Interdiffusion and solid solution strengthening in Ni–Co–Pt and Ni–Co–Fe ternary systems

Diffusion couple experiments are conducted in Co–Ni–Pt system at 1200?°C and in Co–Ni–Fe system at 1150?°C, by coupling binary alloys with the third element. Uphill diffusion is observed for both Co and Ni in Pt rich corner of the Co–Ni–Pt system, whereas in the Co–Ni–Fe system, it is observed for Co. Main and cross interdiffusion coefficients are calculated at the composition of intersection of two independent diffusion profiles. In both the systems, the main interdiffusion coefficients are positive over the whole composition range and the cross interdiffusion coefficients show both positive and negative values at different regions. Hardness measured by performing the nanoindentations on diffusion couples of both the systems shows the higher values at intermediate compositions.     

Atomistic modeling of ternary additions to NiTi and quaternary additions to Ni–Ti–Pd,Ni–Ti–Pt and Ni–Ti–Hf shape memory alloys

The behavior of ternary and quaternary additions to NiTi shape memory alloys is investigated using a quantum approximate method for the energetics. Ternary additions X to NiTi and quaternary additions to Ni–Ti–Pd, Ni–Ti–Pt, and Ni–Ti–Hf alloys, for X=Au, Pt, Ir, Os, Re, W, Ta,Ag, Pd, Rh, Ru, Tc, Mo, Nb, Zr, Zn, Cu, Co, Fe, Mn, V, Sc, Si, Al and Mg are considered. Bulk properties such as lattice parameter, energy of formation, and bulk modulus of the B2 alloys are studied for variations due to the presence of one or two simultaneous additives.     

Temperature dependence of twinning stress – Analogy between Cu–Ni–Al and Ni–Mn–Ga shape memory single crystals

Abstract

To obtain a direct non-magnetic analogy to Ni–Mn–Ga 10M martensite with highly mobile twin boundaries, we present the recalculation of twinning systems in Cu–Ni–Al martensite. In this approach, the twinning planes denoted as Type I, Type II and compound have similar orientations for both alloys (Ni–Mn–Ga and Cu–Ni–Al). In Cu–Ni–Al, compound twinning exhibits the twinning stress of 1 to 2 MPa comparable to twining stress of Ni–Mn–Ga. In contrast Type II twinning stress of Cu–Ni–Al is approximately 20 MPa, i.e. much higher than twinning stress for Type II in Ni–Mn–Ga (0.1 to 0.3 MPa). Similarly to Ni–Mn–Ga, the twinning stress of Type II in Cu–Ni–Al is temperature independent. Moreover, no temperature dependence was found also for compound twinning in Cu–Ni–Al.     

Magnetization anomalies in melt-spun Ni–Mn–Ga ribbons

Temperature and field dependencies of the magnetization of melt-spun ribbons of Ni_45.7Mn_37.2Ga_17.1 (T_C<T_A) and Ni_54.3Mn_20.5Ga_25.2 (T_C>T_A), where T_A and T_C are the reverse martensitic transformation and Curie temperatures, respectively, have been studied in broad ranges of magnetic fields (±30 kOe) and temperatures (10–350 K). It was found that the magnetic and thermomagnetic properties have a number of peculiarities and anomalies. Particularly, the magnetization values measured at both low and high magnetic fields increase significantly after annealing. Low-temperature anomalies of magnetization suggest the presence of the superparamagnetic behavior and/or phenomena related to the concurrent exchange interactions in the as-spun state. The obtained results can be explained by the influence of concentration inhomogeneities and atomic disordering in the rapidly quenched ribbons, which can be reduced by annealing.     

Magnetic after-effect in Ni–Mn–Sb Heusler alloy

The ferromagnetic Heusler-type alloy _Ni50Mn35Sb15${\mathrm{Ni}}_{50}{\mathrm{Mn}}_{35}{\mathrm{Sb}}_{15}$ exhibits well defined shape memory behaviour. We have investigated the transport and magnetic properties of this alloy across the martensitic transformation. Pronounced thermo-magnetic irreversibility between zero-field-cooled and field-cooled susceptibility data was observed below the martensitic transition temperature. We observe significant magnetic after-effect in magnetisation in both austenite and martensitic phases. However, a clear change in the nature of relaxation is observed as the sample is cooled across the martensitic transition temperature. These observations can be explained on the basis of complex domain dynamics in presence of rich micro-structure formation in the martensite.     

