National Institute Of Materials Physics - Romania

Publications

892 articles found

881. ON THE LIMITING FACTORS OF THE CRITICAL CURRENT-DENSITY IN HIGH-TC SUPERCONDUCTING CERAMICS

Authors: MIU, L; CRISAN, A; POPA, S; SANDU, V; NISTOR, L

Published: DEC 1990, JOURNAL OF SUPERCONDUCTIVITY, 3, 394, DOI: 10.1007/BF00617464

The temperature dependence of the critical current density at high temperatures and in weak applied magnetic field for YBa2Cu3O7-y ceramic samples with a pronounced granular character is analyzed. The experimental results can be explained in terms of thermally activated motion of the intergrain Josephson vortices at grain boundaries, which may be an indication that the actual limiting factor for the critical current density in ceramic samples results from a weak pinning force density for the intergrain vortices rather than from the weak-link quenching.

882. ON THE TRANSITION-METAL QUASISUBLATTICE IN ICOSAHEDRAL AL-CR-FE PHASES

Authors: MANAILA, R; FLORESCU, V; JIANU, A; RADULESCU, O

Published: NOV 1989, PHILOSOPHICAL MAGAZINE B-PHYSICS OF CONDENSED MATTER STATISTICAL MECHANICS ELECTRONIC OPTICAL AND MAGNETIC PROPERTIES, 60, 599, DOI: 10.1080/13642818908206041

883. TEA-CO2 LASER-DEPOSITED YBA2CU3O7 SUPERCONDUCTING THIN-FILMS

Authors: SANDU, V; CRISAN, A; GRIGORESCU, D; MIU, L; CHIS, I; ALDICA, G; CRUCEANU, E; GRIGORIU, C; DRAGULINESCU, D

Published: MAY 1989, JOURNAL OF MATERIALS SCIENCE LETTERS, 8, 510, DOI: 10.1007/BF00720279

884. ICOSAHEDRAL PHASES IN THE AL-FE-CR ALLOY SYSTEM

Authors: MANAILA, R; FLORESCU, V; JIANU, A; BADESCU, A

Published: SEP 16 1988, PHYSICA STATUS SOLIDI A-APPLIED RESEARCH, 109, 66, DOI: 10.1002/pssa.2211090105

885. MICROSTRUCTURE, MAGNETIC AND MAGNETOSTRICTIVE BEHAVIOUR IN RAPIDLY QUENCHED OFF-STOICHIOMETRIC Ni-Mn-Ga FERROMAGNETIC SHAPE MEMORY ALLOYS

Authors: Sofronie, M; Tolea, F; Enculescu, M; Pasuk, I; Popescu, B

Published: , ROMANIAN REPORTS IN PHYSICS, 2022, DOI: 503

This work reports the effect of the rapid solidification technique and thermal treatment on the martensitic transformation (MT), magnetic and magnetostrictive properties on the off-stoichiometric Ni49Mn31Ga20 and Ni51Mn28Ga21 ferromagnetic shape memory ribbons. The samples were investigated by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, magnetic and magnetostrictive measurements. The temperature dependence of the X-ray phases analysis shows the presence of martensite structures, both tetragonal and monoclinic, at room temperature and allowed to study their evolution through MT. The thermal treatment induces changes in the microstructure with implications in MT and Curie temperatures evolution. The competition between the magnetization orientation and twin boundary motion within martensitic variants under magnetic field evidenced in the magnetic-strain curves was discussed and correlated with the magnetic data.

886. EXCHANGE COUPLED NANOCOMPOSITES: MAGNETOPLUMBITE Sr FERRITE AND MAGNETITE

Authors: Greculeasa, SG; Comanescu, C; Iacob, N; Kuncser, A

Published: , ROMANIAN JOURNAL OF PHYSICS, 2022, DOI: 606

Exchange coupling in a SrFe12O19 - Fe3O4 nanocomposite magnet was explored in this study. The composition, microstructure, local structure and magnetic properties were investigated by XRD, SEM, Mossbauer spectroscopy, and SQUID magnetometry. The magnetoplumbite SrFe12O19 and spinel Fe3O4 structures were verified by X-ray diffraction. The morphology of the composite reveals the characteristics of the two components. The hyperfine parameters allowed the identification of the Wyckoff positions of the iron ions corresponding to the involved phases. The magnetic measurements of the composite, showing a single-phase-like magnetic hysteresis loop, confirmed the exchange coupling between the hard and soft magnetic phases.

