Materials Science Forum Vols. 654-656

Abstract: The sintered stainless steel produced by the powder metallurgy process (P/M) has attracted a growing interest because it has the advantage of better formability to fabricate complex shape products without machining and welding. The four sintered stainless steel samples; i.e., the mono-phase SUS304L SS P/M sample (hereafter denoted as 304L), the mono-phase SUS316L SS P/M sample (hereafter denoted as 316L), the duplex-phase SUS316L and SUS434L SS P/M sample (hereafter denoted as 316L+434L), and the duplex-phase SUS316L and SUS434L SS P/M sample with copper (hereafter denoted as 316L+434L+Cu) were used in this experiment, and their corrosion behavior was investigated through the electrochemical procedure. It was confirmed from the potentiodynamic polarization test that their corrosion behavior was clearly classified into two groups. The one is for the mono-phase stainless steel group and the other is for the duplex-phase stainless steel group. Both corrosion current density (Icorr) and passivation current density (Ip) for the latter group were smaller than those for the former group, and especially the duplex-phase 316L + 434L SS sample with copper (316L+434L+Cu) showed the lowest value. This implies that the duplex-phase 316L + 434L SS sample with copper (316L+434L+Cu) has the highest corrosion resistance.

Abstract: Multilayered approach to YBCO-based Josephson junction manufacture is introduced. Properties of monolayer YBa2Cu3O7 (YBCO) and multilayer YBCO/NdBCO/YBCO junctions of similar thickness grown by pulsed-laser deposition on MgO (100) substrates has been analysed and compared. The influence of the multilayered structure on junction behaviour and properties are presented and discussed.

Abstract: Superconducting thin films of magnesium diboride (MgB2) has been synthesized on various substrates such as gold, silver, copper and silicon using a novel electroless plating technique. The microstructures and the superconducting properties of these films have been characterized using X-ray diffraction, scanning electron microscopy and temperature dependent magnetometry. X-ray diffraction measurements confirm that the films are crystalline magnesium diboride with some impurity phases. Clear evidence for a superconducting transition in the magnetization measurements was observed.

Abstract: Zn1-xCoxO thin films ( ) have been grown on Si (100) substrates by pulsed laser deposition. The as-prepared films showed paramagnetic characteristics at room temperature, while the films after annealing in a H2 atmosphere exhibited clear ferromagnetic behaviors. Raman scattering has been used to study the influence of the post-deposition H2 annealing on the structural properties and consequently on the magnetic properties of Co-doped ZnO films. It is found that the post-deposition annealing increases defect oxygen vacancies in the host lattice and induces an additional Raman vibration mode. The ferromagnetism of Zn1-xCoxO is believed to be strongly related to the oxygen deficiency in ZnO.

Abstract: The purpose of this research paper is focused on the X40CrMoV5-1 hot work tool steel surface layers improvement properties using high power diode laser. In the effect of laser alloying with powders of carbides occurs size reduction of microstructure, as well as dispersion hardening through fused in but partially dissolved carbides and consolidation through enrichment of surface layer in alloying additions coming from dissolving carbides. Introduced particles of carbides and in part remain undissolved, creating conglomerates being a result of fusion of undissolved powder grains into molten metal base. In effect of convection movements of material in the liquid state, conglomerates of carbides arrange themselves in the characteristic of swirl. Laser alloying of surface layer of investigated steel without introducing alloying additions into liquid molten metal pool, in the whole range of used laser power, causes size reduction of dendritic microstructure with the direction of crystallization consistent with the direction of heat carrying away from the zone of impact of laser beam. Remelting of the steel without introducing into liquid molten pool the alloying additions in the form of carbide powders, causes slight increase of properties of surface layer of investigated steel in comparison to its analogical properties obtained through conventional heat treatment, depending on the laser beam power implemented for remelting. The outcome of the research is an investigation showing the structural mechanisms accompanying laser alloying.

