Reinforcement of Al–Fe–Ni alloys with the in situ formation of composite materials

One of the most effective methods for the improvement of the mechanical properties of metals is their reinforcement with non-metallic materials. In the present work powder of K₂TiF₆ and KBF₄ was added in an Al–Fe–Ni alloy while the alloy was in liquid form at 1060 °C with a 5 wt.% mixture of powders and with simultaneous stirring for 30 min. The liquid was squeeze-casted at 150 bar. The as-cast specimens were examined with electron microscopy and X-ray diffraction. SEM analysis revealed that the as-formed material is composed by needle-like crystallites along with a dentritic form and an interdendritic phase. The composition of the needle-like crystallites may presumably be expressed by the formula (Fe-Ni)Al₃. The rest of the matrix consists of almost pure Al grown dentritically, while the interdendritic phase contains Fe and Ni dissolved in Al. EDS analysis also proved the existence of spots with high Ti concentration, which probably refer to the Ti–B compounds. Finally TEM verified the presence of nanocrystals in the matrix.     

Surface functionalization of multi-walled carbon nanotubes via electron reduction of benzophenone by potassium metal

The covalent sidewall functionalization of multi-walled carbon nanotubes (MWCNTs) via the electron reduction of benzophenone by potassium metal is reported. Fourier transform infrared spectroscopy (FTIR) results show that diphenylcarbinol (DPC) groups were successfully grafted to the MWCNTs sidewalls after 10 days of reaction time. Raman and UV–vis spectroscopies reveal the presence of covalent sidewall functionalization. The percentage of residues for DPC-MWCNTs was found to be lower than that for pristine MWCNTs, which indicates the existence of functional groups on the sidewalls of DPC-MWCNTs. It is shown that the sidewall of the DPC-MWCNTs was covered by non-uniform layer of DPC, as observed by transmission electron microscopy (TEM). Results from Raman spectroscopy, FTIR, TGA, UV–vis spectroscopy and TEM confirm that the functionalization of the covalent sidewalls of MWCNTs was successfully performed by this method.     

A study on electrochemical growth behavior of the Co–Ni alloy nanowires in anodic aluminum oxide template

This study shows the growth behavior of Co–Ni alloy nanowires in AAO template. Growth of nanowires consists of four different stages namely electronucleation, steady state growth, filling of pores, and coverage of filled nanowires and forming of a film on the template surface. TEM study of nanowires showed that the nanowires possess hemispherical head due to the preferable and more rapid growth phenomenon in central section of nanowires instead of edge sides. Studies on the relations between nanowires composition and ion concentration in solution showed that growth of nanowires is a diffusion-controlled process. The compositional, structural and magnetic properties of nanowires were investigated by means of EDX, TEM and VSM.     

The effect of heat treatment on thermal stability of Ti matrix composite

The microstructures of in situ synthesized (TiB + La₂O₃)/Ti composite after β and TRIPLEX heat treatment are investigated. The room temperature tensile properties of the titanium matrix composites (TMCs) are tested, and thermal stability is carried out at 600, 650 and 700 °C for 100 h, respectively. The results show that the microstructure of specimen after β heat treatment is widmanstätten, while it is similar to basketweave after TRIPLEX heat treatment. Room tensile properties of specimen after TRIPLEX heat treatment are better than those of β heat treatment. After thermal exposure, the strength of specimens treated by β and TRIPLEX heat treatment increases, while the ductility decreases sharply, this is attributed to the precipitation of Ti₃Al and silicides. The thermal stability of specimen after TRIPLEX heat treatment is better than that after β heat treatment.     

Characterization of interface between the particles in NiNbZrTiPt metallic glassy matrix composite containing SiC fabricated by spark plasma sintering

We investigated the microstructure, in particular, the interface structure between powder particles in the Ni_52.5Nb₁₀Zr₁₅Ti₁₅Pt_7.5 bulk glassy alloy composites containing 10 vol.%SiC particulates prepared by a spark plasma sintering (SPS) process by means of scanning and transmission electron microscopies. The SiC particulates were dispersed homogeneously in the Ni_52.5Nb₁₀Zr₁₅Ti₁₅Pt_7.5 glassy matrix. No crystallization of the Ni_52.5Nb₁₀Zr₁₅Ti₁₅Pt_7.5 glassy alloy took place during the SPS process. The good bonding states between SiC particulates and glassy matrix, as well as between glassy particles were recognized. No intermediate layer in the bonded interfaces was observed.     

