Materials Science Forum Vols. 783-786

Abstract: The purpose of this study is to make the Ti-Ni-Zr specimen using casting method from P/M ingot and evaluates the shape memory behavior. All samples were square rod shape made by centrifugal casting. The size of all samples was 1 mm wide, 1.3 mm height and 37.5 mm length. The transformation behavior during cooling and heating was investigated using a differential scanning calorimeter (DSC). The phase constituent was determined by XRD analysis from 20 °C to 150 °C. Mechanical properties of the shape memory effects were measured using a tensile machine at 25 °C. The samples were annealed at 400 °C, 500 °C and 600 °C for 3.6 ks followed by water quenching. After annealing, specimens were cold rolled at 0 % (no rolling) and 10 %. The Ti-Ni-Zr square rod specimens are fabricated by centrifugal casting using P/M ingot. All samples had shape memory behavior. From DSC measurement, the highest reverse martensitic transformation temperature is 120 °C. From tensile test, the Luders like deformation stress were not constant and dependence of heat treatment conditions was not clarified. However, 10% cold rolling specimen, shape memory characteristics were stabilized.

Abstract: In recent years, an enormous pressure was put on the need to design and develop products that are compliant with the stringent environmental regulations set up various countries. Among the problems that need to be addressed is the need to design and develop environmentally friendly products that are energy efficient and easy to recycle. In this study, the effect of metal salt generation processing on the tensile strength of the bonded interface of Al/Al and Al/Cu was investigated by SEM observations of interfacial microstructures and fractured surfaces. Aluminum surfaces were modified by boiling in 5% aqueous solution of NaOH for 30 s and 98% formic acid for 60 s. Copper surface were modified by boiling 98% formic acid for 60 s. Solid-state bonding was performed at bonding temperature of 673 ~ 813 K and under a pressure of 6 MPa ( bonding time of 1.8 ks). Using metal salt generation bonding technique, the bonded joint is able to reach 0.2% proof stress at lower bonding temperature and with less deformation.

Abstract: Complex structural tubular components of Titanium and Magnesium alloy can be obtained at a certain temperature by high pressure pneumatic forming (HPPF) with gas medium or warm hydroforming with pressurized liquid medium. At 800°C, through experimental research on HPPF of TA18 Ti-alloy tube with expansion ratio of 50%, the influence of axial feeding on thickness distribution of the workpiece was studied. Using reasonable loading curve, the component with large ratio can be formed with a small thinning ratio as 13% with total axial feeding amount of 40mm. At 850°C, HPPF experiments of TA18 Ti-alloy component with square section were carried out. The influence of gas pressure on thickness distribution and corner filling process were analyzed. The larger the pressure, the sooner the displacement changes at the corner, and the shorter corner filling term. At pressure of 30 MPa, small corner with the relative corner radius of 2.0 can be obtained within 168s. For Mg-alloy tubular part, warm hydroforming with non-uniform temperature field was studied. By using reasonable axial temperature field and loading path, the maximum thinning ratio of Mg-alloy tubular component with expansion ratio of 35% was reduced from 21.6% to 11.6%.

Abstract: Diamond-particle-dispersed aluminum (Al) matrix composites consisting of monomodal and bimodal diamond particles were fabricated in spark plasma sintering process, where the mixture of diamond, pure Al and Al-5mass% Si alloy powders were consolidated in liquid and solid co-existent state. Microstructures and thermal properties of the composites fabricated in such a unique way were investigated and the bimodal and monomodal diamond particle effect was evaluated on the thermal properties of the composites. The composites can be well consolidated in a temperature range between 773 K and 878 K and scanning electron microscopy detects no reaction product at the interface between the diamond particle and the Al matrix. Relative packing density of the composite containing monomodal diamond particles decreased from 99.1% to 87.4% with increasing volume fraction of diamond between 50% and 60%, whereas that of the composite containing bimodal diamond particles was higher than 99% in a volume fraction of diamond up to 65%. The thermal conductivity of the composite containing bimodal diamond particles was higher than that of the composite containing monomodal diamond particles in a volume fraction of diamond higher than 60% and the thermal conductivity of the composite containing 70 vol.% bimodal diamond particles was 578 W/mK at R.T..

Abstract: The effects of Co on the strength of Cu-Ni-Co-Si alloys have been investigated using Cu-2.0wt%Ni-0.5wt%Si (0%Co), Cu-1.4wt%Ni-0.6wt%Co-0.5wt%Si (0.6%Co) and Cu-1.0wt% Ni-1.0wt%Co-0.5wt%Si (1.0%Co) alloys produced by combining cold rolling to a 25% reduction with aging. Aging the 0.6%Co and 1.0%Co alloys at 525 and 425°C produces orthorhombic (Ni, Co)₂Si precipitates that have the same crystal system as Ni₂Si precipitates formed in the 0%Co alloy. The larger the amount of Co in the three alloys is, the higher the strength and electrical conductivity of the alloys initially aged at 525°C, rolled to a 25% reduction and re-aged at 425°C become. The increase in strength with increasing Co content is caused by both of the decrease in inter-precipitate spacing and increase in dislocation density. The increase in strength by re-aging at 425°C becomes more pronounced as the Co content increases. This arises because the larger the amount of Co is, the larger the difference between the equilibrium solubilities at 525 and 425°C becomes, the more the volume fraction of precipitates is increased by re-aging at 425°C.

