Deformation mechanism and influencing factors of thin-walled ceramics under high temperature conditions

一、Deformation mechanism of thin-walled ceramics

      1.1 Deformation caused by thermal stress

       At high temperatures, thin-walled ceramics often experience thermal stress due to their unique physical properties, especially differences in thermal expansion coefficients, when subjected to uneven heating in various parts. This type of thermal stress, which is the internal stress caused by temperature gradients, has a significant impact on the deformation behavior of thin-walled ceramics.

       When thin-walled ceramics are heated, their internal microstructure undergoes changes, such as grain growth and phase transformation, which are manifested macroscopically as material deformation. Especially in high-temperature environments, the difference in thermal expansion coefficient between ceramic materials and the surrounding environment or other materials may lead to significant thermal stress, which in turn can cause deformation. For example, in the composite structure of ceramics and metals, due to the difference in thermal expansion coefficients between the two, significant thermal stress will be generated when heated, which will affect the stability and service life of the entire structure.

        Thermal stress may also cause cracks and fractures inside thin-walled ceramics. Ceramic materials themselves are brittle and sensitive to stress concentration. At high temperatures, the effect of thermal stress may exacerbate stress concentration within ceramics, leading to the initiation and propagation of cracks. These cracks and fractures not only affect the performance of ceramic materials, but may also directly lead to their failure.

       1.2 Deformation caused by changes in material properties

       The material performance changes of thin-walled ceramics under high temperature environment are one of the important factors leading to their deformation. These performance changes include a decrease in elastic modulus, an increase in plastic deformation ability, and changes in internal microstructure.

       As the temperature increases, the elastic modulus of ceramic materials will gradually decrease. Elastic modulus is an important parameter for measuring a material's ability to resist elastic deformation, and its decrease means that the material is more prone to elastic deformation at high temperatures. This deformation behavior is particularly significant in thin-walled ceramics, as their wall thickness is relatively thin and their resistance to deformation is relatively weak. Therefore, the decrease in elastic modulus at high temperatures is one of the important reasons for the deformation of thin-walled ceramics.

       High temperature environments can also enhance the plastic deformation ability of ceramic materials. Plastic deformation refers to the property of a material undergoing irreversible deformation without breaking when subjected to external forces. At high temperatures, the atomic or ionic activity in ceramic materials intensifies, making the material more prone to plastic flow and deformation. The enhancement of plastic deformation ability is also one of the important factors leading to high-temperature deformation of thin-walled ceramics.

       In addition to changes in elastic modulus and plastic deformation ability, high temperature may also cause changes in the internal microstructure of ceramic materials. For example, changes in porosity and migration of grain boundaries may have an impact on the deformation behavior of materials. Porosity refers to the ratio of pore volume to total volume in a material, and its variation can affect the mechanical properties and deformation behavior of the material. Grain boundary migration refers to the movement and recombination of grain boundaries in a crystal, which may lead to the growth or shrinkage of grains, thereby affecting the macroscopic deformation of the material. These microstructural changes are particularly significant at high temperatures and are also factors that cannot be ignored in causing deformation of thin-walled ceramics.

      1.3 The influence of structural design on deformation

       The structural design of thin-walled ceramics plays a crucial role in their deformation behavior at high temperatures. Reasonable structural design can effectively reduce thermal stress concentration, thereby reducing the deformation tendency of ceramics in high-temperature environments. This is mainly achieved by optimizing the shape and size of ceramics and introducing reinforcement structures.

       In terms of shape and size, careful design can make thin-walled ceramics more uniform when heated, thereby reducing thermal stress caused by temperature gradients. For example, using rounded corners and smooth curves to avoid sharp edges and sharp cross-sectional changes can help reduce stress concentration. In addition, adjusting the thickness of ceramic walls appropriately to provide sufficient strength and stability when subjected to thermal loads is also an effective means of reducing the risk of deformation.

        In addition to shape and size optimization, introducing reinforcement structures is also an important way to improve the deformation resistance of thin-walled ceramics. Common reinforcement structures include ribs, reinforcing bars, etc. These structures can effectively enhance the overall stiffness of ceramics and improve their ability to resist deformation caused by thermal stress. At the same time, they can also disperse thermal stress to a larger area, thereby reducing the degree of local stress concentration.

       The design of reinforced structures also needs to consider their impact on the overall performance of ceramics. Excessive reinforcement of the structure may increase the weight and manufacturing cost of ceramics, and in some cases may even lead to new stress concentration points. Therefore, in the design process, various factors need to be comprehensively considered to achieve the best structural optimization effect.

        The selection of materials and preparation processes also have a significant impact on the high-temperature deformation behavior of thin-walled ceramics. For example, selecting ceramic materials with high thermal stability and low creep rate, as well as adopting advanced preparation processes to reduce internal defects and porosity of ceramics, can help improve the deformation resistance of ceramics.

