Assistant Professor
Department of Mechanical Engineering and Engineering Science
The University of North Carolina at Charlotte
9201 University City Blvd., Charlotte, NC 28223-0001
Office: 362 Duke Centennial Hall (DCH).
Tel: 704-687-8213; Fax: 704-687-8345.
Research Interests
1. Processing, Microstructure and Mechanical Properties of Ultrafine Grained and Nanocrystalline Materials: Metals and alloys with ultrafine grained (UFG) and nanocrystalline (NC) microstructures exhibit a number of novel properties. The most famous is the Hall-Petch relation which predicts that the strength of a metal is proportional to the inverse square root of its grain size. Recently, investigators have uncovered many new behaviors of UFG and NC metals. For example, strategies to improve the ductility of UFG/NC metals have been proposed and exploited. It has also been observed that the strain rate effect on the mechanical strength of UFG/NC metals has some unique trend depending on the lattice structure of the metals. Such observations is bringing out new ways to the production of UFG/NC metals and alloys with desired properties. In Dr. Wei's research group, UFG/NC metals and alloys are processed by various technical routes, including powder metallurgy (high-energy ball milling followed by consolidation), severe plastic deformation (SPD), etc. Microstructure engineering for the processing of multi-phase UFG/NC alloys is of particular interest to his group.
2. Dynamic Behavior of Materials: Many materials applications pose the need for knowledge about the materials mechanical behavior under high rate (dynamic loading). Quasi-static loading means the strain rate is within the range of 10-4 s-1-100 s-1; dynamic loading means the strain rate is larger than this range. A well defined technique for the measurement of dynamic behavior of materials is the Kolsky Bar (or Split-Hopkinson Pressure Bar--SHPB) systems. Dr. Wei's lab has a conventional SHPB system under construction. A miniature SHPB will also be built in his lab.
3. Probing of Mechanical Properties at Micro/Nano Scale: Quest for scaling towards smaller devices requires knowledge of the materials behavior at micrometer and nanometer scales. Assumptions that small scale materials behavior being comparable to large scale properties have been proven dubious, inaccurate or even completely erroneous. In light of this, direct probing of mechanical properties of materials at micro/nanometer scale is necessary. Ultimately, it will be necessary to match the volume of the measurement to that of significance for function in a particular application. Conventionally, people have been using nano-indenter, for example, to investigate the mechanical properties of thin films, to examine the indenter size effect, to evaluate the incipient plasticity associated with single crystal metals, to study the phase transformation of diamond cubic semiconductors such as Si and Ge, and so on. However, it is not possible to use conventional nano-indentation to acquire experimental data with regard to the constitutive behavior of small scale materials systems. Dr. Wei's group is working on using a modified nano-instrumentation to probe the stress-strain behavior of materials at the micro/nano scale.
4. Fabrication and Characterization of Thin Films: Thin films or coatings are used in many cutting edge technologies. Dr. Wei's group is working on processing and characterization of advanced thin film materials such as super-hard diamond-like carbon coatings. They use pulsed-laser deposition (PLD) to produce the coatings on various kinds of substrates, and measure their mechanical properties via nano-indentation. One contribution from Dr. Wei's work is successful relief of the large internal compressive stress in such super-hard coating introduced during coating deposition.
5. Materials Characterization Using Modern Techniques: Dr. Wei's group is using state-of-the-art techniques for the characterization of materials. Such techniques include transmission electron microscopy (TEM), X-ray diffraction (XRD), etc. High-resolution TEM is used to observe atomic-level structures of materials, such as grain boundary structures, dislocations, etc.
Recent Representative Publications
Q. Wei, K. T. Ramesh, L. J. Kecskes, S. N. Mathaudhu and K. T. Hartwig, "Ultrafine and nanostructured refractory metals processed by SPD: Microstructure and Mechanical Properties", Materials Science Forum, Vol. 579, pp. 75-90 (2008) (Invited)
P. Jiang, Q. Wei, Y.S. Hong, J. Lu and X.L. Wu, "In situ synthesis of nanocrystalline intermetallic layer during surface plastic deformation of zirconium", Surface and Coatings Technology, Vol. 202, pp. 583-589 (2007).
X.L. Wu, N.R. Tao, Q.M. Wei, P. Jiang, J. Lu and K. Lu, "Microstructural evolution and formation of nanocrystalline intermetallic compound during surface mechanical attrition treatment of cobalt", Acta Materialia, Vol. 55, pp. 5768-5779 (2007).
B.E. Schuster, Q. Wei, M.H. Ervin, S.O. Hruszkewycz, M.K. Miller, T.C. Hufnagel and K.T. Ramesh, "Bulk and microscale compressive properties of a Pd-based metallic glass", Scripta Materialia, Vol. 57, pp. 517-520 (2007).
L.J. Kecskes, K.C. Cho, R.J. Dowding, B.E. Schuster, R.Z. Valiev and Q. Wei, "Grain size engineering of bcc refractory metals: Top-down and bottom-up—Application to tungsten", Materials Science and Engineering: A, Vol. 467, pp. 33-43 (2007).
Q. Wei, "Strain rate effects in the ultrafine grain and nanocrystalline regimes--influence on some constitutive responses", Journal of Materials Science, Vol. 42, pp. 1709-1727 (2007) (Invited).
Q. Wei, K. T. Ramesh, B. E. Schuster, L. J. Kecskes and R. J. Dowding, "Nanoengineering opens a new era for tungsten as well", JOM-US, Vol. 48 (9), pp. 40-44 (2006) (Invited).
Q. Wei, H. T. Zhang, B. E. Schuster, K. T. Ramesh, R. Z. Valiev, L. J. Kecskes, R. J. Dowding, L. Magness and K. Cho, "Microstructure and mechanical properties of super-strong nanocrystalline tungsten processed by high-pressure torsion", Acta Materialia, Vol. 54, pp. 4079-4089 (2006).
Q. Wei, T. Jiao, K. T. Ramesh, E. Ma, L. J. Kecskes, L. Magness, R. Dowding, V. U. Kazykhanov and R. Z. Valiev, "Mechanical behavior and dynamic failure of high-strength ultrafine grained tungsten under uni-axial compression", Acta Materialia, Vol. 54, pp. 77-87 (2006).
H. Zhang, B. E. Schuster, Q. Wei and K. T. Ramesh, "The design of accurate micro-compression experiments", Scripta Materialia, Vol. 54, pp.181-186 (2006).
B. E. Schuster, Q. Wei, H. Zhang and K. T. Ramesh, "Microcompression of nanocrystalline nickel", Applied Physics Letters, Vol. 88, article number: 103112 (2006).
Q. Wei, K. T. Ramesh, E. Ma, L. J. Kecskes, R. J. Dowding, V. U. Kazykhanov and R. Z. Valiev, "Plastic flow localization in bulk tungsten with ultrafine microstructure", Applied Physics Letters, Vol. 86, article number 101907 (2005).
Q. Wei, S. Cheng, K. T. Ramesh and E. Ma, "Effect of nanocrystalline and ultrafine grain sizes on the strain rate sensitivity and activation volume: fcc versus bcc metals", Materials Science and Engineering A, Vol. 381, pp.71-79 (2004).
Q. Wei, L. Kecskes, T. Jiao, K. T. Hartwig, K. T. Ramesh and E. Ma, "Adiabatic shear banding in ultrafine-grained Fe processed by severe plastic deformation", Acta Materialia, Vol. 52, pp. 1859-1869 (2004).
| FOR YOUR EYES ONLY | ||||
Department of Mechanical Engineering and Engineering Science at UNC-Charlotte.
Current Teaching: MEGR3161.