OBSERVATION OF INTERNAL STRUCTURES OF MAR TENSITES OF FE-RH ALLOYS

There have been few crystallographic studies on the phase transition o f Fe rich Fe-Rh alloys and the phase diagram remained obscure in many respects. It was established that the alloys with higher Fe concentrat ion undergo fcc-bcc martensite transformation by quenching from the hi gh-temperature gamma phase. However, no transmission electron microsco pe (TEM) investigation of the martensites has been reported, possibly due to the difficulty in preparing a good TEM specimen of the alloy wi th extraordinarily excellent corrosion resistance. Recently we have de veloped a technique to prepare a TEM specimen by electro-polishing and ion-milling, and examined internal structures of the martensites of F e-5 at%Rh and Fe-25 at%Rh alloys by employing X-ray diffractometry, op tical and transmission electron microscopy. The results are summarized as follows: (1) Both Fe-5 at%Rh and Fe-25 at%Rh alloys show surface r eliefs, which are due to martensite transformation. (2) The martensite s are of a dislocated lath type, whose lattice invariant shear is slip . Burgers vectors of the dislocations are [111] and [001] types. (3) I n an Fe-25 at%Rh alloy twinning shear is also associated with the latt ice invariant shear of the transformation. (4) The Kurdjumov-Sachs ori entation relationship is observed between the retained gamma and marte nsite phases of an Fe-25 at%Rh alloy.