Structural alteratiolls due to rollillg contact fatigue are investigated microscopically fo r two bearing sleels i. e. a S UJ-2 (A1S1 52100) steel alld a O.65% C steel. T wo tylJeS q! structural alteration, the white etching constituent and the dark etching Olle, are revealed. The former originates at nonmetallic inclusions, mostly at alumina, and a microcrack is q{ten seen to be associated with it. The white etelzing constituents grow in number and size with I'epeated C)'cles, but are suppressed at the delJth where the dark etching zone fo rms. T his delJth also corresp onds to that where shear stress becomes maximum. E ach dark etching constituent of which the dark etch• ing zone is made is a variation of original martensite leaves. The hardness of the dark etching constituent is lower than that of the original martensite. The mechanism of the decomposition of martensite is discussed.

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An electroless Ni-Co-P plating solution was developed for preparing soft magnetic thin films. In this plating process, the optimum bath composition and operating condition were obtained by investigating the effect of operating conditions on deposition rate~ film composition, and magnetic properties. Soft magnetic films with low coercive force (lower than 80 A m -~) and high squareness (higher than 0.8) were prepared from these electroless Ni-Co-P plating processes. The alloy film deposited from the optimum bath condition consists of fine-particulated crystallites.

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