Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

DoITPoMS Micrograph Library Full Record for Micrograph 734

Full Record for Micrograph 734

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Micrograph no
Brief description
Ni-Superalloy, as-extruded microstructure
extrusion Link to MATTER Glossary entry for extrusion, nickel
Metal or alloy
Ni, Cr 14.4-15.2, Co 13-18, Mo 3.5-4.5, Al 3.0-3.3, Ti 4.2-4.8, Ta 2.5, Zr 0.05-0.07, C 0.05, B 0.01-0.03 (wt%) (Ni-Superalloy)
Standard codes
Extruded at 1100ºC with a 5.5:1 reduction in area.
Discs are used for high pressure and intermediate pressure turbine discs in Trent 800/900 series gas turbine engines.
Sample preparation
<ul><li>Ground to 4000 Grade SiC paper and then polished at 6 <span class="symbol">m</span>m 3 minutes, 1 <span class="symbol">m</span>m 5 minutes, Colloidal silica 10 minutes</li><li>Etched in 10% Phosphoric acid in water for 5 seconds at 10V. </li><li>Carbon film deposited under high vacuum</li><li>Carbon film removed by etching in 20% Perchloric acid in ethanol at 5V for 10 seconds</li><li>Carbon replica then ‘floated’ onto copper TEM grid</li></ul>
Transmission electron microscopy (TEM) of carbon replica
Length bar
20 μm
Further information
The micrograph shows the three distinct phases of g' present in polycrystalline superalloys. These are primary, secondary and tertiary g', defined by their sizes (primary 0.5-1mm), (secondary 30-200nm), (tertiary 1-25nm) and their locations within the microstructure. Primary g' segregates on the grain boundaries whereas the other forms are more uniformly distributed throughout the matrix. A grain boundary is clearly visible running from top right to bottom left. Due to the technique used, some g' remains on the surface of the specimen and these 'echoes' can be seen in the replica - principally the primary g' shapes on the grain boundary. There is also an increased density of tertiary g' present alongside the grain boundary.

View schematic diagram of g' microstructure
R J Mitchell
Department of Engineering, University of Leicester
Licence for re-use
Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales
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