Joining of Cf/SiC composite to Ti alloy using composite filler materials

Abstract

C_f/SiC was successfully joined to Ti alloy with Ag–Cu–Ti–W, Ag–Cu–Ti–SiC and Ag–Cu–Ti–TiC mixed powders by some suitable brazing parameters. Microstructure and shear strengths of the preformed joint were investigated. The results showed that the W particulate and reaction products can uniformly distribute in the brazing layer of the performed joint. These composite brazing layers relaxed the thermal stress of the joint effectively. These characteristics were beneficial to the joint, which had shear strengths that were significantly higher than the optimal shear strengths of the joint brazed with pure Ag–Cu–Ti at room temperature and 500°C.     

Inferences on plastic properties and coefficient of friction during simultaneous compression deformation of dissimilar sintered powder metallurgical preforms

Abstract

Plastic working of powder metallurgical (PM) material necessitates the development of fundamental data such as flow stress, densification behaviour, coefficient of friction, apparent strength coefficient, apparent strain hardening exponent, plastic Poisson's ratio, etc. In the present work compression and standard ring compression tests have been carried out to generate the fundamental data for simultaneous deformation of sintered steel and copper powder metallurgical preforms. The results reveal that the behaviour of individual materials during simultaneous deformation is strongly influenced by local micromechanical interactions at the metal - metal interface. In addition to this, the test conditions (iso-stress and iso-strain) strongly influence the severity of interaction. The interfacial friction coefficients are less than that of the same material when tested between hard tools. The optimal process parameters with higher interfacial friction, which can enhance the solid state joining of dissimilar materials, have been identified. The flow stress of the composite (steel - copper combination) during simultaneous deformation can be estimated if the flow stress of the individual materials comprising the combination/composite are known. With these studies, it should be possible to extend the inferences to the major deformation processes.     

Characterisation of functionally graded and VC/steel surface alloyed composites produced using powder metallurgy

Abstract

In this study, low carbon steel specimens with surface alloyed composites were produced by means of powder metallurgy. Vanadium carbide, graphite (1·2 wt-%) and Fe were used for the surface alloyed composite, while Fe and graphite (0·2 wt-%) were used for the low carbon steel side. The powder mixtures were compacted together in the same mould. On the surface alloyed side the vanadium carbide content was changed from 5 to 25 wt-%. Microstructural investigations including EDX and X-ray, hardness measurement and abrasive wear tests were performed. The results showed that V₈C₇ formed in the alloyed surface and carbon diffusion from the alloyed surface to the parent metal created a functionally graded material. The hardness values decreased towards the parent metal. Wear resistance increased as the vanadium carbide increased in the surface alloyed composite. Thus, a functionally graded steel having a surface composite that is resistant to abrasive wear can be obtained via the powder metallurgy route.     

Direct observation of ternary solid state transformation in Bi–Cd–In alloy system

Abstract

Cast or solution treated specimens of a Bi–9·0Cd–26·7In (wt-%) alloy were observed to form a fine, three phase microstructure on aging at room temperature, replacing a single phase formed at a higher temperature. The three phases resulting from this solid state reaction were found to grow with a lamellar morphology into the high temperature phase, with a growth rate of 0·5–1·0 μm h^-1 at room temperature. The equilibrium temperature for the transformation was found to be ～25°C. Using a Hitachi S-4500 field emission SEM, the phase transformation was followed in progress at magnifications of 3000 and 10 000 times. It was noted that a volume change was associated with the transformation. It was concluded that the transformation is of the ternary eutectoid type.     

Development of laminated composite materials based on orthorhombic aluminide/titanium alloy and their tensile mechanical properties

Abstract

Laminated composite materials consisting of an orthorhombic Ti₂AlNb based alloy and an (α+β) titanium alloy have been fabricated at a laboratory scale using a two-step process involving diffusion bonding and hot rolling. The feasibility of fabrication of two and three layered materials with high quality bonding between layers was demonstrated. Preliminary assessment of the tensile mechanical properties of the obtained composite materials showed that they were superior to those of the titanium alloy and slightly inferior to the orthorhombic alloy.     

Characteristics of Electrophotographic Papers—Part 1

The primary parameters of electrophotographic papers are surface charge, and the decay of this charge under both dark and illuminated ambient conditions. The inter-relationship of these parometers is of great practical signiftcance in machine design. It is suggested that the results from conventional static methods for their measurement can be misleading. Special equipment has been constructed for the examination of electrophotographic materials under dynamic conditions. Experimental results are presented together with an indication of their value in assessing the practical performance of electrophotographic papers and their influence in machine design.     

