The corrosion fatigue strength of the surface modified SNCM 439 steels by the combined use of magnetoron sputtering and argon ion-mixing treatments was studied at a cathodic potential of -1.2V against Ag/AgCl (saturated with KCl) reference electorode in a 3.5% NaCl aqueous solution. The disk of the material of Cr or ZrO
2-6vol%Y
2O
3 was used as a target of magnetoron sputtering. The thickness of coated films obtained on fatigue specimens was about 0.037μm. The fatigue lives of the SNCM439 steels with or without surface modification were remarkably reduced in a 3.5% NaCl aqueous solution because of hydrogen embrittlement, compared with those in air. But, the corrosion fatigue lives of surface coated specimens were improved, depending on the surface treatments. That is, the fatigue life at a stress amplitude of 515MPa for non-coated specimen, ZrO
2-6vol%Y
2O
3 coated specimen, and ZrO
2-6vol%Y
2O
3 coated and ion-mixed specimen was 1.8×10
4, 9.3×10
4, and 2.6×10
5, respectively. The best coating treatment for improving corrosion fatigue lives was obtained by the combined use of magnetoron sputtering and ion-mixing treatments which led to improved adhesion of the film to the matrix and interference in hydrogen entry into the matrix.
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