Solid Additives to Increase the Service Life of Ceramic Cutting Tool: Methodology and Mechanism

Ceramic tool materials are brittle, sensitive to surface defects, and prone to fracture at the cutting edge when impacted during the cutting process, significantly reducing their application reliability. Improving the reliability of ceramic tool materials can be achieved through material selection, process optimization, surface treatment, and structural design. Selection of suitable ceramic cutting tool material components is to improve the reliability of ceramic cutting tool material basis, embodied in the toughening and reinforcement to reduce crack initiation to hinder crack expansion, self-repair repair surface defects. In favour of the growth of the service life of ceramic tool materials [9,10]. 2.1. Toughening, Strengthening Phenomenon to Increase the Service Life In the field of machining, cutting tools play a crucial role as they significantly impact the surface quality of the workpiece. The characteristics of the cutting tool are closely related to this aspect. Ceramic tools have been widely adopted in industrial part production due to their superior wear and corrosion resistance compared to commonly used metal tools [2,11]. Additionally, ceramic tools possess excellent mechanical properties, making them suitable for processing high-strength difficult-to-machine materials [1]. However, single-phase ceramic tools have limitations; therefore, incorporating solid additives into the ceramic matrix can effectively enhance the overall performance of ceramic tool materials and extend their service life [12]. Furthermore, utilizing solid additives can introduce new properties that broaden the application scenarios for ceramic tools. The matrix phases and solid additives of ceramic materials are typically brittle and difficult to plastically deform, lacking mechanisms for depleting fracture energy. Therefore, the main toughening mechanism of composite ceramic materials is to enhance fracture toughness by increasing the ability of the crack extension process to deplete fracture energy [12,13,14]. Consequently, the toughening mechanism of composite ceramic materials is closely related to the crack extension mechanism. Ceramic materials are primarily toughened and reinforced by mixtures of one or several materials, such as hard particles, whiskers, fibers, rare earth elements, and nanoparticles. However, the type, content, size, and distribution of additives need to be rationally designed in order to significantly enhance the reliability and service life of ceramic tool materials. 2.1.1. Hard Particles The presence of hard particles, as illustrated in Figure 3, can induce block cracking, leading to crack deflection, crack bridging, crack branching, and enhanced fracture toughness and flexural strength of the material. Good hardness with higher toughness and flexural strength greatly improves wear resistance and service life. Some carbides [15,16], nitrides, oxides [17,18,19], and borides [20,21,22,23] have been shown to improve the reliability of conventional ceramic tool materials [24,25]. Chen et al. [15] prepared WC to enhance the mechanical properties of Al₂O₃ nanocomposites, and found that the addition of WC accelerated the sintering process of Al₂O₃ matrix and improved its mechanical properties by hindering its grain growth. Song et al. [16] found that when the H_fC content increased from 15 wt% to 25 wt%, the pore number gradually decreased and the relative density gradually increased. The grain size of TiN and TiB₂ decreased, indicating that H_fC additive can inhibit the growth of TiN and TiB₂ grains and form fine structures which are conducive to improving the bending strength. The toughening mechanism of ceramics mainly includes H_fC grain pull-out, fine crystal, crack deflection and crack bridge. Because the hardness of H_fC is higher than TiN and lower than TiB₂, the increase of H_fC content increases the Vickers hardness of TiN-H_fC composite, but decreases the Vickers hardness of TiB₂-H_fC composite. According to the results of Yu et al. [17], as the volume fraction of ZrO₂ increases from 0% to 50%, the bending strength increases from 291 to 423 Mpa. Yazar et al. [21] showed that the fracture toughness of B₄C-SiC composites increased by 28% when 10% TiB₂ was added to the sample. Xia et al. [26] found that TiSi₂ mainly affected the intermediate sintering process of B₄C and increased the sintering rate, thus shortening the grain growth time and improving the comprehensive mechanical properties of the material. The results show that when the