Mechanical Shock Resistance Research Articles

Effect of Co on thermal and mechanical properties of Si3N4 based ceramic tool material

The use of ceramic cutting tools is limited due to their inherent brittleness. In this paper, metal phase Co is considered to strengthen Si3N4 based ceramic tool materials. The effects of Co on room-temperature and high-temperature mechanical properties and thermal shock resistance of the material are studied. Compared with the composite without Co, the addition of Co can improve room-temperature fracture toughness of Si3N4 based ceramic material at the cost of reducing its hardness. The flexural strength decreases a little in accordance with the reduced relative density. As the testing temperature increases, the fracture toughness first increases gradually and then decreases sharply while the flexural strength decreases gradually. Due to the oxidation inhibition effect, the Co-containing composite maintains higher flexural strength and fracture toughness than the Co-free composite at the specified test temperatures. The critical thermal shock temperature difference of the composite with Co is higher than that without Co, although before reaching the difference its residual bending strength is lower due to pores and thermal mismatch effect. The addition of Co can also inhibit the growth of thermal shock microcracks and improve the thermal fatigue resistance of Si3N4 ceramic material.

Optimized microstructure with nano‐alumina and its effects on properties of corundum spinel castables

AbstractThe mechanical properties, thermal shock resistance, and microstructure evolution of corundum spinel castables with different nano‐alumina contents were investigated. The results show that the addition of nano‐alumina has advantages on the microstructure evolution and properties of castables. An optimum nano‐alumina amount is 2 wt%. When nano‐alumina addition changes from 0 to 2 wt%, the cold modulus of rupture (CMOR) and cold compressive strength (CCS) improved by 69.7% and 78.1% after firing at 1100°C, respectively. The CMOR and CCS increased by 42.5% and 35.2% after firing at 1500°C, respectively. Meanwhile, the hot modulus of rupture (HMOR) was enhanced by 21.5% to 13.4 MPa. The retained Young's modulus values of castables were improved from 49.6% to 59.6% after eight thermal shock cycles. Furthermore, the HMOR and the retained Young's modulus values of castables slightly reduced when nano‐alumina content up to 3 wt%. XRD, DSC, SEM, and EDS analyses revealed that the addition of nano‐alumina leads to the formation of calcium dialuminate (CaO·2Al2O3) at 1100°C and it is beneficial to the formation of more platelet hibonite (CaO·6Al2O3) at 1500°C. As a result of using nano‐alumina with large surface area, the solid phase sintering of the nanoscale particles can occur at lower temperatures. Moreover, the mechanical properties and thermal shock resistance of the castables were improved remarkably.

Enhanced mechanical properties and thermal shock resistance of Si2BC3N ceramics with SiC coated MWCNTs

Bulk Si2BC3N ceramics were reinforced with SiC coated multi-walled carbon nanotubes (MWCNTs). The phase compositions, mechanical properties, and thermal shock resistance, as well as the oxidation resistance of the designed Si2BC3N ceramics were comparatively investigated. The results show that nano SiC coating can be formed on MWCNTs through pyrolyzing polysilazane, which improves the oxidation resistance of MWCNTs. A stronger chemical bonding is formed between the SiC coated MWCNTs and SiC particles, contributing to improved flexural strength (532.1 MPa) and fracture toughness (6.66 MPa·m1/2). Besides, the 2 vol% SiC coated MWCNTs reinforced Si2BC3N ceramics maintains much higher residual strength (193.0 MPa) after thermal shock test at 1000 °C. The enhanced properties should be attributed to: (1) the breaking of MWCNTs and the debonding between MWCNTs and SiC interfaces, which leads to more energy dissipation; (2) the rough surfaces of SiC coated MWCNTs increase the adhesion strength during the “pull out” of MWCNTs.

