and influence factors of the molten marks play an important role to determine the cause of fire. In the present work, microscopic characteristics of copper wires with short-circuit molten marks in electrical fire were investigated. Primary and secondary short-circuit molten marks (PMMs and SMMs) of copper wires were prepared by simulation test. The micro-morphology, microstructure and chemical composition of molten marks were observed and compared. Based on the quantitative characterization, effects of different overload currents and heating temperatures on the microstructure of molten marks were analyzed. The results would provide fundamental information for cause identification of the electrical fire.

In order to explore the effect of in-situ ceramic particles on the microstructure and properties of nickel-based composite coatings, the nickel-based coatings reinforced by the in-situ ceramic were prepared on the surface of 40CrNiMo steel using laser cladding technology. On the basis of NiCrBSi (Ni45) powder, 0 wt%, 5 wt%, 10 wt%, 15 wt%, and 20 wt% of B 4 C and ferrovanadium (FeV50) were added, which the atomic ratio of V to C was 1:1. Microstructure and phase analysis were carried out by metallographic microscope (OM), X-ray diffractometer (XRD), and scanning electron microscope (SEM). The results show that the NiCrBSi coating without B 4 C and FeV50 are mainly composed of γ-Ni, Cr 23 C 6 , Cr 7 C 3, and CrB phases. After adding B 4 C and FeV50, the matrix is mainly composed of γ-Ni(Fe) solid solution, and strengthening phases such as CrB 2 and VB 2 appear in the coating. With the increase of the B 4 C and FeV50, the amount of CrB 2 and VB 2 increased, and the hardness and wear resistance were improved. When the addition amount of B 4 C and FeV50 is 10 wt%, the in-situ reinforced particles were uniformly distributed and the wear resistance of the coating was the best and was about 15 times that of Ni45 coating.

Today, artificially produced tungsten carbide (WC) tools are used as an alternative to diamonds such as mining, drilling, cutting, or machining. Although it is called WC, it also contains a certain amount of cobalt (Co). The most important reason for this is that it increases the wear resistance of the WC. Boriding is a type of surface hardening method that provides wear, hardness, and corrosion resistance to the applied surface. In boriding, which is a kind of diffusion process, there is no change in the dimensions of the materials since the boride layer grows from the outer surface of the materials to the inside. In this study, the development of surface properties by boriding of 90 wt% WC and 10 wt% Co-containing abrasive bits used for drilling were investigated. The samples were borided in an atmosphere-controlled furnace at 1173, 1273, and 1373 K for 1, 2, and 3 h by the pack boriding method. After the boriding processes, the microstructure, hardness, and chemical composition of the boride layers formed on the surface of the samples were examined, and finally, the wear tests were carried out to reveal the differences compared to the unborided sample.

In this study, the mechanical properties, fractography, and microstructure relationship of AlSi10Mg produced by laser powder bed fusion were established. Laser powder bed fusion is an additive manufacturing method that is an innovative technique. Since additive manufacturing is a new technique, utilizing materials requires studies investigating mechanical properties, fractography, and microstructure. This is vital because these characteristics are used before choosing the materials to manufacture the desired parts. The tensile, the Charpy impact, the hardness, and the density tests were applied to identify the mechanical properties of AlSi10Mg specimens. After that, the fractographic features and microstructure of the material were observed via an optical microscope and a scanning electron microscope. Finally, these results were related to each other. The results of tensile, the Charpy impact and fractography revealed that the laser powder bed additively manufactured AlSi10Mg alloy exhibited ductile–brittle type failure behaviour. As-built additively manufactured AlSi10Mg demonstrated higher yield strength, ultimate tensile strength, and microhardness but less density than as-built cast-produced AlSi10Mg.

Linear friction welding (LFW), which is generally used in blisk construction in aviation and space industries, is especially used to reduce costs, extend the life of materials working in hot environments, lighten engine weight, etc. The method, which is a solid state welding, achieves a high welding structure in metal and alloy materials. It can also be applied to different material combinations such as titanium alloys, superalloys, steel, aluminum, nickel, and copper. This study, which was carried out in order to provide lower cost and less raw material consumption in the welding of titanium alloys, reveals the necessity of the LFW method. In this study, the temperature change, oscillation amplitude, and oscillation frequency of the Ti6Al4V couple were investigated using the LFW method using finite elements. In the transient thermal analysis, it was observed that the temperature produced by applying Ti6Al4V welding parameters exceeded the glass transition temperature of the material.

The present study was conducted to uncover effects of partitioning treatment on Cu–Ni–Mo alloyed ductile iron (DI) austempered at different temperatures. For this purpose, the DI samples, produced via sand casting, were austenitized at 900 °C for 60 min, followed by austempering at the temperatures of 275–325–375 °C for 120 min and afterwards a partitioning treatment was applied at 200 °C for 15 min. In the characterization studies, dilatometer, image analysis, JMat-Pro, mechanical tests, XRD, optical microscope, and scanning electron microscope (SEM) equipped with EBSD detector were utilized. Characterization studies showed that the effects of partitioning treatment were directly correlated with austempering temperature and high carbon austenite volume fraction changed in the range of 19.48–35.45%. That redistribution of carbon (C) between bainitic ferrite and high carbon austenite occurred, in turn, the carbon content of high carbon austenite increased with the partitioning treatment irrespective of austempering temperature were uncovered. Furthermore, the partitioning treatment considerably changed the grain morphologies of both high carbon austenite and banitic ferrite. As a consequence of these microstructural differences, the highest tensile strength of 1489.2 MPa was established in the sample austempered at 275 °C and partitioned at 200 °C, whereas the highest ductility of 5.61% acquired at the austempering temperature of 375 °C.

