Publikationsdatum:
2017-06-25
Beschreibung:
Bulk niobium diboride ceramics were consolidated by spark plasma sintering (SPS) at 1900 °C. SPS resulted in dense specimens with a density of 98% of the theoretical density and a mean grain size of 6 μm. During the SPS consolidation, the hexagonal boron nitride (h-BN) was formed from B 2 O 3 on the powder particle surface and residual adsorbed nitrogen in the raw diboride powder. The room-temperature strength of these NbB 2 bulks was 420 MPa. The flexural strength of the NbB 2 ceramics remained unchanged up to 1600 °C. At 1700 °C an increase in strength to 450 MPa was observed, which was accompanied by the disappearance of the secondary h-BN phase. Finally, at 1800 °C signs of plastic deformation were observed. Fractographic analysis revealed a number of etching pits and steplike surfaces suggestive of high-temperature deformation. The temperature dependence of the flexural strength of NbB 2 bulks prepared by SPS was compared with data for monolithic TiB 2 , HfB 2 and ZrB 2 . Our analysis suggested that the thermal stresses accumulated during SPS consolidation may lead to additional strengthening at elevated temperatures. This article is protected by copyright. All rights reserved.
Print ISSN:
0002-7820
Digitale ISSN:
1551-2916
Thema:
Maschinenbau
