Jaromír Drápala

Study of reaction diffusivity in the copper-indium-tin ternary system

Interaction of lead-free solders with copper substrate represents an important phenomenon in the issue of reliability of solder joints. New experimental data describing phase equilibria in the Cu-In-Sn system after long-time diffusion annealing at the 400 °C/50 hours, 600 °C/310 hours and 600 °C/48 hours will be presented. The composition of solders was: 100 % Sn, 75 % Sn + 25 % In, 50 % Sn + 50 % In, 25 % Sn + 75 % In, 100 % In. The fast quenching method was employed to freeze thermodynamic equilibrium after annealing, followed by metallography, microhardness measurements, SEM (Scanning Electron Microscope) and WDX (Wave Dispersive X-ray) analysis. New phase equilibrium data, together with the data from literature, represent the best existing experimental description of phase equilibria in the system in question. The obtained experimental results of the phase equilibria were compared with the thermodynamic modelling by the CALPHAD (Calculation of Phase Diagrams) method and with other authors.

Reactive Diffusion at the Contact of a Solid Phase with the Solder Melt

Problems of reactive diffusion at the solid phase and melt contact are studied theoretically. The rate constant is a fundamental parameter characterizing the dissolving rate at a certain configuration of experiment. Relationships between the solid phase dissolving rate, i.e. the solid phase interface boundary movement in the melt, and rates of growth of intermetallic phases in the metal (Cu) are observed. This procedure enables the creation of surface and subsurface layers of regulated thickness in metallic materials by means of reactive diffusion. The main intention was an experimental study of copper dissolving in melts of various solder alloys and the related reactive diffusion. We used Sn, SnCu, SnAgCu, SnZn and SnIn alloys as a solder material. The problems that need to be solved preferentially are emphasized. It concerns especially the determination of the rate constant of dissolving and verifying whether the proposed model equations can be used for this constant determination in cases of cylindrical and planar dissolving. Rapid growth of phases in the metal (Cu) and determination of the thickness of layers with these phases pose considerable time demands to X-ray microanalyses (WDX, EDX, BSE, SEM) of specimens after their long-time heating.

Effect of Ti and Fe Alloying on Kirkendall Voids Feature in Ni/Ni3Al Welded Joints after the High Temperature Annealing

The study of influence of Fe and Ti alloying elements in the Ni3Al intermetallic alloy on diffusion feature in Ni/Ni3Al-Me (Me = Fe or Ti) joints was performed using the diffusion couple technique. Four sets of diffusion couples of diverse compositions prepared by means of resistance welding or electron beam welding in vacuum were used. The concentrations profiles and diffusivities of welded Ni/Ni3Al-Fe and Ni/Ni3Al-Ti joints were determined after annealing at 1050°C for 100 hours. The concentration profiles were smoothed using suitable types of polynomials. The Kirkendall voids in the area between the Matano plane and the new  interface created after annealing were observed. Metallographic study and qualitative evaluation of voids by means of AFM method revealed different feature of Kirkendall regions in Ni/Ni3Al-Fe couples unlike Ni/Ni3Al-Ti joints.

Development of Titanium Based Biocompatible Materials with Controlled Porosity

This paper is dedicated to the development and optimization of the porous titanium materials suitable for biomedical usage in traumatology. Main aim of the presented research activities is focused on preparation of biocompatible titanium based materials with controlled porosity. It was found that titanium specimens with total porosity approximately 40 % revealed mechanical properties very similar to those of human cortical bone. Two-layer specimens with controlled porosity were prepared and tested by electron microscopy for post-sintering cracks. All tested specimens with controlled porosity were cracks free. Future works will include preparation of geometrically more complicated shapes, machining and in vitro cells proliferation testing.

Study of Fracture Feature of Titanium Based Alloys for Biocompatible Implants after Removal from Human Body

The study of microstructure and fracture surfaces was performed on specimens of reconstruction plate, reconstruction nail and elastic nail. The composition and phase analysis of microstructure was performed by scanning electron microscope (SEM) JEOL JSM - 6490LV equipped with EDS INCA X - ACT probe. Examination of fracture surfaces by SEM confirmed that damage was not simply due to fatigue but contained evidence of corrosion and mechanical fretting as well.

Study of macro- and micro-segregation of iridium in molybdenum single crystals after electron beam zone melting

Abstract The aim of the work was to study the creation of micro- and macro-segregation of iridium in low-alloyed molybdenum single crystals after electron beam zone melting (floating zone technique) depending on various conditions of crystallization. In order to evaluate relations between the chemical inhomogeneity and structural defects and their influence on properties of single crystals, the dependence of concentration and character of distribution of admixtures under various crystallization conditions on the origin of concentration undercooling and dislocation substructure of molybdenum single crystals prepared by electron beam floating zone melting was experimentally investigated.

