Papers by Keyword: Directionally Solidified

Abstract: In this study high temperature deformation and creep behaviors of DS IN738LC were studied. The yield strength and the total elongation decreased gradually with increase of temperature from room temperature to 500°C. The tensile strength and ductility increased rapidly with increase of temperature from 500°C to 660°C. The flow stress of Inconel738LC increases with increasing temperature up to about 600°C in the presence of γ precipitates. For high temperature creep, the stress exponent was observed to increase from 3~9 in the lower stress region to 13~16 in the higher stress region. The significant change of the stress exponent is likely to be attributed to the inverse temperature dependence of flow stress at high temperatures in directionally solidified IN738LC.

Abstract: Modern gas turbines utilize single crystal (SX) and directionally solidified (DS) nickel superalloys which hold a higher cyclic life resistance and an improved creep rupture strength compared to their conventionally cast (CC) version. Both, SX and DS materials feature a significant direction dependence of material properties, which needs to be considered in the constitutive and lifing models. In this context, the paper presents a mathematical framework of cyclic life prediction. Although the method is developed for DS nickel alloys with transverse isotropic material behaviour, a generalisation to common orthotropic materials inclu¬ding SX is straightforward. The proposed procedure is validated by two examples. Moreover, an application to turbine components is shown.

Abstract: The monotonic tensile and creep deformations of a directionally solidified (DS) superalloy are investigated for several loading directions. The material exhibits remarkable anisotropy under elastic and creep loading conditions, whereas it shows isotropy under loading conditions of high strain rates. Tension-torsion creep tests are also conducted to investigate the deformation under multiaxial stress conditions. Referring to the observed behavior, a unified constitutive model, which has two features, is developed for the DS superalloy. One is a static recovery term of back stresses that is prescribed as a transversely isotropic property, which is supposed to have an effect on the deformation behavior under creep loading conditions. The other is the division of inelastic strain into two components, which represent octahedral and cubic slip system deformations, so as to describe multiaxial creep deformation. Calculation results obtained using the constitutive model are compared with the uniaxial and multiaxial experimental results to evaluate the validity of the model.