Zoltán Gácsi

Investigation of sintered and laser surface remelted AlSiC composites

Abstract The present work focuses on the microstructural characterisation of aluminium-base ceramic particle reinforced composites produced by powder metallurgy. Powder mixtures containing different quantities (5, 10 wt.%) and grades (F500, F800) of SiC particles as reinforcement constituents were uniaxially cold pressed. Afterwards the green compacts were sintered in a high purity nitrogen atmosphere. Dimensional changes of specimens occurring during sintering were controlled by dilatometry. Porosity measurements were performed on the polished cross-sections of sintered probes by an automatic image analyser. Laser surface treatments were also carried out on the sintered materials. The surfaces of the specimens were remelted using industrial CO2 laser equipment to achieve compacts with low porosity surface layer. The effect of laser-beam power, of amount and grain size of SiC particles on the remelting process and on the microstructure evolution was investigated.

The Application of Digital Image Processing to Materials Science

The modelling of three-dimensional structure of materials and the computer processing of micro-structure are applied, where the structure of materials is investigated by microscope. It is a relatively new interdisciplinary scientific field, the significance of which has gradually been increasing since the beginning of 1980s and today it has become one of the key field of researches of material structure. The present paper gives a short review about the theory of stereology, which is well founded mathematically. The relatively new fractal models are described from the microstructural models having a great significance from the point of view of materials science. The image transformations, the development of binary images and the binary procedures are illustrated by showing the practical tasks of materials science. The microstructure of metal matrix composites reinforced by carbon fibres, the possibilities of characterising the dendritic structure developing during the solidification of transparent materials, the characterisations of ceramic grains in the Albase composite are shown.

Color etching for characterization the grain orientation in spheroidal graphite cast iron

Color etching is a widely used technique for visualizing different phases in metallic materials. Its advantage to the traditional etching techniques is that it gives additional information within one phase, namely, the color shade of a given phase can change in a certain range. This paper demonstrates that, due to the physics of the color etching, the shade of a phase also depends on the crystallographic orientation of the investigated grain. As a test material, spheroidal graphite cast iron was used, and individual grain orientation was identified by automated electron back scattering diffraction (EBSD). Results showed that there is a strong correlation between grain orientation and the shades obtained by color etching.

The Effect of Melt Flow on the Dendrite Morphology

The anisotropy of dendritic structure is characterized in this paper. The direction of move of liquid/solid interface influence the velocity of the melt flow. In the course of the experiments the liquid/solid interface was moved in three different directions: i) at right angles to the direction of gravity vector, ii) in the direction identical with it and iii) in the direction opposite to it. Our purpose was to investigate the shape of solidifying dendrites as a function of the angle included by the gravity vector and solidification [6]. The measurements were done in real images fixed by us. The following parameters were chosen for characterizeing the anisotropy of dendrites: intersection number of the test lines and dendrite interface (P), orientation factor (), dendritic surface in volume (SV). The material was solidified by using an equipment developed by the authors. The solidification rate is a constant value: 0.001 mm/s and 0.003 mm/s, the composition of material used for modelling purposes is: SCN (succinonitrile) -2.5-3 mass% of acetone. 100 images were processed in each direction. It was necessary to rotate the images in order to count the number of intersections. A program developed by the authors was used for this purpose; the number of intersections was given by the program as a function of the angle of rotation, and the perimeter and area of the dendrites.

Solidification of Al-4wt.-%Cu Alloy under Non-Steady-State Conditions

In this paper the unidirectional solidification methods and the microst ructural investigation of Al-4wt.-%Cu alloys under non-steady-state conditions are reported. Influences of solidification process on the solidification parameters (temperatur gradient, solid/liquid interface velocity) and on the microstructure are investigated. After melt ing he samples were moved downward into the water located under the furnace at three different decelerations. A computerised algorithm was worked out for the calculation of solid/liquid interfa ce velocity and temperature gradient. These data were determined along the whole sample. The dendritic microstructure of samples formed during the solidification was analysed. The secondar y dendrite arm spacing, the dendrite trunk diameter and the volume fraction of the second phase (Al 2Cu) were measured by using the image analyser type Quantimet 500 Image Workstation.