content of TiSi₂ is 10 wt%, the bending strength and fracture toughness of the composite ceramics are 807 MPa and 3.2 MPa·m^1/2. The incorporation of hard particles, such as TiC or TiN, into the ceramic matrix enhances the material’s hardness and wear resistance. However, at temperatures exceeding 800 °C, oxidation and subsequent degradation of titanium carbide and titanium nitride particles occur, resulting in a loss of their reinforcing properties [27]. The addition of TiB₂ particles to the Al₂O₃ matrix by Deng et al. [28] resulted in notable improvements in fracture toughness, hardness, and flexural strength, leading to a significant enhancement in wear resistance and fracture behavior. The investigation unveiled that an increased content of TiB₂ demonstrated enhanced wear resistance. Both sliding wear tests and cutting experiments exhibited reduced friction coefficient and wear rate for Al₂O₃/TiB₂ ceramic cutting tool materials with varying TiB₂ contents (0–40 vol%). However, it is worth noting that the high temperature oxidation of TiB₂ generates B₂O₃ which can easily volatilize [29], potentially negatively impacting the material’s flexural strength and reliability. Therefore, in the actual processing application, the processing temperature to ensure the life of ceramic tools is an important factor. Skopp et al. [30] added TiN or BN to Si₃N₄, which significantly reduced the wear rate. They concluded that in order to improve the wear resistance of conventional Si₃N₄ ceramics, glassy phases should be minimized as much as possible and thermal dispersion and thermal conductivity should be increased to reduce thermal stresses and prevent thermal cracking. Ko et al. [31] found that the optimal content of SiC in Al₂O₃ ceramics varies when machining different workpieces. The tool life of Al₂O₃-10 wt% SiC composite tool was the longest when machining heat-treated AISI 4140 steel, which was 7 times longer than that of Al₂O₃-TiC composite tool, while a 5 wt% SiC composite tool was the longest when machining grey cast iron. It can be observed that the service life of ceramic tool materials is not solely determined by mechanical properties but is closely related to the actual machining application environment. 2.1.2. Nanomaterials The presence of nanophase alters the mode of crack propagation in single-phase ceramic materials, transforming it from a solely along-crystal fracture to a hybrid fracture where both through-crystal and along-crystal fractures coexist [32,33,34]. The location of the nanophase has a significant influence on the material properties, which is also of additional interest [3,35,36]. This consumes more fracture energy and improves fracture toughness [37,38]. The dispersion of carbon nanoparticles in the matrix, the interface bonding state with the matrix and the structural change are the main reasons for the strengthening and toughening of carbon nanoparticles [33]. Yi et al. [34] found that nanoscale CaF₂-induced transgranular fracture enhanced the toughness of the composite. Crack flexure is the main toughening mechanism of nanometer CaF₂ composites. Mustafa et al. [35] pointed out that compared to alumina, The strength and toughness of alumina composites containing 1.5 wt% multi-walled carbon nanotubes (MWCNTs) increased by 58% and 66%, respectively. Liao et al. [36] found that Si₂BC₃N ceramics doped with 1 vol% MWCNTs had higher bending strength and fracture toughness. The toughening and strengthening effect of 462.1 MPa and 5.54 MPa·m^1/2 is mainly due to the highly energy-intensive bridging and drawing. By investigating the toughening mechanism of Al₂O₃ ceramics reinforced with nano-ZrO₂ additives, Du et al. [39] found that the nanophase inside the Al₂O₃ crystal plays a dominant role in altering the fracture mode of nanocomplex ceramic materials. The ZrO₂-Al₂O₃ composite ceramics (ZTA-1), prepared through mechanical grinding and dispersion methods, exhibit a significant presence of “intracrystalline” structures, as depicted in Figure 4a–f. These structures offer more convoluted crack deflection paths and consume higher fracture energy compared to conventional ceramics obtained via direct powder doping (ZTA-2). Consequently, the flexural strength and fracture toughness exhibited a significant enhancement of 50% and 83%, respectively. This observation suggests that the incorporation of nanoparticles within the crystal lattice is imperative for achieving superior outcomes. To summarize the mechanism, the presence of an “intracrystalline” structure gives rise to the formation of subgranular boundaries within the Al₂O₃ particles, resembling