887. SOME ASPECTS REGARDING PRECIPITATES IN THE NiTi SHAPE MEMORY MATERIALS

Authors: Cirstea, CD; Tolea, F; Patroi, D; Cirstea, V; Tsakiris, V

Published: , ROMANIAN JOURNAL OF PHYSICS, 2022, DOI: 903

NiTi cylindrical materials were obtained by spark plasma sintering at 850??C or 900??C from high purity Ni and Ti powders. These mixtures were previously processed by mechanical alloying for 8 and 15 hours. In order to increase the alloy homogeneity, the NiTi materials were subjected to post aging treatment in protective atmosphere at constant temperature 400??C and cooling in water with ice. All samples were characterized by optical microscopy, differential calorimetry (DSC), X-ray measurements (XRD) and micro/nanoindentation measurements. The results demonstrate that the NiTi materials obtained by this preparation route have good mechanical properties and can serve as a quantitative reference for the microstructure design of shape memory materials for various applications, such as the biomedical ones.

888. STUDIES ABOUT STRUCTURAL AND THERMAL INVESTIGATIONS ON Ti50Ni30Cu20 ALLOYS OBTAINED BY DIFFERENT TECHNOLOGICAL PROCESSES

Authors: Cirstea, CD; Lucaci, M; Valeanu, M; Sofronie, M; Bujoreanu, LG; Lungu, MV; Tsakiris, V; Cucos, A; Talpeanu, D; Enescu, E

Published: , ROMANIAN JOURNAL OF PHYSICS, 2021, DOI: 601

The paper presents the research results in the field of TiNiCu shape memory alloys processed by powder metallurgy techniques. The powders mixtures used to synthesize Ti50Ni30Cu20 alloys were obtained by blended constitutive elemental powders or by mechanical alloying of powder mixtures for 10 and 20 hours, respectively. Finally, a subsequent annealing process was carried out, followed by a rapid cooling in ice water. All experiments were performed under 99.9% argon atmosphere. At room temperature, the obtained materials contained monoclinic and orthorhombic martensite type. The structural and thermal investigation of these materials were discussed in view of the potential development of actuators.

889. Soft magnetic composites of carbon fibers decorated with magnetite in an epoxy matrix

Authors: Kornilitsina, EV; Lebedeva, EA; Astaf'Eva, SA; Trukhinov, DK; Badica, P

Published: , SOFT MATERIALS, DOI:

The chemical precipitation was used to obtain carbon fibers (CF) with surface modified by magnetite particles (Fe3O4). Processing was carried out by employing up to three subsequent coating stages of ultrasonic treatments. After each sonication stage, the coating was 17, 33, and 47 wt. % of the total weight of the modified fibers. Raman spectroscopy indicates the presence in the coating of a mixture of iron II and III states. As-decorated fibers were used to fabricate composites with an epoxy resin (ED-20) matrix cured with PEPA. The quantity of the carbon fiber filler was of 1, 3, and 6 wt %. At room temperature, the saturation magnetization of the soft magnetic samples was 0.37, 0.83, and 1.72 emu/g for the indicated compositions. Carbon fiber reinforced polymer materials with extra functions such as magnetic in this case, are expected to be useful in applications from the power and energy industries.

890. Effects of the Severe Plastic Deformation on the Magnetic Properties of Zr13Co87 Ribbons

Authors: Popescu, B; Palade, P; Sofronie, M; Kuncser, A; Gurau, C; Gurau, G; Tolea, F

Published: , METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, DOI: 10.1007/s11661-021-06507-y

The influence of the severe plastic deformation via high-speed high-pressure torsion (HSHPT) on the structural and magnetic properties of the Zr13Co87 alloys is investigated. Moderate applied deformation promotes the growth of the rhombohedral hard magnetic phase leading to the increase of the sample's hardness and magnetic coercivity. A higher degree of deformation affects the samples morphology leading to a critical value of the grain size under which the exchange coupling of the soft phase is less effective. Additionally, it produces a random alignment of the anisotropy axes, which are both detrimental to the hard magnetic properties.