Study of sintering and structure-property relationships in boron suboxide (B6O) - alkaline earthmetal oxide, cobalt, and nickel compound
Date
2010-01-29T08:45:38Z
Authors
Ogunmuyiwa, Enoch Nifise
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Abstract
Recently some progress has been reported in improving the fracture toughness of
boron suboxide (B6O). This involved the introduction of second phases in it at low
levels of doping. This study extends this work through the addition of different
additives and through the improvement of densification, by controlled sintering.
Boron suboxide powders were sintered with and without additives. Pure B6O powders
were sintered at a temperature of 1900oC under a load of 50 MPa for 20 minutes in an
argon environment. B6O powders mixed with different additives, including alkalineearth
metal oxide, nickel and nickel compounds, cobalt compounds and chromium
boride. These powders were sintered at a temperature of 1850oC under loads from 50
-80 MPa, for 20 minutes in an argon environment. Microstructure, phase composition
and properties were investigated.
Boride secondary phases were formed when hot pressing B6O admixed with nickel
and nickel compounds, cobalt compounds and chromium boride additives while the
alkaline earth metal oxide additives resulted in the formation of boride and borate
phases, depending on the oxide used. The mechanisms leading to the achievement of
increased toughness and the possible reasons for toughness variation with the
different additives are critically analyzed.
Good combinations of mechanical properties were achieved for B6O-cobalt compound additive with hardness values from 32.6 -34.9 GPa and fracture toughness from 5.2 to 5.8 MPam o.5 for B60-Co2B and B60-Co0 materials respectively.