Surface Engineering by Expanded Austenite
Treated Unpolished Vs Untreated Unpolished Expansion
The final XRD investigation involved examining the expansion of the crystal lattice due to carburisation on the non-polished face of the samples.
When comparing the expansions of the unpolished sides between the treated and untreated samples, it can be seen that the ranking of the percentage lattice expansions (Table 9) is again in the same order in the [111] plane and {200} plane. The expansions in the {220} plane did not seem to follow the same patterns as that seen in the first two planes.
With regards to the lattice expansions due to carbon supersaturation on the unpolished sides, once again all of the iron based samples reacted responded better to the carburisation process, with all of said samples showing an increase in atomic spacing. This is seen in Table 8. However for the unpolished side of the samples, the percentage lattice expansion that occurred was typically less than the expansions witnessed on the polished side by up to approximately 1.5%. The samples which showed exception to this were Stainless Steel 2343 and Stainless Steel 353 which showed a larger lattice expansion on the unpolished face in some planes. The largest expansions once again occurred in the {200} plane.
The nickel based alloys, as was the case with the polished sides, did not react as well to the carburisation treatments, with the atomic spacing of the Nikrothal sample’s lattice again decreasing; the opposite as to what was expected.
The K22 treatment was again slightly more effective than the K33 treatment when looking at the Inconel 617 nickel sample; that being the only nickel sample that apparently reacted as expected. The effect of surface finishplastic deformation appears to affect both of the different carburisation processes equally.
Looking at the rankings in Table 7 and Table 9 allows for a comparison of the lattice expansion due to carburisation between the polished and unpolished faces of the samples. This reveals rankings of a very similar order, with the only difference being samples SS 2343 and SS R350.
The SS 254 and SS 832 samples correlated with the results in Table 9, once more showing the largest percentage lattice expansion after carburisation. The stainless steel sample which expanded by the smallest amount was the R350 sample.
