Healing Temperature Research Articles

Effect of Healing Temperature on Crack-Healing of Al<sub>2</sub>O<sub>3</sub> Toughened by SiC Particles

Al2O3 Toughened by SiC particles was hot-press sintered. Cracks of ~300μm in diameter were introduced in the surfaces of specimens, which then healed at 1000°C, 1200°C, 1300°C, 1400°C, and individually for 2h, 4h, 6h and 8h. Effect of healing temperature on bending strength, healing mechanism were systematically investigated, the results show that the best bending strength recovered at room temperature was 583.61MPa obtained at 1300°C for 4h, which was the same value as perfect specimens. The recovery of bending strength contributes to three kinds of mechanisms. When specimens were healed individually at 1000°C, 1200°C, 1300°C for 2h, adsorption mechanism and proliferation mechanism were as the dominant healing mechanisms; when healed at 1400°C for 2h, oxidation reaction mechanism was the important healing mechanism. Also, the length of surface cracks is shorter as healing temperature increasing.

Dynamics of Crack Healing and its Molecular Dynamics Simulation of Al<sub>2</sub>O<sub>3</sub>-MgAlON Composite

After preparing samples (3mm long×4mm wide×36mm high) of Al2O3-MgAlON composites and sintered at 1500°C for 2 h in N2 atmosphere, samples’ cracks were carved by a Vickers hardometer’s pressing head on the center of the sample surface (4 mm×36 mm). Subsequently, the cracks were healed at 1000°C-1550°C for 6 h respectively. Effects of healing temperature on sample’s strength, crack healing dynamics and its molecular dynamics simulation were investigated. The results suggested that: the optimum range of cracks healing temperature was 1300°C-1550°C, and the healing process accelerated at 1300°C, meanwhile, the strength of samples increased significantly. Cracks completely healing finished at 1550°C. The dynamics equation of crack healing was lnν = -Q/kT+lnC. Through characterizing the crack healing rate with the recovering rate of sample’s strength, the diffusion activation energy Q = 4.264 × 10-30 J•K-1 and diffusion constant C=7.359 were claimed. The result of the molecular dynamics simulation suggested that cracks healing process was caused by diffusion could be divided into five stages: passivation of crack tips, formation of salient island, crack shrinkage, generation of secondary crack, and complete healing.

Crack‐healing behaviour of ZrO2/SiC composite ceramics

PurposeZirconia ceramics exhibit high strength and fracture toughness. The purpose of this paper is to research a possibility of crack healing in zirconia ceramics.Design/methodology/approachZrO2/SiC composite ceramics are sintered and subjected to three‐point bending. A surface crack of 100 μm in diameter is formed on each specimen. The cracks are healed and the specimens are tested under bending.FindingsThe paper finds that ZrO2/SiC composite ceramic material had a high crack‐healing ability at a considerably low temperature. For example, a crack of 100 μm in diameter is healed even at 600°C.Research limitations/implicationsThe paper provides a low temperature healing and a new mechanism of crack healing.Originality/valueThe paper shows the healing temperature and the minimum time required to heal showed a good proportional relation on the Arrhenius plot at temperatures of 600‐800°C. Moreover, the crack healing is caused by SiO2 cristobalite produced during the healing.

Crack healing in liquid-phase-pressureless-sintered silicon carbide–aluminum nitride composites

Crack healing in liquid-phase-pressureless-sintered SiC–AlN composites was investigated by introducing cracks into specimens and subsequently heat-treating the specimens. It was observed that cracks were healed and the strength was recovered. Cracks were filled with silica or mullite produced by the oxidation of the composites. It was shown that the healing temperature could be fixed in the range 1100–1300 °C and that large cracks up to about 300 μm could be healed completely. Our results imply that a simple oxidation heat-treatment can improve the reliability of silicon carbide–aluminum nitride components.

Kinetics of Self‐Crack‐Healing of Alumina/Silicon Carbide Composite Including Oxygen Partial Pressure Effect

Self‐crack‐healing behavior under a combustion gas atmosphere with a low oxygen partial pressure, , is important for actualizing ceramic gas turbines, but to date only self‐crack‐healing behavior in air has been investigated. In this study, we investigated crack‐healing behaviors at 1273–1773 K under several levels of. Crack‐healing in atmospheres withgave rise to the complete strength recovery of cracked specimens, resulting from passive oxidation. Based on the obtained results, the kinetics for strength recovery by self‐crack‐healing was expressed as a function of healing temperature, TH (K), and(Pa). The strength recovery rate for complete crack‐healing, vH (s−1), could be expressed as image Using this rate equation, one can evaluate the healing time for complete strength recovery under combustion gas in a gas turbine.

