Directionally Solidified Materials:Nickel‐base Superalloys forGas Turbines

Abstract

From the first forged turbine blades made of iron base alloys to the present nickel base single-grain turbine blades and vanes manufactured by directional solidification, an enormous amount of research has been directed to attaining the hottest possible combustion chamber temperatures in jet engines. Temperature has been increased by about 15 K each year for the last two decades, improving the thermodynamic efficiency of the engines. The more recent developments concern the manufacturing of single-grain parts made of nickel base superalloys with large amount of the γ′ hardening phase.This paper first presents the directional solidification process used to produce single-grain parts, the formation of as-cast microstructures and the defects that can arise during solidification. In the second part the thermal treatments that are applied to the nickel base superalloys in order to enhance their mechanical properties are detailed. The effect of crystallographic orientation and of the γ/γ′ microstructure on the mechanical properties is briefly presented, as well as the. microstructural changes that can possibly arise during service.

Elasticity mapping of precipitates in nickel-base superalloys using atomic force acoustic microscopy

“…Hence, using Eqs. (1)(2)(3)(4)(5), the indentation modulus can be determined from the measured contact stiffness values. The equations can be solved using suitable softwares like MATLAB or LabVIEW.…”

“…Subsequently, the indentation modulus maps were obtained using Eqs. (2)(3)(4) and the matrix as reference in every scan line. The isotropic indentation modulus of the matrix (222 ± 2 GPa) was obtained by the ultrasonic velocity measurements in the solution-annealed specimen using the following equation [13]:…”

“…Two types of nickelbase alloys are widely used viz. polycrystalline superalloys [2] and directionally solidified superalloys [3]. Polycrystalline superalloys have applications from intermediate temperatures to high temperatures, whereas directionally solidified superalloys are meant for high-temperature applications, where creep is of utmost concern.…”

“…Dai et al [20] and Yong et al [21] have theoretically calculated the elastic properties of d-phase based on the firstprinciple studies. They reported the values of Young's modulus (E) and Poisson's ratio (m) for Ni 3 Nb with DO a structure to be in the range of 250-270 GPa and 0.33-0.35, respectively. The properties of various types of carbides analyzed by both experimental techniques and first-principle calculations are well documented by Pierson [22].…”

Quantitative Analysis of Scanning Force Microscopy Images of Nickel-Based Superalloys

“…This evolution towards nanometer This type of study was performed in the case of nickel-based alloys used to manufacture singlegrain high-temperature turbine components, i. e. the so-called "single-crystal superalloys" [2,3]. These materials are strengthened by precipitation of hard and brittle sub-micronic particles -the -y' phase -in a more ductile matrix 2013 thé 03B3 phase -, which results in a rather simple microstructure illustrated in Figure la.…”