Indentation-quench Method Research Articles

Comparative evaluation of two different methods for thermal shock resistance of laminated ZrB2-SiCw/BN ceramics

The thermal shock resistance (TSR) of laminated ZrB2–SiCw/BN ceramic was evaluated through indentation-quench and quenching-strengthening methods. It was correspondingly compared to monolithic ZrB2–SiCw ceramic. In the indentation-quench method with consideration to crack propagation on the surface layer, the critical thermal shock temperature of laminated ZrB2–SiCw/BN ceramic with surface residual tensile stress was 550 °C, which was lower than monolithic ZrB2–SiCw ceramic (600 °C). Unlike the microscopic method of crack growth measurement through indentation-quench testing, the quenching-strengthening method, which was based on the macroscopic properties of the material, mainly characterizing the residual strength subsequently to thermal shock, the critical thermal shock temperatures of the laminates and monolithic were 609 °C and 452 °C, respectively. Compared to the brittle fracture of ZrB2–SiCw ceramics, the deflection, bifurcation and delamination of the cracks as the main TSR mechanisms of the laminated ceramics, were revealed through quenching-strengthening method, which was more suitable for the TSR characterization of laminated ceramics.

The indentation thermal shock behavior of laminated ZrB2–SiC ceramics with strong interfaces

The thermal shock behavior of laminated ZrB2–SiC ceramics with strong interfaces has been investigated by indentation-quench method through experiments and modeling, and was compared with that of a reference monolithic ZrB2–SiC ceramic. The residual stress formed in the layers of laminated ZrB2–SiC ceramics was also quantified by indentation technique. Results obtained by indentation-quench tests show that the monolithic and laminated ZrB2–SiC ceramics present a similar crack growth behavior with increasing temperature difference. Nevertheless, the critical temperature difference, ΔTc, of laminated ZrB2–SiC ceramics is much higher than that of the monolithic ZrB2–SiC ceramic. A theoretical model considering all the stress intensity factors at the surface crack tip during thermal shock was established to analyze the mechanism of indentation thermal shock, which is in good agreement with the experimental results. What's more, theoretical results show that the contribution of residual surface compressive stresses in laminated ZrB2–SiC ceramics to stress intensity make a negative contribution to the total stress intensity at the crack tips during thermal shock, which result in a better thermal shock resistance of laminated ceramics than monolithic ceramic.

Thermal shock cracking of porous ZrB2-SiC ceramics

Indentation-quench method is generally used to evaluate the thermal shock resistance of dense ceramics, whereas it is not suitable for porous ceramics. In this paper, we designed a wedge-shaped specimen, as a substitute for the disk-shaped sample, to evaluate the thermal shock behavior of porous ZrB2-SiC ceramics. This method could realize the direct observation of the thermal-shock crack propagation and achieve the measurement of the crack-growth percentage as quenching temperature difference increases. The observation provides the microstructure-evidence of the effect of pores on thermal shock cracking and allows getting an insight into the crack propagation process in porous ceramics.

Toughening mechanism and thermal shock resistance of ZrO2 (3Y)/Fe28at-%Al composites evaluated by indentation techniques

Toughening mechanism and thermal shock resistance of monoclinic ZrO2 (3Y) and ZrO2 (3Y)/Fe28at-%Al composites were investigated by indentation techniques. ZrO2 (3Y)/Fe28at-%Al composites exhibited more pronounced R curve behaviour than the monolithic ZrO2 (3Y). Quantitative analysis of toughening behaviour indicated that the enhanced toughness was attributed to the synergistic effect between crack bridging toughening and phase transformation toughening. Thermal shock resistance of as prepared composite was evaluated by indentation–quench method. Compared with monoclinic ZrO2 (3Y), ZrO2 (3Y)/Fe28at-%Al composites had higher critical thermal shock temperature difference ΔTU at which cracks grow unstably. The thermal shock resistance parameters R, R′ and R′′′′ were also calculated to evaluate the thermal shock resistance. It was found that the addition of Fe28at-%Al particles could lead to higher KIC, thermal conductivity and lower Yong’s modulus, thus resulting in higher ΔTU values of ZrO2 (3Y)/Fe28at-%Al composites than monoclinc ZrO2 (3Y).

