Micromechanical properties of Dy3+ ion-doped (LuxY1-x)3Al5O12 (x = 0, 1/3, 1/2) single crystals by indentation and scratch tests

Three kinds of Dy³⁺ ion-doped (Lu_xY_1-x)₃Al₅O₁₂ (x = 0, 1/3, 1/2) single crystals fabricated by the Czochralski method with 4 at.% Dy³⁺ ion doping were investigated by indentation and scratch techniques under Vickers, Knoop, Berkovich, and spherical indenters to understand the influence of Lu ion on micromechanical properties and fracture behavior of Y₃Al₅O₁₂ (i.e. YAG for x = 0) single crystals. The largest (or smallest) values of hardness, elastic modulus, and fracture toughness were found for x = 1/3 (or 1/2). The indentation size effect was explained by four different models with the Hays-Kendall approach being the most suitable one to determine the true hardness. Fracture toughness values of YAG crystals obtained by the Vickers hardness method agreed with those obtained by scratching with a spherical indenter based on linear elastic fracture mechanics.     

Impact Energy Absorption Analysis of Spark Plasma Sintered Al2O3 Reinforced Bulk Multiwalled Carbon Nanotube Compacts Using Nanoindentation

For utilizing the outstanding energy absorbing capacity of highly elastic carbon nanotube (CNT), bulk multiwalled CNT (MWCNT) structure containing 15 wt% alumina (Al₂O₃) was fabricated using spark plasma sintering at 1600°C for 10 min under 50 MPa. The compacted mass was ~85% dense having morphologically stable MWCNTs. Microindentation studies up to 9.81 N indicated outstanding elastic recovery of the bulk structure leaving only a diffused indentation mark at indenter‐specimen interaction zone. Quantitative estimation of elastic response behavior of the fabricated structure using instrumented nanoindentation in 10–300 mN load range indicated promising applicability of Al₂O₃/MWCNT compact structure as energy absorbing material.     

Investigation of cohesive FE modeling to predict crack depth during deep-scratching on optical glasses

Optical glass scratching can induce various types of cracks, among which median cracks are extremely detrimental and penetrate deeply under the surface. Due to deep-scratching process complexity, it is challenging to devise a method to predict median crack depth. Indentation testing has been examined comprehensively in prior research works. It has been found that using the correlation between scratch and indentation testing can simplify predictive method development. In this research, a numerical method based on indentation testing is proposed to determine median crack depth during deep scratching. In the first step, an FE model is configured to simulate the indentation testing process and the Cohesive Zone Method is applied to describe median crack behavior. The cohesive parameters calibrated through experimental indentation testing are implemented in the FE scratch model, and the results are compared with the experimental scratch test results. According to the results, the FE scratch model was enhanced by mode II fracture energy and the modeled friction coefficient. The indentation and scratch experiments were conducted with BK7, F2, Fused silica, K5, Pyrex, Quartz, SF6, and SF19. The experimental results prove that the nonlinearity of the median crack depth curve correlates with K_Ic. A comparison of the experimental and numerical results demonstrates the model is virtually functional for materials with K_Ic below 1000?kPa?m^1/2. Comparisons between the current findings and other studies infer the model and experimental results are accurate and reliable.     

Characterisation of indentation microstructures for porous SOFC cathodes

In this study, high-resolution focused ion beam sectioning assisted with SEM imaging was used to study the indentation microstructures of porous bulks and films of a solid oxide fuel cell cathode material (La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ) sintered at different temperatures. The crack morphologies and pore-filling densification caused by crushing of particle networks were studied in details. Analysis showed distinct permanent deformation mechanisms of the indentation microstructures between porous bulks and films. Whilst remarkable porosity gradient was found for the porous films under both Berkovich and spherical indenters, the porous bulks were found to behave more like dense materials. Results also showed that radial cracks induced by Berkovich indentation on the bulks could not generate observable pop-in/pop-out events in the loading-unloading curves. However, when indenting with the spherical indenter on a thick film, the shear sliding of the particle networks immediately under the indenter could cause phenomenal disruption in the loading unloading curves shown.     

