Magnetic Compton Scattering Study of Ni2Mn1.4Sn0.6 Shape Memory Alloy

Spin momentum density in Ni2Mn1.4Sn0.6 shape memory alloy has been measured using magnetic Compton scattering technique. The experiment has been performed using 182 keV circularly polarized synchrotron radiation at temperature 10 K at SPring-8, Japan. Experimental magnetic Compton profile has been decomposed to determine the site specific magnetic moments, where the magnetic moment at Mn site was found to be dominating. It is seen that the total spin moment in present non-stoichiometric alloy is smaller than that of stoichiometric Ni2MnSn.

Local Order and Crystallization of Laser Quenched and Ion Implanted Amorphous Ge1-xTex Thin Films

Amorphous films of Ge1-xTex (x=0.37, 0.51, 0.64) prepared by sputtering, by melt quenching or by ion irradiation were annealed up to 450°C. Different phase stability, i.e. crystallization temperature, was observed varying the amorphous status in stoichiometric and Te-rich alloys while no variation was obtained in the Ge-rich alloy. Laser and ion irradiated stoichiometric alloy exhibits lower stability with respect to the sputtered film while irradiated amorphous Te-rich samples are more stable than the as deposited amorphous sample. An enhancement of edge-sharing GeTe4 tetrahedra Raman signal at the expenses of Ge-rich tetrahedra signal occurs in the irradiated samples with respect to the as-deposited amorphous layers both in the stoichiometric and in the Te-rich alloy. The crystallization temperature decreases in GeTe since the system during irradiation is promoted to a state closer to the crystalline phase while in Te-rich alloy the stability increases with the density of Ge-Te bonds since this local rearrangement delays Te precipitation and the subsequent GeTe crystallization. Irradiation does not affect the stability of Ge rich alloy in which crystallization is limited by the Ge mobility and the induced local rearrangements is probably prevented by the low atomic diffusivity.

Magnetic Field-Induced Martensitic Transformation of Heusler-Type Ni2MnGa System

Magnetic field effect on a Heusler-type Ni2MnGa off-stoichiometric alloy having a martensitic transformation temperature around room temperature which is coincident with a Curie temperature has been investigated. The process of martensitic transformation of a single crystal was investigated by neutron diffraction under the magnetic field up to 8 [T]. It was found that the magnetic field, which is applied at a temperature near the transformation temperature, causes the martensitic transformation. The process of the transformation caused by the increase in magnetic field is quite similar to the process caused by the decrease in temperature.

The Ductility of Stoichiometric and Ni-Rich Polycrystals of Ni3Al: The Effect of Strain Rate

ABSTRACTPolycrystals of stoichiometric Ni3Ai are brittle in air at room temperature, at least at strain rates from 10-4 s-1 to 7 s-1. This is indicative of intrinsic brittle behavior. Nickel-rich (Ni24A1) polycrystals, on the other hand, undergo a brittle-to-ductile transition upon raising the strain rate to above about 10-2 s-1. It is argued that the transition reflects the suppression of environmental embrittlement, not of the intermetallic per se but of a Ni-rich solid solution that decorates the grain boundaries of the off-stoichiometric alloy.

The Microchemistry Studies of Ductile Ll2 Ni-Based Intermetallics

Auger electron microscopy (AES) analysis of boron doped Ni3Al have shown boron segregation at grain boundary (GB). Boron segregation was enhanced with increasing bulk boron content independent of stoichiometry, suggesting that hypo-stoichiometric alloy is intrinsically ductile even without boron. A slight Ni cosegregation is confirmed using atom probe field ion microscope (APFIM). In Ni3(Si,Ti), no distinct composition fluctuation was identified between matrix and GB vicinity. These results suggest that atomic bonding atmosphere modification from covalent to metallic in the vicinity of GB is one of factors to modify ductility for Ll2-type intermetallics.

Room Temperature Strength and Fracture of FeAl And NiAl.

ABSTRACTThe yield strengths (σy) of FeA1 and NiAl of various aluminum concentrations were measured as a function of grain size, d, and the results fitted to σy =σo+ kd−1/2. It was found that for NiAl the lattice resistance (σo) and Hall-Petch slope (k) have minima at the stoichiometric composition and increase with decreasing aluminum concentration, whereas for FeAl these parameters have maxima at the stoichiometric composition and decrease off this composition. In tension tests, iron-rich FeAl was shown to be ductile whereas the stoichiometric alloy is brittle. In contrast, stoichiometric NiAl shows ductility but off-stoichiometric compositions are brittle. The fracture modes of the FeAl and NiAl are predominantly intergranular at the stoichiometric compositions and become increasingly transgranular with decreasing aluminum concentration.

Room Temperature Tensile Ductility in Polycrystalline B2 NiAl

ABSTRACTBinary polycrystalline alloys of B2 NiAl, ranging from 47 to 51.5 at% Al, were prepared by casting and extrusion. These were tested in tension at temperatures ranging from 300 K to 873 K. Significant tensile ductility is observed in the near-stoichiometric alloy at room temperature as well as at 473 K in spite of the presence of only <100> dislocations. This anomaly appears to be related to the recrystallized texture, to the lower yield strength and to the presence of residual dislocations at grain boundaries in this alloy.