Dusan Bucevac - Academia.edu (original) (raw)

Papers by Dusan Bucevac

Densification and mechanical properties (hardness, fracture toughness and flexural strength) of t... more Densification and mechanical properties (hardness, fracture toughness and flexural strength) of the SiC-TiB2 composite were studied. Pressureless sintering experiments were carried out on samples containing 0 to 50 vol % of TiB2 created by an in-situ reaction between TiO 2 and C: 2TiO2+B4C+3C→2TiB 2+4CO↑ Al2O3 and Y2O3 were used as sintering additives to create a liquid phase and promote densification at sintering temperatures ranging from 1820 to 1940°C. The sintered samples were subsequently heat-treated at temperatures ranging from 1850 to 1970°C. It was found that the presence of TiB2 formed by the above reaction serves as an effective obstacle to crack propagation thus increasing both the strength and fracture toughness of SiC while maintaining high a hardness of the sintered samples. Densities higher than 98% TD were achieved depending on both the sintering temperature and heat treatment conditions. From a density viewpoint, the optimum volume fraction of TiB2 was from 12 to 24 vol %. Typical microstructures for samples with this volume fraction of TiB2 consist of TiB2 particles (< 5microm) uniformly dispersed in a matrix of elongated SiC plates. The presence of TiB 2 particles in the matrix of SiC inhibited exaggerated grain growth of the SiC grains and activated additional toughening mechanisms. The subsequent heat treatment of the sintered samples improved mechanical properties. The optimum sintering and heat treatment temperatures were 1940 and 1970°C, respectively. The maximum flexural strength of 593 MPa was obtained in sample with 12 vol % TiB2. A maximum fracture toughness of 6.6 MPa·m 1/2 was measured in samples containing 24 vol % TiB2. While both fracture toughness and strength increased with the presence of TiB 2 particles, hardness on the other hand decreased from ˜18 GPa in samples without TiB2 to 16.4 and 15.9 GPa in samples with 12 and 24 vol % TiB2, respectively. A theoretical analysis was conducted to model the effect of microstructure on the fracture toughness of SiC-TiB 2 composites and was experimentally verified.

Science of Sintering, 2008

The α−β phase transformation in Si 3 N 4 was studied for seeded samples using an Y 2 O 3 -Al 2 O ... more The α−β phase transformation in Si 3 N 4 was studied for seeded samples using an Y 2 O 3 -Al 2 O 3 mixture as a sintering aid. The concentration of β-seeds varied from 0 to 5 wt.%.

Journal of Materials Science, 2007

Microstructure development and fracture toughness of Si3N4 composites were studied in the presenc... more Microstructure development and fracture toughness of Si3N4 composites were studied in the presence of seeds and Al2O3 + Y2O3 as sintering aids. The elongated β-Si3N4 seeds were introduced into two different α-Si3N4 matrix powders; one was the ultra fine powder matrix and the other was the coarse powder matrix. The amount of seeds varied from 0 to 6 wt%. The grain growth inhibition and the mechanism of toughening were discussed and correlated with microstructure. The maximum fracture toughness of 9.0 MPa m1/2 was obtained for ultra fine powder with 5 wt% seeds hot pressed at 1,700 °C for 6 h.

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011

Dense SiC-TiB 2 composites with 24 vol% TiB 2 were fabricated by pressureless sintering at 1940 •... more Dense SiC-TiB 2 composites with 24 vol% TiB 2 were fabricated by pressureless sintering at 1940 • C. Al 2 O 3 and Y 2 O 3 were used as sintering additives to create a liquid phase and promote densification. TiB 2 was formed by an in situ reaction between TiO 2 , B 4 C and C. The sintered samples were subsequently heattreated at temperatures ranging from 1850 • C to 2000 • C. The effect of temperature of post-sintering heat treatment on microstructure and mechanical properties of the SiC-TiB 2 composite was presented. Heat treatment at 1970 • C considerably improved the strength and the fracture toughness of sintered samples while maintaining high density. The elongation of ␣-SiC grains during the heat treatment was found to be responsible for an increase in fracture toughness. The presence of liquid phase assisted the elongation of grains which, in turn, activated crack bridging and crack deflection toughening mechanisms. Maximum strength of 540 MPa was found to be the result of improved fracture toughness. Heat treatment at temperatures above 1970 • C led to a deterioration of mechanical properties.

