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Abstract: The in situ TiB/Ti–4.0Fe–7.3Mo composites were fabricated by plasma spark sintering (SPS) technique using mechanical alloying of Ti, Fe65Mo and B powder. The effects of sintering temperature on densification of the composites and microstructure of the in situ synthesized TiB were investigated using scanning electron microscope (SEM) and transmission electron microscope (TEM). A dense composite was obtained after sintering at 1000°C for 5min. Under proper ball milling and SPS conditions in situ TiB reinforced Ti–4.0Fe–7.3Mo composites have been prepared. The in situ TiB showed a typical needle shape grow along [010] direction. The transverse cross-section of TiB grain is a hexagonal shape with the planes of (100), (101) and . The stacking faults in the (100) plane were observed in the TiB needles. [Copyright &y& Elsevier]

LiTaO3/Al2O3 ceramic composites were fabricated by hot pressing and pressureless sintering, respectively, to investigate the effect of piezoelectric secondary phase on the properties of structural ceramics. Phase constitution, microstructure and mechanical properties of the ceramic composites were studied. LiTaO3 could stably coexist with Al2O3 during sintering. LiTaO3 phase was located at the grain boundaries of Al2O3 matrix fabricated by different processing routes. Domain structures were clearly seen in LiTaO3, confirming that LiTaO3 remained hexagonal ferroelectric phase. About 5 vol.%LiTaO3/Al2O3 ceramic composite prepared by pressureless sintering at 1300 °C showed an increase in fracture toughness. Energy dissipation due to domain switching was suggested as a toughening mechanism. With the increasing of LiTaO3 content, the domain switching toughening mechanism was decompensated by the decreased relative density of LiTaO3/Al2O3 ceramic composites. For LiTaO3/Al2O3 ceramic composites prepared by hot pressing at 1500 °C, the bending strength decreased because of the increased grain size of Al2O3 matrix. The toughening effect due to domain switching was also decompensated by the coarsening of Al2O3 matrix grains, the weaker net-like LiTaO3 phase and the weaker bonding strength between LiTaO3 phase and Al2O3 matrix. [Copyright &y& Elsevier]

Abstract: Tantalum carbide with a TaC0.9 composition was sintered to 96% relative density by spark plasma sintering at 1400°C for 5min, using commercial micrometric Ta and TaC powders as the starting materials. This achievement was dependent on the delicate rearrangement of the heating process which limits evaporation–condensation and promotes the mass transportation in association with 0.9TaC+Ta=TaC0.9 reaction. The dense TaC0.9 ceramic had a uniform microstructure composed of equiaxed grains, and showed flexure strength up to ∼498MPa. [Copyright &y& Elsevier]

Abstract: A 20vol.% ZrCp/W composite is fabricated by hot-pressing, and its mechanical properties can be significantly improved by the addition of ZrC particles. On the other side, the residual pores within ZrC particles clustering regions which are some latent microcrack sources are mainly caused by the relative low sinterability of ZrC particles. In order to eliminate the pores within the particle clusters, the as-sintered composite is annealed at 2300°C for 1h. The microstructure of the annealed composite becomes more uniform and densified. Components of the as-sintered and annealed composites are composed of a dilute solid solution tungsten-matrix, (Zr, W)C solid solution particles and a new W2C phase, but the content of W2C phase in the annealed composite increases. After annealing, the strength properties of the composite decrease, but its plasticity increases. [Copyright &y& Elsevier]

Abstract: SiB0.5C1.5N0.5 nanopowders were synthesized by mechanical alloying method, and a predominantly amorphous with a small volume fraction of nanocrystalline phase was formed in the powders. The results showed that the crystallites were SiC, and the polytype of SiC were 3C and 6H. SiB0.5C1.5N0.5 powders were consolidated by spark plasma sintering (SPS) technique at 1800°C under different sintering pressure. The grain boundaries of SiC and BCN phase could not be clearly distinguished for the ceramics sintered under 25MPa. When the pressure increased to 40MPa, SiC phase almost completely crystallized, and its grain size was less than 1μm. BCN phase were mainly distributed at boundary of SiC grain. Some amorphous structures were found in the sintered ceramics. Relative densities of the ceramics increased from 76.6% to 92.4%, and mechanical property values increased two or three times with the increase of sintering pressure. For the ceramics sintered under a pressure of 40MPa, flexural strength, fracture toughness, elastic modulus and Vickers’ hardness attained to 311.5MPa, 3.45MPam1/2, 133.0GPa and 3.68GPa, respectively. The mass of the SiBCN ceramics lose by several percent below 930°C in air, and then keep unchanged above 1100°C. [Copyright &y& Elsevier]

