Fundamental Investigations of Creep and Fatigue of Dispersion Strengthened NbAlloys

摘要

During the three years of this program, the creep studies focused on a selectprecipitation strengthened alloy of niobium shown to possess superior creep resistance at stress levels normally targeted in design applications. The alloy selected was a carbide precipitation strengthened niobium-zirconium-alloy (Nb-1wt%Zr-0.1wt%C) commercially known as PWC-11. The carbide precipitations are produced in-situ during the thermomechanical processing of the material and have proven to be extremely stable at service temperature. Transmission electron microscopy was used to examine both the internal structure of the crept material as well as the size distribution of the carbide particles extracted from the metal matrix. X-ray diffraction analysis of the extracted carbide particles identified their chemical make-up necessary for characterizing their thermodynamic stability. A thermodynamic model was developed which supports the observed parameters of the carbide precipitates and thus is useful in predicting the high temperature mechanical properties of this and similar alloy systems. jg p1.