Weld zone characteristic and mechanical performance of in situ titanium matrix composites using gas tungsten arc welding (GTAW)

Abstract

In situ TiB_w and La₂O₃ reinforced titanium matrix composites were successfully fusion welded by the gas tungsten arc welding (GTAW) process and the weldability and feasibility for composites were studied, and uniform and defect free welds were produced with sound welding parameters. Microstructural observations showed that the joint has a distinctly identified weld zone characteristic. In addition, the distribution and size of TiB_w in the weld became much more homogeneous and smaller. Moreover, the welded joints exhibited good mechanical properties at ambient temperature and the strength equal to the base metal at elevated temperature. The fracture mechanism of TiB_w in the weld also was investigated.     

Influence of reinforcement proportion and matrix composition on pitting corrosion behaviour of cast aluminium matrix composites (A3xx.x/SiCp)

The influence of silicon carbide (SiCp) proportion and matrix composition on four aluminium metal matrix composites (A360/SiC/10p, A360/SiC/20p, A380/SiC/10p, A380/SiC/20p) immersed in 1-3.5 wt% NaCl at 22 °C was investigated by potentiodynamic polarization. The kinetics of the corrosion process was studied on the basis of gravimetric measurements. The nature of corrosion products was analysed by scanning electron microscopy (SEM) and low angle X-ray diffraction (XRD). The corrosion damage in Al/SiCp composites was caused by pitting attack and by nucleation and growth of Al₂O₃ · 3H₂O on the material surface. The main attack nucleation sites were the interface region between the matrix and the reinforcement particles. The corrosion process was influenced more by the concentration of alloy elements in the matrix than by the proportion of SiCp reinforcement and saline concentration.     

Effects of particle arrangement and particle damage on the mechanical response of metal matrix nanocomposites: A numerical analysis

The spatial distribution of reinforcement particles has a significant effect on the mechanical response and damage evolution of metal matrix composites (MMCs). It is observed that particle clustering leads to higher flow stress, earlier particle damage, as well as lower overall failure strain. In recent years, experimental studies have shown that reducing the size of particles to the nanoscale dramatically increases the mechanical strength of MMCs even at low particle volume fractions. However, the effects of particle distribution and particle damage on the mechanical response of these metal matrix nanocomposites, which may be different from that observed in normal MMCs, has not been widely explored. In this paper, these effects are investigated numerically using plane strain discrete dislocation simulations. The results show that non-clustered random and highly clustered particle arrangements result in the highest and lowest flow stress, respectively. The effect of particle fracture on the overall response of the nanocomposite is also more significant for non-clustered random and mildly clustered particle arrangements, in which particle damage begins earlier and the fraction of damaged particles is higher, compared to regular rectangular and highly clustered arrangements.     

Influence of processing conditions on the carbide/matrix interface in sintered composite layers

Metal matrix composite (MMC) coatings composed of nickel-based matrices and tungsten carbides (WC/W₂C) are frequently used to solve problems of reduced life time under severe abrasive and corrosive conditions. The influence of processing conditions on the carbide/matrix interface was studied in the liquid-sintering process with a well defined temperature/time profile. Evaluation of the sintered samples by optical microscopy (OM) showed formation of an interface layer between matrix and carbides. SEM/EDS analysis indicated the formation of mixed Ni- and W-rich carbides on the interface microstructures. XRD measurements revealed the formation of Ni₃B. The layer thicknesses were determined quantitatively by OM-image analysis. The hardness profiles across the interface were examined by nanoindentation. Furthermore, scratch tests were performed for the characterisation of carbide bonding in the matrix and evaluation of the influence of the interface layer on the single abrasion behaviour of the MMC samples.Results show that the carbide/matrix bonding and the single abrasion behaviour were dependent on the gradient of the micro-mechanical properties. Increasing processing temperature or time increased the hardness gradient and consequently decreased the bonding between carbide and matrix. Additions of chromium and iron in the matrix powder caused an improvement of the bonding and the abrasion behaviour under 2-body-condition of the MMC samples.     

