Investigation On The Microstructure,Mechanical Properties And Tribological Behavior For TiAl(Nb) Nitrides/carbides Films

TiAlN/C-based films have been widely used as wear-resistant and protective films in mechanical processing,microelectronic devices,transportation,aerospace and geological exploration due to their high hardness,high melting point,high wear resistance,good thermal stability,chemical stability,structural stability and mechanical rigidity.To further improve the performance of TiAlN/C thin films,such as high hardness,high toughness,low friction and wear resistance,is the goal pursued by researchers,which contributes to cope with harsh working environments and extend the lifetime of the films.In TiAlN/C thin films,aluminum has a great impact on the improvement of thin film performance.However,the impact of aluminum in TiAlN and TiAlC thin films are different:?1?Al can significantly improve the hardness and thermal stability of TiN,while the toughness is low and its performance strongly depends on the existing form of Al;?2?Al can reduce internal stress and improve friction performance in TiC,but its mechanism of Al impact the content and existence form of a-C in the film during the preparation and tribological process is still not clear.Niobium?Nb?alloying is considered as a potential way to improve toughness,and systematic research is urgently needed.In this paper,TiAlN,TiAlNbN,TiAlC,and TiAlNbC thin films were prepared under adjusting processing parameters by magnetron sputtering.Firstly,experiments and theoretical calculations are combined to study the relationship between the microstructure and strengthening-toughening of TiAlN and TiAlNbN thin films,also the toughening effect induced by Nb;Moreover,the effects of C content on the microstructure,growth behavior,hardness,toughness and tribological behavior of TiAlC and TiAlNbC films,the addition of Nb and the formation of nanocomposite structure on the mechanical and tribological properties of TiAlNbC film were studied comparatively.Concluded as follow:1.Different TiAlN and TiAlNbN films were prepared by magnetron sputtering with different N₂ flow rates.The effects of N₂ flow rates on the microstructure,hardness and toughness of TiAlN and TiAlNbN films were studied,and the amplitude modulation decomposition induced by high deposition temperature was observed.?1?For TiAlN films,the increase of N₂ flow rate causes the grain refinement and the appearance of amorphous,which leads to form of polycrystalline structure at low N₂flow rate,and the nanocrystalline@amorphous nanocomposite structure has been formed at high N₂ flow rate.The single polycrystalline TiAlN films shows the lower toughness,while the formation of nano crystalline and amorphous nanocomposite structure is helpful to obtain high hardness and improved toughness of TiAlN films.When the deposition temperature reaches 700?and 800?,it can drive the amplitude modulation decomposition in TiAlN films and achieve the increased hardness and improved toughness.?2?For TiAlNbN films,the change of microstructure with N₂ flow rate at room temperature is consistent with that of TiAlN films.High N₂ flow rate leads to the transformation of TiAlNbN films from polycrystalline structure to nanocrystalline@amorphous nanocomposite structure,and high hardness is obtained in the nanocomposite structure.Spinodal decomposition could be occured only under certain conditions for TiAlNbN films,and the films hardness can be enhanced at the same time,which is different from the TiAlN films.It is further confirmed by theoretical calculation that Nb addition can regulate the valence electron concentration and electronic structure of TiAlN,thus achieve the purpose of toughening.2.TiAlC and TiAlNbC films with different C contents were prepared by changing the methane flow rate by magnetron sputtering.The effects of C content on the microstructure,hardness,toughness and tribological behavior of TiAlC and TiAlNbC films were studied.?1?In TiAlC films,when the C content increases from 22.4%of C to 95.3%of C,three typical nanostructures are formed:?a?Nanocrystalline structures without amorphous phase was formed at low C content?22.4%and 41.9%?;?b?A nanocomposite structure with nanocrystal TiC and amorphous C was formed at 56.2%and 76.7%C content-amorphous C wrapped TiC nanocrystal;?c?A complete amorphous structure was formed at C content of 95.3%.Compared with single nanocrystalline structure and amorphous phase structure,the formation of nanocrystalline@amorphous nc-TiC/a-C nanocomposite structure can significantly improve the toughness of the film,and the film has the maximum hardness when thin amorphous C-coated layer in the 56.2%C content,that means achieves strengthening-toughening.A thicker amorphous C-coated layer is formed in films with a higher content of 76.7%C,the friction coefficient and wear rate are the lowest,⁰.09 and⁸×10^-10mm³/Nm,respectively.?2?In the TiAlNbC films,with the increase of C content can also form three types of nanostructures:?a?A nanocrystalline structure is formed at 36.9%C content;?b?Converted to nanocrystalline@amorphous biphasic structure at 51.7%and 65.4%C content;?c?Transformed into amorphous structure at a higher C content of 84.8%.Compared with TiAlC films,the addition of Nb improves the toughness of TiAlNbC films;Moreover,the inducing of Nb atoms leaded to the formation of a small number of atomic-scale nanographene clusters in the amorphous C coating of the TiAlNbC film with 65.4%C content.At this time,the film obtained the highest hardness,and the friction coefficient and wear rate were also the lowest,⁰.07 and¹2.4×10^-10mm³/Nm,respectively,and exhibited superior tribological properties than TiAlC film.