Effect of NbC addition on the microstructure, mechanical properties and thermal shock resistance of Ti(C,N)-based cermets

In this paper, Ti(C,N)-WC-TaC-xNbC--Mo-Ni cermets were prepared by vacuum sintering. The microstructure, mechanical properties and thermal shock resistance of Ti(C,N)-based cermets with different NbC contents was explored. The results showed that with the increase of NbC content from 0 to 3 wt%, the rim phases around black core became complete, which refined the grain size of the cermets. However, white core appeared with the further increase of NbC content to 9 wt%, and the volume proportion of rim phases increased. Subsequently, the thickness of rim phases around white core increased and the black cores without rim phases appeared. The mechanical properties and thermal shock resistance of the cermets increased first and then decreased with the increase of NbC content from 0 to 9 wt%. When the NbC content was 3 wt%, cermets showed the best mechanical properties with transverse rapture strength of 2387 MPa, hardness of 92.1 HRA and fracture toughness of 8.88 MPa·m1/2. Meanwhile, when the NbC content was 3 wt%, cermets showed the best thermal shock resistance with critical temperature difference of 360 °C, due to its higher transverse rupture strength and lower thermal expansion coefficient.

A novel design of Al2O3-ZrO2 reticulated porous ceramics with hierarchical pore structures and excellent properties

The use of reticulated porous ceramics(RPCs) was of great interest in high-temperature catalytic application owing to their high surface area. In order to further optimize the pore structure and mechanical properties of RPCs, vacuum infiltration with CaCO3-Al2O3 slurries process was applied to fabricate Al2O3-ZrO2 RPCs with hierarchical pore structures. The pores within ceramic struts were prepared by processes of CaCO3 decomposition and calcium hexaluminate grains growth. And the compressive residual stress was formed within multi-layered struts owing to the difference in the thermal expansion of coating layer and ceramic struts, which was established as a key factor in improving the mechanical properties and thermal shock resistance of RPCs. Furthermore, the size of pores within struts ranging from 5 μm to 14 μm affected the thermal shock resistance of RPCs significantly based on grey incidence analysis. And the potential of this materials as high-temperature catalyst supports was demonstrated.

Heightening mechanical properties and thermal shock resistance of low–carbon magnesia–graphite refractories through the catalytic formation of nanocarbons and ceramic bonding phases

The in-situ catalytic formation of nanocarbons and ceramic bonding phases in low–carbon magnesia–graphite refractories is one of the significant strategies for heightening their mechanical properties and thermal shock resistance. Here, effect of aluminum content and nickel–containing catalyst addition on microstructural evolution, mechanical and thermo-mechanical behavior of such refractories was explored. Under the function of the catalyst, addition of aluminum powders allowed the newly growth of plenty of nanocarbons (e.g., carbon nanotubes and carbon onions), and also accelerated the in–situ formation of more ceramic bonding phases (e.g., magnesia whiskers and spinel whiskers/particles, etc.) in samples. This occurrence optimized significantly the microstructure of samples, correspondingly giving rise to their superior mechanical properties and thermal shock resistance. This work might provide a path for exploring low–carbon magnesia–graphite refractories with high performances.

Effects of ZrO2 Addition on Mechanical Strength and Thermal Shock Resistance of Cordierite-Mullite Ceramics

Cordierite composed of an alumina-silica-magnesia compound has a low coefficient of thermal expansion(CTE) and excellent thermal shock resistance. It also has a low dielectric constant and high electrical insulation. However, due to low mechanical strength, it is limited for use in a ceramic heater. In this study, ZrO2 is added to an 80 wt% cordierite-20 wt% mullite composition, and the effect of ZrO2 addition on the mechanical strength and thermal shock resistance is investigated. With an increasing addition of ZrO2, cordierite-mullite formed ZrO2, ZrSiO4 and spinel phases. With sintering conducted at 1400 °C with the addition of 5 wt% ZrO2 to 80 wt% cordierite-20 wt% mullite, the most dense microstructure forms along with an excellent mechanical strength with a 3-point flexural strength of 238MPa. When this composition is quenched in water at ΔT = 400 °C, the 3-point flexural strength is maintained. Moreover, when this composition is cooled from 800 °C to air, the 3-point flexural strength is maintained even after 100 cycles. In addition, the CTE is measured as 3.00 × 10−6·K−1 at 1000 °C. Therefore, 80 wt% cordierite-20 wt% mullite with 5 wt% ZrO2 is considered to be appropriate as material for a ceramic heater.