Reactive Diffusion at the Cylindrical Dissolving of Copper in the Solder Melt

Problems of reactive diffusion at the solid phase and melt contact were studied theoretically and experimentally. The main intention was to calculate the time course of the solid phase dissolving in the case of cylindrical dissolving. These calculations were carried out on the assumption for the rate constant of dissolving K = const. In our work we give heed especially to the dominating process, which is the solid metal A dissolved in the melt B. During the dissolving the melt B saturates with the metal A and the process is influenced by convections which are characteristic for the given experimental configuration. A theoretical description of the kinetics of the solid phase dissolving in the melt will be presented for the case of cylindrical dissolving. The aim is to derive a relation for the interface boundary movement c(t) in dependence on time and a time course of growth of the element A concentration in the melt B. There are problems with accurate determination of the interface boundary movement after certain heating times of specimens, when it is observed experimentally, since intermetallic phases create in the original A metal at both the diffusion and cooling and some phases segregate at the solidifying melt cooling. The main intention was an experimental study of the copper dissolving in the tin melt. Experiments aimed to the determination of the Cu wires (diameters from 0.5 to 3.5 mm) dissolution in the solder melt were carried out at various selected temperatures and times. Rapid growth of phases in the metal A and determination of the thickness of layers with these phases pose considerable time demands to X-ray micro-analyses (WDX, EDX) of specimens after their long-time heating.

Reactive Diffusion upon Planar Dissolving Copper in Solder Melts

Problems of reactive diffusion at a solid phase - melt contact were studied theoretically. The main intention was to calculate the time course of the solid phase dissolving in the case of planar dissolving. In our work we give heed especially to the dominating process, which is the solid metal A dissolving in solder melt B. During the dissolving, melt B saturates with metal A, and the process is influenced by convections which are characteristic for a given experimental configuration. A theoretical description of the kinetics of solid phase dissolving in the melt will be presented for the case of planar dissolving. The aim is to derive a relation for the interphase boundary movement (t) depending on time and a time course of growth of the element A concentration in the melt B. There are difficulties in accurate determination of the interphase boundary movement after heating of specimens for certain time intervals. It should be performed experimentally, since intermetallic phases are formed in original metal A both via diffusion and upon cooling and some phases segregate upon cooling of the solidifying melt. The main intention was to study experimentally the copper dissolving in melts of various solder alloys and the related reactive diffusion. We used pure Sn and Sn-Cu, Sn-Ag-Cu, Sn-Sb, Sn-Zn alloys as solder materials. Experiments aimed at the study of a Cu plate dissolving in the solder melt were carried out at various selected temperatures and times. The problems of reactive diffusion were studied both theoretically and experimentally and the problems that have to be solved preferably were emphasized. Concentration profiles of elements and thickness of layers of phases can be determined with SEM and X-ray microanalyses (WDX, EDX) of specimens after their diffusion heating.

Computer simulation of diffusion processes with moving interface boundary

The solution of the diffusion equation at the non-stationary boundary represents the so-called Stefan problem which can be solved by means of the thermal potential of a double-layer with the accuracy sufficient for description of diffusion phenomena. The results were methods for determination of the mean values of the interdiffusion coefficients. The interface boundary shift and diffusivity in the diffusion joints can be determined very precisely from the areas below and above the concentration curve. The diffusivities in the Ni/Ni-Al and Fe/Fe-Mn diffusion joints were calculated from the experimental data using the balance equations that express the law of conservation of the diffusing material in the specimens and on the interface boundary. A new computer program (in Matlab) for the simulation of diffusion processes has been developed.

Study of the Reactive Diffusion in the Presence of Dissolution of Copper in the Solder Melts

In this work we give heed especially to the dominating process which is the solid metal A dissolving in the melt B. During the dissolving, the melt B saturates with the metal A and the process is influenced by convections which are characteristic for the given experimental configuration. A theoretical description of the kinetics of the solid phase dissolving in melt will be presented for the case of planar and cylindrical dissolving. The aim is to derive a relation for the interface boundary (t) movement in dependence on time and a time course of growth of the element A concentration in the melt B. There are problems with an accurate determination of the interface boundary movement after certain heating times of specimens, when it is observed experimentally, since intermetallic phases create in the original A metal at both the diffusion and cooling and some phases segregate at the solidifying melt cooling. The rate constant is a fundamental parameter characterizing the dissolving rate at a certain configuration. We present a theoretical description of dissolving of a long metallic cylinder submerged into a melt column and relations for the rate constant determination from the time of the whole metallic cylinder dissolution are derived. In our experiments were performed in which Cu was dissolving in the Sn melt for a Cu cylinder (wire) diameters 0.8÷2.5 mm and the rate constant K (T = 350°C) was determined. Relationships between the solid phase dissolving rate, i.e. the solid phase interface boundary movement (t) in the melt and rates of growth of intermetallic phases in the metal A will be observed. This procedure enables to create surface and subsurface layers of regulated thickness in metallic materials by means of reactive diffusion.