• Anxian Lu

Articles written in Bulletin of Materials Science

• Crystallization and microstructures of Y–Si–Al–O–N glass–ceramics containing main crystal phase Y3Al5O12

A glass with the nominal composition of 28Y48Si24Al83O17N (in equal percentage) was chosen as parent glass in this paper to prepare Y3Al5O12-based glass–ceramics. Differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to assess the crystallization process of the parent glass. YAG as the only crystalline phase appears in all glass–ceramics produced under 1250°C. A small amount of O′-Sialon secondary phase starts to precipitate from parent glass samples as heat treatment temperature increases to 1250°C. Grain size of the dendrite crystal which corresponds to YAG phase increases and the dendrite branches get thickened as heat treatment temperature increases. Moreover, grain size of YAG phase resulting from two-stage heat treatment is much smaller than that of YAG phase obtained by one-stage heat treatment. The results are relevant to developing improved crystallization treatments for glasses with potential for crystallization to YAG-based glass–ceramics and for heat treatments of YAG/𝛽-SiAlON materials.

• Effects of MO (M = Mg, Ca, Ba) on crystallization and flexural strength of semi-transparent lithium disilicate glass–ceramics

In this study, semitransparent lithium disilicate glass–ceramics in the Li2O–K2O–Al2O3–Y2O3–La2O3–SiO2 system was investigated by incorporation of P2O5 as nucleation agent and alkaline earth oxides as additive. The influence of alkaline earth oxides on the structure of glasses network, crystalline phases, microstructure and mechanical properties were investigated by means of Raman spectra, differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The mechanical strength was measured corresponding to norm ISO 6872. The Raman spectra predominantly showed that small additions of alkaline earth oxides not only form asymmetrical vibrations of the M–Si–O bonds, but also enhance the intensities of symmetrical vibrations of the P–O bonds, making the glass network more stable. And the small additions of CaO or BaO has more influence on the crystallization behaviour, crystalline phase, microstructure and mechanical properties of the glass–ceramics than the addition of MgO. The additions of alkaline earth oxides enhanced the first exothermic peak temperature but decreased the flexural strength of lithium disilicate glass–ceramics.

• Preparation of Zr50Al15−𝑥Ni10Cu25Y𝑥 amorphous powders by mechanical alloying and thermodynamic calculation

Amorphous Zr50Al15−𝑥Ni10Cu25Y𝑥 powders were fabricated by mechanical alloying at a low rotation speed from commercial pure element powders. The beneficial effect of Al partially substituted by Y in Zr50Al15Ni10Cu25 on glass-forming ability was investigated. The as-milled powders were characterized by X-ray diffraction and transmission electron microscopy. The results show that partial substitution of Al by Y can improve the glass-forming ability of Zr50Al15Ni10Cu25 alloy. Thermodynamic calculation of equivalent free energy shows that Zr50Al13.8Ni10Cu25Y1.2 alloy has the highest glass-forming ability, which is in good agreement with the report of orthogonal experiments.

• In situ synthesis and properties of self-reinforced Si$_3$N$_4$–SiO$_2$–Al$_2$O$_3$–Y$_2$O$_3$ (La$_2$O$_3$) glass–ceramic composites

In-situ-grown $\beta$-Si$_3$N$_4$-reinforced SiO$_2$–Al$_2$O$_3$–Y$_2$O$_3$ (La$_2$O$_3$) self-reinforced glass–ceramic composites were obtained without any $\beta$-Si$_3$N$_4$ seed crystal. These composites with different compositions were prepared in a nitrogenatmosphere for comparison of phase transformation and mechanical properties. The results showed that SiO$_2$–Al$_2$O$_3$–Y$_2$O$_3$ (La$_2$O$_3$) glass can effectively promote $\alpha$- to $\beta$-Si$_3$N$_4$ phase transformation. The crystallized Y$_2$Si$_2$O$_7$–La$_{4.67}$Si$_3$O$_{13}$ phaseswith a high melting point significantly benefited the high-temperature mechanical properties of the composites. TheSi$_3$N$_4$–SiO$_2$–Al$_2$O$_3$–Y$_2$O$_3$(La$_2$O$_3$) glass–ceramic composites exhibit excellent mechanical properties compared with unreinforcedglass–ceramic matrix, which is undoubtedly attributed to the elongated $\beta$-Si$_3$N$_4$ grains. These glass–ceramic Si$_3$N$_4$ composites with excellent comprehensive properties might be a promising material for high-temperature applications.

• # Bulletin of Materials Science

Volume 43, 2020
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019