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Influence of surfactants on microstructure and corrosion resistance of Ni/Al2O3 coatings

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Composite coatings are one possibility to increase the durability and performance of materials for different applications and protect them from detrimental effect of the environment. Metal matrix composite reinforced with ceramic particles generally find wide range of engineering applications due to their enhanced hardness, better wear and corrosion resistance when compared to pure metals or alloys [1, 2]. The most sought after method of producing these kinds of composites is electrodeposition, owing to its advantages like low cost and the operating temperature. Electrodeposition of metals reinforced with dispersoids (mainly oxides or carbides) is an important technique for production of functional coatings. Such coatings are required in different fields of industry including: machinery and various device construction, machining tools, automotive and aircraft parts etc. Nickel composite coatings containing ceramic particles are used as protective coatings [3]. The plating bath for electrodeposition of Ni/Al2O3 composite coatings is frequently used a standard Watts solution with addition of alumina powder. The amount of ceramic particles incorporated into nickel affects the microstructure and properties of electrodeposited nickel composite coatings. The structure and properties of composite coatings depend not only on the concentration, size, distribution, and nature of the reinforced particles, but also on the type of used solution and electroplating parameters (current density, temperature, pH value etc.) [1, 4]. Although the Ni/Al2O3 composite coatings have been improved significantly, certain problems persist with respect to their preparation. The volume content of alumina particles in Ni/Al2O3 coating cannot be controlled quantitatively and the particles are frequently agglomerated in the composite [5]. The small inert particles like nanoalumina are difficult to embed into deposited layer because of their dispersion difficu[...]

Microstructure and kinetics of intermetallic phases growth in Ag/In/Ag joint obtained as the result of diffusion soldering

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Environment protection and improving the quality of joints are two main bases of the present development of modern technologies of different materials joining. The environment protection trend came into being in the 1990’s in the USA and later it also spread over Europe and Japan. The main aim is working out soldering materials able to replace the Sn-Pb solders commonly used so far. This can be obtained by eliminating cadmium and lead which are the components of soft solder used in conventional soldering process. Additionally, RoHS 2002/95/EC directive of the European Parliament and Council of January 27, 2003 orders the member countries to limit the use of some hazardous substances in electrical and electronic equipment. Soon another directive was issued: WEEE 2002/96/EC - Waste Electrical and Electronic Equipment referring to the problem of the used up electrical and electronic equipment and its reusing, recycling, and other forms of recovery. It imposes the responsibility for storing and recycling hazardous substances on the manufactures. Hence, a lot of information concerning new methods of joining materials can be found in the literature. The electronic industry is a good example. Assembly line production of circuits of high integration scale with many units sensitive to high temperature and joined in a very short time enforces applying a special soldering process so that the solder area is as small as possible. Diffusion soldering meets such requirements. The joint made in this way takes up 6 times less space than in the case of conventional soldering and it can work at the temperatures higher than 350°C [1, 2], and it often shows mechanical and thermal stability at temperatures 2÷3 times higher than the joining temperature. Moreover, the surfaces to be joined do not require special preparation, which remarkably shortens the production time [3]. The example here could be circuits on the basis of SiC and semiconduct[...]

Structural investigation of Mg-3Ca, Mg-3Zn-1Ca and Mg-3Zn-3Ca as cast alloys

  Magnesium alloys made of Mg-Zn-Ca system are interesting, because of possible application as bioresorbable cardiovascular stents or orthopaedic implants [1÷3]. During the last ten years, rapid growth of research in the application of magnesium and its alloys as biomaterials has been observed [4÷6]. Usage of magnesium based bone implants instead of those made of titanium or steel allows to avoid the removal surgery. Mg is the lightest of all structural metals with density close to those typical for cortical bone (1.75÷2.1 g/cm3). Other material parameters, like Young’s modulus (~45 GPa) are also similar [3]. Moreover, Mg is considered as biocompatible and non-toxic material and has been shown to increase the rate of new bone formation - it is an important ion in the formation of the biological apatites [3]. It was reported that the adult person normally consumes about 300÷400 mg of magnesium every day and an excess of Mg2+ is excreted through the urine [7, 8]. Magnesium is a cofactor for many enzymes and stabilized the structures of DNA and RNA [7, 8]. It is worth noticing that calcium and zinc are also recognized as biocompatible elements [1, 9]. A lot of studies have been performed on rare elements or/and Al containing alloys [10, 11], but these additions increase the cost of possible implant, and biocompatibility of RE is doubtful. An addition of Al can influence human nerves and induces Alzheimer disease [12]. From the metallurgical point of view, alloys made of Mg-Zn-Ca system can undergo solid-solution hardening and Ca is believed to be an effective grain refiner [13÷15]. In spite of possible benefits from magnesium based bone implants, there are a few important questions, which remain open up to date. There are problems with precise control of corrosion rate, which is usually very rapid and connected with hydrogen evolution. Rapid release of H2 in a high amount may cause inflammation process or even death [16]. Thu[...]