The impact of alumina bubble particle size on the microstructure and physical properties of mullite castables

Mullite castables are widely used in hot metal pretreatment processing equipment. In this work, the effects of alumina bubble particle size on the microstructure and physical properties of mullite castables were studied. Grey relational analysis is a useful method for analyzing patterns in multivariate cases. In this paper, the grey relational analysis was used to estimate the relationship between the properties of samples and the structure of alumina bubbles. Using grey analysis, the specific surface area of alumina bubbles was determined to have the greatest influence on the properties of apparent porosity, cold mechanical properties and thermal shock resistance. The hollow radius of alumina bubbles has the greatest relationship to bulk density, hot modulus of rupture, flow values and coefficient of thermal expansion of samples. Finally, the mullite castables with a high modulus of rupture and thermal shock resistance was obtained by adding alumina bubbles with a particle size between 0.5 and 1 mm. The high modulus of rupture was shown to be caused by the alumina bubble spherical shape, hollow structure and the appropriate bonding at the alumina bubble/matrix interface.

High-speed intermittent turning of GH2132 alloy with Si3N4/(W, Ti)C/Co graded ceramic tool

In this paper, a new Si3N4-based graded ceramic tool was prepared by hot press technology The tool was toughened by microscale (W, Ti)C, nanoscale Si3N4, and metal Co. The graded structure combing with proper composition distribution introduced thermal residual compressive stress into the surface layer of the tool according to the FEM analysis. The performance of the tool in high-speed intermittent turning GH2132 alloy (equivalent to A286) was studied in contrast to one homogeneous tool. The cutting forces analysis indicates that the inserts endure periodic mechanical shock in the intermittent cutting process and the mechanical shock is more serious when the tooth engages the workpiece than when it disengages the workpiece. The tool failure modes observation shows ladder-like fracture under thermal and mechanical shock in the intermittent cutting process. Tool failure mechanisms involve chipping, flaking, microcracks, and adhesion. The graded tool shows better thermal and mechanical shock resistance than the homogeneous tool due to the formation of residual compressive stress.

Nickel-catalyzed preparation of self-bonded SiC refractories with improved microstructure and properties

3C-SiC was synthesized after 3 h firing of Si and expanded graphite in flowing Ar at 1300 °C with in-situ formed Ni nanoparticle (NP) catalyst. First-principles calculations suggest that Ni catalyst accelerated the formation of SiC via weakening the bonds in adsorbed CC bond, and CO and SiO molecules. Apart from this, Ni NP catalyst facilitated the epitaxial growth of SiC nanowires. Based on these findings, self-bonded SiC refractories were prepared by using black SiC grain, expanded graphite and Si powders as raw materials and Ni NP as a catalyst. Large amounts of SiC nanowires were catalytically formed in the fired refractories specimens, which resulted in significant improvements in both mechanical strength (MOR of 32.2 MPa at 1400 °C) and thermal shock resistance. The catalytic formation method investigated in this work could be readily modified and extended to develop many other types of high performance refractories.

Sintering effect of calcium carbonate in high-alumina refractory castables

Calcium hexaluminate (CA6) presents interesting properties and morphology, which can be readily changed depending on specific additives and refractory processing conditions. Aiming to investigate the role of calcium carbonate in inducing the formation of elongated CA6 grains and also identify its sintering effect during the thermal treatments of high-alumina castables, this work focused on evaluating compositions containing calcium aluminate cement, CaCO3 or their blend with the help of in situ techniques (hot elastic modulus, assisted sintering) and other traditional methods (mechanical strength, thermal shock resistance, etc.). A sintering effect derived from CaCO3 addition to alumina castables could be identified during the hot E measurements, pointing out the ability of this compound to undergo a sintering-coarsening-coalescence transformation at 500–900 °C. This process also enhanced the mechanical strength and thermal shock resistance of the designed refractories at intermediate temperatures. Acicular CA6 grains were formed in all analyzed compositions after firing at 1400 °C.

