ZrC Grains Research Articles

Microstructure and mechanical properties of Mo-ZrC-Cu composites synthesized by reactive melt infiltration of Zr-Cu melt into porous Mo2C preforms at 1300 °C

Mo-ZrC-Cu composites have been synthesized by reactive melt infiltration of Zr-Cu binary alloys into porous Mo2C preforms at 1300 °C for 10 min in argon. The influence of Zr content in the Zr-Cu infiltrator on microstructure and mechanical properties of Mo-ZrC-Cu composites are investigated. The as-synthesized composites consist of three major phases of Mo, ZrC and Cu, after a complete reaction of Mo2C(s) + Zr-Cu(l) → Mo(s) + ZrC(s) + Cu(l). Mo2Zr phase is formed when Zr content exceeds 50 at% in the Zr-Cu infiltrator. The formed ZrC grains have sizes less than 1 μm with Mo solid solute inside. Meanwhile, nanoscale zones enriched in Cu and C are also detected in ZrC grains. The angular ZrC particles and rounded Mo grains become larger with increasing Zr content in the Zr-Cu infiltrator. With decreasing Cu content from 43.5 to 31 vol% in Mo-ZrC-Cu composites, the elastic modulus and flexure strength increase from 146 to 156 GPa and from 542 to 569 MPa, respectively.

Fabrication of TiC–ZrC–Co composites with refined microstructure using ultrafine TiC–ZrC mixture powders

Ultrafine TiC–ZrC mixture powders with various Ti/Zr molar ratios (9:1, 8:2, 7:3, and 6:4) were synthesized by carbothermal reduction of high–energy milled TiO2–ZrO2–C. ZrC was found to be insoluble in the TiC lattice at 1400–1500 °C; as a result, carbothermal reduction of TiO2–ZrO2–C mixtures led to the formation of the TiC–ZrC mixture powders rather than the (Ti,Zr)C solid solution. TiC–ZrC–Co composites prepared using the TiC–ZrC mixture powders exhibited a refined microstructure, due to the inhibition of the coalescence of TiC grains by ZrC grains distributed in the TiC–ZrC mixture powders. In other words, the ZrC particles distributed in the mixture powders inhibited the coalescence of TiC grains during liquid–phase sintering, resulting in the formation of TiC–ZrC–Co composites with refined microstructure. The refined microstructure of these composites favorably influenced their properties: in particular, the experimental measurements highlighted a significant improvement in the mechanical properties (HV = 14.8–16.0 GPa, KIC = 7.2–7.6 MPa m1/2) of the composites prepared from the ultrafine TiC–ZrC mixture powders, compared with those (HV = 11.1–13.3 GPa, KIC = 5.7–6.3 MPa m1/2) of conventional TiC–ZrC–Co composites.

In situ synthesis, microstructure and mechanical properties of nano-structured SiC-ZrC composite prepared by spark plasma sintering

The synthesis route, microstructure and mechanical properties of SiC-ZrC composites prepared from a mixture of ZrSi2-C powders by reactive spark plasma sintering (R-SPS) were investigated. The reaction between ZrSi2 and C began to occur at 550 °C and mostly completed at 1300 °C. On the other hand, the densification during SPS occurred mainly between 1490 °C and 1750 °C, indicating that the reaction did not directly promote the densification. A fully dense SiC-ZrC composite (relative density > 99%), in which fine SiC (∼260 nm) and ZrC (∼360 nm) grains distributed homogeneously, was prepared by SPS at 1750 °C under a pressure of 40 MPa. The formation of nano-composites can be ascribed to the high energy ball milling of raw materials, fine ZrC and SiC grains formed during R-SPS, and low sintering temperature by R-SPS process. The Vickers hardness, fracture toughness and Young's modulus of the composite were 23.3 GPa, 2.87 MPam1/2, and 319 GPa, respectively.

