Structure and mechanical properties of Co-Ni-Ga ferromagnetic shape memory alloys

The paper concerns the phase identification and structure analysis of alloys in wide range of their chemical composition. Basing on a crystallographic model, the structure of the martensite can be derived from the B2 structure and described as the BCT (Body Centered Tetragonal) lattice with c/a >1 or as Ll0 (Face Centered Tetragonal) structure with c/a < 1. The structure of the martensite studied by TEM discloses fine twinning of the martensite plates. It coincides with configuration of the ferromagnetic domains obtained by the Bitter method. Studies of the para - to ferromagnetic and martensitic transformation were carried using different methods . The different chemical composition of the alloys and their thermal treatment leads to the two phase microstructure B2 + gamma or Ll0 + gamma. The presence of the gamma phase particles improves the strength and plasticity of the alloys, which was proved by compression test on prism samples. Thus the Co-Ni-Ga alloys containing the gamma - phase particles may decrease the brittleness observed in other ferromagnetic alloys like single - phase martensitic alloys.

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Artykuł zawiera wyniki identyfikacji faz i badań ich struktury dla szerokiego zakresu składu chemicznego stopów. Struktura martenzytu w oparciu o przedstawiony model krystalograficzny może być opisana siecią tetragonalną przestrzennie centrowaną o c/a>l lub ściennie centrowaną komórką LI o o c/a