Mechanical properties and thermal shock resistance of Si2BC3N ceramics with ternary Al4SiC4 additive

Dense Si2BC3N ceramics were prepared through SPS sintering the amorphous Si2BC3N and Al4SiC4 powders obtained from mechanical alloying. The phase compositions, microstructures, and mechanical properties, as well as the thermal shock resistance were investigated. In addition, evaluations of oxidation and the ablation resistance were also preceded. The results show that Al4SiC4 phase can be detected at 1200 and 1400 °C under pressureless sintering. However, Al4SiC4 can be decomposed to AlN and SiC phases under higher temperatures. As for the bulk Si2BC3N ceramics, the Al4SiC4 additive induce the development of turbostratic BN(C) plates and improve the relative density consequently. Besides, the Al4SiC4 plates are embedded in the matrix of ceramics. Therefore, the mechanical properties and thermal shock resistance are improved apparently with the addition of additive. Meanwhile, the additive containing composites have superior ablation resistance than the pristine Si2BC3N ceramics due to their higher relative density.

Investigating the effect of andalusite on mechanical strength and thermal shock resistance of cordierite-spodumene composite ceramics

For increasing working stability of cordierite-spodumene composite ceramics for solar heat transmission pipeline, andalusite was utilized as modified additive to improve mechanical strength and thermal shock resistance of the composite ceramics. The effects of andalusite on densification, mechanical strength, thermal stability, phase composition and microstructure were studied. The experiment results showed that andalusite significantly influenced bending strength and thermal shock resistance of the composite ceramics. Especially, specimen B1 with 5wt% andalusite sintered at 1400°C achieved the best performances. The linear shrinkage, water absorption, apparent porosity, bulk density and bending strength were 5.62%, 0.02%, 0.06%, 2.19gcm−3 and 104.94MPa, respectively. After 30 thermal shock cycles (wind cooling from 1100°C to room temperature), the residual strength of the specimen increased to 110.65MPa, accompanying with −5.44% strength loss rate. The XRD and SEM analysis illustrated that mullite grains with short rod-like shape could prevent crack growth of inter-granular fracture to enhance bending strength of the specimens. Furthermore, the generation of β-spodumene grains with low thermal expansion coefficient after thermal shock improved thermal shock resistance of the composite ceramics. It is considered that the cordierite-spodumene composite ceramics with high densification, good mechanical strength and excellent thermal stability can be a potential material for high temperature thermal transmission pipeline in solar thermal power generation.

Effects of alumina bubble addition on the properties of mullite castables

Injecting lance is a key equipment for hot metal pretreatment. In this work, the lance castables with high mechanical properties and thermal shock resistance were obtained by adding alumina bubbles, due to its spherical shape and hollow structure. It is found that the addition of alumina bubble improves the flow values of castables. The bulk density values of samples with the addition of 4 wt% alumina bubbles (AB4) were the best of all the experimental castables. Alumina bubble addition is effective in heightening the thermal expansion, thermal conductivity of mullite castables and can resist the sharp decrease in thermal expansion above 1300 °C. The addition of alumina bubble can improve the mechanical strength of mullite castables. After heating at 1400 °C, a strong chemical bond forms between the bubbles and the binding phases. Due to the appropriate bonding at the alumina bubble/matrix interface, AB4 castable exhibits a relatively better thermal shock resistance.

Porous SHS-Materials Based on Iron Oxide and Aluminum with Additions of Alloying Elements

An optimum charge composition is developed for preparing porous permeable cermet SHS-materials with prescribed operating properties for cleaning exhaust gases of industrial installations and internal combustion engines. Physicomechanical properties of the materials obtained are determined with a different content of charge components and the range of vibration frequency is established suitable for material operation as filters. It is shown that addition of 0.5 – 1.5 wt.% of alloying elements to a charge increases SHS-material mechanical strength and shock resistance.

Enhanced mechanical properties of SiC reticulated porous ceramics via adjustment of residual stress within the strut

AbstractSilicon carbide reticulated porous ceramics (SiCRPCs) with multi‐layered struts were fabricated by polymer replica technique with SiC slurry, followed by infiltrating alumina slurries containing andalusite under vacuum condition. The effects of andalusite addition on the microstructure and mechanical properties of SiCRPCs were investigated, also the residual stress within the multi‐layered strut was predicted. Theoretical calculations showed that the residual tensile stress generated in the outer layer of SiCRPCs because of its larger thermal expansion coefficient of infiltration slurry than that of SiC slurry at elevated temperature. Furthermore, the addition of andalusite reduced the thermal expansion coefficient and Young's modulus of infiltration slurries, thereby significantly reducing the residual stress of the outer layer in multi‐layered struts. The reduced residual tensile stress within the outer layer was beneficial to eliminate surface cracks on the struts, thus improving the mechanical properties and thermal shock resistance of SiCRPCs.

