Microstructure, mechanical properties and oxidation behavior of powder compacts of the Nb-Si-B system prepared by spark plasma sintering

摘要

Powder compacts with eight differentcompositions in the Nb-Si-B system were prepared by sparkplasma sintering and their microstructure, mechanicalproperties and oxidation behavior were investigated.Oxidation resistance of Nb5Si3B2 compacts is better thanthat of Nb5Si3 compacts, but extremely poorer than that ofNbSi2 compacts. However, since the oxidation experimentwas of short duration, details of the oxidation behaviorof Nb-Si-B compacts have yet to be investigated. Compactswere prepared via the following three different routes:(i) elemental powders were mixed in a rotational ball milland then consolidated by spark plasma sintering method,(ii) elemental powders were mechanically alloyed andconsolidated similarly to (i) and (iii) pulverizingcompacts prepared via route (i) and consolidated onceagain similarly to (i). Compacts prepared via the thirdroute exhibit more homogeneous microstructures andcontain a smaller amount of SiO2 than compacts preparedvia the other two routes. Compacts with compositionsaround the line of Nb5Si3-Nb5Si3B2-NbB2 exhibit a highhardness at room temperature and a high compressivestrength at high temperatures in comparison to those withcompositions away from the line. The strength of compactscontaining NbSi2 decreases with increasing the volume fraction of NbSi2 phase.Keywords: A. Silicides, various; B. Mechanical properties athigh temperatures; B. Oxidation; C. Mechanical alloyingand milling; C. Sintering