Materials Science Forum Vols. 561-565

Abstract: AA6201 with main compositions of Mg-0.5 wt % and Si-0.5 wt %, is a typical electric conductive alloy which shows remarkable combination of high strength and high electric conductivity after heat treatment. Cold working and aging treatment process have a significant effect on its mechanical properties and conductivity. Shearing/Cooling Rolling process (SCR) was proposed to produce the feedstock for all aluminum alloy conductor. The effects of cold drawing on the properties of the alloy produced by SCR process were investigated. There are two methods used in the study, one is the cold drawing and aging heat treatment (CDAH) to produce the wires, the feedstock prepared by SCR and on-line solution, the other is the feedstock prepared by SCR and on-line solution-aging heat treatment plus cold drawing (AHCD). Results show that the AHCD can improve the properties of products due to sub-structural hardening. The tensile strength and equivalent conductivity of the alloy are 315 MPa and 55.03 % IACS respectively, and are much better than those characteristics of the alloy produced by the conventional process (295 MPa, 52.5-53.0 % IACS).

Abstract: Porous Ti6Al4V was attempted to be produced by using the protein forming method. This study characterizes slurry compositions and processing parameters aimed to obtain porous Ti6Al4V with open porosity, an interconnected porous networks and controllable pore size. Laboratory egg white powder was used as a binding and a foaming agent. A porous Ti6Al4V green body was produced through a gelling process at 80°C and a drying process at 120°C. A good strength porous Ti6Al4V specimen is available after a protein burnout process in an air atmosphere and a sintering process in a vacuum environment. Optical microscopy was performed on the porous Ti6Al4V specimens after each processing step to inspect their porous structure. Carbon and oxygen contents were also analyzed in the specimens during intermediate processing steps. Optimal temperature for protein burnout process is identified to be between 400°C to 450°C for an egg white concentration in the range of 6vol% - 24vol%. Pore sizes approximately 200–700 μm were observed after the sintering process. These experimental results demonstrate prospects on fabricating porous titanium and other metals using the protein forming method.

Abstract: In recent years there has been a considerable amount of research into the deformation behaviour of metallic foams. The majority of this research has only addressed size-independent bulk material properties, obtained through uniaxial compression and indentation tests of thick blocks. There is little information in the literature on the indentation response of thin panels, which has motivated the current study. Thin panels of ALPORAS closed-cell foam of ~ 0.25 g/cm3 density were tested in uniaxial compression, and were indented with long flat-plate punches and long cylindrical punches. Cross-sectioning of the samples following interrupted testing revealed the plastic strain evolution process. The deformation was attributed to the progressive crushing of the cell bands, and the combined action of shearing and tearing resistance. Based on energy formalism, a model was developed to estimate the crushing force. By fitting the experimental loaddisplacement curves, the foam ligament tearing energy was deduced for all types of indentation. The absorbed energy was also calculated for the uniaxial compression and indentation experiments.

Abstract: Al-Cu-Co and Al-Cu-Ni ternary alloy nanopowders were prepared via a self-developed solid-liquid reaction milling technique. The milling balls were made of the metals with highest melting point for each alloy systems. And the binary alloy melts of other two elements were used as raw materials. Formation regularities of Phases in the milling process were investigated and solid-liquid reaction mechanism of ternary alloy systems was discussed.

Abstract: A novel process, of melt infiltration combined with diffusion annealing technique, was developed to prepare Ti-Al intermetallics at temperature lower than ingot melting point. In this process, a porous Ti preform was firstly fabricated and the Al melt was reheated to temperature slightly higher than Al melting point to infiltrate the porous Ti preform by capillary force spontaneously. After long-time high-temperature diffusion annealing, Ti-Al intermetallic compound can be finally synthesized from the bulk Tip+melt Al via diffusion. As example, Ti-46Al intermetallics has been fabricated, and the microstructures and the phases of the as-synthesized intermetallics were characterized by XRD and SEM. The compressive behavior of the as-synthesized Ti-Al at elevated temperatures has been studied and the reaction mechanism involved in the process finally analyzed.

Abstract: The halide-activated pack cementation method was utilized to deposit silicide coatings on a multicomponent Nb-Ti-Si based alloy. The siliconized temperature was 1150 °C and the holding time was 10h. Both the specimens with siliconized coatings and without coatings were oxidized at 1250°C for 5, 10, 20, 50 and 100h respectively. The coating possessed a double layer structure with the composition of (Nb,X)Si2 (X represents Ti, Cr and Hf), and the outer layer was denser. The major structure in the outer layer was composed of columnar crystals perpendicular to the interface between the coating and the substrate, and that in the inner layer was mainly composed of equiaxed crystals. A transitional layer about 5μm thick was found between the coating and the substrate. After oxidation at 1250°C, the major constituents in the scale were SiO2 and TiO2 and the mole ratio of these two phases was about 2:1. The thickness of the (Nb,X)Si2 layer decreased and that of transitional layer increased as the oxidation time prolonged. The siliconized coating exhibited excellent oxidation-resistance at 1250°C within 50 hours.

Abstract: Dual two-phase intermetallic alloys composed of geometrically close packed (GCP) structures of Ni3Al(L12) and Ni3V(D022) containing Nb were investigated in terms of the microstructural evolution during low temperature annealing (aging) and the related mechanical properties. The eutectoid region, i.e. the prior Al phase (Ni solid solution) is composed of the lamellar-like structure consisting of Ni3Al(L12) and Ni3V(D022) phases. The lamellar-like structure tended to align along <001> direction and on {001} plane in the prior A1 phase (or the L12 phase). In a wide range of temperature, the dual two-phase intermetallic alloys showed high yield and tensile strength, and also reasonable tensile ductility, accompanied with ductile fracture mode.

Abstract: In order to expand a market share of TiAl turbocharger a second generation TiAl turbocharger was newly developed. The characteristic of this turbocharger is its improved turbine wheel material with excellent creep strength and its low cost manufacturing processes. The usable temperature of this turbocharger is higher than Inconel713C turbocharger, and the cost is much reduced compared with current TiAl turbocharger.

Abstract: A porous Ti-48.0at.%Al (Ti-rich TiAl) crystal, in which lotus-type long cylindrical pores were aligned and (γ/α2) two-phase lamellar structure was simultaneously developed, was fabricated by floating zone method under the pressure of hydrogen and helium mixed gas. Plastic deformation behavior and microstructure of the Ti-rich TiAl crystal with lotus-type aligned pores were investigated by focusing on the elongated pore direction. The as-grown and annealed crystals show a well-developed lamellar structure and no texture accompanied by 52% porosity and a mean pore diameter of 380 μm. Yield stress strongly depends on the loading direction against the elongated pore. When loading directions are parallel and perpendicular to the pore direction, yield stresses obey K=1 and 2.5, respectively, in equation of σ=σ0(1-p)K, where σ is the yield stress with pores, σ0 is the yield stress without pores and p is porosity. This reflects macroscopically homogeneous and locally heterogeneous plastic deformation between pores, respectively.

Abstract: The microstructures evolution of a new type Ni-base superalloy has been investigated after long-term aging at 750°C for 2000h. The results indicate that TCP, a harmful phase greatly affects the mechanical properties of the alloy, is un-precipitated in the aging process. γ´ phase is precipitated in two kinds of sizes during long-term aging. The shape of larger one is transit from spherical to cubic with prolonging of aging time. The M23C6 carbide formed mainly by Cr, and other elements such as Al, Ti, Co and Mo is also precipitated in both γ matrix and grain boundaries, and the quantities of the carbide increase gradually with the increasing of aging time.