Thermal Shock Temperature Difference Research Articles

Mechanical properties and thermal shock resistance of TiB2‒B4C composite ceramic tool materials at microscopic scale

AbstractA finite model incorporating microstructure was developed to investigate the thermal shock resistance of TiB2‒B4C composite ceramic cutting tool materials. Numerical simulations were conducted to analyze changes in the transient temperature field and thermal stress field during the thermal shock process. TiB2‒B4C composite ceramic tool materials were fabricated using discharge plasma sintering technology. With different B4C contents, different sintering temperatures and holding times as study variables, optimization of the sintering process parameters and ceramic material components was achieved through testing the mechanical and microscopic morphology of the ceramics. Thermal shock water quenching experiments were performed, and the strength‐decay method was employed to assess the thermal shock resistance of TiB2‒B4C ceramics. The findings indicate that the optimal sintering conditions are temperature of 1700°C and holding time of 5 min. The TiB2‒B4C ceramic material containing 20 vol% B4C exhibits superior comprehensive mechanical properties and thermal shock resistance, and its relative density, fracture toughness, hardness, and flexural strength were 99.3%, 6.8 MPa m1/2, 22.8 GPa, and 598 MPa, respectively. The critical thermal shock temperature difference falls within the range of 400°C‒500°C.

Microstructure, mechanical properties and thermal shock behavior of 2.5D oxide fiber preform reinforced oxide matrix composites

The 2.5D oxide/oxide composites become attractive for their excellent integrity and mechanical properties. The thermal shock resistance performance of the material is very important in the actual high temperature application. In this work, the evolution of microstructure and mechanical behavior of the 2.5D oxide/oxide composites from thermal shock at different temperatures and cycles was investigated experimentally mainly by optical microscope, X-ray computed tomography and macro-mechanical tests. The thermal shock resistance mechanism of oxide/oxide composites was qualitatively explored. The results showed that cracks propagation was the main manifestation of thermal shock damage in composites. Compared with 2D composites, 2.5D composites exhibited the finite domain effect on crack propagation due to its reinforcement had certain fibers in Z-direction. This directly caused the critical thermal shock temperature difference of the 2.5D composites (∼900 °C) was more than twice that of the 2D oxide/oxide composites (∼400 °C). In addition, the finite domain effect also significantly reduced the damage growth rate of the 2.5D composites from cyclic thermal shock, highlighting its excellent thermal shock damage resistance.

Study of the influence of ZrB2 content and thermal shock on the elastic modulus of spark plasma sintered ZrB2-B4C composites using a non-destructive ultrasonic technique

Non-destructive ultrasound phase spectroscopy (UPS) was used to study the influence of thermal shock on the longitudinal elastic constant (C11) of ZrB2-B4C composites. C11 of the composites was measured in the as-fabricated condition and after different numbers of thermal shock cycles. The relative change in C11 was used as the thermal shock resistance parameter. Composites with 70 and 50 vol% ZrB2 were subjected to three thermal shock temperature differences (ΔT) of 600 °C, 800 °C, and 1000 °C, respectively. The rate of drop in C11 increased significantly with an increase in ΔT and B4C content. The mechanism of thermal shock damage has been discussed considering the influence of processing-induced thermal residual stresses and the average stress state in both phases during thermal shock. It was shown that the powder particle arrangement plays a major role in the damage mechanism and B4C-B4C particle contacts provide easy paths for crack propagation.

Effects of multilayer hydrothermal carbon interphases on mechanical properties and thermal shock resistance of CF/ZrB2-SiCBN

Multilayer hydrothermal carbon coatings (HTCCs) with various thicknesses were constructed on CFs using alternating hydrothermal carbonization and heat treatment approach. Well-established CF/ZrB2-SiCBN composites with distinct multilayer interphases were processed via slurry injection and precursor infiltration pyrolysis method. The multilayer HTCCs with suitable thickness would be pulled-out stepwise from the matrix, which could absorb the impact energy and toughen the composites effectively. Although the outer HTCC would still react with the matrix to form a strong interface, the moderate interfacial binding force between CF and inner HTCC could effectively transfer the load and assure the fiber debonding when the composites deformed drastically. Moreover, the increasing of coating thickness could alleviate the damage of fibers in oxidation environment and improve the critical thermal shock temperature difference of composites, while the excessive thick coating would weaken the fiber strength and limit toughening abilities of the CFs.

