Preparation,Structure And Properties Of Mo Doped CrAlN Coatings

According to statistics,25%of the mechanical parts in production are due to wear failure.Surface coating technology can improve the surface performance and product quality of key parts,prolong their service life and reduce wear and tear.Therefore,it is of great significance to research and develop coatings with high hardness and low friction and wear resistance.The effects of process parameters on the structure and properties of Cr transition layer and CrAlN coating were investigated by magnetron sputtering method and orthogonal experiment.On this basis,the effects of Mo doping on the structure and properties of CrAlN coating with different N₂content were investigated.The main contents are as follows:1.Through the preparation of Cr/CrN coating,it is found that the transition layer not only affects the bonding strength,but also affects the crystal growth of the target coating.The crystal growth of the CrN layer is affected by the Cr transition layer,and the crystal growth direction is basically consistent with that of the Cr transition layer.With the increase of deposition time or power,the crystal growth direction tilts from the vertical substrate direction when the Cr transition layer reaches a certain thickness.When the power and bias voltage are low,the columnar crystal of the Cr transition layer is thicker,and the growth of the Cr transition layer can be improved by increasing the power.In the investigation of sputtering power,deposition time and substrate bias voltage,we found that the influence weight on the hardness of Cr/CrN coating is as follows:power,bias voltage>time.Through the investigation of the transition layer process,it is found that the coating film with high sputtering power and low substrate bias voltage（20 min-1.5 k W–50 V）has the highest bonding strength and the best hardness（21.18 GPa）.2.The amount of N₂in the preparation of CrAlN coating and the concentration and energy of metal ions have great influence on the structure and properties of CrAlN coating.With the increase of N₂flux in the vacuum chamber,the surface energy is dominant in the growth process of the coating,and the preferred orientation of CrAlN crystal changes from（111）plane to（200）plane.When the Ar/N₂flow rate is relatively low,the influence of other process parameters on the hardness of the coating decreases.When the power or bias voltage is small,the CrAlN coating is amorphous,and the crystallinity of the coating can be improved by increasing power and bias voltage.When the sputtering power and substrate bias voltage reach a certain value,with the increase of N₂content,the coating mainly grows in（200）plane with flaky crystal structure,and the friction coefficient of the coating is lower and the wear resistance of the coating is better.When the Ar:N₂is 50:50,the sputtering power is1.5k W and the substrate bias voltage is-50v,the CrAlN coating has the lowest friction coefficient（0.679±0.024）and the lowest wear amount（1.32±0.68）×10^-6mm³/N·m.The sputtering power or bias voltage continues to increase,that is,the energy of the sputtered particles is higher,the strain energy is dominant in the growth process of the coating,the preferred orientation changes from（200）crystal plane to（111）crystal plane,and the structure of the coating is columnar crystal structure.The density of the coating decreases and the hardness decreases.All CrAlN coatings show a wear mechanism dominated by abrasive wear.3.For Mo-doped CrAlN coatings,the main doping modes of Mo are Mo phase（when Mo at%is large）and entering other metal nitride phases（when Mo at%is small）,the maximum doping amount of Mo obtained in this paper is 19.54 at%.With the increase of N₂flow rate,the content of metal elements decreases and the content of N elements increases monotonously.The diffraction peaks of Mo phase and Cr₂N phase in the coating gradually weaken and disappear.The coating mainly exists in the face-centered cubic structure of Cr Al Mo N phase（preferred growth orientation is（200））.At the same time,the coating becomes dense due to the deposition of particles under the action of bias.The hardness of Cr Al Mo N coating depends on the phase in the coating,especially the Mo phase,and is related to the crystal structure and the density of the coating.The hardness of Cr Al Mo N coating increases with the decrease of Mo phase and the increase of density,and the friction coefficient and wear amount decrease at first and then increase with the increase of N₂flow rate.When the nitrogen flux is 50sccm,the Cr Al Mo N coating has the maximum hardness value of（24.66±2.25）GPa and the lowest friction coefficient of（0.46±0.03）,which is significantly lower than that of the CrAlN coating without Mo element.At the same time,the sample has the smallest wear amount（0.98±0.16）×10^-6mm³/N·m,and there is Mo O₃formation in the wear marks,which is helpful to reduce the friction coefficient and improve the wear resistance of the coating.The wear mechanism of Cr Al Mo N series coatings is more complex,including adhesive wear and abrasive wear.