High Temperature Deformation Mechanism in Hierarchical and Single Precipitate Strengthened Ferritic Alloys by In Situ Neutron Diffraction Studies

Abstract

The ferritic Fe-Cr-Ni-Al-Ti alloys strengthened by hierarchical-Ni2TiAl/NiAl or single-Ni2TiAl precipitates have been developed and received great attentions due to their superior creep resistance, as compared to conventional ferritic steels. Although the significant improvement of the creep resistance is achieved in the hierarchical-precipitate-strengthened ferritic alloy, the in-depth understanding of its high-temperature deformation mechanisms is essential to further optimize the microstructure and mechanical properties, and advance the development of the creep resistant materials. In the present study, in-situ neutron diffraction has been used to investigate the evolution of elastic strain of constitutive phases and their interactions, such as load-transfer/load-relaxation behavior between the precipitate and matrix, during tensile deformation and stress relaxation at 973 K, which provide the key features in understanding the governing deformation mechanisms. Crystal-plasticity finite-element simulations were employed to qualitatively compare the experimental evolution of the elastic strain during tensile deformation at 973 K. It was found that the coherent elastic strain field in the matrix, created by the lattice misfit between the matrix and precipitate phases for the hierarchical-precipitate-strengthened ferritic alloy, is effective in reducing the diffusional relaxation along the interface between the precipitate and matrix phases, which leads to the strong load-transfer capability from the matrix to precipitate.

First-Principles Investigations of the Structural, Anisotropic Mechanical, Thermodynamic and Electronic Properties of the AlNi2Ti Compound

“…Then elastic constants c ij can be computed by Hooker's law, as presented in Table 2. Our results are similar to other calculation data [18,35,36] and the values from the GGA-PW91 method are quite close to those from GGA-PBE. All elastic constants satisfy the Born-Huang stability criterion, so the AlNi 2 Ti compound has intrinsic stability [57].…”

“…AlNi 2 Ti with L2 1 structure can provide NiAl or Ni-base and Ti-base alloys with good high-temperature mechanical properties by precipitate strengthening [5][6][7][8][9][10][11][12][13][14][15][16]. Especially the mechanical properties of Fe-Ni-Al-Ti ferritic alloys, such as creep resistance and yield strength, can be significantly enhanced due to the AlNi 2 Ti precipitates [17][18][19][20][21][22][23][24][25][26]. In addition, AlNi 2 Ti precipitate phase has also been observed in microstructures of Al-doped Ni-Ti shape memory alloys that have huge potential to be applied as functional material in many areas such as clinical medicine, biotechnology, automation, energy engineering, electronics industry, aeronautics and astronautics, owing to their pseudoelasticity, superplasticity and shape memory properties [27][28][29][30][31][32].…”

Exploring Structural Changes, Manufacturing, Joining, and Repair of Intermetallic γ‐TiAl‐Based Alloys: Recent Progress Enabled by In Situ Synchrotron X‐Ray Techniques

“…As the strain mapping of several interconnected phases requires a high temporal and spatial resolution, high-energy X-rays (and neutrons) particularly lend themselves to such in situ experiments. [208][209][210] For this reason, synchrotron tensile tests have in fact been conducted already on a multitude of other materials including austenitic stainless steel, [211][212][213] Al-based alloys, [211,[214][215][216] Mg alloys, [217,218] Cu, [211] Ti-base alloys, [219][220][221][222][223][224][225][226] Ni-base and ferritic superalloys, [227][228][229][230][231] and composite materials. [210] In the case of γ-TiAl-based alloys, in situ tensile tests have been carried out on lab scale [205][206][207] as well as using monochromatic high-energy X-rays.…”

“…As the strain mapping of several interconnected phases requires a high temporal and spatial resolution, high‐energy X‐rays (and neutrons) particularly lend themselves to such in situ experiments. [ 208–210 ] For this reason, synchrotron tensile tests have in fact been conducted already on a multitude of other materials including austenitic stainless steel, [ 211–213 ] Al‐based alloys, [ 211,214–216 ] Mg alloys, [ 217,218 ] Cu, [ 211 ] Ti‐base alloys, [ 219–226 ] Ni‐base and ferritic superalloys, [ 227–231 ] and composite materials. [ 210 ]…”

Characterization of Crystallographic Structures Using Bragg-Edge Neutron Imaging at the Spallation Neutron Source

“…A variety of sample environments (load frame, heating furnace, levitation equipment, etc.) have enabled more complex dynamic or real-time microstructure measurements [5][6][7][8][9][10]. Moreover, attenuation-based neutron imaging has been widely adopted to visualize micron-scale structures inside materials (porosity, density inhomogeneity) [11][12][13].…”