Volume 61, Issue 6

For the present contribution phase transformations in primary and secondary mill scales discarded from a hot strip mill have been investigated by using synchrotron X-ray absorption spectroscopy and thermal analysis methods. Phase transformations in the scales are influenced by calcination parameters such as temperature, heating rate and isothermal interval. Magnetite, a highly interesting iron oxide for its availability in wide ranges of applications, increases its fraction after calcination at 673 K at a heating rate of 5.38 K × s −1 . This is confirmed by both characterization techniques. The calcined primary scale is found almost unchanged due to the existing predominant hematite phase. However, the additional promotion of hematite occurs at a longer isothermal calcination period at 1073 K. The majority of the results corresponded to the literature data and corroborate the assumption for a further purification process of industrial iron oxide by-products.

The exposure response function of the carbonyl formation over the bulk has been determined for a high-density polyethylene of a thickness of 200 μm, which was used as a weathering reference material according to ISO TR 19032. To this end, spectral sensitivity was studied by local measurement of the effect of spectrally dispersed irradiation. Both the exposure device and the methodology of determination are described. The temperature dependency of photooxidation was determined by UV exposure at various temperatures between 23 and 80 °C. Deviations from linearity and thus reciprocity below 40 °C are discussed and assumed to be related to diffusion limitations. An Arrhenius approach – based on data of linear carbonyl formation – has been incorporated into the exposure response function. Using this exposure response function, aging in terms of the distribution of a quantitative property change over a plastic component can be predicted for a specific outdoor location with real chronologic weather data as input for the exposure. Thus, artificial and natural weathering can be linked and compared. The established exposure response function has been validated by outdoor exposure results from the literature. If an estimated diffusion limitation is taken into consideration, calculations and published data are in good agreement.

Resistance spot welding (RSW) is widely used in the automotive industry as the main joining method. Generally, an automotive body contains around 2000 to 5000 spot welds. Therefore, it is of decisive importance to characterize the mechanical properties of these areas for the further optimization and improvement of an automotive body structure. The present paper aims to introduce a novel method to investigate the mechanical properties and microstructure of the resistance spot weldment of DP1000 sheet steel. In this method, the microstructure of RSW of two sheets was reproduced on one sheet and on a bigger area by changing of the welding parameters, e. g. welding current, welding time, electrode force and type. Then, tensile tests in combination with digital image correlation (DIC) measurement were performed on the notched tensile specimens to determine the mechanical properties of the weld metal. The notch must be made on the welded tensile specimen to force the fracture and elongation on the weld metal, enabling the characterization of its properties. Additionally, the parameters of a nonlinear isotropic material model can be obtained and verified by the simulation of the tensile specimens. The parameters obtained show that the strength of DP1000 steel and the velocity of dislocations for reaching the maximum value of strain hardening, are significantly increased after RSW. The effect of sample geometry and microstructural inhomogeneity of the welded joint on the constitutive property of the weld metal are presented and discussed.

The principle reason for corrosion failure because of perforation on a fluorination reactor was analyzed by chemical composition tests, microstructure and corrosion products observation tests in combination with the investigation of the working conditions of the reactor. The results show that a certain amount of complex inclusions containing MnS in the failure parts – are the principle cause of perforation. The relatively poor condition of the middle of the reactor, resulting in particular from excess hydrogen fluoride, is another principle cause.

In this contribution, the influences of zircon sand and boron carbide on the mechanical properties of aluminum metal matrix composites (MMC) were predicted. Here, metal matrix composite samples were fabricated by stir-casting process. The prepared samples were tested for their tensile, flexural, impact and hardness strength. It was observed that the hardness of the prepared samples increased by adding Zircon sand and boron carbide particles as compared with pure aluminum alloy. Similarly, the impact and flexural strength increased as a result of the presence of the ceramic particles as compared with pure aluminum alloys. But, there was a decrease in the tensile strength due to an increase in hardness and porosity of the composites. It was clearly observed that the impact, flexural and hardness properties of Type III aluminum matrix increased to 3.89 J, 400.3 MPa and 141.7 BHN by increasing the weight percentage of reinforcements. These results have been compared with Al-Zr MMC and Al-B 4 C MMC and proved that the hybrid composite shows the better results. To study the topography of the samples, scanning electron microscope analysis was carried out. An innovative aspect of this MMC is that, it shows an increase in mechanical properties such as tensile, flexural and impact strength as well as hardness can find practical applications in the aerospace and automobile industries.

