Search

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]

The in situ synthesized TiB reinforced titanium matrix composites have been prepared by spark plasma sintering at 800–1200 °C under 20 MPa for 5 min. The effects of sintering temperature and reinforcement volume fraction on flexural strength, Young’s modulus and fracture toughness of the composites are investigated. The titanium matrix consists of α-Ti and β-Ti phases, and the volume fraction of β-Ti increases with increasing sintering temperatures. The in situ synthesized TiB reinforcements are distributed randomly and uniformly in matrix. The transverse section of TiB has a hexagonal shape aligned along [010] direction, and the crystallographic planes of the TiB needles are always of the type . The 10 vol% TiB reinforced composite sintered at 1000 °C exhibits excellent mechanical properties. The flexural strength, Young’s modulus and fracture toughness of this composite are 1560 MPa, 137 GPa and 8.64 MPa·m1/2, respectively. [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: Yb- and Y-doped α-SiAlON ceramics were effectively bonded by spark plasma sintering in less than 20min without using any interlayer materials at 1650–1700°C. The microstructures and mechanical properties of the joints were investigated by means of SEM, STEM, EDX, and three-point bending tests. The results showed that α-SiAlON joint formation was accompanied by fundamental rare earth diffusion. The intergranular liquids in the α-SiAlON ceramics at the bonding temperatures provided the diffusion paths for the species. α-SiAlON grain growth across the joining interfaces modified the joint microstructures to secure high bonding strength. [Copyright &y& Elsevier]

Monolithic α-SiC particles and in situ β-Si3N4-reinforced barium aluminosilicate (BAS) glass ceramic matrix composites with good mechanical properties were obtained by spark plasma sintering. However, attempts at the synthesis of ternary phase composites in order to maximize the reinforcing effects by co-adding α-SiC and β-Si3N4 were only partly successful. β-Si3N4 grain growth was remarkably hindered by the coexistent α-SiC, thus the resultant composite suffered a loss of reinforcement efficiency. [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]

The 0.8Bi 3.15 Nd 0.85 Ti 3 O 12 (BNdT)-0.2CoFe 2 O 4 (CFO) composite multiferroic ceramics have been fabricated by spark plasma sintering (SPS) at 850 °C. The relative density of as-sintered SPS ceramic reaches 97.4 (±0.3)%. The composites are composed of pure BNdT and CFO phases without any preferred c -orientation. The a -orientation preference is more obvious perpendicular to the pressure direction. The average grain-sizes of BNdT and CFO are 163 and 146 nm, respectively. The BNdT phase has more grains below 100 nm (∼20%). The super energy-dispersive X-ray analyses suggest no serious reaction between BNdT and CFO. The Raman spectrum verifies the nano-structure of the SPS ceramic via the broadening bands and peak shifts. The Curie temperature of the SPS ceramic declines to 560 °C with stabilized dielectric loss. The grain boundary resistance plays a dominant role on impedance above 700 °C. The remanent polarization approaches to 15.2 μC/cm 2 (300 kV/cm) with lower coercive fields (−89/+95 kV/cm). [ABSTRACT FROM AUTHOR]

In this study, amorphous nano-sized Si 3 N 4 powders were surface modified by BN. Then a stable and dense Si 2 N 2 O ceramic was fabricated using the BN surface modified powders, rather than Si 2 N 2 O-Si 3 N 4 composites usually prepared from nano-sized Si 3 N 4 powders without surface modification. The effect of BN surface modification on phase transformation, microstructure and mechanical properties were also investigated. Si 2 N 2 O ceramics obtained by means of the present method have no residual Si, crystal SiO 2 and other oxide additives, which are usually produced by other methods and may seriously influence high-temperature structural and functional applications of Si 2 N 2 O ceramics. [ABSTRACT FROM AUTHOR]

The mixture of 5 wt% LaB 6 and mechanically alloyed Si-B-C-N powders was conventionally ball-milled and then compacted by spark plasma sintering at 1250–2000 °C and 50 MPa. Densification, microstructural evolution and mechanical properties of the as-prepared La/Si-B-C-N monoliths were investigated. At 1360 °C, sintering initiates coupled with rapid densification caused by particle rearrangement and plastic deformation. Grain-boundary sliding and atomic diffusion lead to further densification when sintering continues. Only SiC and La-containing BN(C) phases are detected in La/Si-B-C-N monoliths sintered at temperatures higher than 1900 °C. The monoliths sintered at 2000 °C show a high fracture toughness (4.6 MPa m −1/2 ) attributed mainly to lamellar La-containing BN(C) grains. [ABSTRACT FROM AUTHOR]