Abstract: Silicon is brittle and easily cracks even under a small load. The difficulty in shaping silicon has prevented breakthroughs in the mass production of silicon lenses for terahertz and infrared technology. We developed a novel method of deforming bulk single-crystal silicon into the required shape by one-shot pressing at a temperature just below the melting point of silicon, despite its brittleness and covalent nature, and realized the near-net shaping of the material into the plano-convex shape with the curvature radius R=7.5 mm for a infrared transmission lens. The crystallographic quality of the obtained lens could be improved by primary recrystallization. The simple method of 'pressing' will enable the mass production of not only silicon lenses but also lenses with a complex shape, such as aspherical lenses, and lens arrays by using dies with desired shape.

Abstract: In the Li2O-Nb2O5-TiO2 system, Li1+x-yNb1-x-3yTix+4yO3 (0.06  x  0.33, 0  y  0.09) (LNT) forms with a superstructure, which is the so-called M-phase. In this work, as a first step toward application of the unique qualities of an electro-ceramic with an anisotropic structure, we prepared an oriented LNT balk ceramic by slip casting in a strong magnetic field of 12 T. The direction of the magnetic field was parallel to the casting direction. The compact was densified by cold isostatic pressing and then heated at 1373 K. The obtained specimen was analyzed by X-ray diffraction, scanning electron microscope, and transmission electron microscope. Consequently, the c-axis of the LNT powders was aligned parallel to the magnetic field and a high orientation degree was achieved in a strong magnetic field of 12 T

Abstract: The materials used for fuel cell separators require a bending strength of more than 70 MPa. Therefore, the contact resistance is required to be 10 mΩ∙cm², respectively. In the present study, vapor grown carbon nanofibers (VGCF) were added to Ti composite using the compression shearing method at room temperature. The mechanical properties of the compacted powder were then measured. The microstructure of the Ti/VGCF composite material was Ti with dispersed VGCF (not alloyed). In addition, the bending strength of all Ti/VGCF composites was more than 800 MPa, and the bending strength of 0-1 vol% VGCF composites was twice as much as that for Ti rolled material (ASTM grade 2). Ti/VGCF thin plates also exhibited excellent electrical property. The contact resistance of 5 vol% VGCF was found to be three times smaller than that of Ti rolled material. These properties make the Ti/VGCF composite material suitable as a separator material.

Abstract: Superalloys have been developed for specific, dedicated properties and applications. One of the main application for this material is advanced, high-performance aircraft engines elements. Turbine engine creates harsh environments for materials due to the high operating temperature and stress level. Hence, as described in this article, many alloys used in the turbine section of these engines are very complex and highly optimized. This article provides an overview of structural changes that occur during the aging process of wrought and cast alloys and provides insight into the use of precipitated particles to achieve desired structures. Example will focus on alloy Inconel 718 and CMSX-4. Functional properties of these alloys can be achieved by choosing proper heat treatment parameters to obtain required rate between secondary phases. The paper also attempts to determine structural perfection and changes of crystallographic orientation along the axis of growth of single crystal nickel superalloys cast using X-ray topography and Laue diffraction method. Single crystal bars and turbine blades were manufactured in VIM furnace using the Bridgeman method. Withdrawing rates typical for CMSX-4 superalloy were used. It has been found that with increasing withdrawing rate the nature of distribution along the axis of growth of the angle of [001] direction deviation from the axis of single crystal blades growth had changed. The change of the withdrawing rate results also in the rotation of γ’ phase in the form of cubes against the axis of single crystal blades growth.

Abstract: Effects of Zr addition and annealing on the magnetostriction of Tb-Dy-Fe alloy crystals were investigated. The (Fe_1.9Tb_0.27Dy_0.73)_1-xZr_x (x: 0, 0.0125, 0.025, 0.05, 0.075) crystal fibers about 2 mm in diameter were grown by the micro-pulling-down (μ-PD) method. The grown crystals showed the low chemical segregation along longitudinal direction and the growth direction was oriented in the <311> direction. The saturation magnetostriction of the fiber increases with increasing the Zr content, annealing temperature and annealing time. The fiber-shape Tb-Dy-Fe crystals prepared by the μ-PD method are promising for the applications as sensors and actuators.