A multiscale damage prediction model for the thermal shock of carbon fiber-reinforced silicon carbide matrix composites

In this study, under the heating rate of 1300 °C/min, the thermal shock tests of 2D C/SiC composites with different thermal shock cycles and temperature differences (680 °C, 980 °C, 1280 °C) were carried out. Based on thermal shock damage mechanisms, a two-step residual properties prediction model using thermal-mechanic-oxygen coupling and cross-scale methods was established. The damage field calculation and residual properties prediction were carried out according to the thermal shock condition in the first. The test results show that matrix cracking caused by thermal gradient stress, interfacial debonding caused by thermal mismatch and fiber failure caused by oxidation are the main reasons for thermal shock damage of 2D C/SiC composites. The prediction results show that the residual strength, stiffness and stress–strain curve of the thermal shock obtained by the prediction have little difference from the test results, which reflects the accuracy of the prediction model.

The effect of thermal shock temperature difference on the structural, dynamics and mechanical properties of carbon materials characterized by ultrasonic test technology

The effect of thermal shock temperature difference on the structural, dynamics and mechanical properties of carbon materials characterized by ultrasonic test technology

Microstructure and mechanical and thermal shock properties of hierarchically porous ceramics

Hierarchically porous Al2O3 ceramics with a porosity of 30–69% containing small intergranular pores and large pores created by a pore-forming agent were fabricated by gel-casting followed by partial sintering with starch addition. The influence of various pore types on the mechanical and thermal shock properties of the ceramics was subsequently investigated. A thermal shock parameter K was introduced to evaluate the dependence of strength degradation rate on the thermal shock temperature difference, and a new method for calculating the intergranular porosity and extrinsic porosity of the porous ceramics was developed. A low thermal shock strength degradation rate was obtained at a high ratio of fracture toughness (KIC) and elasticity modulus (E) of the material, which was achieved by decreasing the relative fraction of spheroidal extrinsic pores. However, the presence of these pores increased both the KIC and E values.

Thermal shock resistance and crack growth behavior of Aurivillius phase Bi4Ti3O12-based ferroelectric ceramics

A type of W/Cr co-doped Bi4Ti3O12 (ab. BTWC) ceramics were synthesized utilizing the traditional solid-state reaction process, and its thermal shock resistance (TSR) as well as the crack growth behavior was systematically investigated by water quenching technology. It can be found by the succeeded fractographic analysis that many edge thermal cracks began to appear in the samples subjected to thermal shock with ΔT ​= ​400 ​°C. According to an integrated TSR model, the critical thermal-shock temperature difference ΔTCwas calculated to be 356 ​°C. Moreover, it can be noticed that the indenter induced crack growth behaviors under thermal shock loads presented three stages, i.e. no growth, large growth, and moderate growth, along with ΔT increasing from 0 ​°C to 700 ​°C. Finally, the asymmetry of P-E hysteresis loops was observed and understood by the orientated polarization of defect dipoles after the sample was thermally shocked, while the water-quenching process above the Curie temperature of the ceramics could lead to a random orientation of the defect dipoles. This research can not only evaluate the service conditions of Bi4Ti3O12 high-temperature piezoceramics, but also understand the failure mechanism of bismuth layer structured ferroelectric ceramics in the case of thermal shock.

