It has been found that the hardness and fracture toughness of ceramic materials are the key factors affecting the wear rate of spray coatings. Scholars in various countries have carried out a lot of research work, which can be divided into the following three aspects, ceramic grain size, second phase materials, and coating tribological mechanism.
First, they study grain size of alumina ceramic spray coating. Alumina ceramics can be divided into single-phase ceramics and multiphase ceramics. In the research field of the correlation between the grain size and the tribological properties of ceramics, researchers mainly investigated the effect of the grain size of the matrix phase (or the second phase) on the tribological properties of ceramics.
The results show that the wear rate of submicron ceramics spray coating is much lower than that of micron ceramics in bovine serum albumin environment, and the grain pull-out and grain boundary microcracks of submicron ceramics are significantly less than those of coarse-grained alumina ceramics. Sedlacek and other researchers studied the effect of different grain sizes of alumina matrix on the wear properties. The grain size of alumina matrix varies from 0.8 μ m to 4 μ m, while the second phase SiC is nano size. The results show that the wear resistance of alumina matrix with submicron size is better than that of nano composite ceramics with micron size; there is no obvious relationship between wear resistance and fracture toughness when the matrix with submicron size, but the wear rate of alumina composite ceramics with micron size decreases with the increase of hardness.
Obviously, from the above examples, it can be seen that grain refinement can effectively help to improve the structural uniformity of materials, including increasing the density of materials and reducing the defects of materials. Wococarbide adopts advanced equipment and manufacturing process. The powder produced by wococarbide has fine grain and meets the requirements of good wear resistance. However, previous experiments show that there is no obvious relationship between wear resistance and fracture toughness when the matrix grains are in submicron scale.
Second, they study the Second phase materials of alumina ceramic spray coating.
In the field of tribological properties of alumina composite ceramics, the composition compounding, that is, the formation of composite materials by adding various second phase, particles (or whiskers) is also the main way to improve the tribological (or cutting) properties of alumina ceramic coating. According to the different influence mechanism, it can be divided into the second phase self lubrication mechanism, the second phase grain boundary enhancement, the second phase tribochemical reaction mechanism and so on.
① Second phase self lubrication mechanism
The second phase solid lubricants such as graphite, CaF2, PbWO4, MoS2, BN and soft metal can effectively reduce the friction coefficient of the coating, and improve the tribological properties of the coating. Deng Jianxin et al introduced 10% CaF2 solid lubricant into the alumina / TiC composite ceramic matrix. Through cutting and friction experiments, it was found that CaF2 was extruded and coated on the friction surface to form a self-lubricating film, which can effectively prevent the adhesion between the material and the friction pair, reduce the friction coefficient and play a self-lubricating role.
② Strengthening effect of second phase grain boundary
The second phase (mainly particles and whiskers) is introduced into the alumina ceramic matrix, and the residual stress is produced during the cooling process of the material preparation by using the difference of thermal expansion coefficient between the dispersed particles and the matrix material, so as to achieve the effect of grain boundary strengthening. When the crack propagates along the grain boundary, it is necessary to overcome not only the inherent grain boundary energy of the matrix material, but also the additional energy caused by the residual compressive stress On the other hand, because the coefficient of thermal expansion of the second phase particles is less than that of the matrix, volume effect will be produced during the cooling process, and microcracks will be generated around the second phase particles, which will induce the deflection of the cracks and consume more energy for crack propagation; in addition, the second phase particles are generally spherical, which makes the crack tip The end passivation can reduce the stress concentration and prevent crack propagation, thus improving the tribological properties of the coating.
③ Mechanism of second phase tribochemical reaction
The tribochemical reaction mechanism of the second phase is that the second phase doped in the alumina matrix reacts with the gas in the air (mainly oxygen) or with the material of the counter wear pair when it rubs against the material of the counter wear pair to produce lubricating film and reduce the friction coefficient of the material, so as to improve the tribological properties of the material.
Deng Jianxin et al introduced TiB2 particles into the alumina ceramic matrix to prepare the Al2O3 / TiB2 composite ceramic tool. When the tool was cutting with 45 # hardened steel, it was found that when the cutting speed was greater than 120m / min, that is, the cutting temperature was greater than 800 ℃, TiB2 in the alumina / TiB2 composite ceramic tool reacted with oxygen to form TiO2 and B2O3, because the elastic modulus and hardness of TiO2 were lower than that of the matrix material Much, the shear strength is reduced, so the friction factor of material coating decreases, the adhesion wear of the tool is reduced and the wear resistance of the tool is improved.
Third, they study the tribological mechanism of alumina ceramic spray coating.
The application of alumina ceramic spray coating has different mechanisms. At present, researchers have carried out extensive research on this aspect and obtained some regular knowledge. Deng Jianxin and other researchers studied the Tribological Mechanism of two kinds of High Temperature Self-lubricating Ceramic Tool Materials: Al2O3 / TiB2 and Al2O3 / TiC / CaF2. The results show that: in low speed dry cutting, the wear mechanism of Al2O3 / TiB2 ceramic tool is adhesive wear and abrasive wear; while in high speed dry cutting, the wear mechanism of tool is oxidation wear, and the reaction film formed by tribochemical reaction on the tool surface plays a solid lubrication role, which improves the wear resistance of the tool. With the increase of TiB2 content and cutting speed, the reaction mechanism increases The friction reducing and anti-wear effect of the membrane is enhanced. Yao Shuqing and other researchers studied the tribological properties and mechanism of three kinds of Al2O3 based ceramic tool materials with different second phases. The results show that the tribological properties of the ceramic tool materials are related to the types of additives, and the order of their anti-wear properties is al2o3gsicw, Al2O3 / Ti (C, N) The wear rate w increases with the increase of E / h and decreases with the increase of KIC; the wear mechanism of Al2O3 / TiC ceramic tool materials is mainly adhesive wear, while that of Al2O3 / Ti (C, n) and Al2O3 / SiCw Ceramic Tool Materials is mainly abrasive wear.
In conclusion, the friction and wear performance of the coating on the material surface is a comprehensive performance, which is affected by many factors. However, all aspects of research show that the refinement of grain size and composition can effectively improve the strength and fracture toughness of alumina ceramics, and then improve its tribological properties. If the research in this field can continue to improve, it will effectively promote the further application of alumina ceramic spray coating in various fields.
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