Alumina ceramic parts are usually formed by hot pressing sintering. As sintering often leads to deformation and shrinkage, further precision machining is generally required to ensure the dimension and shape accuracy of the parts.
However, alumina ceramic materials generally have large elastic modulus, high hardness, high brittleness and high crack sensitivity. Therefore, its mechanical processing difficulty is mainly reflected in machining hardness and brittleness.
Alumina ceramic processing hardness: main AL203 are alpha, beta, gamma three crystal morphology, the crystal morphology of alpha AL203 most stable, 1300 ℃ I3 almost completely into the alpha and gamma crystallization crystallization.
Crystal morphology chinalco in alpha AL203 ions and oxygen ions formed by atomic bonds are covalent bond, ionic bond, or their mixture, so the high binding energy between atoms and have very strong directivity, the specific performance for brittle materials, plastic deformation is small, easy to produce crack;
Its hardness is equivalent to the hardness of carbide carbide, several times higher than steel, usually high purity alumina ceramic density of up to 3980 Kg - the m4), tensile strength of 260 (MPa), modulus of elasticity between 350-400 (GPa), compressive strength of 2930 (MPa), especially its hardness is 99 hra.
The strength and hardness of alumina ceramics have been decreased. According to our test sample, the hardness of alumina ceramics also reached 70HRA at room 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 phenomenon of collapse and gap are as follows:
(1) the final separation of the excised part of the material from the processed surface is caused by tensile failure, which is not the result of normal cutting.
(2) the avalanche crushed cutting deformation cracks usually bring along the surface has been cracking down, at this point, the phase bonding of tensile stress will be cutting and cutting workpiece o matrix spalling together to form a collapse phenomenon.
It should be noted that the greater the tensile stress, the more serious the crack phenomenon will be, which may lead to the waste of the entire workpiece.
