Bulk Metallic Glass (BMG) Composites
The group secured funding through the EU Marie Curie Research Training Networks (MCRTN) initiative. This 4-year, €2.0 million project which began in Jan. 2004 focused on Bulk Metallic Glass (BMG) Composites and was coordinated by Institut National Polytechnique de Grenoble and involves ten other European participants as outlined below.
WIT’s primary responsibility within this MCRTN is mechanical characterisation of BMG Composites at both room and elevated temperature.
The group has previously participated in a €1.4 million EC funded project on Nanostructured Aluminium Alloys' (Nano Al). . This 3-year project which concluded in 2003 was coordinated by the University of Oxford, and was undertaken in collaboration with seven other European participants. Significantly, this project represented a new departure for WIT in that it enabled the appointment of the first two postdoctoral researchers at the Institute.
WIT (Participant No. 6) - Mechanical Characterisation
- Tensile properties of melt spun nanostructured ribbon
- Tensile, compressive and fatigue behaviour of bulk materials at room and elevated temperatures
- SEM fractography
- Numerical modelling
The group is conducting research on the mechanical properties of novel metallic foams and is currently collaborating with Northwestern University , USA, as part of this initiative
Unlike conventional metallic foams these materials have been produced by infiltrating ceramic (mullite) shell performs via squeeze casting. This work has been undertaken in collaboration with Prof. David C. Dunand and Dr. Dorian K. Balch, Department of Materials Science and Engineering, Northwestern University.
Characteristics of Foam
Diameters range from 12 to 75mm, with a 45mm mean size. The wall thickness of shells was approximately 10% of the sphere diameter. These mullite shells had the following nominal composition (wt. %): 59% silica, 39% alumina, 1.5% titanium oxide, and 0.5% iron oxide.
Density of Material
||Al Alloy 7075
||AL 7075 Foam
|Density (g.cm -3)
||0.6 - 0.8
Microstructure of Al Alloy 7075 based Foam
Optical micrographs indicate excellent filling of space by the aluminium alloy, with very little porosity between mullite shells. Approximately 10% of shells have been infiltrated. A significant amount of dark grey inclusions containing silicon that has been removed from the shell walls by the molten alloy and precipitated during cooling are evident. These inclusions are both blocky and script-like, and located both inside and outside filled shells together with small amounts of a light grey precipitate containing Al, Cr, and Fe.
Optical Micrograph Al 7075 Foam
Optical Micrograph Al 7075 Foam Larger
Optical Micrograph AL 7075 Foam Largest
The mechanical response of these foams under compressive loading has been characterised at room temperature using both conventional and interrupted test studies. Small testpieces (2x2x4mm) were manufactured using the machining stage of a microtomography facility that enabled surface quality, similar to that achieved by standard materialographic techniques, to be obtained. This high surface quality permitted the use of optical microscopy to track the evolution of surface deformation and damage as a function of engineering strain as indicated below.
The Group has undertaken investigations of damage accumulation in metallic foams and composites using X-ray microtomography facilities at theEuropean Synchrotron Radiation Facility, Grenoble; Argonne National Laboratory, USA, and Queen Mary, University of London. X-ray microtomography (XMT) is an advanced examination technique that allows the visualisation and measurement of internal microstructure non-destructively. This technique has been used to investigate the evolution of damage in metallic foams that were subjected to compressive loading. The work has been undertaken in collaboration with Prof. James C. Elliott and Dr. Graham R. Davis, Department of Oral Growth and Development, Queen Mary, University of London.
These studies focused primarily on damage accumulation in small testpieces (2x2x4mm) of Al 7075 based foam with a limited comparative study of deformation and damage in a similar material having a pure aluminium matrix. Significantly, this non-destructive XMT technique enabled full testpiece reconstruction.