Synthesis of ultrafine (Ti, W, Mo, V)(C, N)–Ni composite powders by low-energy milling and subsequent carbothermal reduction–nitridation reaction

Ultrafine (Ti, W, Mo, V)(C, N)–Ni composite powders with globular-like particles of 50–300 nm were synthesized at static nitrogen pressure from oxides by a simple and cost-effective route which combines traditional low-energy milling plus carbothermal reduction–nitridation (CRN) techniques. Reaction path of the (Ti, W, Mo, V)(C, N)–Ni system was discussed by X-ray diffraction (XRD) and thermogravimetry–differential scanning calorimetry (TG–DSC), and microstructure of the milled powders and final products was studied by scanning electron microscopy (SEM) and transmission electron microscope (TEM), respectively. The results show that CRN reaction has been enhanced by nano-TiO₂ and nano-carbon powders. Thus, the preparation of (Ti, 15W, 5Mo, 0.2V)(C, N)–20Ni is at only 1300 °C for 1 h. During synthesizing reaction, Ni solid solution phase forms at about 700 °C and reduction–carbonization of WO₂ and MoO₂ occurs below 900 °C. The reactions of TiO₂ → Ti₃O₅, Ti₃O₅ → Ti(C, O) and Ti(C, O) → Ti(C, N) take place at about 930 °C, 1203 °C and 1244 °C, respectively.     

A mechanistic approach to extract the mechanical properties of individual constituents in plasma-sprayed metal matrix composite coatings

A mechanistic approach to determine the in-situ properties of individual constituents in a plasma sprayed metal matrix composite (MMC) coating was proposed. The approach was based on micro-indentation and inverse analysis techniques. Utilising the indentation data obtained from the micro-indentation experiments, elastic moduli of each constituent were calculated using a well-established method whereas yield strength and hardening exponent were extracted using the inverse procedure based on finite element analysis. Finite element results gave a satisfactory agreement between the numerically simulated and the measured indentation load-depth curves. Further studies using three dimensional finite element analyses of Vickers indentation on the MMC coating based on its actual microstructure also showed that the indentation behaviour of the MMC coatings is strongly dependent on its morphology, volume fraction, size and distribution of the reinforcing phase.     

Influence of reinforcement grade and matrix composition on corrosion resistance of cast aluminium matrix composites (A3xx.x/SiCp) in a humid environment

A study of the influence of the silicon carbide (SiC_p) proportion and the matrix concentration of four aluminium metal matrix composites (A360/SiC/10p, A360/SiC/20p, A380/SiC/10p, A380/SiC/20p) exposed to high relative humid environment was carried out under simulation in a climatic chamber. The matrix of A360/SiC/xxp composites was virtually free of copper while the A380/SiC/xxp matrix contained 3.13‐3.45wt% Cu and 1.39‐1.44wt% Ni. The kinetics of the corrosion process was studied on the basis of gravimetric tests. The nature of corrosion products was analysed by Scanning Electron Microscopy (SEM) and Low Angle X‐Ray Diffraction (XRD) before and after accelerated testing to determine the influence of microstructural changes on corrosion behaviour during exposure to the corrosive environment. The corrosion damage to Al/SiCp composites was low at 80% Relative Humidity (RH) and increased with temperature, SiCp proportion, relative humidity and Cu matrix concentration. The main attack nucleation sites were the interface region between the matrix and the reinforcement particles. The corrosion process was influenced more by the concentration of alloy elements in the matrix than by the proportion of SiCp reinforcement.     

The in situ synthesis and wear performance of a metal matrix composite coating reinforced with TiC-TiB2 particulates, formed on Ti-6Al-4V alloy by a low oxygen partial pressure fusing technique

A metal matrix composite coating reinforced with TiC-TiB₂ particulates has been successfully fabricated utilizing the in situ reaction of Al, Ti and B₄C by the low oxygen partial pressure fusing technique to improve the wear resistance of Ti-6Al-4V alloy. The results show that increasing the B₄C content is adverse to forming the coating for the formation of interfacial stress; however, the addition of TiC powder as a diluent can favor the formation of this coating and the addition of small amounts of Y₂O₃ can greatly improve the adhesion of the coating. After a pin-on-disc wear test, the wear mass loss of the coating is only about 1/12 that of the Ti-6Al-4V alloy and the wear mechanism of coating is a mixed type of slight peeling-off, adhesion and abrasion.