| 1. |
- Candelario, Victor M., et al.
(författare)
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Liquid-phase assisted spark-plasma sintering of SiC nanoceramics and their nanocomposites with carbon nanotubes
- 2017
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 37:5, s. 1929-1936
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Tidskriftsartikel (refereegranskat)abstract
- The appropriate conditions for liquid-phase assisted spark-plasma sintering (SPS) were identified for the fabrication of both SiC nanoceramics and their nanocomposites with carbon nanotubes (CNTs). A parametric study of the nanoceramics and nanocomposites with a given type of CNTs showed that the SPS temperature (as measured by the radial optical pyrometer) optimizing their densification, nanograin size, and mechanical properties is 1700 degrees C (soaking for a few minutes), below which there is incomplete densification, and above which there is obvious grain growth with no benefit in hardness or toughness in the case of the nanoceramics, and prejudicial to both properties in the case of the nanocomposites due to the CNT degradation. It was also shown that the nanocomposites have smaller nanograins than their nanoceramic counterparts, and are softer but tougher. Extension to nanocomposites with different types of CNTs confirmed these trends, and showed that the CNT features do not condition the densification, microstructure or mechanical properties of these nanocomposites.
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| 2. |
- Ciudad, Esther, et al.
(författare)
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Sliding-wear resistance of ultrafine-grained SiC densified by spark plasma sintering with 3Y(2)O(3)+5Al(2)O(3) or Y3Al5O12 additives
- 2013
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 69:8, s. 598-601
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Tidskriftsartikel (refereegranskat)abstract
- The sliding-wear behavior of ultrafine-grained SiC densified by spark plasma sintering (SPS) with 3Y(2)O(3) + 5Al(2)O(3) or Y3Al5O12 additives was compared to elucidate the effect of the intergranular-phase source. Significantly greater sliding-wear resistance (i.e. lower mild- and severe-wear rates, and delayed mild-to-severe wear transition) is observed with the Y3Al5O12 additive, due to its carbothermal reduction during SPS resulting in a harder YAlO3 phase while reducing the intergranular phase content. Implications for the processing of superior SiC triboceramics are discussed.
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| 3. |
- Nunez-Gonzalez, Beatriz, et al.
(författare)
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Improvement of the Spark-Plasma-Sintering Kinetics of ZrC by High-Energy Ball-Milling
- 2012
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Ingår i: Journal of The American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 95:2, s. 453-456
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the duration of high-energy ball-milling on the spark-plasma sintering (SPS) kinetics of additive-free ZrC ultra-high-temperature ceramics (UHTCs) was investigated. It was found that the crystallite size of ZrC is refined progressively from the as-purchased condition down to a few nanometers with increasing high-energy ball-milling time, and that this crystallite size refinement progressively enhances the SPS kinetics, reducing the characteristic temperatures of the sintering process. While this enhancement was found to be only moderate with the refinement to the ultra-fine range, it was highly marked with the refinement to the nanometer range. Implications for the lower-temperature processing of ZrC UHTCs are discussed.
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| 4. |
- Nunez-Gonzalez, Beatriz, et al.
(författare)
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Spark-plasma-sintering kinetics of ZrC-SiC powder mixtures subjected to high-energy co-ball-milling
- 2013
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Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 39:8, s. 9691-9697
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Tidskriftsartikel (refereegranskat)abstract
- The effect of SiC addition (5, 17.5, or 30 vol%) on the spark-plasma sinterability of ZrC ultra-high-temperature ceramics (UHTC) was investigated as a function of the intensity of high-energy co-ball-miffing. It was found that the spark-plasma-sintering (SPS) kinetics of the ZrC- SiC powder mixtures is enhanced progressively with increasing co-milling time, which is due to the progressive refinement of the crystallite sizes. It was also found that in practice the SiC addition is beneficial for the SPS kinetics of ZrC if the co-milling time is short enough so as to refine the SiC crystallite size only to the submicrometre range, although the improvement in sinterability does not correlate with the SiC content. On the contrary, the SiC addition is increasingly detrimental for those co-milling times that promote SiC refinement to the nanoscale. This unexpected trend is due to slower ZrC crystallite size refinement in the presence of SiC and, especially, to the complex role played during SPS by the passivating SiO2 films formed on the SiC particles, and is different from what has been observed in ZrB2-SiC. Finally, implications of interest for the UHTC community are discussed.
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| 5. |
- Zamora, Victor, et al.