Mechanical properties and grain orientation evolution of zirconium diboride-zirconium carbide ceramics

The effect of ZrC on the mechanical response of ZrB2 ceramics has been evaluated from room temperature to 2000°C. Zirconium diboride ceramics containing 10vol% ZrC had higher strengths at all temperatures compared to previous reports for nominally pure ZrB2. The addition of ZrC also increased fracture toughness from ∼3.5MPam for nominally pure ZrB2 to ∼4.3MPam due to residual thermal stresses. The toughness was comparable with ZrB2 up to 1600°C, but increased to 4.6MPam at 1800°C and 2000°C. The increased toughness above 1600°C was attributed to plasticity in the ZrC at elevated temperatures. Electron back-scattered diffraction analysis showed strong orientation of the ZrC grains along the [001] direction in the tensile region of specimens tested at 2000°C, a phenomenon that has not been observed previously for fast fracture (crosshead displacement rate=4.0mmmin−1) in four point bending. It is believed that microstructural changes and plasticity at elevated temperature were the mechanisms behind the ultrafast reorientation of ZrC.

Low-temperature fabrication of porous ZrC/C composite material from molten salts

In this work, biological ceramic-wood porous ZrC/C materials were prepared in a KCl-KF molten salt reaction medium, using Zr as a metal source and a C template as C source. The effects of reaction temperature and salts/Zr mole ratio on the formation of porous biomorphic ZrC/C ceramics were investigated. The phase compositions and morphological structures of the C templates and porous ZrC/C ceramics were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and pore size analysis. The results showed that the ZrC grains were equiaxed and enhanced the oxidation resistance of the material. Furthermore, a possible reaction mechanism for the formation of porous biomorphic ZrC/C ceramics in molten salt is proposed.

Ultra high-pressure spark plasma sintered ZrC-Mo and ZrC-TiC composites

Ultra-high-pressure spark plasma sintering was applied to ZrC-20wt%Mo and ZrC-20wt%TiC composites with a pressure up to 7.8GPa and temperatures of 1550°C and 1950°C. Mechanical performance of the composites was benchmarked against a plain ZrC produced by the same method. Both composites outperformed the pure ZrC with superior hardness and indentation fracture toughness of 2239HV1 and 5.4MPam1/2, and 1896HV1 and 5.9MPam1/2, respectively, for ZrC-Mo and ZrC-TiC composites. It was shown that ultra-high compaction pressure affected the ZrC-20 wt%TiC miscibility gap by lowering the temperature threshold from the usually applied 1800°C down to 1550°C resulting in formation of the solid state solution of (Zr,Ti)C. In contrast, the high pressure does not inhibit the carburisation of Mo with ZrC to form MoC, even when experiments were performed in a graphite free environment. The equiaxed morphology of ZrC grains along with a right-shift in XRD peaks for ZrC indicates dissolution of Mo in ZrC resulting in formation of the solid solution of (Zr,Mo)C. High-temperature X-ray diffraction analysis under oxidation conditions was performed on the samples showing degradation of ZrC-20wt%Mo due to the oxidation of Mo at high-temperature leading to MoO3 vaporisation. Conversely, the oxidation of ZrC-20wt%TiC composites was characterised by formation of ZrO2 and TiO2 remaining stable up to 1500°C.

Reactive hot-pressing of ZrB2-ZrC-SiC ceramics via direct addition of SiC

A series of ZrB2-ZrC-SiC composites with various SiC content from 0 to 20vol% were prepared by reactive hot-pressing using Zr, B4C and SiC as raw materials. Self-propagating high-temperature synthesis (SHS) occurred, and ZrC grains connected each other to form a layered structure when the SiC content is below 20vol%. The evolution of microstructure has been discussed via reaction processes. The composite with 10vol% SiC presents the most excellent mechanical properties (four-point bending strength: 828.6±49.9MPa, Vickers hardness: 19.9±0.2GPa) and finest grain size (ZrB2: 1.52µm, ZrC: 1.07µm, SiC: 0.79µm) among ZrB2-ZrC-SiC composites with various SiC content from 0 to 20vol%.

Spark plasma sintered ZrC-Mo cermets: Influence of temperature and compaction pressure

The microstructure analysis and mechanical characterisation were performed on a ZrC-20wt%Mo cermet that was spark plasma sintered at various temperatures ranging between 1600 and 2100°C under either 50 or 100MPa of compaction pressure. The composite reached ~98% relative density for all experiments with an average grain size between 1 and 3.5µm after densification. The nature of SPS technology caused a faster densification rate when higher compaction pressures were applied. The difference in compaction pressures produced different behaviors in densification and grain structure: 1900°C, 100MPa produced excessive grain growth in ZrC; 1600°C, 50MPa revealed a very clear ZrC grain structure and Mo diffusion between carbide grains; and 2100°C, 50MPa exhibited the highest overall mechanical properties due to small clusters of Mo phases across the microstructure. In fact, this particular sintering regime gave the most optimal mechanical values: 2231 HV10 and 5.4MPa*m1/2, and 396GPa Young's modulus. The compaction pressure of SPS played a pivotal role in the composites’ properties. A moderate 50MPa pressure caused all three mechanical properties to increase with increasing sintering temperature. Conversely, a higher 100MPa pressure caused fracture toughness and Young modulus to decrease with increasing sintering temperature.