The Influential Factors Analysis of Surface Crack Propagation Behavior of ZrB2-20%SiC-10%AlN Ceramic Subjected to Thermal Shock

The indentation-quench method for investigating surface crack propagation has been studied through both experiments and model. The influential factors for surface crack propagation such as specimen thickness, thermal fatigue property, and quench temperature difference (ΔT) and one single specimen being used throughout a whole test ΔTwere surveyed in this paper. Practical results were obtained for ZrB2-20%SiC-10%AlN (ZSA) ultra-high temperature ceramic. The percentage crack growth versus ΔTcurves showed stable crack growth in a relative low ΔTinterval and unstable crack growth above a certain ΔT, and these regimes were sensitive to the thickness. The total stress intensity factor (KI) combining residual stress and thermal stress considering dynamical behavior during the quenching test was calculated by a surface crack theoretical model, the result of calculation was analyzed influential factors and crack propagation .

Thermal shock resistance of in situ toughened α-SiAlONs with barium aluminosilicate as an additive sintered by SPS

The thermal shock properties of 5 wt% BAS/α-SiAlON ceramics fabricated by spark plasma sintering (SPS) technique have been valuated with an indentation-quench method based on Vickers cracks. The obtained materials possessed excellent thermal shock resistance due to the formation of self-reinforced microstructure. The co-doped α-SiAlONs exhibited better thermal shock resistance, undergoing a more stable crack growth than the single-doped ones. It is attributed to the higher fracture toughness.

Reasearch on Heat-Shocking Resistance of SiC<sub>(w)</sub>/ZrO<sub>2</sub>-MoSi<sub>2</sub> Ceramic Composites

The heat-shocking resistance of SiC(w)/ZrO2-MoSi2 ceramic composites prepared by hot-pressing sintering was studied by indentation-quench method together with the calculation of the crack propagation rate of ceramic nanocomposites. The results showed that the crack propagation rate of MoSi2 matrix ceramics samples decreased remarkably with the addition of ZrO2 and SiC nanoparticles. The crack propagation rate of SiC(w)/ZrO2-MoSi2 ceramic composites was obviously lower than that of ZrO2-MoSi2 ceramic composites, which revealed that the synergism between SiC(w) and ZrO2 was more advantageous to enhance the heat-shocking resistance of MoSi2 ceramic. Moreover, the ability of ZrO2 particles to hinder the heat-shocking crack propagation was better than that of SiC whiskers. The synergism between SiC(w) and ZrO2 changed the crack propagation path and shape in MoSi2 ceramics. The mechanisms of ZrO2 to improve the heat-shocking resistance of the MoSi2 ceramic were mainly phase transfer toughening, while that of SiC whiskers to improve the heat-shocking resistance of the MoSi2 ceramic were mainly crack deflection and bridge union.

Research on thermal shock resistance of ZrB 2–SiC–AlN ceramics using an indentation-quench method

The indentation-quench method has been used to evaluate the thermal shock behavior of hot-pressed ZrB 2–20 vol.%SiC–10 vol.%AlN ceramics through both experiments and modeling. The samples with indented cracks are thermal shocked in a series of temperature differences (Δ Ts) into water bath of 20 °C. The percentage crack growth is calculated from the individual cracks along the surface to evaluate the thermal shock resistance of this material. The mechanical and thermal properties controlling the stress intensity response of residual stress and thermal stress have been determined as well as R-curve behavior has been studied by indentation-bending method. The curves of percentage crack growth versus Δ Ts show that crack propagates stably with increasing Δ Ts from 100 to 400 °C, at low Δ Ts (Δ T < 100 °C) no significant crack growth is detected, otherwise when Δ Ts are greater than 400 °C the crack extends unstably. Whereafter, a theoretical model considering both residual stress and thermal stress is established to analyze this process which is in good agreement with the results of experiments.

Thermal shock resistance of dense zirconia matrix composites evaluated by indentation techniques

The thermal shock behavior of 3Y-TZP/LaPO 4 composites containing 0, 15, 30 vol.% LaPO 4 was evaluated with an indentation-quench method based on propagation of Vickers cracks. The effect of LaPO 4 particle size on the thermal shock behavior of 3Y-TZP/LaPO 4 composites was investigated preliminarily. Results showed that the composite containing 15 vol.% 900 °C sintered LaPO 4 exhibited better resistance to crack propagation and thermal shock under water quenching condition. Larger grain size or higher content of LaPO 4 would deteriorate the thermal shock resistance of 3Y-TZP/LaPO 4 composites. The calculation of thermal shock resistance parameter R st for the composites gives a possible explanation for the difference in thermal shock behavior.

