NSUF 16-CINR-639: Beamline Examination of a Hf-Al Metal-Matrix Composite Material
This project proposes to conduct post-irradiation examination of HfAl3 Al composite specimens previously irradiated at the Advanced Test Reactor (ATR) using synchrotron x-ray diffraction and spectroscopy techniques at the MRCAT beamline at the Advanced Photon Source (APS). Through post-irradiation examination (PIE), mechanical and thermophysical properties have been characterized and many features of the microstructure have been determined and compared with those of the unirradiated material.However, during PIE difficulties were encountered when performing scanning electron microscopy (SEM) with electron backscatter diffraction (EBSD) and electron dispersive spectroscopy (EDS). Four different microscopists could not successfully identify the intermetallic phases present in the material. The aluminum indexes nicely, but the HfAl3 does not. The instrument vendor was consulted and even provided several new libraries, but the Kikuchi patterns obtained do not match any of those in the libraries. Considerable resources have been spent on SEM/EDS analysis without much success. According to the literature, the intermetallic particles should index as tetragonal, but the Kikuchi patterns suggest a cubic structure. If the intermetallic indeed has a cubic structure, then there is likely some type of metastable phase that forms in the material. According to the Hf-Al phase diagram, a mixture comprised of 7 at% Hf should form a stable HfAl3 intermetallic. The material was carefully fabricated to crystallize in the low-temperature D023, rather than high-temperature D022, phase. The tetragonal unit cell of type D023 contains four HfAl3 molecules with an axis ratio c/a ~ 4. It is well known that the EBSD patterns between the FCC (Fm3m, Al) and tetragonal (I4/mmm, Hf-Al) crystal systems do not differ greatly, such as those differences normally seen between a cubic and hexagonal system. Therefore, we are proposing a beamline study to obtain information on lattice parameters, coordination chemistry, distances, coordination number, species of the neighbors of the absorbing atom (i.e., Hf), etc. The low divergence, high intensity, and tunability of synchrotron X-rays make possible many powder diffraction experiments that are not practical or possible with a laboratory source. The low divergence of the synchrotron beam with a highly monochromatic beam allows extremely high resolution, whereas the high intensity provides much greater sensitivity to weak peaks or minor phases. Thus, it is possible to utilize synchrotron-derived data for much more accurate phase determination studies and for the solution and refinement of structures. X-ray absorption near edge structure (XANES) spectroscopic data will be collected near the Hf L3-edge (9.555 keV) since it has the highest cross-section of the L-edges. X-ray diffraction will be performed to determine crystal structure and lattice parameters. Information concerning the presence of possible metastable structures and the corresponding lattice mismatch and disregistry.The focus of this proposal is to obtain essential data to help us understand the structure and chemistry of this metal matrix composite material. The NSUF has invested significant resources towards the characterization of this new material. However, the PIE is incomplete until we resolve this remaining technical question.
Additional Info
| Field | Value |
|---|---|
| Abstract | This project proposes to conduct post-irradiation examination of HfAl3 Al composite specimens previously irradiated at the Advanced Test Reactor (ATR) using synchrotron x-ray diffraction and spectroscopy techniques at the MRCAT beamline at the Advanced Photon Source (APS). Through post-irradiation examination (PIE), mechanical and thermophysical properties have been characterized and many features of the microstructure have been determined and compared with those of the unirradiated material.However, during PIE difficulties were encountered when performing scanning electron microscopy (SEM) with electron backscatter diffraction (EBSD) and electron dispersive spectroscopy (EDS). Four different microscopists could not successfully identify the intermetallic phases present in the material. The aluminum indexes nicely, but the HfAl3 does not. The instrument vendor was consulted and even provided several new libraries, but the Kikuchi patterns obtained do not match any of those in the libraries. Considerable resources have been spent on SEM/EDS analysis without much success. According to the literature, the intermetallic particles should index as tetragonal, but the Kikuchi patterns suggest a cubic structure. If the intermetallic indeed has a cubic structure, then there is likely some type of metastable phase that forms in the material. According to the Hf-Al phase diagram, a mixture comprised of 7 at% Hf should form a stable HfAl3 intermetallic. The material was carefully fabricated to crystallize in the low-temperature D023, rather than high-temperature D022, phase. The tetragonal unit cell of type D023 contains four HfAl3 molecules with an axis ratio c/a ~ 4. It is well known that the EBSD patterns between the FCC (Fm3m, Al) and tetragonal (I4/mmm, Hf-Al) crystal systems do not differ greatly, such as those differences normally seen between a cubic and hexagonal system. Therefore, we are proposing a beamline study to obtain information on lattice parameters, coordination chemistry, distances, coordination number, species of the neighbors of the absorbing atom (i.e., Hf), etc. The low divergence, high intensity, and tunability of synchrotron X-rays make possible many powder diffraction experiments that are not practical or possible with a laboratory source. The low divergence of the synchrotron beam with a highly monochromatic beam allows extremely high resolution, whereas the high intensity provides much greater sensitivity to weak peaks or minor phases. Thus, it is possible to utilize synchrotron-derived data for much more accurate phase determination studies and for the solution and refinement of structures. X-ray absorption near edge structure (XANES) spectroscopic data will be collected near the Hf L3-edge (9.555 keV) since it has the highest cross-section of the L-edges. X-ray diffraction will be performed to determine crystal structure and lattice parameters. Information concerning the presence of possible metastable structures and the corresponding lattice mismatch and disregistry.The focus of this proposal is to obtain essential data to help us understand the structure and chemistry of this metal matrix composite material. The NSUF has invested significant resources towards the characterization of this new material. However, the PIE is incomplete until we resolve this remaining technical question. |
| Award Announced Date | 2016-04-12T00:00:00 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | |
| Irradiation Facility | None |
| PI | Donna Guillen |
| PI Email | [email protected] |
| Project Type | CINR |
| RTE Number | 639 |