Microstructural and compositional design of Ni-based single crystalline superalloys ― A review

Precipitation behavior of grain boundary (GB) M23C6 and its effect on tensile properties at elevated temperature were investigated systematically in a Ni–Cr–W based superalloy. The results show that the M23C6 precipitation behavior is influenced obviously by grain boundary character (GBC) and interfacial energy. The Σ≤9 GBs and low angle GBs have low interfacial energy, and no M23C6 carbide precipitates at these GBs. Plenty of M23C6 carbide particles precipitate at the large angle GBs with high interfacial energy. The coherent orientation relationship between M23C6 and the matrix plays an important role on the precipitation morphology of M23C6. M23C6 carbides with four typical morphologies distribute at the large angle GBs, including lamellar carbide which grows into the matrix near one side or both sides of the GBs, rod-like carbide and small lamellar carbide both of which grow along GBs. Moreover, the decrease of both tensile and yield strength of the aged alloy is mainly caused by the lamellar M23C6 carbide breaking. The tensile properties vary irregularly with increasing aging time.

Precipitation behavior of grain boundary M23C6 and its effect on tensile properties of Ni–Cr–W based superalloy

https://research-information.bris.ac.uk/ws/files/105834373/Full_text_PDF_final_published_version_.pdf

An Atom Probe Tomography study of site preference and partitioning in a nickel-based superalloy

The quasi-static tensile experiment and Split-Hopkinson Tension Bar (SHTB)experiment of AZ31B magnesium alloy have been studied under a strain rate range of 0.001–3000 s −1 at a temperature range of 20–250 °C. A empirically based constitutive and fracture model, Johnson–Cook (J–C) model, have been proposed to incorporate strain rates and temperatures effect on the stress–strain relation. The models can describe the stress–strain relations of metals over a wide range of strain rates and temperatures. The effects of strain rates and temperatures on the material's behavior were discussed. Based on the tensile state experimental technique, the aim was to determine the material constants of the constitutive and fracture models according to the experiments. The constitutive model and fracture model of J–C employed in 3D finite element software ANSYS and ABAQUS to describe AZ31B magnesium alloy electromagnetic bulging and failure behavior. Good agreement is obtained between the numerical simulation results and the experiment results. It indicates that it is valid using the J–C constitutive and failure models to describe or predict the electromagnetic bulging and failure response of materials.

A constitutive and fracture model for AZ31B magnesium alloy in the tensile state

Effect of lattice misfit on the evolution of the dislocation structure in Ni-based single crystal superalloys during thermal exposure

Microstructural analyses have been carried out to investigate the relationship between Ti/Al ratio and stress-rupture properties of nickel-based superalloy Ni–19.5Cr–(0.8–3.5)Al–(0.5–3.2)Ti–0.06C. The γ′ phase coherently precipitates in the γ matrix, the volume fraction and average diameter of the spherical γ′ phase decrease slightly with the increase of Ti/Al ratio after full heat treatment. The precipitate of β-NiAl in the γ matrix for the alloys with low Ti/Al ratio leads to the propagation of cracking into the grain interior. High Ti/Al ratio leads to the precipitate of η-Ni3Ti at grain boundaries, which weakens the strength of grain boundaries. Both the precipitates of β-NiAl and η-Ni3Ti phases are harmful to the stress-rupture life and a peak stress-rupture life appears when Ti/Al ratio is about 1.22 with elongation and reduction in area higher than 5% and 9.7%, respectively.

Relationship between Ti/Al ratio and stress-rupture properties in nickel-based superalloy

Effects of heat treatments on the microstructure and mechanical properties of Rene 80

Nickel-based superalloy Nimonic 80A with various carbon contents has been developed. Various strengthening mechanisms of carbon were analyzed by optical microscope, X-ray diffraction, scanning electron microscope equipped with energy dispersive spectroscopy and transmission electron microscope. Detailed microstructural analysis revealed that with the increase of carbon content from 0.01% to 0.10%, both the lattice parameters of γ′ and γ phases decreased, and the misfit δ between the coherent γ′ and γ phases increased slightly from 0.289% to 0.317% after full heat treatment at 1070 °C/8 h, A.C. + 700 °C/16 h, A.C. The diameter of spherical γ′ phase decreased from 22.24 nm of 0.01%C alloy to less than 15.76 nm of 0.06%C and 0.10%C alloys. Cr23C6 carbide precipitated at the grain boundary in the alloys with carbon content higher than 0.06%, and when carbon content increased to 0.10%, Cr23C6 carbide had an orientation relationship with the γ matrix: [ 00 1 ¯ ] Cr23C6 [ 00 1 ¯ ] γ matrix and ( 100 ) C r 23 C 6 (1 0 0) γ matrix, which can enforce the grain boundary strength. The growth of room temperature tensile strength with the increase of carbon content was primarily due to the coherent strain strengthening and the precipitate strengthening of Cr23C6 carbide. After stress-rupture test at 750 °C/310 MPa, the misfit δ increased from 0.182% to 0.237% with the increase of carbon content, but the values were lower than those after full heat treatment. The precipitate of blocky Cr23C6 in 0.10%C alloy tended to become spherical and dislocation lines were found in the γ matrix channels between γ′ phases, the combination of the dislocation strengthening and precipitate strengthening of Cr23C6 carbide at grain boundary was beneficial to the stress-rupture properties.

Strengthening mechanisms of carbon in modified nickel-based superalloy Nimonic 80A

Nickel based superalloy Nimonic 80A modified with various Ti contents has been developed. Microstructure evolutions were investigated by optical microscope, X-ray diffraction, scanning electron microscope and transmission electron microscope in relation to the room temperature tensile properties and stress-rupture properties at 750 °C/310 MPa. After full heat treatment, the precipitate changed from γ ′ phase to γ ′ +  η phases, the volume fraction of γ ′ phase, lattice misfit of γ ′/ γ and room temperature tensile strength increased with the increase of Ti content. With the increase of lattice misfit, the orderly {1 1 1} atomic planes in the γ ′/ γ interface changed to slight distorted atomic planes and edge dislocations with Burgers vector of a/3 〈1 1 1〉 were identified. The stress-rupture life first increased and then decreased with the increase of Ti content, and the decrease was primarily due to the precipitate of intermetallic η phase at grain boundaries. After stress-rupture tests, the precipitate of Cr 23 C 6 carbide exhibited an orientation relationship with the γ ′ and γ phases, the spherical morphology of γ ′ phase transformed to cubic shape for the alloy with longest stress-rupture life and the morphology transformation process of γ ′ phase was schematically suggested.

Guoqing Jia

Papers

Relationship between Ti/Al ratio and stress-rupture properties in nickel-based superalloy

Effects of heat treatments on the microstructure and mechanical properties of Rene 80

Strengthening mechanisms of carbon in modified nickel-based superalloy Nimonic 80A

Evolution of microstructure and mechanical properties of Ti modified superalloy Nimonic 80A

Microstructure evolution and stress-rupture properties of Nimonic 80A after various heat treatments