Microstructure and mechanical properties of the Cu/SnAuCu/Cu joints

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The European Union regulations forced the manufactures to limit the use of certain hazardous substances such as cadmium and lead in the electrical and electronic equipment and also make them responsible for its storage and recycling [1, 2]. In a consequence the lead-free interconnection technology is one of the most active branches of the nowadays materials science. PbSn replecements are mainly the tin alloys, among which a special class are those consisted of tin and noble metals such as copper, silver and gold. They are possesing two characteristic features - the high melting point and high concenteration of Sn compared to that of eutectic PbSn. Moreover, the composition of the lead-free solders can be described as eutectic or near-eutectic, which ensures the best manufacturability. The microstructure of these solders is a mixture of tin and the intermetallic phase (IP). Since both mechanical and electrical properties of the tin are anisothropic they are also anisothropic in the case of eutectic solders. Therefore, the intermetallics may take a form of the inhomogenous structures (for example Ag3Sn in the shape large plate-like crystals). To avoid of such IP creation the concentartion of silver in SnAg solder should be less than 3% wt. and copper should not go over than 0.7% wt. in SnCu solders. In the case of SnAu solders gold must not exceed the value of 5% wt. otherwise it leads to the formation of AuSn4 phase which causes britlle “cold" joint. Ternary solders are mainly SnAgCu solders (SAC) where the amounts of silver and copper (corresponding to the eutectic composition) are 3.5±0.3 and 0.9±0.2 (wt. %), respectively [3÷5]. Other ternary solder is SnAuCu alloy which may be used as a joining material for the joints in so-called noble electronics. They are applied in devices with the highest degree of reliability, such as biomedical devices. It should be noted that such products after their exploitation und[...]

Effect of MgO single crystal orientation on microstructure of reaction products formed in liquid Al/MgO couples

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Aluminium is a common alloying addition in many industrially important high temperature alloys, while MgO is either main constituent or sintering aid in advanced refractories used in melting and casting of such alloys. Thus information on reactivity in Al/MgO system is of a great practical importance. Furthermore, knowledge on interaction at the Al/MgO interface is vital for understanding the mechanism of in-situ synthesis of DIMOX (Direct Matrix Oxidation) type composites, i.e. Al-Al2O3 [1, 2]. The early wetting experiments [3?€6] performed in vacuum with Al/MgO system showed that liquid Al reacts with MgO to form inside the substrate a thick reaction product region (RPR). Both its thickness and structure were found to depend on substrate structure (monocrystalline or polycrystalline, crystallographic orientation). Mcevoy et al. [3] suggested the formation of MgAl2O4 inside the RPR, while Fujii and Nakae [4] reported Al2O3. However, the more recent study of the group led by Fujii [5] clearly evidenced that both MgAl2O4 and Al2O3 phases can be formed. Simultaneously, they claimed that the type of alumina formed in RPR depends on the substrate orientation, i.e. ?ż-Al2O3 for (100) MgO and ?Č?Ś- ?Č- and ?Â-Al2O3 for (110) MgO and (111) MgO, respectively. Our experiments involving [100], [110] and [111] MgO substrates showed that in all cases, the reaction starts with the formation of Al2O3 separated by Al channels [6?€8]. Only in later stages, locally the layer composed of MgAl2O4 and Al starts to form as well [6, 7]. The analysis of the electron diffraction patterns acquired from the Al2O3 crystallites indicated that they were always of the same corundum ?ż-Al2O3 type, independently of substrate orientation. The characterization of RPR microstructure in the Al/MgO is as important as phase identification but the former so far gained much less attention. The early investigation performed with the help of optical micros[...]

Microstructure and chemistry of Pb-Sn solder/ENIG interconnections

  The recent directive of EU concerning the restriction of the use of certain hazardous substances, like lead, in electrical and electronic devices, does not apply to such an equipment as missiles, battlefield computers, satellites space probes, computers installed in aircraft, production and processing lines cranes, lifts, conveyor transport, cars, commercial vehicles, aircraft, trains, boat systems, hydraulic excavators, fork-lift road maintenance equipment, harvester, pacemakers, solar arrays and watt balances [1]. One of the very important issue is the plating system of electroless nickel with immersion gold (ENIG) which has been widely used to finish solder pads of printed circuit boards (PCBs), as well as ball-grid array (BGA) and flip chip substrates in many mentioned above devices [2÷4]. The goal of the present study was to provide more details about the microstructure and chemistry of the solder joints on ENIG finish obtained with widely used Pb-Sn alloy. EXPERIMENTAL STUDY Copper pad (35 m thick) with 4÷6 m of deposited Ni-P layer and 0.075 to 0.125 m thick plating of immersion gold was covered with Pb-Sn solder paste (Alpha Metals, 62Sn36Pb2Ag, wt %). The Pb-Sn/ENIG samples produced in such a way were subjected to the sessile drop method by contact heating procedure described in [6] at 503 K for 5 minutes. Then, samples were crosssectioned and examined using the FEI E-SEM XL30 Scanning Electron Microscope (SEM) equipped with the EDAX energy X-ray dispersive spectrometer (EDS). The thin foils for the transmission electron microscopy (TEM) observations were all cut using the Quanta 3D Focused Ions Beam (FIB). The TEM studies were performed on the TECNAI G2 FEG super TWIN (200 kV) microscope equipped with High Angle Annular Dark Field (HAADF) detector integrated with the EDS manufactured by EDAX. RESULTS AND DISCUSSION The SEM image of the cross-sectioned plating after interaction with Pb-Sn so[...]

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