Fatigue crack growth characteristics for powder nickel based metallurgical superalloys at elevated temperatures

Abstract

AbstractThis study presents experimental results regarding the fatigue crack growth characteristics of nickel‐based powder metallurgical superalloys used in aircraft turbine disks. The powder metallurgy alloys are manufactured using metal powders with a particulate diameter of less than 1 mm. The powder metallurgy alloys used in aircraft parts or turbine blades have excellent mechanical properties, fatigue resistance, oxidation resistance, and corrosion resistance at elevated temperatures. However, fatigue cracks arising from defects in the materials are unpredictable because they depend upon the manufacturing technique. As it is known that structural components may need to operate at elevated temperatures, the behavior of fatigue crack propagation at elevated temperatures is considered. The fatigue crack growth tests are conducted at typical operating conditions of stress ratios and elevated temperatures. Fatigue crack growth rate is measured using the direct current potential drop method, and evaluated by the Forman‐Mettu equation. Considering ΔKth as an important design variable, empirical constants were derived so that the analytic ΔKth value can be obtained directly at a given temperature. Fractography of the fractured specimens was performed using a scanning electron microscopy.