Cu 70, Ni 30 (wt%), cored dendrites
This alloy is typical of many copper based alloy systems. The dendrite structure shows coring (variation in solute concentration). The light areas are rich in nickel and the darker areas are low in nickel. Chill casting extracts heat quickly enough to prevent significant solid state diffusion, resulting in cored dendrites. The centres of the dendrites that cool near the liquidus temperature, are nickel rich compared to the outer layers that solidify at progressively lower temperatures. Because t
Author(s): Prof T W Clyne, Department of Materials Science an

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X-ray tomography image of open cell polyurethane foam
If a gas is injected into a liquid it forms a cellular foam structure. When a thermoset prepolymer of low viscosity is foamed, the polymer can drain from the cell walls (driven by surface tension) before it sets at the cell edges, leaving an open-celled foam. The cell edges have three concave sides. The average co-ordination number for the nodes (where struts meet) is four, giving tetrahedral junctions. The deformation behaviour of the foam was observed by X-ray microtomography at the ESRF in Gr
Author(s): Dr J A Elliott, Department of Materials Science an

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Rapid solidification in an atomised droplet
Because of the fine scale of the droplet, heat extraction is very rapid, and large undercoolings are achieved before crystal nucleation can begin. Thus, in this droplet, the solidification front has advanced very rapidly through the droplet from the nucleation point (on the surface at the left of the image). Its velocity is initially so great that no interfacial breakdown is possible. As the front advances, however, latent heat is evolved and this 'recalescence' reduces the rate of solidificatio
Author(s): Prof T W Clyne, Department of Materials Science an

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Fe, Ni 30, C 0.3 (wt%), quenched - martensite plates
This sample was quenched to -80 °C to give a metastable martensitic microstructure. The martensite plates show a lenticular morphology as the material attempts to shear as it transforms but is unable to open up voids at the grain boundaries. The plates form in a similar way to mechanical twins but the shear processes lead to changes in crystal structure as well as crystallographic orientation.
Author(s): Prof T W Clyne, Department of Materials Science an

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Silal
This sample shows the typical structure of silal, irons with high Si content (5.5-7.9 wt%). It is a grey cast iron alloyed with 4-6wt% Si to provide good oxidation resistance. The high Si content forms a dense, adherent iron silicate surface film, which is resistant to oxygen penetration. The flake graphite iron Silal was one of the first heat resisting cast irons developed. Spheroidal graphite Si irons have higher strength and improved ductility. The structure shows cored dendrites of ferrite w
Author(s): Dr R F Cochrane, Department of Materials, Universi

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Fe, C 0.9 (wt%), martensite
Martensite is a metastable supersaturated solid solution of C in steel. The excess carbon atoms sufficiently strain the matrix to produce a b.c.t (body centred tetragonal) structure. In order to minimise interfacial strain between the parent austenite and the transforming martensite the martensites assume a lath or needle shape.
Author(s): Prof T W Clyne, Department of Materials Science an

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Silal
This sample shows the typical structure of silal, irons with high Si content (5.5-7.9 wt%). It is a grey cast iron alloyed with 4-6wt% Si to provide good oxidation resistance. The high Si content forms a dense, adherent iron silicate surface film, which is resistant to oxygen penetration. The flake graphite iron Silal was one of the first heat resisting cast irons developed. Spheroidal graphite Si irons have higher strength and improved ductility. The structure shows cored dendrites of ferrite w
Author(s): Dr R F Cochrane, Department of Materials, Universi

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Ni-hard iron
This is a Ni-hard iron, one of the first cast irons to be developed. These white irons contain Ni to ensure that the austenite transforms to martensite following heating and chromium to increase the hardness of the eutectic carbide.Ni-hard irons are normally stress relieved at 200-300 °C for approximately four hours to relieve the martensitic transformation stresses and to promote the transformation of retained austenite. The structure consists of proeutectic austenite dendrites containing mart
Author(s): Prof T W Clyne, Department of Materials Science an

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Cu 60, Zn 40 (wt%), quenched and held at 300°C - Widmanstätten microstructure
This sample was quenched and held at 300 °C for one hour. It has a Widmanstätten microstructure with the α phase precipitating out of the single β phase during cooling to give α plates in a β matrix. The low temperature at which the transformation takes place leads to less diffusion and results in a finer structure.
Author(s): Prof T W Clyne, Department of Materials Science an

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Wrought-grade aluminium alloy
The micrograph shows Al-Mg-Fe-Si containing < 1wt.% of each solute; refined with TiB2 particles. Deformation of grain structure is due to cutting of sample with scissors. This micrograph illustrates the effect of deformation on a previously equiaxed structure. Strain causes the elongation of grains and the subsequent anodising produces 'mottled' grain colours; the oxide layer is not of constant orientation or thickness across a grain.The Barker's etch and applied electrical field produce a thick
Author(s): T Quested, Department of Materials Science and Met

