We have constructed a complete hydrodynamic theory of nucleation and growth in a one–dimensional version of an elastic shear martensitic transformation with open boundary conditions where we have accounted for interfacial energies with strain–gradient contributions. We have studied the critical martensitic nuclei for this problem: Interestingly, the bulk critical nuclei are twinned structures, ...

Due to thermomechanical hysteresis in solids undergoing martensitic type of structure transformations the macroscopic strain and volume fraction of martensite are not a single-valued function of stress and temperature, but they become functions of the process of their change. Some of the phenomenological approaches describing ma~n thermomechanical properties of shape-memory alloys (SMA) connect...

Kinetic dependence of martensitic transformation and properties changes in Fe-24%Ni5%Mo alloys with different carbon content have been obtained. Internal friction method was used for the precise investigation of structural changes after austenization, during martensitic transformation at sub zero temperature and during the postheat. The influence: (i) of frequency of oscillations, (ii) rate of ...

We show that in metamagnetic shape memory alloys exhibiting a magnetostructural first order phase transition the direct transition from ferromagnetic austenite to nonmagnetic martensite is isothermal. In contrast to the direct transformation, the reverse one nonmagnetic martensite–ferromagnetic austenite is athermal, just as are athermal both direct and reverse martensitic transformations in co...

Hot–press forming steels are formed in a fully austenitic state followed by die– quenching in order to generate martensite and achieve a strong steel. The ductility however, tends to be limited. We explore in this work a novel steel design in which the forming operation is in the two–phase austenite and ferrite field, so that the quenching results in a dual–phase ferrite and martensite microstr...

In this paper we discuss the microstructure of lath martensitic steels and the mechanisms by which it controls cleavage fracture. The specific experimental example is a 9Ni (9 wt% Ni) steel annealed to have a large prior austenite grain size, then examined and tested in the as-quenched condition to produce a relatively coarse lath martensite. The microstructure is shown to approximate the recen...

Ni-Mn-Ga is a ferromagnetic shape memory alloy that deforms by twin boundary motion. The magneto-mechanical properties depend strongly on the twin microstructure. A thermomechanical treatment was applied to a Ni-Mn-Ga single crystal with coexisting 10M and 14M martensite structures to create twin boundaries and align the short crystallographic c direction preferentially perpendicular to the sur...

NiTi wires were brazed together via eutectic reaction between NiTi and Nb powder deposited at the wire contact region. Phase transformation and deformation behavior of the NiTi-Nb eutectic microstructure were investigated using transmission electron microscopy (TEM) and cyclic loading-unloading tests. Results show that R phase and B19' martensite transformation are induced by plastic deformatio...

Strength and toughness are a couple of paradox as similar as strength-ductility trade-off in homogenous materials, body-centered-cubic steels in particular. Here we report a simple way to get ultrahigh toughness without sacrificing strength. By simple alloying design and hot rolling the 5Mn3Al steels in ferrite/austenite dual phase temperature region, we obtain a series of ferrite/martensite la...