SiC Powder Mixtures Research Articles

Spark plasma sintering of hard wear‐resistant graphene nanoplatelet–reinforced TiB2 + SiC composites from TiC–B4C–SiC

AbstractGraphene nanoplatelet (GNP)–reinforced TiB2 + SiC composites were fabricated by reactive spark plasma sintering (SPS) from a TiC–B4C–SiC powder mixture with equal‐volume percentages, optimizing their SPS temperature and evaluating their unlubricated sliding wear against diamond. First, it is shown that during the heating ramp of the SPS cycle, TiC and B4C react according to the chemical reaction 2TiC + B4C → 2TiB2 + 3C, and that the thus‐formed C is graphenized as GNPs, leading to composites with microstructures consisting of a ceramic matrix of fine TiB2 and SiC grains with abundant randomly oriented GNPs at grain boundaries. It is also shown that this reactive SPS is optimal at 2000°C (under 75 MPa pressure and 5 min soaking), resulting in a very hard (∼28.5–29.9 GPa) and very tough (∼6.7(3) MPa m1/2) composite. And second, it is shown that these two properties and its proneness to develop an oxide tribolayer make this composite very resistant to unlubricated sliding wear against diamond (∼2.8(1)·108 (N m)/mm3), undergoing only very mild two‐body abrasion. Finally, opportunities for the fabrication of toughened and very hard ceramic composites for contact‐mechanical and tribological applications are discussed.

The Crystal Structure of Al4SiC4 Revisited.

Al4SiC4 is a ternary wide-band-gap semiconductor with a high strength-to-weight ratio and excellent oxidation resistance. It consists of slabs of Al4C3 separated by SiC layers with the space group of P63mc. The space group allows Si to occupy two different 2a Wykoff sites, with previous studies reporting that Si occupies only one of the two sites, giving it an ordered structure. Another hitherto unexplored possibility is that Si can be randomly distributed on both 2a sites. In this work, we revisit the published ordered crystal structure using experimental methods and density functional theory (DFT). Al4SiC4 was synthesized by high-temperature sintering at 1800 °C from a powder mixture of Al4C3 and SiC. Neutron diffraction confirmed that Al4SiC4 crystallized with the space group of P63mc, with diffraction patterns that could be fitted to both the ordered and the disordered structures. Scanning transmission electron microscopy, however, provided clear evidence supporting the latter, with DFT calculations further confirming that it is 0.16 eV lower in energy per Al4SiC4 formula unit than the former. TEM analysis revealed Al vacancies in some of the atomic layers that can introduce p-type doping and direct band gaps of 0.7 and 1.2 eV, agreeing with our optical measurements. Finally, we propose that although the calculated formation energy of the Al vacancies is high, the vacancies are stabilized by entropy effects at the high synthesis temperature. This indicates that the cooling procedure after high-temperature synthesis can be important in determining the vacancy content and the electronic properties of Al4SiC4.

An empirical study of the impacts of parameters in micro electrochemical drilling of Al 7075 alloy composites with SiC and fly-ash

The Electrochemical Drilling Technique (EDT) is utilized to bore metal alloys into the desired geometric forms. The present study investigates that various typical electrochemical drilling process variables, line supply-voltage (VT), electrolytic solution (ES), and pulse-on time (PT), impact the output responses namely material extraction rate as well as surface-roughness of stir cast Al7075 alloy, SiC, and fly-ash powder mixtures. These aluminum-matrix composites could be used to construct bridges, frames, and containers that will store pollutants, dairy, as well as other corrosive compounds; they can also be used to replace stainless steel, which is used in salty areas to avoid corrosion. Taguchi's experimental design is utilized in this study to investigate the effects of every input parameter on the Material-Extraction Rate (MER) and surface-roughness. Also, the significance of each parameter has been identified using an analysis of variance.