Si-B-C-N ceramic monoliths with LaB 6 additive were prepared by mechanical alloying followed by spark plasma sintering. The microstructures and mechanical properties were investigated compared to LaB 6 -free Si-B-C-N counterparts. After sintered at 1900 °C/50 MPa, the La/Si-B-C-N monoliths provide well-developed BN(C) flakes (≤100 nm in thickness) and improved fracture toughness, while the BN(C) ones show no lamellar microstructures in Si-B-C-N systems. The solid-solution of La in BN(C) grains promotes ordered arrangement of BN(C) along the (0002) plane causing in situ growth of BN(C) thus leading to an increase in toughness by 40% (from 5.6 to 7.8 MPa m −1/2 ). [ABSTRACT FROM AUTHOR]

The possibility of incorporating graphene platelets (GPL) as nanofillers in SiBCN nanocomposites was studied to evaluate the potential improvement on mechanical properties. GPL-SiBCN mixed powders prepared by ball milling of graphene platelets and SiBCN amorphous powders with Al 2 O 3 balls was consolidated by spark plasma sintering technique to form bulk samples with different contents of graphene platelets. The effect of added graphene platelets on the improvement of fracture toughness is particularly significant and the fracture toughness increases rapidly with increasing GPL content in the composites. Nearly 650% increase in fracture toughness of GPL/SiBCN ceramic with 5 vol% GPL content, reaching a maximum of 5.40±0.63 MPa·m 1/2 . Results show that the nanofillers in ceramic nanocomposites remained uniformly and survived at high temperature. Main toughening mechanisms in graphene platelets reinforced SiBCN ceramic are pull-out, bridging, crack penetration graphene and crack deflection. [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 20vol.% SiC addition were densified by spark plasma sintering at 1600–1900°C for 5min under 40MPa. Effects of sintering temperatures on the densification, microstructures and mechanical properties of composites were investigated. The results showed the materials achieved >98% of theoretical density at a temperature as low as 1600°C. While the TaC grains grew slightly with the sintering temperature increasing, the SiC particles in materials decreased in size. Equiaxed to elongated grain morphology transformation was observed in the SiC phase in the 1900°C material to obtain a higher flexural strength and fracture toughness of 715MPa and 6.7MPam1/2, respectively. Lattice enlargement of the TaC phase in the 1900°C material suggested possible Si diffusion into TaC grains. Ta was also detected in SiC grains by energy dispersive spectroscopy. Glassy pockets present at multi-grain junctions explained the enhanced densification. [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: 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 novel solution and aging (STA) heat treatment was proposed to improve the strength and ductility of Ti-6Al-4V alloy simultaneously. Effects of the novel heat treatment on microstructure and mechanical properties of the Ti-6Al-4V alloy prepared by spark plasma sintering (SPS) were studied in this work. The crystalline structure and microstructure of both the as-fabricated Ti-6Al-4V alloy and the STA Ti-6Al-4V alloy were observed using X-ray diffraction (XRD) technique, optical microscope (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), respectively. The XRD patterns indicated that the two Ti-6Al-4V samples have the similar crystalline structure with α phase and β phase. However, the results of OM images suggested that the microstructure of Ti-6Al-4V alloy was transformed from the Widmanstätten structure to a hierarchical structure which included the basket-weave structure and the Widmanstätten structure after the STA heat treatment. Apart from the above-mentioned microstructure, the hierarchical structure also exhibited specifically some fine dispersed β surrounded by some equiaxed α. Moreover, the results of the room temperature tensile tests revealed that the STA heat treatment could improve the strength and ductility of the Ti-6Al-4V alloy simultaneously. Based on the observation of TEM images, the increment of the elongation of the STA Ti-6Al-4V alloy can be attributed to the effect of annealing twins and equiaxed α, and the total strength increments should be caused by the dispersion strengthening effect of the dispersed β. • After the STA heat treatment, the microstructure of the Ti-6Al-4V alloy can be transformed from the Widmanstätten structure to the hierarchical structure • The improvement of the strength and elongation of STA Ti-6Al-4V alloy can be attributed to the comprehensive effects of annealing twins, equiaxed α, and the fine β, respectively [ABSTRACT FROM AUTHOR]