Mechanisms of Ytterbium Monosilicate/Mullite/Silicon Coating Failure During Thermal Cycling in Water Vapor

An air plasma spray process has been used to apply a model tri‐layer Yb₂SiO₅/Al₆Si₂O₁₃/Si environmental barrier coating system on SiC test coupons. Significant differences in the thermal expansion of the component layers resulted in periodically spaced mud cracks in the Yb₂SiO₅ and Al₆Si₂O₁₃ layers. Upon thermal cycling between 1316°C and 110°C in a 90% H₂O/10% O₂ environment flowing at 4.4 cm/s, it was found that partial delamination occurred with the fracture plane located within a thermally grown oxide (TGO) at the Al₆Si₂O₁₃–Si interface. Delamination initiated at test coupon edges where the gaseous environment preferentially oxidized the exposed Si bond coat to form β‐cristobalite. Simultaneous ingress of the gaseous environment through mud cracks initiated local formation of β‐cristobalite (SiO₂), the thickness of which was greatest directly below mud cracks. Upon cooling, cristobalite transformed from the β to α phase with a large, constrained volume contraction that resulted in severe microfracture of the TGO. Continued thermal cycling eventually propagated delamination cracks and caused partial spallation of the coatings. Formation of the cristobalite TGO appears to be the delamination life‐determining factor in protective coating systems utilizing a Si bond coat.     

Erosion mechanism of refractories in a pyro-processing furnace for recycling lithium-ion secondary batteries

The refractory lining in a furnace is always damaged and peels off when spent lithium-ion secondary batteries (LIB) are pyro-processed in a rotary kiln. To develop highly durable refractories and to elucidate the erosion behavior, various analyses such as scanning electron microscopy/energy dispersive X-ray spectroscopy, laser-induced breakdown spectroscopy, inductively coupled plasma atomic emission spectroscopy, ion chromatography, and X-ray diffraction were performed on the linings sampled from different sections of a refractory. Our results suggested the following mechanisms in Al₂O₃–SiO₂–CaO refractory damage during pyro-processing of spent LIB packs. First, Li₂O, P₂O₅, LiF, and HF were formed by thermal decomposition of electrolyte constituents of the lithium-ion secondary batteries. When HF reacts with SiO₂, Al₂O₃, and CaO on the surface of the refractory, each fluoride that forms vaporizes and melts. When Li₂O and P₂O₅ (as well as LiF) react with the Al₂O₃–SiO₂ refractory, an Li₂O–Al₂O₃–SiO₂–P₂O₅(-LiF) phase with a low melting point forms and penetrates into the refractory through pores, grain boundaries, and cracks, resulting in peeling off.     

CO2 and CO adsorption equilibrium on ZSM-5 for different SiO2/Al2O3 ratios

CO₂ and CO adsorption on MFI type zeolites with different SiO₂/Al₂O₃ ratios (ZSM-5(30), ZSM-5(50), ZSM-5(280), and silicalite) were investigated in this study by a static gravimetric analyzer for pure isotherms at 30°C, 65°C, 100°C, and 135°C over the pressure range of 0–10 atm. Adsorption capacity of CO increases with decreasing SiO₂/Al₂O₃ ratios within ZSM-5. The adsorption of CO₂ for decreasing SiO₂/Al₂O₃ ratios, showed stronger adsorption at lower pressures and at higher pressures, the highest capacity varied from ZSM-5(50) to ZSM-5(30). ZSM-5(280) was found to have the highest selectivity for CO₂ within the widest range of pressures and temperatures tested.     

Phase Equilibrium Studies of “Cu2O”–SiO2–Al2O3 System in Equilibrium with Metallic Copper

Phase equilibria of the “Cu₂O”–Al₂O₃–SiO₂ system have been experimentally investigated at metallic copper saturation. High‐temperature equilibration, rapid quenching, and electron probe X‐ray microanalysis (EPMA) techniques have been used. Containerless equilibration technique has been developed to enable the phase equilibrium of this chemically reactive system to be investigated. The microstructures and compositions of all phases present in the quenched sample were measured accurately using EPMA. The isothermals between 1150°C and 1300°C have been determined in the “Cu₂O”–Al₂O₃–SiO₂ system at metallic copper saturation. The following primary phase fields were identified in the system: SiO₂ (tridymite), Cu₂O (cuprite), Cu₂O^.Al₂O₃ (delafossite), Al₂O₃ (corundum), and 3Al₂O₃·2SiO₂ (mullite). The implications of the phase diagram on making of the copper aluminosilicate glass have been demonstrated.     

