More Like this

1. Multi-Scale Microstructural Characterization of Aluminum Alloys Subject to Advanced Processing Techniques for Improving Mechanical Properties

   Wu, Yun-Hsuan (August 2025, Oregon State University)

   This work presents a multi-scale microstructural characterization of aluminum alloys processed by high-pressure torsion (HPT) and cold angular rolling process (CARP) to improve their mechanical properties. Mechanical properties such as microhardness and tensile strength were correlated with microstructural features. To understand the processing-structure-property relationships, characterization methods spanning nano- to millimeter scales were used, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM) EDS. TEM and STEM EDS were used to show that HPT of a Mg sheet sandwiched between Al sheets successfully produced a supersaturated solid solution (SSSS) of Mg in Al and several Al-Mg intermetallic phases, leading to significant grain refinement and increases in microhardness over pure Al. Although CARP has potential to induce the severe plastic deformation (SPD), the CARP system used in this work was not able to achieve SPD aluminum alloys. However, SEM EBSD characterization shows that CARP achieves an increase of the low-angle grain boundaries (LAGBs) and geometrically necessary dislocation (GND) density in Al-1043,which improves the mechanical properties. Moreover, a preliminary study was conducted on CAPR processed Al-6061 alloys to understand the synergistic effects precipitation and CARP-processing on the microstructure and properties. This research provides the critical insights into the capabilities and current limitations of CARP as a continuous SPD technique for aluminum alloys, and demonstrate the importance of integrated multi-scale characterization in understanding advanced materials processing. 

   more » « less
2. Influence of Degree of Severe Plastic Deformation on Thermal Stability of an HfNbTiZr Multi-Principal Element Alloy Processed by High-Pressure Torsion

   https://doi.org/10.3390/nano12193371  

   Hung, Pham Tran; Kawasaki, Megumi; Szabó, Ábel; Lábár, János L.; Hegedűs, Zoltán; Gubicza, Jenő (October 2022, Nanomaterials)

   Severe plastic deformation (SPD) is an effective route for the nanocrystallization of multi-principal element alloys (MPEAs). The stability of the refined microstructure is important, considering the high temperature applications of these materials. In the present study, the effect of SPD on the stability of a body-centered cubic (bcc) HfNbTiZr MPEA was investigated. SPD was performed using a high-pressure torsion (HPT) technique by varying the number of turns between ½ and 10. The evolution of phase composition and microstructure was studied near the disk centers and edges where the imposed strain values were the lowest and highest, respectively. Thus, the shear strain caused by HPT varies between 3 (½ turn, near the center) and 340 (10 turns, near the edge). It was found that during annealing up to 1000 K, the bcc HfNbTiZr alloy decomposed into two bcc phases with different lattice constants at 740 K. In addition, at high strains a hexagonal close packed (hcp) phase was formed above 890 K. An inhomogeneous elemental distribution was developed at temperatures higher than 890 K due to the phase decomposition. The scale of the chemical heterogeneities decreased from about 10 µm to 30 nm where the shear strain increased from 3 to 340, which is similar to the magnitude of grain refinement. Anneal-induced hardening was observed in the MPEA after HPT for both low and high strains at 740 K, i.e., the hardness of the HPT-processed samples increased due to heat treatment. At low strain, the hardness remained practically unchanged between 740 and 1000 K, while for the alloy receiving high strains there was a softening in this temperature range. 

   more » « less
3. Primary recrystallization of a magnesium hybrid material fabricated by high-pressure torsion

   https://doi.org/10.1016/j.mtcomm.2024.108305  

   Mohamed, Ouarda Ould; Bazarnik, Piotr; Huang, Yi; Azzeddine, Hiba; Baudin, Thierry; Brisset, François; Kawasaki, Megumi; Langdon, Terence G (February 2025, Materials Today Communications)

