Materials Science Forum Vol. 879

Abstract: Ferritic ODS 14Cr steels reinforced by means of Yttrium oxide nanoclusters represent one of the options for future structural applications in nuclear Generation IV reactors. Due to their high tensile properties and resistance to irradiation damage, Oxide Dispersion Strengthened Steels (ODS-S) have been suggested for nuclear fusion applications. The present paper describes the experimental procedure of mechanical alloying, canning and hot extrusion adopted to produce ODS rods. The effect of variations in the processing parameters are also discussed. Hot extrusion has been successfully applied to produce a batch of about 10 kg of ODS steel. Full size ASTM E21 and E8 specimens have been tested from room temperature up to 800 °C. The microstructure characterization of the manufactured materials has been carried out by transmission electron microscopy. Ultimate tensile stress higher than 1350 MPa have been obtained in the as-extruded material and higher than 1100 MPa in samples annealed for 4 hours at 800 °C.

Abstract: Shape memory composite (SMC) structures are of great interest for the aerospace applications. In previous works, the authors have studied SMC lab-scale deploying prototypes manufactured by using two carbon fiber composite layers with a shape memory polymer interlayer. The prototypes were produced in an initial configuration and subsequently it was changed in the memorizing step. The initial configuration was then recovered by heating. Memorization and recovery phases were performed by means of conventional heating (by hot air gun or heater plate). In this work, for the first time the authors evaluate the SMC heating by means of radiating lamps. A square plate was purposely produced and recovered after different memory steps. Time, temperature and recovery are measured during and after the tests. The radiating lamp power and type, and the distance of the SMC from the lamp are fundamental parameters for the heating phase. As result of the irradiation tests, the initial configuration can be successfully recovered without failures. This study is especially aimed to future space applications in which the deployment (recovery) phase will be initiated only by exposure to solar radiation.

Abstract: The use of Ferritic Stainless Steels has become indispensable due its lower cost and the possibility to replace austenitic stainless steels in many applications. In this study, cold rolled sheets of two stabilized ferritic stainless steels with 85% thickness reduction were annealed by applying a heating rate of 24 oC/s and a soaking time of 24 s. The niobium stabilized ferritic stainless steel type ASTM 430 (430Nb) was annealed at 880 oC while the niobium and titanium bi-stabilized steel ASTM 439 was annealed at 925 oC. The annealed samples were tensile tested and due to the smaller grain size, steel 430Nb, showed a higher yield stress and a higher total elongation. Concerning drawability the steel ASTM 439 presented a better performance with higher average R-value, lower planar anisotropy coefficient and a greater value for Limit Drawing Ratio (LDR). These results are explained in terms of the differences in size and volume fraction of precipitates between the two steels.

Abstract: The ferritic stainless steel type 430 stabilized with Nb, with and without annealing after hot rolling, was cold rolled and subjected to isothermal annealing at temperatures 650, 700 and 750°C for times ranging between 10 to 86400 s. The recrystallization kinetics was evaluated by JMAK model through microhardness measurements and KAM and GOS parameters. The Avrami exponent data indicate the occurrence of an unidimensional grain growth due only to high angle boundaries migration, with values ranging between 0.9 and 1.2. The nucleation rate and grain growth decreased continuously with time. The evolution of the texture was analyzed via EBSD analysis by ODF maps. The steel recrystallization is based on combination of ON and SG theories, due to presence of {111}<121>, {554}<225> and {111}<112> related to γ fiber. The rotated cube component, feature of the hot rolled steel, decreased with annealing time.

Abstract: Magnetic pulse welding (MPW) is a solid state joining process, successfully utilized to join dissimilar metals. This advantage attracted manufacturing industries to fabricate hybrid materials to attain materials with a combination of multiple attributes. The high speed impact during the welding process causes various interfacial phenomena, which have been reported in previous research studies. Combined high speed collision, Joule heating due to eddy current and plastic heat dissipation cause noticeable heating in the workpiece. The heating from the plastic work and collision energy could particularly be significant at the vicinity of the interface compared to other regions of the workpiece. The Joule heating due to eddy current affects the entire workpiece that is prominent before the collision. There is a sharp increase of the temperature at the onset of weld formation due to dissipation of plastic work during the collision. 3D simulations of coupled electromagnetic-mechanical-thermal were carried out to investigate the heating due to the combined Joule heating and plastic dissipation. A case study of MPW, consist of a one turn coil combined with a field shaper, is used to investigate the welding process. The simulations were performed using LS-DYNA^®, which has the capability of using both finite and boundary elements to solve the thermo-mechanical problem during electromagnetic forming. The predicted temperature distributions from numerical simulations show expected phenomena of Joule heating and plastic heat dissipation while the analytical approach used to estimate the localized increase in temperature due to supersonic gaseous compression. Minimizing the heating effect by identifying the influencing factors could help to optimize and control the quality of the magnetic pulse welded parts.