Oxidation-induced crack healing in Zr 2Al 4C 5 ceramic

The crack-healing behavior of Zr 2Al 4C 5 was investigated by oxidizing the pre-cracked sample. A Vickers indentation (∼80 μm in size) was introduced and the crack was healed under different temperature. Cracks could heal completely in air above 1000 °C, with oxidation products consisting primarily of t-ZrO 2 and α-Al 2O 3. The bending strength of crack-healed specimen (188–283 MPa) is higher than that of cracked samples (182 MPa), but all of them are lower than the strength of as-sintered and polished specimens (420 MPa). This composite has self crack-healing ability at temperatures ranging from 800 to 1200 °C, with 1000 °C being the optimum healing temperature.

Healing behavior of a matrix crack on a carbon fiber/mendomer composite

The cure kinetics of a thermally mendable polymer based on Diels-Alder (DA) and retro-Diels-Alder (rDA) reactions, mendomer 401, was investigated using dynamic differential scanning calorimetry (DSC). The resulting behavior was modeled using a conventional cure kinetic model for thermosetting polymers. A composite panel with two layers of carbon fabric and mendomer 401 was fabricated following the cure cycle suggested by the cure kinetics model. Micro-indentation tests were performed to investigate mechanical properties and dynamic mechanical thermal analysis (DMTA) was conducted to study thermal behavior and to find the trigger temperature for healing. Self-healing behavior of the carbon fiber/mendomer composite was demonstrated using electrical resistive heating over the glass transition temperature.

Crack -Healing Behaviour of Zirconia/SiC Composite Ceramics

ZrO2/SiC composite ceramics were sintered and subjected to three-point bending. A surface crack of 100μm in diameter was made on each specimen. We studied crack-healing behavior. The main conclusions are as follows. (1) ZrO2/SiC composite ceramics could heal a crack. Then the best healing condition is 800°C × 30h in air. (2) A crack was healed even at 600°C, which was a very low temperature compared with other ceramics. (3) The ZrO2/Y2O3/SiC system ceramics caused an extensive corrosion at over 1000°C. (4) Healing temperature and the minimum -time to heal were in the good proportional relation on the Arrhenius diagram at 600–800°C.

Si3N4세라믹스의 균열 치유와 굽힘 강도 특성

Crack-healing behavior of Si₃N₄ composite ceramics has been studied as functions of heat-treatment temperature and amount of additive SiO₂ colloidal. Results showed that optimum amount of additive SiO₂ colloidal and coating of SiO₂ colloidal on crack could significantly increase the bending strength. The heat-treatment temperature has a profound influence on the extent of crack healing and the degree of strength recovery. The optimum heat-treatment temperature depends on the amount of additive SiO₂ colloidal. Crack healing strength was far the better cracked specimen with SiO₂ colloidal coating on crack surface. After heat treatment at the temperature 1,273 K in air, the crack morphology almost entirely disappeared by scanning prob microscope. At optimum healing temperature 1,273 K, the bending strength with additive SiO₂ colloidal 0.0 wt.% without SiO₂ colloidal coating recovered to the value of the smooth specimens at room temperature for the investigated crack sizes 100 ㎛. But that with SiO₂ colloidal coating increase up to 140 %. The amount of optimum additive SiO₂ colloidal was 1.3 wt.% and crack healed bending strength with SiO₂ colloidal coating increase up to 160 % to smooth specimen of additive SiO₂ colloidal 0.0 wt.%. Crack closure and rebonding of the crack due to oxidation of cracked surfaces were suggested as a dominant healing mechanism operating in Si₃N₄ composite ceramics.

Crack-healing behavior of zirconium diboride composite reinforced with silicon carbide whiskers

The crack-healing behavior of zirconium diboride ceramic composite reinforced with silicon carbide whiskers has been investigated through pre-cracking, crack-healing and flexural strength testing processes. A Vickers indentation (∼70 μm in size) was introduced and the crack was healed under different conditions. Cracks could heal completely in air, but did not heal in a vacuum. This composite has good self crack-healing ability at temperatures ranging from 800 to 1200 °C, with 1000 °C being the optimum healing temperature.

