Papers by Keyword: Interfacial Reaction

Abstract: Brazing with active filler alloys containing some active elements, which promotes wetting of ceramics surfaces, is one of the most widely methods for joining ceramics to metals. The joints formed by brazing A12O3 to metal by using copper-titanium-nickel (Cu-Ti-Ni) as brazing filler were investigated. The metals/ceramics joints were produced at a vacuum level of 10-2-10-3 Pa at 1273K, using a constant holding time of 10 min. The surfaces were studied both morphologically and structurally using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD). In the brazing process, copper and titanium in the braze alloy form a series of reaction products. The formation of Ti3Cu3O and Ti2Ni at the interface is characteristic of these joints. The estimated free energies of formation of the Ti3Cu3O and Ti2Ni are -119kcal/mol and -245.92 kJ ~-263.78kJ/mol at 1200~1288K respectively. The highly negative values for the free energies of formation suggest that these compounds are thermodynamically stable.

Abstract: Metallic fibers (Fe-Cr-Si) with an excellent high temperature strength are expected to be use as a reinforced material of the engine piston head. However, the high reactivity of Al with most metals has disturbed the use of metallic fibers in aluminum composites until now. In this study, the influence of the reaction products at the fiber/matrix interface on high temperature properties of the composites was investigated by different solution treatment conditions. It is found that hardness and strength increase with an increase the solution treatment temperature (Tst). Reaction products (Al-Fe intermetallic compounds) resulting from solution treatments were formed along the fiber/matrix interface at 773 K or higher. The composites without interfacial reaction products (Tst=763 K) showed excellent rotating-bending fatigue life at 573 K. The fatigue crack propagation in this composite occurred at the necking region of the metal fiber because no cracks were observed in the interfacial reaction products.

Abstract: A novel Mg-based composites (Al63Cu25Fe12)p /AZ91 was prepared by pressure die casting protected by CO2/SF6 condition. The–200mesh quasicrystalline powders were poured into the molten AZ91Mg alloy and then rapidly stirred for 30 min in 720°C. The phases and phase transformation in the process of heat treatment for Al63Cu25Fe12 powder, and the reaction between matrix metal AZ91 and Al63Cu25Fe12 particle has been investigated using Scanning Electron microscopy (SEM) and Energy spectrum diffraction analysis technology（EDAX）. It is shown that i-phase decomposed in process of stir and the Cu atoms diffuse from powders into the matrix and combine with Mg and Al in the matrix, which produces metallic-compound dispersing along the grain boundary. The Mg atoms diffuse into the powders and substitute the Cu atom sites. After heated with solution and ageing, composites of (Al63Cu25Fe12)p /AZ91 is different from magnesium alloy, they need less time to get the ageing hardness peak. The mechanics properties of composites have been improved outstandingly by hot-extruded and treatment of solution and ageing, the tensile strength σb is from 189.54MPa up to 359.38MPa. However, because of their brittleness, the plasticity of composites decreased.

Abstract: The glass molding process (GMP) is regarded as a very promising technique for mass producing high precision optical components such as spherical/ aspheric glass lenses and free-form optics. However, only a handful of materials can sustain the chemical reaction, mechanical stress and temperature involved in the glass molding process. Besides, almost all of these mold materials are classified as hard-to-machine materials. This makes the machining of these materials to sub-micrometer form accuracy and nanometer surface finish a rather tough and expensive task. As a result, making mold life longer has become extremely critical in the GMP industry. The interfacial chemical reaction between optical glass and mold is normally the main reason for pre-matured mold failure. This research aimed to investigate the interfacial chemical reaction between various optical glasses, different anti-stick coating designs and several mold materials. The results showed that glass composition, coating design (composition, microstructure, thickness), environment (vacuum, air or in protective gas), reaction temperature and time could all have profound effects on the interfacial chemical reaction. Based on the results, a design developed specially for certain glasses is more likely to be the viable way of optimizing the effect of the protective coating.

Abstract: The intermetallic compound Nb3Al is widely investigated because of its high temperature strength, superior superconductivity and relatively small density. As Nb3Al has an extremely high melting point and lack of deformability, it is impossible to prepare it by using the conventional metallurgy. In this study, a Nb-Al intermetallic compound was prepared by multi-layered roll-bonding of elemental Nb and Al foils. The process consisted of the accumulative roll-bonding (ARB) for making a laminated Nb/Al sheet and the subsequent heat treatment promoting a solid-phase reaction in the laminated Nb/Al sheet. Accumulated foils were roll-bonded at 573 K. The rolling reduction at 1 pass was ~50%, and the final rolling reduction at 4 passes was ~94%. A pulsed electric current sintering (PECS) process was used for the subsequent heat treatment. The microstructures produced at each processing stage were characterized by X-ray diffraction (XRD), optical microscopy and scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS). A homogeneous intermetallic compound of Nb3Al could be obtained after the subsequent heat treatment for 1.8 ks at 873 K and for 0.9 ks at 1673 K.