   The static recrystallization and grain growth of a hybrid AZ31/Mg-0.6Gd (wt%) material fabricated by high pressure torsion (HPT) through 20 turns were explored after isochronal annealing at 150, 250, 350 and 450 ◦C for 1 h using electron backscatter diffraction, transmission electron microscopy and Vickers microhardness measurements. The results reveal heterogeneity in the grain size distributions of the AZ31 and Mg-0.6Gd regions after annealing at the lower temperatures of 150 and 250 ◦C leading to a clear AZ31/Mg-0.6Gd interfacial border. At the higher temperatures of 350 and 450 ◦C the AZ31/Mg-0.6Gd interfaces were not well-defined owing to the occurrence of grain growth. It is shown that grain growth is restricted in the AZ31 and Mg-0.6Gd regions due to the presence of stable nano-size Al8Mn5 particles and the precipitation of Mg17Al12 and Mg12Zn at 250 ◦C and of Mg5Gd and Mg12Gd phases at 350 and 450 ◦C. The distribution of the basal texture in both regions was strongly controlled by dynamic recrystallization, precipitation and grain growth. The values of the microhardness over the radial cross-sections of the hybrid discs decrease and become more uniform, in the range of ~35–66 Hv, with increasing annealing temperature. 

   more » « less
4. Digital Image Correlation Analysis of Uniform Deformation and Necking in Solid‐State Welded Nanocrystalline Aluminum via High‐Pressure Torsion

   https://doi.org/10.1002/adem.202400439  

   Bhatta, Laxman; Lee, Isshu; Figueiredo, Roberto B; Bay, Brian K; Kawasaki, Megumi (October 2024, Advanced Engineering Materials)

   Solid‐state welding of Al 1043 sheets is achieved via high‐pressure torsion (HPT) processing to produce bulk nanostructured Al disks. A homogeneous nanostructure without segregation is observed, with grain sizes of ≈430–470 nm. Miniature tensile testing, coupled with the digital image correlation (DIC) technique, is employed to determine the room‐temperature tensile deformation behavior, particularly the nonuniform behavior with necking, of the HPT‐bonded ultrafine‐grained (UFG) aluminum, comparing it with annealed coarse‐grained counterpart. The HPT‐bonded UFG Al exhibits a large fraction of post‐necking strain, which is supported by the estimated high strain rate sensitivity value ofm = 0.085, suggesting the delay of local necking leading to tensile fracture. Detailed DIC analysis reveals prolonged diffuse necking, thus delaying local necking, in the HPT‐bonded UFG Al, while the annealed samples show high fractions of local necking during the nonuniform deformation. Moreover, the DIC data illustrate that local necking predominantly occurred at a limited neck zone, maintaining a plateau strain distribution at the out‐of‐neck zone throughout necking deformation toward tensile failure for both annealed and UFG aluminum. The DIC method offers an alternative means to demonstrate the transition in necking behaviors of materials by estimating the plastic lateral contraction exponent. 

   more » « less
5. Zero-Valent iron nanoparticles induce reactive oxygen species in the cyanobacterium, Fremyella diplosiphon.

   Gichuki, S. M. (November 2021, ACS omega)

   Dr. Krishna Ganesh (Ed.)

   Nanoscale zero-valent iron nanoparticles (nZVIs) are known to boost biomass production and lipid yield in Fremyella diplosiphon, a model biodiesel-producing cyanobacterium. However, the impact of nZVI-induced reactive oxygen species (ROS) in F. diplosiphon has not been evaluated. In the present study, ROS in F. diplosiphon strains (B481-WT and B481-SD) generated in response to nZVI-induced oxidative stress were quantified and the enzymatic response determined. Lipid peroxidation as a measure of oxidative stress revealed significantly higher malondialdehyde content (p < 0.01) in both strains treated with 3.2, 12.8, and 51.2 mg L–1 nZVIs compared to untreated control. In addition, ROS in all nZVI-treated cultures treated with 1.6–25.6 mg L–1 nZVIs was significantly higher than the untreated control as determined by the 2′,7′-dichlorodihydrofluorescein diacetate fluorometric probe. Immunodetection using densitometric analysis of iron superoxide dismutase (SOD) revealed significantly higher SOD levels in both strains treated with nZVIs at 51.2 mg L–1. In addition, we observed significantly higher (p < 0.001) SOD levels in the B481-SD strain treated with 6.4 mg L−1 nZVIs compared to 3.2 mg L–1 nZVIs. Validation using transmission electron microscopy equipped with energy-dispersive X-ray spectroscopy (EDS) revealed adsorption of nZVIs with a strong iron peak in both B481-WT and B481-SD strains. While the EDS spectra showed strong signals for iron at 4 and 12 days after treatment, a significant decrease in peak intensity was observed at 20 days. Future efforts will be aimed at studying transduction mechanisms that cause metabolic and epigenetic alterations in response to nZVIs in F. diplosiphon. 

   more » « less