| Abstract: |
Thermal stresses are inherently present in surface engineering applications due to the mismatch contraction/expansion of the coatings and the substrate material. Therefore, precise determination of the coefficient of thermal expansion (CTE) in coatings is of vital importance for designers. The well-known technique of push-rod dilatometry (single and dual) was used in this study to report the property of expansion of several pure metals, alloys, cermets, and ceramics. The experimental procedure is discussed in detail for thermal spray (TS) coatings. A large compendium of CTE values are presented from experiments conducted by the authors and from literature. It was found that all coatings present irreversible changes in the microstructure during the first heating cycle that alters the CTE value. Therefore, all reported values of the CTE are extracted from the second heat cycle. The possible processing effects on the CTE were explored by 1) depositing the same material by different spraying techniques (cold spray, HVOF, APS, arc spray, etc); and 2) within the same technique, by varying the spray parameters largely in the context of a process map (YSZ via APS, and Ni-20Cr via HVOF). It is concluded that neither the spraying technique nor the spraying condition affect the CTE value of the coated material significantly. When possible, the CTE of the coating was compared to the bulk value to conclude that the CTE of the coating is the same as the bulk. The CTE was found not to be an anisotropic property despite the anisotropic nature of TS coatings.
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