Wang M.,University of Illinois at Urbana - Champaign |
Vo N.Q.,University of Illinois at Urbana - Champaign |
Vo N.Q.,Northwestern University |
Vo N.Q.,NanoAl LLC |
And 6 more authors.
Shear mixing of the ternary alloy system Ag-Cu-Ni during ball-milling and high-pressure torsion was investigated to elucidate the effects of chemical interactions on phase formation. First, ball-milling of pure Ni with homogeneous Ag67Cu33 alloy powders at room temperature (RT) was studied for average Ni atomic concentrations of 4%, 9%, 15% and 25%. Additional samples with an average composition of Ag50Cu25Ni 25 were ball-milled at ∼-15 C or subjected to high pressure torsion at ∼-125 C. X-ray diffraction and atom probe tomography measurements showed that Cu largely transferred from the Ag-Cu alloy phase to the Ni-rich phase at all temperatures, but that Ag and Ni did not significantly intermix. The Cu concentration in the steady state, moreover, was surprisingly higher in the Ni-rich phase than in the Ag-rich phase, and it was further enriched at the interphase boundary, even at -125 C. High-resolution transmission electron microscopy revealed that the sizes of the Ni/Cu precipitates and the grain size of the Ag-rich matrix were reduced to a few nanometers during RT or cryo-ball-milling, which is much finer than those observed after ball-milling of Cu-Ag or Ni-Ag binary powders. These findings illustrate that chemical effects can play an important role in phase formation during severe plastic deformation, but they also show that other kinetic factors can influence the final microstructure as well. © 2013 Elsevier B.V. All rights reserved. Source
Tai K.,Chinese Academy of Sciences |
Averback R.S.,University of Illinois at Urbana - Champaign |
Bellon P.,University of Illinois at Urbana - Champaign |
Vo N.,NanoAl LLC |
And 2 more authors.
Journal of Nuclear Materials
Irradiation of dilute Cu-W alloys with 1.8 MeV Kr+ between 300 K and 573 K is found to induce nucleation of a high density of W nano-precipitates. HRTEM and aberration-corrected STEM reveal that the ∼3 nm precipitates have a preferred orientation relationship with the matrix. A variant of the Bain relationship exists with preferred alignment occurring along Cu〈2 2 0〉|| W〈010〉, with small angular differences amongst the particles, which is compensated by interfacial dislocations or strain. The formation mechanism for such an orientation relationship is rationalized on the basis that small W clusters form within the local melt of an energetic displacements cascade, resulting in the partial alignment of the nanoprecipitates with the Cu lattice as the Cu solidifies.© 2014 Elsevier B.V. All rights reserved. Source
Pang E.L.,Northwestern University |
Vo N.Q.,Northwestern University |
Vo N.Q.,NanoAl LLC |
Philippe T.,CNRS Material Physics Group |
Voorhees P.W.,Northwestern University
Journal of Applied Physics
The Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation is widely used to describe phase transformation kinetics. This description, however, is not valid in finite size domains, in particular, thin films. A new computational model incorporating the level-set method is employed to study phase evolution in thin film systems. For both homogeneous (bulk) and heterogeneous (surface) nucleation, nucleation density and film thickness were systematically adjusted to study finite-thickness effects on the Avrami exponent during the transformation process. Only site-saturated nucleation with isotropic interface-kinetics controlled growth is considered in this paper. We show that the observed Avrami exponent is not constant throughout the phase transformation process in thin films with a value that is not consistent with the dimensionality of the transformation. Finite-thickness effects are shown to result in reduced time-dependent Avrami exponents when bulk nucleation is present, but not necessarily when surface nucleation is present. © 2015 AIP Publishing LLC. Source
Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 149.71K | Year: 2014
