HIGH-CYCLE FATIGUE BEHAVIOR OF POLYCRYSTALLINE NIAL-0.28 MOL-PERCENT-FE

The high cycle fatigue (HCF) behavior of NiAl-0.28Fe (Ni-50.3 mol%Al-0 .28 mol%Fe) was determined at four temperatures between 673 K and 928 K, below and above its ductile to brittle transition temperature, DBTT , (=730 K) obtained from tensile tests. Fracture and surface slip band -characteristics were examined using an optical microscope and a scann ing electron microscope. The fatigue resistance of NiAl-0.28Fe decreas ed significantly with increasing temperature, due to a creep-fatigue i nteraction above the DBTT. Below the DBTT cracks initiated at or near the surface with fatigue zones and overload zones consisted of a mixtu re of intergranular and transgranular fracture paths. Above the DBTT c rack initiation occurred internally at or near microvoids (without obs erved fatigue zones), leading to transgranular fracture paths. Cross s lip and wavy slip were exhibited in tensile and HCF specimens below an d above the DBTT. NiAl-0.28Fe displayed higher fatigue resistance than Astroloy (powder metallurgy nickel-based superalloy) and Ni3Al+B in t he range 673 K to 823 K.