99 alumina ceramics refer to engineering ceramics with an alumina content higher than 99%. 99 alumina ceramic materials have high hardness and strength, and are widely used in aerospace, petrochemical and other fields. So, what are the processing hardness and brittleness of 99 alumina ceramics?
Processing hardness of 99 alumina ceramics
AL203 mainly has three crystal forms: alpha, beta, and gamma. Among them, the alpha AL203 crystal form is relatively stable, and at 1300 ℃, I3 and gamma crystals almost all transform into alpha crystals.
In the crystalline form of α - AL203, the atomic bonds formed between aluminum ions and oxygen ions are mostly covalent, ionic, or mixed bonds, resulting in high interatomic binding energy and strong directionality.
The hardness of 99 alumina ceramics is equivalent to that of carbide hard alloys, several times higher than that of steel. Typically, high-purity alumina ceramics have a density of 3980 (Kg-m4).
The tensile strength reaches 260 (MPa), the elastic modulus is between 350-400 (GPa), the compressive strength is 2930 (MPa), and especially its hardness can reach 99HRA. The strength and hardness of 99 alumina ceramics have decreased.
According to our measurement of the experimental sample, its hardness at room temperature also reached 70HRA.
Processing brittleness of 99 alumina ceramics
Under normal circumstances, the microstructure of alumina ceramics consists of equiaxed grains and a polycrystalline structure composed of ionic or covalent bonds, resulting in lower fracture toughness.
Under the action of external loads, stress will cause subtle cracks on the surface of ceramics, which will rapidly propagate and lead to brittle fracture. Therefore, during the cutting process of alumina ceramics, the phenomenon of collapse often occurs, that is, small cracks appearing on the ceramic surface.
Reasons for the occurrence of collapse phenomenon
(1) The separation between the cut portion of the material and the processed surface is caused by tensile failure, which is not the result of normal cutting.
(2) The cracks caused by crushing and cutting deformation generally propagate downwards along the surface of the workpiece. At this time, due to the cutting tensile stress, the cutting and the bonded workpiece substrate are peeled off together, forming a fracture phenomenon.
It should be noted that the greater the tensile stress, the more severe the collapse phenomenon caused, which may lead to the waste of the entire workpiece.
