Key Engineering Materials Vol. 674

Abstract: Dense B₆O based materials were prepared by reactive spark plasma sintering of B/B₂O_3, B/B₂O₃/ZrO₂ B/ZrO₂, B₆O/ZrO₂ powders and parameters of the materials were determined. The reactive plasma sintering ensured preparation of dense B₆O materials at 1800 °C and pressure of 30 MPa. Additives of nanocrystalline ZrO₂ to boron precursors led to formation of ZrB₂-B₆O composite with decreased amount of B₆O. The crystallite size of the bulk materials was in the range of 18–40 nm but the size of unregular grains was in the range of 1.5–3.0 μm.

Abstract: Variable angle tow (VAT) laminates have shown enhanced stiffness/strength performance compared to conventional straight fiber laminates. Employment of VAT allows utilizing variable stiffness design of composite structure, thus it widens the design possibilities. As a result, composite structure with improved mechanical characteristics can be manufactured. The main aims of the current study are to give an overview on methods and algorithms used for analysis and design of VAT laminates, and to develop technology and equipment for manufacturing laminate with improved structural performance. In order to improve the accuracy of the compaction process, a set of experiments were carried out using a simple testing device. For measuring the compaction force, a pneumatic cylinder, pressure regulator and digital manometer were used. The temperature of the consolidation area and the heat distribution were screened with the thermal camera. Infrared heater was used as a heating source. Material used in the experiment was carbon fiber reinforced polyamide.Findings show that in addition to the main parameters – the compaction force and temperature, there are many minor factors, such as the compaction wheel diameter, material and surface roughness of the compaction roller, the material and surface roughness of the mold and the pretension in the laminating tape and also the laminating speed, all influence the quality of the final product.Key words: Advanced Fiber Placement Technology, Automated Fiber Placement, Automated Tape Laying, Fiber Reinforced Composites, Laminates

Abstract: Metakaolin is considered as one of most promising pozzolanic microfiller material in concrete industry. Metakaolin is a high value product obtained from kaolin clay calcined at high temperatures which also can be effectively used in ceramic industry therefore its application in concrete industry is rather limited. In present research metakaolin containing waste (MKW) by-product was studied as a partial cement replacement in high strength self compacting concrete (SCC). Obtained waste material derives from the foam glass granule production plant where kaolin clay is used as releasing agent during heating process and in the end metakaolin with glass impurities is obtained as by-product. In present research 5 to 15 wt.% of cement was replaced by MKW. A constant water amount was used for all mixtures and workability (>600 mm by cone flow) was ensured by changing the amount of superplasticizer. Compressive strength was tested at the age of 7, 28 and 180 days. To determine durability of SCC the chloride penetration was tested according to NT BUILD 492, freeze-thaw test according to LVS 156-1:2009 annex C and alkali-silica reactivity test according to RILEM TC 106-AAR-2. The results indicate that cement replacement by MKW did not affect the strength of SCC significantly. At the age of 28 days SCC with 15 wt.% of MKW reached compressive strength of 70 MPa comparing to 68 MPa to reference mixture. The chloride penetration test results indicated that the non-steady-state migration coefficient of reference samples was reduced 3.7 times and it was concluded that SCC resistance to chloride penetration can be increased by incorporation of MKW in mixture composition. Freeze-thaw test results indicated that obtained SCC can withstand at least 500 freeze-thaw cycles without surface damage and weight loss. It was concluded that up to 15 wt.% of cement can be replaced by metakaolin containing waste without strength loss and the durability of SCC could be increased.

Abstract: The vacuum infusion process is widely used for the manufacture of fiber reinforced polymer composites. Current research concentrates on the comparison of three alternative methods. The aim is to determine if the Membrane Tube Infusion (MTI) and the Vacuum Assisted Process (VAP) that both use membrane fabric are able to produce higher quality laminate compared to the more established Vacuum Assisted Resin Transfer Moulding (VARTM). The laminate quality was evaluated by the void content, fiber volume fraction and mechanical properties. In addition, the thickness was measured in different segments of the laminate in order to determine if the thickness changes along the laminate. The MTI and VAP process did not give a significant improvement of the measured properties, on the contrary, the VARTM outran the aforementioned in many aspects.

Abstract: In this work, a catalyst-free direct deposition of multi-layered graphene closed shells around highly aligned alumina nanofibers with aspect ratio of 10⁷ is demonstrated for the first time. A single – step chemical vapor deposition process of specified parameters was used for development of hybrid structures of carbon shells around the core alumina nanofibers. Transmission electron microscopy and Raman spectroscopy were used to confirm formation of graphene layers and to understand the morphology of the various structures. The developed routine for growth of peculiar carbon nanostructures opens new opportunities for deposition of the tailored carbon structures on dielectric substrates.

