Papers by Keyword: Interface Reaction

Abstract: The effects of Si on the interfacial characteristics of Al-6.25 Si alloy/SiC and Al-11.12 Si alloy / SiC were investigated. The different compositions of aluminium and silicon carbide samples were prepared at various processing temperatures with constant holding time. The characteristics of interface between Al alloy and SiC were evaluated using tensile test and microhardness test. The interface morphologies were evaluated using scanning electron microscope and energy dispersive spectroscopy. The results shown that the interface fracture strength and microhardness values increased at the interface when Si concentration levels were increased.

Abstract: The reaction behavior and growth kinetic of reaction layer were investigated in the Ni contact to n-type 6H-SiC. Annealing was performed at temperature in the range between 800 and 1000 °C for 1 to 240 minutes in Ar atmosphere. The interface reaction of Ni/SiC starts with Ni diffusion into SiC. Ni3Si is initially precipitated and subsequently forms the continuous layer of d-Ni2Si. Kirkendall voids are formed at the reaction front. Carbon is segregated in the interface layer of nickel silicide. The growth rate of the interface layer follows a parabolic law, meaning that the growth rate is controlled by diffusion. The growth occurs in two steps at all examined temperatures: a fast growth is followed by a slow growth. In addition, in the late stage, the growth rate changes dramatically below and above 850°C. The observed growth kinetic can be explained by the difference of Ni diffusivity and the required concentration change for phase transition depending on the phase composition and structure. The d-Ni2Si is formed in the early stage, while the e-Ni3Si2 and q-Ni2Si are formed in the late stage below and above 850°C, respectively.

Abstract: The glass molding process is considered to have a great potential for the mass production of aspherical glass lenses with high precision and low cost. However, glass molding has a serious problem of mold sticking with glass which needs to be resolved. This research investigates the interface reaction between glass and mold by high temperature wetting experiment, which provides the reference for the designing anti-stick coatings. The SUMITA K-PSK200 optical glass gobs with low Tg were used in this study. The influence of operation temperature, ambient gas, substrate materials, and thin film composition on wettability of glass at high temperature were studied. The results show that the higher the temperature, the smaller the wetting angle between glass gob and substrate could be observed. This indicates that severe interface chemical reaction occured and resulted in the loss of transparency in glass appearance. The wetting experiment in nitrogen ambient improved the sticking situation. The combination of chemically stable substrates and coatings, such as Sapphire (substrate) / GaN (film) and Glass (substrate) / Al2O3 (film) can achieve the best antistick propose. The precious metal films, such as Pt, Ir, coated on the ceramic substrates can effectively reduce the interface reaction between the glass and substrates.

Abstract: A Nb-Si system in-situ composite Nb-16Si-24Ti-6Cr-6Al-2Hf(at%) was fabricated using vacuum arc melting method, and then was metallurgically reacted with four kinds of ceramics ZrO2, Y2O3 stabilized ZrO2, Y2O3, SiC+Si3N4 at elevated temperature. The microstructures in the interface reaction zones were investigated by SEM and EDS. The results showed that different extent chemical reactions between the composite and these four kinds of ceramics took place. It has been found that HfO2 riched layer formed near the interfaces between the Nb-Si in-situ composite and three ceramics of ZrO2, Y2O3 stabilized ZrO2 and Y2O3, and thickness of the reaction zones were about 100μm, 10μm, 1μm respectively. C and N elements in SiC+Si3N4 ceramic diffused to the composite at elevated temperature, and a new phase that rich of Ti, C and N elements appeared nearby the interface and accumulated inhomogenously. It may be concluded that the interface reactions of both ZrO2 and SiC+Si3N4 with Nb-Si composite were very violent, therefore they are not suitable as face-coat materials of shell molds for investment casting; the interface reaction of Y2O3 stabilized ZrO2 and Nb-Si composite was slighter than ZrO2 and SiC+Si3N4, and it can be used as face-coat material of shell molds, the interface reaction of Y2O3 and Nb-Si composite was very slight, and is recommended as an ideal face-coat materials of shell molds.

Abstract: Ag+-doped TiO2 films on stainless steel were prepared by a sol-gel method and their microstructures and compositions were studied with X-Ray Diffractometer, Scanning Electron Microscope (SEM) and X-ray Photoelectron Spectroscopy. It was shown that Fe atoms in untreated stainless steel react with Ag+ in the TiO2 film and form FeTiO3, which has an acicular crystal form under SEM observation. As a result, Ag+ in the film is reduced to the silver atom, which degrades the antibacterial property of the film. However, after an oxidization of the substrate, a layer of ferric oxide is formed, which reacts with Fe atoms that would otherwise react with and reduce Ag+, and then forms FeTiO3. Thus, the penetration of Fe atoms is stopped and Ag+ in the anatase-structure TiO2 film is protected from the reduction, which enhanced antibacterial property of the film.

Abstract: Dissimilar joining of Al alloys and steel was carried out using diffusion bonding process. The effects of Si and Mg contents of Al alloys and bonding parameters on the interfacial reaction were fundamentally investigated. While the reaction layers consisting of Fe-Al type intermetallic compounds (IMCs) formed at the interfacial region, in the joint with Al alloys including 1mass% Si or more a ternary Fe-Al-Si IMC layer formed at the Al alloy side. The growth of the reaction layers followed the parabolic growth low. A maximum joint strength was obtained at an average reaction layer thickness ranging from 0.5 to 1μm. The thicker reaction layer caused the fracture of the joints at a lower stress because of brittleness of the IMCs, and the thinner reaction layer including un-bonded interface also resulted in a low joint strength. As a result a thin and uniform reaction layer including less un-bonded interface can realize a high joint strength. Since the Fe-Al-Si IMC layer uniformly formed more rapidly than the binary Fe-Al IMCs in the joint with Al alloys including 1mass% Si or more, a higher joint strength was obtained at a thinner average reaction layer. As a result, it was found that the chemical compositions of 6000 series Al alloy controlled to be Mg (0.6 to 1.0mass%) and Si (more than 1.0mass%) were appropriate to obtain the better bonding characteristics.

Abstract: To meet the requirements of weight-saving and low-cost production of components for future transport vehicles, the concept of multi-material mix is of increasing importance. In this context aluminum-iron compounds produced by means of compound casting are considered to be of particular importance. An essential and critical aspect of such compound castings is the formation of intermetallic phases (IMP) at the Al-Fe interface. Both the nature and the kinetics of potential IMPs are not well understood and require a systematic investigation. In this paper we document the interface formation of pure Al and binary Al-alloys on a mild steel substrate by means of isothermal wetting experiments. Tests were carried out employing the sessile droplet method in a controlled atmosphere. Using pure Al and Al7Si, Al7Cu, and Al7Zn alloys the interface reactions were investigated by quantitative metallography (LOM, SEM/EDX). Special attention was paid to the influence of the alloying elements on the type and sequence of IMPs at the interface.

Abstract: An influence of a surface finish of a Cu electrode on joint properties of a lead-free solder joint with Sn-3mass%Ag-0.5mass%Cu has been investigated. As the surface treatment method, Ni/Au electroplating, Au electroplating and organic solderability preservative (OSP) treatments were conducted to Cu electrodes. A heat exposure treatment was conducted at 150°C up to 500h in order to investigate the reliability of the solder joint under heat exposure conditions. Ball shear test was performed to examine joint strength. Microstructural observation was conducted to investigate growth kinetics of a reaction layer formed at a joint interface and microstructural revolution in the solder layer.