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Sintering boron carbide ceramics without grain growth by plastic deformation as the dominant densification mechanism.

Ji W, Rehman SS, Wang W, Wang H, Wang Y, Zhang J, Zhang F, Fu Z - Sci Rep (2015)

Bottom Line: A new ceramic sintering approach employing plastic deformation as the dominant mechanism is proposed, at low temperature close to the onset point of grain growth and under high pressure.Based on this route, fully dense boron carbide without grain growth can be prepared at 1,675-1,700 °C and under pressure of (≥) 80 MPa in 5 minutes.Such a process should also facilitate the cost-effective preparation of other advanced ceramics for practical applications.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China.

ABSTRACT
A new ceramic sintering approach employing plastic deformation as the dominant mechanism is proposed, at low temperature close to the onset point of grain growth and under high pressure. Based on this route, fully dense boron carbide without grain growth can be prepared at 1,675-1,700 °C and under pressure of (≥) 80 MPa in 5 minutes. The dense boron carbide shows excellent mechanical properties, including Vickers hardness of 37.8 GPa, flexural strength of 445.3 MPa and fracture toughness of 4.7 MPa•m(0.5). Such a process should also facilitate the cost-effective preparation of other advanced ceramics for practical applications.

No MeSH data available.


Related in: MedlinePlus

The details of change in relative density and grain size with changing temperature for B4C sintered under 80 MPa, held for 5 min.(a) Relative density and grain size of B4C as a function of temperature, sintered under 80 MPa, with soaking for 5 min. (b) Relationship between grain growth (D/Do) and relative density in different sintering methods. (c–f) Polished and etched surfaces of B4C sintered under 80 MPa, with soaking for 5 min, at 1,600 °C, 1,700 °C, 1,750 °C and 1,800 °C, respectively.
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f3: The details of change in relative density and grain size with changing temperature for B4C sintered under 80 MPa, held for 5 min.(a) Relative density and grain size of B4C as a function of temperature, sintered under 80 MPa, with soaking for 5 min. (b) Relationship between grain growth (D/Do) and relative density in different sintering methods. (c–f) Polished and etched surfaces of B4C sintered under 80 MPa, with soaking for 5 min, at 1,600 °C, 1,700 °C, 1,750 °C and 1,800 °C, respectively.

Mentions: Figure 3 reveals the details of change in relative density and grain size with changing temperature for dense B4C sintered under 80 MPa, held for 5 min. As shown in Fig. 3a, the relative density increases dramatically with temperature from 1,500 °C, which indicates that the onset temperature for densification (Td) is about 1,500 °C. The high value of relative density (~95%) cannot be reached until 1,650 °C. The trend of grain growth differs from that of densification. The average grain size remains unchanged, as the raw particle size 2.36 μm until the temperature increases up to 1,700 °C, which indicates that the critical temperature for grain growth (Tg) is about 1,700 °C, which is higher than that for densification. The polished and etched surfaces of B4C specimens sintered at different temperatures are shown in Fig. 3c–f. The grain sizes of B4C sintered at 1,600 °C, 1,700 °C, 1,750 °C and 1,800 °C are 2.36 μm, 2.36 μm, 2.96 μm and 3.65 μm, respectively. Therefore, there exists a useful temperature range “M” in Td–Tg; the optimal range might be 1,675–1,700 °C for the micro-sized B4C in this work, in which high density can be achieved, but grains do not to grow (shown as the green range “M” in Fig. 3a). Chen’s idea is in fact to carry out the final-stage sintering in the Td–Tg region in 20 hours, which realizes densification, but keeps the grains from growing3. Kang’s attempt is sintering near the Td–Tg region to realize densification with limited grain growth, intentionally extending the holding time to 100 hours4. It is expected that densification will continue to develop with even longer soaking because of atomic diffusion, but will be very slow. Too long a soaking period in sintering is uneconomical. In fact, commonly, a sintering process is carried out in tens of minutes or several hours. In most cases, sintering temperatures are chosen bigger than Tg, to attain high enough density in an acceptable time, which is why grain growth is inevitable26. It is worth pointing out that the temperature range “M” depends on the particles’ size (micro-size or nano-size) and the size distribution. Nano-sized particles with a big surface area are expected to complicate the region more, which needs to be studied in the future.


