Yogendra Prasad Yadava

Study of phase transformations In API 5L X80 Steel in order to increase its fracture toughness

Phase transformations in API 5L X80 steel were studied in different thermomechanical sequences with a view to increasing the fracture toughness of this steel. Dilatometry tests performed on the quenched steel detected a phase transformation occurred, during heating, in the temperature range 593-618 K. This phase transformation was identified as the dissolution of M-A islands. Based on preliminary dilatometric tests, ten thermal and thermomechanical treatments were performed on X80 steel samples. Initially, the material was hot rolled and quenched and only quenched. On the material without deformation, aging was also performed at temperatures of 603, 673, 723, 773, 823 and 873 K. These treatments resulted in the formation of the acicular ferrite constituent, among others. Tensile tests showed that the aging treatments produced reductions in yield strength and increases in the elongation and toughness of X80 steel. All the treatments resulted in an increase in the tensile strength of steel.

EDX analysis, microstructure and magnetic properties of CuS doped Bi-2212 superconductors

In this work we have studied the effect of CuS doping on Bi-2212 (nominal composition Bi 2+y Sr 3-y- n Ca n [(CuO) 1-x (CuS) x ] 2 O 6+δ , (0 < x < 0.1, 0 < y < 0.1 and 0.8 < n < 1) superconductors. An improvement in T c of the CuS doped Bi-2212 superconductors is observed in these studies. Most likely improvement in T c of the CuS doped Bi-2212 superconductors is caused by the modifications in the oxygen stoichiometry of the samples due to incorporation of S in the Bi-2212 lattice, with a consequent improvement in hole concentration.

Structure, microstructure, magnetic properties and chemical stability of HoBa2SbO6 with Yba2Cu3O7−δ superconductor

Abstract A complex perovskite oxide HoBa 2 SbO 6 in the Ho–Ba–Hf–O, rare-earth based oxide system, has been synthesised and sintered as a single phase material. The structure, microstructure, quantitative elemental analysis and magnetic properties of this material have been studied by X-ray diffraction, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) techniques and magnetic susceptibility measurements. Significant presence of superstructure reflection lines in the XRD spectra of HoBa 2 SbO 6 reveals that it is an ordered complex perovskite oxide. Magnetic susceptibility measurements show that HoBa 2 SbO 6 presents a paramagnetic behaviour at low temperature (5–300 K). Microstructure and EDX analysis show that sintered HoBa 2 SbO 6 has homogeneous surface morphology with uniform particle size (1–2 μm) distribution and there is no evidence of impurity in the single phase sintered HoBa 2 SbO 6 . The chemical stability of HoBa 2 SbO 6 with YBa 2 Cu 3 O 7− δ superconductor was studied. This study shows that HoBa 2 SbO 6 is chemically compatible with YBa 2 Cu 3 O 7− δ and it did not have deleterious effect on the superconducting transition temperature of YBa 2 Cu 3 O 7− δ . Also, HoBa 2 SbO 6 melts congruently and single crystals could be grown from the melt. In view of these favourable characteristics, HoBa 2 SbO 6 could be used as a potential substrate material for YBa 2 Cu 3 O 7− δ superconductor film.

Microestrutural evolution in a CuZnAl shape memory alloy: kinetics and morphological aspects

The microstructural evolution of the CuZnAl shape memory alloys was studied by indirect techniques relating to the atomic migration rate of grain boundaries. Addition elements were used in a Cu-15,5Zn-8,0Al alloy to provide a comparison with the same alloy without microelement additions. The alloys were melted in an induction furnace of 24 kVA. After casting, the bulk samples of the alloys were homogenized. Then they were solution treated and hot-rolled followed by water-quenching to initiate the recrystallization. Finally, annealing produced at different temperature ranges was made in different samples in order to establish a law for the grain growth. Following the heat treatments, all annealed samples were examined by statistical metallography and the grain sizes were measured. After measurements, the same empirical law of grain growth was found for the different alloys and the ln [D-Do] x 1/T diagrams were plotted in order to establish the kinetic behavior. Based on the estimated values of the activation energy, important conclusions were obtained concerning the addition elements.

Chemical and physical stability of MgO with superconductors

Chemical and physical compatibility of MgO with (LBCCO) high- superconductors have been studied by x-ray diffractometry and magnetic measurements on composites containing 0-100 vol% of MgO component. X-ray diffractometry studies carried out on composite show that MgO is chemically non-reactive with LBCCO superconductors even up to 80 vol% addition of MgO and severe heat treatment at for 30 h. Lattice matching between MgO and unit cells is fairly well (lattice mismatch ). Magnetization measurements carried out on composite show that no deleterious effect on the superconducting properties of is caused by MgO addition. Thus we infer that MgO is chemically and physically compatible with superconductors and MgO substrates could be used for the fabrication of high- LBCCO superconducting films.