Abstract: . Glass molding process is considered to have a great potential for the mass production of optical components with lower cost. Up to now, the service life of molding dies is still not satisfied. This study mainly focuses on the development of sol-gel derived Al2O3 coatings in order to extend the service life of glass molding dies. High temperature glass wetting experiment was carried out to investigate the high temperature interfacial reaction between the coatings and glass gobs. The 304 stainless steel were used as the substrate materials. The sol-gel coated Al2O3 was selected as the protective coating. OHARA L-BAL42 glass gobs were chosen as the test materials. It can be observed that very severe interfacial reaction occurs between stainless steel and glass at high temperature. The contact angle dramatically decreases from initial and then gradually approaches 25° at 825°C after 2 minutes holding time. The severe interface chemical reaction also results in the loss of transparency in glass appearance. The reaction products such as Zn and Ba are mainly from glass material. For the case of Al2O3 coated substrate, the variation of the contact angles varied from 152 to 138°, presents anti-sticking or non wetting behavior. There are no reaction products can be found on the glass contacted area after wetting test.

Abstract: In order to dominate the wetting behavior of molten Ag-Cu-Ti alloy and control the brazing reaction at the joining interface, CBN abrasive grains were brazed using the composite filler of Ag-Cu-Ti alloy and 8 wt.% TiB2 particles. Ag-Cu-Ti alloy without reinforcing particles was also applied in the current investigation to compare with the composite filler. The characteristics of the joining interface and the reaction products were examined using optical microscope, scanning electron microscope, and X-ray diffraction instruments. Finally, the morphology of the CBN grains on the working surface of the brazed abrasive tools was observed. Results obtained show that the composite filler containing TiB2 particles distribute uniformly in the filler layer. Moreover, the interfacial chemical reaction of CBN grains and Ag-Cu-Ti alloy is restrained when TiB2 particles are added. The sharp edges of CBN grains are exposed fully due to the decreased wetting behavior of the composite filler.

Abstract: The reaction between Sn-Ag (-Co) solder and electroless Ni-P plating was investigated in order to clarify the effect of the addition of Co to Sn-Ag solder on the formation of intermetallic compound (IMC) at the interface and the joint strength at the interface. Sn-Ag-Co solder was specially prepared. The results show that there is little effect of the addition of Co to the Sn-Ag solder on the IMC formation and the thickness of the IMC at the interface. For the pull strength of the solder bump joint, the addition of Co to the solder didn’t strongly affect the pull strength of the solder joints, but it affected the fracture mode of the solder joints.

Abstract: One of the major attributes of glass-ceramics is an ability to tailor their thermal expansion characteristics and this makes them ideal candidates for sealing to a wide variety of metals and alloys; however, during the sealing process, reaction of diffusing metal species with glass constituents may occur, and this can lead to the formation of undesirable phases within the interfacial region. In addition, diffusion of metal species into the bulk glass away from the interface may affect the overall crystallization kinetics and can result in the formation of unwanted crystalline phases which may be detrimental to the lifetime behaviour of a seal component. This contribution outlines and discusses the factors affecting the crystallization behaviour of glasses employed in seal manufacture and describe methods by which undesirable reactions can be alleviated or minimized through effective control of the process parameters and starting glass composition.

Abstract: The microstructure evolution and the growth behavior of intermetallic compounds (IMCs) at Sn-xZn-2Cu/Cu (x=6.5, 8.8, 10 and 12, wt%) interfaces during soldering were investigated. The results indicate that planar Cu5Zn8 layer is formed at each interface of Sn-8.8Zn-2Cu/Cu, Sn-10Zn- 2Cu/Cu and Sn-12Zn-2Cu/Cu couples for all soldering time. However, for Sn-6.5Zn-2Cu/Cu couple, it is Cu5Zn8 phase that formed at the interface within shorter soldering time (1 h and 4 h), but the interfacial reaction products become a double layer structure of Cu6Sn5 phase (near Cu substrate) and CuZn phase (near solder) for longer soldering time (25 h and 49 h). The thickness of IMC layers in all couples increases exponentially with the soldering time. It is also found that for the same soldering time, the thickness of IMC layers increases with increasing Zn content in the solder.