Solid-state Spark Plasma Sintering Research Articles

Effect of TiB2 content on microstructure and mechanical properties of SiC composite ceramics by solid-state spark plasma sintering

Effect of TiB2 content on microstructure and mechanical properties of SiC composite ceramics by solid-state spark plasma sintering

Microstructure and mechanical properties of SiC composite ceramics modified by (TixZr1–x)B2 solid solution

Dense SiC-(TixZr1–x)B2 composite ceramics were prepared via solid-state spark plasma sintering (SPS) by controlling the proportion of ZrB2 (in the range of 5–25 vol%). Through data fitting, a linear functional relationship was established between x and 2θ for the (TixZr1–x)B2 solid solution, which rendered it amenable to characterization analysis. The results show that the 2-D morphology of (TixZr1–x)B2 tended to transform from angular to round as the ZrB2 proportion was increased, which was beneficial in crack deflection and increasing the fracture toughness. Moreover, the growth of SiC grains around the solid solution was inhibited, which improved its mechanical properties. The composite ceramic containing 15 vol% of ZrB2 had the best mechanical properties, with its Vickers hardness, bending strength and fracture toughness reaching 26.12 GPa, 499 MPa, and 6.45 MPa•m1/2, respectively.

β→α Phase Transformation and Properties of Solid-State-Sintered SiC Ceramics with TaC Addition.

Dense SiC-based composite ceramics were fabricated by means of the ex situ addition of TaC using solid-state spark plasma sintering (SPS). Commercially available β-SiC and TaC powders were chosen as raw materials. Electron backscattered diffraction (EBSD) analysis was conducted to investigate the grain boundary mapping of SiC-TaC composite ceramics. With the increase in TaC, the misorientation angles of the α-SiC phase shifted to a relatively small range. It was deduced that the ex situ pinning stress from TaC greatly suppressed the growth of α-SiC grains. The low β→α transformability of the specimen with the composition of SiC-20 vol.% TaC (ST-4) implied that a possible microstructure of newly nucleated α-SiC embedded within metastable β-SiC grains, which could have been responsible for the improvement in strength and fracture toughness. The as-sintered SiC-20 vol.% TaC (ST-4) composite ceramic had a relative density of 98.0%, a bending strength of 708.8 ± 28.7 MPa, a fracture toughness of 8.3 ± 0.8 MPa·m1/2, an elastic modulus of 384.9 ± 28.3 GPa and a Vickers hardness of 17.5 ± 0.4 GPa.

Solid-state spark plasma sintering of super wear resistant B4C–SiC–TiB2 triplex-particulate composites

B4C–SiC–TiB2 ceramic composites with equal volume fractions of the three phases (i.e., 1B4C–1SiC–1TiB2) were fabricated by solid-state spark-plasma sintering (SPS) from commercially available B4C, SiC, and TiB2 powders, first optimizing their densification temperature and then investigating for the first time the unlubricated sliding wear of the optimally SPS-ed composite. It is shown that SPS is optimal at 1800 °C (under 75 MPa pressure and 5 min soaking), which is much lower than the temperatures used so far for both the solid-state hot-pressing and SPS of this and other B4C–SiC–TiB2 composites. It is also shown that the optimally SPS-ed 1B4C–1SiC–1TiB2 composite has a triplex-particulate microstructure with evenly distributed carbide and boride grains whose sizes are essentially those of the corresponding starting powders, and that it is ultrahard (i.e., ∼35 GPa) and relatively tough (i.e., ∼4 MPa⋅m1/2). Moreover, it is demonstrated that, due to its ultra-high hardness and proneness to form a coherent oxide tribolayer, it is also very immune to wear, possessing an unprecedented super wear resistance to unlubricated sliding contact (i.e., ∼1.6·108 (N⋅m)/mm³), thanks to which it only undergoes very mild abrasion in the form of superficial plastic scratches with hardly any material removal by micro-fracture. Finally, implications of interest for the ceramics and hard-materials communities are discussed.

Study on the toughening mechanism of in-situ synthesis (TixZr1−x)B2 in solid-state sintered SiC composite ceramics

High-dense SiC-(TixZr1−x)B2 composite ceramics were fabricated by in-situ synthesis of (TixZr1−x)B2 solid solution using solid-state spark plasma sintering (SPS). 64 vol% SiC, 20 vol% ZrB2, 15 vol% TiB2, and 1 vol% graphite powders are chosen as raw materials. The composite ceramics has the relative density of 99.97 %, the Vickers hardness of 24.71 GPa, the flexure strength of 435 MPa and the fracture toughness of 8.05 MPa • m1/2. Compared with the single-phase SiC ceramics and SiC-TiB2 composite ceramics, the fracture toughness of SiC-(TixZr1−x)B2 composite ceramics increased by 242.6 % and 53.6 %, respectively. A shell-core structure is found in the SiC-(TixZr1−x)B2 composite ceramics, in which (TixZr1−x)B2 solid solution is the core and fine SiC grain is the shell. The results show that the toughening effect of solid-state sintered SiC-(TixZr1−x)B2 composite ceramics is attributed to the shell-core structure.

