Excellent Thermal Shock Resistance Research Articles

Microstructure, mechanical properties and thermal shock resistance of ZrB 2 -SiC-C f composite with inhibited degradation of carbon fibers

Abstract ZrB 2 -SiC-C f composite with carbon coated carbon fibers was successfully prepared by low temperature hot pressing. This composite showed an excellent thermal shock resistance compared with those composites fabricated by hot pressing and spark plasma sintering using as-received carbon fibers. Toughening mechanisms such as crack deflection, crack branching, fibers pull-out and fibers bridging were obviously detected in ZrB 2 -SiC-C f owing to the inhibited degradation of carbon fibers and the relatively weak fiber/matrix interfacial bonding, leading to a non-brittle fracture mode of the composite. Moreover, the composite exhibited an excellent thermal shock resistance with a high critical thermal shock temperature difference of 773 °C which is about twice those of the reported ZrB 2 -based ultra-high temperature ceramics. This work provides valuable guidance in the preparation of ZrB 2 -based ultra-high temperature ceramics with a combination of excellent properties.

High-performance ZrB2-SiC-Cf composite prepared by low-temperature hot pressing using nanosized ZrB2 powder

High-performance ZrB2-SiC-Cf composite was successfully prepared by low temperature (1450°C) hot pressing using nanosized ZrB2 powder. Such material exhibited a non-brittle fracture feature, high work of fracture (321J/m2) and excellent thermal shock resistance as well as good oxidation resistance. Composite incorporating carbon fibers in which the degradation of the carbon fiber was effectively inhibited through low-temperature sintering displayed remarkably improved thermal shock resistance with a critical temperature difference of 754°C, almost twice those of the reported ZrB2-based ultra-high temperature ceramics. The thermal and chemical stability of the carbon fiber and ceramic matrix were further analyzed by thermodynamic calculation and HR-TEM analysis.

Gradient structure high emissivity MoSi2-SiO2-SiOC coating for thermal protective application

This study presents a one-pot preparation of gradient porous high emissivity coatings on ceramic fibrous insulations. MoSi2-SiO2-SiOC coatings have been prepared on mullite fibrous substrates with polysiloxane-derived SiOC glass as low-temperature adhesive, SiO2 as high-temperature ceramic aggregate, MoSi2 as emission agent and polydimethylsiloxane (PDMS) as pore former by slurry-spraying, drying and sintering. Scanning electron microscopy shows the MoSi2-SiO2-SiOC coating gradually changes from a porous structure into a dense structure with obviously decreasing porosity from substrate to surface. The pore size and porosity of the bonding-layer increase with the PDMS content and the density of the surface-layer increases with the sintering temperature suggesting the gradient porous structure is formed by two-steps of “low-temperature decomposition pore-forming” and “high-temperature sintering pore-sealing” during sintering. Firstly, the pores come into formation after decomposition of PDMS and the organic-to-inorganic transformation of the SiOC glass at lower temperature (<1000 °C). Secondly, the formed pores are partly sealed accompanied by carbothermal reduction of the SiOC glass and carburization reaction of the MoSi2 at higher temperature (>1400 °C). The gradient MoSi2-SiO2-SiOC coating increases the bonding strength between the coating and substrate up to 0.6 MPa, which is nearly twice as high as that of dense MoSi2-SiO2 coating. The MoSi2-SiO2-SiOC coating exhibits high spectral emissivity (0.90 at 700 °C), excellent thermal shock resistance (90 cycles without cracking at 25–1500 °C) and oxidation resistance up to 1500 °C, all of which can meet requirements of high temperature application.

A review on the utilization of natural graphite and graphite-based materials

As a type of inorganic non-metallic resources, the natural graphite has a small thermal expansion coefficient (1×10−6–30×10−6 K), a high coefficient of thermal conductivity (129 W m−1 K−1), high temperature resistances, excellent electrical conductivity (resistivity 8×10−6–13×10−6 Ω m), brilliant lubricity with a friction coefficient of 0.08–0.16, plastic feature, good chemical stability, excellent thermal shock resistance and other properties, which makes it well-known as one of the “universal” mineral materials. Graphite has been widely used in the machinery, metallurgy, petrochemicals, light industry, electronics, electrical appliances, military defenses, aerospace and other economic fields. China is one of the countries that have the largest resources of natural graphite in the world. Based on data of the graphite mineral resources, production/consumption, and the international trade of China during the past several years, this paper gives an overview of the development of graphite mining, technologies in purifying raw ores, comprehensive utilization of graphite, applications and the technological innovations of graphite-base materials. The most important three types of graphite products including the expanded graphite, the fluorinated graphite, and graphene (2D graphite) are particularly reviewed. The production process based imported graphite products, technological innovation and the gap between China and developed countries are analyzed, and the development of the comprehensive utilization of graphite resources is introduced. Finally, the future direction of the graphite science was proposed according to the disciplinary development in the non-metallic mineral materials.

