Materials Science Forum Vol. 1016

Abstract: Shape memory alloys (SMAs) have the disadvantage that cooling is difficult and the actuating speed during cooling is slow. To resolve this problem, shape memory material actuators that operate only with heating is required. SMAs are characterized by a low apparent Young's modulus below the transformation temperature and a strong shape recovery force above the reverse transformation temperature. Alternatively, shape memory polymers (SMPs) have two properties: shape fixability and shape recovery. The SMPs are hardened below the glass transition (Tg) temperature and the material is recovered to memorized shape above the Tg temperature. The other hand, 3D printer is a machine that can directly output a 3D-designed product designed by a computer in 3D, and molded materials such as polymer, resin, metal, and ceramics. In this research, we developed the SMC of SMA wire and SMP sheet using adhesive that develops actuates into two shapes only by heating.

Abstract: In this study, the temperature increase of the Ti-17 alloy (Ti–5Al–2Sn–2Zr–4Cr–4Mo, wt.%) during isothermal forging in the (α + β) dual-phase region was investigated using large-size workpieces forged between hot dies in a 1500-ton forging press. The temperature increase was predicted using finite element analysis (FEA). The tip of a thermocouple was inserted into the center of the workpiece (diameter: 100 mm; height: 50 mm). The forging temperatures were 1023 K (750 °C) and 1073 K (800 °C) in the (α + β) dual-phase region. The strain rate was 0.05 s⁻¹ and 0.5 s⁻¹ at each temperature. Meanwhile, the compression percentage was 75%. The true stress–true strain curves were inversely obtained by fitting the load–stroke curves using the FEA. The predicted temperature was in a good agreement with that in the experimental results when the value of 1.0 was used as the conversion factor for plastic deformation energy to heat energy in the FEA under the current forging conditions. At the strain rate of 0.5 s⁻¹, the temperature instantly increased to a β-transus temperature in 3 s at 1073 K (800 °C). In contrast, the temperature logarithmically increased at both 1023 K (750 °C) and 1073 K (800 °C) at 0.05 s⁻¹ in 28 s (e.g., 42 K at 1023 K (750 °C)). The obtained true stress–true strain curves indicate that flow softening occurred during the forgings, which is attributed to dynamic recrystallization and/or dynamic recovery. The temperature increase in the Ti-17 alloy was smaller than that in the Ti–6Al–4V alloy under the same forging condition.

Abstract: We performed a systematic study of the crystal structure, physical properties, and electronic structure of PbFCl-type intermetallic APX(A=Zr, Hf, X=S and Se) superconductor. We successfully synthesized single-phase polycrystalline samples for the Se substitution range of 0.4≤x≤0.8 in Zr(P_2-xSe_x) using high pressure technique. On the other hand, S substitution range in Zr(P_2-xS_x) was narrow of 0.4≤x≤0.6, the S substitution range in Hf(P_2-xS_x) was narrow of x≈0.55, and the Se substitution range in Hf(P_2-xSe_x) was also very narrow of x≈0.4. Zr(P_2-xSe_x) exhibits a dome-like superconducting phase diagram for the substitution amount x. The superconducting transition temperature (T_c) is achieved at approximately x≈0.75 at which point the T_cis 6.3 K for Zr(P_1.25Se_0.75), 5.5 K for Hf(P_1.30Se_0.70), 5.0 K for Zr(P_1.325S_0.675), and 4.6 K for Hf(P_1.50S_0.50), respectively. T_cfor Zr(P_1.25Se_0.75) is increased from 6.3 K to 7.6 K by partially substituting a non-magnetic rare earth Sc atom for Zr. Single crystals of Zr(P_1.25Se_0.75) and partially substituted by Sc atom for Zr site of the ZrP_2-xSe_xwere also grain grown using high pressure technique. Plate-like single crystal with approximate edge sizes of up to 500 × 300 × 20 μm³for (Zr_0.50Sc_0.50)PSe nominal composition was obtained. T_c= 8.36 K was reached and the H_c1//c-axis(0) and H_c1⊥c-axis(0) roughly determined are 0.0045 T and 0.0038 T, respectively. Assuming the type-II superconductivity in dirty limit, the H_c2//c-axis(0) value of 1.33 T was also obtained. In this presentation, the crystal growth and physical properties of this APX(A=Zr, Hf, X=S and Se) superconductor has reported.

Abstract: Severe plastic deformation (SPD) with strong shear component is required to promote both grain refinement and texture randomization. When Asymmetric rolling (AR) is applied as asymmetric accumulative roll bonding (AARB), it enables the production of architectured microstructures and metallic composites. Finite element (FE) simulations of AR and AARB were employed to understand the influence of pass thickness reduction (PTR) on the through thickness variation of the velocity gradient. The influence of the PTR up to a total thickness reduction of 50% and the effect of a single 50% reduction step in a bi-layer bonding condition was analyzed. The influence of these process parameters on the strain and rigid body rotation components was compared with the experimental data obtained on an AA1050 aluminum. A better shear to compression ratio across the sheet thickness is achieved by PTRs lower than 30%; at a PTR of 50% the texture is dominated by the frictional shear generated at the roll-sheet interface and the process has a stronger compressive character. This indicates that simple ARB followed by AR with smaller PTRs should generate a better shear distribution than AARB alone.

