Berlin 2018 – scientific programme
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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur
KFM 3: Crystal Structure, Defects, Real Structure and Microstructure in Materials
KFM 3.9: Talk
Monday, March 12, 2018, 12:30–12:50, E 124
On the microstructure of the shape memory alloy Co-Ni-Al using complementary diffraction techniques — •Leonid Potapov1, Enrico Langer1,2, Katerina Krátká1, Jaromir Kopeček3, and Siegfried Däbritz1 — 1TU Dresden, IFMP, Dresden, Germany — 2TU Dresden, IHM, Dresden, Germany — 3Institute of Physics of the CAS, Prague, Czech Republic
Shape memory alloys can have a quite complex microstructure, making the investigation of their properties very challenging. This work deals with the characterization of austenitic samples of Co38Ni33Al29, grown by the Bridgeman method at different pulling rates. In this alloy, a mixture of ordered bcc crystal β matrix and a secondary dendritic fcc γ phase enriched with Co was observed by the combination of X-ray Kossel microdiffraction, EBSD and EDX methods. Thereby the Kossel technique reveals the presence of anisotropic superstructure reflections of the {100} type in the β phase. EBSD linescans into heavily strained β matrix areas suggest a superposition of diffraction patterns of bcc and fcc even at great distances from the phase boundaries. This makes the evaluation of patterns very intricate and may cause problems for automated EBSD. Furthermore, the fcc pattern appears to dominate deeply inside the matrix. This might be caused by Co-rich γ-like micro/nano precipitates, embedded in the matrix and inducing internal strains. In analogy to our previous Kossel measurements, pairs of parallel Kikuchi bands from both patterns can be used to retrieve the orientation relationship between β matrix and γ precipitates, which appears to be close to the Nishiyama-Wasserman relationship.