Journal of Alloys and Compounds, 2011

SiC-TiB 2 particulate composites were fabricated by converting TiO 2 to TiB 2 through the reactio... more SiC-TiB 2 particulate composites were fabricated by converting TiO 2 to TiB 2 through the reaction between TiO 2 , B 4 C and C. The presence of initially very fine, in-situ created, TiB 2 particles increased driving force for sintering and enabled fabrication of a dense composite utilizing pressureless sintering and the liquid phase created between Al 2 O 3 and Y 2 O 3 additives. The effect of volume fraction of the in-situ formed TiB 2 on density, microstructure and flexural strength was discussed. It was found that the presence of TiB 2 particles suppressed the growth of SiC grains and enhanced fracture strength. The fracture strength of samples containing 12 vol% TiB 2 was more than 30% higher than that of the monolithic SiC. The effect of SiC grain size on fracture strength was also analyzed.

Ceramics International, 2010

SiC–TiB2 composites with up to 50vol% TiB2 were fabricated by in-situ reaction between TiO2, B4C ... more SiC–TiB2 composites with up to 50vol% TiB2 were fabricated by in-situ reaction between TiO2, B4C and C. The densification of the uniaxially pressed samples was done using pressureless sintering in the presence of sintering aids consisting of Al2O3 and Y2O3. The influence of the volume fraction of TiB2 and sintering temperature on density and fracture toughness was examined. It was found that fracture toughness is strongly affected by the volume fraction of TiB2. The presence of TiB2 particles suppresses the grain growth of SiC and facilitates different toughening mechanisms to operate which, in turn, increases fracture toughness of the composite. The highest value for fracture toughness of 5.7MPam1/2 was measured in samples with 30vol% TiB2 sintered at 1940°C.

Science of Sintering, 2008

The α−β phase transformation in Si 3 N 4 was studied for seeded samples using an Y 2 O 3 -Al 2 O ... more The α−β phase transformation in Si 3 N 4 was studied for seeded samples using an Y 2 O 3 -Al 2 O 3 mixture as a sintering aid. The concentration of β-seeds varied from 0 to 5 wt.%.

Journal of Materials Science, 2007

Microstructure development and fracture toughness of Si3N4 composites were studied in the presenc... more Microstructure development and fracture toughness of Si3N4 composites were studied in the presence of seeds and Al2O3 + Y2O3 as sintering aids. The elongated β-Si3N4 seeds were introduced into two different α-Si3N4 matrix powders; one was the ultra fine powder matrix and the other was the coarse powder matrix. The amount of seeds varied from 0 to 6 wt%. The grain growth inhibition and the mechanism of toughening were discussed and correlated with microstructure. The maximum fracture toughness of 9.0 MPa m1/2 was obtained for ultra fine powder with 5 wt% seeds hot pressed at 1,700 °C for 6 h.

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011

Dense SiC-TiB 2 composites with 24 vol% TiB 2 were fabricated by pressureless sintering at 1940 •... more Dense SiC-TiB 2 composites with 24 vol% TiB 2 were fabricated by pressureless sintering at 1940 • C. Al 2 O 3 and Y 2 O 3 were used as sintering additives to create a liquid phase and promote densification. TiB 2 was formed by an in situ reaction between TiO 2 , B 4 C and C. The sintered samples were subsequently heattreated at temperatures ranging from 1850 • C to 2000 • C. The effect of temperature of post-sintering heat treatment on microstructure and mechanical properties of the SiC-TiB 2 composite was presented. Heat treatment at 1970 • C considerably improved the strength and the fracture toughness of sintered samples while maintaining high density. The elongation of ␣-SiC grains during the heat treatment was found to be responsible for an increase in fracture toughness. The presence of liquid phase assisted the elongation of grains which, in turn, activated crack bridging and crack deflection toughening mechanisms. Maximum strength of 540 MPa was found to be the result of improved fracture toughness. Heat treatment at temperatures above 1970 • C led to a deterioration of mechanical properties.

