Materials Science Forum Vol. 1176

Abstract: Thermosets play an important role in composite processing, adhesive bonding and coating. In all these applications, shrinkage my cause a significant amount of residual stress, leading to distortion, reduced load carrying capacity and cracking. The chemical curing reaction is accompanied by a reduction in volume called “chemical shrinkage”. If curing is performed at elevated temperature, cooling to ambient conditions afterwards is accompanied by “thermal shrinkage” and further shrinkage due to so-called “physical ageing”. A skillful combination of available methods makes it possible to separate chemical shrinkage in the viscous state from shrinkage in the gelled and vitrified state. Modeling of the time-and temperature-dependent properties is the prerequisite for the prediction and control of residual stresses caused by shrinkage in thermoset polymers.

Abstract: This study investigates the effect of Sr (0.1, 0.15, and 0.2 wt.%) modification on the microstructure and morphological evolution of the in-situ Al-15%Mg₂Si-4.5%Si composite. The composites are developed via Low superheat casting (LSC) technique, at the onset of gravity, and subsequently characterized through optical microscope, X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Electron Probe Microprobe Analysis (EPMA), and XRD texture analysis. It is found that, with the increase of Sr content in the Al-15%Mg₂Si-4.5%Si composite, the morphology of primary Mg₂Si particles changes from irregular dendritic and hopper structure to nearly perfect cubic morphology. The addition of 0.2 wt.% Sr reduces the average primary magnesium silicide (Mg₂Si) particle size from ~56 µm to 36 µm and the Al grain size from ~63 µm to ~44 µm, indicating significant refinement. The XRD texture analysis through Orientation Distribution Function (ODF) reveals that the cubic texture and rotated cubic texture are the predominant orientations for Al and Mg₂Si phases, respectively. However, the composite modified with 0.2 wt.% Sr exhibits a weak texture and more random grain distribution, highlighting the role of Sr in reducing grain size and promoting uniformity. These findings underscore the potential of Sr addition to enhance the microstructural and mechanical properties of Al-15Mg₂Si-4.5Si composites for advanced applications.

Abstract: The trade-off between strength and toughness remains a major challenge in structural materials engineering, especially for titanium-based materials. This study explores the potential of titanium-based laminates for lightweight armor, aimed at improving anti-ballistic properties through the use of layered structures. Titanium alloy Ti-6Al-4V (Ti64) was combined with metal matrix composites (MMCs) reinforced with TiC or TiB particles (up to 40 vol%) using two powder metallurgy (PM) techniques. The first approach used press-and-sinter blended elemental powder metallurgy (BEPM) to create the laminates in a single step, while the second involved post-processing via hot isostatic pressing (HIP) to enhance material properties. Both fabrication methods produced laminates that significantly outperformed commercial alternatives in ballistic testing against 7.62 mm armor-piercing bullets. The use of HIP post-BEPM enhances material properties by reducing porosity and increasing hardness, highlighting the complementary nature of these technologies in producing efficient and cost-effective armor materials.

Abstract: Semi-solid processing over a cooling slope has emerged as an efficient technique for producing near-spherical grain structures in metallic composites. In this study, an Al-15Mg₂Si-4.5Si composite processed using this method exhibited globular Mg₂Si particles embedded within an α-Al matrix. The addition of 0.01% Sr further refined the microstructure by reducing the size of the Mg₂Si particles, acting as a grain-refining agent. To gain deeper insight into the effect of Sr addition on microstructure evolution during semi-solid processing, a two-dimensional phase field model is developed. Wherein, rather than modelling the nucleation of Sr-containing phases explicitly, the influence of Sr is realised by modifying the relevant phase field parameters. The simulations predicted key microstructural characteristics—including grain size, sphericity, area fraction and grain density of P-Mg₂Si —along with interfacial energy and mobility coefficients for both the base and Sr-modified composites. The phase field results show good agreement with experimental observations, validating the modelling approach. Keywords: Semi-solid, Magnesium silicide, Phase field, grain refinement

Abstract: To investigate the effect of the oxygen amount involved in mechanical alloying (MA) of Al and Y₂O₃ powders on the phase evolution of the alloy powders, two types of MA were performed: MA with low and high oxygen content in the MA atmosphere. Analyses of the lattice parameter and composition of the Al matrix by X-ray diffraction and scanning electron microscopy with energy dispersive X-ray spectroscopy, respectively, and the integrated intensity of Y₂O₃ indicated that in the low-oxygen MA, the driving force for Y₂O₃ precipitation was small and Y and O dissolved into the matrix, producing supersaturated solid solution powder, while in the high-oxygen MA, the driving force for Y₂O₃ precipitation was large, resulting in the formation of Y₂O₃-precipitated powder.

