Picosecond Laser Machining of Deep Holes in Silicon Infiltrated Silicon Carbide Ceramics

Silicon infiltrated silicon carbide （Si-SiC） ceramics, as high hardness materials, are difficult to machine, especially drilling micro-holes. In this study, the interaction of picosecond laser pulses （1 ps at 1 030 nm） with Si-SiC ceramics was investigated. Variations of the diameter and depth of circular holes with the growth of the laser energy density were obtained. The results indicate that the increase of machining depth follows a nonlinear relation with the increasing of laser energy density, while the diameter has little change with that. Moreover, it is found that some debris and particles are deposited around and inside the holes and waviness is in the entrance and at walls of the holes after laser processing.

Progress in densification and toughening of high entropy carbide ceramics

High entropy carbide ceramics(HECC)are solid solution of inorganic compounds with five or more prin-cipal metal cations.Research interests in HECC are dramatically sparked by the enormous possibilities in composition-microstructure-property tailoring.As widely acknowledged,HECCs enjoy higher hardness and oxidation/corrosion/wear resistance,as well as lower thermal conductivity than conventional engi-neering carbide ceramics,making them the most potential candidates for state-of-the-art structural and functional applications in extreme service conditions.Despite the advantages,however,the poor den-sification coupled with low fracture toughness significantly limited the practical applications of HECC.Adding to the difficulty,the literature available for toughening HECC is woefully limited.In considera-tion of this insufficiency,we apply towards offer a comprehensive,critical review of the mechanical be-havior of HECC,highlighting the densification enhancing strategies(carbon content,sintering techniques,grain size,sintering aids,etc.)as well as toughening methods including particle toughening,whisker/fiber toughening,synergistic toughening,graphene-carbon nanotube toughening,to further the service reliabil-ity of HECC in practical industrial applications.Furthermore,despite some significant successes,important directions for further development of HECC are given as multi-dimensional gradient HECC,additive man-ufacturing of HECC,processing-composition-microstructure-property relationship prediction and genomes of HECC based on machine learning,and high-throughput computing,etc.

High-entropy carbide ceramics: a perspective review

High-entropy carbide ceramics(HECCs)exhibited a series of property superiority,such as high hardness,high oxidation resistance and adjustable range of thermal conductivity,making them great candidates for structural materials used in extreme service conditions.However,current HECC-related reports can only provide limited guidance for the design of HECC materials with promising properties and stable structure or for their high-quality fabrication.To fill this gap,we proposed in the current review that integrated efforts should be taken in the following three aspects to advance the design and fabrication of high-performance HECCs.First,the rule for the single-phase formation needs to be theoretically identified using high-throughput density functional theory calculations(HTDFT)and a highly accurate predictive model for rapid compositional design warrants establishment through the combination of HTDFT and machine-learning studies.In parallel with the compositional design,the lack of theoretical foundation and guidance for the synthesis of highly dense and highly pure HECC materials necessitates extensive studies focusing on the principle for the synthesis of HECC pre-alloy powders and on the powder densification mechanisms during high-temperature sintering.Moreover,great attentions are to be paid to the mechanistic understandings on the mechanical,oxidation and thermal conduction behaviors of HECC materials;for example,the toughening and strengthening mechanisms of HECC materials could be elucidated through discerning the"HECC composition-stacking fault energy distribution/bonding state-dislocation behavior"correlations.

Ablation effects and mechanism of sintered silicon carbide ceramics by an ArF excimer laser

The ablation of sintered silicon carbide ceramics by an ArF excimer laser was studied. Three zones are generated： the ablation zone that presented molten morphology and was composed by the Si and C phase; the condensation zone formed by vaporized SiC; and the oxidation zone that showed the characteristics of thermal oxidation. The ablation depth and oxidation range increase linearly with fluence and pulses within 0.5-4 J/cm2, but the normalized ablation efficiency is constant （3.60± 0.60 μm · mm2/J）. The theoretical photochemical ablation depth supplies 25% of the total depth at 1 J/cm2 but decreases to 16% at 4 J/cm2. The ablation is dominated by the photothermal effect and conforms to the thermal evaporation mechanism.

