Resume

• 2009

  English

  Chinese

  French

  Doctor of Philosophy (PhD)

  Materials Science

  University of Sydney

• 2004

  Bachelor of Engineering (B.Eng.)

  Biomedical/Medical Engineering

  University of Sydney

  Bachelor's Degree

  Finance

  General

  University of Sydney

• I go to local primary schools and interact with kids in science projects to kindle their interests in science and engineering.

  SABES

  Nanotechnology

  Statistics

  Biomedical Engineering

  Mathematical Modeling

  Spectroscopy

  Simulations

  Science

  Materials Science

  Biochemistry

  Microscopy

  Scanning Electron Microscopy

  Characterization

  Breaking the icosahedra in boron carbide

  Kevin Hemker

  Julie Cairney

  William Goddard III

  Simon Ringer

  Takanori Sato

  Qi An

  Findings of laser-assisted atom probe tomography experiments on boron carbide elucidate an approach for characterizing the atomic structure and interatomic bonding of molecules associated with extraordinary structural stability. The discovery of crystallographic planes in these boron carbide datasets substantiates that crystallinity is maintained to the point of field evaporation

  and characterization of individual ionization events gives unexpected evidence of the destruction of individual icosahedra. Statistical analyses of the ions created during the field evaporation process have been used to deduce relative atomic bond strengths and show that the icosahedra in boron carbide are not as stable as anticipated. Combined with quantum mechanics simulations

  this result provides insight into the structural instability and amorphization of boron carbide. The temporal

  spatial

  and compositional information provided by atom probe tomography makes it a unique platform for elucidating the relative stability and interactions of primary building blocks in hierarchically crystalline materials.

  Breaking the icosahedra in boron carbide

  Simon P Ringer

  Julie M Cairney

  Peter J Felfer

  The current study investigates the strengthening of an Nb-microallyed CASTRIP® steel at 798 K (525 °C) by nitriding in a KNO3 salt bath. Nitriding up to 1 hour dramatically increased the yield strength of the steel by ~35 pct (from 475 to 645 MPa) with no sacrifice of ductility (~16 pct). Further nitriding led to brittle fracture. Hardness profiles of the nitrided steels through the thickness reveal hard surfaces and a relatively softer core. The hardening of the shell in the nitrided steels is thought to be the combined effect of solid solution strengthening from nitrogen and dispersion strengthening from clusters and precipitates. The retained ductility is attributed to the hard-shell–soft-core structure through nitriding.

  High Strength and Retained Ductility Achieved in a Nitrided Strip Cast Nb-Microalloyed Steel

  Kevin Hemker

  Zafir Alam

  Pyramidal I slip was observed to be the dominant slip mode in magnesium single crystals compressed quasi-statically along c-axis at room temperature. The slip trace angles resulted from pyramidal I and pyramidal II slips projected on (0 − 1 1 0) and (2 − 1 − 1 0) surfaces were initially calculated

  and then measured on 3% deformed magnesium single crystals. The measured angles indicate the prevalence of pyramidal I slip ({10–11}< 11–23 > with the critical resolve shear stress of 54 MPa). The pyramidal slip traces are dense but very fine

  suggesting limited < c + a > dislocation activities.

  Julie M. Cairney

  Simon P. Ringer

  David R. Smith

  Cluster-strengthened Nb-microalloyed strip cast steels are of interest as clustering during aging leads to an enhancement in strength without compromising ductility

  resulting in desirable mechanical properties. However

  the precise strengthening mechanism is not well understood. Using in situ heating transmission electron microscopy

  clustering was found to impede the movement of dislocations during aging. The attractive combination of ductility and strength was attributed to the effects of recovery and the restricted movement of dislocations through clustering.

  The effect of clustering on the mobility of dislocations during aging in Nb-microalloyed strip cast steels: In situ heating TEM observations

  The effect of pre-existing defects on the strength and deformation behavior of α-Fe nanopillars

  Simon P Ringer

  Julie M Cairney

  Xiaozhou Liao

  Yanbo Wang

  Peter J Felfer

  Yang Cao

  The effects of two types of pre-existing defects

  dislocations and clusters

  on the strength and deformation behavior of body-centered cubic Fe nanopillars with a diameter of ∼150 nm were investigated using in situ nanocompression in a transmission electron microscope. The plastic deformation of nanopillars containing high initial dislocation densities was observed to be relatively continuous

  proceeding via a series of small- and intermediate-scale strain bursts that were associated with the movement/escape of dislocations and the formation of slip bands. Mechanical annealing was observed in nanopillars with high dislocation densities. When the dislocation density was reduced by in situ heating

  the nanopillars were much stronger and the plastic deformation behavior transformed to a more abrupt and explosive mode. The introduction of a dispersion of solute atom clusters into nanopillars caused further strengthening as a higher stress level is required for dislocations to pass the clusters. The strengthening effect of cluster dispersion in nanopillars is comparable to that observed in the bulk steel. These phenomena are universal for Fe nanopillars with different crystallographic orientations.