Mechanical Properties and Thermal Shock Resistance Analysis of BNNT/Si3N4 Composites

BNNT/Si3N4 ceramic composites with different weight amount of BNNT fabricated by hot isostatic pressing were introduced. The mechanical properties and thermal shock resistance of the composites were investigated. The results showed that BNNT-added ceramic composites have a finer and more uniform microstructure than that of BNNT-free Si3N4 ceramic because of the retarding effect of BNNT on Si3N4 grain growth. The addition of 1.5 wt.% BNNT results in simultaneous increase in flexural strength, fracture toughness, and thermal shock resistance. The analysis of the results indicates that BNNT brings many thermal transport channels in the microstructure, increasing the efficiency of thermal transport, therefore results in increase of thermal shock resistance. In addition, BNNT improves the residual flexural strength of composites by crack deflection, bridging, branching and pinning, which increase the crack propagation resistance.

Mechanical stability of monolithic catalysts: Improving washcoat adhesion by FeCrAl alloy substrate treatment

Alumina-washcoated FeCrAl alloy sheets are prepared to investigate the effects of metallic substrate pretreatments on the mechanical stability of monolithic catalysts. It is shown that chemical and thermal pretreatments produce different effects on the metallic surface morphology and phase, and different mechanisms are involved in their ways of improving the washcoat adhesion. Combination of chemical and thermal pretreatments leads to the formation of α-alumina whiskers on corroded and rough metallic surface, thus giving the most satisfactory washcoat adhesion. It is also pointed out that not only mechanical shock resistance but also thermal shock resistance is crucial to metallic monolithic catalysts.

A nitride whisker template for growth of mullite in SiC reticulated porous ceramics

Abstract Silicon carbide reticulated porous ceramics (SiC RPCs) were fabricated by polymer replica technique. The effects of nitride whisker template on the growth of mullite, the strut structure and mechanical properties of SiC RPCs were investigated. Prepolyurethane (PU) open-cell sponge was first coated by SiC slurry consisting of SiC, reactive Al 2 O 3 , microsilica and Si powder, then it was nitridized at 1400 °C in a flowing N 2 atmosphere to prepare SiC preforms. Subsequently, these preforms were treated by vacuum infiltration of alumina slurry and fired at 1450 °C in air. The results showed that Si 2 N 2 O whiskers grew on the surface and in the matrix of SiC preforms after nitridation. The diameter of struts in SiC RPCs increased after vacuum infiltration process because alumina slurry was easily adhered by the surface nitride whiskers. In addition, such whiskers inside the strut of SiC preforms acted as the template to promote the growth of column-liked mullite in SiC RPCs. The mechanical properties and thermal shock resistance of SiC RPCs were greatly improved due to the special interfacial characteristics of multi-layered struts as well as better interlocked column-liked mullite in SiC skeleton.

The effect of carbon and polypropylene fibers on thermal shock resistance of the refractory castable

This work investigates medium cement refractory castable with additives of carbon and polypropylene fibers. The peculiarities of microstructure changes in the fiber and castable matrix contact zone, channel formation, and changes of cold crushing strength of fiber additives, which have a refractory castable matrix under temperature treatment, were investigated. The investigation results allowed to predict that using a mix of fibers more effective than using them indi­vidually. The influence of fiber additives on the mechanical characteristics and thermal shock resistance of the refractory castable with fiber additives was tested. It was found that the addition of carbon fiber has a positive impact on the ther­mal shock resistance of the investigated castable, which is confirmed by the results obtained by thermal cycling, as well as by the values calculated for thermal shock resistance R4 and Rst. In addition, the results of the investigation of thermal cycling show that the value of the thermal shock resistance was highest when a mixed fiber additive (CF+PP) was used.