Papers by Keyword: Covalent Ceramics

Abstract: This paper presents results of experiments on pressureless sintering of boron carbide (B₄C) with addition of titânia (TiO₂) and titanium diboride (TiB₂). The TiB₂ powder was added as a second phase and the TiO₂ powder for reactive sintering and in-situ formation of TiB₂. The final concentrations of TiB₂ in the composites were 0 to 10 vol%. Sintering was performed at 2050 °C/30min in argon atmosphere. TiO₂ was completely transformed into TiB₂ with fine equiaxed grains distributed homogeneously. Composites obtained by in-situ reaction showed a densification increase with the concentration increase, while the composites with TiB₂ powder mixture showed low densification in all compositions. Relative Density of the composite with 10 vol% of TiB₂ obtained in-situ was 91% (TD) compared to 86 % for B₄C only. Vickers hardness was about 29 GPa.

Abstract: One suitable material candidate to improve B₄C mechanical properties is SiC. B₄C-SiC ceramic composites are very promising armor materials because B₄C and SiC are intrinsically very hard. In this work a pressureless sintering study of B₄C-SiC ceramics was made. B₄C-SiC mixtures were prepared with SiC concentration from 10 to 50 wt%. Without the external applied pressure during sintering it was necessary to add sintering aid. The additive system AlN-Y₂O₃ was investigated as sintering aid. Samples were densified by pressureless sintering at 2000 °C/30 min in an argon atmosphere. B₄C-SiC composites were analyzed by XRD and SEM. Bulk density and total weight loss were also measured. Density higher than 93 % of the theoretical value was determined and microhardness of 30.3 GPa was achieved for composite with 10 wt% of SiC sintered with AlN-Y₂O₃ additive.

Abstract: The effect of three different sintering additive systems on densification of boron carbide powder was investigated. The sintering additives were Al2O3:Y2O3, AlN:Y2O3 and BN:Y2O3 compositions. Powder mixtures were prepared with 10 vol% of sintering aids following conventional powder technology processes. Samples were sintered by pressureless sintering at 2050 °C/30min in argon atmosphere. Sintered samples were compared to a sintered B4C without sintering additive. Samples were characterized by XRD to analyze the crystalline phases after sintering and SEM to observe the microstructure and the second phase distribution. YB4 and YB2C2 were identified in all samples, indicating a reaction between Y2O3, B4C and B2O3 present at the B4C particle surface. The best densification result was achieved with Al2O3:Y2O3 additive system, showing 92.0 % of theoretical density, low porosity and 15.2 % of linear shrinkage. But this sample showed the highest weight loss.