Investigation on aluminum based surface composite through FSP using metal (Fe-Sn-Mn) and ceramic (SiC) reinforcements

In the present study, the surface composite was fabricated via friction stir processing on AA5083 using mixture of Fe powder, SiC, Sn and Mn powder. Microstructural characterization with the help of bead geometry and micro-hardness analysis were performed to study the various zones of the processed samples. L4 orthogonal array from the Taguchi method is used for analysis. Improvement in microstructure and hardness is achieved at a rotational speed of 900 rpm, traverse speed of 50 mm/min and 24 mm shoulder diameter. Grain size is varying from one zone to another and enhanced properties are obtained because of grain refinement after friction stir processing.

Oxidation behavior of Al-doped Ti3SiC2-20 wt.%Ti5Si3 composite

In this work, an aluminum-doped Ti3SiC2-20 wt.% Ti5Si3 composite was prepared through reactive spark plasma sintering (SPS) from a powder mixture of Ti, SiC, C, and Al. The microstructure evolution of the formed oxide scales onto this composite were investigated in the temperature range of 1000–1400 °C in air. Up to 1200 °C, the exposed surfaces were highly protected by a continuous and dense α-Al2O3 layer with a good adherence that acts as a barrier diffusion. Above this temperature, the breakaway oxidation occurs, leading to an oxidation speed-up, which results in a thick oxide scale formation with low oxidation protective capacity. Scanning electron microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), X-Ray Diffraction (XRD), and Raman spectroscopy analysis of the oxide scales at different temperatures revealed that Al2TiO5 grain growth is the main deterioration factor of the protective α-Al2O3 layer. The oxidation kinetics of this composite at 1100 °C is comparable with that of the best MAX phases in terms of oxidation resistance, with a parabolic rate constant (Kp) of 3.08 × 10−10 kg2/m4s.

Diffusivity of Oxygen in Yttrium Silicates Estimated By Using High-Temperature Oxidation of Their Composites Dispersed with SiC Particles

Yttrium silicates, Y2SiO5 and Y2Si2O7, have been studied as candidate materials for the environmental barrier coating (EBC) system on SiC/SiC composites for advanced gas turbine blades because of low oxygen permeability, low volatility in steam conditions, and comparable thermal expansion with SiC/SiC composites. In order to design the EBC system, diffusion properties of yttrium silicates are important. In this work, diffusivity of oxygen in yttrium silicates is estimated by using kinetics of high-temperature oxidation of their composites dispersed with SiC particles. Assuming oxidation of SiC particles dispersed in yttrium silicates is promoted mainly with inward diffusion of oxygen, diffusion of oxygen in yttrium silicates can be estimated. Y2SiO5 powder was synthesized by using the solid-state reaction technique with Y2O3 and SiO2 powders at 1400ºC for 20 h in air. Y2Si2O7 powder was prepared with the solid-state reaction process from powder mixture of Y2O3 and SiO2 at at 1500ºC for 24 h in air. Densified bulks of yttrium silicates dispersed with 5 vol% SiC particles were obtained with the pulsed electric current sintering of powder mixture of yttrium silicate and SiC. The bulk samples were oxidized at 1300ºC in air. Depth of the zone in which SiC particles are oxidized was measured by observing the cross-section with scanning electron microstructure. Thickness of the oxidized zone obeys the parabolic law. In the both cases, the oxidation product layers were not observed significantly on the surface of the composites after high temperature oxidation. These results mean that outward diffusion of Y or Si did not occur significantly for oxidation of SiC dispersed in the yttrium silicates. That is, the oxidation of the SiC dispersoid was conducted with inward diffusion of oxygen. Diffusion coefficient of oxygen in yttrium silicates can be obtained as shown in Table 1. The value for Y2SiO5 is larger than that for Y2Si2O7. This fact means that the protection performance of oxygen diffusion on Y2Si2O7 is better than that on Y2SiO5 for the EBC applications.Table 1 Diffusion coefficients of oxygen in yttrium silicates at 1300°C. Y2SiO5 Y2Si2O7 D O/ m2s-1 2.8×10-16 1.3×10-18

