Abstract
The effect of phosphorus content in nickel film on the fatigue strength of electroless nickel plated steel was studied by a rotary bending method. In addition, the change in microstructure of the film during the fatigue test was examined by transmission electron microscopy.
The results obtained are as follows;
(1) The fatigue strength of steel is improved by electroless nickel plating regardless of phosphorus content in the plating film. The hardness of film and the degree of fatigue strengthening decrease with increasing phosphorus content in the film.
(2) The baking at a temperature above 300∼350°C induces crystallization and grain-growth in the nickel film. The fatigue strength of plated steel after baking is lower than that of the non-plated one.
(3) The electroless nickel film has a tendency to crystallize during the fatigue test under cyclic over-stress.
(4) The fatigue damage of steel is suppressed by the electroless nickel film. Fatigue cracks initiate and propagate from a place just under the plating film, i. e., near the surface of substratum.
(5) The nickel and phosphorus contents in plating films depend upon the pH value of the plating bath and show homogeneous distributions when the pH value in the plating bath is 5∼4.
