Materials Science Forum Vols. 783-786

Abstract: The amorphousization of Zr₆₅Nb₃₅ alloy was performed. The Zr-Nb based alloys contained Al and Co elements were fabricated by arc-melting and melt-spinning methods. The superconducting property of the Zr_(65-x)Nb_35-xAl_x (x = 0~15 at%) and Zr_(65-x)Nb₂₀Al₁₅Co_x alloys (x = 3~10 at%) was investigated by magnetic susceptibility measurements. The Zr_(65-x)Nb₂₀Al₁₅Co_x metallic glasses (x = 6~10 at%) with superconducting nanocrystalline particles dispersed in an amorphous matrix exhibited a superconductivity below about 3.5 K. The addition of Co element led drastically to the amorphousization of the superconducting Zr₆₅Nb₂₀Al₁₅ alloy.

Abstract: Shape memory composites and structures were produced by using carbon fiber reinforced prepregs and a shape memory epoxy resin. The matrix of the prepregs was an epoxy resin as well but without remarkable shape memory properties. This way, two different technical solutions were adopted. Shape memory composite tubes and plates were made by adding a shape memory layer between two carbon fiber reinforced skins. An optimal adhesion between the different layers was achieved thanks to the compatibility of the prepreg matrix and the shape memory material. Shape memory composite structures were also produced by joining composite shells with shape memory foams. Mechanical, dynamic mechanical and shape recovery tests were carried out to show the properties of the composite materials and structures. Results confirm the ability of this class of materials to easily change their shape without affecting the mechanical stiffness of the recovered structures.

Abstract: The phase transformation behavior of Ti-50Pd-5x (x =Zr, Hf, V, Nb, Ta, Cr, Mo, W) (at.%) alloys was studied by X-ray diffraction measurements from room temperature to 800 oC. In all the alloys, B19 martensite was observed at room temperature and it transformed to B2 phase upon heating. In addition, peaks corresponding to formation of (Ti, x)₂Pd₃ phase was seen for all the alloys. However, the temperature of formation of (Ti, x)₂Pd₃, interestingly, varied with respect to the elements group from the periodic table. Elements except from group IV (Zr and Hf) have been identified to accelerate the formation of (Ti, x)₂Pd₃ phase even at low temperatures (~400 oC).

Abstract: Shape memory epoxy foams are a new class of materials for aerospace applications as light actuators, structural parts with reduced size during transport, and expandable/deployable structures. They were tested in an experiment onboard of the International Space Station in May 2011 (Shuttle Mission STS 134) and in April 2013, on board the BION-M1 capsule through the Soyuz-2 launch vehicle, with the aim to study the behavior in microgravity for future applications. The experiments were performed by an autonomous device which was in turn composed of control and heating system, battery pack and data acquisition system. Micro-gravity does not affect the ability of the foams to recover their shape but it poses limits for the heating system design because of the difference in heat transfer on earth and on orbit. This could be very significant for the behaviour of complex multi-functional structures in which shape memory epoxy foams are integrated. In this work, the main results of the experiments in microgravity are discussed and some results of tests on ground are shown in order to evaluate new possible developments in the field.

Abstract: In order to simulate the large deformation surrounding the rotational tool of friction stir welding (FSW) precisely, the moving particle semi-implicit (MPS) method was employed and the temperature distributions near the tool were obtained. Also, the temperature distributions in the whole model except for the area computed by MPS were calculated by the finite element method (FEM) and then the elastic-plastic analysis was conducted using the temperature distributions obtained by MPS and FEM. The inhomogeneous temperature distributions through the thickness near the joint line could be simulated and the maximum temperature distributions computed had a good agreement with the experiments. In addition, the longitudinal plastic strain distributions indicates that this plastic strain near the tool is not governed by only the temperature distributions and the influence of plastic flow should be taken into account.