Spark plasma sintering of graphene reinforced silicon carbide ceramics

Abstract Silicon carbide (SiC) ceramics have superior properties in terms of wear, corrosion, oxidation, thermal shock resistance and high temperature mechanical behavior, as well. However, they can be sintered with difficulties and have poor fracture toughness, which hinder their widespread industrial applications. In this work, SiC-based ceramics mixed with 1 wt% and 3 wt% multilayer graphene (MLG), respectively, were fabricated by solid-state spark plasma sintering (SPS) at different temperatures. We report the processing of MLG/SiC composites, study their microstructure and mechanical properties and demonstrate the influence of MLG loading on the microstructure of sintered bodies. It was found that MLG improved the mechanical properties of SiC-based composites due to formation of special microstructure. Some toughening mechanism due to MLG pull-out and crack bridging of particles was also observed. Addition of 3 wt% MLG to SiC matrix increased the Vickers hardness and Young's modulus of composite, even at a sintering temperature of 1700 °C. Furthermore, the fracture toughness increased by 20% for the 1 wt% MLG-containing composite as compared to the monolithic SiC selected for reference material. We demonstrated that the evolved 4H-SiC grains, as well as the strong interactions among the grains in the porous free matrices played an important role in the mechanical properties of sintered composite ceramics.

Correlation between processing conditions, microstructure and charge transport in half-Heusler alloys

Abstract Five bulk samples of n-type Zr 0.25 Hf 0.75 NiSn 0.975 Sb 0.025 half-Heusler (HH) alloy were fabricated by reacting elemental powders via (1) high temperature solid state (SS) reaction and (2) mechanical alloying (MA), followed by densification using spark plasma sintering (SPS) and/or hot pressing (HP). A portion of the sample obtained by SS reaction was mechanically alloyed before consolidation by hot pressing (SS–MA–HP). X-ray powder diffraction and transmission electron microscopy studies revealed that all SS specimen (SS–SPS, SS–HP, SS–MA–HP) are single phase HH alloys, whereas the MA sample (MA–SPS) contains metallic nanoprecipitates. Electronic and thermal transport measurements showed that the embedded nanoprecipitates induce a drastic increase in the carrier concentration ( n ), a large decrease in the Seebeck coefficient (S) and a marginal decrease in the lattice thermal conductivity ( κ l ) of the MA–SPS sample leading to lower ZT values when compared to the SS–HP samples. Constant values of S are observed for the SS series regardless of the processing method. However, a strong dependence of the carrier mobility ( μ ), electrical conductivity ( σ ) and κ l on the processing and consolidation method is observed. For instance, mechanical alloying introduces additional structural defects which enhance electron and phonon scattering leading to moderately low values of μ and large reduction in κ l . This results in a net 20% enhancement in the figure of merit (ZT=0.6 at 775 K). HH specimen of the same nominal composition with higher ZT is anticipated from a combination of SS reaction, MA and SPS (SS–MA–SPS).

Sealants Aim to Reduce Noise Levels in Automobiles

Silicon carbide (SiC) ceramics have superior properties in terms of wear, corrosion, oxidation, thermal shock resistance and high temperature mechanical behavior, as well. However, they can be sintered with difficulties and have poor fracture toughness, which hinder their widespread industrial applications. In this work, SiC-based ceramics mixed with 1 wt% and 3 wt% multilayer graphene (MLG), respectively, were fabricated by solid-state spark plasma sintering (SPS) at different temperatures. We report the processing of MLG/SiC composites, study their microstructure and mechanical properties and demonstrate the influence of MLG loading on the microstructure of sintered bodies. It was found that MLG improved the mechanical properties of SiC-based composites due to formation of special microstructure. Some toughening mechanism due to MLG pull-out and crack bridging of particles was also observed. Addition of 3 wt% MLG to SiC matrix increased the Vickers hardness and Young's modulus of composite, even at a sintering temperature of 1700 °C. Furthermore, the fracture toughness increased by 20% for the 1 wt% MLG-containing composite as compared to the monolithic SiC selected for reference material. We demonstrated that the evolved 4H-SiC grains, as well as the strong interactions among the grains in the porous free matrices played an important role in the mechanical properties of sintered composite ceramics.