J. Wojewoda-Budka

Interactions between molten aluminum and Y2O3 studied with TEM techniques

Complementary structural characterization of the reaction product region formed due to high‐temperature interaction (1273 K) between molten aluminum and dense polycrystalline yttria substrate was performed. The reaction product region extending up to 1 mm into the oxide substrate was characterized by a wavy shape morphology and multilayer structure consisted of three‐layered zones. The application of transmission electron microscopy coupled with focused ion beam preparation technique allowed the detailed structural examination of reactively formed compounds and interfaces between different zones and phases. Fine crystalline precipitates of Al5Y3O12 (YAG) phase surrounded by the Al3Y were detected within the first zone. The second layer consisted of much bigger AlYO3 (YAP) crystals and the third one, which was the widest zone, revealed a typical C4 microstructure where elongated YAP precipitates accompanied the Al2Y metallic channels.

Influence of phosphorous content on microstructure development at the Ni-P Plating/SAC interface

Studies of the commonly used Ni-P surface finish of 4.3 and 11.6 wt. % of P content electroless plated on nickel substrates followed by their reaction with SAC305 solder were performed. It was demonstrated that the Ni-4.3P plating was crystalline, while the Ni-11.6P was mostly amorphous. The transformation of the Ni-P into Ni3P phase took place at 672 K and 605 K for low and high P amount, respectively. The activation energy (Ea) of the crystallization processes in the Ni-P plating was lower for the Ni-11.6P plating. Interaction of SAC305 solder with both types of the inspected plating showed the creation of (Cu,Ni)6Sn5 phase in the form of thin layer and large scallops, while for Ni-11.6P/SAC305 interface also (Ni,Cu)3Sn4 phase. The thickness of these phases was larger in the case of low phosphorous containing plating. The Ni-11.6P plating after the reaction with SAC305 totally transformed into Ni12P5, while the enrichment in P up to 10.5 wt. % occurred in the Ni-4.3P which did not lead to the appearance of any NixPy type phases. After the reaction of plating with solder the Ni2SnP phase was not identified. This was related to the absence of spalling phenomenon of the intermetallics into solder.

Microstructure Characteristics of the Reaction Product Region Formed due to the High Temperature Contact of Molten Aluminium and ZnO Single Crystal

Interface reactions between liquid aluminium and ZnO single crystal substrates of <1-100> orientation (at 1273 K under vacuum) were examined using scanning and transmission electron microscopy techniques. The substrates were subjected to the “pushing drop” tests when liquid is deposited from the capillary on the substrate surface and then, after appropriate contact time, it is pushed away. After short time of interaction with <1-100>ZnO substrate, three phases were detected: α-Al2O3, the alumina of unknown type and ZnAl2O4 spinel formed due to the solid state reaction between Al2O3 and ZnO.

Age Hardening of Mg-3Zn-xCa (X = 0, 0.5, 1.0) wt.% Alloys

Alloys of nominal composition Mg-3Zn-xCa (x = 0, 0.5, 1.0) wt.% were prepared by resistance melting and casting under a protective argon atmosphere. All specimens were examined by hardness tests during ageing at 175 °C. It was shown that calcium addition causes the increase in hardness. A detailed characterisation of microstructure of metastable phases has been carried out using transmission electron microscopy (TEM). Calcium addition resulted in much refined and more homogeneous distribution of the precipitates when compared with the binary Mg-3%Zn alloy. The age-hardening of the ternary alloy is attributed to the fine disc-shape plates lying on the basal plane of the matrix.

Microstructure of Ni/Al2O3 Electrodeposited Coatings Studied with XRD and SEM Techniques

Our interests are focused on the Ni/Al2O3 nanocomposite coatings electrochemically deposited in modified Watt’s-type baths into which α-Al2O3 nanopowder is added on steel substrates. The effect of different amounts of α-Al2O3 phase in the electrolyte baths on microstructure of electrodeposited Ni/Al2O3 coatings is investigated. In order to study the coatings the non-destructive X-ray diffraction techniques are applied. As indirect techniques, they are supported by imaging methods, especially scanning electron microscopy.

TEM investigation of reaction zone products formed between molten Al and CoO monocrystalline substrate

The research was aimed at microstructure characterization of the reaction products formed between molten aluminium and CoO single crystal during a sessile drop wettability test performed in vacuum at 700 and 1000°C for 120 min using contact heating procedure. The solidified Al/CoO couples were sectioned and used for cutting thin foils with focused ion beam. The transmission electron microscopy and energy dispersive X‐ray spectroscopy were used for microstructure and local chemical analysis. The interaction of molten aluminium with CoO substrate at 700°C caused the formation of a corrugated 10–40 μm thick reaction zone (RZ). It consisted of aluminium matrix and Al2O3 crystallites varying in size, i.e. of ∼0.2 μm near the Al drop/RZ interface, growing up to 1–2 μm at the RZ centre and very fine nano‐crystallites near the RZ/CoO interface. The reaction of aluminium with CoO at 1000°C produced much thicker RZ of ∼280 μm characterized by layered microstructure of alternating fine crystalline Al2O3 and coarser Al13Co4 layers. Moreover, at the RZ/CoO interface the presence of a cobalt layer was also identified.

Morphology and chemical composition of Ag/Sn/Ag interconnections

The main goal of the present contribution was to describe morphology and chemical composition of the intermetallic phases, which were formed during diffusion soldering process of the silver using tin. The Ag3Sn intermetallics is the main constituent of the joint after diffusion soldering at 235°C and 265°C. A closer inspection of the Ag/Ag3Sn interface revealed also the small crystallites of the second intermetallic phase, Ag5Sn, which was not previously observed using scanning electron microscope. Both phases are characterized by high melting temperatures: 480°C and 724°C, respectively. Therefore, their presence guarantees high thermal stability of the interconnection, which can be even three times higher than the temperature used for soldering.