Structure evolution in annealed and hot deformed Al–V2 O5 composite

Abstract

Structural observations and hot deformation tests were carried out on mechanically alloyed Al-10 wt-%V₂ O₅ composite. Initial annealing experiments revealed a hardening of the material during the first stage of annealing. The material hardness increased from 114 HB for as extruded material to 167 HB after annealing at 873 K for 6 h. Differential scanning calorimetry tests conducted on as extruded material confirmed the development of an exothermic reaction during heating of the material within the temperature range 650–870 K. The amount of heat released was reduced with increasing annealing time at 873 K. Transmission electron microscopy (TEM) and X-ray analysis of annealed material revealed new intermetallic grains and very fine aluminium oxide particles, which resulted from the chemical reaction between the aluminium matrix and vanadium oxides. The development of voids in long aged specimens was found to be an undesirable effect of local specific volume reduction during the course of the chemical reaction that was not fully compensated by the local volume increase due to the growth of intermetallic particles. As a result, the material hardness was reduced in long time annealed specimens. The mechanical properties of as extruded and annealed specimens were investigated by means of hot compression testing within the temperature range 623–903 K. These tests revealed that the flow stress of as extruded material was reduced from 180 to 22 MPa when tested at 623 and 903 K, respectively. Annealed specimens exhibited higher flow stresses of 195 and 32 MPa at the same temperatures. The results indicate that the strength of the material can be effectively increased owing to a change of material structure as a result of the chemical reaction taking place during high temperature annealing.     

Strength of CFRP open hole laminates made from NCF,TFP and braided preforms under cyclic tensile loading

Abstract

Tensile tests and tension–tension cyclic tests were performed on carbon fibre reinforced plastics open-hole laminates. Specimens made from non-crimp fabric preforms, tailored fibre placement preforms and braided preforms in three different lay-up configurations ([+45]_{8 s}, [+45/0/?45]_{6 s}, [0/90]_{8 s}) were investigated and compared. The laminates were manufactured using a vacuum assisted processing technology and Hexcel RTM6 epoxy resin. Tensile strength and residual tensile strength values were measured and compared with unnotched specimens in order to evaluate the notch sensitivity. To evaluate deterioration during cyclic testing a two-dimensional digital image correlation system was used to capture deformation images of the specimen surface in the open-hole area. Observed similarities and differences in deformation and in load–elongation graphs of the tested specimens are discussed.     

Surface modification of bioceramics by grafting of tailored allyl phosphonic acid

Abstract

A new route to interfacial bonding between ceramic and matrix in biocomposites is identified. A tailored allyl phosphonic acid is used as a coupling agent bound to the surface of a bioceramic to form a 'grafted' calcium phosphate (CAP). The allyl phosphonic acid coupling agent is synthesised by reaction of allyl halide and trialkyl phosphite. Successful synthesis was confirmed by nuclear magnetic resonance and Fourier transform infrared spectroscopy (FTIR). The allyl phosphonic acid was incorporated onto calcium phosphate using a wet chemical coprecipitation synthesis route. The resulting 'grafted' CAP was characterised using FTIR coupled with photoacoustic sampling, and Fourier transform Raman spectroscopy (FTR). The spectroscopic data suggest an interaction between the allyl phosphonic acid and calcium phosphate resulting from observed reductions in intensity of the hydroxyl (3570 cm^?1) and phosphate ν ₃ (1030 cm^?1) peaks. The continued presence of C=C functionality on the surface of the grafted CAP was indicated by FTIR and FTR spectra (peaks at 1650 and 1635 cm^?1 respectively) and confirmed by X-ray photoelectron spectroscopy (XPS). On the basis of these results, it is concluded that grafted CAP may be used to produce a chemically bonded composite with superior mechanical properties.     

Effect of La2O3 Particles on the Oxidation of Electrodeposited Nickel Films

Electrodeposited Ni-La₂O₃composite films with nanometer-sizeLa₂O₃ oxide inclusions werefabricated by the codeposition of nickel withLa₂O₃ particles. The comparativeoxidation behavior in air at 900 and 1000°C of nickel coated with theNi-La₂O₃ composite and films withand without nickel-plating was studied by TGA, AE,SEM/EDX, EPMA, and TEM/EDX. In general, theNi-La₂O₃ composite-coated nickelhad the slowest rate and the best resistance tothermal cycling. AE tests revealed that cracking eventsin NiO scales on Ni-La₂O₃composite-coated nickel was significantly reduced incomparison to that of the scale on nickel-coated nickel during thermalcycling at 900°C. SEM investigation showed that theLa₂O₃-free NiO scale was composedof outer coarse columnar grains and inner equiaxed ones.By contrast, the scale on the Ni-La₂O₃composite-coated nickel consisted of only fine equiaxedNiO grains. The scale on theLa₂O₃-free samples wascharacterized by cracks that originated at thescale-substrate interface and spanned the scale thickness. By contrast,no scale cracks formed at theLa₂O₃-doped NiO scale-substrateinterface, but small voids were created at the triplepoints of the grain boundaries of NiO. In the La₂O₃-doped NiOscale, segregation of La ions to the NiO grainboundaries near the scale-surface was observed by EDXmicroanalyses in the TEM. It is believed that the Laions segregated at the grain boundaries of NiO led to an increase in thecohesion between nickel oxides and in a reduction of thescaling rate and the formation of scale with fineequiaxed crystal structure by blocking the outward and lateral growth of scale. The latter was dueto the predominant outward diffusion of nickel along NiOgrain boundaries being inhibited effectively by thesegregated La ions. The mechanism of the effect of the added La₂O₃particles on the nickel electrodeposits is discussed indetail.