The impact of densification on indentation fracture toughness measurements

The fracture toughness was measured by the Vickers indentation method and by chevron notch for a series of xCaO-xAl₂O₃-(100 − 2x)SiO₂ glasses. As the silica content was increased, the fixed ξ value Vickers indentation fracture toughness (IFT) values increased, while the chevron notch values decreased. Glasses with higher silica contents deform with more densification and less shear when indented with a Vickers tip, thus resulting in reduced residual stress in the region surrounding the indent. The reduction in residual stress for high silica glasses results in less median/radial crack extension and unreasonably high Vickers IFT values. This indicates that a fixed ξ value of 0.016 is not appropriate for the glasses in this series. By repeating the IFT method with a sharper 110° four-sided pyramidal diamond indenter, it is demonstrated that indentation toughness and chevron notch toughness values now trend in the same direction and are in good agreement with a fixed ξ value of 0.0297. With the sharper indenter tip, the densification component to the deformation is substantially reduced for all glass types such that it no longer has such a prominent influence on the residual stress field. This result suggests that a fixed ξ value IFT method may be appropriate for all glass types if a sharper indenter tip is substituted in the place of the Vickers tip.     

Corrosion resistance and anti-reaction mechanism of Al2O3-based refractory ceramic under weak static magnetic field

A slag resistance experiment of the Al₂O₃-based refractory ceramic with CaO–Al₂O₃–SiO₂ slag at 1600°C under a milli-Tesla static magnetic field was conducted. The magnetic flux density effect on the corrosion at the two- and three-phase interfaces of the Al₂O₃-based refractory ceramic, excluding the ‘electromagnetic damping’, was studied. The slag resistance of the Al₂O₃-based refractory was enhanced and quasi-volcanic corrosion at the three-phase interface was eliminated gradually with an increase in the magnetic flux density. A hypothesis and mechanism for the inhibition effect of the static magnetic field based on the free radical pair reaction model was proposed.     

Reactions between Synthetic Mica and Simple Oxide Compounds with Application to Oxidation-Resistant Ceramic Composites

Reaction-couple experiments have been pursued in order to evaluate the potential of a phyllosiiicate to act as a chemically protective, fracture-deflecting, oxidation-resistant interphase for oxide fiber–oxide matrix composites. The synthetic mica fluorophiogopite (KMg₃[AlSi₃]O₁₀F₂) was reacted with single-phase substrates of alumina (Al₂O₃), mullite (3Al₂O₃·2SiO₂), forsterite (Mg₂SiO₄), or enstatite (MgSiO₃). X-ray spectroscopy, X-ray diffraction, and scanning electron and transmitted polarized light microscopy were applied to the analysis of the reaction couples. Fluorophlogopite reacts strongly with alumina, mullite, and enstatite, resulting in substantial damage to the substrate as well as the breakdown of the mica. The chemical reactions between mica–alumina and mica–mullite are examined critically. In the case of alumina, the reaction results in the formation of a planar spinel (MgAl₂O₄) layer separating the substrate from the breakdown products of the mica. This unvarying result suggests, therefore, that a spinel diffusion barrier would prove effective in protecting alumina from fluorophlogopite. Experiments revealed such effectiveness: local equilibrium is established in the layer sequence alumina–spinel–fluorophlogopite; i.e., planar interfaces are established amongst these phases that are stable under conditions of high temperature and high oxygen fugacity. A similar chemical approach for protection of mullite is not obvious. Based on an understanding of its intrinsic fracture energy, the fluoromica interphase is expected to be effective in mechanically protecting adjacent oxides from propagating cracks, a behavior qualitatively demonstrated by indentation experiments on the kinetically persistent alumina–spinel–fluorophlogopite–spinel–alumina laminates.     