Enhanced mechanical properties and thermal shock resistance of Cf/ZrB2-SiC composite via an efficient slurry injection combined with vibration-assisted vacuum infiltration

An efficient slurry injection combined with vibration-assisted vacuum infiltration process has been developed to fabricate 3D continuous carbon fiber reinforced ZrB2-SiC ceramics. Homogenous distribution between carbon fiber and ceramic was achieved successfully, leading to an enhancement in mechanical properties. The Cf-PyC/ZrB2-SiC composite exhibited a typical non-brittle fracture mode with a superior fracture toughness of 6.72 ± 0.21 MPa·m1/2 and an extraordinary work of fracture of 2270 J/m2, respectively, increasing by nearly 14.8 % and 36 % as compared with those of a parent composite fabricated by only slurry injection and slurry infiltration. The enhancement in fracture toughness and work of fracture were attributed to multiple toughening mechanism including crack deflection, PyC coated fiber bundles pull-out and fiber bridging. Moreover, a critical thermal shock temperature difference of 814 °C was achieved, higher than that of traditional ZrB2-based ceramics. This work presents an efficient approach to fabricate high-performance Cf/UHTCs with uniform architecture.

Fabrication and properties of three-directional orthogonal aluminosilicate fiber fabric-reinforced mullite composite

In this study, a three-directional orthogonal aluminosilicate fiber fabric-reinforced mullite composite with excellent properties was prepared by the precursor impregnation and pyrolysis (PIP) method. The influence of the number of PIP cycles on the microstructure and mechanical properties of the composite was studied. The density and mechanical properties of the composite enhanced with increasing number of PIP cycles. After the 6th PIP cycle, the density of the composite increased by only 0.8%, and the flexural strength and fracture toughness of the composite reached 130.1 MPa and 4.91 MPa m1/2, respectively. Moreover, the thermal shock resistance of the composite was investigated by the high-low temperature (from 1300 °C to room temperature) thermal treatment and water quenching method. The strength retention rate of the composite after 10 high-low temperature thermal cycles was 90.1%; the retention rate dropped to 79.5% after 15 thermal cycles. The composite with the critical thermal shock temperature difference 843.9 °C displayed excellent thermal shock resistance.

Fabrication and thermal shock behavior of Si3N4 whiskers toughened γ-Y2Si2O7 coating on porous Si3N4 ceramics

In order to prevent water from entering the porous Si3N4 ceramics, α-Si3N4 whiskers toughened γ-Y2Si2O7 coatings were prepared by a liquid infiltration and filling method. Effects of α-Si3N4 whiskers content on the microstructure, waterproof performance, mechanical properties and thermal shock behavior of the ceramic coatings were systematically studied in this paper. Results indicated that the addition of whiskers could effectively improve the performance of the coatings under thermal shock due to the toughening mechanism of whiskers including crack deflection, whisker bridging, whisker pulling out and other energy dissipation processes. The coating with a α-Si3N4 whisker/γ-Y2Si2O7 mass ratio of 1/9 possessed a flat, dense and defect-free surface microstructure. After five thermal cycles under a thermal shock temperature difference of 1200 °C, water absorption of the coating increased slightly from ~3.2% to ~6.0%. The whisker reinforced coating is promising to be used for high temperature wave-transmitting materials in long-time service.

Effects of micro and macro features on the thermal shock resistance of laminated Al2O3–MgO composites

The thermal shock resistance (TSR) of laminated Al2O3–TiN–MgO/Al2O3–ZrB2–MgO ceramic (LAMC) and Al2O3–TiN–MgO ceramic (ATMC) composites were investigated systematically by combining experimental data with stress intensity state theory. The microstructures and relative displacements before and after quenching, crack propagation, residual flexural strengths, and critical thermal shock temperature differences (ΔTc) of the LAMC and ATMC composites were identified and investigated. The TSR of the LAMC composite was higher than that of the ATMC composite as determined by comparing micro and macro features of LAMC and ATMC composites. The effects of different experimental approaches on the TSR of LAMC and ATMC composites were analysed. The analysed values of ΔTc for LAMC and ATMC composites, acquired based on stress intensity state theory, were consistent with the experimental data of crack propagation.