This contribution summarizes the results an investigation of the wear resistance of as received initial state and nano-structured Ti-13Nb-13Zr alloy obtained by hydrostatic extrusion. The tribological behavior was examined using a ball-on-disc tribometer under unlubricated sliding contact conditions against an Al 2 O 3 ceramic ball. Friction coefficient, material transfer and wear debris of the samples were observed after the wear tests. Wear characteristics of the samples were investigated by means of an optical profilometer, mechanical profilometer and scanning electron microscope for wear debris morphology and wear tracks. Although friction coefficients are very similar according to tribological observations, the domestic distribution of wear characteristics varied for samples of various grain sizes. Morphological observations have shown that surface responses to abrasive ceramic balls involve localized long and short wear debris, fracture, surface plowing causing adhesive wear and the formation of larger surface debris, and material transfer between titanium and the ceramic counterpart.

In this study, AISI 1050 steel was boronized at temperatures of 800, 850, 900, 950 and 1000 °C for 3, 6, and 9 hours by means of a pack boronizing process. The formation of the boride layer was investigated. The characterization of the boronized surfaces was determined by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). Although dual phase, FeB and Fe 2 B were observed in the boride layer, the intensity of the FeB was slight and collected only near the outer surface which is the desired structural morphology. As the boronizing temperature and holding time strongly affect the results of both boride layer thickness and the surface hardness of the material, multi-objective mathematical models were developed for optimization. Energy consumption during boronizing was also considered. Hence, the optimum values for both temperature and holding time were determined, both of which maximize surface hardness and boride layer thickness while minimizing energy consumption.

Hard ceramic particle reinforced aluminum matrix composites (AMCs) are considered a distinct category of advanced materials which command outstanding strength, good corrosion resistance and excellent wear resistance compared to conventional materials. In the present work, an Al-Zn-Mg aluminum alloy-based metal matrix composite was prepared by stir casting. The AA7075 matrix was reinforced with 0, 3, 6, 9 and 12 wt.-% aluminum nitride particles for producing AMCs. Flexural strength, tensile strength and micro-hardness were studied. The microstructure of the matrix alloy and the composites was examined by scanning electron microscopy (SEM). Micron-sized aluminum nitride particles were added to the aluminum matrix to enhance the micro-hardness and the flexural and tensile strength of the composite. SEM micrographs reveal the fairly uniform dissemination of aluminum nitride particles in the composite. The results obtained indicate that the mechanical properties of the composite were increased with an increase in weight percentages of the aluminum nitride reinforcement content.

This work was undertaken to study the effect of some of the main electro-discharge machining process parameters such as flushing pressure, current, pulse-on-time, and vibration on the tool wear rate (TWR), and metal removal rate (MRR) of Al 6061 alloy with 10 wt.-% TiB 2 p (titanium boride particulate) composites. The response surface methodology was used to determine the most important criteria to maximize the MRR and minimize the TWR. The experimental procedure was designed based on second-order rotatable central composite design. Sensitivity analysis was used to identify the important criteria and classify them by their order of importance in model validation. Many efforts were made to compare the calculated output of the data obtained. Pulse-on-time sensitivity was found to exert a more significant effect on MRR and TWR than did other criteria. The surface plots were prepared for both MRR and TWR. MRR value increases with an increase in peak current. It occurs in a workpiece that transfers the heat directly to the workpiece, and these functions increase TWR. This occurs because of an increase in MRR and a decrease in TWR.

Since surface hardness affects wear resistance and case depth affects fatigue strength, the optimum value of both is extremely important with respect to the area of use. The aim of this study was to investigate the possibility of predicting case depth and surface hardness in ion nitrided AISI 4340 steels as a function of process time and temperature by using artificial neural networks and to obtain useful case depth and surface hardness data from an artificial neural networks model. Two projections were created for ion nitrided case depth and surface hardness, both depending on process time and temperature, and the conclusion was reached that the experimental data provides sufficient predictability regarding the artificial neural networks model. In the multilayer perceptron artificial neural networks architecture designed, two outputs (case depth and surface hardness) were determined in the same network according to the inputs, thus providing the integrity of the system characterization. The system was created by means of a Matlab simulink graphical user interface, which determined the artificial neural networks outputs according to the specified input with the purpose of visualizing the process. Different input values could be entered for visually determining the output values of the process.

Crane hooks are frequently used in material handling systems for grasping loads to be lifted to keep them from dropping, thus preventing catastrophic accidents in such situations. In this study, the response of crane hooks to their payload is investigated theoretically and experimentally. The approximate calculation method and curved beam theory are used for a theoretical calculation of maximum and minimum normal stress values occurring on crane hook. In addition, a computer aided model of a crane hook, adhering to DIN 15401 is used, and a stress analysis is performed by means of finite element simulation. Experimental data acquisition regarding crane hooks and their payload are conducted by means of strain gage sensors. The theoretical method solutions and the experimental results are compared. The results obtained are in good harmony with the experimental measurements, curved beam theory and finite element analysis.