Obtaining the glass transition temperature by measuring the crack healing process of glassformers

By the study of a series of molecular liquids of fragilities covering almost the entire known range by the mechanical spectroscopy of quantitatively monitoring the healing of stress-induced microcracks recently developed by W. H. Wu et al. [Appl. Phys. Lett. 92, 011918 (2008)], we show that the cracking healing temperature coincides with the onset glass temperature Tg, quite independent of the liquid fragility. Another interesting observation is that the major part of the modulus recovery occurs below Tg. Thus, our study establishes an additional approach to the study of the glass dynamics and glass transition which lends itself to a variety of potential applications.

Threshold Stress for Crack Healing of Mullite Reinforced by SiC Whiskers and SiC Particles and Resultant Fatigue Strength at the Healing Temperature

A mullite/SiC whisker/SiC particle multi‐composite, having excellent crack‐healing ability and mechanical properties, was hot pressed in order to investigate the crack‐healing behavior under stress and the resultant fatigue strength at the temperature of healing. A semi‐elliptical surface crack 100 μm in surface length was introduced on each specimen. The pre‐cracked specimens were crack healed under cyclic or constant stress by using a three‐point bending stress at 1473 K, and the resultant bending strength and cyclic fatigue strength were measured at 1473 K. The pre‐crack on the surface of the specimens could be healed even under stress. The threshold stresses for crack healing, as determined by evaluating the strengths of crack‐healed specimens at a healing temperature of 1473 K, were 170 MPa for both constant and cyclic stresses, corresponding to 77% of the bending strength of the pre‐cracked specimens. The static and cyclic fatigue behaviors of crack‐healed specimens were also investigated at a healing temperature of 1473 K.

OS16-3-3 Crack-healing behavior of mullite/SiC multi-composite under stress and resultant fatigue strength

A mullite/SiC whisker/SiC particle multi-composite, having excellent crack-healing ability and mechanical properties, was hot-pressed in order to investigate the crack-healing behavior under stress and the resultant fatigue strength at the temperature of healing. A semi-elliptical surface crack of 100 μm in surface length was introduced on each specimen. The pre-cracked specimens were crack-healed under cyclic or constant stress by using a three-point bending stress at 1473 K, and the resultant bending strength and fatigue strengths were measured at 1473 K. The pre-crack on the surface of the specimens could be healed even under stress. The threshold stresses for crack-healing, as determined by evaluating the strengths of crack-healed specimens at a healing temperature of 1473 K, were 170 MPa for both constant and cyclic stresses, corresponding to 77% of the bending strength of the pre-cracked specimens. The static and cyclic fatigue strengths of crack-healed specimens were also investigated at a healing temperature of 1473 K.

The effect of clay particles on film formation from polystyrene latex

AbstractFilm formation from surfactant‐free polystyrene (PS) latex was performed in the presence of 5% Na‐montmorillonite (NaMMT). The composite films were prepared from pyrene (P)‐labeled PS particles at room temperature and annealed at elevated temperatures above the glass‐transition (Tg) temperature of polystyrene. Scattered light (Is) and fluorescence intensity (IP) from P were measured after each annealing step to monitor the stages of composite film formation. Minimum film formation temperature, T0, and healing temperatures, Th, were determined. Void closure and interdiffusion stages were modeled and related activation energies were measured. From these results, it was found that the presence of NaMMT in the PS latex film only affects the minimum film formation, but does not affect the void closure and backbone motion activities. POLYM. COMPOS., 27:299–308, 2006. © 2006 Society of Plastics Engineers

P59 ムライト/炭化ケイ素マルチ複合材料の応力下におけるき裂治癒挙動と応力下治癒材の高温疲労強度特性(OS13)

Mullite reinforced with SiC whiskers and SiC particles, called here Mullite/SiC multi-composite, having high crack-healing ability and high fracture toughness was hot-pressed. A semi-elliptical surface crack was introduced on the test specimen. To heal the surface crack, the specimens were heat-treated at 1200℃ for 5h in air under constant or cyclic stress, and the resultant bending strength and fatigue strength were investigated at the healing temperature. The main conclusions are as follows: (1) The specimens could be healed even under stress, and the threshold stress for crack-healing was 170MPa. (2) The crack-healed specimens had high bending strength and high fatigue strength even at the healing temperature.