Analysis of SiC mixture densification in explosive compaction

The paper presents the results of research into how the binder content and the Shockwave compression parameters affect SiC and Ti powder mixture densification in explosive compaction. The microstructure of the resulting compacted metal was studied by scanning electron microscopy. Phase and chemical composition was studied by X-ray crystallography and energy-dispersive analysis. It was found that at higher silicon carbide concentrations and higher powder heating temperatures, Shockwave compression reduced the residual porosity of the compacted metal to 2%. The microstructure was a carbide-silicon matrix with titanium inclusions. The obtained material matched the initial components in phase composition.

Formation of the Structure of Powder Materials Based on Silicon Carbide by Explosive Compaction

The possibility of producing powder composite materials in the SiC–Ti system by explosive compaction without subsequent sintering was studied. It was found that, under these conditions, the densification of SiC and Ti powder mixtures is due to the interparticle displacement and deformation of particles of the carbide phase. It was shown that the main condition for the consolidation is the heating of the initial powder mixture by shock-wave compression to temperatures above 780°C.

Effect of SiC Content on the Microstructure and Properties of Zr2Al4C5/SiC Composites in situ Fabricated by Spark Plasma Sintering

Zr2Al4C5/SiC composite ceramics were successfully fabricated from the powder mixture of Zr, Al, C and SiC by spark plasma sintering method. The composition-dependent densification, phase evolution, microstructure and mechanical properties of the composite ceramics were studied. With increasing the SiC content in the starting powder mixture, the densification behavior of sintered samples was promoted. It is found that the as-sintered products are mainly composed of Zr2Al4C5 matrix and SiC reinforcement, and the fine SiC particles tend to disperse on the matrix grain boundaries. Besides, the addition of SiC particles can evidently hinder the coarsening of Zr2Al4C5 grains. Both the Vickers hardness and Young’s modulus of composites ceramics gradually increase as increasing the SiC content. The fracture toughness of the composites decreases first then increases with the increase in the SiC and the Zr2Al4C5/30vol%SiC sample possesses the maximum value of 4.4MPa·m1/2.

Microstructure and mechanical properties of B4C–TiB2–SiC composites fabricated by spark plasma sintering

Boron carbide ceramics have broad application prospects due to their excellent performance. However, their poor sinterability and low fracture toughness limit their application, especially in the field of bulletproof armor. In this work, B4C–TiB2–SiC composites were successfully prepared by spark plasma sintering (SPS) with B4C, TiB2, and SiC powder mixtures. The effects of different SiC contents on the mechanical properties and microstructure of B4C–TiB2–SiC composites were investigated. The B4C–TiB2–SiC composites with 15 wt% SiC combined a relative density of 98.43%, a fracture toughness of 4.17 MPa m1/2, as well as Vickers hardness of 30.07 GPa. The addition of SiC can increase the toughness of B4C–TiB2–SiC composites while maintaining high hardness. The main reason for this behavior is grain refinement of B4C and TiB2 due to the pinning effect of the SiC phase.

Highly concentrated aqueous SiC slurry containing fine SiC powder: A new approach for ultra‐dense green body

AbstractSiC slurry with ultra‐high concentration up to 70 vol% was prepared using oxidized fine and coarse SiC powder mixture, and dense SiC green body with a relative density of 76% was fabricated by drying the slurry at ambient condition. Three approaches were performed to prepare highly concentrated SiC slurry; preparation of SiC powder having good dispersion behavior, optimization of the oxidation condition, and optimization of bi‐modal particle size distribution. An aqueous slurry with the solid loading up to 62 vol% could be prepared using fine (150 nm) SiC powder prepared by the mechanical alloying of Si and carbon. The surface property of the fine and coarse (10 μm) SiC powders was optimized using an oxidation treatment. The maximum solid loading of the fine SiC slurry prepared using oxidized powder was 66 vol%. By optimizing the mixing ratio of the oxidized fine and coarse SiC powder to 75:25, the solid loading of the SiC slurry could increase up to 70 vol%. The relative densities of the green bodies after drying 66, 68, and 70 vol% slurries were 69, 75.7, and 76.1%, respectively, which values were higher than those (58%) prepared by cold isostatic pressing under 200 MPa.

