Cu-W Alloys Research Articles

FEM simulations of tensile deformation and fracture analysis for CuW alloys at mesoscopic level

Considering the mechanical properties and fracture mechanism of CuW alloys determined by microstructures, finite element method (FEM) is employed to analyze the mesoscopic model using Voronoi tessellation technology. Heterogeneous plastic strain and stress distributions are obtained at mesoscopic level in order to reveal the deformation process and fracture mechanism of CuW alloys. Shear bands or microcracks induced by shear band appear at the Cu/W and W/W interfaces mostly, and then propagate along the interfaces. Therefore, mechanical strength of CuW alloys is determined by sintering neck mainly. Additionally, the microstructures of fracture surfaces are applied to verify the simulation results.

Effect of Fe on vacuum breakdown properties of CuW alloys

CuW alloys with different Fe additions were prepared by the infiltration method. The microstructures of the CuW alloys prepared were characterized by a transmission electron microscope (TEM). The effect of Fe content on the surface erosion morphology was observed by a scanning electron microscope (SEM). The distribution of cathode spots was analyzed by a digital high-speed video camera. The results show that Fe addition can improve the relative density and thermal conductivity of CuW alloy with less than 0.6 wt.% Fe. However, excessive Fe addition can deteriorate the relative density and thermal conductivity. TEM results show that Fe addition can promote the formation of CuW solution. The area and depth of the erosion pits on the surface of CuW alloy depend on the breakdown position. Fe addition can strengthen the interface bond of Cu and W, improve the arc stability and the division of the cathode spots and, thus, avoid the concentration erosion.

Alloying Effect of Ni And Cr on the Wettability of Copper On W Substrate

By the sessile drop technique, the wettability of Cu/W systems with the additions of Ni and Cr has been studied under vacuum atmosphere. Effects of Ni and Cr contents and wetting temperatures on the wettability and the wetting mechanisms of copper on W substrate have been investigated in detail. The results show that the wetting angles of Cu on the W substrate are decreased with an increase in the content of Ni or Cr, and also decrease with raising the wetting temperatures. SEM, EPMA, and X-ray diffraction have been used to analyze the interfacial characteristics of the CuNi/W and CuCr/W systems. The results reveal that there is a transition layer about 2–3μm in the interface of Cu-4.0 wt pct Ni/W, in which the intermetallic phase Ni4W is precipitated. As to CuCr/W system, no reaction occurs at the interface. The two factors are that the contents of Cr and Ni and the infiltration temperature must be chosen appropriately in order to control the interfacial dissolution and reaction when the Cu-W alloys are prepared by the infiltration method.

Synthesis and structural studies of the Cu-W alloys prepared by mechanical alloying

Cu-W supersaturated solid solutions have been prepared by mechanical alloying. Structural refinement due to mechanical pulverization apparently plays a critical role in the extension of solid solubility. The structure and stability of samples have been investigated by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy and differential thermal analysis.

Electronic structure of amorphous and disordered crystalline Cu-W alloys of similar composition

The electronic structures of amorphous and disordered crystalline transition-metal alloys of similar composition are studied with photo- emission experiments and self-consistent electronic structure calculations. The calculated densities of states are in good agreement with the observed photoemission spectra. The lack of long-range structural order in the amorphous system is reflected in the changes in its electronic structure compared to that of the crystalline disordered alloy.

Formation of Metastable Structures and Amorphous Phases in cu-w Alloys Using the Triode Sputtering Technique

ABSTRACTThe triode sputtering technique and a “split-target” arrangement were used to produce metastable crystalline and amorphous phases in the Cu-W system under essentially oxygen-free conditions. Large metastable extensions of solid solubility were observed both from the Cu (fcc) and W (bcc) sides of the phase diagram, and a wide range of metallic glass formation was observed, approximately between 30 and 65 at.% W. The thickness of the amorphous Cu-W phase (40–160 pm) that can be deposited without the formation of the metastable bcc phase appears to be dependent on the Cu-W alloy composition. On heating, the crystallization temperature of the amorphous alloys was higher than 350°C. The behavior of the lattice parameter and near-neighbor distance has been studied with x-ray diffraction, showing small positive deviations from an assumed Vegard's Law. Hardness measurements indicate that the metastable crystalline phases are relatively harder than the amorphous phase.

集電用Cu-Fe合金の油潤滑における耐摩耗性

Contact materials used in oil-filled tap changers for regulating the voltage of transformers or electric locomotives must be wear resistant, because the accumulation of particles produced from the wear of sliding contacts tends to cause a high voltage breakdown. The purpose of this investigation was to find out the most desirable pair of electro-conductive materials, which would make the oil-lubricated current collector maintenance-free for a long period of time.A series of wear tests were carried out with fourteen different materials contacted with a copper plate, using (a) a horizontal sliding type wear tester without current flowing, and (b) an actual high voltage tap changer for the electric locomotive with current flowing through the contacts.Materials tested were Cu-Fe cast alloys, Ag-W and Cu-W sintered alloys, aluminium bronze, manganese bronze, etc. The results are summarized as follows:(1) By measuring the weight loss and roughness of the worn surfaces, the group of Cu-Fe alloys, especially the one containing 40%Cu, were found to have excellent wear resistant properties, followed by Ag-W and Cu-W alloys.(2) The wear resistance of the Cu-Fe alloys was improved by heat treatments; by quenching and tempering, a hard contact material with relatively high conductivity was obtained. The microstructure of Cu-Fe alloys consisted of two phases, hard iron-rich phase and soft copper-rich one. The difference of micro-hardness between the two phases was enhanced by heat treatments. This was considered to account for the superior wear resistance of the alloys, particularly when heat-treated.When Cu-Fe alloys were contacted with Cr-Cu alloys, the total weight loss was much less than that when contacted with pure copper.