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| CORROSION FATIGUE BEHAVIOUR OF THERMALLY COATED STEEL |
| Yu Weicheng and Yuan Jincai (Institute of Metal Research;Academia Sinica) |
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Abstract Flame sprayed welding with secondary remelting was adopted to improve the fatigue property of steel 45.The effect of the plasma sprayed Ni/Al coating on fatigue strength of steel 45 in air and in corrosive medium were compared with that of the flame sprayed welding Ni60.It was demonstrated that all the coatings reduced the fatigue limit in air,the plasma spraying (P.S)gave a reduction of 12% and the flame sprayed welding(F.S.W), 7%.On the contrary,thermal coating shows an advantageous effect on corrosion fatigue strength in 3.5%NaCl solution.F.S.W can increase over 70% in corrosion fatigue strength at 10~7 cycles and P.S can only increase 29%.It can be seen by fractographic analysis that fatigue cracks initiated at such places of coating which contain more defects,and the cracks grew more rapidly in cleavage or mixed mode through the Ni/Al or Ni60 coating. Occasionally,the interface between coating Ni/Al and matrix may be separated.It is found that coating Ni60 consisting of Ni-Cr solid solution and borides can decrease the passive current density.Obviously the micros- tructure and strength of the coating and bonding strength are related to the lifetimes of fatigue crack initiation.
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Received: 25 February 1989
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[7] Bertram.W.;Schemmer.M.,The Proc.of 10th Int,Thermal Spraying Conference.(Essen)(5) ,242-244(1983) |
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