Sintering, microstructure and mechanical properties of NbC0.8-NbxOy composites and single-phase NbC polycrystals
Marian Rączka, Agnieszka Gubernat, Ludosław Stobierski, Justyna Mucha, Dariusz Zientara, Agata Wnuk, Kamil Kornaus
Quarterly No. 4, 2015 pages 183-191
DOI:
keywords: metal-like carbides, NbC1-x-NbxOy composites, pressureless sintering, qualitative and quantitative analysis of the microstructure, hardness, fracture toughness
abstract The study presents the results of investigations of the influence of niobium oxides and the addition of carbon on the pressureless sintering of niobium carbide powder and the properties of the obtained sinters. For this purpose, niobium carbide of a specific deviation from stoichiometry was synthesized (NbC0.8). After the crushing process, all the characteristics of the powder were determined and the powder was found to contain niobium oxides in the quantity of a few percentage of the weight. Next, samples were prepared without any additives and with additives of 1 and 2% of carbon weight. The samples were pressureless sintered at the following temperatures: 1900, 2000 and 2100°C in argon flow by heating them at the final temperature for 1 hour, then their apparent density was measured. A qualitative and quantitative analysis of the microstructure was performed on metallographic micro-sections and the phase composition of the sinters was determined. It was found that the presence of niobium oxides in the NbC powders has an advantageous influence on the sintering process. Single-phase polycrystals can be prepared by the addition of carbon. Some mechanical properties were additionally determined from the sinters including: hardness and fracture toughness and next, an attempt was made to correlate them with the image of the microstructure of the composites and single-phase polycrystals.