Berlin 2018 – wissenschaftliches Programm

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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: Vortrag

Montag, 12. März 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 Langer^1,2, 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.