The role of stress relaxation and creep during high temperature deformation in Ni-base single crystal superalloys – Implications to strain build-up during directional solidification

Abstract

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The contrasting roles of creep and stress relaxation in the time-dependent deformation during in-situ cooling of a nickel-base single crystal superalloy

“…Thereafter, a stress relaxation test under strain control (fixed ends of the sample) was carried out for an additional 12 mins. The measured lattice strain corresponded to that of the composite (200) γ + γ′ peak 14 , 15 . The strain is reported as a function of temperature and stress normalised by the 0.2% yield stress, , i.e.…”

“…Uniaxial as-cast tensile specimens of CMSX-4 were manufactured via the investment casting route, after 14 . The specimens having diameter 5.9 mm and gauge length 29 mm were directionally solidified as single crystals.…”

“…The measurement of lattice spacing was restricted to the longitudinal direction, i.e . specimen axis 14 – 16 , 18 . Heating was carried out at 10 °C min −1 from room temperature to 800 °C and then at 5 °C min −1 to the set temperature under zero load to allow for thermal expansion.…”

“…Such models implicitly assume a certain constitutive law where stress is considered as a function of time-dependent plastic strain rate, plastic strain and temperature. While it is accepted that visco-plasticity is primarily derived from mechanisms associated with creep, under certain conditions the role of stress relaxation must also be considered 12 – 14 . Identifying the micromechanisms that control such deformation requires the use of techniques that ideally possess both high spatial and angular resolution.…”

Grain Orientation Optimization of Two-Dimensional Grain Selector during Directional Solidification of Ni-Based Superalloys

“…Jet engine turbine blades are located in the harsh environment behind the burner and rotate at high speed to extract energy from the high-temperature gas stream. Generally speaking, single-crystal Ni-based superalloy is usually used in the gas turbine to optimize its functions and to perform the roles of energy conservation, emission reduction and environmental protection [1][2][3]. To obtain an excellent performance of superalloys, a lot of research has been carried out.…”