Nb-Si-B alloys with Nb-rich compositions are fabricated by spark plasma sintering for high-temperature structural applications. Three compositions are selected: 75 at% Nb (Nb0.7), 82 at% Nb (Nb1.5), and 88 at% Nb (Nb3), the atomic ratio of Si to B being 2. The microstructures of the prepared alloys are composed of Nb and T₂ phases. The T₂ phase is an intermetallic compound with a stoichiometry of Nb₅Si_3-xB_x (0 ≤ x ≤ 2). In some previous studies, Nb-Si-B alloys have been prepared by spark plasma sintering (SPS) using Nb and T₂ powders (SPS 1). In the present work, the same alloys are prepared by the SPS process (SPS 2) using Nb powders and hypereutectic alloy powders with composition 67at%Nb-22at%Si-11at%B (Nb67). The Nb67 alloy powders comprise T₂ and eutectic (T₂ + Nb) phases. The microstructures and hardness of the samples prepared in the present work have been compared with those previously reported; the samples prepared in this study exhibit finer and more uniform microstructures and higher hardness.

Microstructural examination of the Nb-Si-B alloys at Nb-rich compositions is performed. The Nb-rich corner of the Nb-Si-B system is favorable in that the constituent phases are Nb (ductile and tough phase with high melting temperature) and T₂ phase (very hard intermetallic compound with favorable oxidation resistance) which are good combination for high temperature structural materials. The samples containing compositions near Nb-rich corner of the Nb- Si-B ternary system are prepared by spark plasma sintering (SPS) process using T₂ and Nb powders. T₂ bulk phase is made in arc furnace by melting the Nb slug and the Si-B powder compact. The T₂ bulk phase was subsequently ballmilled to powders. SPS is performed at 1300°C and 1400°C, depending on the composition, under 30 MPa for 600s, to produce disc-shaped specimen with 15 mm in diameter and 3 mm high. Hardness tests (Rockwell A-scale and micro Vickers) are carried out to estimate the mechanical property.

Citations

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• Fabrication of Nb-Si-B Alloys Using the Pulverized Nb-T₂ Alloy Powder
  Min-Ho Cho, Sung-Jun Kim, Hyun-Ji Kang, Sung-Tag Oh, Young Do Kim, Seong Lee, Myung Jin Suk
  Journal of Korean Powder Metallurgy Institute.2019; 26(4): 299.     CrossRef
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The powder injection molding process having advantages in manufacturing three-dimensional precision parts essentially requires a debinding process before sintering to remove the binders used for preparing feedstock. In this study, powder injection molding of translucent alumina was performed, and carbon dioxide (CO₂) is used as a supercritical fluid that makes it possible to remove a large amount of binder, which is paraffin wax. The relationship between the optical property of translucent alumina and the debinding condition (temperature and pressure) of supercritical CO₂ was investigated. As temperature and pressure increased, extraction rate of the binder showed rising tendency and average grain size after sintering process was relatively fine. On the other hand, optical transmittance was reduced. As a result, the debinding condition at 50° and 20 MPa that represents the lowest extraction rate, 8.19 × 10⁻³ m²/sec, corresponds to the largest grain size of 14.7 μm and the highest optical transmittance of 45.2%.

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• Experimental and numerical analysis of effects of supercritical carbon dioxide debinding on Inconel 718 MIM components
  Dugauguez Olivier, Agne Aboubabky, Jimenez-Morales Antonia, Torralba José Manuel, Barriere Thierry
  Powder Technology.2019; 355: 57.     CrossRef