ABSTRACT The major objective of the work is to explore the mechanical properties of biphasic calcium phosphates (BCP), a biomaterial derived from marine resources like prawn (Fenneropenaeus Indicus) shell biowaste through wet chemical treatment of CaO. We report the BCP, a mixture of hydroxyapatite and octa calcium phosphate from prawn shell biowaste using wet chemical synthesis at 80°C under pH 10. XRD of BCP revealed the coexistence of secondary phases like β-TCP and α-TCP along with HA upon sintering at different temperatures. Furthermore, the SEM and EDS opened well-sintered uniaxial grains and the presence of trace elements like Fe, Mg, Si, and Na. The specimens sintered at 1100°C showed the highest compression strength of 56.8 MPa due to MgO at the grain boundaries, which plays an important role in grain boundary diffusion. Therefore, the prawn shell biowaste-derived BCP has good mechanical properties, making them suitable materials for high-strength bone substitutes.

ABSTRACT SiC-reinforced SiC ceramic matrix composites (SiC/SiC CMCs) are considered promising candidates to replace their super alloy counterparts due to higher temperature capabilities and lower densities. However, high-temperature and high-pressure water vapour sourced from the hydrocarbons’ combustion reactions inhibit the potential of SiC/SiC CMCs by leading to rapid surface recession. In order to address this challenge, environmental barrier coatings (EBCs) have been developed. The emphasis of this review is on the materials and processing techniques for the development of EBC systems. In the first part of the review, the characteristics of the SiC/SiC CMCs and the most common EBC materials are summarised. Then, the interrelationship between processing methods, microstructures and the resulting properties is reviewed. Finally, an overview of the future directions is outlined to assist developments in advanced and novel EBCs for next generation gas turbines.

ABSTRACT Carbon fibre has excellent mechanical properties at high temperatures but weak oxidation resistance. The paper prepared the anti-oxidative silica coating on the surface of needled carbon fibre felt by the sol–gel method and discussed the effects of sol content and sintering temperature on the coatings’ performance. The phase composition, density, thermal conductivity and thermal stability of derived composites were characterised, and the structure and morphology of SiO2 coatings were also analysed by scanning electron microscopy. The results indicated that a uniform and complete coating could be formed on the fibre surface when the sol content exceeds 20%. Ceramic particles sintered below 1200°C were amorphous silica, while those sintered at 1350°C were cristobalite. Compared with other processes, 20% silica sol content or sintering at 1350°C could provide better antioxidant protection. The new coating process is significant for retarding fibre oxidation in a high-temperature environment.

ABSTRACT ZrSi2 was fabricated via reactive hot-pressing technique for 45 min at 1250°C and 1350°C, respectively. The hot-pressed sample exhibited Vickers hardness of 10.93 ± 0.32 GPa and indentation fracture toughness of 3.16 ± 0.54 MPa.m1/2. Thermal conductivity (RT-2.99 W (m.K)−1) and diffusivity (RT–18.2 mm2 s−1) of the sample decreased with increasing temperature due to phonon scattering. Oxidation studies were carried out for the hot-pressed samples from 1000°C to 1200°C for 5, 48 and 100 h in air. The oxidation test results showed that ZrSi2 followed selective oxidation with Si diffusing into the oxide layers at high temperatures. At 1200°C, the surface of ZrSi2 oxidised completely to form a high-temperature stable phase, zircon (ZrSiO4). The autoclave test at 250°C and 250 bar shown negligible mass gain (∼0.022 g) which suggests the usage of ZrSi2 for nuclear fuel cladding applications.

ABSTRACT The temperature dependence of ageing in the commercial zirconia ceramic is crucial in the applications of dental implants. This study investigated the relationship between structure and mechanical properties of the zirconia dental ceramics and their susceptibility to human body temperature in a prolonged time. Commercial samples were put into exaggerated low-temperature degradation (LTD) as per ISO standard and three-quarters of its ageing temperature to see its effect on LTD in zirconia-based ceramics. The results reveal a negligible effect of LTD on the material at a temperature lower than 134°C, which is the standard LTD temperature for zirconia.