Microstructural effects on the sliding-wear resistance of ZrC–MoSi2 triboceramics fabricated by spark-plasma sintering

The effects were individually investigated of ZrC grain size and MoSi2 content on the lubricated sliding-wear resistance of ZrC–MoSi2 triboceramics densified by spark-plasma sintering (SPS). Microstructures with different average grain sizes were obtained by varying the high-energy ball-milling time of the ZrC–MoSi2 powder mixtures and their SPS temperature, while the microstructures with different secondary phase contents were obtained by varying the relative concentrations of ZrC and MoSi2 in the powder batches. Experimentally, it was found that the ZrC–MoSi2 triboceramics are all highly wear resistant, but also that wear resistance decreases as the ZrC grain size and MoSi2 content increase. The dominant wear mode was identified as abrasion, and the prevailing wear mechanism was plastic deformation accompanied by localized fracture. Accordingly, the wear trends are explained in terms of the hardness of the ZrC–MoSi2 triboceramics. Finally, the implications are discussed of providing the electrically-conductive ZrC–MoSi2 triboceramics with greater wear resistance via controlled processing.

Synergetic roles of ZrC and SiC in ternary ZrB2–SiC–ZrC ceramics

SiC and ZrC were used to tailor microstructures and improve properties of hot-pressed ZrB2-based ceramics. Grain growth kinetics and microstructural stability during annealing were studied. Compared with ZrC, SiC grains grew slower and were more effective to inhibit ZrB2 grain growth. ZrB2–20SiC–20ZrC (number in vol%) had the finest and the most stable microstructure, indicating synergistic effects of SiC and ZrC on grain growth. Also, ZrC and SiC played different roles on mechanical properties. Thermal residual stresses on SiC particles decreased from ∼800MPa in ZrB2–SiC to ∼400MPa in ZrB2–SiC–ZrC, due to the plastic deformation of ZrC. Crack deflection around ZrC grains was the major toughening mechanism (∼1 MPam1/2) in ZrB2–ZrC-based ceramics. The flexural strengths of ZrB2–SiC–ZrC were improved to 800MPa, due to smaller SiC cluster sizes and lower residual stresses. ZrB2–20ZrC had the largest Weibull modulus of 14.1, and the modulus decreased with an increase in SiC content.

Thermomechanical properties of a spark plasma sintered ZrC–SiC composite obtained by a precursor derived ceramic route

The thermomechanical behaviour of a spark plasma sintered ZrC-30wt% SiC composite, made with a ceramic precursor, are characterised and compared with monolithic ZrC. At room temperature, the composite and monolith materials exhibit similar elastic properties. The fine microstructure of the composite leads to an improvement of fracture toughness and flexural strength. During sintering of composite, the overall strain associated to the applied load is preferentially accommodated by the plastic deformation of ZrC and to a more restricted degree by the formation of stacking faults through β→α phase transition operating within SiC. As evidenced in the ZrC monolith, the plastic deformation in the ZrC grains of the composite corresponds to dislocation motion and formation of dislocation walls defining cells. The composites and monolithic material show similar compressive creep strain rates, at temperatures from 1500 to 1600°C and stresses between 60 and 100MPa. As suggested by the identified creep parameters and structural observations, it appears that the main deformation mechanism of the composite is preferentially accommodated by the SiC phase through dislocation motion in the crystal core that is rate-controlled by lattice diffusion of Si.