The analysis and fabrication of a novel tin-nickel mixed salt electrolytic coloured processing and the performance of coloured films for Al-12.7Si-0.7Mg alloy in acidic and alkali corrosive environments

We present for the first time the analysis and fabrication of a novel Tin-Nickel mixed salt electrolytic coloured processing and the performance of coloured films for Al-12.7Si-0.7Mg alloy. This alloy is a novel alloy containing high silicon aluminum alloy extrusion profile which presents excellent mechanical properties as well as broad market prospects. Nevertheless, this kind of material is urgent in need of surface treatment technology. The orthogonal design and single factor tests were applied to optimize for electrolytic coloured technological conditions. By controlling operation conditions, the uniform electrolytic coloured films with different color were obtained. Analysis of microstructure showed that tin particles had been deposited in the coloured film. The coloured films, about 10 μm thick, were uniform, dense and firmly attached to the substrate. After the coloured samples were maintained at 400oC for 1 h, or quenched from 300oC to room temperature, the coloured films did not change, demonstrating excellent thermostability and thermal shock resistance. Acid and alkali corrosion tests and potentiodynamic polarization showed that corrosion resistance of coloured sample was much better than those of untreated samples. After 240 h neutral salt spray test, protection ratings and appearance ratings of coloured films were Grade 9.

Preparation and characterization of amorphous SiO2 coatings deposited by mirco-arc oxidation on sintered NdFeB permanent magnets

Amorphous SiO2 coatings were prepared on sintered NdFeB magnets by micro-arc oxidation (MAO) in silicate solution. The surface and cross-sectional morphologies, element and phase composition, corrosion resistance and magnetic properties of the coatings were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), potentiodynamic polarization test and physical properties measurements system (PPMS). The results showed that the surface morphologies of the coatings exhibited the “coral reef” like structure, different from the typical MAO porous structure. With increasing the voltages, the thickness of the coatings increased from 12.72 to 19.90µm, the content of Si element increased, while the contents of Fe, Nd and P elements decreased. The coatings were mainly composed of amorphous SiO2 and a few amorphous Fe2O3 and Nd2O3. The amorphous SiO2 coatings presented excellent thermal shock resistance, while the thermal shock resistance decreased with increasing the voltages. The corrosion resistance of the coatings increased with increasing the voltages, and it could be enhanced by one order of magnitude compared to the uncoated NdFeB magnets. The MAO coatings slightly decreased the magnetic properties of the NdFeB samples in different degrees.

Microstructure, mechanical properties and thermal shock behavior of h-BN-SiC ceramic composites prepared by spark plasma sintering

h-BN-SiC ceramic composites with different SiC contents were fabricated by spark plasma sintering. The results indicate that the addition of hard SiC particles has a remarkable effect on the densification, microstructure, mechanical properties and thermal shock resistance of the composites. Compared with pure h-BN ceramic, the relative density and mechanical properties of h-BN-SiC ceramic composites were improved obviously. The optimal properties of h-BN-SiC ceramic composites were obtained at SiC content of 25%, and the relative density, flexural strength and fracture toughness reached 97.8%, 289.2MPa and 3.45MPam1/2, respectively. Moreover, the relationship of fracture toughness and fracture mode was discussed. The thermal shock test results showed that the h-BN-SiC ceramic composite with the SiC content of 25% exhibited excellent thermal shock resistance, presenting critical temperature difference up to 900 °C. The high temperature oxidation of h-BN and SiC on material surface led to the formation of borosilicate glass phase, which could heal the surface microcracks and then improve the thermal shock resistance.

Preparation and Performance Study of Mullite/Al2O3 Composite Ceramics for Solar Thermal Transmission Pipeline

For lowering sintering temperature of mullite/Al2O3 composite ceramics for solar thermal transmission pipeline, kaolin, potassium feldspar, quartz, and γ‐Al2O3 were used as raw materials to in situ synthesize the composite ceramics with pressureless sintering method. Densification, mechanical properties, thermal expansion coefficient, thermal shock resistance, phase composition, and microstructure were investigated. The experiment results demonstrated that the introduction of potassium feldspar and quartz decreased the lowest sintering temperatures greatly to 1300°C. The optimum sample A3 sintered at 1340°C obtained the best performances. The water absorption, apparent porosity, bulk density, bending strength, and thermal expansion coefficient of A3 were 0.04%, 0.12%, 2.71 g/cm3, 94.82 MPa, and 5.83 × 10−6/°C, respectively. After 30 thermal shock cycles (wind cooling from 1100°C to room temperature), no cracks were observed on the surfaces of the sample, and the bending strength increased by −7.96%. XRD analysis indicated that the main phases of samples before and after 30 thermal shock cycles were consistently mullite, corundum, and α‐cristobalite, while the content of mullite increased after thermal shock. SEM micrographs illustrated that the mullite grains growth and micro‐cracks appeared after thermal shock endowed the composite ceramics with excellent thermal shock resistance.