Structural, mechanical, electronic properties, and Debye temperature of quaternary carbide Ti3NiAl2C ceramics under high pressure: A first-principles study

Quaternary carbide Ti3NiAl2C ceramics has been investigated as a potential nuclear fusion structural material,and it has advantages in certain aspects compared with Ti2AlC,Ti3AlC2,and Ti3SiC2 structural materials.In this paper,quaternary carbide Ti3NiAl2C ceramics is pressurized to investigate its structural,mechanical,electronic properties,and Debye temperature.Quaternary carbide Ti3NiAl2C ceramics still maintains a cubic structure under pressure(0–110 GPa).At zero pressure,quaternary carbide Ti3NiAl2C ceramics only has three bonds:Ti–Al,Ni–Al,and Ti–C.However,at pressures of 20 GPa,30 GPa,40 GPa,60 GPa,and 70 GPa,new Ti–Ni,Ti–Ti,Al–Al,Ti–Al,and Ti–Ti bonds form.When the pressure reaches 20 GPa,the covalent bonds change to metallic bonds.The volume of quaternary carbide Ti3NiAl2C ceramics can be compressed to 72%of its original volume at most.Pressurization can improve the mechanical strength and ductility of quaternary carbide Ti3NiAl2C ceramics.At 50–60 GPa,its mechanical strength can be comparable to pure tungsten,and the material changes from brittleness to ductility.However,the degree of anisotropy of quaternary carbide Ti3NiAl2C ceramics increases with the increasing pressure.In addition,we also investigated the Debye temperature,density,melting point,hardness,and wear resistance of quaternary carbide Ti3NiAl2C ceramics under pressure.

Influence of pyrolysis temperature on structure and dielectric properties of polycarbosilane derived silicon carbide ceramic

β-SiC ceramic powders were obtained by pyrolyzing polycarbosilane in vacuum at 800-1200 °C. The β-SiC ceramic powders were characterized by TGA/DSC, XRD and Raman spectroscopy. The dielectric properties of β-SiC ceramic powders were investigated by measuring their complex permittivity by rectangle wave guide method in the frequency range of 8.2-18 GHz. The results show that both real part ε′ and imaginary part ε″ of complex permittivity increase with increasing pyrolysis temperature. The mechanism was proposed that order carbon formed at high temperature resulted in electron relaxation polarization and conductance loss, which contributes to the increase in complex permittivity.

Application of Reaction-Bonded Silicon Carbide in Manufacturing of Spacecraft Combustion Chamber

Silicon carbide (SiC) ceramics is a good structural ceramics material, which have a lot of excellent properties such as superior high-temperature strength up to a temperature of 1 350 ℃, chemical stability, good resistance to thermal shock and high abrasion resistance. The silicon carbide ceramics material has so far been used widely for manufacturing various components such as heat exchangers, rolls, rockets combustion chamber. Sintering of ceramics structural parts have many technological method, the reaction-bonded is one of important sintering technology of ceramics structural parts. The preparation of reaction-bonded silicon carbide (RBSC) is based on a reaction sintering process, whereby a compacted body of α-SiC and carbon (graphite) powders is heated in contact with liquid silicon or gas silicon, which impregnates the body, converting the carbon (graphite) to β-SiC which bonds the original alpha grain. This process is characterized by low temperature and a short time sintering, and being appropriate to the preparation of large size and complex-shaped components, and so on. Besides, during compacting process of reaction sintering, it can maintain a stable dimension of ceramics parts. Therefore, the method of reaction-bonded silicon carbide ceramics has been identified as a technology suitable for producing complicated and highly exact dimensions’ ceramics parts. In this paper, the method of reaction-bonded silicon carbide was applied to the manufacturing of a complex-shaped spacecraft combustion chamber of SiC ceramics. SiC and carbon powder of 4～30 μm were chosen as the raw materials, green compacts containing appropriate wt.% carbon were formed using the mold press method, sintering was performed in a graphite electric furnace under an argon atmosphere. It was introduced in detail that the technological parameters and technological flow of reaction sintering silicon carbide ceramics. At the same time, physical and mechanical experiments such as bending strength, coefficient of thermal expansion, coefficient of thermal conductivity, gastight property, heat resisting property etc. have been carried out. The results demonstrated that spacecraft combustion chamber made from reaction sintering of silicon carbide ceramics is feasible and the results of experiment is satisfactory. The strength of high-temperature structural parts made by reaction sintered SiC varied with silicon content; Under the this article testing condition, the optimum silicon content is 10.5% for the part investigated. The method of reaction sintered SiC ceramics is suitable for manufacturing of complicated spacecraft parts with a working temperature of 1 500 ℃.

