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High frequency fatigue behavior of near surface of turbine disk are critical for its application and operation. High frequency indentation fatigue tests of GH4169 alloy under different load amplitudes, frequencies and mean loads at small length scale were conducted, and the dependence of load amplitude, load frequency and mean load on high frequency indentation fatigue property of GH4169 alloy are discussed in this paper. Depth amplitude (ha), mean depth (hm) and depth propagation rate (dh/dN) were employed as evaluation indicators of the indentation behavior. Results show that depth amplitude is only relevant with load amplitude, while mean depth is related to all the adopted influencing factors, ranked in an ascending order as load amplitude, mean load and frequency with a ranking relation of nm1=1.4 < nm2=1.71 < nm3=2.02. Furthermore, a modified Paris law was utilized to reveal the fatigue mechanism, and found the fatigue mechanism is dominated by intrinsic mechanism under the influence of mean load and load amplitude, while for the influence of frequency, the fatigue mechanism is governed by extrinsic mechanisms. Combined with SEM results and three-dimensional morphology analysis, it can be deduced that dislocation movement mode in high frequency indentation fatigue is dislocation slip. [ABSTRACT FROM AUTHOR]

Fatigue damage of rail steel is an important issue affecting economic and human safety. In this paper, the effect of different quenching rates on the fatigue crack growth of hypereutectoid rail is analyzed. The material parameters C and m of the Paris formula are measured. The results show that an increase in cooling rate of rail decreases the value Paris law parameter C, increases the value m and decreases fatigue crack growth rate. This can be attributed to the decreased in the lamellar spacing and cluster diameter of the pearlite with an increase in cooling rate. More specifically, the smaller lamellar spacing and the cluster diameter make the crack pass easily through the cluster boundary of pearlite, which increases the number of zigzag crack growth paths and branching cracks that can help restrain fatigue crack growth. The fatigue fracture characteristic of hypereutectoid rail is that with an increase in cooling rate, the fatigue striation spacing and river pattern of the fracture surface become smaller, the crack growth path tends to zigzag, the tearing edges become deeper and the surface is relatively rougher. [ABSTRACT FROM AUTHOR]