Effect of two-step reduction on ZrC size and dispersion

A two-step carbothermal reduction process produced zirconium carbide particles with less aggregation and smaller ZrC grains than those produced by one-step reduction. Reduction at 1500°C for 10min (1st step) and then at 1300°C for 30min (2nd step) produced significantly smaller agglomerations (1–8μm) and particles (33nm) than those produced using other reduction processes, which were 2–200μm and >1μm, respectively. The first high-temperature step allowed effective reduction, while the subsequent cooler step inhibited grain growth and agglomeration. The resulting ZrC particles showed a stoichiometric composition of ZrC0.97 through control of the carbon content. A sintered W–ZrC composite made using the two-step-reduced ZrC was harder and showed a more homogeneous dispersion of ZrC in the tungsten matrix than a composite made using one-step sintered ZrC.

Reactive Hot Pressing and Properties of Zr1−xTixB2–ZrC Composites

Reactive hot pressing was used to prepare Zr1−xTixB2–ZrC composites with advantageous microstructure and mechanical properties from ZrB2–TiC powders. The reaction mechanisms and the effects of different levels of TiC on the physical and mechanical properties of the resulting composite were explored in detail and compared to conventionally hot‐pressed ZrB2 and ZrB2–ZrC. Incorporation of 10 to 30 vol% TiC enabled full densification and restrained grain growth, reducing the final average grain size from 5.6 μm in pure ZrB2 to a minimum of 1.4 μm in samples with 30 vol% TiC. The flexural strengths and hardnesses of the composites sintered with TiC were consequently greater than the conventionally processed ZrB2–ZrC materials, increasing from 440 MPa and 17.4 GPa to a maximum of 670 MPa and 24.2 GPa at 10 vol% TiC. However, despite a decrease in the total average grain size, the flexural strength at higher TiC levels was limited by an increase in ZrC grain growth, which was observed to determine the flexural strength of the reaction sintered composites similar to the case of ZrB2–SiC.

Plasma arc welding of ZrB2–20vol% ZrC ceramics

Zirconium diboride ceramics containing 20 vol% zirconium carbide were preheated to 1450 ◦ C and plasma arc welded to produce continuous joints. Arc welding was completed using a current of 198 A, plasma flow rate of 0.75 l/min, and welding speed of ∼8 cm/min. Two fusion zones, having penetration depths of 4.4 and 2.3 mm, resulted in different microstructures. One fusion zone contained ZrB2 crystals, up to ∼1 mm in length, and a ZrB2–ZrC eutectic. The second fusion zone revealed ZrB2 and ZrC, along with C that was attributed to diffusion from the graphite support used during welding. ZrB2 and ZrC grains in the latter fusion zone were asymmetric, having an average maximum Feret diameter of 52.4 ± 53.2m and 10.8 ± 8.1m, respectively. Hardness, used to identify a heat affected zone for both weldments, increased from 12 GPa at the fusion zone boundary, to the hardness of the parent material, 15.2 ± 0.1 GPa. © 2014 Elsevier Ltd. All rights reserved.

Microstructure, Mechanical, and Thermal Properties of (ZrB2 + ZrC)/Zr3[Al(Si)]4C6 Composite

The microstructure, mechanical, and thermal properties of in situ hot‐pressed 30 vol% (ZrB2+ZrC)/Zr3[Al(Si)]4C6 composite have been investigated and compared with monolithic Zr3[Al(Si)]4C6 ceramic. The composite is composed of ZrB2 and ZrC grains embedded in a Zr3[Al(Si)]4C6 matrix. The composite shows superior hardness (Vickers hardness of 16.4 GPa), stiffness (Young's modulus of 415 GPa), strength (bending strength of 621 MPa), and toughness (fracture toughness of 7.37 MPa·m1/2) compared with monolithic Zr3[Al(Si)]4C6. The composite retains high modulus of 357 GPa at 1430°C (86% of that at ambient temperature) due to clean grain boundaries with no glassy phase. In addition, the composite exhibits higher specific heat capacity and thermal conductivity but slightly lower coefficient of thermal expansion compared with monolithic Zr3[Al(Si)]4C6. The calculation of the thermal stress fracture resistance parameter (R) predicts a much improved thermal shock resistance of the composite. Based on these results, (ZrB2+ZrC)/Zr3[Al(Si)]4C6 composites show promising potential for high‐temperature and ultra high‐temperature applications.