Abstract: Since Fe-Cu-C sintered steels are easily rusted, they are coated with rust preventive oils. High viscosity of those rust preventive oils decrease workability, and low viscosity deteriorates rust preventive performance. Therefore, it is necessary to develop new rust preventive oils with contradictory properties of low viscosity and superior rust prevention. However, precise methodology to evaluate rust prevention ability has not been established. In this study, we developed new technique to quantitatively evaluate rust prevention ability by measuring the open circuit potential through thin corrosive solution on Fe-Cu-C sintered steels coated with a rust preventive oils. As a result, the ability for rust prevention can be measured quantitatively, and it decreases slowly over time, with repeating destruction and restoration. Furthermore, it was found that the deteriorating processes of rust prevention ability for rust prevention oils are composed of three characteristics steps respectively. That is, in the first step the great open circuit potential changes from 0V to-0.3V with repetition were observed where the excellent rust prevention ability was kept, in the second step it decreases slowly from-0.1V to-0.4V with oscillation of the small potential changes where the gradual decrease of rust prevention ability was recognized and in the third step it decreases monotonously in the lower potential than-0.4V where the rust was observed because of the remarkable deteriorating of the rust prevention ability.

Abstract: The effect of alloying to TiPd and TiPt on phase transformation temperature, phase equilibria, and shape recovery were investigated for TiPt and TiPd base high-temperature shape memory alloys. Ru, Ir, Co and Zr were chosen for additional elements and Zr was found as the most effective element to improve shape recovery of TiPd and TiPt.

Abstract: This paper presents an overview of the microstructures found in a range of two-phase FeNiMnAl alloys ranging from near-equiatomic very high-strength nanostructured alloys, such Fe₃₀Ni₂₀Mn₂₅Al₂₅, to more ductile f.c.c./B2 alloys, such as Fe₃₀Ni₂₀Mn₃₅Al₁₅. The effect of annealing at 823 K on the room temperature hardness is presented together with the temperature dependence of the yield strength.

Abstract: The effect of warm-rolling on the evolution of microstructure and microtexture was investigated in a duplex steel. For this purpose annealed duplex steel plates were cold and warm-rolled up to 90% reduction in thickness at room temperature and at 625°C, respectively. The austenite volume fraction decreased consistently during cold-rolling indicating that austenite was not stable during cold-rolling. In contrast, austenite was found to be very stable during warm-rolling at 625°C. Development of an ultrafine lamellar deformation structure with alternate arrangement of the ferrite and austenite bands could be observed during warm-rolling. A strong pure metal or copper type texture was observed in the austenite in the warm-rolled material in contrast to brass texture developed during cold-rolling. Development of RD (RD//<110>) fiber and ND-fiber (ND//<111>) was observed in ferrite during both cold and warm-rolling. However, the strength of the RD-fiber was much higher as compared to the ND-fiber in ferrite in cold-rolled DSS as compared to the ferrite in warm-rolled DSS.

Abstract: In this work, NiMnGa thin film composed of non-modulated martensite (NM) and seven-layered modulated martensite (7M) was produced. The crystal structure and lattice constants were determined by X-ray diffractometer (XRD). The preferred crystallographic orientation of martensite was determined using the four-circle XRD. SEM/EBSD was employed to verify the crystal structure of the martensite and to reveal its crystallographic features correlated with the microstructure. According to the XRD patterns, the crystal structure of NM and 7M was determined as tetragonal and monoclinic crystal structure, respectively. Pole figures measured by four-circle diffractometer revealed that the NM martensite possesses (004)_NM and (220)_NM preferred plane texture close to the substrate surface, whereas the 7M martensite has (2 0 20)_7M, (2 0 )_7M and (040)_7M preferred plane texture close to the substrate surface. SEM/EBSD analysis shows that the surface layer of the film is mainly composed of NM martensite that is organized in variant groups. In each variant group, all the martensite plates consist of paired lamellar (112)_NM compound twins and there are eight orientation variants in each variant group.