Sintering boron carbide ceramics without grain growth by plastic deformation as the dominant densification mechanism.

Ji W, Rehman SS, Wang W, Wang H, Wang Y, Zhang J, Zhang F, Fu Z - Sci Rep (2015)

The details of change in relative density and grain size with changing temperature for B4C sintered under 80 MPa, held for 5 min.(a) Relative density and grain size of B4C as a function of temperature, sintered under 80 MPa, with soaking for 5 min. (b) Relationship between grain growth (D/Do) and relative density in different sintering methods. (c–f) Polished and etched surfaces of B4C sintered under 80 MPa, with soaking for 5 min, at 1,600 °C, 1,700 °C, 1,750 °C and 1,800 °C, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4622079&req=5

f3: The details of change in relative density and grain size with changing temperature for B4C sintered under 80 MPa, held for 5 min.(a) Relative density and grain size of B4C as a function of temperature, sintered under 80 MPa, with soaking for 5 min. (b) Relationship between grain growth (D/Do) and relative density in different sintering methods. (c–f) Polished and etched surfaces of B4C sintered under 80 MPa, with soaking for 5 min, at 1,600 °C, 1,700 °C, 1,750 °C and 1,800 °C, respectively.
Mentions: Figure 3 reveals the details of change in relative density and grain size with changing temperature for dense B4C sintered under 80 MPa, held for 5 min. As shown in Fig. 3a, the relative density increases dramatically with temperature from 1,500 °C, which indicates that the onset temperature for densification (Td) is about 1,500 °C. The high value of relative density (~95%) cannot be reached until 1,650 °C. The trend of grain growth differs from that of densification. The average grain size remains unchanged, as the raw particle size 2.36 μm until the temperature increases up to 1,700 °C, which indicates that the critical temperature for grain growth (Tg) is about 1,700 °C, which is higher than that for densification. The polished and etched surfaces of B4C specimens sintered at different temperatures are shown in Fig. 3c–f. The grain sizes of B4C sintered at 1,600 °C, 1,700 °C, 1,750 °C and 1,800 °C are 2.36 μm, 2.36 μm, 2.96 μm and 3.65 μm, respectively. Therefore, there exists a useful temperature range “M” in Td–Tg; the optimal range might be 1,675–1,700 °C for the micro-sized B4C in this work, in which high density can be achieved, but grains do not to grow (shown as the green range “M” in Fig. 3a). Chen’s idea is in fact to carry out the final-stage sintering in the Td–Tg region in 20 hours, which realizes densification, but keeps the grains from growing3. Kang’s attempt is sintering near the Td–Tg region to realize densification with limited grain growth, intentionally extending the holding time to 100 hours4. It is expected that densification will continue to develop with even longer soaking because of atomic diffusion, but will be very slow. Too long a soaking period in sintering is uneconomical. In fact, commonly, a sintering process is carried out in tens of minutes or several hours. In most cases, sintering temperatures are chosen bigger than Tg, to attain high enough density in an acceptable time, which is why grain growth is inevitable26. It is worth pointing out that the temperature range “M” depends on the particles’ size (micro-size or nano-size) and the size distribution. Nano-sized particles with a big surface area are expected to complicate the region more, which needs to be studied in the future.

Bottom Line: A new ceramic sintering approach employing plastic deformation as the dominant mechanism is proposed, at low temperature close to the onset point of grain growth and under high pressure.Based on this route, fully dense boron carbide without grain growth can be prepared at 1,675-1,700 °C and under pressure of (≥) 80 MPa in 5 minutes.Such a process should also facilitate the cost-effective preparation of other advanced ceramics for practical applications.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China.

ABSTRACT
A new ceramic sintering approach employing plastic deformation as the dominant mechanism is proposed, at low temperature close to the onset point of grain growth and under high pressure. Based on this route, fully dense boron carbide without grain growth can be prepared at 1,675-1,700 °C and under pressure of (≥) 80 MPa in 5 minutes. The dense boron carbide shows excellent mechanical properties, including Vickers hardness of 37.8 GPa, flexural strength of 445.3 MPa and fracture toughness of 4.7 MPa•m(0.5). Such a process should also facilitate the cost-effective preparation of other advanced ceramics for practical applications.

No MeSH data available.


Related in: MedlinePlus