Materials Science Forum Vol. 941

Abstract: Advanced materials such as aluminum alloys and composites offer great potential for weight reduction applications in automotive and aerospace vehicles construction. In order to investigate the feasibility of using such materials in the form of laminates, sheet bulging with single-layer aluminum and the aluminum/Composite laminate with the carbon cloth as the middle layer is investigated under uniform liquid pressure conditions. The aluminum sheet stress-strain, wall thickness distribution, carbon fiber radius stress-strain distribution and the effect of die entrance radius etc. are discussed and compared in details. FE results validate that the numerical method can predict the same fracture regions for bulging-blank as observed in experimental tests. Furthermore, the study validates that multi-layer sheet hydro-bulging process with composite fiber as a middle layer is not feasible to form laminates due to rupture of composite fibers near edge regions. Further study is needed to improve the methodology.

Abstract: We successfully synthesized Li_1+x-yM_1-x-3yTi_x+4yO₃ solid solutions (M = Nb or Ta, LMT, 0.07 ≤ x ≤ 0.33, 0 ≤ y ≤ 0.175) that have a superstructure. The materials formed a superstructure known as the M-phase, which is formed by the periodical insertion of an intergrowth layer in a matrix having a trigonal structure. The homogeneous and periodical structure of M-phase in LNT needed to sinter at 1393 K for 40 h-200 h using a conventional electric furnace. In order to form the homogeneous intergrowth layers rapidly, millimeter-wave or air-pressure control atmos furnaces were also used as smart processing techniques. We concluded that atomic diffusion was promoted in the useful reaction-fields: millimeter-wave radiation or high oxygen pressure.

Abstract: It is possible for lamination of metal and plastic plates to add functionality such as damping and thermal insulation while maintaining the specific strength. IF steel/polyethylene/IF steel laminates were fabricated by warm rolling at two rolling reductions in thickness of 40% and 50%, and strength of the laminates and textures of the constituent layers were investigated in detail. From the ODF measurement, when the rolling reduction is high, polyethylene was oriented not only to [100]//RD but also to [001]//ND, resulting in biaxial orientation. Tensile strength of the IF steel layer was about 9 times higher than that of the polyethylene layer, and that of the laminate was almost consistent with the calculated value by the rule of mixture. The IF steel layer with much higher strength showed isotropic tensile strength related to the γ-fiber texture of <111>//ND, although the polyethylene layer showed remarkable in-plane anisotropy resulting from the strong texture. As a result, tensile strength of the laminates was isotropic for both rolling reductions.

Abstract: Aluminum-Carbon nanoFibers (CNF) composites produce by stir casting process present a yield strengths (YS) and an ultimate tensile strength (UTS) improved up to 33%. The hardening of the Al-CNF composite was considered as the sum of elementary contributions of effects: natural hardness of pure Al; grain size; dislocation density; elements in solid solution; CNF. In order to quantify CNF effect, calculation was performed to quantify the contribution to yield strength of each other’s mechanisms. This theoretical calculation was compared to experimental results and the real effect of CNF on yield strength increase was estimated between 10 and 16%. Figure SEQ Figure \* ARABIC 1: Graphical Abstract (copper dots on CNF / stir casting process / contributions to hardening) Keywords: Aluminum matrix composite; copper-coated carbon nanofibers; liquid metallurgy elaboration; mechanical properties; hardening effect

Abstract: Dislocation densities of dispersion-strengthened copper with aluminum oxide, namely GlidCop were evaluated employing the X-ray line profile analysis using the modified Williamson-Hall and modified Warren-Averbach method. X-ray diffraction profiles for GldCop samples with compressive strains applied at ambient temperature were measured with synchrotron radiation. The dislocation densities of GlidCop with compressive strain ranging from 0 – 2.7 % were on the order of 1.5×10¹⁴ – 6.6×10¹⁴ m^-2.