Influence of carbide ceramic reinforcements in improving tribological properties of A333 graded hybrid composites

Aluminium hybrid functionally graded metal matrix composites(FGMMCs),meet growing demands for supreme tribo-mechanical performance in automotive and aviation industry.This research experimentally compares the influence of carbide ceramics(B_(4)C,SiC,TiC)as reinforcements,in improving reciprocating tribology performance and mechanical strength of A333 hybrid composites against alloy.Hollow cylindrical samples of A333/6 wt%B_(4)C/4 wt%TiC and A333/6 wt%B_(4)C/4 wt%SiC hybrid FGMMCs were developed using horizontal centrifugal casting.Metallography analysis on both composites revealed increasing ceramic gradient distribution towards outer composite wall.Particle rich zone of A333/B_(4)C/SiC hybrid FGMMC showed maximum micro-hardness(198.9 HV)and tensile strength(267.9 MPa).Elemental mapping confirmed effective distribution of ceramics and detected elemental composition of both composites.Particle rich layer of A333/B_(4)C/SiC hybrid FGMMC exhibited improved wear resistance in comparison with all three layers of A333/B_(4)C/TiC hybrid FGMMC and alloy.Third-body abrasion and tribo-chemical wear were the predominant mechanisms revealed for both composites during worn surface analysis.

Properties of B4C-TiB2 ceramics prepared by spark plasma sintering

By doping titanium hydride(TiH2) into boron carbide(B4C), a series of B4C + x wt% TiH2(x = 0, 5, 10, 15, and 20)composite ceramics were obtained through spark plasma sintering(SPS). The effects of the sintering temperature and the amount of TiH2 additive on the microstructure, mechanical and electrical properties of the sintered B4C-TiB2 composite ceramics were investigated. Powder mixtures of B4C with 0–20 wt% TiH2 were heated from 1400℃ to 1800℃ for 20 min under 50 MPa. The results indicated that higher sintering temperatures contributed to greater ceramic density. With increasing TiH2 content, titanium diboride(TiB2) formed between the TiH2 and B4C matrix. This effectively improved Young’s modulus and fracture toughness of the composite ceramics, significantly improving their electrical properties: the electrical conductivity reached 114.9 S·cm-1 at 1800℃ when x = 20. Optimum mechanical properties were obtained for the B4C ceramics sintered with 20 wt% TiH2, which had a relative density of 99.9±0.1%, Vickers hardness of 31.8 GPa,and fracture toughness of 8.5 MPa·m1/2. The results indicated that the doping of fine Ti particles into the B4C matrix increased the conductivity and the fracture toughness of B4C.

Preparation of SiC Porous Ceramics by Crystalline Silicon Cutting Waste

SiC porous ceramics were prepared at 1 400 ℃ for4 h with crystalline silicon cutting waste and activated carbon as main starting materials and NH4HCO3 as the pore-forming agent. Effects of NH4HCO3 additions( 0,20%,30%,40%,by mass) on the phase composition,microstructure,sintering properties,cold compressive strength and thermal shock resistance of as-prepared Si C porous ceramics were investigated. The results show that:( 1) addition of NH4HCO3 remarkably influences the apparent porosity and cold compressive strength of specimens. The apparent porosity achieves its maximum value( 63. 40%) when 40% NH4HCO3 is added,while the minimum cold compressive strength is 4. 77 MPa;( 2) the specimen with 40% NH4HCO3 has the best thermal shock resistance. The thermal cycling times between1 000 ℃ to room temperature reach 62;( 3) the addition of NH4HCO3 does not remarkably affect the phase composition of the specimens;( 4) the specimens include a large number of SiC particles and a small amount of SiC whiskers.

Gradient Structure of Ti-Al-C Ternary Carbide Prepared by Hot-pressing Sintering

X-ray diffraction (XRD) analysis on different polished surfaces normal to the hot pressing direction reveals that the phase compositions of the polished surfaces from the outside to the inside are pure TiC, Ti_3AlC_2+TiC, pure Ti_3AlC_2 and Ti_2AlC+Ti_3AlC_2, no matter elemental powder or TiC is used as raw materials. It is found that ternary-layered carbide Ti_2AlC samples synthesized at 1500 ℃ by hot-pressing sintering are inhomogeneous and have a gradient structure.Electron probe X-ray micro-analysis (EPMA) indicates that the Al content along the hot pressing axis is parabolic, it is the highest in the center and the lowest at the both ends, while the Ti content is constant along the axis. The experimental result reveals that the evaporation of Al in samples in an open system during hot pressing sintering results in a gradient structure.

