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    Effect of AlN addition on the reaction sintering of Al2TiO5 composites fabricated by spark plasma sintering
    (2023-01-01)
    Kitiwan, Mettaya
    ;
    Atong, Duangduen
    ;
    Endo, Fumio
    ;
    Goto, Takashi
    Fully dense Al<inf>2</inf>TiO<inf>5</inf>–Al<inf>2</inf>O<inf>3</inf>–TiN (ATN) composites were fabricated by reactive sintering using spark plasma sintering at 1400°C for 5 min under 100 MPa in vacuum. An equimolar ratio of Al<inf>2</inf>O<inf>3</inf>:TiO<inf>2</inf> was used as the starting powder, while the addition of 0–36 mol% AlN was investigated. The thermodynamic calculation indicates that the initial reaction was that of TiO<inf>2</inf> and AlN, forming TiN and Al<inf>2</inf>O<inf>3</inf>, and then the remaining TiO<inf>2</inf> reacted with Al<inf>2</inf>O<inf>3</inf> to produce Al<inf>2</inf>TiO<inf>5</inf>. With the increase in AlN precursor, Al<inf>2</inf>TiO<inf>5</inf> gradually decreased, while Al<inf>2</inf>O<inf>3</inf> and TiN increased. The lattice parameters of Al<inf>2</inf>TiO<inf>5</inf> were enlarged with AlN addition, implying the incorporation of N atoms in the Al<inf>2</inf>TiO<inf>5</inf> unit cell. The addition of AlN effectively produced fully densified bodies with small grain size, and microcrack-free, which therefore enhanced the mechanical properties of ATN composites. At 36 mol% AlN addition, the composite shows Vickers hardness and fracture toughness of 16.26 ± 1.61 GPa and 5.20 ± 0.46 MPa.m<sup>1/2</sup>, respectively.
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    Microstructure and mechanical properties of Ti-Zr alloys fabricated by two-step spark plasma sintering from TiH2 and ZrH2 powders
    (2023-01-01)
    Banjongaxsorn, Kunpot
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    Khantachawana, Anak
    ;
    Watanabe, Chihiro
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    Srirussamee, Kasama
    ;
    Kondoh, Katsuyoshi
    Ti is well-known for its high strength-to-weight ratio and biocompatibility. It can be alloyed with Zr to improve mechanical properties. Currently, Ti-Zr alloys can be fabricated by powder metallurgy using Ti and Zr powders, although high oxidation reactivity and cost could still be an issue. In this study, premixed TiH<inf>2</inf> and ZrH<inf>2</inf> powders were used to prepare Ti-Zr binary alloys with different Zr contents of 0–30 mass% ZrH<inf>2</inf> via dehydrogenation and sintering by spark plasma sintering (SPS) process. α-Ti and δ-TiH<inf>2</inf> phases coexisted in the sintered Ti-Zr alloys, and a characteristic lamellar microstructure was formed. The tensile strength of the Ti-Zr alloys increased with increasing Zr content due to the solid solution effect, grain refinement and the appearance of δ-TiH<inf>2</inf> phases, although the elongation was reduced. This study shows that the fabricated Ti-Zr alloys possess controllable mechanical properties, which can be beneficial for biomedical and other engineering applications.
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    Effect of Nb Content and water quenching on microstructure and mechanical properties of Ti-Nb alloys fabricated by spark plasma sintering
    (2022-01-01)
    Suesawadwanid, Nattawood
    ;
    Khantachawana, Anak
    ;
    Srirussamee, Kasama
    ;
    Kondoh, Katsuyoshi
    Titanium-niobium (Ti-Nb) alloys have been extensively studied for medical implants due to their advantageous mechanical properties and biocompatibility. However, the stress shielding effect remains a challenge. This research investigated the effects of Nb content and enhancement of α′′ formation on the mechanical properties of Ti-xNb alloys (x = 0, 5, 15 and 25%) fabricated by spark plasma sintering. Water quenching from the β phase induced α′′ phase formation in Ti-5Nb and Ti-15Nb samples, thereby reducing their Young’s modulus values but was not observed in commercially pure titanium (CP-Ti) and Ti-25Nb. Results showed that heat treatment with water quenching induced α′′ phase formation and can be used to tailor the properties of Ti-Nb alloys fabricated by SPS. This technique can also be used to enhance material ductility at high β-stabilizer content, as observed in Ti-25Nb samples.
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    Preparation of SiO2-diamond composites by spark plasma sintering
    (2021-01-01)
    Kitiwan, Mettaya
    ;
    Katsui, Hirokazu
    ;
    Goto, Takashi
    SiO<inf>2</inf>-diamond composites with 65–85 mass% diamond were fabricated by spark plasma sintering at 1873 K under 130 MPa for 300 s using bimodal diamond particle size of 2 and 25 µm in diameter. The diamond particles were coated with a SiC layer by chemical vapor deposition. The effects of diamond content on relative density, microstructure, and Vickers hardness of the SiO<inf>2</inf>-diamond composites were investigated. The SiO<inf>2</inf>-diamond composites exhibited relative density of 96%, and Vickers hardness of 36.2 ± 3.6 GPa at 75 mass% diamond content.
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