Abstract: The obtained generalized equation for description of a fundamental property of solid crystalline materials i.e. first-order phase transition of the grain boundaries with formation of two-dimensional liquid has been used for calculating of transition temperature of any metals, which value lies in range 0.55 – 086 of melting point. Based on these conclusions to develop strategies for effective forming of coatings by synthesis of nitrides and carbonitrides on surface layers of hard metals and chromium steels have been made. It was shown the hardening of thin surface layer (0.1-0.5mm) due enriched of a nitrides in steels and carbonitrides with diamond like structure and strengthening the following layer by recristallization of W carbides in WC-Co and WC-TiC-Co hard metal. These result to increase of alloys hardness, ductility, and resistance to wear and decrease of sensibility to fragile rupture. Industrial tests have been made.

Abstract: To extend the mould cycle duration and to reduce cost, a TiB2 particulate reinforced Cu based composite coating was produced on hot-working die steel substrate using laser cladding. The experimental results showed that TiB2 particles embedded in copper based alloy were in-situ synthesized during laser processing. An excellent bonding between the coating and the substrate was obtained. The microstructure of the coating was mainly composed of -Cu dendrites and dispersed TiB2 particles. The maximum microhardness of the coating was about 800HV0.2. The wear resistance of the coating was evaluated under room temperature dry-sliding wear test condition. Due to the presence of a large amount of TiB2 particles, the composite coating exhibited excellent wear resistance compared with that of substrate.

Abstract: Comprehensive studies of the fracture morphology and the sequence of fracture patterns during tensile loading are important to understand the performance of ceramic coatings during operation. The ceramic coatings are applied to relatively rough surfaces with edges and corners. When the substrate is not perfectly smooth and flat, large stress concentrations are generated in the coated system. The stress concentrations due to the shape of the substrate also affect the initiation and propagation of cracks in the coatings. The mechanical integrity of TiN coating is studied using a new test specimen, known as the Cylindrically-Notched-Tensile (CNT) specimen that can mimic real life situations. The coated specimens under tensile loading are then examined using a scanning electron microscope to study the response of the coatings to the applied loads. The interfacial shear strength of the coatings is determined using the Agrawal-Raj model. Multiple cracks are observed in the coating and the fracture morphology was found to depend on the stress concentration at notch corners.

Abstract: A Fep/Cu composite coating was developed based on laser cladding process in immiscible liquid system. The microstructure of the coatings is characterized by a homogeneous distribution of Fe-rich spherical particles dispersed in the Cu-rich matrix. The size of the Fe-rich spheres decreases and their number density increases with the decrease of the heating input. The micro-hardness and wear resistance results show that the micro-hardness of the composite coating (spherical particle (380 ~ 450 HV0.2) and the Cu-rich matrix about 200 HV0.2) is far better than that of the copper (70 HV0.2), the wear resistance of the composite coating is almost twice of the copper. Such Fep/Cu structure composite coating have a good combination of high strength and corrosion resistance (Fe-rich phase) and high electric and thermal conductivities (Cu-rich phase) with many potential advanced applications in electronic devices.

Abstract: Two kinds of mixed powders:Ti-6Al-4V/B/C and Ti-6Al-4V/B4C which are pre-pasted on Ti-6Al-4V substrates separately were scanned by a 500W pulsed YAG laser to induce in situ formation of titanium composite coatings contained TiBx and TiC ceramic reinforced phases. The influences of laser processing parameters including Pulse Frequency (PF), Pulse Width (PW), Laser Power (P) and Scanning Speed (V) together with the powder proportions on the microstructure and properties of the coatings were investigated. Microstructure, phase components and micro-hardness of the coating were analyzed by OM, SEM, TEM, XRD and micro-hardness tester respectively. The optimized processing parameters of a single path laser scanned specimen in this case are as follows: PF: 15Hz, PW: 3ms, for the Ti-6Al-4V/B4C specimens the laser line energy ~12.5J/mm, for the Ti-6Al-4V/B/C specimens the laser line energy ~11J/mm. TiB and TiC ceramic were formed evenly reinforced in the matrix of Ti-6Al-4V with the morphology of needle, tiny dendrites and disperse spherical particles. The maximum micro-hardness of single-path layers is up to 750 Hv, which is over twice of that of the substrate (367Hv).The wear weight loss decreased nearly 3 times that of the substrate.