Precipitation and fracture behaviour of Fe–Mn–Ni–Al alloys

The effects of Al addition on the precipitation and fracture behaviour of Fe–Mn–Ni alloys were investigated. With the increasing of Al concentration, the matrix and grain boundary precipitates changed from L1₀ θ-MnNi to B2 Ni₂MnAl phase, which is coherent and in cube-to-cube orientation relationship with the α′-matrix. Due to the suppression of the θ-MnNi precipitates at prior austenite grain boundaries (PAGBs), the fracture mode changed from intergranular to transgranular cleavage fracture. Further addition of Al resulted in the discontinuous growth of Ni₂MnAl precipitates in the alloy containing 4.2?wt.% Al and fracture occurred by void growth and coalescence, i.e. by ductile dimple rupture. The transition of the fracture behaviour of the Fe–Mn–Ni–Al alloys is discussed in relation to the conversion of the precipitates and their discontinuous precipitation behaviour at PAGBs.     

Large magnetoresistance in Ni1–xVxS

Large magnetoresistance (MR) was observed in Ni_1−x V_xS(x=0, 0.02, 0.04, 0.06 and 0.08), MR=1530% at 268 K for x=0, MR=1180% at 255 K for x=0.02, MR=980% at 248 K for x=0.04, MR=810% at 224 K for x=0.06 and MR=490% at 198 K for x=0.08 in magnetic field 4 T. The large MR is due to magnetic field-induced magnetic and electrical transition from antiferromagnetic (AFM) nonmetal phase to paramagnetic (PM) metal phase.     

Magnetic ordering in Ni–Cd ferrite

A series of Ni_1−xCd_xFe₂O₄ (0.0≤x≤0.8) were prepared by conventional double sintering ceramic method and sintered at 1200 °C for 6 h. X-ray diffraction results confirmed the single-phase spinel structures of all the samples. The Curie temperature decreases linearly with increasing Cd content, which is explained due to the weakening of the A–B exchange interaction. The sample with x=0.7 shows re-entrant type of spin glass phase transitions. The magnetic moment and saturation magnetization at 20 K are found to increase with Cd content up to x=0.5 and then tends to decrease for x>0.5. The increase in magnetic moment with cadmium is attributed to Neel's two sublattice (A- and B-sublattice) collinear models according to which the magnetic moment is the vector sum of the lattice magnetic moment. The decrease in magnetization for x>0.5 obeys the Yafet–Kittel (Y–K) model. The increase in Y–K angles for x>0.3 indicates the increased tendency for triangular spin arrangements on B-sites. This suggests the existence of a canted spin structure in the ferrite system with higher content of Cd.     

Phase transformations and structure of Ni–Mn–In alloys with varying ratio Ni/Mn

The fine structure of Ni–Mn–In alloys has been studied when manganese atoms are substituted for nickel atoms in an annealing state. The concentration dependence of the critical temperatures and the structures of the alloys have been discussed. It has been found that, as manganese atoms replace nickel atoms, the structure after annealing is changed from a two-phase (L2₁ + martensite) to single-phase L2₁ structure. The martensitic transformation in Ni₄₇Mn₄₂In₁₁ alloy is accompanied by the formation of modulated 14M martensite.     

Synthesis and performance of Zn–Ni–P thin films

The electroplating of Zn–Ni–P thin film alloys from a sulfate bath containing phosphoric and phosphorous acid was investigated. The bath composition and the deposition parameters were optimized through Hull cell experiments, and the optimum experimental conditions were determined(p H = 2, temperature = 298–313 K, zinc sulfate concentration =30 g·L-1, EDTA concentration = 15 g·L-1, and current density = 1.0–2.0 A·dm-2). The SEM analysis of the coating deposited from the optimum bath revealed fine-grained deposits of the alloy in the presence of EDTA. Optical microscopy analysis indicated an electrodeposited thin film with uniform thickness and good adhesion to the steel substrate. The good adherence of the coatings was also demonstrated by the scratch tests that were performed, with a maximum determined value of 25 N for the critical load. Corrosion resistance tests revealed good protection of the steel substrate by the obtained Zn–Ni–P coatings, with values up to 85.89% for samples with Ni contents higher than 76%. The surface analysis of the thin film samples before and after corrosion was performed by X-ray photoelectron spectroscopy(XPS).     

Auger parameters of ternary Pd–Ni–P amorphous alloys

A series of bulk ternary amorphous alloys of Pd_{100?3 x} Ni_{2 x} P _x were prepared and their amorphicity checked by X-ray diffraction (XRD) and neutron scattering. Auger parameters of these alloys have been derived from X-ray photoelectron spectroscopy (XPS) and X-ray excited Auger electron spectra (AES). Experiments of XPS and AES on each elemental metal and Ni₂P were also performed for comparison. The results show a clear compositional dependence for the 3d binding energies and the MNN Auger energies of Pd on alloying, while Ni 2p core levels and the Ni LMM Auger lines show a weaker variation. Analysis of the data using “excited atom” models indicates electron transfer from Pd, with P carrying negative charge, but the differences in behaviour of the two metallic species suggests that covalent bonding changes may be significant.     

