2009 Volume 49 Issue 11 Pages 1784-1791
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 R.T. It is concluded that the growth behaviour of the butterfly-type α′ during tensile deformation depends on the change of the accommodation process.