Synthesis and study of the structural characteristics of a new complex perovskite oxide Sr2HoHfO5.5 for its use as a substrate for YBCO superconducting films

Abstract A new complex cubic perovskite oxide Sr 2 HoHfO 5.5 has been prepared by solid state reaction process. X-ray diffraction studies show that Sr 2 HoHfO 5.5 has a A 2 BB ′ O 6 type complex cubic perovskite structure and presence of the significant intensities of superstructure reflections in the X-ray spectrum reveal that it is an ordered complex cubic perovskite oxide. The experimental value of the lattice parameter of Sr 2 HoHfO 5.5 , is a =8.1725 A. Based on the doubling of primitive ABO 3 cubic perovskite unit cell, (1/2) a =4.0862 A of Sr 2 HoHfO 5.5 is comparable to the lattice parameter a =3.8227 A of YBCO superconductor. Sr 2 HoHfO 5.5 has good lattice matching (lattice mismatch ∼6%) with YBCO superconductor. The dc magnetic susceptibility of Sr 2 HoHfO 5.5 , measured in the temperature range 5–300 K shows a Curie–Weiss behavior. Using a Curie–Weiss law fitting we obtain a effective magnetic moment per Ho 3+ ion in Sr 2 HoHfO 5.5 of 9.76 μ B . This value is slightly lower than the spin-only moment (10.60 μ B ) expected for an isolated Ho 3+ ion.

Development of methodology for measurements of residual stresses in welded joint based on displacement of points in a coordinated table

Residual stresses in a welded joint of ASTM A131 grade AH32 steel was measured either by the X-ray diffraction or by displacements of referenced points measured on a coordinate measuring machine before and after heat treatment. For all tests, the welding was performed with Shielded Metal Arc Welding, vertical-up position, by a certified welder. After welding, some specimens were subjected to marking, made through small holes evenly spaced and mapped on a coordinate measuring machine. After labeling, the samples were subjected to heat treatment at temperatures nearby recrystallization. After heat treatment, the samples were subjected to new measurements by coordinate measuring machine to evaluate the displacements of the points produced by the recrystallization. In parallel, residual stress measurements were made by XRD for validation of this new methodology. The results obtained either by X-ray or by coordinate measuring machine showed a good correlation between the two measurement methodologies employed.

Matrix consolidation mechanism in 1D-Ti/SiC/C composites produced by continuous binder-powder coating

In this workmatrix consolidation mechanism has been investigated in 1D-Ti/SiC/C composites produced by Continuous Binder-Powder Coating - CBPC. Titanium metal matrix composites reinforced with continuous SiC/C filaments were analysed in different densification conditions. The results show that during processing, densification occurs by several mechanisms including a complex elasto-viscoplastic flow and diffusion bonding. The matrix consolidation depends on many processing conditions such as pressure and temperature, mainly. Using correct conditions of pressure and temperature, the titanium matrix composites produced by this process present a good matrix consolidation without porosity and a weak interaction between matrix and fiber. These good agreements between matrix consolidation and weak chemical interaction between matrix and fibre are obtained when pressures up to 150 MPa and temperatures below β-transus are applied. In these conditions, supplementary heat treatments can be performed either in alpha or beta domains.

High Density Ba2AlWO5.5 Ceramic Compacts Produced through Liquid Phase Sintering Route for Temperature Sensores

Structural and functional characteristics of ceramic components highly depend on their microstructure and mechanical properties. In the production of such ceramics sintering plays extremely important role. Recently, we are working on the development and fabrication of temperature sensors for the petroleum wells. In this connection, we have developed a new alumina based ordered complex cubic peroviskite oxide ceramic Ba2AlWO5.5. During our study, we found that Ba2AlWO5.5ceramics compacts could not be densified by normal sintering route. To overcome this hurdle, we have utilized the liquid phase sintering process, using CuO additives. By addition of 1 to 2 wt% CuO, we succeeded to sinter this ceramic in the temperature range 1200 to 14000 C. Sintered Ba2AlWO5.5 ceramics were examined by X-diffraction and scanning electron microscopy to verify the presence of any extra phase due to CuO addition in the Ba2AlWO5.5 matrix. Our studies revealed that CuO addition did not affect the structural characteristics, but considerably modified the densification process, microstrutural characteristics and consequently mechanical properties of the Ba2AlWO5.5 ceramics.

Study of Sintering Behavior of Ba2AlSnO5.5 Ceramic Powder Compacts as Substrate for Temperature Sensing Devices

Ceramic components are frequently used as substrates for the production of temperature sensing devices in petroleum industries, in view of their high thermal and electrical resistance and inertness in hostile ambient conditions. Complex cubic perovskite oxide ceramics have a great advantage in terms of their varied physico-chemical characteristics with the substitution of structural elements in the respective formula units. In this context, we have produced Ba2AlSnO5.5 ceramics by solid state reaction process. Structural characteristics, studied by powder x-diffraction, reveal that Ba2AlSnO5.5 ceramic has an ordered complex cubic perovskite structure. Ba2AlSnO5;5 ceramics were sintered in the form of circular discs of 10 and 15 mm diameters and 2 mm thickness, in the temperature 1200 to 14000C by normal sintering process. The microstrutural characteristics were studied by scanning electron microscopy on both polished and fracture surfaces. The SEM micrographs show homogenous surface morphology and particle size distribution. Mechanical hardness of the sintered Ba2AlSnO5.5 ceramics were studied by Vicker´s hardness tests. The results of these studies have been presented and discussed in this work