Dongguan Ming Rui Ceramic Technology Co., Ltd
Ceramics have a common, that is, hardness, but very brittle, so the processing is very difficult, then purity of 99 alumina ceramics processing hardness and brittleness how?
Yue Fei pottery factory gives everybody analysis below.
99 alumina ceramics refers to the alumina content is higher than 99% of engineering ceramics, according to the provisions of the national standard GB/T5593-1999, 99 alumina ceramics material hardness, high strength, low coefficient of expansion, and insulation, wear resistance, corrosion resistance, in the machinery manufacturing, aerospace, precision instrumentation, petrochemical and other fields have a wide range of applications.
Alumina ceramic parts are usually formed by isostatic sintering, because sintering often brings deformation and shrinkage, generally need further finishing to ensure the dimensional accuracy and shape accuracy of the parts.
However, alumina ceramic materials generally have large elastic modulus, high hardness, brittleness and strong crack sensitivity. Therefore, the machining difficulty is mainly reflected in the machining hardness and machining brittleness.
The processing hardness of alumina ceramics: Al203 mainly has three crystalline forms: α, β and γ, among which α-Al203 crystalline forms are the most stable, and I3 and γ crystals almost completely transform into α crystals at 1300℃.
In the crystal form of α-Al203, most of the atomic bonds formed by aluminum ions and oxygen ions are covalent bonds, ionic bonds or their mixed bonds, so the binding energy between atoms is very high and has strong directivity, which is characterized by large brittleness, small plastic deformation and easy cracking.
Its hardness is equivalent to the hardness of carbide carbide carbide, several times higher than steel, usually high purity alumina ceramic density up to 3980 (kg-m4), tensile strength up to 260 (MPa), elastic modulus between 350-400 (GPa), compressive strength of 2930 (MPa), especially its hardness up to 99HRA.
The strength and hardness of 99 alumina ceramics are reduced. According to our determination of experimental samples, the hardness of 99 alumina ceramics reaches 70HRA at normal temperature.
Alumina ceramics machining brittleness: normally alumina ceramic microstructure of equiaxed grain, is made up of polycrystalline ionic bond or covalent bond structure, fracture toughness is low, therefore, under the action of external load, the stress will make the ceramic surface produces slight crack, the crack will rapidly expanding and appear brittle fracture, therefore in the process of alumina ceramic cutting, o often occurrence collapse phenomenon, namely in the ceramic surface cracks, small gouges where whole pieces were missing.
The reasons for the collapse phenomenon are as follows:
(1) The final separation between the excised part of the material and the machined surface is caused by tensile failure, which is not the result of normal cutting.
(2) Crack brought by crushing cutting deformation is generally cracking down along the surface of the workpiece, at this time, due to the cutting tensile stress will cut and bonded workpiece matrix together peeling and forming the phenomenon of collapse and clearance.
It should be noted that the greater the tensile stress, the more serious the collapse phenomenon caused, may lead to the waste of the entire workpiece.
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