Fiber reinforced recycled polypropylene composites (FRRPC) are developed by reinforcing chopped basalt fiber (BF) and glass fiber (GF) in recycled polypropylene (RPP) using injection molding techniques. The composites are differentiated by varying the fiber volume at 10, 20 and 30 vol.-%. This investigation has been conducted to study the mechanical properties of FRRPC by means of tensile, flexural and impact tests. In addition to that, fracture surfaces have been cut and observed under a scanning electron microscope (SEM). Degradation processes were carried out to assess the amount of oxygen used by the bacteria to stabilize the organic matter under controlled conditions of time and temperature. Flue gas analysis revealings carbon monoxide(CO) and carbon dioxide (CO2), is within the allowable limit. From the above results, it became evident that basalt fiber reinforced polypropylene (BFRP) is superior to glass fiber reinforced polypropylene (GFRP).

A mechanistic exposure experiment was performed on the commercially available precipitation hardened VDM ® alloy C–263 (Nicrofer ® 5120 CoTi) Ni-Cr-Co-Mo alloy samples (21 wt.-% Cr, 21 wt.-% Co, 6.1 wt.-% Mo, 2.4 wt.-% Ti, 0.7 wt.-% Fe, 0.6 wt.-% Al, 0.6 wt.-% Mn, 0.4 wt.-% Si, 0.2 wt.-% Cu, 0.08 wt.-% C and bal. Ni) at coal gasification pilot plant facilities affiliated with the Institute for Advanced Engineering in Yongin, South Korea. Thermodynamic Ellingham–Pourbaix stability diagrams were constructed to provide insight into the mechanism of the observed corrosion behavior prevailing in the piping materials between the particulate removal unit and water scrubber of the coal gasification pilot plant. The thermodynamic inference on the corrosion mechanism was supplemented with the morphological, compositional and microstructural analyses of the exposed samples using scanning electron microscopy and energy-dispersive X-ray spectroscopy analyses performed on the external and cross–sectional surfaces of the recovered corrosion test samples to comprehensively examine the corrosion scale. Corrosion products with conspicuous spallation were observed after 139 h exposure to the corrosive environment (60 vol.-% CO, 28.4 vol.-%H 2 , 2.5 vol.-% CO 2 , 0.8 vol.-% CH 4 , 600 ppm H 2 S, and 110 ppm carbonyl sulfide under 2.005 MPa and 170 °C). Scanning electron microscopy and energy-dispersive X-ray spectroscopy positively identified formation of rather extensively peeled–off oxides as corrosion scales on the post–exposure alloy samples, which were attributed to the combined effects of evaporation of hydrated Fe, Al, and Cr chlorides and their subsequent transformation into thin (spalled) oxides. This article contains technical contents on the effects of Cr, Mo, Fe, and Al on the observed corrosion behavior which supplement and cast engineering insight into the previously published MP 2-2018 article on corrosion behavior of Ni-Cr-Mo-Fe alloy in a similar environment.

In order to study the effects of different loading systems and stress history on the damage evolution of concrete, the acoustic emission characteristic parameters, the acoustic emission release rate, acousto-ultrasonic pulse wave velocity and the Rv value were compared and analyzed in the process of axial compression damage of concrete with different water cement ratios under step and intermittent loading. In this paper, the intermittent period led to a certain degree of “closure” in the internal microcracks of concrete, thus in the same HB to HD holding period, the acoustic emission release rate, mean value of acoustic emission characteristic parameters and mean acousto-ultrasonic pulse wave velocity under intermittent loading were all higher than that of step loading. The acousto-ultrasonic pulse wave velocity decreased with the increasing of the stress level and increased during the IA to ID intermittent period. Among them, with the decreasing of water cement ratio (from 0.6 to 0.4), the acoustic emission cumulative hits and the acoustic emission release rate increased, while the acousto-ultrasonic pulse wave velocity increased, and there were some differences in the acoustic emission release rate of the two loading systems at different water cement ratios. Furthermore, the R v value decreased with the decreasing of water cement ratio in the IA to IC intermittent period and in the ID intermittent period, the R v value increased with the decreasing of water cement ratio, thus the R v value could reflect the evolution law of concrete with different water cement ratios during the intermittent period. The obtained results show that the acoustic emission and acousto-ultrasonic characteristic parameters are not consistent under two different loading systems, so research in this paper can provide a theoretical basis for the damage identification and analysis of concrete structures under cyclic loading based on the acousto-ultrasonic technology in practical engineering.