a re-refinement of their organization and resulting in reinforcement through small particle effects. As shown in Figure 4g,h, W₂C/Al₂O₃ nanocomposites exhibit only crack deflection, while WC/Al₂O₃ nanocomposites exhibit crack bridging, crack deflection, and secondary cracking. The additional mechanism provided by WC with small particles to absorb the fracture energy leads to an increase in the overall mechanical properties of the material. The effect of TiC nanoparticles on the mechanical properties of Al₂O₃/SiC_w materials was investigated by Zhao et al. [40]. It was observed that the incorporation of nanoparticles significantly enhanced the bending strength, thermal hardness, and high temperature fracture toughness of Al₂O₃/SiC_w ceramic tool materials at room temperature. However, at high temperatures, these composites were prone to fracturing along the crystal structure, resulting in low high-temperature bending strength for Al₂O₃/SiC_w/TiC_n composites. This hindered the improvement of high-temperature bending strength. Yin et al. [41] prepared ceramic tools containing both TiC nanoparticles and micron-sized TiC particles in an alumina-based matrix for machining austenitic stainless steel. They discovered that these tools exhibited superior wear resistance compared to alumina-based ceramic tools enhanced only with micron-sized TiC particles. The use of nanoparticles enhanced tool life. 2.1.3. Whiskers and Fibres Adding whiskers [42,43] or fibers [44,45] to the ceramic matrix can improve the fracture toughness of the material through crack branching, bridging and flexural behavior [46,47]. Yu et al. [42] introduced mineral bridging agent, and the bending strength and fracture toughness of aluminum-based ceramics were increased by 33.97% and 33.52%, respectively. More crack deflection, crack bridging and whisker pulling out occurred on the fracture surface. Zhu et al. [43] found that the introduction of SiC whisker could significantly improve the mechanical properties of SiCO ceramics. When the SiC whisker content varies from 0 to 5 wt%, the bending strength of the sample increases from 44.2 ± 4.1 MPa to 260.1 ± 49.7 MPa. The fracture toughness increased from 1.48 ± 0.03 MPa·m^1/2 to 3.23 ± 0.12 MPa·m^1/2. The mechanism of SiCO ceramic SiC whisker toughening mainly includes whisker breaking and pulling out, deflection, crack bridging, directional distribution of whisker and compressive stress of SiC whisker on ceramic matrix. Chen et al. [44] constructed polycrystalline cubic boron nitride/hexagonal boron nitride (PcBN/hBN) fiber monolithic ceramics with long fiber arrangement structure using cubic boron nitride/hexagonal boron nitride (PcBN/hBN) fiber as the grain boundary. The failure of composite ceramics was non-brittle, which was mainly attributed to the multi-scale crack effect in the layered structure. The maximum crack propagation toughness is extremely high (about 21 MPa·m^1/2), which is 270% higher than the crack initiation toughness. Lang et al. [47] significantly strengthened and toughened porous Yttria-stabilized zirconia (YSZ) by using Al₂O₃ fiber. When the addition of Al₂O₃ fiber was 10 vol%, the strength of porous YSZ ceramics reached the maximum, with a compressive strength of 100.2 ± 25.4 MPa. The bending strength is 61.5 ± 11.3 MPa. With the increase of Al₂O₃ fiber content, the fracture toughness of YSZ ceramics increased monotonously, from 0.5MPa·m^1/2 to 1.2MPa·m^1/2, an increase of 140%. A large number of researchers have revealed the toughening mechanism of SiC fibers by studying the crack extension mode of SiC_f/SiC composites. When the applied load is large, the ceramic matrix will crack earlier than the fibers [48,49]. Under continuous loading, cracks in the matrix extend to the matrix-fiber interface, resulting in two different scenarios [50,51]. In cases where the bond strength at the matrix-fiber interface is weak, cracks propagate along the interface and bypass the fibers. Conversely, when there is a strong bond at this interface, cracks propagate through or around individual fibers. Regarding how crack extension modes influence properties of fiber-reinforced ceramic matrix composites, Yang et al. [52] explained their connection with material properties from an interfacial bond strength perspective. The length of fiber pull-out demonstrates this bond strength at the matrix-fiber interface. When interfacial bond strength between fiber and matrix is weak, it hampers effective transfer of applied load from fiber to matrix and reduces overall strength of SiC_f/SiC material; conversely, when interfacial bond strength