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99 alumina ceramic processing difficulties and solutions
Time: 2018-12-29   Writer: mingrui

99 alumina ceramic processing difficulties and solutions

99 alumina ceramics refers to engineering ceramics with alumina content higher than 99%. According to the standard regulations, 99 alumina ceramic materials have high hardness, high strength, low expansion coefficient, and insulation, wear resistance and corrosion resistance. Aerospace, precision instruments, petrochemical and other fields have a wide range of applications. Alumina ceramic parts are usually formed by hot press sintering. Since sintering often causes deformation and shrinkage, further finishing is required to ensure dimensional accuracy and shape accuracy of the parts. However, alumina ceramic materials generally have large elastic modulus, high hardness, high brittleness and strong crack sensitivity. Therefore, the mechanical processing difficulty is mainly manifested in processing hardness and processing brittleness.
Difficulties in processing alumina ceramics

99 alumina ceramic suction cup
Processing hardness of alumina ceramics: AL203 mainly has three crystal forms of α, β and γ, among which α-AL203 is the most stable crystal form, and I3 and γ crystals are almost completely converted into α crystal at 1300 °C. In the crystal form of α-AL203, the atomic bonds formed by aluminum ions and oxygen ions are mostly covalent bonds, ionic bonds or their mixed bonds, so the bonding energy between atoms is very high and has strong directionality. The material has large brittleness, small plastic deformation and easy cracking; its hardness is equivalent to the hardness of carbide cemented carbide, which is several times higher than steel. Generally, the density of high-purity alumina ceramic can reach 3980 (Kg-m4), tensile strength. Up to 260 (MPa), the modulus of elasticity is between 350-400 (GPa), the compressive strength is 2930 (MPa), especially its hardness can reach 99HRA. The strength and hardness of 99 alumina ceramics have been reduced. According to our measurement of experimental samples, the hardness at room temperature also reached 70HRA.

Processing brittleness of alumina ceramics:
Usually, the microstructure of alumina ceramics is equiaxed grains, which is a polycrystalline structure composed of ionic bonds or covalent bonds, so the fracture toughness is low. Under the action of external load, the stress will make the ceramic surface Fine cracks are generated, and the cracks expand rapidly and brittle fracture occurs. Therefore, in the alumina ceramic cutting process, the collapse phenomenon often occurs, that is, a small gap which is cracked on the surface of the ceramic.

The reasons for the collapse phenomenon are:

(1) The final separation of the cut portion of the material from the machined surface is caused by tensile failure, which is not the result of normal cutting.

(2) The crack caused by the chipping deformation is generally cracked down the surface of the workpiece. At this time, the cutting tensile stress causes the cutting and the bonded workpiece base to peel off together to form a collapse phenomenon. It should be noted that the greater the tensile stress, the more serious the collapse phenomenon is caused, which may result in waste of the entire workpiece.

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