Effect of Al Speciation on the Structure of High‐Al Steels Mold Fluxes Containing Fluoride

To design suitable mold fluxes for the casting of high‐Al steels, the structure of mold fluxes based on CaO–SiO₂, CaO–SiO₂–Al₂O₃, and CaO–Al₂O₃ was examined by Raman spectroscopy and magic‐angle spinning nuclear magnetic resonance. The results showed that Si atoms are replaced by Al atoms as the network formers with the increase in Al₂O₃ in the mold fluxes. This converts the silicate slags (CaO–SiO₂ mold fluxes) into aluminosilicates slags (CaO–SiO₂–Al₂O₃ or CaO–Al₂O₃ mold fluxes). The F^? ions in the mold flux containing Al₂O₃ are classified into three categories, according to function: Bridging F's, Nonbridging F's, and Free‐F's. The Al³⁺ ion holds three distinct coordination environments: ^IVAl, ^VAl, and ^VIAl. The addition of F affects the coordination environment of Al³⁺ to form AlO₃F and AlO₂F₂ that accommodate the network structure of slags. The network structure in the CaO–SiO₂ mold fluxes is mainly connected through Si–O–Si linkage. However, the network structure of the mold fluxes containing elevated content of Al₂O₃ is mainly connected through Si–O–Si, Al–O–Al, Al–O–Si, and Al–F–Al linkages. Hence, the structural characteristics of high‐Al steels mold fluxes must be considered during the designing step of the mold fluxes.     

Fracture behavior of Al2O3–SiO2 castables by the wedge splitting test and digital image correlation technique

The fracture mechanisms are helpful for the optimization and design of toughness and microstructure of refractories. Fracture behavior of ultra-low cement bonded Al₂O₃–SiO₂ castables was researched using the wedge splitting test coupled with digital image correlation technique (WST-DIC). Flexibility of Al₂O₃–SiO₂ castables is improved by introducing andalusite aggregates into the castables. The characteristic length L_CH, a parameter used to assess flexiblity of materials, was observed to reach 287.2 mm in andalusite-containing Al₂O₃–SiO₂ castables, more than 5 times that of reference castables. Microcracks toughening is the main toughening mechanisms for flexibility improvement of the Al₂O₃–SiO₂ castables containing andalusite. Microcrack network in the Al₂O₃–SiO₂ castables could be designed by exploiting the volume expansion caused by mullitization of andalusite and the coefficient of thermal expansion (CTE) mismatch between the andalusite aggregate and the matrix. Unlike andalusite-free castables, castables containing andalusite possess a distinct fracture process zone (FPZ), the crack branching and deflection can be observed around the main crack during the fracture process, which leads to the prolong of the crack propagation path, the increase of the dissipation energy during the fracture, and the enhancement of resistance to crack propagation.     

Competitive effects of free volume,rigidity, and self-adaptivity on indentation response of silicoaluminoborate glasses

Lithium aluminoborate glasses have recently been found to feature high resistance to crack initiation during indentation, but suffer from relatively low hardness and chemical durability. To further understand the mechanical properties of this glass family and their correlation with the network structure, we here study the effect of adding SiO₂ to a 25Li₂O–20Al₂O₃–55B₂O₃ glass on the structure and mechanical properties. Addition of silica increases the average network rigidity, but meanwhile its open tetrahedral structure decreases the atomic packing density. Consequently, we only observe a minor increase in hardness and glass transition temperature, and a decrease in Poisson's ratio. The addition of SiO₂, and thus removal of Al₂O₃ and/or B₂O₃, also makes the network less structurally adaptive to applied stress, since Al and B easily increase their coordination number under pressure, while this is not the case for Si under modest pressures. As such, although the silica-containing networks have more free volume, they cannot densify more during indentation, which in turn leads to an overall decrease in crack resistance upon SiO₂ addition. Our work shows that, although pure silica glass has very high glass transition temperature and relatively high hardness, its addition in oxide glasses does not necessarily lead to significant increase in these properties due to the complex structural interactions in mixed network former glasses and the competitive effects of free volume and network rigidity.     

Understanding the solidification and leaching behavior of synthesized Cr-containing stainless steel slags with varying Al2O3/SiO2 mass ratios