Abstract: The plasma beams were generated in a Rod Plasma Injector (RPI) operated in the Deposition by Pulsed Erosion (DPE) and Pulse Implantation Doping (DPE) modes. Samples of unalloyed and austenitic stainless steels were irradiated with short (μs scale) intense (energy density 2.0-5.0 J/cm²) pulses. The near surface layer - thickness in μm range - was melted and simultaneously doped with active element like nitrogen, cerium and lanthanum. Heating and cooling processes were of non-equilibrium type. The most important obtained results were: (i) austenitic structure was present in unalloyed steels after HIPPB modification processes and (ii) modified surface layers of austenitic stainless steel showed significant improvement of tribological properties and increase of high temperature oxidation resistance as compared with initial material.

Abstract: Pure aluminum (Al) has been used as high performance heat sink, electrical line and power supply line because of its light-weight, good thermal and electrical conductivities and high cost performance. On the other hand, the higher performance heat sink and eletrtorical line at room and high tempertture are reqired because of the increment of the power density and higher integration of semiconductor and LED. The use of Al matrix composites is one of suilable solution, because these parts needs multi functional propertes. In this study, titanium die-broide (TiB₂) particles was selected as the dispersant in Al matrix composites because of its good thermal and electrical conductivity, and good mechanical propertes. At first, the mixed power of Al and TiB₂ particles was obtained from six kinds of mixing process, which parameters are conventional boll milling, ultrasonic vibration after conventinal milling, planetary ball milling, which milling process was performed in wet process with ethanol and dry process. 20 vol. % TiB₂/ Al composites was obtained from spark plasma sintering. The dence comopsites with over 98% in relative density with highly dispersed TiB₂ particles was obtained from wet mixing process. But the tensile strength of the composites prepared from dry mixing process is higher than that of wet mixing process. The thermal conductivity of the composites is about 120 W/mK, and the obvious diferrence between the wet process and dry process was not observed.

Abstract: This paper describes a fundamental experiment on X-ray stress measurement of austenitic stainless steel (JIS SUS316L) with a new equipment which was developed in this study. An image plate (IP) as a two-dimensional X-ray detector and the cosα method as a principle of the measurement of stress were used in it. An experiment was conducted with CrKβ characteristic X-ray and γFe-311 diffraction line, and the results were compared to those that were obtained with the conventional sin²ψ method under the similar X-ray conditions. It was found that the accuracy of stresses obtained with the equipment developed are almost as same as those of the sin²ψ method. However, the measuring time can be shorten by several times by using it.

Abstract: Today physical modelling is a commonly used tool in modelling metallurgical processes. It can be applied both in steel metallurgy and non-ferrous metals metallurgy processes. It gives the opportunity to determine the hydrodynamic conditions of the processes. Although, the flow of mass and gas is not totally presented by such modelling, this kind of research is very often and willingly used. That is because it is really difficult to conduct experimental research in industrial conditions. Typically water is used as a modelling agent, so the physical modelling is not as expensive as the one carried out in industrial conditions. To obtain representative research from physical modelling the physical models have to be built according to the strict rules coming from the theory of similarity. The results obtained from the experimental test on the physical model, after verification, can be transferred to the real conditions. The article shows the obatined results coming from physical modelling of the steel production process. In the Institute of Metals Technologies of Silesian University of Technology the appropriate test stand was built to simulate the steel flow and mixing in the ladle. The visualization results have been presented. To simulate processing condition during aluminium refining additional test stand was also built. The exemplary results have been shown for different flow rate of gas, rotary impeller speed and different shapes of impellers. All presented results have been discussed and presented for the perspectives of further research.

Abstract: As one of processing methods of functionally graded materials (FGMs), centrifugal mixed-powder method has been proposed. The centrifugal mixed-powder method is the casting process combined of centrifugal casting and powder metallurgy. This processing method has advantage that fine ceramics-particles, whose wettability with matrix melt is low, can be compounded into metallic material. However, effects of particle size on microstructure and mechanical properties of the FGMs fabricated by the centrifugal mixed-powder method are unclear. In this study, two kinds of Al-TiO₂ FGMs rings are fabricated by the centrifugal mixed-powder method. One contains TiO₂ particles having similar diameter with Al matrix particles (hereafter, small different-size (SD) TiO₂ particles), and the other one compounds TiO₂ particles with much smaller diameter than Al matrix particles (hereafter, large different-size (LD) TiO₂ particles). In case of the Al-TiO₂ FGMs ring containing SD-TiO₂ particles, the TiO₂ particles are homogeneously dispersed in Al matrix on outer surface of the ring. On the other hand, the TiO₂ particles in the Al-TiO₂ FGMs ring with LD-TiO₂ particles are distributed along grain boundary of Al matrix. Moreover, Vickers-hardness and wear resistance around outer surface of the Al-TiO₂ FGMs ring containing the SD-TiO₂ particles is higher than that of the Al-TiO₂ FGMs ring with LD-TiO₂ particles. Since Al particles in the mixed-powder with LD-TiO₂ particles are surrounded by the TiO₂ particles, the Al particles can be hardly melted by heat of molten Al at casting process. As a result, the Al-TiO₂ FGMs ring with LD-TiO₂ particles has low hardness and wear resistance. Therefore, it is found that TiO₂ particles having similar diameter with Al matrix particles are more suitable for fabrication of the Al-TiO₂ FGMs rings.