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<p>[QUOTE=&quot;desertgem, post: 3205983, member: 15199&quot;]My last response also to the idea that alloys can not produce crystals, there are many of these also.This one on alloys that make up airplane engine turbines</p><p><br /></p><p>&quot; The single-crystal structure isn’t intended to cope with temperature, however; it’s to make the blades resistant to the huge mechanical loads that result from their rotational speed. “Every single blade extracts power from the gas stream equivalent to a Formula One car engine,” Glover said. “And the centrifugal force on them is equivalent to the weight of a double-decker bus.”</p><p><br /></p><p><span style="color: #ff0000">Normally, metals are composed of many crystals – ordered structures of atoms arranged in a regular lattice, which form naturally as the metal cools from a molten state. These crystals are typically of the&nbsp; order of tens of microns in size, positioned in many orientations. At high temperatures and under strain, the crystals can slide against each other, and impurities can diffuse along the boundaries between the grains. This is known as creep, and it badly affected early turbine blades, which were forged from steel and later nickel bars.</span></p><p><br /></p><p>The first stage in development was to get rid of any grain boundaries at right angles to the centrifugal loading, which led to the development&nbsp; of blades that were cast so the metal crystals all ran from top to bottom. <span style="color: #ff0000">Later, this was optimised further by casting single crystals, with no grain boundaries at all. It’s a highly complex process: not only must the blades be cast with the internal cooling channels already in place, but the crystals are not homogeneous. Rather, zones of different composition&nbsp; and crystallographic structure exist within the blade.</span></p><p><span style="color: #ff0000"><br /></span></p><p><span style="color: #ff0000">&nbsp;</span></p><p><span style="color: #ff0000">“You can think of nickel superalloys like these as being like composites,” said Rolls-Royce aerofoil turbine materials technologist Neil D’Souza. “It’s a mixture of two phases, one of which – gamma-prime – gives rise&nbsp; to the sustained increase in strength at high temperature.”</span></p><p><br /></p><p>When it crystallises, nickel forms a structure known as face-centred cubic (fcc); each cube has a face with five atoms, one at each corner and one in the middle. When alloys are made, generally the atoms just swap in and out of the fcc lattice. But under the right conditions, aluminium and nickel combine in such a way that nickel goes to the centre of the faces and aluminium to the corners. This is known as a precipitate; it forms islands of greater order within the bulk of the alloy, about half a micron in dimension, packed closely together in a rectilinear formation. Because the size of the lattices of the precipitate and the less ordered bulk alloy are almost identical, they are all part of the same crystal.&nbsp; end quote)</p><p><br /></p><p><a href="https://www.theengineer.co.uk/rolls-royce-single-crystal-turbine-blade/" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://www.theengineer.co.uk/rolls-royce-single-crystal-turbine-blade/" rel="nofollow">https://www.theengineer.co.uk/rolls-royce-single-crystal-turbine-blade/</a>&nbsp; </p><p><br /></p><p>Now Debate closed on crystallization of alloys if you wish,&nbsp; ( I made no comment on authenticity , nor Did Sears say there is never crystallization in alloys)&nbsp; Jim[/QUOTE]</p><p><br /></p>

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