Dynamic elastic properties and magnetic susceptibility across the austenite-martensite transformation in site-disordered ferromagnetic Ni-Fe-Al alloy

Besides permitting an accurate determination of the ferromagnetic-to-paramagnetic phase transition temperature and the characteristic temperatures for the beginning and end of the growth of martensite (austenite) phase at the expense of austenite (martensite) phase while cooling (heating), the results of an extensive ac susceptibility, sound velocity and internal friction investigation of the thermoelastic martensitic transformation in melt-quenched (site-disordered) Ni55Fe20Al25 alloy provide a clear experimental evidence for the following. Irreversible thermoelastic changes (thermal hysteresis) occur in the austenite phase in the premartensitic regime. In the heating cycle, the system retains the "memory" of the initiation and subsequent growth of the martensitic phase (at the expense of the parent austenite phase) that had taken place during the cooling cycle in the austenite-martensite phase coexistence region. We report and discuss these novel findings in this communication.Comment: 5 figure

Basic Principles in Physical Metallurgy - II

The structure and stability of metallic materials needs to be understood before dealing them for a particular service. The materials depends on chemistry and processing condition. Various structures evolves during processing. Therefore one has to understand the distinction among the structures from crystallographic point to view.Here, we have presented a brief account relevant to the structural aspect. This will help in understanding and identification of the phases by metallographic techniques. The road maps for phase stability, which may be called as phase diagram have been discussed. From phase diagram, we can extract the information about the relative amounts of the various phases, which can be verified and confirmed from micro-structures of the materials. The various invariant liquid state and solid state reactions have been introduced. A few examples of nonequilibrium structures such as nano-crystal, glass and quasicrystal etc.arising due to non-equilibrium processing has been highlighted. A brief mention has been made about diffusion, precipitation, order-disorder reaction and spinodal decomposition

Failures due to hydrogen embrittlement

The effect of hydrogen in metals and alloys are discussed. The various trapping and cracking processes by which hydrogen affects the behaviour of materials are summarized. Hydrogen may be introduced during melting and entrapped during solidification or it may be picked up during heat treatment, electroplating, acid pickling ,or welding. Hydrogen also can be introduced by cathodic reaction during corrosion. Embrittlement mechanisms have been described by highlighting the models such as: (i) planar pressure, (ii) cohesive energy, (iii) surface energy, (iv) dislocation, (v) hydride formation and (vi) methanation. Unlike most embrittlement phenomena, hydrogen embrittlement is enhanced by slow strain rates. The strain rate sensitivity, temperature dependence and susceptibility to delayed fracture are main characteristics of hydro¬gen embrittlment. Two case studies of failure analysis of high C steel wire products are presented. The tools and techniques for such analysis have been pointed out. It has been shown that planar pressure model and cohesive energy model can explain well the failures observed in those two cases

Synthesis of nanocrystalline and amorphous phases in complex metallic alloys during mechanical milling

The synthesis of nanocrystalline, amorphous and their composite phases in complex metallic alloys (CMAs) appears to be beneficial in order to overcome the brittleness problem of these alloys. Mechanical milling among the various processing techniques, have been adopted for the purpose of synthesizing nano-phase/amorphous and their composites. The aim of the present work is to investigate the stability and phase evolution on some complex metallic alloys during mechanical milling. The milling is carried out in a planetary ball mill at various milling intensity with varying the ball to powder ratio in a suitable milling medium. The samples are characterized with the help of XRD, SEM and TEM. It is found that these alloys can give rise to the formation of nanocrystalline phases of grain sizes to a certain minimum value as well as amorphous phase. At present it is not clear why, given a milling energy, some alloy systems restrict to the formation of nanograin of a particular size and do not lead to the complete formation of amorphous phase. Attempts will be made to discuss the evolution and stability of these nano/amorphous phases based on the modified Miedema model of free energy by including the contribution from grain size effects generated during milling

Dynamics of electromagnetic waves in Kerr geometry

Here we are interested to study the spin-1 particle i.e., electro-magnetic wave in curved space-time, say around black hole. After separating the equations into radial and angular parts, writing them according to the black hole geometry, say, Kerr black hole we solve them analytically. Finally we produce complete solution of the spin-1 particles around a rotating black hole namely in Kerr geometry. Obviously there is coupling between spin of the electro-magnetic wave and that of black hole when particles propagate in that space-time. So the solution will be depending on that coupling strength. This solution may be useful to study different other problems where the analytical results are needed. Also the results may be useful in some astrophysical contexts.Comment: 15 Latex pages, 4 Figures; Accepted for publication in Classical and Quantum Gravit

Studies on Some N-Acyl-N-phenylhydroxylamines as Metal Complexing Ligands: Part X - Formation Constants of Fe(III) Complexes of Some N-Hydroxysuccinamic Acids

413-41

Behaviour of spin-1/2 particle around a charged black hole

Dirac equation is separable in curved space-time and its solution was found for both spherically and axially symmetric geometry. But most of the works were done without considering the charge of the black hole. Here we consider the spherically symmetric charged black hole background namely Reissner-Nordstrom black hole. Due to presence of the charge of black-hole charge-charge interaction will be important for the cases of incoming charged particle (e.g. electron, proton etc.). Therefore both gravitational and electromagnetic gauge fields should be introduced. Naturally behaviour of the particle will be changed from that in Schwarzschild geometry. We compare both the solutions. In the case of Reissner-Nordstrom black hole there is a possibility of super-radiance unlike Schwarzschild case. We also check this branch of the solution.Comment: 8 Latex pages and 4 Figures; RevTex.style; Accepted for Publication in Classical and Quantum Gravit