High emissivity MoSi2–TaSi2–borosilicate glass porous coating for fibrous ZrO2 ceramic by a rapid sintering method

A MoSi2-TaSi2-borosilicate glass porous coating was designed and prepared on fibrous ZrO2 ceramic with slurry dipping and subsequent rapid sintering method. The microstructure, radiative property and thermal shock behavior of the coating have been investigated. The results show the coating presents a top Ta-Si-O compound glass layer and a porous MoSi2-TaSi2-borosilicate glass inner layer. The total emissivity of the coating is up to 0.88 in the range of 0.3–2.5 μm and 0.87 in the range of 2.5–15 μm at room temperature. The increased surface roughness leads to the increased emissivity, which can be explained by “V-shaped grooves” model. The coating turns into a dense structure and presents an interlocking structure in the interfacial layer after thermal cycling between 1673 K and room temperature 10 times, exhibiting excellent thermal shock resistance, which was attributed to the synergistic effect of porous structure and the match of thermal expansion coefficient between the coating and substrate.

Fabrication and thermal shock resistance of β-Si3N4-based environmental barrier coating on porous Si3N4 ceramic

A dense β-Si3N4-based waterproof environmental barrier coating was fabricated using the liquid infiltration and filling method on porous Si3N4 ceramic. Microstructure and thermal shock resistance of the coating were investigated. The results showed that the coating consisted of β-Si3N4, Y10Al2Si3O18N4 and Y-Si-Al-O glass. As-prepared coating exhibited excellent thermal shock resistance. During thermal shock at ∆T=1200°C, cracks were formed within the coating, but they did not penetrate through the whole coating due to the toughening mechanisms of the coating, including β-Si3N4 particle bridging and crack branching. In addition, the coating had a good crack self-sealing ability during thermal cycling, which is mainly attributed to glass flow and oxidation of β-Si3N4 particles within the crack. After thermal cycling for 25 times, the coating still had a good waterproof ability, and the water absorption of the coated porous Si3N4 sample increased slightly from 4.5% to 9.3%.

Thermal shock resistance and oxidation behavior of in-situ synthesized MgAl2O4–Si3N4 composites used for solar heat absorber

MgAl2O4–Si3N4 ceramics were fabricated via pressureless sintering by using α-Si3N4, α-Al2O3 and MgO as starting materials. MgAl2O4 was in-situ synthesized in the composite ceramics to improve the sintering process and high-temperature performance of Si3N4. Results show that the composite with approximately 30wt% MgAl2O4 sintered at 1620°C exhibits the best physical properties, excellent thermal shock resistance, oxidation resistance and solar absorptance. No cracks were found after 30 thermal shock cycles (1100–25°C, wind cooling). At the same time, the bending strength has experienced an improvement of 24.5%, which increases to 248MPa. A dense oxide film is formed on the surface of the sample during oxidation at 1300°C, which protects it from further oxidation. The oxidation kinetics of MgAl2O4–Si3N4 ceramic transforms from passivation oxidation into activation oxidation with increasing MgAl2O4 content. Only moderate amount of MgAl2O4 (10–30wt%) can provide the excellent oxidation resistance. These in-situ MgAl2O4–Si3N4 composites could be a promising candidate for solar heat absorbing material.

Oxidation behavior of carbon/carbon composites coated with a Si[sbnd]SiOx/BN[sbnd]B2O3[sbnd]SiO2[sbnd]Al2O3 oxidation protection system at intermediate temperature

To improve the oxidation behavior of carbon/carbon composites at intermediate temperature, we developed a SiSiOx/BNB2O3SiO2Al2O3 coating by chemical vapor deposition and sol-gel slurry method. The coating exhibited a dual-layer structure with a dense SiSiOx inner layer and a BNB2O3SiO2Al2O3 multi-phase outer layer. The influence of SiSiOx on the C/C composites surface densification was investigated. The results showed that the weight losses of the coated C/C composite after oxidation for 162 h at 700 °C, 162 h at 800 °C, 162 h at 900 °C, 142 h at 1000 °C and 102 h at 1100 °C were 0.92, 3.04, 2.66, 2.93 and 3.81 wt%, respectively. It also performed excellent thermal shock resistance in the above temperature range. The oxidation kinetics of the coated carbon/carbon composites was proposed by Arrhenius equation as two different oxidation phases and mechanisms. The great oxidation resistance and thermal shock resistance were attributed to the formation of a dense B2O3 glass or SiO2-rich borosilicate glassy film covering on the C/C substrate during oxidation. This study provided an oxidation protection system at intermediate temperature.

