Laser energy interaction with novel fine-grained materials
The effect of laser irradiation on metal and ceramic structures and properties including:
- Low fluence, high repetition rate femtosecond pulse irradiation, which can modify optical properties of Yttria-Stabilized Zirconia with non-linear absorption for applications in integrated optical devices;
- high energy nanosecond pulses irradiation, capable of creating nanoscale surface structures (LIPSS) to change the hydrophobicity and color of metals like magnesium and titanium;
- custom milling and continuous wave laser heating of tailored metallic nanocrystalline alloyed powders for enhanced laser densification and coalesced properties with the goal of high throughput material development for additive manufacturing (metal 3D printing).
Deformation behavior in nanocrystalline magnesium alloys
Magnesium alloys are the lowest density structural metals available making them useful in mass-critical operations. Unfortunately, they also suffer from low plasticity due to basal plane slip as the dominating mechanism, and thus have limited formability near room temperature. The current strategy to promote other deformation modes is to increase temperature, a truly ancient technique. This research attempts to increase room temperature plasticity through grain size reduction and minor alloying. High-energy ball milling along with spark plasma sintering are utilized to increase solubility, refine grains, and achieve full density without significant grain growth or segregation.
Researchers: Christian Roach
Concurrent strength and ductility in magnesium
Magnesium alloys are of great interest due to the low density of magnesium which can lead to significant weight savings in transportation vehicles which will contribute to reduced emissions. Magnesium alloys exhibit lower bulk strengths than aluminum alloys, and typical methods toward strengthening result in reduction in ductility leading magnesium alloys to be unsuitable for load-bearing applications.
This research focuses on circumventing the paradox of simultaneous increases in strength and ductility in hexagonal close-packed materials, i.e. magnesium alloys:
- Introduction of nano-spaced stacking faults: by introducing nano-spaced stacking faults through severe plastic deformation, it is possible to increase strength while maintaining or increasing ductility in magnesium alloys. These defects provide boundaries for dislocation motion along slip planes which contribute to strengthening, while providing alternate dislocation slip pathways along less-accessible planes allowing for maintained or increased ductility with the increase of strength.
- Nanograined Dual-Phase Magnesium-Lithium Alloy: One of the major issues with the decreased ductility gained through increased strength in magnesium alloys is caused by the limited slip systems in hexagonal close-packed materials. However, by alloying magnesium with lithium at high enough quantities, it is possible to produce both hexagonal close-packed and body-centered cubic structures within the alloy. In this configuration, it is possible to increase the strength of the alloy via reducing grain size while maintaining or increasing ductility by taking advantage of the increased dislocation motion pathways available to body-centered cubic structures.
Researchers: Heather Salvador
Relationships between microstructure and mechanical properties of novel binary alloys, including bioresorbable Fe-Mn alloys and microstructurally stable Cu-Ta alloys
- Fe-Mn alloys are being considered for potential bioresorbable implant materials due to their reported combination of biocompatibility, strength, high stiffness and adjustable corrosion rate. The effect of nanostructure and grain size on the corrosion rate and physical properties are explored in Fe-Mn alloys processed via high-pressure torsion (HPT) and spark plasma sintering (SPS). The corrosion and mechanical properties are compared between “top-down” HPT and “bottom-up” SPS nanostructured materials and the as-cast dendritic microstructures. The results forecast the ability to tailor microstructural features to control desirable mechanical response and biocompatibility.
- Thermally stable Cu-Ta alloys: Understanding fatigue crack growth (FCG) mechanisms in microstructurally stable, fully dense, nanocrystalline (NC) Cu-Ta alloys, including a clear understanding of the true microstructural grain size effects on salient FCG mechanisms in stable, bulk NC alloys, and to reconcile key theories and hypotheses pertaining to the mechanisms by which microstructure characteristics affect FCG behavior of NC alloys.
Researchers: Anqi Yu
Electrical conductivity and wear properties of ultra-fine grain materials
- The conductivity and wear properties of materials processed by high-pressure torsion (HPT) are characterized to elucidate property evolution due to severe plastic deformation.
- Dispersion strengthening of nanoparticles in metal melt systems to create novel metal-interstitial matrices.
Plasma synthesis and sintering of nanoparticles
Research focused on creating non-stoichiometric nano-powders through nonthermal plasma synthesis, followed by sintering via spark plasma sintering (SPS) to consolidate nano-powders into bulk, metastable samples with unique enhanced properties.
Researchers: Steven Herzberg
Bottom-up and top-down nanostructuring of soft face-centered cubic alloys by severe plastic deformation and consolidation
Research focused on production of high strength nanostructured dilute silver alloys for high strain rate/structural/electronics applications. Elemental silver has high formability, good corrosion resistance, disinfectant properties, and possesses the highest thermal and electrical conductivity of any metal, however, these useful properties are overshadowed by its poor mechanical strength. Bottom-up processing and consolidation through a combination of mechanical alloying (MA) and spark plasma sintering (SPS) or top-down processing by high-pressure torsion (HPT) are used to produce high strength nanocrystalline and ultrafine-grained silver alloys. These alloys possess increased strength compared to their coarse-grained counterparts, achieved through a combination of solid solution strengthening, nanoscale dispersion strengthening, and grain boundary strengthening and forecast the ability to process high-strength, high-conductivity silver alloys for electronic and structural applications.
Metal (high-strength steel, aluminum) processing, microstructure evolution and mechanical properties
Current projects include:
- Understanding the relationship between processing parameters, microstructure refinement, and mechanical properties in an ausformed ultra high strength steel and achieving an optimum combination of strength and ductility in the final product.
- Strengthening Mg alloys with nano-scale stacking faults. Previous research focused on deformation processing of commercial aluminum alloys.
Researchers: Yiwei Sun