The evolution of phase composition, microstructure and martensitic transformations in diffusion zone of nitrided TiNi under tension

X-ray data about the gradients of phase and chemical compositions in diffusion zone of nitrided TiNi are presented. “In situ” observations of microstructural evolution and martensitic transformations were made under tension. The shape memory effect was studied in nitrided TiNi

Neutron diffraction effects before the B2 →\to B19 martensitic transformation in single crystal of binary TiNi based alloy

Experimental results of the microstructure changes of the B2 phase before the B2$\to$B19$'$ martensitic transformation are presented in the paper. The neutron diffraction patterns from the B2 phase of the Ti$_{49}$Ni$_{51}$ single crystal were obtained in the wide range of the reciprocal space. The neutron diffraction features in the [110]$_{\rm B2}$, direction and perpendicular to it are in details investigated in the work

Premartensitic Phenomena in Ti

The evolution of microstructure in the bulk of a massive Ti4 9 Ni51 single crystal has been studied above the start temperature of martensitic transformations (MT) B2→R and B2→B19' (T and Ms, correspondingly).The intermediate shear of a first type (ISS-1) forms as a result of the second kind phase transformation. It is characterized by the appearance of transverse atomic displacement waves with incommensurate wave vectors q̅'1 =(1/3±δ)2π/a and q̅''1= (l/3±δ)2π/a in the parent crystal lattice within the temperature range 55 degrees before T . ISS-1 becomes a commensurate phase at cooling and 25 degrees before T . The stretched diffuse extra-reflections of (1/2±δ) type appear on (110)B2 neutron diffraction patterns before the beginning of MT B2→B19' (Ms = 180 K) at cooling of samples below 420 K. It is caused by the development of a short-range order and the long-range order of transverse atomic displacement waves with incommensurate wave vectors q̅2=(l/2±δ)2π/a. In this case atomic displacement waves with q̅'1, and q̅''1 are also developing but it is observed at more lower temperatures

The Hydrostatic Pressure Effect on Elastic Properties of B2-Phase Single Crystals Ti

At first, velocities of longitudinal and transverse ultrasonic waves have been measured by a pulse echo overlap method at 3-5 MHz frequency under hydrostatic pressure in the 0 - 0 .6 GPa range in single-crystals of Ti50Ni48Fe2 and Ti50Ni45Fe5 alloys, having and orientations in B2-phase state. The pressure dependences of C11’ C'=(C11-C12)/2, C44 elastic constants, adiabatic and isotermic compression moduli, Grüneisen microscopic parameters γLA’ γTA1’ γTA2 have been calculated on the basis of these data. It was found that unlike the temperature dependences the anomalous pressure dependence has the modulus - C' (dC'/dP 0, but decreases with increasing pressure in both of alloys. The data obtained indicates a rising inclination of B2-phase lattice of these alloys to Zener classical instability (instability relative to the shear of (110)[110]) with a pressure increase

Deformation and Fracture Behavior of Metallic Glassy Alloys and Glassy-Crystal Composites

International audienceThe present work demonstrates the deformation behavior of Zr-Cu-Ni-Al bulk glassy alloys and Zr-Ni-Cu-Al-Pd glassy foils as well as Ni-Cu-Ti-Zr bulk crystal-glassy composites. Fracture of Zr(60)Cu(16)Ni(14)Al(10) and Zr(64.13)Ni(10.12)Cu(15.75)Al(10) bulk glassy alloys is featured by nearly equal fraction areas of cleavage-like and vein-type relief. The observed pattern of alternating cleavage-like and vein-type patterns illustrates a result of dynamically self-organizing shear propagation at the final catastrophic stage. The deformation behavior of Zr(64.13)Ni(10.12)Cu(15.75)Al(10) alloy has also been tested at LN(2) temperature. The strength of the sample decreases with temperature, and no clear serrated flow typical for bulk glassy samples tested at room temperature is observed in the case of the samples tested at LN(2) temperature. We also studied the deformation behavior of Zr-Ni-Cu-Al-Pd glassy foils thinned to electron transparency in situ in tension in a transmission electron microscope. We also present a Ni-Cu-Ti-Zr crystal-glassy composite material having a superior strength paired with a considerable ductility exceeding 10 pct. The metastable cP2 crystalline phase promotes a strain-induced martensitic transformation leading to pseudoelastic behavior as well as enhanced plasticity at room temperature. Underlying mechanisms of plastic deformation are discussed in terms of the interplay between the dislocation slip in the crystalline phase and the shear deformation in the glassy matrix