Thermal shock resistance and fracture toughness of liquid-phase-sintered SiC-based ceramics

The effect of the heat treatment on the toughness and thermal shock resistance of the silicon carbide–silicon nitride composites prepared by liquid-phase-sintering was investigated. The fracture toughness has been estimated using the indentation method and the thermal shock resistance was studied using the indentation-quench method. The results were compared to those obtained for a reference silicon carbide material, prepared by the same fabrication route. The indentation toughness increased from 2.88 to 5.39 MPa m 1/2 due to the toughening mechanisms (crack deflection, mechanical interlocking and crack branching) occurring in the heat-treated materials during the crack propagation. Similarly the thermal shock resistance increased after the heat treatment of the experimental materials.

Microstructure, mechanical properties and thermal shock resistance of nano-TiN modified TiC-based cermets with different binders

Abstract Microstructure, mechanical properties and thermal shock resistance of TiC-based cermets modified by nano-TiN were studied. The highest transverse rupture strength, fracture toughness and hardness were obtained for the cermets with the compositions 14Mo–20Ni (cermet A), 4Mo–10Co–10Ni (cermet B) and 4Mo–20Co (cermet C), respectively. The quenching-strength method and indentation-quench method were used for studying the thermal shock resistance of nano-TiN modified TiC-based cermets. The results of quenching-strength test denote that the critical temperature differences for sharp decline of residual strength are about 410, 370 and 330 °C for cermets A, B and C, respectively. The results of indentation-quench test show that the micro crack length increases and the micro cracks propagate fast with increasing thermal shock temperature and cycles. The propagation rate of the crack is controlled by the stress intensity of crack tip. Both tests show that cermets with high transverse rupture strength have excellent thermal shock resistance. Thermal shock resistance parameter R and R st calculated are in good agreement with the experimental results.

Mechanical properties and thermal shock behaviour of an alumina/zirconia functionally graded material prepared by electrophoretic deposition

Mechanical properties of a symmetrical planar functionally graded material (FGM) of Al 2O 3 + 10% ZrO 2/Al 2O 3 + 30% ZrO 2/Al 2O 3 + 10% ZrO 2 prepared by electrophoretic deposition (EPD) and pressureless sintering were studied. Hardness and fracture toughness were measured using indentation methods on cross sections of samples. From the difference between lengths of cracks parallel and perpendicular to layers the residual stresses (arisen due to the thermal expansion coefficient mismatch) were calculated. Thermal shock resistance of particular layers was studied using indentation-quench method. The results were compared to those obtained from a reference non-layered composite material, prepared by the same fabrication technique.

Thermal Shock Resistance of the RE-Oxide and Oxynitride Glasses

Thermal shock resistance of the RE-Si-Mg-O-N glasses (RE = La, Nd, Yb, Lu) with 0 and 20 eq.% of nitrogen was investigated by the indentation-quench method based on propagation of Vickers cracks. Crack growth was measured on the same sample for a test series of different quenching temperatures. Thermal shock resistance of the studied materials was determined as a temperature difference resulting in 10 % growth of the initial cracks (∆T10) and by the thermal shock parameter R calculated from the material properties. Although the comparison of ∆T10 and R values as a function of glass composition revealed some differences between these two approaches, also a common trend was observed. Thermal shock resistance increased with the fractional glass compactness resulting from RE type and N content increase.

Microstructure and mechanical properties of titanium carbonitride whisker reinforced β-sialon matrix composites

The microstructure, hardness, fracture toughness and thermal shock resistance were investigated for 15 vol.% TiC 0.3N 0.7 whisker reinforced β-sialon (Si 6− z Al z O 2N 8− z with z=0.6) composites with additions of three different volume fractions 2, 5 and 20 vol.%, of an yttrium-containing glass oxynitride phase. The composites were prepared by hot pressing at 1750°C for 90 min under a uniaxial pressure of 30 MPa in nitrogen atmosphere. The TiC 0.3N 0.7 whiskers were found to survive without deteriorating in morphology or reacting with the β-sialon matrix and/or the glass phase. The TiC 0.3N 0.7 whiskers had no obvious influence on the matrix microstructure, but their presence improved both the hardness and the fracture toughness of the composites. The highest hardness was obtained for the whisker composite with 2 vol.% glass phase ( H v=18.6 GPa). The fracture toughness and thermal shock resistance improved with increasing glass content. The whisker reinforced composite containing 20 vol.% glass showed the highest fracture toughness ( K 1C=6.8 MPa m 1/2). No unstable crack extension occurred during the thermal shock test of the obtained composites in the temperature interval 90–700°C, but above 700°C severe oxidation of the whiskers precludes further evaluation of thermal shock properties by the indentation-quench method applied.