SiC and Al surface cladding of Ti-6Al-4V for improved wear properties – The binary advantage

Ti-6Al-4V enjoys high specific strength, toughness and excellent corrosion resistance, but suffers high friction coefficient, severe adhesive wear and sensitivity to fretting wear. Laser surface cladding is one of the surface modification techniques used for improving on these demerits. Using a 4.4Kw continuous wave Nd-YAG laser processor, the surface cladding of as received Ti-6Al-4V alloy was done with mixtures of SiC and Al powders in different ratios. The SiC powder can serve as reinforcing particles and helps improve surface wear properties in resulting surface metal matrix composite while aluminium improves on the wetting between the metal and the reinforcement SiC phase. The success of this, however, depends on the careful optimisation of the powder ratio, which dictates the resulting phases and microstructural evolutions. Study of the cladding with scanning electron microscope (energy dispersive spectroscopy), optical microscope and x-ray diffraction revealed formation of intermetallic phases such as AlSiTi2, Ti7Al5Si12, TiSi2, AlSi3Ti2, Al6Ti19, Ti2VAl, AlTi3, AlCTi2, Ti3SiC2 and Ti5Si4, which should enhance micro-hardness and tribological properties of the surface relative to the bulk as-received alloy. 90:10 weight percentage ratio of SiC and Al powder mixture gave the best microhardness with a value of 1169.95 Hv, compared to 323.67 Hv of the as-received, and mass loss under abrasive wear tests was only 40% of the as received. The morphology obtained for the abraded surfaces is also indicative of this improvement. In carefully optimised proportions and laser condition, the binary combination of Al and SiC powders suffice for well improved Ti-6Al-4V surface properties.

Preparation and properties of dense ZrB2 composite reinforced by elongated SiC and Al3BC3 grains

AbstractDense ZrB2‐SiC‐Al3BC3 ultra‐high temperature ceramic composite was fabricated by hot pressing sintering at 1900°C for 1 hour under a pressure of 20 MPa using Zirconium diboride (ZrB2) as the raw material and a powder mixture of SiC, B4C, Al, and carbon as the sintering additive. Al and B4C underwent in situ reaction with carbon powder to produce Al3BC3, which promoted the densification of ZrB2 ceramic. SiC grains were found to be elongated during sintering. The ZrB2‐SiC‐Al3BC3 composite exhibited excellent mechanical properties, such as high flexural strength of 589 ± 147 MPa and fracture toughness of 7.81 ± 1.09 MPa m1/2. Oxidation behavior of the ZrB2‐SiC‐Al3BC3 composite was studied in air at 1500°C for 1 hour. A continuous layer of oxides consisting of a mixture of SiO2, Al2SiO5, and Al2O3 was formed on the surface of the ZrB2‐SiC‐Al3BC3 composite. This layer of oxides efficiently prevented oxygen from diffusing into the specimens during oxidation, which improved the oxidation resistance of the ZrB2 ceramics.

Effects of random chopped short carbon fibers on microstructure and mechanical properties of joints for Cf/SiC composites by reaction bonding process

Random chopped short carbon fibers (Csf)/phenol-formaldehyde resin (PF)/SiC powder mixtures are used as filler for the joining of Cf/SiC composites to obtain SiC interlayer at the joining region. The influences of Csf on the microstructure and mechanical properties have been investigated. Research shows that the introduction of Csf can improve the microstructure uniformity of the joint and reduce residual silicon content in the interlayer. The joint achieve a high flexural strength of 232 ± 33 MPa as the carbon fiber content is 30 wt.%, which is similar to that of the Cf/SiC composites (220 ± 21 MPa). The decrease in residual silicon content and the formation of nano-sized SiC particles are the main reasons for high joining strength.