Effects of Frequency on the Crack-Healing Behavior of Si3N4/SiC Composite under Cyclic Stress

Si3N4/SiC ceramics were hot-pressed to investigate the effect of stress frequency on the crack-healing behavior under cyclic stress. The specimens having pre-crack of 100µ m were subjected to crack-healing under constant or cyclic bending stresses of 300MPa at temperatures between 800 and 1200°C. The resultant bending strength of the crack-healed specimen was investigated. At a healing temperature of 900°C, the pre-cracks had been completely healed both under constant stress and cyclic stress of 0.5Hz. However, the pre-cracks had not completely healed under a cyclic stress of 5 and 10Hz. Thus, the stress frequency affects crack-healing behaviors at 900°C. On the other hand, when the healing temperature was higher than 1000°C, the pre-cracks were healed completely under both constant stress and cyclic stress up to 10Hz. The effects of stress frequency were dependent on the healing temperature. The reasons for this were discussed from the viewpoint of competitive mechanism of fatigue crack growth and crack-healing.

2738 ムライト/炭化ケイ素マルチ複合材の応力下における自己き裂治癒挙動(S28-3 セラミックスおよびセラミックス系複合材料(3),S28 セラミックスおよびセラミックス系複合材料)

A mullite / SiC whisker / SiC particle multi-composite, having excellent crack-healing ability and mechanical properties, was hot-pressed in order to investigate the crack-healing behavior under stress and the resultant fatigue strength at the temperature of healing. A semi-elliptical surface crack 100 μm in surface length was introduced on each specimen. The pre-cracked specimens were crack-healed under cyclic or constant stress by using a three-point bending stress at 1473 K, and the resultant bending strength and cyclic fatigue strength were measured at 1473 K. The pre-crack on the surface of the specimens could be healed even under stress. The threshold stresses for crack-healing, as determined by evaluating the strengths of crack-healed specimens at a healing temperature of 1473 K, were 170 MPa for both constant and cyclic stresses, corresponding to 77% of the bending strength of the pre-cracked specimens. The static and cyclic fatigue strengths of crack-healed specimens were also investigated at a healing temperature of 1473 K.

A new methodology to guarantee the structural integrity of ceramics components

Recently, the authors developed Si3N4, Al2O3 and mullite ceramics with good self-crack-healing abilities. It was shown that the optimized condition to get high temperature strength was: 1573K, 1 h, in air, and the healed zone exhibited the same strength as the base material. Using this good healing ability, a new methodology to guarantee the reliability of ceramic components crack-healing + proof was proposed. However, if a crack initiated during service, reliability would be severely impaired. Therefore, if a material can crack-heal during service, and if the healed zone has enough strength at the temperature of healing, it would be very desirable for structural integrity. From the above points of view, a new methodology to guarantee the structural integrity of ceramic components using in-situ ability was proposed and the usefulness was discussed using the test results in terms of behavior and proof test theory by the authors.

Crack Healing Behavior with Healing Temperature in Si3N4/SiC Composite Ceramics

To investigate the microcrack healing behavior of $Si_3N_4-20wt\%SiC-8wt\%Y_2O_3$ composite ceramics(SNCY8), we observe the crack length evolution a! the time of 20, 40, 60 minutes with in-situ optical microscopy by varying healing temperature of $800\~1200^{\circ}C$ . Crack healing obviously oc...

Effect of Heat Treatments on the Crack‐Healing and Static Fatigue Behavior of Silicon Carbide Sintered with Sc2O3 and AlN

Crack‐healing behavior of silicon carbide ceramics sintered with AlN and Sc2O3 has been studied as a function of heat‐treatment temperature and applied stress. Results showed that heat treatment in air could significantly increase the indentation strength whether a stress is applied or not. After heat treatment with no applied stress at 1300°C for 1 h in air, the indentation strength of the specimen with an indentation crack of ∼100 μm (≈2c) recovered its strength fully at room temperature. In addition, a simple heat treatment at 1200°C for 5 h under an applied stress of 200 MPa in air resulted in a complete recovery of the unindented strength at the healing temperature. However, higher applied stress led to fracture of the specimens during heat treatment. The static fatigue limit of the specimens crack healed at 1200°C for 5 h under 200 MPa was ∼450 MPa at the healing temperature. The ratio of the static fatigue limit of the crack‐healed specimen to the unindented strength was ∼80%.