RESEARCH ON EROSION OF SILICON CARBIDE CERAMIC BLADE

In this paper, three linds of silicon carbide ceramic materials are chosen to perform the tests of material erosive wear. The relationship of ambient parameters, abrasive property and target property is studied in these experiments. Some main factors affecting erosive wear rate are determined by analysis of testing results, step wise regression analysis is completed according to the nondimensional quantities obtained by dimensional analysis. Relative hardness (partide to target Hp/Ht and erosion factor (Hpd1/2/Kic) are put for-ward to evaluate erosion property.

Cr-assisted low-temperature densification of(Ti,Zr,Nb,Ta,Mo)C high-entropy carbides with ultrafine grain and enhanced hardness

While the use of low-melting-point metals as sintering aids for high-entropy carbide(HEC)ceramics has been well established,their existence can compromise hardness due to residual metallic inclusions.This study demonstrates an innovative strategy to meet this challenge,where(Ti,Zr,Nb,Ta,Mo)C high-entropy carbide ceramics with ultrafine grains and enhanced hardness are obtained through chromium(Cr)-metal-assisted spark plasma sintering(SPS)at a temperature as low as 1600℃.The results show that the addition of 5 vol%Cr promotes the formation of highly densified single HEC phase ceramics with a high relative density(98.4%)and an ultrafine-grained microstructure(0.17μm).This low-temperature densification mechanism can be attributed to Cr’s solid-solution effect within the matrix and the increased carbon vacancies generated during sintering.The grain size of the(Ti,Zr,Nb,Ta,Mo)C ceramics with 5 vol%Cr metal addition is significantly smaller than that of Cr-free(Ti,Zr,Nb,Ta,Mo)C ceramics sintered at 2000℃(3.03μm)or via traditional low-temperature liquid-phase sintering(1.3–1.5μm).Importantly,the addition of 5 vol%Cr substantially increased the hardness of the ceramics,with a remarkable increase from 23.57 to 28.16 GPa compared to that of the pure(Ti,Zr,Nb,Ta,Mo)C ceramics,owing to the fine-grain strengthening and solid-solution strengthening mechanisms.This work highlights the uniqueness of Cr metal as a sintering aid in achieving densification and hardness improvements in(Ti,Zr,Nb,Ta,Mo)C ceramics,offering a promising strategy for improving the properties of HEC materials for further development in the near future.

From sawdust waste to high-value hierarchical ceramics-based phase change materials: Efficient dual functional thermal and solar energy storage

Latent heat thermal energy storage(LHTES) technology is gaining extensive attention due to its capability to balance supply and demand mismatch in solar energy utilization. However, phase change material as the core of storing latent heat still suffers from low thermal conductivity and poor shape stability, which severely restricts its practical application. Here, an eco-friendly strategy for achieving high-performance dual functional thermal and solar energy storage is proposed via turning wood processing waste into high-value hierarchical porous SiC ceramic-based composite phase change materials. The porosity of prepared porous SiC skeletons is highly adjustable from 59.4% to 90.2%, overcoming low porosity limitations of traditional wood materials and enabling tunable energy storage density for various applications. High thermal conductivity is achieved by benefiting from large grains and continuous skeletons with a value up to 37.93 and 1.87 W/(m K) for porosity of 59.4% and 90.2%, respectively.Excellent stabilities are demonstrated with only slight decreases of thermal conductivity and energy storage density over 1000 cycles and good anti-leakage properties are confirmed due to capillary adsorption forces induced by hierarchical pores. Benefiting from high thermal conductivity and high solar absorptance, fast and efficient solar thermal energy storage is successfully demonstrated. This work provides a new strategy for the high-value utilization of wood processing waste and efficient thermal/solar energy storage.

Relationship Between Electric Properties and Temperature of ZrB_2-SiC Composite Ceramic Heating Element

ZrB2 -SiC composite ceramic has been successfully introduced as heating element in super high temperature .field. This paper further investigated the microstructure of ZrB2 - SiC composite ceramic heating element and the relationship between electric properties and temperature. SEM photos show that the heating element consists of SiC grains and ZrBz grains smaller than 10 μm. The voltage and current gradually increase and the furnace tempera- ture rises lineally with heating time prolonging. The electric resistance increases linearly with the temperature rising. The service temperatltre of the heating element can reach 1 800 ℃ and 2 150 ℃ in air and argon at- mosphere, respectively.

