ON THE ROLE OF PITCH DEFORMATION DURING γ – α MARTENSITIC TRANSFORMATIONS
10.25712/ASTU.1811-1416.2022.01.001
Keywords:
martensitic transformations, orientation relations, Pitch deformation, polar decomposition of the tensor, martensite nanocrystalsAbstract
Orientational relations (OR) refer to a set of uniquely related morphological features indicating the cooperative nature of the martensitic transformation (MT). ORs demonstrate parallelism (or close to that) of the corresponding phase planes and directions lying in the planes. For γ – α MP in iron-based alloys with relatively large crystals of martensite, Groeninger-Troyano (GT) ORs are observed, which are close to the idealized Kurdyumov-Zaks (K-Z) and Nishiyama (N) ratios. The question of the possible role of Pitch ORs fixed in thin foils is considered in detail. Within the framework of crystal geometric analysis, it was shown that there are no grounds for choosing the Pitch deformation as preferable in relation to the traditional variants (Bain deformation with subsequent rotations), since this deformation leads to a large relative change in volume under MT. The polar decomposition of the Pitch distortion tensor demonstrates that tensile deformations exceed Bain's, causing high values of the volumetric effect. A qualitative conclusion has been made about the possible realization of Pitch OR for nanocrystals arising in strongly distorted retained austenite between relatively large crystals with OR G-Т. The expediency of confirming the formation of nanocrystals in the dynamic theory of magnetic fields is noted.