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Austenitic stainless steel
Shows the grain structure of an austenitic stainless steel NF709, observed using light microscopy on a specimen polished and etched electrolytically using 10% oxalic acid solution in water. Many of the grains contain annealing twins. NF709 is a creep-resistant austenitic stainless steel used in the construction of highly sophisticated power generation units. Source: http://www.msm.cam.ac.uk/phase-trans/abstracts/annealing.twin.html.
Author(s): Prof H K D H Bhadeshia, Department of Materials Sc

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Silal
This sample shows the typical structure of silal, irons with high Si content (5.5-7.9 wt%). It is a grey cast iron alloyed with 4-6wt% Si to provide good oxidation resistance. The high Si content forms a dense, adherent iron silicate surface film, which is resistant to oxygen penetration. The flake graphite iron Silal was one of the first heat resisting cast irons developed. Spheroidal graphite Si irons have higher strength and improved ductility. The structure shows cored dendrites of ferrite w
Author(s): Prof T W Clyne, Department of Materials Science an

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Alporas' closed cell aluminium foam
Additions are made to molten aluminium or aluminium alloy to modify the melt viscosity and make it suitable for foaming. 1 to 3 wt% titanium hydride is then added to the melt, and this foams the melt by releasing hydrogen. The foamed melt solidifies to yield a closed cellular structure with an average cell size of 4.5 mm
Author(s): Dr V Gergely, Department of Materials Science and

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Ni-hard iron
This is a Ni-hard iron, one of the first cast irons to be developed. These white irons contain Ni to ensure that the austenite transforms to martensite following heating and chromium to increase the hardness of the eutectic carbide.Ni-hard irons are normally stress relieved at 200-300 °C for approximately four hours to relieve the martensitic transformation stresses and to promote the transformation of retained austenite. The structure consists of proeutectic austenite dendrites containing mart
Author(s): Prof T W Clyne, Department of Materials Science an

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Cu 55, Zn 45 (wt%) brass, as cast, dendritic
A cast alloy of high zinc brass, consisting of β dendrites. The α precipitates out of solution at the crystal boundaries, forming a structure of β dendrites surrounded by α. This is known as a Widmanstätten structure because a geometrical pattern of α forms on certain crystallographic orientations of the β lattice.
Author(s): Dr R F Cochrane, Department of Materials, Universi

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Cross-section of an aluminium foam slab produced by gas injection
This is a continuous casting process which obviates foaming agents and the restrictions that they impose on temperature and processing time. However, molten metal drains through the structure due to gravitational forces and the resulting foam has a pronounced density gradient.
Author(s): Dr V Gergely, Department of Materials Science and

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SEM image of open cell polyurethane foam
If a gas is injected into a liquid it forms a cellular foam structure. When a thermoset prepolymer of low viscosity is foamed, the polymer can drain from the cell walls (driven by surface tension) before it sets at the cell edges, leaving an open-celled foam. The cell edges have three concave sides, giving rise to the tri-cuspid cross section visible at the bottom of this image. The average co-ordination number for the nodes (where struts meet) is four, giving tetrahedral junctions.
Author(s): J A Curran, Department of Materials Science and Me

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Zn, cold rolled - mechanical twins
This sample was cold rolled. Zinc has a hexagonal structure so it contains only two independent slip systems. However, for slip to occur, five slip systems are required so zinc does not undergo general plasticity. Instead it forms mechanical twins as an alternative to dislocation motion to accommodate the deformation.
Author(s): Prof T W Clyne, Department of Materials Science an

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Silal
This sample shows the typical structure of silal, irons with high Si content (5.5-7.9 wt%). It is a grey cast iron alloyed with 4-6wt% Si to provide good oxidation resistance. The high Si content forms a dense, adherent iron silicate surface film, which is resistant to oxygen penetration. The flake graphite iron Silal was one of the first heat resisting cast irons developed. Spheroidal graphite Si irons have higher strength and improved ductility. The structure shows cored dendrites of ferrite w
Author(s): Dr R F Cochrane, Department of Materials, Universi

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Cu 55, Zn 45 (wt%) brass, as cast, dendritic
A cast alloy of high zinc brass, consisting of β dendrites. The α precipitates out of solution at the crystal boundaries, forming a structure of β dendrites surrounded by α. This is known as a Widmanstätten structure because a geometrical pattern of α forms on certain crystallographic orientations of the β lattice.
Author(s): Dr R F Cochrane, Department of Materials, Universi

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