In situ synthesis mechanism of ZrB2–ZrC–C composites

In situ ZrB2–ZrC–C composites were synthesized via pyrolysis of a boron and zirconium containing precursor (PBZC), which was prepared by using phenol, paraformaldehyde, boric acid, ZrOCl2·8H2O, and acetylacetone as raw materials. The structure and thermal properties of PBZC were characterized by Fourier transform infrared spectra (FTIR) and thermogravimetry–derivative thermogravimetry (TG–DTG), respectively. The synthesis mechanism of ZrB2–ZrC–C composites was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that boron and zirconium are successfully introduced into the polymer. Decomposition of PBZC is completed at about 800°C with ZrO2, B2O3 and carbon as pyrolysis products. ZrB appears at 1350°C as an intermediate phase and will transform into ZrB2 at a relatively high temperature. ZrB2 forms at about 1500°C, followed by the appearance of ZrC when the amount of B2O3 is limited. The ZrB2–ZrC–C composites are hard and dense solids with ZrB2 and ZrC grains uniformly embedding in the carbon matrix.

Fabrication of Cf/ZrC composites by infiltrating Cf/C performs with Zr–Cu alloys

Carbon fiber-reinforced zirconium carbide matrix (Cf/ZrC) composites were fabricated at 1200°C, by vacuum infiltrating Cf/C performs with molten Zr7Cu10, ZrCu and Zr2Cu intermetallic compound respectively. The influences of Cu contents in the infiltrators on composition, microstructure and ablation resistance of the final composites were investigated. Results showed that: the products were composed of either single- or polycrystalline ZrC, C and Cu. With the increasing Cu content in the infiltrators, both the growth and crystallization of ZrC grains were inhibited, and the yield of ZrC decreased from 43.7vol% to 27.9vol%. Tested by an oxyacetylene torch, the composites show excellent anti-ablation properties affected apparently by the Cu contents.

Microstructure and ablation resistance of ZrC nanostructured coating for carbon/carbon composites

In order to improve the ablation resistance of carbon/carbon (C/C) composites, a ZrC nanostructured coating was prepared on C/C composites by chemical vapor deposition. Results show that the coating contains ZrC grains with the size of 20–30nm and the structure displays a high consistent orientation. This nanostructured coating has improvements in linear and mass ablation rates of 50.7% and 42.1% compared with those of the conventional ZrC coating. The good ablation resistance could be attributed to the efficient prevention of the coating cracking and the formation of the dense ZrO2 layer during ablation.

Microstructure and mechanical properties of Cf/ZrC composites fabricated by reactive melt infiltration at relatively low temperature

Abstract Carbon fiber-reinforced zirconium carbide matrix composites (Cf/ZrC) were prepared by vacuum infiltrating porous carbon/carbon preforms with molten Zr2Cu alloy at 1200 °C. X-ray diffraction, scanning electron microcopy and transmission electron microscopy analysis were used to characterize the composition and microstructure of the final composites. It was found that the matrix of the composites were composed of the Cu–Zr–C amorphous phase dispersed with either single- or polycrystalline ZrC. Based on the microstructural analysis, the formation mechanism of the matrix was proposed to be a solution-precipitation and grain coalescence process. The influence of the heat treatment at 1800 °C was also investigated. Results indicated that at very high temperature the volatilization of residual metal somewhat deteriorated the flexural strength and the elastic modulus, but the fracture toughness of the composites was improved due to the sintering of ZrC grains.

Modification of ZrB2 powders by a sol–gel ZrC precursor—A new approach for ultra high temperature ceramic composites

A simple method of integrating a powder processing technique with a sol–gel process to produce ultra high temperature ceramic (UHTC) composites is reported. ZrB2 powder was treated with a zirconium oxide-carbon sol–gel coating. Carbothermal reduction produced nanosized crystalline ZrC grains on the surface of ZrB2 powder. Detailed refinement of carbon content in the sol–gel coating was necessary to control the oxide reduction on the ZrB2 surface, while providing intrinsic carbon for the nanoparticle sol–gel phase. Microstructures and crystalline phases were analyzed using TEM, SEM, and XRD. It was found that carbothermal reduction of ZrO2 to form nano ZrC can be completed on the surface of ZrB2 at 1450 °C. The sol–gel coating creates a homogenous mix of ~200 nm ZrC in close proximity to the ZrB2 surface. Densification of the ZrB2-ZrC composite can be achieved by spark plasma sintering at 1800 °C. The amount of carbon added to the sol–gel precursor needs to be carefully tailored to dictate the final porosity and grain size of sintered composites.