The extensive use of hard films has stimulated considerable interest in their properties. It is significant to research the relation between the preparation process and films’ mechanical properties. In this dissertation, at first, a new method was set up to determine the residual stresses of hard films; subsequently, the effects of the technology process were investigated on mechanical properties of (Ti,Al)N films by arc ion plating. We put forward to a new method to test the residual stresses in hard films layer by layer, which is based on the substrate curvature method and aiming at hard films. And, we designed an accurate optical system to test the change of the curvature of the samples. The detailed results of this work were shown as follows.
Above all, the feasibility of the residual stress measurement was proven and the errors of it were estimated through the successful measurement of the depth distribution of the residual stresses in the (Ti,Al)N films. The compressive residual stresses at the GPa level existed in the (Ti,Al)N film deposited by Arc Ion Plating, and the depth distribution of the residual stresses has a trend of “bell” with the peak appearing in the middle of the film. The thicker the films, the higher the average residual stresses of total film thickness.
The effects of the bias voltage on mechanical properties of the films are obvious. Increasing bias voltage causes a rise in compressive stresses and hardness in (Ti,Al)N films. Periodically alternating the bias voltage during deposition can smoothen out the distribution of stresses, enhance the adhesion of films and maintain the high hardness. Based on optimized parameters, a film of 7.57 μm in thickness was created directly on the substrate with the stresses significantly relieved. Following the same procedure, gradient films and multilayer films with large thickness can be prepared, due to the slow accumulation of stresses. Alternating bias voltage during deposition is an effective means to create gradient and uniform stress distributions, which in turn benefit the improvement of film properties.
Nitrogen partial pressure is another important factor for the mechanical properties of hard films. It was found that the deposition rate decreases, film hardness increases and adhesion strength decreases when N2 partial pressure is increased from 0.2Pa to 0.8Pa. Based on the above results, the technology process of changed N2 partial pressure was adopted during deposition of the (Ti,Al)N films. The residual stresses of the films notably decreased and the distribution profiles of the stresses in the films got more even than the films at high N2 partial pressure. Finally, the thick gradient (Ti,Al)N coating (about 68μm) with a Ti interlayer was successfully deposited on a substrate by continuously increasing nitrogen flow rate during deposition. Such an achievement can be attributed to the gradient distribution of element, hardness and stresses across the coating thickness.
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