Journal of Alloys and Compounds, 2011

SiC-TiB 2 particulate composites were fabricated by converting TiO 2 to TiB 2 through the reactio... more SiC-TiB 2 particulate composites were fabricated by converting TiO 2 to TiB 2 through the reaction between TiO 2 , B 4 C and C. The presence of initially very fine, in-situ created, TiB 2 particles increased driving force for sintering and enabled fabrication of a dense composite utilizing pressureless sintering and the liquid phase created between Al 2 O 3 and Y 2 O 3 additives. The effect of volume fraction of the in-situ formed TiB 2 on density, microstructure and flexural strength was discussed. It was found that the presence of TiB 2 particles suppressed the growth of SiC grains and enhanced fracture strength. The fracture strength of samples containing 12 vol% TiB 2 was more than 30% higher than that of the monolithic SiC. The effect of SiC grain size on fracture strength was also analyzed.

Ceramics International, 2010

SiC–TiB2 composites with up to 50vol% TiB2 were fabricated by in-situ reaction between TiO2, B4C ... more SiC–TiB2 composites with up to 50vol% TiB2 were fabricated by in-situ reaction between TiO2, B4C and C. The densification of the uniaxially pressed samples was done using pressureless sintering in the presence of sintering aids consisting of Al2O3 and Y2O3. The influence of the volume fraction of TiB2 and sintering temperature on density and fracture toughness was examined. It was found that fracture toughness is strongly affected by the volume fraction of TiB2. The presence of TiB2 particles suppresses the grain growth of SiC and facilitates different toughening mechanisms to operate which, in turn, increases fracture toughness of the composite. The highest value for fracture toughness of 5.7MPam1/2 was measured in samples with 30vol% TiB2 sintered at 1940°C.

Densification and mechanical properties (hardness, fracture toughness and flexural strength) of t... more Densification and mechanical properties (hardness, fracture toughness and flexural strength) of the SiC-TiB2 composite were studied. Pressureless sintering experiments were carried out on samples containing 0 to 50 vol % of TiB2 created by an in-situ reaction between TiO 2 and C: 2TiO2+B4C+3C→2TiB 2+4CO↑ Al2O3 and Y2O3 were used as sintering additives to create a liquid phase and promote densification at sintering temperatures ranging from 1820 to 1940°C. The sintered samples were subsequently heat-treated at temperatures ranging from 1850 to 1970°C. It was found that the presence of TiB2 formed by the above reaction serves as an effective obstacle to crack propagation thus increasing both the strength and fracture toughness of SiC while maintaining high a hardness of the sintered samples. Densities higher than 98% TD were achieved depending on both the sintering temperature and heat treatment conditions. From a density viewpoint, the optimum volume fraction of TiB2 was from 12 to 24 vol %. Typical microstructures for samples with this volume fraction of TiB2 consist of TiB2 particles (< 5microm) uniformly dispersed in a matrix of elongated SiC plates. The presence of TiB 2 particles in the matrix of SiC inhibited exaggerated grain growth of the SiC grains and activated additional toughening mechanisms. The subsequent heat treatment of the sintered samples improved mechanical properties. The optimum sintering and heat treatment temperatures were 1940 and 1970°C, respectively. The maximum flexural strength of 593 MPa was obtained in sample with 12 vol % TiB2. A maximum fracture toughness of 6.6 MPa·m 1/2 was measured in samples containing 24 vol % TiB2. While both fracture toughness and strength increased with the presence of TiB 2 particles, hardness on the other hand decreased from ˜18 GPa in samples without TiB2 to 16.4 and 15.9 GPa in samples with 12 and 24 vol % TiB2, respectively. A theoretical analysis was conducted to model the effect of microstructure on the fracture toughness of SiC-TiB 2 composites and was experimentally verified.

