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mMINING METALLURGY MATERIALS<br />
m m<br />
WWW.UNILEOBEN.AC.AT<br />
Heterogeneous Nucleation<br />
Mechanisms in Al Alloys<br />
Universitätslehrerverband der<br />
<strong>Montanuniversität</strong> <strong>Leoben</strong> (<strong>ULV</strong>)<br />
This study employs the metallic glass technique to investigate nucleation mechanisms<br />
on heterogeneous TiB 2 particles in Al alloys with an aim to develop more potent grain<br />
refiners.<br />
Grain refined and non<br />
grain refined sample<br />
Melt-spinner<br />
Al-5Ti-1B rod: (a) TiB 2 particle; (b) Al 3 Ti particle; (c) Al matrix<br />
Results indicate that Al nucleates on the basal faces of boride<br />
particles. Dissolved Al 3 Ti particles from the rod provide excess<br />
Ti in the melt. HRTEM of the boride interface has revealed<br />
Al 3 Ti monolayers approximately 1 nm thick. Microchemical<br />
STEM analysis shows that Ti seggregates to the boride interface.<br />
The Al 3 Ti layers are believed to be a requisite for potent<br />
nucleation at low undercoolings due to a reduction in lattice<br />
mismatch with the Al.<br />
Brian McKay<br />
Chair of Casting Research<br />
at MUL since: 2003<br />
Zur Person:<br />
1997-2001 DPhil. Oxford University<br />
2002- 2003 Postdoc University of Manchester<br />
Institute of Science and Technology (UMIST)<br />
2003 - Present University Assistant MUL<br />
In cast houses and foundries it is common to grain refine Al<br />
alloys. This results in a small uniform equiaxed grain structure<br />
which can facilitate casting practice and improve mechanical<br />
properties in the final as-cast product. The most common grain<br />
refiner used in industry is Al-5Ti-1B rod. The rod contains<br />
hexagonal TiB 2 platelets and Al 3 Ti particles distributed within an<br />
Al matrix.<br />
Heterogeneous nucleation on the boride particles has been<br />
examined using the metallic glass technique. This technique<br />
freezes the growth of the nuclei at an early stage within a glass<br />
matrix by rapidly quenching the melt using a melt-spinner.<br />
The nuclei are embedded within a glass which readily permits<br />
examination of the nucleation events by electron microscopy.<br />
TEM micrograph of Al nucleating<br />
on boride particle<br />
HRTEM micrograph of boride<br />
interface.<br />
Forschungsschwerpunkte:<br />
Characterisation techniques: HRTEM, TEM, STEM, SEM, FIB,<br />
EDX, EBSD, DSC, and XRD.<br />
Casting Techniques<br />
Grain Refinement<br />
Metallic Glasses<br />
Al and Mg Aerospace Alloys