Currently, cast-iron is nearly exclusively used for car brake rotors. Replacing cast-iron by a high- temperature, creep-resistant aluminum alloy could translate into about 80 lbs (36 kg) in weight reduction for a typical car, thus improving its gasoline mileage and reducing its greenhouse gas emissions. Current commercial, castable, age-hardening aluminum alloys cannot withstand temperatures above 430 F (220 C). Thus, replacing cast-iron in car brake rotors by these aluminum alloys is impossible, due to the high heat generation during harsh braking events of the front brakes. Aluminum-scandium based alloys are good candidates to replace cast-iron as they are creep- and coarsening-resistant to 570-750 F (300-400 C). Scandium, however, is very rare and expensive, prohibiting its usage for large-scale, cost-sensitive automotive applications. NanoAl LLC, a high-technology start-up company with leading expertise in designing novel precipitation-strengthened aluminum alloys, proposes under this SBIR program to develop a new, affordable, aluminum-zirconium alloy, which is completely free of scandium, while having improved room-temperature mechanical strength and high-temperature creep-resistance as compared to scandium-containing alloys. NanoAl LLC will design and assess castable, heat- treatable aluminum-zirconium alloy ingots with nanometric Zr-based precipitates nucleated by trace levels of novel elements and will demonstrate their applicability in terms of strength, creep- and coarsening-resistance to brake rotor applications. Using the designed aluminum alloy, NanoAl LLC will manufacture (by casting and heat-treating) and testing a prototype functional brake rotor. Commercial applications and other benefits include providing automakers a novel solution to safely and economically reduce an automobiles mass and emissions, while reducing gasoline consumption to meet the new Corporate Average Fuel Economy (CAFE) regulations and standards. Replacing cast-iron in automobile brake-rotors by high-temperature creep-resistant aluminum- alloys translates into 80 lbs weight reduction, and much improvement in gasoline mileage and reduced emissions. NanoAl LLC, a leading expert in designing novel aluminum alloys, proposes to develop a cost-effective aluminum-zirconium alloy strong enough to replace cast-iron in car brake-rotor applications.
Agency: NSF | Branch: Standard Grant | Program: | Phase: SMALL BUSINESS PHASE I | Award Amount: 149.99K | Year: 2016
This Small Business Innovation Research Phase I project involves development of a new family of thermally-stable, high-strength aluminum casting alloys for engine cylinder head applications. There is a strong push globally to improve internal combustion (IC) engine efficiency, through down-sizing, turbo or supercharged boost, and through the use of alternative fuels. All of these approaches increase the operational temperature of the engine beyond what current aluminum engine alloys can sustain, leading to dimensional changes which can cause engine failure. At these higher temperatures, the new alloys to be developed will retain engine performance and life, while maintaining the low weight, castability, and cost-effectiveness of standard aluminum alloys. Our initial focus is on two-wheeled motorcycles and other recreational vehicles that represent a total market capitalization of $35 million, just for cylinder heads. There are many follow-on markets including diesel generators, and engines for outboard marine, small aircraft and even automobile vehicles, where the total markets are estimated in the billions of dollars.
The intellectual merit of this project is the replacement of traditional gravity- and die-cast aluminum alloys with higher performing materials at a competitive cost. These aluminum alloys will contain heat-resistant nano-precipitates, which will not dissolve at high operating temperature and pressure, thus retaining the component strength, toughness and microhardness. With production of millions of IC engines each year, a new high-temperature alloy will lead to significant energy reductions. Current automotive and motorcycle aluminum engine components, such as cylinder heads, blocks and pistons, are limited to an operating temperature of roughly 220 deg. C. Modern and future engines require higher operating temperatures of up to 290 deg. C and pressures up to 21 MPa to meet demands for higher engine efficiency, reduced vehicle mass and fuel consumption, increases in the power-to-mass ratio, and lower emissions. The 2025 Corporate Average Fuel Economy (CAFE) regulations require an efficiency of 54.5 miles per gallon for light duty vehicles by 2025. The need for improved IC engine efficiency is urgent, thus increasing the demand for novel high temperature aluminum casting alloys.