F. A. Calvo

Special features of the formation of the diffusion bonded joints between copper and aluminium

A metallographic study of diffusion bonds between aluminium and copper has been made in order to further understanding of the mechanism of bond formation for joints between dissimilar metals that form intermediate phases or intermetallic compounds. A three-stage mechanistic model based upon sintering principles has been proposed to explain this kind of diffusion joint.

Diffusion bonding of Ti-6Al-4V alloy at low temperature: metallurgical aspects

The diffusion bonding of the Ti-Al-4V alloy at low temperature (850°C) has been studied. The principal objective of this investigation was the development of a diffusion bonding procedure suitable for Ti-6Al-4V alloy and capable of being used as part of a superplastic forming/diffusion bonding process. It was found that high-quality joints can be obtained by bonding at 850°C, with pressures of 4 MPa and times in the range 90–120 min. Mechanical properties of the joints were determined using cylindrical and plane test pieces. Tensile, shear and peeling tests were used to determine the strength of the joints. On bonding with the above conditions, the parent alloy strength was reached. Little reduction in these values was measured because the heat treatment was applied during bonding. A metallographic study by scanning electron microscopy and energy dispersive spectroscopy was performed to determinate the influence of the previous parameters on the microstructural changes that occur in the joint. Grain growth kinetics and ratio of bonding area were also studied. The results shows that a new method of diffusion bonding for Ti-6Al-4V alloy has been developed. This method can be carried out using lower bonding temperatures than in conventional processes.

Solid-state transformations during diffusion bonding of copper to iron

Solid-state bonding between dissimilar metals, produced at elevated temperatures with the application of a bonding pressure, causes structural changes in the microstructure of the zones nearest to the bond interface. These metallurgical transformations, produced by interdiffusion in the vicinity of the bond, decide the final properties of the joint. In the present paper, such diffusional transformations have been investigated for diffusion-bonded joints of Armco iron and copper with different oxygen contents (ETPC and OFLPC). The formation of iron oxide (wustite) has been observed in the ETPC-Armco iron joints. This oxide did not appear in OFLPC-Armco iron diffusion-bonded joints. This suggests that iron oxide forms by reaction of iron with oxygen dissolved in the ETPC base metal. The formation of copper particles in the iron base matrix, near the bond interface, has been observed. This may be due to two different processes: the solid-state precipitation of copper into iron and the eutectoid reaction (γ →ε +α) at bonding temperatures above 900° C.

Diffusion bonding of grey cast iron to ARMCO iron and a carbon steel

The microstructure transformations produced during the diffusion bonding of grey cast iron to pure iron (ARMCO iron) and to a hypoeutectic steel (0.55% C) have been studied. The indirect determination of the carbon concentration profiles has produced a diffusion equation that relates the microstructure of the bond interface to the bonding temperature and time. A new tensile test specimen is described; this specimen has a variable circular section which allows the determination of true tensile strength of dissimilar diffusion bonds. Metallographic and fractographic studies have shown that the optimum bonding conditions for both types of joint are a bonding temperature at 980° C, for 5 min at a bonding pressure of 4.5 MPa.

Tensile strength of Armco iron-ETP copper diffusion bonds

Etude de la reaction chimique (precipitation du fer) lors des assemblages par diffusion. Caracterisation de la microstructure par microscopie electronique et par fractographie

Metallography of magnesium amalgams with peritectic microstructures

Abstract The microstructures of alloys that show peritectic formation of the compounds Mg 3 Hg and Mg 5 Hg 2 were studied after continuous cooling. Identification of phases present was performed by means of x-ray diffraction, microhardness tests, and differential thermal analysis.

Diffusion Bonding of Ti-6Al-4V Alloy: Metallurgical Aspects and Mechanical Promotes

This paper presents the results obtained on the diffusion bonding of Ti-6 A1-4 V alloy for aeronautical applications. It main objetive is the development of a new diffusion bonding procedure to produce joints in ti tanium alloys at lower temperature than the current methods.

Study by SEM-EDS of the in situ dynamic leaching of mercury ores

The present work studies the surface evolution of cinnabar, when it is leached with HBr acid for different conditions. The dynamicin situ test has been studied by scanning electron microscopy and EDS techniques. According to the acid condition, time, and temperature, the HgS presents different mechanisms of dissolution, and the results prove that the cinnabar does not present “memory effect”, as proposed by other authors.16

Formation of γ phase in the Ag-Sn system

Abstract The homogenization mechanism of a Ag-26.8 weight % Sn alloy which solifies by a peritectic reaction giving rise to a nonequilibrium γ phase has been studied. From annealing treatments for various times at different temperatures above the (γ + Sn) eutectic temperature it was established that the transfer of atoms of the eutectic phase to the γ matrix at the γ/liquid interface controlled the homogenization kinetics of the γ phase.

Precipitation of iron carbides in ferrite during diffusion bonding

Abstract Specimens of a steel (0.35% C) and a pearlitic cast iron (C.E. = 4.3%) were diffusion bonded to Armco iron by heat treatment at 880°C for times ranging from 10 to 30 min. The ferrite phase of Armco iron became enriched with carbon from the steel, or from the cast iron, and eventually part of it was transformed to austenite when the carbon content was sufficiently high. At room temperature, two well-defined zones were delineated. One was adjacent to the junction with a ferrite-pearlite structure, indicating that diffusion of carbon was sufficient to form austenite. The other, next to the first, was formed by large ferrite grains containing grain boundary and intragranular cementite precipitates of varying morphology (spherical, acicular, or dendritic).