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Ceramics have a common denominator, that is, high hardness, but very brittle, so the processing is very difficult, 

so the purity of 99 alumina ceramics processing hardness and brittleness how? Let's analyze it.

99 alumina ceramics refers to engineering ceramics with alumina content higher than 99%, according to the provisions of the national standard GB/T5593-1999, 

99 alumina ceramic materials have high hardness, high strength, low expansion coefficient, and insulation, wear resistance, corrosion resistance, 

and have a wide range of applications in pump valves, machinery manufacturing, aerospace, precision instruments, petrochemical and other fields.

 Alumina ceramic parts are usually formed by isostatic pressing sintering, because sintering often brings deformation and shrinkage,

 it is generally necessary to further finish 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, 

so the difficulty of machining is mainly reflected in the processing hardness and processing brittleness. 

The processing hardness of alumina ceramics: AL203 mainly has α, β and γ three crystal forms, of which α-AL203 crystal form is the most stable, 

and I3 and γ crystals are almost completely transformed into α crystals at 1300℃. 

In the α-AL203 crystal form, the atomic bonds formed by aluminum ions and oxygen ions are mostly covalent bonds, ionic bonds or their mixed bonds, 

so the binding energy between the atoms is high and has a strong direction, which is manifested in the material brittleness, plastic deformation is small, 

easy to crack; Its hardness is equivalent to the hardness of carbide carbide, several times higher than steel, usually high purity alumina ceramics 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 have been reduced, and the hardness of 99 alumina ceramics has reached 70HRA at room temperature, 

according to the determination of our experimental samples.

Processing brittleness of alumina ceramics: Under normal circumstances, the microstructure of alumina ceramics is equiaaxial grain, 

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 produce fine cracks, and the cracks will expand rapidly and brittle fracture, so in the process of alumina ceramic cutting,

 often collapse phenomenon. That is, small cracks appear on the ceramic surface. The reasons for the collapse phenomenon are:

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

(2) The cracking caused by the collapse cutting deformation is generally cracking down along the surface of the workpiece, 

at this time, due to the cutting tensile stress will be cut and bonded workpiece matrix spalling together to form the collapse phenomenon.

 It should be noted that the greater the tensile stress, the more serious the collapse phenomenon will be, which may lead to the waste of the entire workpiece.