Characteristics of lath martensite: Part II. The martensite-austenite interface

Abstract

This investigation, using an Fe-20 pct Ni-5 pct Mn (wt pct) alloy, deals with the nature of the lath martensite-austenite interface. For the first time the misfit dislocation structure associated with a martensite interface has been observed experimentally. The interface consists of a single set of parallel dislocations having Burgers vector α/2[l•1l]martensite = α/2[011]austenite. Relative to the austenite, the observed dislocation line direction is [0•57], and the dislocation line deviates about 10 and 15 deg from the pure screw orientation in the austenite and martensite, respectively. However, the dislocations are in screw orientation on an atomic scale, although the interface step structure causes them to deviate from the exact screw orientation macroscopically. The spacing of the interface dislocations varies from 26 to 63A. The observed interface dislocation array satisfies the requirements for a glissile interface, which suggests that the dislocations are misfit dislocations which accomplish the lattice invariant shear of the crystallographic theories.