Thermal shock properties of β-sialon ceramics

An indentation–quench method based on Vickers cracks for measuring thermal-shock properties has been applied to β-sialon materials. The thermal-shock properties have been correlated with the morphology of the β-sialon grains, the z value in the β-sialon solid solution Si 6− z Al z O z N 8− z and the amount of residual intergranular glass phase. z Values in the range 0.6–3.0 were tested, and the amount of residual yttrium-containing glass phase was varied between 0 and 20 vol.%. The best thermal-shock resistance was found at low z values, and was further improved by adding an intergranular glass phase. The poorest resistance to thermal shock was found for the highest z value where the presence of glass had no measurable influence. One composition ( z =1.5, 10 vol.% glass) was selected for studying the influence of the microstructure on the thermal-shock properties. The microstructure was varied by applying different sintering conditions. An improvement of the thermal-shock properties and the fracture toughness was found in samples containing elongated β-sialon grains formed in situ. In general, in-situ reinforced β-sialon materials with low z values and containing an intergranular glass phase exhibited the best thermal-shock resistance and improved fracture toughness ( K 1 c >4 MPa m 1 2 ).

Thermal Shock Resistance of Silicon Nitrides Using an Indentation–Quench Test

Thermal shock resistance of silicon nitrides is investigated using an indentation–quench method. Four commercially available silicon nitrides with different microstructures are investigated. The extension of Vickers radial cracks is measured as a function of quenching temperature for each material, up to the critical temperature for failure. An indentation fracture mechanics analysis is used to account for the crack responses, with due allowance for R‐curve behavior. The analysis confirms the important role of microstructure in thermal shock resistance.

Parameters for measuring the thermal shock of ceramic materials with an indentation-quench method

Abstract An indentation-quench method for measuring thermal shock has been evaluated. Experimental parameters such as sample thickness, initial crack length, and water bath temperature were surveyed. It was found that one single sample could be used throughout a whole test series of different quenching temperatures. The method can detect small differences in thermal shock resistance between materials, and was applicable to investigating thermal fatigue. The tested materials were two β-sialons with intergranular glass phase and with completely different thermal shock behaviour. The best resolution was obtained with a sample diameter O=12 mm, height h =4 mm, initial crack length=100 μm. and a water bath temperature=90 °C.

Thermal shock resistance of α/β-sialon ceramic composites

Abstract The thermal shock properties of α/β-sialon composites have been evaluated with an indentation-quench method based on propagation of Vickers cracks. Nominally the z value of the β-phase (Si6-zAlzOzN8-z) was held constant at 0.6, and the composition of the α-sialon phase YxSi12-(m+n)Alm+nOnN16-n was x=0.33, m=1.0, n=1.2. Different α/(α+β) ratios were tested, and the amount of sintering aid (a yttrium-containing glass phase) was varied between 0 and 20 vol.%. The thermal shock resistance increases with increasing fraction of β-phase, and the presence of a glass phase also has a positive influence on the thermal shock resistance.

Influence of Thermal Conductivity and Fracture Toughness on the Thermal Shock Resistance of Alumina—Silicon–Carbide–Whisker Composites

The thermal shock resistance (indentation–quench method), fracture toughness, and thermal conductivity of three alumina–silicon–carbide–whisker composites and alumina have been investigated. A new procedure for the evaluation of thermal conductivity data is suggested, and higher room‐temperature thermal conductivity than that reported in the literature is determined for silicon carbide whiskers. The ranking of the materials according to thermal shock resistance is consistent with the ranking according to fracture toughness but disagrees with the ranking according to thermal conductivity. This finding supports the analytically obtained result that, in defining thermal shock resistance, fracture toughness is more important than thermal conductivity.

Analysis and prediction of thermal shock in brittle materials

The indentation quench method has been studied through both experiments and modeling. Practical results are obtained for alumina, whisker reinforced alumina, cermet and high speed steel. The crack growth vs temperature difference curves show no crack growth at very low Δ Ts, stable crack growth at medium Δ Ts and unstable crack growth above a certain Δ T (Δ T U) and these regimes are explained in the analysis. The stable and unstable crack growth are governed by the combination of residual and thermal stress. An expression has been derived for the prediction of thermal shock resistance and it is shown that the fracture toughness is of great importance. The presence of residual stress results in the greater sensitivity of the indentation-quench method compared to other approaches, and also makes it possible to define specific values of Δ T adapted to specific applications. The method can be used to explore susceptibility to thermal fracture in a range of brittle materials on condition that it is possible to insert an indentation precrack.