Crystal structural refinement of the new compound TmAlB14

Single crystals of the new phase TmAlB₁₄ were grown using the high-temperature solution method. The crystal structure of TmAlB₁₄ was refined from X-ray powder diffraction data using the Rietveld method. The structure is of MgAlB₁₄-type with the space group Imma and unit cell parameters a = 5.8212(3) Å, B = 10.3837(2) Å and C = 8.1762(3) Å. The final, conventional R-valve and profile R-value are 0.031 and 0.064, respectively. The structure is characterized by a partial occupancy of both metal positions and a splitting of the thulium atomic position.     

Synthesis mechanism of titanium carbide nano-fiber during self-propagating high temperature synthesis

Titanium carbide nano-fiber was synthesized by self-propagating high temperature synthesis (SHS) method. The final products after the SHS reaction were titanium carbide containing excess carbon and metallic titanium, which were removed by additional leaching process. TEM observation revealed that the average diameter is about 20 nm. Neutron diffraction analysis was carried out to study non-stoichiometric number of the titanium carbide. The non-stoichiometric numbers of the titanium carbide were 0.89–0.94. The Rietveld refinement of each patterns converged to good agreement (÷2=0.49–1.34). The formation mechanism of the carbide is related to a liquid-solid reaction including the preferential diffusion process of carbon atom into liquid titanium. This article is based on a presentation made in the 2002 Korea-US symposium on the “Phase Transformations of Nano-Materials,” organized as a special program of the 2002 Annual Meeting of the Korean Institute of Metals and Materials, held at Yonsei University, Seoul, Korea on October 25–26, 2002.     

Measurement of drill point geometry by using laser sensor

Accurate measurement for the drill geometry is essential to drill design and reconditioning. In recent years, a number of non-contact drill measuring instruments, using CCD camera are reported in the literature. But these systems are not suitable in measuring three-dimensional surface, especially the concave ones. As an effectual remedy, a geometry measurement instrument using laser sensor is developed. This paper describes its configuration and calibration. In addition, the measurement method for a drill flute is detailed. Validity of the system and proposed method are demonstrated by an example. The deviations of the data measured from that inspected by using a microscope are no more than 0.0061 mm.     

Banding formation and eutectic lamellar growth in directional solidified Ni50Al20Fe30 alloy

Banding formation and eutectic lamellar growth in a directionally solidified Ni₅₀Al₂₀Fe₃₀ alloy were investigated. It was found that the banding area consists of two layers. The first layer is a γ layer, while the subsequent one is a γ layer. The composition of various phases around the banding area changes with the solidification process. The banding is formed by two steps process and caused by factors such as the fractions during the sample growth process. It was found that the band was found at relatively low growth rate. Therefore. this study indicates that increasing the growth rate is an effective method to eliminate the band formation. Eutectic lamellae nucleate and grow again after the banding formation. During the initial transition lamellar growth, the relationship between the square lamellar spacing, γ₂, and the distance from, the banding, d, can be described by the following equation: γ₂ = K [1-exp(A.d)] where K and A are constant.     

Cooling strategies for cryogenic machining from a materials viewpoint

This article discusses the cooling strategies for cryogenic machining from a materials viewpoint. It is argued that, because different materials respond to temperature and machining processes differently, different cooling strategies are needed to improve the machinabilities of materials by cryogenic machining. In this work, five workpiece materials such as AISI1010 low-carbon steel, AISI1070 high-carbon steel, AISIE52100 bearing steel, titanium alloy Ti-6Al-4V, and cast aluminum alloy A390 were studied experimentally at various temperatures. Based on the experimental results of the cryogenic properties of the materials and their known machining characteristics, the cooling strategies for cryogenic machining of these materials were analyzed.     

Oxidation Behavior of Rh–30Ni–18Nb Refractory Superalloy

The isothermal-oxidation behavior of Rh–30Ni–18Nb refractory alloy was investigated up to a period of 312 hours in air from 1000 to 1350°C. A comparison of the oxidation behavior of this alloy with a conventional Ni-base superalloy (Inconel 713 C) shows an order-of-magnitude higher oxidation resistance. This experimental alloy oxidizes by forming alternate layers of Nb₂O₅ and RhO while NiO is on the surface in contact with air. Optical and scanning-electron microscopy (SEM) was used to study the microstructure and morphology for the characterization of the oxides. Thermal stability of the alloy for extended periods of exposure to air at 1400°C was studied using transmission-electron microscopy (TEM).     

Mechanical Behavior and Evolution of the Lamellar Microstructure of Alloy VT9 as a Function of the Ratio of Axial and Shear Components of Hot Deformation

Results of a study of the effect of hot deformation under isothermal conditions under bicomponent (twisting + stretching) proportional loading with various ratios of the axial and shear components of the deformation on the mechanical behavior and evolution of the initial coarse lamellar microstructure and crystallographic texture in alloy VT9 are presented. It is shown that the ratio of the axial and shear components of the deformation is responsible for the degree of localization of plastic yield of the material and the fullness and intensity of transformation of the lamellar microstructure into a globular microcrystalline microstructure in the functional zone of deformed specimens.     

The Cd−Sm (Cadmium-Samarium) system

This program was supported by the Department of Energy through the Joint Program on Critical Compilation of Physical and Chemical Data coordinated through the Office of Standard Reference Data, National Bureau of Standards. Additional support was contributed by: Molycorp, Inc., Union Oil Co. of California, Los Angeles, CA; Reactive Metals and Alloys Corp., West Pittsburg, PA; Ronson Metals Corp., Newark, NJ; and Santoku Metal Industry Co., Ltd., Kobe, Japan. Literature searched through 1984. Professor Gschneidner is the ASM/NBS Data Program Category Editor for binary rare-earth alloys.     

Intermetallic phase formation in directionally solidified Al−Si−Fe alloy

The present study has been undertaken to better understand the solidification behavior of Al−Si−Fe alloys containing 7wt.% Si and 0.9wt.% Fe, with particular regard to the formation of phase during controlled solidification and influence of growth rates on intermetallic phase selection. The alloys studied were Al-7Si-0.9Fe alloys, which were produced by a modified Bridgman solidification arrangement. These alloys were solidified unidirectionally with different growth rates (1–30mm/min). The solidified microstructure of these alloys consists of the growth of primary aluminum and multiple second phase reactions.     

Anodic Dissolution of Nickel from the Individual and NiZn Intermetallic Phases in Acidic Sulfate Solutions. II. NiZn Intermetallic Compound

Comparative investigation of the anodic behavior of nickel in its own phase and in NiZn intermetallic compound in acidic sulfate solutions showed that the kinetics of anodic process is the same in both cases, but the partial anodic curve and the passivation potentials of nickel in NiZn phase are shifted in the negative direction by 140 mV. The passivation current is larger, and the dissolution rate of nickel from NiZn phase at the cathodic polarization is higher. The peculiarity of the behavior of nickel in NiZn phase is related to the activity of surface nickel atoms and the increase in the number of active sites of anodic dissolution. It is shown that introducing an electrochemically negative metal into an alloy can, under certain conditions, facilitate the passivation of the latter irrespective of the passivability of the former.