Impact of Additional gamma' Strengthening on the Strength and Fatigue Behavior of Oxide Dispersion Strengthened Ni-Base Superalloys

摘要

The impact of additional gamma' precipitation hardening on the strength and fatigue life of oxide dispersion strengthened nickel-base superalloys is investigated using the novel alloy, PM 3030. A typical coarse and elongated grain structure is used to compare PM 3030 with a solely oxide dispersion strengthened superalloy PM 1000 having similar chemical composition and grain structure [1]. Constant extension rate tests (CERT) and high cycle fatigue (HCF) tests are performed in the temperature range between room temperature and 1250 deg C in order to evaluate the material performance. Furthermore, optical microscopy, scanning and transmission electron microscopy (SEM and TEM) are performed for the characterization of the microstructure prior to and following mechanical testing. It is found that additional gamma' strengthening in PM 3030 results in an increase in quasi-static strength by about factor 2 and in HCF life at a given stress amplitude by more than factor 4 at temperatures up to 850 deg C as compared to PM 1000. This advantage decreases at temperatures above 850 deg C due to accelerated creep processes, circumvention of gamma' particles, as well as microstructural softening by dissolution of gamma' precipitates [2-3]. When the fatigue behaviour is compared at a fixed ratio of stress amplitude to ultimate compression strength ratio, PM 3030 shows a shorter life time compared to PM 1000 indicating that the gain in quasi-static strength is greater than that in fatigue strength. It can be concluded that combining oxide dispersion and precipitation strengthening has a great potential for intermediate temperature applications, i.e. at service temperatures between 600 and 1160 deg C.