Effect of tensile mean stress on fatigue behavior of single-crystal and directionally solidified superalloys

Conference · Mon Jan 01 04:00:00 EST 1990

OSTI ID:5765218

Kalluri, S; Mcgaw, M A

Two nickel base superalloys, single crystal PWA 1480 and directionally solidified MAR-M 246 + Hf, were studied in view of the potential usage of the former and usage of the latter as blade materials for the turbomachinery of the space shuttle main engine. The baseline zero mean stress (ZMS) fatigue life (FL) behavior of these superalloys was established, and then the effect of tensile mean stress (TMS) on their FL behavior was characterized. At room temperature these superalloys have lower ductilities and higher strengths than most polycrystalline engineering alloys. The cycle stress-strain response was thus nominally elastic in most of the fatigue tests. Therefore, a stress range based FL prediction approach was used to characterize both the ZMS and TMS fatigue data. In the past, several researchers have developed methods to account for the detrimental effect of tensile mean stress on the FL for polycrystalline engineering alloys. However, the applicability of these methods to single crystal and directionally solidified superalloys has not been established. In this study, these methods were applied to characterize the TMS fatigue data of single crystal PWA 1480 and directionally solidified MAR-M 246 + Hf and were found to be unsatisfactory. Therefore, a method of accounting for the TMS effect on FL, that is based on a technique proposed by Heidmann and Manson was developed to characterize the TMS fatigue data of these superalloys. Details of this method and its relationship to the conventionally used mean stress methods in FL prediction are discussed.

• Research Organization: National Aeronautics and Space Administration, Cleveland, OH (USA). Lewis Research Center
• OSTI ID: 5765218
• Report Number(s): N-91-18452; NASA-TM--103644; E--5827; NAS--1.15:103644; CONF-901184--
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360103* -- Metals & Alloys-- Mechanical Properties
ALLOYS
CRYSTALS
DUCTILITY
FATIGUE
HEAT RESISTANT MATERIALS
HEAT RESISTING ALLOYS
MACHINERY
MATERIALS
MECHANICAL PROPERTIES
MONOCRYSTALS
NICKEL ALLOYS
NICKEL BASE ALLOYS
PHASE TRANSFORMATIONS
POLYCRYSTALS
SOLIDIFICATION
STRESS ANALYSIS
TENSILE PROPERTIES
TURBINE BLADES
TURBOMACHINERY