Magnetic and spin-dependent transport properties of reactive sputtered epitaxial Ti1−xCrxN films

Reactive-sputtered epitaxial Ti_1?xCr_xN films are ferromagnetic in the range of 0.17 ? x ? 0.51 due to the Cr–N–Cr double-exchange interaction below the Curie temperature (T_C). The T_C first increases, then decreases as x increases, and a maximum of 120 K appears at x = 0.47. All of the films are metallic with a transition near T_C. A resistivity minimum ρ_min is observed below 60 K in the films with 0.10 ? x ? 0.51 due to the effects of the weak localization and electron–electron interaction. The negative magnetoresistance (MR) is caused by the double-exchange interaction below T_C and the weak localization can also contribute to MR below T_min where ρ_min appears. The x-dependent electron carrier densities reveal that the ferromagnetism is not from the carrier-mediated mechanism. The anomalous Hall resistivity follows the relation of ${\rho }_{\mathit{xy}}^{\text{A}}\propto {\rho }_{\mathit{xx}}^2$, which is from the side-jump mechanism.     

An experimental investigation of crack initiation in thin sheets of nitinol

An experimental investigation into the fracture properties of 160-μm-thick edge-cracked specimens of austenitic nickel–titanium (nitinol) under uniaxial tension is presented. Using the in situ optical technique of digital image correlation (DIC), strain fields directly relating to phase boundary nucleation and propagation of fracture samples were observed for the first time. The shape and size of the saturation and transformation zones as a function of loading near the crack tip were examined. An average plane strain crack initiation fracture toughness (K_C) of 51.4 ± 3.6 MPa $\sqrt{m}$ for fine grained polycrystalline nitinol sheets at room temperature was measured. The extent and nature of the phase transformation obtained from DIC, combined with the relatively high value of K_C, underscores the importance of crack tip shielding in the fracture of shape memory alloys.     

Measurement of grain boundary triple line energy in copper

Recent studies have demonstrated that grain boundary triple junctions are crystal defects with specific thermodynamic and kinetic properties. In this study we address the energy of triple lines. Previously, a geometrical model was proposed to determine the grain boundary line tension. The current study introduces a thermodynamically correct approach which allows direct and precise measurement of the triple line energy. The experimental technique utilizes the measurement of the surface topography of a crystal in the vicinity of a triple junction by atomic force microscopy. The grain boundary triple line tension ${\gamma }_{\mathit{TP}}^l$ of a random triple line in a copper tricrystal was measured to be 6.3 ± 2.8 × 10^?9 J m^–1.     

Grain boundary diffusion and segregation of Ni in Cu

Grain boundary (GB) diffusion of ⁶³Ni in polycrystalline Cu was investigated by the radiotracer technique in an extended temperature interval from 476 to 1156 K. The independent measurements in Harrison’s C and B kinetic regimes resulted in direct data of the GB diffusivity D_gb and of the so-called triple product P = s · δ · D_gb (s and δ are the segregation factor and the diffusional GB width, respectively). Arrhenius-type temperature dependencies for both the D_gb and P values were measured, resulting in the pre-exponential factors $D_{\mathrm{gb}}^0=6.93\times {10}^{-7}$ m² s⁻¹ and P₀ = 1.89 × 10⁻¹⁶ m³ s⁻¹ and the activation enthalpies of 90.4 and 73.8 kJ mol⁻¹, respectively. Although Ni is completely soluble in Cu, it reveals a distinct but still moderate ability to segregate copper GBs with a segregation enthalpy of about −17 kJ mol⁻¹.