(författare)
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Effect of graphite addition on the spark-plasma sinterability of ZrB2 and ZrB2-SiC ultra-high-temperature ceramics
- 2014
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Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 40:7, s. 11457-11464
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Tidskriftsartikel (refereegranskat)abstract
- The effect of a 2 wt% addition of particulate graphite on the spark-plasma sintering (SPS) kinetics of both ZrB2 and ZrB2+30 vol% SiC was investigated using to that end two broad sets of powder mixtures prepared by high-energy co-ball-milling. It was observed that the particulate graphite addition enhances the SPS kinetics of both systems, and it was identified that, contrary to the case in conventional sintering, this improvement in sinterability is not due to the carbothermal reduction of oxides in situ during SPS but to the lubrication imposed by the graphite flakes inducing a greater green-body densification. Consequently, the graphite is not consumed during SPS but remains in the microstructure of the resulting ultra-high-temperature ceramics (UHTCs) as flaky particles dispersed homogeneously at grain boundaries. Implications of interest for the UHTC community are discussed.
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| 6. |
- Zamora, Victor, et al.
(författare)
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In situ formation of ZrB2-ZrO2 ultra-high-temperature ceramic composites from high-energy ball-milled ZrB2 powders
- 2012
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 518, s. 38-43
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Tidskriftsartikel (refereegranskat)abstract
- The in situ formation is reported of a fine-grained ZrB2 ultra-high-temperature ceramic (UHTC) containing evenly distributed ZrO2 of uniform size located at triple joints and grain boundaries of the ZrB2 grains, discovered during the spark-plasma sintering of ZrB2 powders subjected to high-energy ball-milling in air. It is found that this type of microstructure forms because the oxide film of ZrO2, developed on the surface of the ZrB2 particles during the high-energy ball-milling in air, creeps towards the ZrB2 multigrain joints under the application of pressure during sintering, and then crystallizes there during the fast cooling down to room-temperature. Together with the mechanism by which these dense ZrB2-ZrO2 UHTC composites form, it is also shown that they are simultaneously harder and much tougher than their ZrB2 monolith counterpart.
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| 7. |
- Zamora, Victor, et al.
(författare)
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On the enhancement of the spark-plasma sintering kinetics of ZrB2-SiC powder mixtures subjected to high-energy co-ball-milling
- 2013
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Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 39:4, s. 4191-4204
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Tidskriftsartikel (refereegranskat)abstract
- The spark-plasma sintering (SPS) kinetics of ZrB2-SiC powder mixtures was investigated as a function of the degree of high-energy co-ball-milling and of the SiC content (5, 17.5, or 30 vol%). As in ZrB2 without SiC, it was found that the crystal size refinement induced by the continued milling progressively enhances the SPS kinetics of ZrB2-SiC, again only moderately if the refinement is to the ultra-fine range, but very marked if the refinement is to the nanoscale. It was also found that the SiC addition further enhances the SPS kinetics of ZrB2, although the improvement did not scale directly with the SiC content, and became less relevant with the refinement of the ZrB2 crystal sizes to the nanoscale. The improved kinetics induced by the SiC addition was identified as being due to the formation of amorphous borosilicate from the oxide passivating layers on the ZrB2 and SiC particles. This not only speeds up the interparticle diffusion, but also it is segregated under the application of pressure into the multi-grain joints, filling pores. The enhanced kinetics induced by the progressive milling is due to the continuous reduction of the diffusion distances and to the development of a greater density of grain boundaries available as faster diffusion paths, together with the greater formation of amorphous borosilicate. Implications of interest for the ultra-high-temperature ceramics community are discussed.
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| 8. |
- Zamora, Victor, et al.
(författare)
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Spark-plasma sintering of ZrB2 ultra-high-temperature ceramics at lower temperature via nanoscale crystal refinement
- 2012
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 32:10, s. 2529-2536
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Tidskriftsartikel (refereegranskat)abstract
- We have explored the feasibility of reducing the spark-plasma-sintering (SPS) temperature of additive-free ZrB2 ultra-high-temperature ceramics (UHTCs) via crystal size refinement of the starting powder down to the low nanoscale. We found that under otherwise the same SPS conditions (75 MPa pressure, and 100 degrees C/min heating ramp) nanoscale ZrB2 can be densified at temperatures about 450 degrees C lower than for the typical micrometre and submicrometre ZrB2 powders, and at least 250 degrees C below the ultra-fine powder temperature. Furthermore, the nanoscale crystal refinement also promotes the production of fine-grained ZrB2 UHTCs. We also found that elimination of the B2O3 impurities plays an important role in the complete densification. The unequalled sinterability of the nanoscale ZrB2 powders highlights the need to use high-energy ball-milling for the comminution of the typical commercially available ZrB2 powders.
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