2018 Volume 53 Issue 1 Pages 43-56
The fatigue strength of high-speed tool steel, JIS SKH51, with TiAlN/DLC nano-multilayered coating film was investigated to verify the effectiveness of its coating in improving the fatigue strength of SKH51. Four-point static and fatigue bending tests were conducted to examine the static bending strength and S-N property. The AIP+UBMS hybrid coating system was adopted for deposition of nano-multilayered hard coating film on SKH51. TiAlN coated SKH51 and SKH51 were used as comparative materials. As a result of experimental tests, the average value of bending strength of TiAlN/DLC coated SKH51 was 2912 MPa, which is approximately 17 % less than that of SKH51 substrate. The bending strength of TiAlN coated SKH51 was 3034 MPa, approximately equal to that of the TiAlN/DLC material. Even in the low cycle region, the fatigue strengths of TiAlN/DLC, TiAlN coated SKH51 and SKH51 substrate were the same, and the superiority of TiAlN/DLC nano-multilayered coating was not so much. On the other hand, in the high cycle region, fatigue strength of the TiAlN/DLC material increased in fatigue strength of approximately 150 MPa relative to SKH51 substrate. This tendency was different from TiAlN coated SKH51 in which the improvement of fatigue strength was limited, and the superiority of TiAlN/DLC nano-multilayered coating to ordinary TiAlN coating was confirmed. As a result of fracture surface observation and residual stress measurement of the film, it was found that the superiority of fatigue strength of TiAlN/DLC coated SKH51 in the high cycle region is due to high residual stress in the film and high adhesiveness of the film.
