EFFECT OF BIAS VOLTAGE ON THE FATIGUE LIFE OF MARTENSITIC STAINLESS STEEL WITH TiN FILM COATED USING ARC ION PLATING METHOD

To investigate the effect of TiN coating on the fatigue strength of high-strength steel, four-point bending fatigue tests were carried out for martensitic stainless steel with TiN film coated using arc ion plating (AIP) method. A 2-μm-thick TiN film was deposited onto the substrate surface under bias voltage of four kinds: V_B = 0, -60, -160 and -260 V. For V_B = 0, -160 V and -260 V, the fatigue limit increased. The highest fatigue limit of σ_max = 900 MPa was obtained for V_B = -160 V. But some samples for V_B = -260 V showed the decrease of fatigue limit due to film delamination during the fatigue test. For V_B = -60 V, the fatigue limit was unchanged by coating. As a result of a coating property analysis, the following conclusions were obtained. Fatigue crack propagation was almost independent of the bias voltage. Fatigue crack initiated from the subsurface in the substrate and the crack initiation behavior depended on the film property of the adhesion, residual stress, elastic modulus, and the film's hardness depended on the bias voltage especially for low fatigue stress level.