ABSTRACT High entropy carbides (HECs) are novel materials developed in recent years that have attracted a lot of research interests. Unlike traditional carbides (containing one or two metals), HECs with multiple metals could form a very large number of different compositions that could have interesting and promising properties. The high entropy effect stabilises multi-component carbide phases and forms compositions that might otherwise not be stable. After several years of investigation of HECs, several methods of synthesising HECs have been developed. The microstructures and properties of HECs have been studied and compared with traditional carbides. Many interesting discoveries in HECs have been made. This paper reviews the theories, technologies, findings and insights gained from previous studies on HECs. The basic theory of HECs, the prediction of synthesisability of HEC phases from theoretical calculations, and some rules observed from experimental results are summarised. The preparation methods of HECs (powders, coatings, films and ceramics) and their microstructures are reviewed. Their properties, including thermal and electrical, mechanical and tribological, and oxidation, irradiation, and corrosion resistance of HECs are reviewed and discussed. Compared with traditional carbides, there is a great potential to develop new HECs due to their designable and complex compositions, and this review can guide future studies.

ABSTRACT The CrAlTiCN coatings have been prepared by multi-arc ion plating technology on 316L and TC4 substrates, respectively. The microstructure of the prepared CrAlTiCN coatings has been characterised by X-ray diffraction, scanning electron microscopy and energy disperse spectroscopy, respectively. The mechanical properties, electrochemical corrosion behaviour and tribological performance of the prepared coatings were tested by microhardness tester, scratch tester, electrochemical workstation, and friction and wear tester, respectively. Results show that all the coatings includes many nanocrystalline and presents compact structure, weak columnar crystal structure and refine grain. The prepared coating on TC4 titanium alloy substrate presents a better tribological performance than that on 316L stainless steel substrate.

ABSTRACT The enhancement of surface acidity for tungsten-doped CeTiOx was investigated through electronic structure. Tungsten doping increased the ratio of Ce3+ from 12.0% to 29.6%, which was confirmed by XPS. The doped tungsten was present as W5+ in a ratio of 71.5%. In O K-edge XAS spectra, increase in indicated the formation of oxygen vacancies through tungsten doping. The decrease in W 5d-eg peak intensity demonstrated the occupation of the W 5d orbital by electrons formed at the oxygen vacancies. The enrichment of W5+ was owing to transfer of electrons to 5d-eg orbital of tungsten rather than to cerium ions. The acid sites were analysed using FTIR and NH3-TPD. The peak intensity of Brønsted acid sites and amount of NH3 desorption increased from 66.2 to 136.1 µmol g−1 with tungsten doping. The doped tungsten formed Brønsted acid sites and led to enhanced surface acidity and catalytic activity.

ABSTRACT This paper develops a numerical model that contained random lip-shaped matrix cracks based on the maximum energy release rate criterion for the prediction of failure progress of Continuous Fibre-reinforced Ceramic Matrix Composites (CFCC) under transverse tension. Fibre distribution layout is created based on the actual microstructure and the Random Sequential Adsorption algorithm is used to generate the distribution of lip-shaped matrix cracks. The influence of the lip-shaped matrix crack distribution and crack density on the failure progress and stress–strain response was investigated. It was found that the onset of damage initiation commenced from the lip-shaped matrix crack when the interface fracture energy was smaller than the critical interface fracture energy. The failure progress and the predicted results were in good agreement with the experimental results. The different matrix cracks distribution affected the failure progress. Finally, the tensile strength and the elastic modulus both decreased with the crack density increasing.

ABSTRACT Fully dense WC-Al2O3 platelet composites with VC additive were fabricated by hot-press sintering. Their mechanical properties and microstructure were examined. The contents of Al2O3 platelet (Al2O3pl) and VC were optimised. The fracture toughness of WC-based composites would be obviously improved with Al2O3pl addition. The defined addition of VC was beneficial for the densification and improved mechanical properties of the WC-based composites. The microstructure of the composites was fine, compact and homogeneous compared with the composites without VC addition. The range of fracture toughness of WC-Al2O3pl composites was 9.3–13.5 MPa m1/2. The flexural strength of the composites varied a little and the maximum was 1289 MPa when the content of Al2O3pl was 5 vol.-%, the content of VC was 0.5wt-%.