Anna Wierzbicka-Miernik

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.

Kinetics of intermetallic phase growth and determination of diffusion coefficients in solid–solid-state reaction between Cu and (Sn+1at.%Ni) pads

The influence of nickel addition to tin substrate on microstructure, kinetics parameters as well as diffusion coefficients was studied on Cu/Sn diffusion couples. The results revealed that the presence of nickel did not affect the growth of Cu3Sn phase in comparison with that of the binary Cu/Sn diffusion couple. However, it substantially influenced the morphology and chemical composition of the (Cu1−xNix)6Sn5 phase, which grew with dual morphology and different chemical composition. The layer of the phase was poorer in nickel, whereas detached grains were richer in nickel concentration. The calculated kinetic parameters showed that the growth of the Cu3Sn and Ni-poor (Cu1−xNix)6Sn5 phases was controlled by volume diffusion, but in the case of Ni-rich (Cu1−xNix)6Sn5 phase, the growth was controlled by a complex mechanism. The calculations of diffusion coefficients and activation energies of Cu3Sn and Ni-poor (Cu1−xNix)6Sn5 phases revealed that the presence of nickel in the tin substrate did not affect the rate of formation/growth of those phases in comparison with the binary Cu/Sn diffusion couples.

Study of phase transformations in CMSX-6 and CMSX-8 superalloys

Nickel-based superalloys are extensively used mainly in the aircraft and aeronautic industry, particularly in the hottest parts of engines or turbo-reactors. The phase reactions occurring in these heat-resistant materials play a crucial role in many aspects of the processing and service of the highly alloyed materials. Cast Ni-based superalloys are obtained in a complex way and their structure is complicated. Differential scanning calorimetry (DSC) technique was applied for determination of temperature ranges of the phase transformations occurring in the CMSX-6 and CMSX-8 superalloys during heating/cooling processes. Thermophysical properties, including temperatures of the phase transformation, are the critical input parameters in mathematical models of solidification and casting of metallic materials. The literature data concerning phase transformations and performance of the heat treatment for CMSX-6 and CMSX-8 are incomplete and ambiguous. DSC results accompanied by scanning electron microscopy characterization of microstructure of CMSX-6 and CMSX-8 superalloy was applied. The present study will improve the understanding of the fundamental mechanisms of phase transformations of single-crystal nickel-based superalloys.

Microstructure, Chemistry and Mechanical Properties of the Ni/AgBiCuSn/Ni Interconnections

The paper presents results of electron microscopy studies on the microstructure, chemical composition and mechanical properties of the Ni/AgBiCuSn/Ni interconnections obtained due to the conventional soldering. The scanning (SEM) and (TEM) transmission electron microscopy combined with an energy dispersive X-ray spectroscopy allowed to reveal the presence of two intermetallic phases (Ag3Sn and Cu6Sn5) in the whole interconnection area for all the applied solders and soldering times. In the vicinity of Ni substrate both phases were modified with Ni (2-4.5 %at.). Some of Ag3Sn precipitates took the elongated shape and they were located across whole interconnection width. The SEM examination after shear test showed that the joints ruptured in a ductile manner, as manifested by the dimples present on the fracture surfaces. The dimples prove also that the plastic deformation occurred along the loading direction.

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.