Abstract: At present, to increase competitiveness of shipyards for manufacturing of shipbuilding parts new high technologies are used. Additive production methods, including direct laser deposition (DLD) technology, which meets all the requirements of competitiveness, are increasingly being applied. Heavy-duty large-size parts such as propellers, blades, hubs and other critical parts used in shipbuilding have become possible to produce with DLD. In the process of DLD it is possible to produce parts, including shipbuilding steels used in the Arctic conditions, with the required mechanical characteristics not inferior to similar brands of materials obtained by casting or plastic deformation methods. The work is devoted to research of thermal process influence on structure and mechanical properties formation of deposited samples from steel powder 06Cr15Ni4CuMo. Features of formation of microstructure components by means of optical microscopy, X-ray structure analysis (XRD) are investigated, and also CCT diagram is constructed. Tensile and impact toughness tests have been conducted. As a result, it was found that the material obtained by the DLD method in its initial state significantly exceeds the strength characteristics of heat-treated castings of similar chemical composition, but is inferior to it in terms of plasticity and viscosity. The increase of viscosity and plasticity up to the level of cast material in the grown samples is achieved during the subsequent heat treatment, which leads to the formation of the structure of tempered martensite and reduction of its content in the two-stage tempering in the metal structure. The strength of the material is also reduced to cast metal after heat treatment.

Abstract: Various high strength steel sheets for weight reduction and safety improvement of vehicles have been developed. TRIP-aided steel with transformation induced plasticity of the retained austenite has high strength and ductility. Conventional TRIP-aided steels are subjected to austempering process after austenitizing. Generally, elongation and formability of TRIP-aided steel are improved by finely dispersed retained austenite in BCC phase matrix. The finely dispersed retained austenite and grain refinement of TRIP-aided steel can be achieved by hot rolling with heat treatment. Therefore, the improvement of mechanical properties of TRIP-aided steel is expected from the manufacturing process with hot rolling and then isothermal transformation process. In this study, thermomechanical heat treatment is performed by combining hot rolling and isothermal holding as the manufacturing process of TRIP-aided steel sheets. The complex phase matrix is obtained by hot rolling and then isothermal holding. Although the hardness of the hot rolled and isothermal held TRIP-aided steel is decreased, the volume fraction of retained austenite is increased.

Abstract: Metals with a three-dimensional microstructure film can be joined to plastics by the anchor effect. The three-dimensional microstructure films can be electrodeposited by a Ni-Cu alloy. In this study, the effects of the ratio of the concentration of Ni amidosulfate and Cu sulfate in the plating solution and plating current density on the shapes and microstructures of electrodeposited films were investigated. When the ratio of the concentration of the Ni amidosulfate and the Cu sulfate is 0.47-1.4:0.06 (M/L), a dendritic-type electrodeposited structure was generated at plating current density of 10 mA/cm². When the ratio of the concentration of the Ni amidosulfate and the Cu sulfate is 0.47:0.6-1.2 (M/L), a feathery-type and needle-type electrodeposited structure was generated.

Abstract: Improvement of fuel efficiency and reduction of carbon dioxide emission are important issues in the automotive and aviation industries. To achieve these issues, materials that are lightweight and have excellent heat resistance are required. For this reason, various alloys have been proposed. Among them, TiAl intermetallic compounds have excellent low specific gravity and high strength at high temperature. However, TiAl is difficult for machining and easily oxidized, so casting is difficult. For this reason, a method using reaction sintering has been studied, though it is difficult to obtain low oxygen concentration TiAl alloy powder. Therefore, the process to produce TiAl parts from Ti powder and Al powder is studied. However, in this method, when a mixed powder of Ti and Al is sintered, a phenomenon called ignition with a rapid temperature increasing may occurs, and ignited parts are swelling and becomes high porosity.

Abstract: MoSi₂/Mo₅Si₃ eutectic composites have been considered as one of the promising candidates for ultra-high temperature structural applications owing to their high melting point, good oxidation resistance, and low mass density. Their mechanical properties can be improved by controlling the eutectic structure (i.e. script lamellar structure) in directional solidification. It is important to elucidate the dominant factors underlining the unique pattern formation. We conducted a comprehensive phase field study to examine the influence of various factors on the MoSi₂/Mo₅Si₃ eutectic microstructure with complicated morphology. First, the inclined lamellae have been attributed to the minimization of elastic strain energy due to the lattice mismatch between MoSi₂ and Mo₅Si₃, which are partially relaxed by forming semi-coherent phase boundaries. Second, the maze-like pattern on the horizontal cross-section appeared when a two-fold anisotropy of interfacial energy is superimposed on the MoSi₂/Mo₅Si₃ boundary. Third, the random and intersected lamellae have been obtained by assuming the instability of the solid-liquid interface and introducing successive nucleation of Mo₅Si₃ phase. These findings provide guidance for manipulating the eutectic structure and act as footsteps for further theoretical investigation.

Abstract: Electron beam melting (EBM) is one of the constantly developing powder bed fusion (PBF) additive manufacturing technologies (AM) offering advanced control over the manufacturing process. Development of the additive manufacturing today is targeting both widening of the available materials classes, and introducing new manufacturing modalities. Present research is related to the new possibilities in tailoring different properties within additively manufactured components effectively adding “fourth dimension to the 3D-printing”. Through manipulating beam energy deposition (scanning strategy) it is possible to tailor quite different material properties selectively within each manufactured component, including crystalline and amorphous state, effective material density, as well as mechanical, thermal, electrical and acoustic properties. With the blends of precursor powder, it is also possible to acquire by choice both metal-metal composite and completely alloyed material. Specific examples are given in relation to the EBM, but majority of the conclusions are valid for the other PBF techniques as well.