Interfacial reaction and strength of SiC fibres coated with aluminium alloys

Silicon carbide fibres (Nicalon) were coated with pure aluminium and aluminium alloys containing silicon. The coated fibres were annealed to produce an interfacial reaction zone between the coated layer and the fibre. The effect of this reaction zone on the tensile strength of the fibre was investigated. During the early stages of growth the reaction zone of the fibre is thin, and the strength of the fibre is controlled by inherent defects so that the fibre retains its original strength. After the early stages, notches are formed in the reaction zone of the fibre on loading at a small strain and the fibre fractures when a notch extends into the fibre. In this stage the fibre strength is dependent on the thickness of the reaction zone. An alloying addition of 1 or 5 at % Si to the aluminium matrix was found to be effective in retarding the growth rate of the reaction zone.On leave from Institute of Metal Research, Academia Sinica, Shenyang, China.On leave from Instituto Superior Tecnico, Departamento de Metalugia e Materais, Lisbon, Portugal.On leave from Hitachi Research Laboratory, Hitachi Ltd, Saiwai-Cho, Hitachi, Ibaraki 317, Japan.     

Interfacial effects between molten aluminium and sapphire

The sessile-drop technique has been used to examine the interfacial effects that occur between molten aluminium and single-crystal -Al₂O₃ when heated in vacuo. In the region of 1300° C the growth of crystallites, probably of -Al₂O₃, at the liquid-solid and liquid-vapour interfaces has been observed, together with the formation of etch pits on the sapphire plaque as the result of vapour attack. These effects are described and discussed.     

High temperature reactions between SiC and platinum

Solid state reactions between SiC and platinum have been studied at temperatures between 900 and 1100 °C. In the reaction zones, alternating layers of Pt₃Si and carbon, and Pt₂Si and carbon were formed at 900 and 1000 °C, respectively. Both the Pt₃Si and Pt₂Si phases were stable at respective temperatures. Annealings at 1100 °C, however, produced alternating layers of mixed Pt-silicides and carbon. The formation of platinum silicides gave rise to interfacial melting between SiC and platinum at all the temperature regimes. Laser Raman microprobe indicates that SiC decomposes into carbon and silicon at all the temperatures. The silicon reacts with platinum and forms platinum silicides, while the carbon forms clusters and stays unreacted. Based on the Raman results, the carbon exists in two different crystalline states depending upon its location from the SiC reaction interface. The reaction kinetics between SiC and platinum and the formation of periodic structure, respectively, are discussed based on the decomposition of the SiC and the phase separation of carbon from platinum silicides.     

Interfacial reactions between palladium thin films and InP

Palladium appears to be an important component in ohmic contact metallizations to III–V semiconductors. Very little is known about its interaction with InP. Consequently, the reaction between a thin layer of Pd (100 nm) and an InP substrate has been studied at annealing temperatures ranging from 250–450 °C for up to 30 sec, i.e., typical annealing conditions encountered during contact fabrication. Palladium reacts readily with InP, initially forming an amorphous ternary phase, which transforms to crystalline Pd₂InP on annealing. Pd₂InP has an ordered cubic structure, with a lattice parameter of 0.830 nm, and grows epitaxially on InP. Microtwins, 2–3 atomic layers thick, have been identified in the ternary phase and these form along the (110) and ( 10) planes.     

Hydroxyapatite-coated metals: Interfacial reactions during sintering

Electrophoretic deposition (EPD) is a low cost flexible process for producing HA coatings on metal implants. Its main limitation is that it requires heating the coated implant in order to densify the HA. HA typically sinters at a temperature below 1150C, but metal implants are degraded above 1000C. Further, the metal induces the decomposition of the HA coating upon sintering. Recent developments have enabled EPD of metathesis-synthesised uncalcined HA which sinters at 1000C. The effects of temperature on HA-coated Ti, Ti6Al4V, and 316L stainless steel were investigated for dual coatings of metathesis HA sintered at 1000C. The use of dual HA coatings (coat, sinter, coat, sinter) enabled decomposition to be confined to the undercoat (HA layer 1), with the surface coating decomposition free. The tensile strength of the three metals was not significantly affected by the high sintering temperatures (925C < T < 1000C). XRD/SEM/EDS analyses of the interfacial zones revealed that 316L had a negligible HA:metal interfacial zone (1 m) while HA:Ti and HA:Ti6Al4V had large interfacial zones (>10 m) comprising a TiO₂ oxidation zone and a CaTiO₃ reaction zone.     