Mechanical properties of laminated HfB2-SiC/SiCw material modified with silicon carbide whisker layer

This study reports the preparation of laminated HfB2-SiC/SiCw ceramic (LHSw) with interfacial SiC whiskers (SiCw) by tape-casting followed by hot-pressing. The microstructure and mechanical properties of LHSw were studied in detail. The results showed that the flexural strength and fracture toughness of LHSw materials were 408 ± 24 MPa and 10.6 ± 0.4 MPa m1/2, respectively. The fracture toughness of the LHSw material was higher by 2.6 times than that of a monolithic HfB2-SiC ceramic (HS) (4.1 ± 0.2 MPa m1/2). This improvement was ascribed to the SiC whiskers with high aspect ratio in the interfacial layer, which was beneficial for the deflection and bifurcation of cracks. In addition, LHSw showed excellent resistance to thermal shock. It is found that the critical thermal shock temperature difference was approximately 553 °C, which is 1.2 times higher than that of HS (457 °C) and can be attributed to the porous structures formed in the interfacial layer of LHSw. Thus, micro-cracks formed in LHSw, but it was not penetrating cracks that formed in the HS after thermal shock.

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.

Processing and mechanical performance of 3D Cf/SiCN composites prepared by polymer impregnation and pyrolysis

Abstract The processing of 3D carbon fiber reinforced SiCN ceramic matrix composites prepared by polymer impregnation and pyrolysis (PIP) route was improved, and factors that determined the mechanical performance of the resulting composites were discussed. 3D Cf/SiCN composites with a relative density of ∼81% and uniform microstructure were obtained after 6 PIP cycles. The optimum bending strength, Young's modulus and fracture toughness of the composites were 75.2 MPa, 66.3 GPa and 1.65 MPa m1/2, respectively. The residual strength retention rate of the as-pyrolyzed composites was 93.3% after thermal shock test at ΔT = 780 °C. It further degraded to 14.6% when the thermal shock temperature difference reached to 1180 °C. The bending strength of the composites was 35.6 MPa after annealing at 1000 °C in static air. The deterioration of the bending strength should be attributed to the strength degradation of carbon fibers and decomposition of interfacial structure.

Microstructures and mechanical properties of Cf/ZrB2-SiC composite fabricated by nano slurry brushing combined with low-temperature hot pressing

The Cf/ZrB2-SiC composite was successfully fabricated via brushing nano ZrB2-SiC slurry followed by low-temperature hot pressing technique, in which the UHTC phases were uniformly introduced into intrafascicular space of the subdivided fiber bundles. The fabricated composite exhibited a non-brittle fracture behavior and excellent mechanical properties with a high work of fracture of 1338 J/m2, one order of magnitude higher than that of the ZrB2-SiC ceramic, which was attributed to the hybrid toughening mechanisms such as crack deflection, fiber bridging, fiber pull-out and crack branching. The fiber/matrix interfaces were analyzed by the high resolution transmission electron microscopy, and no obvious chemical reaction was detected, suggesting the degradation of carbon fiber was effectively inhibited. Moreover, the Cf/ZrB2-SiC composite showed a good thermal shock resistance with a thermal shock temperature difference of 764 °C, almost twice those of the ZrB2-SiC ceramic. This work provides a facile and effective approach to fabricate high-performance continuous carbon fiber reinforced ceramic composites with uniform component distribution.

Microstructural evolution and performance of carbon fiber-toughened ZrB2 ceramics with SiC or ZrSi2 additive

ZrB2–SiC/ZrSi2 ceramics containing 30 vol% carbon fiber (Cf) additive were fabricated by hot pressing at low temperature (1500 °C) using submicron ZrB2 powders, and their microstructural evolution and performance were investigated. The addition of SiC or ZrSi2 significantly reduced the onset sintering temperature and enhanced the densification of ZrB2. ZrB2–ZrSi2–Cf showed poor performance owing to the serious fiber degradation, while the fiber degradation was effectively inhibited in ZrB2–SiC–Cf resulting in high fracture toughness, substantial fiber pull-out, and non-brittle fracture mode for such material. The critical thermal shock temperature difference of ZrB2–SiC–Cf was up to 741 °C, significantly higher than those of ZrB2–SiC/ZrSi2 and ZrB2–ZrSi2–Cf. Moreover, this composite displayed a good oxidation resistance at 1500 °C in air.

