Structural metallic materials working at high temperatures need to face challenging conditions, since they have to withstand loads for extended period of time without failure. For some applications, e.g. gas turbine blades, even small strains have to be avoided.
Service conditions lead to the presence of a number of overlapping processes that need to be tested, and this can be done in a wide range of temperatures, up to about 1000 °C. However, tests alone might not be enough since the actual working conditions can’t be reproduced on a laboratory scale. So, it is required to derive constitutive equations which allow to extrapolate the actual behavior in service conditions and, if possible, to account for the superposition of different phenomena.
For example, an accurate description of the uniaxial creep behavior of nickel based superalloys used for gas turbines as a function of test conditions allows to extrapolate the mechanical behavior in service, namely their properties at longer times (lower stress and temperatures with respect to the ones experienced during a standard creep test), under variable loads and temperature or under a triaxial stress state.
Dynamic solicitations, causing fatigue at high temperature, can be also present, making it necessary to elaborate rules to describe/predict the lifetime reduction induced by the complex deformation and damage phenomena.
At ICMATE, these aspects are investigated especially for high-performance alloys (typically for power generation and manufacturing industry) through high temperature testing as creep, low cycle and thermomechanical fatigue, stress relaxation and tensile tests and relative modeling/characterization.