Science of Sintering, 2008

The α−β phase transformation in Si 3 N 4 was studied for seeded samples using an Y 2 O 3 -Al 2 O ... more The α−β phase transformation in Si 3 N 4 was studied for seeded samples using an Y 2 O 3 -Al 2 O 3 mixture as a sintering aid. The concentration of β-seeds varied from 0 to 5 wt.%.

Journal of Materials Science, 2007

Microstructure development and fracture toughness of Si3N4 composites were studied in the presenc... more Microstructure development and fracture toughness of Si3N4 composites were studied in the presence of seeds and Al2O3 + Y2O3 as sintering aids. The elongated β-Si3N4 seeds were introduced into two different α-Si3N4 matrix powders; one was the ultra fine powder matrix and the other was the coarse powder matrix. The amount of seeds varied from 0 to 6 wt%. The grain growth inhibition and the mechanism of toughening were discussed and correlated with microstructure. The maximum fracture toughness of 9.0 MPa m1/2 was obtained for ultra fine powder with 5 wt% seeds hot pressed at 1,700 °C for 6 h.

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011

Dense SiC-TiB 2 composites with 24 vol% TiB 2 were fabricated by pressureless sintering at 1940 •... more Dense SiC-TiB 2 composites with 24 vol% TiB 2 were fabricated by pressureless sintering at 1940 • C. Al 2 O 3 and Y 2 O 3 were used as sintering additives to create a liquid phase and promote densification. TiB 2 was formed by an in situ reaction between TiO 2 , B 4 C and C. The sintered samples were subsequently heattreated at temperatures ranging from 1850 • C to 2000 • C. The effect of temperature of post-sintering heat treatment on microstructure and mechanical properties of the SiC-TiB 2 composite was presented. Heat treatment at 1970 • C considerably improved the strength and the fracture toughness of sintered samples while maintaining high density. The elongation of ␣-SiC grains during the heat treatment was found to be responsible for an increase in fracture toughness. The presence of liquid phase assisted the elongation of grains which, in turn, activated crack bridging and crack deflection toughening mechanisms. Maximum strength of 540 MPa was found to be the result of improved fracture toughness. Heat treatment at temperatures above 1970 • C led to a deterioration of mechanical properties.

Journal of Alloys and Compounds, 2011

SiC-TiB 2 particulate composites were fabricated by converting TiO 2 to TiB 2 through the reactio... more SiC-TiB 2 particulate composites were fabricated by converting TiO 2 to TiB 2 through the reaction between TiO 2 , B 4 C and C. The presence of initially very fine, in-situ created, TiB 2 particles increased driving force for sintering and enabled fabrication of a dense composite utilizing pressureless sintering and the liquid phase created between Al 2 O 3 and Y 2 O 3 additives. The effect of volume fraction of the in-situ formed TiB 2 on density, microstructure and flexural strength was discussed. It was found that the presence of TiB 2 particles suppressed the growth of SiC grains and enhanced fracture strength. The fracture strength of samples containing 12 vol% TiB 2 was more than 30% higher than that of the monolithic SiC. The effect of SiC grain size on fracture strength was also analyzed.

Ceramics International, 2010

SiC–TiB2 composites with up to 50vol% TiB2 were fabricated by in-situ reaction between TiO2, B4C ... more SiC–TiB2 composites with up to 50vol% TiB2 were fabricated by in-situ reaction between TiO2, B4C and C. The densification of the uniaxially pressed samples was done using pressureless sintering in the presence of sintering aids consisting of Al2O3 and Y2O3. The influence of the volume fraction of TiB2 and sintering temperature on density and fracture toughness was examined. It was found that fracture toughness is strongly affected by the volume fraction of TiB2. The presence of TiB2 particles suppresses the grain growth of SiC and facilitates different toughening mechanisms to operate which, in turn, increases fracture toughness of the composite. The highest value for fracture toughness of 5.7MPam1/2 was measured in samples with 30vol% TiB2 sintered at 1940°C.