Multiscale toughening of ZrB2‐SiC‐Graphene@ZrB2‐SiC dual composite ceramics

AbstractThe design of bioinspired architectures is effective for increasing the toughness of ceramic materials. Particularly, a dual composite equiaxial architecture is ideal for fabricating weak interface‐toughened ZrB2‐SiC ceramics with isotropic performance. In this paper, ZrB2‐SiC‐Graphene@ZrB2‐SiC dual composite ceramics were synthesized via an innovative processing technique of granulating‐coating method. ZrB2‐20 vol.% SiC containing 30 vol.% Graphene was selected as weak interface to realize multiscale toughening and improve the thermal shock resistance of ZrB2‐SiC ceramic materials. The incorporation of ZrB2‐SiC‐Graphene weak interface into the ZrB2‐SiC matrix improved the damage tolerance and critical thermal shock temperature difference. The design of equiaxial structures moderated the anisotropy of performance in different planes. The graphene sheets incorporated in the ZrB2‐SiC‐Graphene interface phase played a key role in multiscale toughening, including macroscopic toughening of crack deflection and microcracks, and microscopic toughening of graphene bridging and pull‐out.

Mechanical, thermal physical properties and thermal shock resistance of in situ (TiB2+SiC)/Ti3SiC2 composite

Dense (TiB2+SiC)/Ti3SiC2 composite with 20 vol% TiB2 and 10 vol% SiC was synthesized by in situ reaction hot pressing. The room and high temperature mechanical and thermal physical properties, as well as thermal shock resistance of the composite were investigated and compared with SiC/Ti3SiC2 composite as prepared by the same process. The synergistic action of TiB2 and SiC produced a significant strengthening and toughening effect and (TiB2+SiC)/Ti3SiC2 composites exhibit superior room- and high-temperature mechanical properties compared with SiC/Ti3SiC2 composite. Especially, (TiB2+SiC)/Ti3SiC2 composite shows higher Young's modulus from 25 °C to high temperature and can retain a high modulus of 313 GPa (about 81% of room temperature value) up to 1200 °C. From 25 °C to 800 °C, (TiB2+SiC)/Ti3SiC2 composite has higher thermal conductivity and slightly lower coefficient of thermal expansion. Both water quenching test results and calculation of thermal shock resistance parameters, R, Rst and RIV indicate an improved thermal shock resistance of (TiB2+SiC)/Ti3SiC2 composite, with an increase of the critical thermal shock temperature difference ΔTc from 325 °C for SiC/Ti3SiC2 to 440 °C for (TiB2+SiC)/Ti3SiC2. Superior properties render (TiB2+SiC)/Ti3SiC2 composite a promising prospect as high temperature structural materials.

Rapid heating thermal shock study of ultra high temperature ceramics using an in situ testing method

In this paper, the rapid cooling thermal shock behaviors of ZrB2–SiC ceramics were measured using traditional water quenching method, and the rapid heating thermal shock behaviors of ZrB2–SiC ceramics were investigated using a novel in situ testing method. The measured critical thermal shock temperature difference for rapid cooling thermal shock was 373.6 °C; however, the critical thermal shock temperature difference for rapid heating thermal shock of ZrB2–SiC ceramics was measured to be as high as 1497.2 °C. The thermal stress distribution states after rapid cooling thermal shock and rapid heating thermal shock testing were analyzed using finite element analysis (FEA) method. The FEA results showed that there is a tensile stress existed on the surface for rapid cooling thermal shock, whereas there is a compressive stress existed on the surface for rapid heating thermal shock. The difference of thermal stress distribution resulted in the difference of the critical temperature difference for rapid cooling thermal shock and rapid heating thermal shock.