In-situ observation of butterfly-type martensite in fe-30mass%ni alloy during tensile test using high-resolution EBSD

Abstract

The microstructual change of the thermal butterfly-type martensite (α') in Fe-30mass%Ni alloy during a tensile test was investigated by in-situ observation using high-resolution electron backscatter diffraction (EBSD). When the specimen is plastically deformed, the α' plate in a thermal butterfly-type α' starts to grow toward its width direction from the α'-γ interface with {2 2 5}γ habit plane. As the α' plate grows, the crystal orientation relationship (OR) between α' and γ changes from Greninger-Troiano to Kurdjumov-Sachs. Moreover, an orientation gradient is formed in the α' plate as its growth proceeds. The latter is due to the inheritance of the piled-up transformation dislocations into the α' plate. On the other hand, the orientation gradient in the γ matrix around the α'-γ interface decreases. These results indicate that the thermal butterfly-type α' changes its character to lath-type during growth. This is caused by the change of the accommodation process from single slip for butterfly-type martensite to multiple dislocation slip due to the tensile deformation at RT. It is concluded that the growth behaviour of the butterfly-type α' during tensile deformation depends on the change of the accommodation process. © 2009 ISIJ.