Microstructure Formation and Resistivity Change in CuCr during Rapid Solidification
Abstract
:1. Introduction
2. Material and Methods
3. Results and Discussion
3.1. Microstructure
3.2. Local Texture Analysis
3.3. Global Texture Analysis
3.4. Cr-Content in the Cu Solid Solution
3.5. Propagation of Cr-Content into the Depth
3.6. Influence on Electrical Conductivity
3.7. Heat Distribution
4. Conclusions
- (1)
- The Cu matrix in the initial state already incorporates a small amount of dissolved Cr in the range of 0.1–0.3 at %. This leads to a decreasing electrical conductivity of bulk material down to 21.7 MS/m (CC57) and 31.5 MS/m (CC75). These electrical conductivities can be estimated by applying the according Hashin-Shtrikman formula for Cr-particles incorporated in a Cr-enriched Cu solid solution matrix with reduced electrical conductivity.
- (2)
- Region 1 contains fine Cr-particles and a Cu-Cr solid solution with about 2.25 at % Cr. Hence, the electrical conductivity of the contact material in this region is further reduced to 10 MS/m or lower. R1 also exhibits a common solidification texture with <001> in parallel to the solidification direction. Indicated by microstructure and texture formation, it can be concluded that both phases Cu and Cr being present in the as-manufactured state are considered to be liquid during the switching process. The temperature must be above 1800 °C during arcing and very high cooling rates between 4.5 × 104 K/s and 1.86 × 105 K/s are expected due to the small Cr-particle size of about 450 nm.
- (3)
- Region 2 is characterized by large elongated Cu-grains (up to a length of 200 µm) perpendicularly aligned to the surface. The Cu-grains are still aligned with <001> in parallel to the solidification direction. In this region, only Cu is considered to be completely melted during interruption. The Cr-particles remain virtually unaffected when compared to the initial state. Therefore, it is concluded that the temperature in R2 was between 1175 °C and 1800 °C. This temperature is high enough to melt the Cu and still yields a Cu solid solution supersaturated with Cr.
- (4)
- The total Cr-content of the contact materials showed only negligible influence on microstructure formation and resulting supersaturated Cr in Cu solid solution. However, the texturing during solidification is stronger for CC75, which might be caused by its higher thermal conductivity and therefore higher cooling rates during re-solidification when compared to CC57 material.
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Alloy | Nominal Cr-Content in wt % | Nominal Cr-Content in at % | Nominal Cr-Content in vol % | Exp. Cr-Content in vol % | Ip in kA | tarc in ms | Q in As |
---|---|---|---|---|---|---|---|
CC75 | 25 | 28.95 | 29.5 | 33 ± 2 | 6.25 | 10.4 | 43.6 |
CC57 | 43 | 47.97 | 48.5 | 53 ± 3 | 6.7 | 9.5 | 43.7 |
CuCr0.72 | 0.72 ± 0.01 | 0.89 ± 0.01 | reference sample |
Alloy | Depth of R1/µm | Depth of R1 + R2/µm |
---|---|---|
CC75 | 101 ± 9 | 170 ± 12 |
CC57 | 81 ± 9 | 219 ± 22 |
Sample | /MS/m | /MS/m |
---|---|---|
CC57 | ||
CC75 | ||
CuCr0.72 | - |
Sample | /MS/m | /MS/m | Penetration Depth at 960 kHz/µm |
---|---|---|---|
CC57 | 21.7 ± 0.4 | 7.3 ± 0.1 | 190 |
CC75 | 31.5 ± 0.2 | 10.6 ± 0.1 | 158 |
CuCr0.72 | 20.87 ± 0.01 | - | - |
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Hauf, U.; Kauffmann, A.; Kauffmann-Weiss, S.; Feilbach, A.; Boening, M.; Mueller, F.E.H.; Hinrichsen, V.; Heilmaier, M. Microstructure Formation and Resistivity Change in CuCr during Rapid Solidification. Metals 2017, 7, 478. https://doi.org/10.3390/met7110478
Hauf U, Kauffmann A, Kauffmann-Weiss S, Feilbach A, Boening M, Mueller FEH, Hinrichsen V, Heilmaier M. Microstructure Formation and Resistivity Change in CuCr during Rapid Solidification. Metals. 2017; 7(11):478. https://doi.org/10.3390/met7110478
Chicago/Turabian StyleHauf, Ulla, Alexander Kauffmann, Sandra Kauffmann-Weiss, Alexander Feilbach, Mike Boening, Frank E. H. Mueller, Volker Hinrichsen, and Martin Heilmaier. 2017. "Microstructure Formation and Resistivity Change in CuCr during Rapid Solidification" Metals 7, no. 11: 478. https://doi.org/10.3390/met7110478