Abstract: The production of high-temperature components is of great importance for the transport and energy sector. Forging of high-temperature alloys often requires expensive dies, multiple forming steps and leads to forged parts with large tolerances that require machining to create the final shape. Additive manufacturing (AM) offers the possibility to print the desired shapes directly as net-shape components. AM could provide the advantage of being more energy-efficient compared to forging if the energy contained in the machining scrap exceeds the energy needed for powder production and laser processing. However, the microstructure and performance of 3D-printed parts will not reach the level of forged material unless further processes such as hot-isostatic pressing are applied. Combining AM and metal forming could pave the way for new process chains with little material waste, reduced tooling costs and increased part performance. This study investigates the hot working properties and microstructure evolution of Ti–6Al–4V pre-forms made by selective laser melting and electron beam melting. The results show that both materials are hot workable in the as-built state. Due to its martensitic microstructure, the SLM material shows a lower activation energy for hot working than EBM and wrought material and a faster globularization during forming, which is beneficial for hot forming since it reduces the forming forces and tool loads.

Abstract: Functionally graded aluminium (Al) matrix composite materials reinforced with carbon nanotubes (CNT) and silicon carbide nanoparticles (nSiC) or nanodiamond (nD) were fabricated using a powder-metallurgical route. The nSiC and nD were not only used as a reinforcement but also as an active solid mixing agent for dispersing the CNT in the Al powder. Dual-nanoparticle-reinforced functionally graded multiple-layered composites were found to exhibit different mechanical characteristics. In particular, the hardnesses of the CNT-and nSiC-reinforced composites were dramatically increased, being up to eight times greater (330 HV) than that of bulk pure Al. In the case of the combination of the CNT and nD nanoparticles, the reinforced Al matrix composites exhibited the highest flexural strength (about 760 MPa). This functionally graded dual-nanoparticle approach could also be applied to other nanoreinforced systems, such as ceramics or complex hybrid-matrix materials. Keywords: Carbon nanotubes (CNT), nanosilicon carbide (nSiC), nanodiamond (nD), functionally graded materials (FGM), Powder metallurgy

Abstract: Regarding materials development, our studies have been mainly focused on ZrB₂-SiC and HfB₂-SiC compositions with TaSi₂ or Y₂O₃ additions using hot pressing and spark plasma sintering. These additives have been used to decrease the sintering temperature and to improve the oxidation resistance. Interesting mechanical properties at room and high temperature have been measured. Moreover, excellent oxidation behaviors have been observed up to 2000-2200°C with Y₂O₃. Last developments are centered on the manufacturing of ultrahigh temperature ceramic matrix composites (UHTCMC) using slurry infiltration and pyrolysis for example. First results are encouraging.

Abstract: The present study includes a detailed analysis of titanium based composite foam developed by powder metallurgy route and to understand the role of process parameters and the particle size of the space holder (cenosphere) on the kinetics and mechanism of wear. Cenosphere of varying particle size (<150 μm; 150-212 μm; > 212 μm) were mixed with titanium in a ratio of 1:3, compacted at 100 MPa and sintered at 1000°C and 1200°C for a period of 2,4 & 6 hrs in each temperature. The kinetics of wear and frictional coefficient of sintered composites were evaluated by reciprocating wear testing machine against diamond indenter at applied load of 10 N. The mechanism of wear was studied by a detailed analysis of the post wear microstructure. The composite foam with cenosphere particle size in the range of 150-212 μm showed minimum wear rate. The mechanism of wear was found to be a combination of adhesive and abrasive.

Abstract: In the present work, the Mg/Al bimetallic composites were successfully prepared by the lost foam casting (LFC) process, and the characteristics and formation mechanism of the interface of the Mg/Al bimetallic composites were investigated. The results show that a uniform and compact metallurgical interface with an average thickness of about 1400 μm was formed between magnesium alloy and aluminum alloy. The interface layer of the Mg/Al bimetallic composites was composed of three different reaction layers, namely the Al₁₂Mg₁₇+δ(Mg) eutectic layer adjacent to the magnesium matrix, the Al₁₂Mg₁₇+Mg₂Si interlayer and the Al₃Mg₂+Mg₂Si layer close to the aluminum matrix. The microhardnesses of the interface layer were remarkably higher than those of the magnesium and aluminum matrixes. The stress strength of the Mg/Al bimetallic composites was up to 47.67 MPa. The fractograph of the push out sample mainly showed a brittle fracture nature. The formation of the interface of the Mg/Al bimetallic composites was attributed to the fusion and diffusion bonding. With the variations of the concentrations of the different elements at the interface, the Al₃Mg₂ intermetallic phase first formed near to the aluminum matrix, and then the Al₁₂Mg₁₇ and Mg₂Si successively generated toward the magnesium matrix, finally obtaining the interface layer of the Mg/Al bimetallic composites.