Abstract: 20/0/20vol% Al₂O₃/Mg laminated spark plasma sintering compacts (20/0/20vol% laminated SPS compacts), which were fabricated by mechanical milling / SPS method, have proved to possess lightweight like that of general practical Mg alloys and higher surface hardness than them. Moreover, the diffusion layer formed at their 0/20vol% layer interface has been found to exhibit high adhesion to the 20 and 0 vol% layers. The microstructures and the properties of diffusion layer were investigated using XRD, EPMA, TEM-EDS and so on. From the results of XRD, the constitutive phases were identified as αMg and MgO. Moreover, from the results of EPMA and TEM-EDS microstructure observation and elemental analysis, it was estimated that the microstructures were composed of reticulate MgO and in the MgO, Mg-Al solid solution αMg, fine needle-like Mg₁₇Al₁₂ and fine MgO particles. The cross-sectional hardness was 145 to 155 HV and was higher than that of the general practical Mg alloys. The width grew almost linearly rather than parabolic with sintering time. It is considered that the solid-state reaction of Mg and Al₂O₃ proceeded with sintering time, the amount of Al decomposition from Al₂O₃ increased, resulting in an increase in Al diffusion.

Abstract: The harmonic structure composites with Ti-Ni alloy and Cu were fabricated by mechanical milling (MM) / spark plasma sintering (SPS) process and were investigated mechanical and thermal properties in detail. Fine Ti-Ni alloy powder and coarse Cu powder were mechanically milled using planetary ball mill equipment at cryogenic temperature. The MM powder was sintered by using the SPS apparatus at 1073 to 1273 K. Tensile tests carried out at 383 K as mechanical properties evaluation. Thermal expansion to 1073 K was evaluated using thermomechanical analyzer equipment. Microstructural observation of the MM powders and SPS compacts was achieved using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SPS compacts is the harmonic structure composite having the network structure with Ti-Ni alloy and the dispersive area with Cu. Such a Ti-Ni/Cu harmonic structure composite exhibits unique mechanical properties. T ensile strength and elongation increase with increasing the sintering temperature in the Ti-Ni/Cu harmonic structure composite. The coefficient of linear thermal expansion of the Ti-Ni/Cu harmonic structure composite lies between that of Ti-Ni alloy and Cu, and a sufficient reduction in the coefficient of linear thermal expansion is confirmed.

Abstract: Tantalum-containing phosphate invert glasses were prepared using a liquid phase method under ambient conditions. In our previous study, the ion-releasing behavior (i.e. chemical durability) of phosphate glasses was controlled by the amount of intermediate oxides. In this work, Ta₂O₅ (intermediate oxide) was used to improve the chemical durability of the glasses. Ta-containing phosphate invert glasses were prepared and their structures were characterized. X-ray diffraction (XRD) patterns of the glasses exhibited broad halos, indicating an amorphous state. The amount of P₂O₅ in the glasses increased with increasing Ta₂O₅ content, while the amount of CaO decreased. The glasses prepared with a nominal P : Ta molar ratio of 2 : 1 showed a value of 1.87 : 1. Thus, almost all the Ta used in the synthesis was contained in the resulting glass. Raman spectra showed bands corresponding to short phosphate units such as ortho-and pyrophosphate, and the P-O-P peak was blue-shifted with increasing Ta₂O₅ content. The P-O-Ta bonds were formed with TaO₄ tetrahedra, as new peaks at 970 cm^-1 (P-O-Ta bonds) and 825 cm^-1 (observed in YTaO₄) were observed. The glasses containing higher amounts of Ta₂O₅ exhibited TaO₆-rich phases, as shown by the Raman band at 630 cm^-1 (Ta-O-Ta bonds) and broad XRD peaks at 2θ = 5 ~ 10°. Therefore, Ta in the phosphate invert glasses prepared by the liquid-phase method crosslinks phosphate units in the form of TaO₄ tetrahedra, and the excess Ta exists in the form of TaO₆ octahedra as a network modifier and/or Ta₂O₅-rich phase.

Abstract: The high-voltage application to silver ion-doped borosilicate glass induces the growth of silver dendritic crystals precipitation inside the substrate. This phenomenon holds significant potential for applications such as buried electric circuits and fine-hole drilling. Therefore, understanding the underlying mechanism of this phenomenon is essential for its practical utilization. In this study, we conducted in-situ observation and quantitative evaluation of the silver dendrite growth based on the temperature and the precipitation area over time. The measurements revealed that the growth rate accelerated as the precipitation progressed and increased with higher temperatures. Moreover, a model proposed here explained that these changes were attributed to the variations in the electrical resistance of the specimens and difference in the flux of the silver ions. This study provides valuable insights into the mechanism of silver dendritic precipitate growth inside glass, enabling the formation of arbitrary shapes of in-glass silver.