#doitpoms

[materialsscienceandengineering]

Strain-induced birefringence in a polycarbonate bar

Applications Polycarbonate is a clear and relatively tough plastic used to make shatterproof windows, lenses and even helmets. It is also used to make compact discs. Sample preparation A four-point bending rig is used to apply stress. Technique Cross-polarised light microscopy Length bar 14 mm Further information The colours in the image are the result of birefringence and relate to the strain-induced alignment of the polycarbonate molecules. Because the specimen is below the glass transition temperature of PC (145 deg C), the material will relax when the stress is removed and there will be no residual alignment. The colours reveal the pattern of stress concentration around the points of contact with the rig, with a neutral axis along the centre and opposite values of birefringence on either side. Contributor J A Curran Organisation Department of Materials Science and Metallurgy, University of Cambridge

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[materialsscienceandengineering]

Annealed steel structures

You'll have to clarify exactly what you're looking for from me, but yes. I agree.

Annealed steel structures. Very neat.

Here:

Low alloy medium carbon steel, containing Ni, Cr, Mo, annealed

Dual-phase steel water quenched from 800°C

[materialsscienceandengineering]

Cu 60, Zn 40 (wt%), air cooled

Processing Homogenised at 850 °C, air cooled [...] Sample preparation Etched in NH4OH/H2O2 Technique Reflected light microscopy Length bar 400 μm / 80 µm Further information This sample has been air cooled. The fast cooling rate changes the morphology to a 'basket weave' appearance known as a Widmanstätten microstructure. The α phase precipitates out of the single β phase during cooling to give α plates in a β matrix. The plates form in order to minimise strain energy. Contributor Prof T W Clyne Organisation Department of Materials Science and Metallurgy, University of Cambridge

Sources: (Image 1) (Image 2)

[materialsscienceandengineering]

Fe, C 0.8 (wt%) steel, eutectoid transformation, normalised at 900ºC

Processing Normalised 900 ºC [...] Sample preparation Nital Technique Reflected light microscopy Length bar 400 μm / 100 µm Further information This steel is of the eutectoid composition. Once the temperature is lowered below the eutectoid temperature the steel becomes simultaneously supersaturated with both ferrite and cementite. A eutectoid transformation results (g to a + Fe3C). The resultant microstructure, known as pearlite, comprises lamellae of cementite (dark) embedded in ferrite (white). The platelets are parallel to each other and do not follow a specific crystallographic direction. Contributor Dr R F Cochrane Organisation Department of Materials, University of Leeds

Sources: ( 1 ) ( 2 )

[materialsscienceandengineering]

Aligned array of nanotubes

Processing Chemical vapour deposition onto a quartz substrate, using a fine solution of ferrocene dissolved in toluene Applications Such architectures may be of interest as nanocomposites for use in nanodevices. More generally, carbon nanotubes may be used for hydrogen storage or for fuel cell applications Sample preparation The specimen has been sputter-coated with gold to avoid charging in the SEM Technique Scanning electron microscopy (SEM) Length bar 25 μm Further information Chemical vapour deposition (CVD) allows the synthesis of high purity nanotubes of controlled length and diameter. The nanotubes in this specimen were deposited on quartz using ferrocene dissolved in toluene. They are approximately 40 nm in diameter and 60 microns long. Contributor C Singh Organisation Department of Materials Science and Metallurgy, University of Cambridge

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[materialsscienceandengineering]

Cu 70, Zn 30 (wt%), partial recrystallisation - annealing twins

Processing Annealed, cold rolled 50% and annealed again for 30 minutes at 600 °C [...] Technique Reflected light microscopy Length bar 400 μm / 40 µm Further information This sample was annealed and 50% cold rolled, with subsequent annealing for 30 minutes at 600 °C. This has caused partial recrystallisation to occur creating new dislocation-free grains with some annealing twins. The temperature is too low for significant grain growth preventing complete recrystallisation. Contributor Prof T W Clyne Organisation Department of Materials Science and Metallurgy, University of Cambridge

Sources: ( 1 ) ( 2 )

[materialsscienceandengineering]

Grey cast iron core with white cast iron periphery

Composition Fe, C 2-4, other constituents (wt% typical) (Cast iron) [...] Technique Reflected light microscopy Length bar 200 μm / 40 µm Further information This sample shows a combination of white and grey cast irons. The core consists of a grey cast iron with a periphery of white cast iron. Contributor Prof T W Clyne Organisation Department of Materials Science and Metallurgy, University of Cambridge

Sources: ( 1 ) ( 2 )

[materialsscienceandengineering]

Sintered salt (NaCl)

Processing The salt has been compacted (20MPa) and sintered for four hours at 785 degrees C Applications A sintered preform of salt can be used as a preform in the investment casting of open celled metal foams. The preform can then be washed out. Sample preparation The sample has been sputter-coated with gold Technique Scanning electron microscopy (SEM) Length bar 140 μm Further information The interconnectivity of pores in the reticulated aluminium foam was found to be strongly dependent on the degree of sintering of the salt. The sintering occurs by a non-densifying mechanism but the necks grow progressively wider with time. Four hours provides sufficient interconnectivity for the salt to be readily washed-out. Contributor J A Curran Organisation Department of Materials Science and Metallurgy, University of Cambridge

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