between fiber and matrix is very high, it does not favor manifestation of overall toughness in SiC_f/SiC material. Huang [2] and Jia [8] employed silicon carbide whisker (SiC_w) reinforcement to fabricate ceramic tools exhibiting enhanced flexural strength, fracture toughness, and resistance to cutting wear. Guo et al. [53] and Liu et al. [54] used Al₂O₃-reinforced ceramic tools with SiC_w to machine Inconel718 parts, which exhibited good machinability. The toughening mechanism of SiAlCN ceramics reinforced by SiC whiskers or graphene nanoparticles (GNPs) was investigated by Li et al. [55]. As depicted in Figure 5, the high fracture toughness of SiAlCN ceramics is attributed to alternating along-crystal and through-crystal fractures combined with grain bridging. The toughening mechanisms of SiC_w/SiAlCN and GNP/SiAlCN ceramics exhibit similarities, encompassing crack deflection, bridging, and pullout; however, their frequencies of occurrence and effects manifest distinct variations. Due to the strong interfacial bonding between SiC_w and SiC grains, crack deflection induced by SiC_w is limited, while the pull-out length is reduced without any occurrence of crack branching phenomenon; thus slightly enhancing the toughness of SiC_w/SiAlCN ceramics. The GNP/SiAlCN ceramics exhibit enhanced fracture toughness compared to other materials due to a larger specific surface area and improved interfacial bonding between GNPs and the matrix, which facilitates effective toughening mechanisms such as crack deflection/branching and GNP bridging/pull-out. It is evident that bond strength between fibers/whiskers/nanoparticles/matrix has a significant influence on material properties. Zhao et al. [56] discovered that TiC nanoparticles within Al₂O₃ particles can induce perforation fracture and deflect cracks, thereby synergistically enhancing the overall performance of the material when combined with whiskers. Zhang et al. [7] incorporated SiC whiskers and particles into the matrix, improving their reliability significantly. Therefore, the collaboration between whiskers and nanoparticles or hard particles can result in ceramic tool materials exhibiting enhanced overall performance. Whiskers and nanoparticles or hard particles demonstrate a synergistic toughening or strengthening mechanism, thereby enabling the achievement of ceramic tool materials with exceptional performance. 2.1.4. Rare Earth Elements The utilization of rare earth elements has become indispensable in the preparatory procedure of novel ceramic tool materials. The incorporation of rare earth elements can enhance the sintering process of ceramics, while the addition of a mixture of these elements reduces porosity in composites and optimizes the microstructure of ceramic cutting tool materials, thereby improving performance and extending service life [57,58,59]. Xu et al. [60] found that the action mechanism of Y element additive was mainly to purify the interface, thereby improving the binding strength of the interface and strengthening the effect of nano-sized particles. Due to the coexistence of strong interface and weak interface, the synergistic effect of crack bridging, crack branching, crack defects and micro-cracks was enhanced. Zhang et al. [57] incorporated a blend of rare earth elements (RE), namely Nd, Ce, La, and Pr, into the Al₂O₃ matrix to investigate the influence of this mixed rare earth element addition on properties and microstructure. The addition of RE improved the mechanical properties, as demonstrated in Table 1. The pure alumina particles, as shown in Figure 6a, exhibited irregular shapes and abnormal growth, with the fracture mode primarily being along-crystal fracture. As shown in Figure 6b,c, although the fracture mode did not change, the addition of mixed rare earths resulted in uniform size and regular shape of alumina particles and additive particles in the composites. Rare earth elements are widely used as effective additives in current research on advanced ceramic materials [61,62]. They serve not only as stabilizers for tetragonal zirconia but also as sintering aids for ceramics such as Al₂O₃, TiB₂, TiC, SiC, Si₃N₄, Sialon and AlN [63,64]. The mechanical properties of all these ceramic materials can be significantly enhanced. Using yttrium oxide as a liquid phase sintering agent, Kennametal introduced their syalon ceramic tool [65]. Choi et al. [66] prepared Yb/Y co-doped SiAlON ceramics using rare earth oxide Yb₂O₃ as the main sintering additive. Intercrystalline fracture was predominantly observed in the Yb/Y co-doped SiAlON ceramics in terms of crack propagation. The