Particle rearrangement and densification: In liquid-phase sintering, the generation of liquid phase and particle rearrangement are key steps in densification. Small particles have a large specific surface area and surface energy. After the liquid phase is generated, the solid phase is wetted by the liquid phase and infiltrates into the gaps between particles. If the amount of liquid phase is sufficient, the solid phase particles will be completely surrounded by the liquid phase and approximate a suspended state. Under the surface tension of the liquid phase, they will undergo displacement and adjustment of position, thus achieving the most compact arrangement. At this stage, the density of the sintered body increases rapidly.
Dissolution precipitation process: In liquid-phase sintering, the solubility of solid particles in the liquid phase varies. Small particles or areas with large surface curvature dissolve more, while dissolved substances precipitate on the surface of large particles or areas with negative curvature. This process causes the shape of solid particles to gradually become spherical or other regular shapes, small particles to gradually shrink or disappear, large particles to grow, and particles to move closer together, thereby increasing densification.
Capillary pressure effect: In liquid-phase sintering, fine particles have a large capillary pressure, which drives the transport of materials in the liquid phase, causing the particles to rearrange and obtain a tighter packing, resulting in an increase in the density of the green body. The ratio of shrinkage to total shrinkage in this stage depends on the amount of liquid phase. When the number of liquid phases exceeds 35% (volume), this stage is the main stage for completing the shrinkage of the billet, and its shrinkage rate is equivalent to about 60% of the total shrinkage rate.
The influence of sintering temperature: Increasing the sintering temperature will increase the amount of liquid phase, thereby promoting the sliding and rearrangement of particles and improving the density of ceramics. However, excessively high sintering temperatures can exacerbate decomposition and liquid-phase volatilization, leading to an increase in the number of pores and a decrease in density.
Relative density and open porosity: With the increase of sintering temperature, the relative density of ceramics first increases and then decreases, and the open porosity first decreases and then increases. When the sintering temperature is at its optimal value, the relative density is the highest, the open porosity is the smallest, and the ceramic has the best density
The effect of sintering temperature on density: The higher the sintering temperature, the higher the density of the final product. When the temperature rises from 1000 ° C to 1050 ° C, the density increases sharply due to the activation of liquid-phase sintering. However, as the temperature continues to rise, the rate of increase in density will decrease.
The relationship between material properties and temperature: Sintering temperature plays a crucial role in determining material properties. High temperature sintering can improve tensile strength, bending fatigue strength, and impact energy. For example, a study showed that the tensile strength of high-temperature sintered components increased by 30%, the bending fatigue strength increased by 15%, and the impact energy increased by 50%.
Optimization of sintering temperature: From experimental data, sintering temperature is the most important factor affecting relative density and flexural strength. For example, in the sintering of 8YSZ ceramics, the optimal sintering temperature is 1500 ℃, which can achieve the highest relative density and bending strength.
The influence of sintering temperature on microstructure and properties: For TiN ceramics, when the sintering temperature is 1800 ℃, the relative density is the highest, the porosity is the smallest, and the ceramic has the best density. At this time, its bulk density reaches 98.3% of the theoretical density.
The effect of sintering temperature on quality loss rate and shrinkage rate: With the increase of sintering temperature, the shrinkage of TiN ceramics first increases and then decreases. When the sintering temperature is below 1800 ℃, TiN ceramics have more internal pores, resulting in lower shrinkage rate; When the sintering temperature is 1800 ℃, the ceramic has the lowest porosity and highest density, resulting in the highest shrinkage rate.
The influence of sintering temperature on mechanical properties: The flexural strength of TiN ceramics first increases and then decreases with the increase of sintering temperature. When the sintering temperature is 1800 ℃, the flexural strength is the highest.
The effect of sintering temperature on densification: The density of the sintered body rapidly increases with the increase of sintering temperature, reaching its highest point at around 2190 ℃. Then, as the temperature continues to rise, the density tends to decrease. Both high and low sintering temperatures affect the density of the sintered body.
In summary, in order to achieve optimal density, the control of sintering temperature should be determined based on the specific characteristics and sintering behavior of the material. It is usually necessary to determine the optimal sintering temperature through experiments to ensure that the material achieves the highest relative density and optimal mechanical properties.
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