A New High Emissivity Coating on Ni-Based Superalloy Substrate

Abstract In the present paper, we prepared a new high emissivity coating by a spray painting method. The coating contains amorphous borosilicate glass, Mg 2 B 2 O 5 , MoSi 2 and SiB 4 and has the thickness of about 50 μm. Results show that the coating exhibits excellent thermal shock resistance (more than 100 thermal cycles from 950 °C to water temperature). The average emissivity of the coating is 0.905±0.024 at 950 °C and has a slight degradation after 100 thermal cycles.

High emissivity MoSi2–ZrO2–borosilicate glass multiphase coating with SiB6 addition for fibrous ZrO2 ceramic

To develop a high emissivity coating on the low thermal conductivity ZrO2 ceramic insulation for reusable thermal protective system, the MoSi2–ZrO2–borosilicate glass multiphase coatings with SiB6 addition were designed and prepared with slurry dipping and subsequent sintering method. The influence of SiB6 content on the microstructure, radiative property and thermal shock behavior of the coatings has been investigated. The coating prepared with SiB6 included the top dense glass layer, the surface porous coating layer and the interfacial transition layer, forming a gradient structure and exhibiting superior compatibility and adherence with the substrate. The emissivity of the coating with 3wt% SiB6 addition was up to 0.8 in the range of 0.3–2.5μm and 0.85 in the range of 0.8–2.5μm at room temperature, and the “V-shaped grooves” surface roughness morphology had a positive effect on the emissivity. The MZB-3S coating showed excellent thermal shock resistance with only 1.81% weight loss after 10 thermal cycles between 1773K and room temperature, which was attributed to the synergistic effect of porous gradient structure, self-sealing property of oxidized SiB6 and the match of thermal expansion coefficient between the coating and substrate. Thus, the high emissivity MoSi2–ZrO2–borosilicate glass coating with high temperature resistance presented a promising potential for application in thermal insulation materials.

Fabrication of porous SiC ceramics through a modified gelcasting and solid state sintering

With starch as pore forming agent, porous silicon carbide (SiC) ceramics were successfully fabricated by gelcasting. A novel and simple gelling system of isobutylene and maleic anhydride (Isobam) can gel in air at room temperature was used. The rheological behaviors of SiC slurries were investigated as a function of starch content. The gelled SiC green bodies were sintered at 2050–2150°C through solid state sintering with B4C and carbon as sintering additives. Porosity of the porous SiC ceramics sintered at 2100°C was well controlled from 34.20% to 42.68% with the starch content increasing from 0 to 20wt%. With increasing the sintering temperature from 2050 to 2150°C, flexural strength and porosity of porous SiC ceramics with 20wt% starch varied from 61.0 to 128.0MPa and 48.1% to 34.2%, respectively. The porous SiC ceramics fabricated with 20wt% starch addition and sintered at 2100°C were proved to possess excellent thermal shock resistance. The ceramics after water-quenching at 1500°C showed an average flexural strength of 95.8MPa, which was higher than the strength of samples without quenching.

High-Temperature Die Attachment Using Sn-Plated Zn Solder for Power Electronics

Pure Zn is a Pb-free die-attach material considered suitable for application in high-temperature electronics such as widebandgap semiconductor devices, as it has both the requisite electrical/thermal conductivity and an excellent thermal shock resistance. The high melting point of Zn (419.5 °C), however, means that die-attachment using pure Zn would require higher bonding temperatures (>430 °C), whereas a lower temperature is more desirable for mass production. This paper, therefore, presents a bonding method based on using Sn-plated Zn solder (Sn/Zn/Sn structure) to achieve a lower bonding temperature than pure Zn die attachment. The resulting shear strength of this bonding exceeds 25 MPa at 350 °C for 30 min, which is attributed to a uniform and complete Ni–Zn IMC ( $\gamma $ -Ni5Zn21) reaction layer. Furthermore, this bonding strength is retained beyond 25 MPa without serious degradation, even after thermal shock testing within a temperature range of −50 °C–300 °C; and thus, the Sn-plated Zn solder proposed has great potential as a die-attach material for high-temperature applications such as power devices.