fracture toughness increased by 53.6% from 4.6 to 7.0 MPa⋅m^1/2, and the content of sintering additives was optimized. Qiu et al. [67] found that the addition of different amounts of Y₂O₃ or CeO₂ to Al₂O₃ ceramics could significantly reduce the sintering temperature and greatly improve the material properties. Xu et al. [17,68] utilized Y-reinforced Al₂O₃/(W, Ti)C ceramics and observed that the maximum flexural strength and fracture toughness were approximately 20% higher compared to those of the corresponding materials without added Y element. The researchers concluded that the primary mechanisms of action exhibited by the Y element additive encompass interface purification, enhancement of interface bonding strength, and nanoparticle augmentation. After machining hardened 45 carbon steel and HT20-40 cast iron, it was found that the wear resistance of the new tool was superior to that of the corresponding material without rare earths. The improvement in cutting performance of Al₂O₃/(W, Ti)C ceramic tool materials by rare earth elements was achieved through enhancing their microstructure and mechanical properties. Therefore, high-performance structural ceramics, such as fully stabilized zirconia ceramics (FSZ), tetragonal zirconia polycrystals (TZP), and other high-performance structural ceramics, can be synthesized by incorporating various rare earth oxides in different types and quantities. The addition of rare earth oxides not only suppresses the phase transition of the ceramics but also improves their flexural strength and toughness. Adding rare earth oxides as additives, stabilizers, and sintering aids greatly enhances the performance and extends the service life of advanced ceramics. 2.2. Self-Repairing Phenomenon Increases Service Life The most intuitive effect of the self-repairing phenomenon of ceramic tool materials is the improvement of service life. During the preparation and machining of ceramic tools, defects such as porosity and microcracks can occur [69], which can lead to a decrease in the mechanical properties of ceramic tools, making them more susceptible to wear or fracture failure in the process of use, and decreasing the service life of ceramic tools. Therefore, processes to eliminate surface defects are very important to safeguard the performance and lifetime of ceramic materials. Such as grinding, polishing and heat treatment. In order to reduce defects such as surface porosity and microcracks, ceramic materials are prevented from premature failure due to surface damage [70]. A significant number of scholars have improved the service life of ceramic tools through the self-repair function of ceramic materials [4,71], showing that self-repairing ceramic tools can effectively utilise the heat of cutting to produce a liquid phase that fills the cracks and achieves crack self-repairing. Researchers have classified the self-repairing mechanisms and repair methods of ceramic materials into three types: adsorption repair, chemical reaction repair, and diffusion repair. Adsorption repair has a low treatment temperature but limited repairing effect [71,72]. The temperature for diffusion repair needs to be close to the sintering temperature [73,74], which consumes excessive resources. Therefore, chemical reactions are primarily used for repairing surface defects during the actual cutting process [75,76]. However, when using chemical reactions for surface defect repair, attention should be paid to the impact of repair temperature and reaction products on the effectiveness of the repair. Gupta et al. [71,77,78] discovered that MgO and Al₂O₃ ceramic materials can undergo crack self-repair through annealing treatment. After conducting numerous experiments, researchers discovered that materials such as Al₂O₃, Si₃N₄, SiC [79,80,81], BC₄ [82], ZrB₂ [83], ZrN [84], mullite [85], MAX materials, (e.g.: Ti₂AlC, Ti₃AlC₂) [86,87] and their composites [88,89,90,91] exhibit a phenomenon of self-repairing cracks. Chu et al. [92] found that amorphous silica formed by oxidation of silicon and silicon carbide could fill cracks and heal cracks. Houjou et al. [93] found that the cracks of Si₃N₄/SiC composite ceramics completely healed in air, but did not heal in argon, N₂ gas and vacuum. Wang et al. [94] found that the cracks of SiC-Al₂O₃-B₄C ceramics could be completely healed in the air above 700 °C. The ceramic composite material had the best effect when repaired at 700 °C for 30 min, and its bending strength could be restored to 94.2% of the original. Self-repairing ceramic materials can restore the attenuation strength caused by cracks and other