Studying Pressure Induced Whiskers Formation from Sn-Rich Surfaces

Whiskers formed on the lead-free tin surfaces pose a serious risk to small electronic devices causing a short circuit and leading to the component/device failure. The present research was focused on the investigation of tin whisker formation on a motor control unit sockets made of tin coated copper, applying to the specimen mechanical load alone or together with heat treatment/electric current. Scanning Electron Microscopic (SEM) imaging was applied in order to study the microstructure of tin whiskers obtained, their length and number at the boundary of each imprint. If the mechanical stress increases from 1000 to 5000 MPa, the average number of whiskers and possible formation spots also increase from 570 to 1300. The length of whiskers varied from 3 μm after 0.5 h to 5.5 μm after 3 hours of exposition. It has been found that heat treatment at 150°C for 1 hour significantly reduces the number of whiskers (on average 6 times as few) formed. Therefore, the threat of failure of the electronic equipment is reduced.

Arrangement of the Al–Ni phases in Al/SiC(Ni)p composites

In the course of the production of Al/SiC composites made by powder metallurgical method, the interfacial bond between the reinforcing phase and the matrix is not acceptable in all cases. So the ceramic particles can suffer different kinds of damage by the stress which can mean the dropping out of the particles from the matrix, or their cracking. In order to improve the interfacial bond, the surface coating of the ceramic particles is recommended. One of the surface treatment methods is the electroless nickel plating (EN plating). The successfulness of the electroless nickel plating depends on the pre–treatment methods. By using the EN plated SiC particles in the Al/SiC composites, the nickel deposit of the silicon particles and the matrix can react with the formation of the different Al–Ni phases during the sintering. These phases were examined by scanning electron microscopy (SEM) and X–ray diffraction (XRD).

Copper Coating by Electroless Process for Aluminium Matrix Composite

The central problem of producing of Al/SiCP composites is to avoid the forming of brittle Al4C3, which leads to a poor corrosion resistance and degraded mechanical properties [Mingyuan, 1999]. The possible way is the covering of the SiC particles. This paper deals with the covering of SiC. The coated particles will be applied for producing aluminium matrix composites. We have covered three different grain sizes of particles. We have applied the nonelectrolytic method of deposition from solution for coating. Before the covering the surface needs to be catalysed. We have compared the effects of different type of catalysators, then we have analysed the effects of plating time by means of the scanning electron microscopy.

Investigating the microstructural and mechanical properties of pure lead-free soldering materials (SAC305 & SAC405)

Abstract The Sn–Ag–Cu (SAC) solders with low Ag or Cu content have been identified as promising candidates to replace the traditional Sn–Pb solder. In this study, an extensive discussion was presented on two major area of mechanical properties and microstructural investigation of SAC305 and SAC405. In this chapter, we study the composition, mechanical properties of SAC solder alloys and microstructure were examined by optical microscope and SEM and mechanical properties such as tensile tests, hardness test and density test of the lead solder alloys were explored. SAC305 and SAC405 alloys with different Ag content and constant Cu content under investigation and compare the value of SAC305 and SAC405. From this investigation, it was reported that tensile strength is increased, with an increase of Ag content and hardness and density were also increases in the same manner.

Microstructural investigations and mechanical properties of pure lead-free (Sn–3.0Ag–0.5Cu and Sn–4.0Ag–0.5Cu) solder alloy

The Lead-free solders (SAC) with low Ag content have been identified as crucial solder to replace the traditional Sn–Pb solder. The main discussion was presented in two major area of microstructural investigation and mechanical properties of SAC305 and SAC405. Composition and microstructure of SAC solder alloys were investigated by an optical microscope and SEM (Scanning Electron Microscopy). Mechanical properties such as tensile tests and hardness test of the lead-free solder alloys have been tested in this research. Different Ag content and constant Cu content of lead-free solder has been considered in this investigation and compare the mechanical properties of SAC305 and SAC405 solders. From this investigation, tensile strength and hardness have been increased with increased of Ag content.