I don't know about your house, but in ours, talk of Christmas is off limits until at the very least December 1st but once that date comes the yuletide log levees break and the eggnog floodwaters surge through every aspect of one's life, including worklife.
Usually, at TCT Towers we'll get a few Christmas themed press releases and chuck them out for being frivolous flights of fancy. However, a story that dropped into our mailbox from LPW adds a festive twist to a fascinating piece of research.
The Halton-based metal additive manufacturing powder eco-system company has been experimenting with a range of exotic materials including metal carbides like Tungsten Carbide (WC), ceramics, and cermets (ceramic and metal composite materials).
These kinds of materials have unparalleled hardness and strength properties but have previously been difficult to form.
The advent (ahem) of Additive Manufacturing (AM) could potentially open the doors for applications to use these advanced materials. To get to the point where these powders can be processed by metal laser sintering equipment the materials need to be available in an appropriate form, specifically spherical powder - a speciality of LPW.
LPW uses plasma spheroidisation technology to process the rawer granular materials. The company has recently been trialling carbides and cermets on the spheroidiser, using Scanning Electron Microscopy (SEM) imaging to assess the morphology and size of the product.
In the main, the results are just grey spheres of different sizes, but occasionally the complexities of the metallurgy result in particles that are somewhat intriguing. LPW explain the science behind these Christmas bauble-esque looking particles:
LPW
Figure 1
Early trial of spheroidised WC showing particles with differing elemental composition
The initial spheroidisation run looked at material that had not been extensively screened prior to the trial. The above are particles, see figure 1, were found in this early Tungsten Carbide (WC) trial, prior to any material optimisation. The homogeneous light grey particles are those containing the specified 4 wt% (wt% = wight percentage) of carbon. However, the three particles running through the centre of the image were found to have different ratios of carbon (C) to tungsten (W), leading to the clear variations in particle microstructure compared to the general population. From left to right, carbon content was measured to be 21 wt% C, 7 wt% C and 9 wt% C.
Given that carbon has a significantly lower atomic weight than tungsten, 21 wt% converts to an atomic percent of 80 at%, therefore carbon is actually the primary element in this particle. As a result, it is homogeneous in appearance but is considerably darker due to it being significantly less dense than the general population.
The other two particles display inhomogeneous microstructures, due to solute redistribution during solidification – either in carbon-tungsten or tungsten-carbon systems. As the molten material solidifies, the small carbon particles diffuse ahead of the solidification front creating difference concentration of solution. As the crystals grow, the higher solution concentration liquid is pushed to the boundaries. The different ratios of W to C result in different solidification kinematics, and hence we end up with a range of fascinating structures, figure 2.
Figure 2
WC ratios reveal fascinating structures in metal powder particles
Such microstructural phenomenon is not limited to the WC system. In figure 3, we see a different type of surface feature when processing Fe-WC cermet. This time we observed geometric precipitations on the surface of the particles, which after chemical analysis were revealed as a W rich secondary phase. Given the time of year of these observations, we could not help but draw comparisons with the most recognisable of crystal structures – and certainly this are the most festive of powder particles we have ever come across!
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Figure 3.1
Bright coloured tungsten rich features in Fe-WC cermet powder material
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Figure 3.2
Bright coloured tungsten rich features in Fe-WC cermet powder material