Abstract: A six-layer functionally gradient material (FGM) of Ti–TiB–TiB2 was rapidly fabricated by spark plasma sintering (SPS) in vacuum. Both B and TiB2 were used and reacted with Ti to synthesize TiB. Adjusting the content ratio of B to TiB2 in individual layers could control the amount of synthesized TiB by two steps during sintering. The composition and microstructure of the layers in FGM were investigated by XRD, SEM and TEM. The synthesized TiB has needle-like, agglomerated and elongated morphologies. The content of agglomerated TiB increased and that of needle shape TiB decreased with increasing the target TiB volume fraction ranging from 20 to 60%. The elongated TiB was observed in the other two layers with higher target TiB volume fraction, which structure is similar to the agglomerated TiB. The FGM with Ti on one side to Ti–TiB–TiB2 on the other were fabricated at relative low sintering temperature and short dwelling time by spark plasma sintering. [Copyright &y& Elsevier]

MWCNTs modified Si 2 BC 3 N ceramics were prepared through SPS sintering mechanically alloyed amorphous Si 2 BC 3 N powder and MWCNTs at 1900 °C in N 2 atmosphere. The phase evolutions, microstructures and mechanical properties of the prepared ceramic were characterized by XRD, SEM and TEM (SAED and HRTEM), as well as the properties testing. The results show that the Si 2 BC 3 N ceramics are mainly composed of β-SiC, α-SiC and BN(C) phases. The introduction of MWCNTs can stimulate the formation of β-SiC in comparison with the pure Si 2 BC 3 N ceramics. Meanwhile, the particle sizes of BN(C) and SiC are reduced with the introduction of MWCNTs. Furthermore, the MWCNTs are mainly embedded in the Si 2 BC 3 N matrixes, contributing to enhanced bonding. Judging from the interfacial characteristic, the strengthening and toughening mechanisms of MWCNTs in Si 2 BC 3 N ceramics can be classified as “crack bridging”, “pull-out” and “crack deflection”. Based on these effects, the 1 vol% MWCNTs incorporated Si 2 BC 3 N ceramics have much higher flexural strength and fracture toughness of 462.1 MPa and 5.54 MPa·m 1/2 , respectively. [ABSTRACT FROM AUTHOR]

A novel pressure-assisted transient viscous phase sintering process has been used to fabricate dense BN-ZrO 2 -SiC composites at relatively low sintering temperatures. The sintering behavior and densification mechanism of BN-ZrO 2 -SiC composites incorporated with B 2 O 3 as transient viscous phase have been investigated. A rapid densification process occurs at about 1300 °C, which is attributed to the in-situ formation of SiO 2 by chemical reactions among ZrO 2 , SiC and B 2 O 3 . BN-ZrO 2 -SiC composites sintered at 1300 °C under 100 MPa exhibit a relative density of 95.9%, a flexural strength of 242 MPa and a fracture toughness of 4.1 MPa m 1/2 . [ABSTRACT FROM AUTHOR]

Abstract: Alumina ceramics were prepared by spark plasma sintering (SPS). Effects of manipulating the SPS power output on densification, microstructure and flexural strength of the obtained alumina ceramics were investigated. The results showed that use of a few discrete high amplitude units as the heating power instead of the low continuous conventional power output for heating significantly improved compaction of the alumina particles in the early stage of densification, hence more homogeneous microstructures in the consolidated materials. The better flexural strength of the resultant alumina ceramics indicated the higher efficiency of the SPS heating power rearrangement. [Copyright &y& Elsevier]

Abstract: TaC/SiC composites with 5–40vol.% 6H–SiC were fabricated by spark plasma sintering at 1800°C for 5min. Effects of SiC concentrations on the densification, microstructure, and mechanical properties of the materials were investigated. The results showed the densification process of the TaC/SiC composites was composed of six sequent stages. SiC addition was effective in eliminating the closed porosities in the final stage to yield fully dense TaC/SiC composites at 20vol.% SiC concentrations and above. TaC grain sizes decreased with SiC concentration increase. The 40vol.% SiC composition had the highest flexure strength and fracture toughness up to 703MPa and 6.8MPam1/2 due to the reinforcement of the SiC agent. The TaC/SiC composites with 20 and 40vol.% SiC showed good flexural strength at 1400°C. [Copyright &y& Elsevier]