micro-defects after heat treatment [95,96,97,98]. Yoshioka et al. [95] determined the lowest temperature at which the strength of the crack healed sample of Mullite /TiSi₂ composite recovered to the strength of the unbroken sample, and determined it to be 600 °C. Burlachenko et al. [96] found that regardless of SiC content, ZrB₂-SiC ceramic composite had the best defect self-healing effect after annealing at 1600 °C. Monteverde et al. [97] found that silica glass phase generated by SiC oxidation had a repairing effect. Dedova et al. [98] found that the thickness of the oxide layer of the ceramic composite (ZrB₂-ZrC-SiC)-ZrO increased with the increase of the volume fraction of zirconia, and that the temperature of 1600 °C had a complete healing effect on the defects of the ceramic composite regardless of the content of ZrO₂. Furthermore, they can even eliminate residual stress while achieving complete crack repair [99], thereby enhancing the mechanical properties of the material and bolstering the reliability of ceramic materials. However, it should be noted that subjecting some materials to high heat treatment temperatures can result in the formation of porosity, which adversely affects their performance [100]. Shi et al. [24] used TiSi₂ to reduce the porosity of the repair surface and reduce gas volatilization (Figure 7). A significant number of scholars [101,102,103] have investigated the repairing effect of Al₂O₃/SiC nanocomposite ceramics and have discovered that heat treatment at temperatures ranging from 1273 K to 1773 K can effectively repair cracks measuring less than 250 µm in length and no more than 100 µm in depth. The room-temperature flexural strength of Al₂O₃/SiC nanocomposite ceramic materials can be fully restored. It is worth noting that if the cracks are repaired by transporting the glass phase generated in a high-temperature environment to them, then the ceramic material used for repairing will soften at high temperatures, thereby reducing its strength [73]. However, if the self-repairing phenomenon can promote the precipitation of the glass phase at the fracture, it will improve the high temperature strength of the ceramic material. Therefore, not only does the self-repairing function of ceramics cracks [104,105,106] help restore material strength, but it also enhances mechanical strength, thereby increasing lifetime and reliability. Takahashi et al. [107] and Ando et al. [92] studied the self-repairing effect of Al₂O₃/SiC_w and Si₃N₄/SiC The effect of self-repairing of ceramic materials was investigated at 1300 °C. It was found that the room temperature fatigue strength of ceramic materials after crack repair was restored to that of the original smooth specimen, and the static fatigue strength of Si₃N₄/SiC was also comparable to that of the original smooth specimen at 1000 °C, which indicated that the fatigue strength in the region of self-repairing was better restored. Liu et al. [108] investigated the repair effect of Mullite/ZrO₂/SiC_p after heat treatment at 800 °C and found that the cracks on the material’s surface were almost completely repaired, and the fracture toughness of the material recovered. However, due to the sensitivity of bending strength to surface defects, there is no significant recovery in strength. Sun et al. [109] found that the smaller the particle size of Al₂O₃-MgO composites, the better their repairing ability. The self-repairing properties of alumina ceramic materials containing SiO₂ and MgO were investigated by Moffatt et al. [110]. It was observed that the fracture toughness gradually increased with increasing heat treatment temperature. However, a significant decrease in fracture toughness was observed when the temperature reached 800 °C. This is because the inflow of intergranular glass phases into the cracks to achieve the material repair will lead to the material softening phenomenon in the high temperature environment. However, for Al₂O₃-17 vol% SiC ceramic materials, the room temperature fracture toughness reaches its maximum value when the repair temperature reaches 1200 °C, and there is no significant decrease in the fracture toughness with the increase of the test temperature. Savchenko et al. [111] observed in the friction experiment of ZrB₂-20 vol% SiC ceramics that liquid borosilicate glass has the self-repairing effect of subsurface defects. This is because the low shear resistance viscous mechanical mixed layer composed of borosilicate glass, trioxide and transfer products can reduce friction, repair subsurface cracks, and keep the wear rate at an acceptable level. Cui et al. [112] prepared