二、analysis of influencing factors

       2.1 temperature factor

       The influence of temperature on the high-temperature deformation of thin-walled ceramics cannot be ignored. Studies have shown that as the temperature increases, the deformation of thin-walled ceramics shows a significant increasing trend.

       High temperature can cause softening of ceramic materials, making them more prone to deformation under external forces. The mechanical properties such as hardness and strength of ceramic materials will decrease at high temperatures, which directly leads to a decrease in their ability to resist deformation.

       High temperature may also cause changes in the internal microstructure of ceramic materials, which further exacerbate the deformation of thin-walled ceramics. For example, under high temperature conditions, the grains in ceramic materials may grow, leading to changes in the microstructure of the material. At the same time, high temperature may also induce phase transition reactions in ceramic materials, generating new phases, and the formation of these new phases will also affect the deformation behavior of the material. These microstructural changes not only affect the mechanical properties of ceramic materials, but may also lead to internal defects and cracks, further increasing the amount of deformation.

        The influence of temperature on the high-temperature deformation of thin-walled ceramics is also manifested in thermal stress. Due to uneven heating in various parts of thin-walled ceramics in high-temperature environments, thermal stress is generated. The magnitude of thermal stress is related to factors such as temperature gradient and material properties. When thermal stress exceeds the bearing capacity of ceramic materials, it can cause deformation or even fracture. Therefore, when designing and applying thin-walled ceramics, it is necessary to fully consider the thermal stress caused by temperature factors and take corresponding measures to reduce thermal stress concentration and deformation tendency.

        Temperature is one of the important factors affecting the high-temperature deformation of thin-walled ceramics. When designing and applying thin-walled ceramics, it is necessary to fully consider the influence of temperature factors and take appropriate measures to control their high-temperature deformation behavior. For example, the influence of temperature on the high-temperature deformation of thin-walled ceramics can be reduced by optimizing structural design to reduce thermal stress concentration and improve the thermal shock resistance of materials.

       2.2 Material factors

       The influence of material factors on the high-temperature deformation behavior of thin-walled ceramics cannot be ignored. The composition and microstructure of ceramic materials largely determine their macroscopic properties, including their ability to resist deformation.

       Impurities and defects in ceramic materials have a significant impact on their high-temperature deformation behavior. Impurities and defects may originate from impurities in raw materials or contamination during processing, which can introduce additional stress concentration points inside the material and reduce its overall strength. In high-temperature environments, these stress concentration points are prone to become the starting points of deformation, leading to an increase in the deformation of thin-walled ceramics. Therefore, when preparing thin-walled ceramics, high-purity raw materials should be selected and pollution during the processing should be strictly controlled to reduce the introduction of impurities and defects.

       The microstructure characteristics such as grain size, shape, and distribution of ceramic materials also have a significant impact on their high-temperature deformation behavior. Fine grains and uniform distribution help improve the strength and toughness of materials, thereby reducing their tendency to deform at high temperatures. On the contrary, coarse grains and uneven distribution may lead to stress concentration and performance degradation. Therefore, in the preparation of thin-walled ceramics, it is necessary to control the size and distribution of grains through appropriate process conditions to obtain the desired microstructure.

       In addition to impurities, defects, and grain structure, additives and sintering processes in ceramic materials can also affect high-temperature deformation behavior. The type and content of additives can alter the sintering and mechanical properties of materials, thereby affecting their ability to resist deformation. The sintering process directly affects the density and microstructure of ceramic materials, thereby affecting their high-temperature stability.

       2.3 technology factor

       The manufacturing process plays a crucial role in the high-temperature deformation behavior of thin-walled ceramics. Every manufacturing process, from the selection and mixing of raw materials to molding, sintering, and even subsequent cooling treatment, may have an impact on the final performance of ceramics.

       During the molding process, pressure, temperature, and time constitute the three key factors that affect the microstructure and properties of ceramics. Pressure not only affects the tightness between ceramic particles, but also directly affects the size and distribution of internal pores in ceramics. Temperature affects the chemical reaction rate between raw materials and the sintering activity of ceramic particles. Excessive or insufficient temperature can lead to abnormal internal structure of ceramics. The time factor cannot be ignored, and appropriate insulation time can ensure the sufficient internal reaction of ceramics, thereby obtaining a more uniform and dense microstructure.

        The firing process is another critical step in ceramic manufacturing, where the heating rate, holding time, and cooling rate also have a significant impact on the performance of ceramics. Excessive heating rate may cause excessive thermal stress inside the ceramic, leading to cracks or deformation; Insufficient insulation time may result in incomplete internal reactions of ceramics, affecting their mechanical properties and heat resistance. The cooling rate is also a parameter that requires precise control. Excessive cooling may lead to microcracks inside the ceramic, thereby affecting its overall performance.

       The selection and optimization of process parameters are particularly important in the manufacturing of thin-walled ceramics. By precisely controlling various parameters during the molding and firing processes, not only can the deformation of ceramics at high temperatures be effectively reduced, but their overall performance and service life can also be significantly improved.