Mechanical, dielectric properties and thermal shock resistance of porous silicon oxynitride ceramics by gas pressure sintering

Porous silicon oxynitride (Si2N2O) ceramics were prepared by gas pressure sintering with 2.5–10.0mol% Li2O as additive. The influences of Li2O content on phase, microstructure, mechanical and dielectric properties of the Si2N2O ceramics were investigated. XRD analysis showed that the increase of Li2O content facilitate both the densification and the decomposition of Si2N2O into Si3N4. The elongated Si2N2O crystals contribute to the high flexural strength (161.3–228.4MPa at room temperature) of the products. The thermal shock resistance was greatly influenced by the sample porosity, and the highest critical temperature difference (ΔTc) could be up to 1300°C. The dielectric properties were mainly affected by the sample porosity. The as-sintered Si2N2O ceramics showed both low dielectric constant (ε<4.59) and loss tangent (tanδ<0.0049) with good mechanical properties and excellent thermal shock resistance, indicating the gas pressure sintered Si2N2O ceramics could be used as promising high temperature wave transparent material.

Double layer ZrSi2–ZrC–SiC/SiC oxidation protective coating for carbon/carbon composites

A ZrSi2–ZrC–SiC/SiC double layer coating was prepared on the surface of carbon/carbon (C/C) composites by pack cementation. The microstructure, oxidation and thermal shock resistance of the coating were studied. These results show that the outer coating is mainly composed of ZrSi2, ZrC, SiC and Si respectively. Oxidation tests were conducted in air at 1173 K for 100 min and 1773 K for 67 h and a weight decrease of 0·37 and 0·12% were recorded. After 20 times thermal shocks between 1773 K and room temperature, the weight of the coated specimens increased by only 0·12%. The excellent thermal shock resistance is attributed to the aptness to oxidation of the minor phases distributing in the gaps among the SiC particles and the coarseness of the coating.

DEVELOPMENT OF A CERAMIC FOAM FILTER FOR FILTERING MOLTEN ALUMINUM ALLOY IN CASTING PROCESSES

Metal casting component are found in 90 percent of manufactured goods and equipment, from critical components for aircraft and automotive industry to home applications. However, molten metal used to produce metal casting in practice generally contains impurities and inclusions which are deleterious to final cast metal product. Currently, filtration technique by using ceramic foam filter has been accepted as a successful method of reducing inclusions from molten metal during the casting of metal parts. The present research has been done to fabricate and improve a ceramic foam filter for using in filtration of molten metal, especially aluminium based alloys. It is an objective of the present innovation to provide a ceramic foam filter characterized by cost of raw materials. Ceramic foam filters are produced by impregnating polyurethane foam with ceramic slurry, drying, baking and finally firing the foam in the oven. Experimental tests were carried out to the filters to measure dimensions, weight, cold compression strength, and permeability properties before pouring process. After pouring process, the filter was cut into several sections to measure the macro and microstructure of the filter and ensure that impurity particles captured by a filter. Thermal shock properties, obtained from pouring liquid aluminium when filter was placed in the gating system to ensure that the filters could withstand temperatures of aluminium alloys. Further experiments were carried out to investigate and determine the efficiency of produced ceramic foam filter on quality of cast products. The result obtained in this investigation, the mechanical properties for aluminum LM6 alloy sand casting increased when ceramic foam filter was inserted into the gating system. A produced filter by using new materials is economical to be produced. Further more, the analysis data shows present innovation filter which can be made in any shape and size, has excellent thermal shock resistance, adequate compressive strength, acceptable density and permeability properties.

Influence of TiO2- and ZrO2-addition on the interaction of alumina castable with molten coal and gasifier slag

Gasification is a key process of chemical and energy industry. In order to improve the economic feasibility of gasifiers, new refractory lining materials with a long service life have to be developed, which can substitute the currently used high chromia bricks. TiO2 and ZrO2 were added to an Al2O3-refractory in order to improve its thermal shock and corrosion resistance against molten slags. Next to the investigation of material properties and structure, cup tests with holding time of 3 and 150h at 1450°C in different gasification-similar reducing atmospheres have been performed and the corrosion mechanism identified by analysing the slag–refractory interface in SEM. During sintering, the addition of 2.5wt.% TiO2 causes the formation of needle-shaped Na2Al2Ti6O16 crystals, which essentially influence the microstructure and provide excellent thermal shock resistance. In addition, in contact with coal slag, the presence of titania and zirconia promotes the formation of a protective MgAl2O4-layer, which stops slag infiltration and dissolution.