Stages of Toughness and Machinability of Structural Ceramic Materials

Zirconia ceramics have been widely used in all walks of life in recent years, and can be used as structural ceramics or some ceramic parts, which have a lot to do with their toughness. The following Kezhong Ceramics Factory will introduce the machinability experience of structural ceramics several stages.

As mentioned above, the brittle nature of ceramic materials affects its application. The main reason is that there are defects inside the ceramics. In order to overcome this shortcoming, there have been many research booms around Al2O2 ceramic matrix composites and other ceramic matrix composites in the past 20 years. These ceramic materials have experienced the following efforts and attempts in design, preparation, processing and testing.

The design of ceramics and their composites has gone through the following stages around improving the toughness and machinability of ceramic materials:

(1) Phase change toughened ceramics use the volume expansion effect of ZrO2 when it transforms from a tetragonal phase to a monoclinic phase under stress to inhibit the expansion and initiation of cracks, thereby improving the fracture toughness of ceramic materials. Its application at low temperatures has achieved Great success, mainly ZrO2 ceramics and their toughened Al2O3 ceramics.

(2) High-precision ceramics are typical of nano-ceramics and nano-Al2O ceramic composite materials. The purpose is to eliminate the internal defects of ceramics as much as possible, reduce the scale and number of internal defects of ceramics, and prevent cracks.

(3) High toughness/high hardness a-Sialon ceramics This material uses aSi3N as a raw material, and due to partial phase transformation during sintering, a self-toughening ceramic composed of elongated B-SiN4 crystals interspersed in equiaxed a-Si3N4 can be obtained , Among them, the newly developed -sialon with high aspect ratio can obtain high hardness and high fracture resistance.

(4) Plastically deformable ceramics, represented by Tii3SiC2, is a kind of ternary synthetic ceramic material that always has a slip system from room temperature to high temperature. It has dual properties of metal and ceramic, and it has good thermal shock resistance, electrical conductivity, thermal conductivity, and high temperature resistance. (use temperature 1400°C), anti-oxidation, especially machinable, is a new type of exotic material.

(5) Fiber and whisker reinforced ceramic matrix composites. Such materials tolerate defects in the ceramic matrix, but the defects are not sensitive to crack propagation. It relies on the stability of the reinforcement fibers to maintain high strength and relies on the fracture process of the fibers and the matrix. The energy consumption improves the fracture toughness and work of fracture of the material. This type of material is especially widely used in important structural parts (such as aviation, aerospace parts, cutting tools, molds, etc.).

(6) Laminated structure ceramic matrix composite material This material is also called biomimetic composite phase Zhouci. It is a structural composite material formed by alternately laminating SiC flakes and graphite flakes. Its fracture toughness and fracture work are several to dozens of times higher than conventional ceramics, reaching 15MPa·m12 and 4250J·m-2 respectively. Its guiding idea is to artificially create a defect layer (graphite) and use the defect layer to block the expansion of cracks. This is the latest research hotspot and has achieved good results.

To sum up, the development process of ceramic materials is also the development process of ceramic toughening, and the design idea has gone through the change process of "restricting and reducing defects-tolerating defects-utilizing defects"

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