  The effect of pre-existing defects on the strength and deformation behavior of α-Fe nanopillars

  TEM observations have provided insight into the processing and microstructural evolution of a commercial hot-pressed boron carbide. Fine dispersions of nano-scale AlN precipitates and individual submicron AlN precipitates were observed in a modest fraction of the grains. The nano-precipitates were found to be coherent with a well-defined crystallographic relationship to the matrix. The chemistry

  size and distribution of both types of precipitates and the coherency of the nano-precipitates indicate that both intragranular homogeneous and heterogeneous precipitation occurred during cooling.

  Precipitation of AlN in a commercial hot-pressed boron carbide

  Kevin Hemker

  William Goddard III

  Rich Haber

  Jim McCauley

  Fatih Toksoy

  Qi An

  Recent observations of planar defects in boron carbide have been shown to deviate from perfect mirror symmetry and are referred to as “asymmetric twins.” Here

  we demonstrate that these asymmetric twins are really phase boundaries that form in stoichiometric B4C (i.e.

  B12C3) but not in B13C2. TEM observations and ab initio simulations have been coupled to show that these planar defects result from an interplay of stoichiometry

  atomic positioning

  icosahedral twinning

  and structural hierarchy. The composition of icosahedra in B4C is B11C and translation of the carbon atom from a polar to equatorial site leads to a shift in bonding and a slight distortion of the lattice. No such distortion is observed in boron-rich B13C2 because the icosahedra do not contain carbon. Implications for tailoring boron carbide with stoichiometry and extrapolations to other hierarchical crystalline materials are discussed.

  Atomic-Level Understanding of “Asymmetric Twins” in Boron Carbide

  Julie M. Cairney

  James G. Williams

  Harold Kaul

  Simon P. Ringer

  This study investigated the microstructure and mechanical properties of Nb-microalloyed ultra-thin cast strip (UCS) steels produced by the CASTRIP® process aged at temperatures below and above the Ac1 temperature (525–800 °C). Aging provided a rapid strength increase without loss in ductility. This is significant because

  ordinarily

  one of these properties would increase at the expense of the other. Atom probe tomography (APT) and transmission electron microscopy (TEM) revealed that the strengthening was associated with the formation of Nb-rich solute atom clusters and nanoscale precipitates within the microstructure

  which retard the movement of dislocations during deformation. The changes in strength and hardness were compared to the microstructural evolution across a range of different aging temperatures and explained in terms of the nucleation kinetics. Cluster-finding algorithms were used to analyse atom probe data

  providing quantitative information about the dispersion of these clusters and precipitates. Optimum strengthening was observed where the clusters particles had a radius of 1–2 nm and a volume fraction of 0.027±0.004%.

  Cluster strengthening of Nb-microalloyed ultra-thin cast strip steels produced by the CASTRIP® process

  Rich A. Haber

  Kevin J. Hemker

  Luoning Ma

  William Rafaniello

  Submicrometer boron carbide powders were synthesized using rapid carbothermal reduction (RCR) method. Synthesized boron carbide powders had smaller particle size

  lower free carbon

  and high density of twins compared to commercial samples. Powders were sintered using spark plasma sintering at different temperatures and dwell times to compare sintering behavior. Synthesized boron carbide powders reached >99% TD at lower temperature and shorter dwell times compared to commercial powders. Improved microhardness observed in the densified RCR samples was likely caused by the combination of higher purity

  better stoichiometry control

  finer grain size

  and a higher density of twin boundaries.

  Densification and characterization of rapid carbothermal synthesized boron carbide

  Kelvin

  Xie

  Johns Hopkins University

  UNSW Australia

  ANSTO

  University of Sydney

  Texas A&M University

  Baltimore

  Maryland Area

  TEM investigation of defects in Mg and boron carbide to understand their deformation mechanisms.

  Assistant Research Scientist

  Johns Hopkins University

  1. Designed a bio-reactor.\n2. Culture mesenchymal stem cells.

  Research Student

  Sydney

  Australia

  UNSW Australia

  Using ABAQUS to simulate the thermal stress in power station components.

  Research Student Engineer

  Sydney

  Australia

  ANSTO

  Bryan/College Station

  Texas Area

  Assistant Professor

  Texas A&M University

  1. Prepare optical

  SEM and TEM specimens.\n2. Optical

  SEM and TEM imaging.\n3. Draft scientific journal papers

  Part-time Research Assistant

  Sydney

  Australia

  University of Sydney

  In-house TEM expert characterizing chemistry and atomic level defects in Mg and boron carbide.

  Post-doctoral Research Fellow

  Baltimore

  Maryland Area

  Johns Hopkins University

  A nitrided steel product or thin cast steel strip comprising

  by weight

  less than 0.25% carbon

  between 0.20 and 2.0% manganese

  between 0.05 and 0.50% silicon

  less than 0.01% aluminum

  niobium between 0.01 and about 0.20%

  and between 0.01 and 0.075% nitrogen

  and having a majority of the microstructure comprised of bainite and acicular ferrite

  having more than 70% niobium in solid solution prior to nitriding and having after nitriding for one hour yield strength between 600 MPa and 800 MPa and tensile strength between 650 MPa and 900 MPa and no more than a 2% decrease in total elongation from the steel product prior to nitriding.

  Nitriding of niobium steel and product made thereby

  US 20120186703 A1

  Simon Ringer

  Harold Kaul

  Chris Killmore

  Julie Cairney

  Peter Felfer