The Influence of Activation Preprocessing of the B4C and SiC Powder Mixture with Al on the Phase Composition, Structure, and Properties of Hot-Pressed Composites

The paper examines how the conditions of activation preprocessing (dry and wet grinding) of B4C–Al and SiC–Al powder mixtures in a planetary-ball mill influence the formation of phases in the mixtures and the phase composition, structure, and mechanical properties of the associated hot-pressed materials. It is shown that dry grinding, unlike the conventional powder charge preparation method, induces the mechanochemical synthesis of new phases in the B4C–Al powder mixture along with its mechanical activation. The formation of new phases in the SiC–Al powder mixture does not depend on the conditions of activation preprocessing. Secondary phases form in the hot pressing of the B4C–Al and SiC–Al powder mixtures. The structure and micromechanical characteristics of the materials indicate that dry grinding of the B4C–Al and SiC–Al powder mixtures has a greater activation effect on the hot pressing process, structural uniformity, phase composition, and mechanical properties compared to the conventional powder charge preparation method.

Mechanical Properties of Liquid Phase Sintered SiC Materials by the Addition of Unimodal and Bimodal Particles

Both the mechanical properties and probability distribution of liquid phase sintered SiC (LPS-SiC) materials were investigated, based on a detailed analysis of their microstructures. In particular, the effect of the starting sizes of SiC particles on the characterization of LPS-SiC materials was evaluated. LPS-SiC materials were fabricated with a constant applied pressure, using a complex powder of different sized SiC particles. Two types of initial SiC powders used for the fabrication of LPS-SiC materials were a unimodal SiC single powder with the average particle size of 0.3 μm, and a bimodal SiC powder mixture with average particle sizes of 0.3 μm and 30 nm, respectively. A complex powder of Al2O3 and Y2O3 particles was also utilized as an additive material for the consolidation of the LPS-SiC materials. The characterization of the LPS-SiC materials was performed using microstructural observation, three-point bending test and micro Vickers hardness test. The LPS-SiC materials containing the unimodal SiC powder exhibited a good sintered density of about 3.11 g/cm3 and a low porosity of about 5.4%. The bimodal mixture of different SiC particles did not significantly affect the sintered density of LPS-SiC materials. However, LPS-SiC materials containing the bimodal SiC powder exhibited an average flexural strength about 630 MPa higher than that of unimodal SiC powder, accompanied by the creation of fine SiC grains in the range of about 0.2~1.4 μm. The LPS-SiC materials exhibited a similar hardness level of about 2200 Hv regardless of the starting SiC powders. The bimodal SiC powder also produced a higher shape parameter and variability in hardness in the Weibull statistical analysis. Key words: silicon carbide, liquid phase sintering, initial SiC particle size, grain size, weibull distribution, mechanical property

Microstructure, formation mechanism and property characterization of Ti + SiC laser cladded coatings on Ti6Al4V alloy

Surface modification of Ti6Al4V alloy was conducted by additive manufacturing using ball-milling treated mixture of Ti and SiC powder particles. Two laser cladded layers of 90%Ti + 10%SiC and 80%Ti + 20%SiC were deposited onto the Ti6Al4V substrate by single channel feeding system. This single channel feeding process using the ball-milled Ti+SiC powder mixture could offer a more homogeneous SiC distribution and thus cause a better fluidity during the laser cladding process. The microstructures of the cladded layers were analyzed by a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS). An X-ray diffraction (XRD) and a transmission electron microscope (TEM) were used for the determination of the phase products. The Vickers hardness of the cladded coatings was measured by H450-SVDH microhardness tester. Chemical reactions took place between the Ti and SiC particles in the composite layers, and the reaction products consisted of TiC and Ti5Si3. The average three-point bending strength of the sample from the Ti6Al4V substrate to the 80%Ti + 20%SiC coating was 515 MPa at room temperature. The 80%Ti + 20%SiC cladded layer increased the hardness of the Ti6Al4V matrix from 339.1 HV to 932.2 HV. As a consequence, the wear resistance was improved remarkably.