Science of Sintering, 2008

The α−β phase transformation in Si 3 N 4 was studied for seeded samples using an Y 2 O 3 -Al 2 O ... more The α−β phase transformation in Si 3 N 4 was studied for seeded samples using an Y 2 O 3 -Al 2 O 3 mixture as a sintering aid. The concentration of β-seeds varied from 0 to 5 wt.%.

Journal of Materials Science, 2007

Microstructure development and fracture toughness of Si3N4 composites were studied in the presenc... more Microstructure development and fracture toughness of Si3N4 composites were studied in the presence of seeds and Al2O3 + Y2O3 as sintering aids. The elongated β-Si3N4 seeds were introduced into two different α-Si3N4 matrix powders; one was the ultra fine powder matrix and the other was the coarse powder matrix. The amount of seeds varied from 0 to 6 wt%. The grain growth inhibition and the mechanism of toughening were discussed and correlated with microstructure. The maximum fracture toughness of 9.0 MPa m1/2 was obtained for ultra fine powder with 5 wt% seeds hot pressed at 1,700 °C for 6 h.

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011

Dense SiC-TiB 2 composites with 24 vol% TiB 2 were fabricated by pressureless sintering at 1940 •... more Dense SiC-TiB 2 composites with 24 vol% TiB 2 were fabricated by pressureless sintering at 1940 • C. Al 2 O 3 and Y 2 O 3 were used as sintering additives to create a liquid phase and promote densification. TiB 2 was formed by an in situ reaction between TiO 2 , B 4 C and C. The sintered samples were subsequently heattreated at temperatures ranging from 1850 • C to 2000 • C. The effect of temperature of post-sintering heat treatment on microstructure and mechanical properties of the SiC-TiB 2 composite was presented. Heat treatment at 1970 • C considerably improved the strength and the fracture toughness of sintered samples while maintaining high density. The elongation of ␣-SiC grains during the heat treatment was found to be responsible for an increase in fracture toughness. The presence of liquid phase assisted the elongation of grains which, in turn, activated crack bridging and crack deflection toughening mechanisms. Maximum strength of 540 MPa was found to be the result of improved fracture toughness. Heat treatment at temperatures above 1970 • C led to a deterioration of mechanical properties.

Journal of Alloys and Compounds, 2011

SiC-TiB 2 particulate composites were fabricated by converting TiO 2 to TiB 2 through the reactio... more SiC-TiB 2 particulate composites were fabricated by converting TiO 2 to TiB 2 through the reaction between TiO 2 , B 4 C and C. The presence of initially very fine, in-situ created, TiB 2 particles increased driving force for sintering and enabled fabrication of a dense composite utilizing pressureless sintering and the liquid phase created between Al 2 O 3 and Y 2 O 3 additives. The effect of volume fraction of the in-situ formed TiB 2 on density, microstructure and flexural strength was discussed. It was found that the presence of TiB 2 particles suppressed the growth of SiC grains and enhanced fracture strength. The fracture strength of samples containing 12 vol% TiB 2 was more than 30% higher than that of the monolithic SiC. The effect of SiC grain size on fracture strength was also analyzed.

Ceramics International, 2010

SiC–TiB2 composites with up to 50vol% TiB2 were fabricated by in-situ reaction between TiO2, B4C ... more SiC–TiB2 composites with up to 50vol% TiB2 were fabricated by in-situ reaction between TiO2, B4C and C. The densification of the uniaxially pressed samples was done using pressureless sintering in the presence of sintering aids consisting of Al2O3 and Y2O3. The influence of the volume fraction of TiB2 and sintering temperature on density and fracture toughness was examined. It was found that fracture toughness is strongly affected by the volume fraction of TiB2. The presence of TiB2 particles suppresses the grain growth of SiC and facilitates different toughening mechanisms to operate which, in turn, increases fracture toughness of the composite. The highest value for fracture toughness of 5.7MPam1/2 was measured in samples with 30vol% TiB2 sintered at 1940°C.