This study investigated the effect of Al₂O₃/SiO₂ mass ratios on the equilibrium crystallization behavior of synthesized CaO–SiO₂–MgO–Al₂O₃–Cr₂O₃ stainless steel slags to understand the selective concentration behavior of Cr into a primary Mg(Cr,Al)₂O₄ spinel phase during slag solidification and to determine the leaching stability of Cr-containing slags. The spinel solid solution was precipitated within the temperature range of 1600-1400 °C, where the Cr/(Cr+Al) mole ratio in the Mg(Cr,Al)₂O₄ spinel phase gradually decreased for slags with higher Al₂O₃/SiO₂ mass ratios. When the Al₂O₃/SiO₂ mass ratio increased from 0.125 to 0.5, the Cr content in the amorphous glass phase gradually decreased, with a subsequent increase in the Cr content in the crystalline phase. For slags with a unit Al₂O₃/SiO₂ mass ratio and MgO mole percent comprising less than the combined sum of the Cr₂O₃ and Al₂O₃ mole percents, the Cr content in the amorphous glass phase increased, which was correlated with the enhanced substitution of Cr³⁺ with Al³⁺ in the spinel. The trend of the amount of Cr-related ions in the leachate was consistent with the trend of Cr in the amorphous glass phase: the amount decreased for slags with Al₂O₃/SiO₂ mass ratios from 0.125 to 5 and then increased for slags with an Al₂O₃/SiO₂ mass ratio of 1. The results suggest that the addition of appropriate amounts of Al₂O₃ to stainless steel slags could be conducive to stabilizing Cr into the primary spinel phase to minimize Cr leaching into the environment.     

Degradation of Al2O3f/SiO2 composites exposed to Na2SO4 environment and MMH/N2O4 bipropellants test

Al₂O_3f/SiO₂ composites were fabricated efficiently using sol-gel process. The degradation behavior exposed to Na₂SO₄ environment at 1100℃ and MMH/N₂O₄ bipropellants test were investigated and compared. The results showed that the strength of Al₂O_3f/SiO₂ composites gradually decreased as the ratio of Na₂SO₄:water increased; the strength of the composites was only 23.56 MPa at 20% (Na₂SO₄:water), which suggested that the composites maintained lower strength. Cracks began to appear in SiO₂ matrix, and the structure of Al₂O₃f/SiO₂ composites could be corroded which would corrode the SiO₂ matrix, leaving naked fibers. Developing a protective layer with higher stability for Al₂O_3f/SiO₂ composites would be considered for long time use. The composites showed higher ablation resistance to MMH/N₂O₄ bipropellant test; the flexural strength was (77.15 ± 4.56) MPa and the retention ratio was 98.7%. The degradation of Al₂O_3f/SiO₂ composites was promoted owing to the thermal-mechanical and chemical factors. SiO₂ matrix became weak and fragile at elevated temperature; some SiO₂ matrix became loosened and porous after being washed away through the shearing of MMH/N₂O₄ bipropellants, which prevented cracks from penetrating Al₂O₃ fibers. With ongoing test, the fibers were worsened by thermal-mechanical corrosion.     

Thermodynamic Stability of Spinel Phase at the Interface Between Alumina Refractory and CaO–CaF2–SiO2–Al2O3–MgO–MnO Slags

The interfacial reaction between alumina refractory and CaO–CaF₂–SiO₂–Al₂O₃–MgO–MnO slag was observed at 1873 K to estimate the stability of the spinel phase using computational thermodynamics under refining conditions of Mn‐containing steels. The concentration of MnO formed by the slag–steel reaction in the CaO–CaF₂–SiO₂–Al₂O₃–MgO melts generally increased by decreasing the CaO/SiO₂ ratio of the initial melts. No intermediate compounds were formed at the refractory–slag interface when the initial CaO/SiO₂ ratio was 0.5, whereas CaAl₁₂O₁₉ (CA6) and Mg(Mn)Al₂O₄ (spinel), identified from TEM analysis using EDS mapping and SAED patterns, were observed at the refractory–slag interface when the CaO/SiO₂ ratio was 1.0 or greater. The (at.%Mg)/(at.%Mn) ratio in the spinel solution increased by increasing the CaO/SiO₂ ratio, which originated from the fact that MgO activity continuously increased as the CaO/SiO₂ ratio increased. From thermodynamic analysis considering the equilibrium constant (K_SP) and activity quotient (Q_SP) of the spinel formation reaction at the slag–refractory interface and the bulk slag phase, the precipitation–dissolution behavior of the spinel phase was predicted, which exhibited good consistency with the experimental results. Hence, the dissolutive corrosion mechanism of alumina refractory into the CaO–CaF₂–SiO₂–Al₂O₃–MgO–MnO slag was proposed.     