Interfacial reactions between Ti-6Al-4V alloy and zirconia mold during casting

The interface of Ti-6Al-4V casting and ZrO₂ mold with silica binder was investigated by using electron probe microanalyses (EPMA), X-ray diffraction (XRD), and analytical transmission electron microscope (TEM). The interfacial reactions were proceeded by the penetration of liquid titanium through open pores near the mold surface. The metal side consisted of an -phase layer on the top of the typical + two-phase substrate. In the ceramic side, zirconia was reduced by titanium to form oxygen-deficient zirconia ZrO_2–x and evolved a gaseous phase (presumably oxygen). The SiO₂ binder, dissolved in the ZrO₂ mold, could react with titanium to form Ti₅Si₃ in the metal side. Meanwhile, titanium could transform to titanium suboxides Ti_yO (y 2) and the lower phase boundary of cubic ZrO_2–x was shifted to ZrO_1.76. Some amount of the stabilizer CaO, dissolved in Ti along with ZrO₂, could react with Ti(O) to form Ca₃Ti₂O₇ and CaAl₄O₇ in the reaction zone.     

Interfacial reaction and adhesion between SiC and thin sputtered nickel films

Thin sputtered nickel films grown on SiC were annealed in an Ar/4 vol % H2 atmosphere at temperatures between 550 to 1450 °C for various times. The reactivity and the reaction-product morphology were characterized using optical microscopy, surface profilometry, X-ray diffraction, scanning electron microscopy and electron probe microanalysis. The reaction with the formation of silicides and carbon was observed to first occur above 650 °C. Above 750 °C, as the reaction proceeded, the initially formed Ni3Si2 layer was converted to Ni2Si and carbon precipitates were observed within this zone. The thin nickel film reacted completely with SiC after annealing at 950 °C for 2 h. The thermodynamically stable Ni2Si is the only observed silicide in the reaction zone up to 1050 °C. Above 1250 °C, carbon precipitated preferentially on the outer surface of the reaction zone and crystallized as graphite. The relative adhesive strength of the reaction layers was qualitatively compared using the scratch test method. At temperatures between 850 to 1050 °C the relatively higher critical load values of 20–33 N for SiC/Ni couples are formed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Interfacial reaction and adhesion between SiC and thin sputtered cobalt films

Thin sputtered cobalt films on SiC were annealed in an Ar/4 vol% H₂ atmosphere at temperatures between 500 and 1450 °C for various times. The reaction process and the reaction-product morphology were characterized using optical microscopy, surface profilometry, X-ray diffraction, scanning electron microscopy and electron probe microanalysis. The relative adhesive strength between the film and substrate was determined by the scratch test method. Below 850 °C sputtered cobalt with a thickness of 2 m on SiC showed no detectable reaction products. Cobalt initially reacted with SiC at 850 °C producing Co₂Si and unreacted cobalt in the reaction zone. At 1050 °C the first-formed Co₂Si layer reacted to CoSi, and carbon precipitates were formed in the reaction zones. Sputtered thin cobalt layers reacted completely with SiC after annealing at 1050 °C for 2 h. Above 1250°C only CoSi was observed with carbon precipitates having an oriented structure in the reaction zone. Above 1450°C, a significant amount of graphitic carbon in the reaction zone was detected.     

Interfacial reactions in aluminum/SiC fibre composite electric power cable using low oxygen SiC fibre reinforcement

We have evaluated the interfacial reactions of SiC fibre reinforced Al electrical power cable using low oxygen SiC fibre (Si : 62.4, C : 37.1, 0 : 0.5 mass%), and determined the relationship between the tensile strength and the amount of reaction products at the interface. The following are occurring at the SiC/Al interface: i) diffusion of Al atoms into the SiC fibre, ii) formation of needle–shape Al₄C₃ compounds, and iii) formation of Al₉Si compounds. Formation of Al₄C₃ and Al₉Si compounds at the interface causes the strength of SiC/Al composite electric power cable to deteriorate.     

Interfacial reactivity of aluminium/fibre systems during heat treatments

The interfacial reactivity of specimens composed of aluminium coated on SiC-based fibres, carbon fibres and protected carbon fibres, was investigated. The woven fibres were coated with aluminium by physical vapour deposition and the obtained materials were heat treated in a furnace which was connected to a mass spectrometer. It was shown that reactions occur between CO and CO₂ gases, which are released by the fibres, and aluminium, when the temperature is above 650°C. These gases react during their passage through the aluminium layer and form aluminium carbide. Aluminium carbide is also produced by reactions between the solid-species constituents of the fibres and the metal. The amount of aluminium carbide formed at the fibre/metal interface during heat treatment was determined by hydrolysis. It was thus possible to ascertain that the aluminium carbide is mainly formed by the latter reactions. The efficiency of various protective coatings against the formation of aluminium carbide was also investigated.     

Interfacial reactions between SnAg1.0Ti and Ni metallization

The effect of Ti on the solid state reactions between Sn and Ni has been investigated in this work. Based on the experimental results the following statements can be made: Firstly, the presence of Ti does not have measurable effects on the thickness evolution of Ni₃Sn₄ during solid state annealing. Secondly, the results from long term heat treatments show that there is no marked solubility of Ti to Ni₃Sn₄. Rather Ti reacts with Sn to form large Ti₂Sn₃ platelets inside the solder matrix. The Sn-rich part of the Ni–Sn–Ti phase diagram was assessed in order to rationalize the experimental results. By utilizing this information, the absence of any marked effects of Ti on the growth of Ni–Sn intermetallic compounds (IMC) was analysed. As there is no solubility of Ti to SnAg solder or to Ni–Sn IMC’s, Ti cannot change activities of components in the solder nor influence the stability of the IMC layers. Hence, these results throw significant doubts over the concept of trying to influence the Ni–Sn IMC layer thickness or quality by Ti alloying.     