The effects of welding current and welding time on the shear resistance of spot welded joints of dissimilar Ni-base superalloys and austenitic stainless steels are investigated for expanding the limits of their use in automotive, naval and aerospace industries. The macro- and micro-structural characteristics, microhardness, and shear strength of the welded joints were examined in order to characterize the resulting joints. It was found that the shear resistance of the heterogeneous welded joints reaches values of 742–849 MPa, much higher than the one specific of the weaker material, which is the austenitic stainless steel with low carbon content, AISI 316 L. The diameter of the welded cores increased for higher current and welding time. Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and X-ray diffraction (XRD) were used to evaluate the microstructure of the welded joints from the two dissimilar materials.

The current research was aimed to investigate atmospheric corrosion behaviors of 6005A and 6082 aluminum alloys for a certain application in high-speed railway employed for service in Thailand. Actual exposure atmospheric test with the maximum period of 18 months was conducted at urban and marine–coastal environments. After completion of actual exposure test, corrosion behaviors of the uncoated alloys were determined based on corrosion mass loss and pitting corrosion aspects. It turned out that remarkable corrosion severity found at marine–coastal environment with respect to urban environment was attributed to higher deposition rates of cumulative chloride (around 1331 mg m −2  day −1 ) and sulfur dioxide (around 200 mg m −2  day −1 ) together with higher levels of RH (>80%) for the entire year of exposure. The alloys exposed at marine–coastal environment for 18 months long revealed the corrosion mass loss of approximately 2 g m −2 , average pit depth of greater than 80 μm, and density of around 3 pits⋅cm −2 .

In this study, laminated composite plate was produced from fiber reinforced fabric by vacuum infusion method. Composite plate was produced using glass fiber and epoxy resin. During production, B 4 C, TiC, TiO 2 , Al, Fe, and Ti powders were added to the resin in micro size and at 3 to 5 wt%. Test samples were obtained from the produced plate and subjected to wear test on pin-on disc type bench. For samples with 3 wt% additives, the wear rate increased significantly as the wear distance increased for each sample. In the case where the wear distance is maximum, the wear rate decreased the most in the TiC added sample. At the same time, TiC additive gave the lowest wear rate at 900–1800 m wear distance. For each sample with non-additive and 5 wt% additive, the wear rate increased linearly as the wear distance increased. When the wear distance is maximum, the wear rate decreased the most in the TiO 2 added sample. The highest tensile strength reduction was obtained in B 4 C added sample as 50 wt% for 3 wt% additive and 61 wt% for 5 wt% additive.

Utilizing the waste liquid derived from graphene oxide synthesis as raw material, hydrated manganese oxide (HMO) was prepared by a chemical precipitation method with sodium hydroxide solution or aqueous ammonia solution. The HMO samples were analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, Zeta potential analyzer, and scanning electron microscopy. The adsorption characteristics of the HMO samples were examined through lead ion adsorption from water. The effects of adsorption temperature, starting lead ion concentration, and adsorption time on the lead ion adsorption capacity were investigated. The relevant data agreed well with the pseudo-second-order kinetic model and the Langmuir isotherm model. Additionally, the maximum adsorption capacities of HMO-1 are 70.897 mg g −1 , 76.660 mg g −1 , and 79.424 mg g −1 for the lead ions at 298 K, 308 K, and 318 K, respectively. The lead ion adsorption mechanism of HMO has been explained. The findings indicate the as-synthesized HMO can be used as an efficient adsorbent material for eliminating lead ions from water.

In this study, 10 mm thick DUROSTAT 500 and AISI 430 grades were joined by double sided keyhole tungsten inert gas (K-TIG) welding method without using filler material. The characterization of the microstructure of the weld zone was investigated by optical analysis methods and the mechanical properties of the welded parts were examined by mechanical tests. The fracture surface structure of the parts that were broken as a result of the tests were examined. No deterioration was observed in the welded samples. It was determined that the weld penetration increased as a result of the increase in the amount of heat entering the weld zone with the increasing welding current.

Solid-state joining is used for welding similar or dissimilar materials due to its many advantages like avoiding fusion and formation of a thick intermetallic layer, etc. Determination of the right process parameters (feed rate and rotation speed) and tool geometry (shoulder and pin) is of critical importance in friction stir welding in order to achieve adequate weld quality. The experiments were performed using three process parameters: feed rate (mm min −1 ), rotation speed (rpm) and pin geometry for friction stir welding of Al5083 and Al6061. Eighteen experiments were performed with different process parameters and mechanical tests (microhardness and tensile measurements) have been carried out to determine the weld quality. Results showed that the best results of ultimate strength (198.5 MPa) were achieved by the triangle pin geometry, 1250 rpm rotation speed and 100 mm min −1 feed rate. Similar results were observed in microhardness tests. Effects of tool geometry, feed rate, and rotation speed on the vibration properties and weld quality are also investigated experimentally. The effects of the FSW parameters used were assessed using vibration analysis.