Al₂O₃/TiC/TiB₂ (ATB) ceramic tools and discovered that the cutting heat during the cutting process enabled the tools to repair certain micro-defects, thereby enhancing their tool life. As depicted in Figure 8, TiB₂ oxidation caused by the cutting heat is identified as the primary factor contributing to tool restoration during cutting. Zhao et al. [113] investigated the cutting performance of a ceramic tool reinforced with whiskers and nanoparticles (Al₂O₃/SiC_w/TiC_n) for dry cutting Inconel718 and high-speed machining of Inconel718. The new ceramic tool can be reliably used at high speeds up to 400 m/min. The tool material undergoes oxidation to a glassy phase at a high temperature of 1200 °C, which repairs thermal cracks on the tool edge, inhibits crack expansion, prevents instant damage to the tool, and assists in improving its lifespan. Shi et al. [8] investigated the Al₂O₃/TiC/10 vol% TiB₂/5 vol% hBN@Al₂O₃ (AT10B@5) ceramic. The cracks were partially repaired by the addition of B₂O₃ and TiO₂ during dry turning of 40Cr hardened steel. This filling process effectively prevented the accumulation of micro-cracks in the ceramic tool material during cutting, thereby reducing the risk of brittle fracture. As a result, tool wear was reduced and tool life was extended. Some scholars evaluated the service life of ceramic tool materials through simulation [114]. A constitutive model was developed to analyze the behavior of self-healing ceramic materials in a finite element framework. Ozaki et al. [115] proposed a damage repair constitutive model for self-healing ceramics, incorporating an oxidation kinetics-based crack repair behavior evolution law. The time-dependent relationship of strength recovery obtained by finite element analysis is quantitatively compared with the reported experimental data of Al₂O₃/15 vol% SiC particles, Al₂O₃/30 vol% SiC particles and monolithic SiC. The findings demonstrate that the finite element analysis method employed in this study effectively replicates the fundamental characteristics of strength recovery observed in self-healing ceramics. Maeda et al. [116] used this model and finite element method to calculate the self-healing properties of surface cracks, and the results showed that the method could estimate the healing conditions and verify the stress by obtaining the microstructure information and oxidation kinetic parameters of ceramic components in advance. Bellezza et al. [117] proposed a model for predicting the tensile life of self-healing, long SiC fiber-reinforced ceramic matrix composites in an oxidizing environment. The model can accurately describe the physical and chemical phenomena of the crack with time, especially the oxygen concentration field, the degradation of the reactive matrix layer and the formation of related oxides, and the oxidation of the interface around the fiber. In the machining process is a dynamic process, the surface will continue to be damaged, repair speed is an important parameter. The effectiveness of TiC restorers in the low-temperature self-healing behavior of Al₂O₃-based self-healing ceramics was evaluated by Nakao et al. [118]. The 30% TiC-70% Al₂O₃ intermediate layer was the best restorers for self-healing ceramics, and good healing effect could be achieved within 10 min at 600 °C. A successful development of a prototype for low pressure turbine blades has been achieved, featuring fiber reinforced self-healing ceramics. However, there are few studies on the repair rate, and a few scholars make up for the lack of relevant data through simulation [115]. Some researchers have looked at ways to increase the rate of repair. Greil [119] accelerates crack filling by reducing the healing agent particles to the nanoscale, forming a low viscosity polysilicate or borate melt phase and forming a solid solution, thereby reducing the healing temperature and shortening the healing time. Huang et al. [120] found that the synergistic effect of oxidation-induced healing and precipitation-induced healing of SiC particles and whiskers could indeed improve the crack repair rate and oxidation resistance of sic coatings. This collaborative repair mechanism may broaden the potential applications of existing self-healing ceramic coatings in high-temperature oxidation environments. Through the above research, it can be seen that the repair speed is an important factor affecting the service life of ceramic tools in actual machining engineering. There are few experimental data on the repair speed of various repair agents. Collaborative repair is an effective method to improve the repair speed.