Microstructures and mechanical properties of B4C-TiB2-SiC composites fabricated by ball milling and hot pressing

B4C-TiB2-SiC composites were fabricated via hot pressing using ball milled B4C, TiB2, and SiC powder mixtures as the starting materials. The impact of ball milling on the densification behaviors, mechanical properties, and microstructures of the ceramic composites were investigated. The results showed that the refinement of the powder mixtures and the removal of the oxide impurities played an important role in the improvement of densification and properties. Moreover, the formation of the liquid phases during the sintering was deemed beneficial for densification. The typical values of relative density, hardness, bending strength, and fracture toughness of the composites reached 99.20%, 32.84 GPa, 858 MPa and 8.21 MPa m1/2, respectively. Crack deflection, crack bridging, crack branching, and microcracking were considered to be the potential toughening mechanisms in the composites. Furthermore, numerous nano-sized intergranular/intragranular phases and twin structures were observed in the B4C-TiB2-SiC composite.

Solid Solution and Phase Relations in SiC-AlN-Pr2O3 System

The phase relations in the Si-Al-Pr-O-N-C systems, involving SiC-AlN-Pr2O3, AlN-Pr2O3-Al2O3 and SiC-AlN-Pr2O3-Al2O3 systems were determined by XRD phase analyses of the solid-state reacted samples from powder mixtures of SiC, AlN, Pr2O3, as well as Al2O3. Pr2Al(Si)O3N(C) solid-solution (1:1 ss) between SiC and Pr2AlO3N (1:1 compound) was discovered with the limited solubility of 0.6 SiC at 1650 °C. Subsolidus phase diagram of SiC-AlN-Pr2O3 system was presented, SiC was compatible with AlN, Pr2O3 and 1:1 ss, respectively. Two-aluminates PrAlO3 (PrAP) and PrAl11O18 [β(Pr), β-Al2O3 type] were formed when Al2O3 impurity was introduced in AlN powder. They establish the equilibrium relationships respectively with SiC, AlN, Pr2O3 and Pr2AlO3N. Accordingly, the phase relations in the AlN-Pr2O3-Al2O3 ternary system and SiC-AlN-Pr2O3-Al2O3 quaternary system containing four quaternary phases compatible tetrahedrons were presented.

Fabrication and Characterization of Ni-SiC Nanocomposite Coatings on Al Substrates by Ball Impact Deposition Method

Micron-size Ni and SiC powder mixtures were used to prepare Ni-SiC nanocomposite coatings on an Al substrate by employing a high-energy ball milling technique. Ni:SiC weight ratio was varied over a wide range to explore the effect of the charge composition on the microstructure, composition, microhardness, and wear properties of the depositions. It was observed that the composition of the produced coating was correlated to the charge composition in a complex manner, which suggests that deposition rates for Ni and SiC particles significantly vary depending on the charge composition; SiC deposition rate was higher than that of Ni when Ni:SiC weight ratio was greater than 3:1. Diffusion of Al from the substrate into the Ni matrix provided evidence for the metallurgical bonding at the interface. Both microstructural and mechanical properties of the produced coatings were found to be crucially dependent on the charge composition. By increasing the SiC content in the charge from about 5 to 33 wt pct, the mechanical properties enhanced due to the dispersion strengthening effect of the incorporated SiC particles in the coatings and the crystallite size of the Ni matrix decreasing to the nanometer range. However, a further increase resulted in the formation of a coating with a poor degree of compaction. It was found that the composite coating with about 15 vol pct SiC, produced from the charge with Ni:SiC weight ratio of 2:1, showed a microhardness as high as 830 HV0.05 along with excellent wear resistance. Despite the current sample size limitations for applying high-energy ball milling, the present findings demonstrate that the adopted technique holds good prospect for the synthesis of nanostructured metal matrix composite coatings with enhanced and tunable properties.