Phase Formation and Process Analysis of SiC-Al_2O_3-Al_6Si_2O_(13) Composite Powder via Carbothermal Reduction of Fly Ash at 1 550 ℃

Silicon carbide（SiC）-alumina（Al_2O_3）-mullite（Al_6Si_2O_（13）） composite powder was successfully synthesized at 1 550 ℃ for 5 h via carbothermal reduction reaction,and the effects of various mass ratios of active carbon to fly ash（0.38,0.44 and 0.58） on the phase composition and microstructure of products were investigated,and the formation process of the powder was also analyzed in detail.The products mainly consist ofβ-SiC,α-Al_2O_3,Al_6Si_2O_（13） and FeSi.Increasing carbon content favors the decomposition of Al_6Si_2O_（13） and formation of SiC.The average particle size of β-SiC andα-Al_2O_3 is about 1 μm and that of Al_6Si_2O_（13） is 5-10μm.The formation process of SiC-Al_2O_3-Al_6Si_2O_（13）powder includes the decomposition of mullite in fly ash and formation of SiC.

Frist-principles prediction of elastic, electronic,and thermodynamic properties of high entropy carbide ceramic (TiZrNbTa)C

High-entropy carbide ceramics (HECs) have drawn increasing attention as their excellent mechanical and thermal properties. In this work, the crystal stability,mechanical behavior, electronic and thermodynamic properties of (TiZrNbTa)C HEC are investigated by the first-principles calculations. Obtained results reveal that the disordered transition-metal (TM) atoms result in serious local lattice distortion within the crystal. The lattice distortion plays a key role for the structural stabilization,mechanical anisotropy and thermodynamic behaviors of(TiZrNbTa)C. Increasing pressure leads to decrease the lattice parameter, volume and brittleness, meanwhile increase the elastic constants, elastic moduli, mechanical anisotropy, sound velocity, and Debye temperature. It is also discovered that charge delocalization occurs with the increase in pressure. The mechanical stability and anisotropy of (TiZrNbTa)C are attributed primarily to TM-C bonding.

Textured and toughened high-entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C-SiCw ceramics

High-entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C ceramics,with different contents(0,5,10,and 20 vol.%)of Si C whiskers(SiCw),were fabricated by spark plasma sintering using raw powders synthesized via carbothermal reduction.The application of a uniaxial compaction force led to texture development of the SiCw within the(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C matrix.Fracture toughness increased with the increase in SiCw content,while Vickers hardness remains almost unchanged.The toughness of(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C-20 vol.%SiCw ceramics reached 4.3±0.3 MPa m^(1/2),which was approximately 43%higher than that of the monolithic(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C ceramic(3.0±0.2 MPa m1/2).The main toughening mechanisms were attributed to crack deflection,whisker debonding,and whisker pullout.

Low-temperature densification of high-entropy(Ti,Zr,Nb,Ta,Mo)C-Co composites with high hardness and high toughness

In order to prepare high toughness(Ti,Zr,Nb,Ta,Mo)C ceramics at low temperatures while maintaining high hardness,a liquid-phase sintering process combined with Co-based liquid-phase extrusion strategy was adopted in this study.The densification temperature can be lowered to 1350℃,which is much lower than the solid-state sintering temperature(~2000℃)generally employed for high-entropy carbide ceramics.When sintered at 1550℃and 30 MPa applied pressure,part of the Co-based liquid-phase was squeezed out of the graphite mold,such that only~3.21 vol%of Co remained in the high-entropy ceramic.Compared to the Co-free solid-state sintered(Ti,Zr,Nb,Ta,Mo)C ceramics,prepared at 2000℃and 35 MPa,the hardness was slightly decreased from 25.06±0.32 to 24.11±0.75 GPa,but the toughness was increased from 2.25±0.22 to 4.07±0.13 MPa·m^(1/2).This work provides a new strategy for low-temperature densification of high-entropy carbides with both high hardness and high toughness.

Long-term ceramic matrix composite for aeroengine

Three strategies were proposed to prolong the service life of continuous fiber-reinforced silicon carbide ceramic matrix composite(CMC-SiC),which served as thermal-structure components of aeroengine at thermo-mechanical-oxygenic coupling environment.As for some thermal-structure components with low working stress,improving the degree of densification was crucial to prolong the service life,and the related process approaches were recited.If the thermal-structure components worked under moderate stress,the matrix cracking stress(σ^(mc))should be improved as far as possible.The fiber preform architecture,interface shear strength,residual thermal stress,and matrix strengthening were associated withσ_(mc)in this review.Introducing self-healing components was quite significant with the appearance of matrix microcracks when CMC-SiC worked at more severe environment for hundreds of hours.The damage can be sealed by glass phase originating from the reaction between self-healing components and oxygen.The effective self-healing temperature range of different self-healing components was first summarized and distinguished.The structure,composition,and preparation process of CMC-SiC should be systematically designed and optimized to achieve long duration target.