Cyclic thermal shock resistance of h-BN composite ceramics with La2O3–Al2O3–SiO2 addition

The effects of La₂O₃–Al₂O₃–SiO₂ addition on the thermal conductivity, coefficient of thermal expansion (CTE), Young's modulus and cyclic thermal shock resistance of hot-pressed h-BN composite ceramics were investigated. The samples were heated to 1000 °C and then quenched to room temperature with 1–50 cycles, and the residual flexural strength was used to evaluate cyclic thermal shock resistance. h-BN composite ceramics containing 10 vol% La₂O₃–Al₂O₃ and 20 vol% SiO₂ addition exhibited the highest flexural strength, thermal conductivity and relatively low CTE, which were beneficial to the excellent thermal shock resistance. In addition, the viscous amorphous phase of ternary La₂O₃–Al₂O₃–SiO₂ system could accommodate and relax thermal stress contributing to the high thermal shock resistance. Therefore, the residual flexural strength still maintained the value of 234.3 MPa (86.9% of initial strength) after 50 cycles of thermal shock.     

Integrated experimental phase equilibria study and thermodynamic modelling of the binary ZnO–Al2O3, ZnO–SiO2, Al2O3–SiO2 and ternary ZnO–Al2O3–SiO2 systems

Phase equilibria of the ZnO–SiO₂, Al₂O₃–SiO₂ and ZnO–Al₂O₃–SiO₂ systems at liquidus were characterized at 1340–1740 °C in air. The ZnO–Al₂O₃ subsolidus phase equilibria were derived from the experiments with the SiO₂- and CaO + SiO₂-containing slags. High-temperature equilibration on silica or platinum substrates, followed by quenching and direct measurement of Zn, Al, Si and Ca concentrations in the phases with the electron probe X-ray microanalysis (EPMA) was used to accurately characterize the system. Special attention was given to zincite phase that was shown to consist of two separate ranges of compositions: round-shaped low-Al zincite (<2 mol.% AlO_1.5) and platy high-Al zincite (4–11 mol.% AlO_1.5). A technique was developed for more accurate measurement of the ZnO solubility in the low-ZnO phases (corundum, mullite, tridymite and cristobalite) surrounded by the ZnO-containing slag, using l-line for Zn instead of K-line, avoiding the interference of secondary X-ray fluorescence. Solubility of ZnO was found to be below 0.03 mol.% in corundum and cristobalite, and below 0.3 mol.% in mullite. Present experimental data were used to obtain a self-consistent set of parameters of the thermodynamic models for all phases in this system using FactSage computer package. The modified quasichemical model with two sublattices (Zn²⁺, Al³⁺, Si⁴⁺) (O^2?) was used for the liquid slag phase; the compound energy formalism was used for the spinel (Zn²⁺,Al³⁺)[Zn²⁺,Al³⁺,Va]₂O^2-₄ and mullite Al³⁺₂(Al³⁺,Si⁴⁺) (O^2?,Va)₅ phases; the Bragg-Williams formalism was used for the zincite (ZnO, Al₂O₃); other solid phases (tridymite and cristobalite SiO₂, corundum Al₂O₃, and willemite Zn₂SiO₄) were described as stoichiometric. Present study is a part of the research program on the characterization of the multicomponent Pb–Zn–Cu–Fe–Ca–Si–O–S–Al–Mg–Cr–As–Sn–Sb–Bi–Ag–Au–Ni system.     

Erosion mechanism of the postmortem Al2O3-Ti2O3-Al sliding gate containing novel Al2O3-Ti2O3 raw materials

Al₂O₃-Ti₂O₃-Al sliding gates were prepared from Al₂O₃-Ti₂O₃ raw materials, sintered corundum and aluminum, and used in trials at steel works. The sliding gate with 30 wt% Al₂O₃-Ti₂O₃ added was used on an 80 t ladle for 4 cycles without macrocracks. The postmortem sliding gate can be divided into the permeation layer (0–0.1 mm), transition I layer (0.1–10 mm), transition II layer (10–20 mm) and unchanged layer from the hole working face outward. XRD, SEM and industrial CT were used to analyze the postmortem sliding gate. The results show that, in the Al₂O₃-Ti₂O₃-Al sliding gate, both Al and Ti₂O₃ are involved in reactions, Ti₂O₃ transforms into Ti₂O and TiO in the transition I layer, and part of the Ti₂O₃ in the transition II layer transforms into Ti₈O₁₅. Titanium compounds with different densities are dispersed in the matrix and form microcracks to improve the thermal shock resistance of the sliding gate, which improved the performance.