Three-dimensional constitutive equations for Ni–Mn–Ga single crystals

This paper presents a formulation of isothermal three-dimensional (3D) quasi-static magneto-mechanical constitutive equations and 3D magnetisation constitutive equations for tetragonal martensite Ni–Mn–Ga FSMA single crystals (c/a<1)$(c/a<1)$ with both ends restrained from twin-boundary motion. The formulated 3D constitutive equations model the 3D quasi-static magnetic fields as well as the coupling between uniaxial strains and stresses, and shear strains and stresses. The constitutive equations are compared with experimental results available in the literature and are found to correlate well with the experimental results, including magnetic field reversals. Both sets of 3D constitutive equations require only macroscopic parameters that are readily obtainable from magnetisation and mechanical stress–strain curves.     

Relaxation in Ni–Mn–Ga ferromagnetic shape memory alloys

Evidence of relaxation has been observed in ferromagnetic Ni–Mn–Ga single crystals. The relaxation may be explained by a change in symmetry-conforming short-range ordering according to Ren and Otsuka in this off-stoichimetric ordered alloy. Martensite stabilization has also been found after martensite ageing.     

The abnormal direct-current resistivity of Ni–Mn–Ni triple-layered magnetic thin-films and their magnetic wall observations

We have observed an abnormal electron transport characteristic from the Ni–Mn–Ni triple-layered magnetic thin-films. Due to the intercalated Mn ultra-thin interlayer, the magnetic domain structure and the electron transport characteristic differ a lot from their original magnetic (Fe, Co, and Ni) films. As inspected by a magnetic force microscopy (MFM), we observed the variation of the domain configuration with Mn interlayer thicknesses (for 1, 5, and 10 nm). Moreover, we also examined and found that the direct current (DC) resistivity have no significant change as the current conducts from the current-in-wall (CIW) to the current- perpendicular-to-wall (CPW), which are opposite to the results of single layered films.     

Exchange-induced phase separation in Ni–Cu films

Magneto-structural properties of films of diluted ferromagnetic alloys Ni_xCu_1−x in the concentration range 0.7<x<1.0$0.7<x<1.0$ are studied experimentally. Films deposited by magnetron sputtering show partial phase separation, as evidenced by structural analysis and ferromagnetic resonance measurements. The phase diagram of the Ni_xCu_1−x bulk system is obtained using numerical theoretical analysis of the electronic structure, taking into account the interatomic exchange interactions. The results confirm the experimentally found partial phase separation, explain it as magnetic in origin, and indicate an additional metastable region connected with the ferromagnetic transition in the system.     

Characterization of Ni–Cu mixed spinel ferrite

Crystal structure, X-ray density, porosity, compressive strength of Ni_1−xCu_xFe₂O₄ have been investigated along with scanning electron microscopy (SEM) to study the effect of composition and microstructure on the magnetic and electrical properties. The formation of single-phase ferrite is confirmed by the X-ray diffraction. Tetragonal deformation is observed for the sample of composition x=1, i.e. for pure CuFe₂O₄ Crystal structure for samples of other compositions are face centered cubic (FCC). SEM micrographs exhibit increase in grain size with the increase of copper content. Compressive strength decreases with the increase of Cu. Initial magnetic permeability and saturation magnetization is maximum for the composition of x=0.2, i.e. for Ni_0.8Cu_0.2Fe₂O₄, which can be attributed to the maximum sintered density obtained for this composition. Resistivity decreases with the increase of Cu content.     

Solidification mechanism transition of liquid Co–Cu–Ni ternary alloy

We report a solidification mechanism transition of liquid ternary Co₄₅Cu₄₅Ni₁₀ alloy when it solidifies at a critical undercooling of about 344 K. When undercooling at ΔT<344 K, the solidification process is characterized by primary S (Co) dendritic growth and a subsequent peritectic transition. The dendritic growth velocity of S (Co) dendrite increases with the rise of undercooling. However, once ΔT>344 K, the solidification velocity decreases with the increase of undercooling. In this case, liquid/liquid phase separation takes place prior to solidification. The minor L₂ (Cu) droplets hinder the motion of the solidification front, and a monotectic transition may occur in the major L₁ phase. These facts caused by metastable phase separation are responsible for the slow growth at high undercoolings.