| 其他摘要 | Recently it has been found that the hard film deposited on soft substrate can not effectively display their protection in wear resistance and antiftiction. The more failure of film/substrate system is due to earlier film delamination which always results from unsuitable selection of thickness of film, mechanical property difference between film and substrate, film plating technical parameter, as well as residual stress inside film. So it is necessary to analyse the friction and wear behavior of film/substrate system in different condition to investigate the effect of film thickness, hardness of substrate on its wear resistance to make sure the protection of hard film for soft substrate. This paper takes TiN film as mainly study object and study the indentation test、scratch test、friction-wear test and relevant FEM simulation to disucuss the influence of film thickness、substrate mechanical property and technical parameter on wear resistance and antiftiction of film/substrate system.
Firstly, the influence of film thickness on film/substrate friction and wear behavior was discussed. The residual stress was found uneven distribution along film thickness and the stress becomes higher in a certain range of film thickness. With the increase of film thickness, the film/substrate system hardness and load bearing capacity in scratch test become stronger, but when film thickness is too thick to get the good adhesive strength between film and substrate. In the finite element analysis for indentation, tensile stresses σxx and σyy were produced outside the contact region; while compressive stress was mainly produced inside the contact region, and surface film fracture was happened firstly in tensile stress region. The frictional coefficient of thick film fall down fast and the value is lower when GrC15 ball was used as a rubbing pail in friction and wear test. The wear resistance of thick film is better than thin film. Comparison with GCr15 ball, the frictional coefficient of diamond pin is lower, worn track is smoother and plastic deformation was produced in film/substrate system during wear test of film/substrate system with diamond pin rubbing pail. The suddenly change of frictional coefficient saltation and total failure of film were observed, which means there has failure load for film/substrate when frict with diamond pin rubbing under the condition of wear. As the film thickness increase the failure load was improved.
The wear process of TiN film/ Q235 substrate system can be divided into four stages: ie. (Ⅰ)running-in stage (Ⅱ)film steady wear stage (Ⅲ)film failure stage (Ⅳ)film/substrate mixture wear stage. The lost protection of film for substrate mainly happened in stage Ⅲ. In edge of worn track, the cracks were observed firstly and stress concentration in FEA simulation produced by multiform stress in earlier wear stage. The cracks in edge propagate easily inside and outside worn track and made the detachment even total failure of film. The maximum shear stress was found in subsurface, which makes film detachment from substrate before the indenter reaches the substrate surface. The shear stress can promote the big strain amplitude, and only film can compromise the deformation with substrate coordinately, the film will not be detached easily from substrate. The failure mechenica was offered for hard film/ soft substrate system in wear test with small load: crack was originated and propergated in film by stress concentration and tensil stress, and stress concentration in edge of worn track caused by system deformation play most important function on earlier film fail.
The indentation and scratch test resulte show that when soft Q235 steel was sustrate the film substrate has low hardness and film lost protection for substrate in scratch test. In FEA simulation for scratch test, the plastic deformation of film/substrate is rather big, shear stress σxy is unsteady, and tensile stress σxx can promote the production of crack on film surface. Big plastic deformation can make stress concentration in front of contact region between indenter and film. For TiN film/Ti6Al4V substrate, the maxium difference value of σxy at the interface between film and substrate appeared, and it could make the detachment of film from substrate totally, while substrate of Q235 with good plasticity, the damage form is fracture and detachment inside film by tensile stress as a result of large plastic deformation. When TiN film was deposited on different hardness and strength substrate, it could be seen that for film/soft substrate such as Q235 system, film protection lost early in indentation and scratch test, while TiN film/ quenched T8 steel substrate with highest hardness would show the highest load bearing capacity. Two failure mechenica were offered in scratch test: film brittle failure by stress and film detachment by adhesive failure The specific hardness of film/substrate of Ti6Al4V is highest in present paper. ie. TiN film improves the hardness of Ti6Al4V most effectively and through scratch simulation and test, the adhesive strength is the best among three film/substrate systems. Although the critical load value is highest for T8 substrate results from its higher load bearing, the wear resistance for TiN/T8 system is worse than TiN/Ti6Al4V system with lower load bearing capacity. It means the material hardness and load bearing capacity could not be used as the criterion for estimating adhesive strength and wear resistance of film/soft substrate system
In multi arc ion-plating of TiN film process, different bias-voltage and nitrogen partial pressure can influent its crystal orientation, surface morphology and mechanical property., The residual stress inside TiN film increase with bias-volatge rising. Only the bia-voltage is controlled properly, the good adhesive strength and wear resistance can be obtained. At low partial pressure of nitrogen, Ti2N phase increases and the droplet size becomes small; as the pressure rise, the droplet size increase and TiN (200) phase grow preferentially. When partial pressure of nitrogen is increase, the hardness of film/substrate becomes higer. Lower or higher partial pressure of N2 can reduce the critical stress in scratch test, and so it is very important to consider the substrate property for pressure choice. Although high hardness and low friction coefficient could be obtained in high nitrogen partial pressure, the wear resistance was not improved in test of this paper. |
修改评论