Abstract: Nano-sized Si–B–C–N powders nearly amorphous with different mole ratio of Si/C were prepared by mechanical alloying (MA) technique using cubic silicon (c-Si), hexagonal boron nitride (h-BN) and graphite powder (Cp) as starting materials, then consolidated at 1800°C under a pressure of 40MPa for 3min by spark plasma sintering (SPS). Sub-micrometer sized β-SiC and nano-sized BCN phase were formed as the final components in the ceramics. The grain size of the β-SiC tend to be a little coarser with the increase of the Si/C ratio as well as their total content, but no changes are observed for the fine sub-micrometer structure characteristics of β-SiC and BCN grains. Mechanical properties of the Si–B–C–N ceramics were found remarkably increased with the increase of the mole ratio of Si/C and their total relative content. Thermal physical properties, including thermal diffusivity, heat capacity, thermal conductivity, as well as thermal expansion coefficient were also studied. [Copyright &y& Elsevier]

Abstract: cBN/β-SiAlON composites with different cBN contents were fabricated by spark plasma sintering (SPS) process. The densification, thermal stability of cBN, microstructure and mechanical properties of the resultant composites were investigated. The addition of cBN particles to β-SiAlON could increase the Vickers hardness, flexural strength and fracture toughness of β-SiAlON. It is attributed to the high density, no obvious cBN to hBN transformation and good interface bonding between cBN grains and β-SiAlON matrix. [Copyright &y& Elsevier]

Abstract: Short-carbon-fiber-reinforced silicon carbide composites were prepared by hot-pressing with SiC powder, Polycarbosilane as precursor polymer and MgO–Al2O3–Y2O3 as sintering additives. The phase composition, microstructure and mechanical properties of the composites with different Polycarbosilane content were investigated. The results showed that, dense composites could be prepared at a relatively low temperature of 1800°C via the liquid-phase-sintering mechanism and the highest mechanical property was obtained for the composites with 20wt.% PCS and 8wt.% sintering additives. The amorphous interphase formed during sintering process in the composites not only contributed to the densification of the composites, but also improved the fiber–matrix bonding. The nano-silicon carbide derived from Polycarbosilane, could also play a role of improving the relative density of the composites. [Copyright &y& Elsevier]

Abstract: Y-α-SiAlON (Y1/3Si10Al2ON15) ceramics with 5wt.%BaAl2Si2O8 (BAS) as an additive were synthesized by spark plasma sintering (SPS). The kinetic of densification, phase transformation sequences and grain growth during sintering process were investigated. Full densification could be achieved by 1600°C without holding and using a heating rate of 100°Cmin−1, but the transformation from α-Si3N4 to α-SiAlON is not completed simultaneously with the densification process. The equilibrium phase assemblage could be reached after SPS at 1800°C for 5min and the resultant material possesses self-reinforced microstructure with high hardness of 19.2GPa and fracture toughness of 6.8MPam1/2. The complete crystallization of BAS is beneficial to the high temperature mechanical properties. The obtained could maintain the room strength up to 1300°C. [Copyright &y& Elsevier]

A series of TiB 2 –TiC composites were successfully fabricated through one-step and two-step pressureless sintering using powders obtained by high-energy ball-milling. Effects of ball-milling time on crystal size and morphology of powders as well as microstructural evolution and mechanical properties of TiB 2 –TiC composites were investigated. The crystal size of TiB 2 –TiC powders decreases to 14.7 nm after ball milling for 30 h. Two-step pressureless sintering is beneficial to the densification process without obvious grain coarsening. The core-rim structure of carbides in TiB 2 –TiC composites is formed by nonuniform diffusion of W atoms from the outside to the interior of TiC grains. The phenomenon of selective solution of WC into TiC grains was carried out through experiments and verification of first-principles DFT calculations. An in-situ TiB 2 plate toughened microstructure is developed for TiB 2 -40 wt %TiC composites two-step sintered at 1500 °C for 4 h and 2000 °C for 1 h with excellent comprehensive performances. [ABSTRACT FROM AUTHOR]