Effect of Target Current on the Structure and Properties of TiB2 Thin Films Prepared by Magnetron Sputtering
With the continual advancement of machining processes,cutting tools are facing increasingly demanding requirements.However,traditional tools often exchange hardness for toughness and have poor resistance to high temperatures and oxidation,which presents challenges in meeting high-speed cutting conditions.The deposition of a hard oxidation-resistant film on the tool surface can effectively address these issues.However,conventional protective films such as TiN and TiC fail to meet the demands of high-speed cutting and high-precision machining in terms of tool hardness,high-temperature resistance,and anti-adhesion.TiB2 is an ideal protective film for high-speed cutting tools due to its high hardness,high-temperature resistance,antioxidation properties,and low chemical affinity for intermetallic materials.In this study,a closed-field unbalanced DC magnetron sputtering technique was employed to deposit thin-film materials on P(100)-type silicon wafers and Inconel 718,which is a high-temperature nickel-based alloy.The results revealed a close correlation between the properties of the deposited TiB2 films and the magnitude of the target current during sputtering deposition.Specifically,increasing the TiB2 target current led to a higher target power,resulting in the deposition of thicker films within the given time frame,where the average thickness increased from 1.468 to 2.168 μm.In addition,increasing the frequency of target sputtering particle bombardment and the temperature in the deposition chamber enhanced the crystallinity of the films and increased the grain size,where the half-peak width of the preferred crystal plane decreased from 2.795° to 1.993°.The difference in the thermal expansion coefficients of the film bases resulted in residual stresses in the films after cooling to room temperature.As the target current strength increased,the chamber temperature increased,leading to a greater temperature difference between the chamber and room.Consequently,the residual stress of the film increased with the target current.Specifically,the minimum residual stress of the deposited film under a target current of 3.0 A was 0.109 9 GPa,whereas the maximum residual stress under a target current of 6.0 A was 0.382 9 GPa.Moreover,the hardness of the film initially increased and then decreased with an increase in the target current,reaching a peak of 3.0 A under a hardness of 0.382 9 GPa.The lowest hardness of the film occurred under the condition of 3.0 A,measuring 14.40 GPa,whereas the highest hardness was under the condition of 5.0 A,measuring 18.66 GPa.This hardness was closely associated with the crystallinity of the film and the ratio of boron-rich tissue phases.Enhancing the crystallinity of the film reduced the number of defects and concentrated the boron-rich phases at the grain boundaries,thereby preventing slippage when an external force was applied.This improvement was beneficial in enhancing the mechanical properties of the films.Depositing the film at 4.0 A yielded the highest hardness of 0.382 9 GPa.In addition,films deposited at 4.0 A exhibited the lowest wear rate(W=6.347×10-6 mm3/(N·m))within the system.This study explored the optimal DC magnetron sputtering preparation of TiB2 and elucidated the effects of different current strengths on the crystallinity,hardness,and antiwear properties of TiB2 thin films during sputtering deposition.The deposition of TiB2 thin films on cutting tool surfaces effectively mitigates wear problems caused by frictional wear during high-speed cutting,serving as a protective film that efficiently prevents excessive tool failure resulting from high temperature and oxidation.Additionally,it safeguards against wear caused by high temperature and oxidation,prolonging the tool's service life and improving machining accuracy.These findings provide valuable insights for the research and development of protective films for high-speed cutting tools.
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