Abstract: Continuous casting is the most productive method of casting. Manufacturers often tend to increase casting velocity without taking into account the fact that it can cause latent defects within the casting and accordingly lead to a deterioration of the mechanical properties of product. The casting process of tin bronzes encumbers high shrinkage and high segregation in the cross section of the castings. The research was performed on three types of tin bronze alloys CuSn12-C, CuSn5Zn5Pb2-C, and CuSn7Zn3Pb7-C (EN 1982:2008). Influence of casting velocity on mechanical properties and macrostructure was studied and optimal velocity parameters were given. The following study revealed a significant effect of the velocity of continuous casting on the mechanical properties of tin bronze, which was also reflected in the macrostructure of the selected samples. Based on the results of the study the recommendations about the optimal casting parameters to increase a quality of end-product were given. The recommendations were later implemented in the manufacturing confirming the value of this study.

Abstract: The paper discusses the basic methods of combined magnetic pulse compaction of ceramic powder materials. One important direction is a method that combines axial compaction of the powder, carried out with the help of a hydraulic press, and magnetic pulse compaction (MPC). Experimental studies were carried out on materials such as Al₂0₃-Si0₂. The influence of compaction of specific energy on the compressibility of materials has been shown. It has been established that the combined compaction allows to increase the density of the material, to improve the uniformity of properties in the bulk of the product and to reduce shrinkage during sintering.

Abstract: ZrC – TiC composites containing 20 wt.% TiC, along with and without 0.2 wt.% graphite were prepared by spark plasma sintering (SPS) at temperatures between 1600 - 1900 °C for 10 min under pressure up to 100 MPa. The addition of free carbon tends to reduce the appearance of tertiary phases in the microstructure according to scanning electron microscope (SEM) images. However, free carbon also reduced the mechanical properties of Vickers’ hardness and fracture toughness of the composites. SPS data showed when pressure was increased to 100 MPa, evident grain growth started to occur at a temperature as low as 1600 °C resulting in relative density > 100%. Samples produced at 1600 °C, but with maximum allowable pressure according to the SPS machine, yielded samples with greater hardness and fracture toughness compared to samples produced at 1900 °C.

Abstract: Flame cutting is commonly used thermal cutting method in metal industry when processing thick steel plates. Cutting is performed with controlled flame and oxygen jet, which burns steel and forms cutting edge. Flame cutting process is based on controlled chemical reaction between steel and oxygen at elevated temperature. Flame cutting of thick wear-resistant steels is challenging while it can result in cracks on and under the cut edge. Flame cutting causes uneven temperature distribution in the plate, which can introduce residual stresses. In addition, heat affected zone (HAZ) is formed and there both volume and microstructural changes as well as hardness variations are taking place. Therefore flame cutting always causes thermal stress, shape changes and consequently residual stresses to the material. Material behaviour under thermal and mechanical loading depends on the residual stress state of the material. Due to this, it is important to be able to measure the residual stresses. The aim of this study was to examine residual stresses on the cutting edge as a function of different flame cutting parameters. Also resulting microstructures and hardness values were verified. Varying parameters were the cutting speed, preheating and post heating procedures. Flame cut samples were investigated with X-ray diffraction method to produce residual stress profiles of the heat affected surface layer. Results indicated that different cutting parameters provide different residual stress profiles and that these profiles can be modified by changing the cutting speed and pre-or post-treatment procedures. Cutting parameters also affect the depth of the reaustenized region in the surface. The results correlate well with the actual industrial flame cutting and thus they provide an effective tool for optimizing the flame cutting process parameters.

Abstract: The paper deals with the study of optical and electrical properties of inkjet-printed graphene oxide (GO) layers, which can be used e.g. for the preparation of various types of electronic devices. To ensure stable inkjet printing conditions of GO solution, mixture was thoroughly stirred for 1 h at room temperature or sonicated in the bath for 30 min. The thicknesses of prepared layers were determined by spectroscopic ellipsometry and profilometry. An electrical conductivity of GO was increased by the multistep reduction (due to annealing) – the conductivity was changed by these processes about seven orders of magnitude (GO is an isolator and reduced GO is a conductor). For electrical and dielectric measurements, samples with GO and mixture of GO with PEDOT were prepared. All current-voltage characteristics have a diode character. From AC measurements the bulk electrical conductivity and geometric capacity of prepared layers were determined.