Interfacial reactions between AZ91D magnesium alloy and plaster mould material during investment casting

Abstract

Reactions at the mould/metal interface play an important role in determining the quality of investment castings. They are particularly critical in the case of magnesium alloys cast in industrial plaster moulds. In this work, reactions of molten magnesium alloy with plaster mould were studied. First the potential interactions with mould materials (including gases) were examined using thermodynamic considerations. Then thin sheets of AZ91D magnesium alloy were cast in industrial plaster moulds using vacuum assistance: the surface of sheets and plaster mould were characterised. The analysis of reaction products indicates that magnesium vapours diffuse through the plaster and reduce the silica present in the investment material according to the following reaction: 4Mg + SiO₂=2MgO + Mg₂Si. The extent of reactions is controlled by mould temperature and thickness of castings.     

Interfacial reactions in Al/SiC composites produced by low pressure plasma spray

Metal matrix composite tapes, reinforced by long silicon carbide fibres produced by low pressure plasma spray are characterised by the scarce presence of reaction compounds at the fibre/matrix interface. However, a complete and comprehensive investigation of the dissolution, diffusion and chemical reaction phenomena taking place in the interfacial area during the deposition is most important for the evaluation of the adhesion strength between the reinforcement and the base material and, consequently, of the mechanical behaviour of the material. In the case of interest for the present paper, the characterisation of the interface has been carried out by means of scanning electron microscopy, energy dispersive spectroscopy and X ray difraction analysis. Moreover, the quality of the fibre/matrix interface of the Al/SiC composites was evaluated by means of push-out tests, aimed to the identification of the transmission mechanism of the load from the matrix to the fibre, and to quantify the adhesion strength.Paper presented at the AIM National Conference on Metal Matrix Composites, Milan, Italy, April 1992.     

Interfacial reactions and intermetallic compound growth between indium and copper

The growth kinetics of intermetallic compound layers formed between pure indium solder and bare Cu substrate by solid-state isothermal aging were examined at temperatures between 343 and 393 K for 0–4×10⁶ s. A quantitative analysis of the intermetallic compound layer thickness as a function of time and temperature was performed. Experimental results showed that the Cu₁₁In₉ intermetallic compound was observed for bare copper substrate. Additionally, the thickness of the Cu₁₁In₉ intermetallic compound was increased with the aging temperature and time. The layer growth of the intermetallic compound in the couple of the In/Cu system followed a parabolic law over the given temperature range. As a whole, because the values of time exponent (n) were approximately 0.5, the layer growth of the intermetallic compound was mainly controlled by a diffusion mechanism over the temperature range studied. The apparent activation energy of Cu₁₁In₉ intermetallic compound in the couple of the In/Cu was 34.16 kJ mol^–1.     

Exchange diffusion phenomenon between free-silicon in reaction bonded SiC and liquid aluminium

Journal of Materials Science Letters -     

Interfacial properties and stability in bonded aluminium

The localized interfacial region between an aluminium substrate and an epoxy adhesive has been extensively investigated. It has been found that a transitional region exists between the substrate surface and the bulk adhesive in which the physical and/or chemical properties of the polymer differ from those of the bulk polymer. Different surface treatments prior to bonding are observed to have little effect on the formation of the transitional region. Two types of transitional layers have been identified; one extending up to 1m from the substrate interface, the other generally restricted to 10 nm from the substrate interface. Examination of regions immediately in front of a propagating crack indicate that the interfacial integrity of both an etched-bonded substrate and a pretreated-bonded substrate are maintained. In contrast, regions of the fracture surface behind a propagating crack show the existence of corrosion products on an etched substrate but not on a pretreated substrate.     

Oxidation behaviour of carbon/aluminium and SiC/aluminium composites

Isothermal oxidation of 6061 Al, reinforced with chopped carbon fibres and SiC particles, was studied to investigate the applicability of these composites in the temperature range 300–500 °C, in terms of their degradation due to oxidation. Carbon/aluminium composite suffered a tremendous loss in weight at 350 °C. The extent of the damage due to oxidation for SiC/Al composites depended upon the concentration of nucleation sites, which formed the interface between the composite and the matrix. The number of such sites depended upon the volume fraction and size of the dispersed particles. Analysis of the oxide scale was carried out using SEM/EDAX and X-ray diffraction. The deterioration in strength of the composites, due to oxidation, was determined by tensile testing of exposed specimens.     

Oxidation effects during laser cladding of aluminium with SiC/Al powders

Aluminium substrates were covered with a layer of an Al-SiC powder mixture. The surface was scanned with a laser beam during which the surface was melted. The top layer of the laser tracks contained oxide plates apart from some large SiC particles. In the bottom layer a cellular network was found with aluminium cells and silicon-rich cell walls.