Abstract
The residual stress generated in a superalloy during heat treatment affects the subsequent processing of the workpiece and may even adversely affect its performance. This paper investigates the effects of pre-stretching (in the range from 0% to 9%) before aging treatment on residual stress generated during quenching process and microstructure of Inconel 718 superalloy. After pre-stretching treatment, the residual stress deriving from quenching process can be well reduced. When the pre-stretch level was 3%, the quenching residual stress reached a maximum reduction of 72%, and the strength increased by 7.1%, while the product of strength and elongation hardly changed. Simultaneously, the microstructures of the pre-stretched specimens are observed by electron back scatter diffraction (EBSD) and transmission electron microscopy (TEM). It was found that the fraction of high-angle grain boundaries in the alloy decreased while that of low-angle grain boundaries increased with increasing pre-stretch level. As the pre-stretch level was further increased to 9%, the proliferating entanglement of internal dislocations in the specimen was intensified, resulting in rod-shaped γ″ precipitates coarsening and volume fraction reduction of precipitates, which further led to a reduction in the product of strength and elongation of material.
Highlights
Inconel 718 alloy (IN718) is a nickel-based high-temperature alloy, which has good high-temperature oxidation and corrosion resistance, and high high-temperature strength, creep strength and endurance strength, as well as good fatigue resistance
Due to its excellent mechanical properties, it is widely used in components that operate under high temperatures and has become a key material for a large number of applications in the aerospace, nuclear energy, and petroleum fields [1,2,3,4,5]
Pre-stretching has a significant effect on the residual stress of IN718 alloy
Summary
Inconel 718 alloy (IN718) is a nickel-based high-temperature alloy, which has good high-temperature oxidation and corrosion resistance, and high high-temperature strength, creep strength and endurance strength, as well as good fatigue resistance. IN718, is a precipitation-strengthened nickel-based superalloy composed of γ matrix, δ phase, carbide, γ (Ni 3 Nb), and γ (Ni3(Al, Ti, Nb). The δ (Ni3Nb) phase is mainly precipitated at the grain boundary, controls the grain size of the superalloy, and hinders the movement of dislocations [6,7]. The main strengthening phase γ (Ni3Nb, DO22) is a metastable phase with a body-centered tetragonal ordered structure, which is dispersed and coherently precipitated in the matrix in the form of a disc. The amount of secondary strengthening phases γ (Ni3 (Al, Ti, Nb), LI2) is inferior to that of γ phases, which are dispersed in a spherical shape and play a role in the strengthening of the alloy
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