Formation Of Interfacial Carbides Research Articles

Optimization of the mechanical properties of CNTs/Cu composite by regulating the size of interfacial TiC

The formation of interfacial carbides by in-situ reaction is a valid way to improve the interfacial bonding strength and mechanical performance of metal matrix composites. In this study, Cu matrix composites reinforced by carbon nanotubes (CNTs) were fabricated by molecular level mixing (MLM) combined with subsequent powder metallurgy (PM) to obtain the interfacial TiC with suitable size. In contrast to typical PM, CNTs were homogeneously distributed and partially incorporated in Cu matrix in the composite powders prepared by MLM, which was a critical factor in generating nanoscale interfacial TiC. The TiC nanoparticles can not only adhere firmly to CNTs, but also form semi-coherent interfaces with Cu matrix, thus achieving strong interface bonding by bridging the gaps between them. The ultimate tensile strength of the prepared composite is as high as 364 MPa with a CNTs content of 0.8 vol% and a noticeable strengthening efficiency of 206, which is considered to be the full exertion of load-transfer. This work can provide a novel perspective for the fabrication of CNTs/Cu composites by introducing nanosized interfacial carbides to improve the mechanical properties.

Formation of the orientation relationship-dependent interfacial carbide in Al matrix composite affected by architectured carbon nanotube

In-situ formed carbides at interface can enhance the interfacial bonding and load-transfer effect in nanocarbon/Al composites, but always sacrifice the structure integrity of reinforcement, inevitably degrading the strengthening efficiency. To alleviate such limitation, a novel hybrid leaf-like carbon nanotube (CNT)-graphene nanoribbon (GNR), architectured via partially longitudinal unzipping of multi-walled CNT (UZCNT), was adopted to reinforce Al matrix composites. Results show that the prominent mechanical properties of UZCNT/Al over CNT/Al were achieved, which originates from the in-situ formed interfacial Al4C3 together with the well-retained integrity of UZCNT. The regulated interfacial reaction between UZCNT and Al generates dense nano-sized Al4C3 (diameter: 14–19 nm, length: 36–82 nm), rather than its submicron-sized counterpart (diameter: 26–37 nm, length: 111–186 nm) with low number density which forms in unmodified CNT/Al composites. Systematic analysis indicates that the interfacial Al4C3 in UZCNT/Al forms via “nucleation-growth” pattern, contrary to the predominant epitaxial growth of Al4C3 in CNT/Al. It is revealed that UZCNT can stimulate Al4C3 nucleation via reducing the nucleation energy barrier and increasing the number of nucleation sites. Meanwhile, finite active C atoms and low-defective inner walls in UZCNT retard the fast growth of Al4C3 after nucleation. Such “nucleation-growth” pattern renders the formation of high number-density nano-sized Al4C3 at GNR margin in UZCNT/Al. Atomic-scale characterizations demonstrate that the coherent/semi-coherent Al4C3-Al interfaces in UZCNT/Al preferentially exhibit specific orientation relationships, most of which are reproducible by the edge-to-edge matching model. The present work is supposed to provide important insights on interfacial carbide formation in nanocarbon/metal composites.

Characterization of interfacial bonding strength at Al(Si)/diamond interfaces by neutron diffraction: Effect of diamond surface termination and processing conditions

Interfacial bonding plays a vital role and is of eminent importance for thermo-physical and mechanical properties in particulate and fibrous composites. Moreover, the formation of interfacial carbides in the reactive system Al/diamond dominates the thermal and mechanical response. The amount of interfacial carbides can be controlled by the nominal composition of the matrix and process parameters like contact times between the liquid aluminium and the diamond particles during and the surface termination of the diamonds before the liquid metal infiltration processing. Neutron diffraction experiments were performed to study the influence of those parameters on interfacial bonding strength and show a direct correlation between thermo-physical properties, concentration of interfacial aluminium-carbide Al4C3 and micro strain concentrations during neutron diffraction experiment. Furthermore, the oxygenation of the diamond particle surface has a major contribution to the interfacial bonding and thermal conductivity of the composites, respectively. This effect, however, almost diminishes when Al3Si is used as a matrix.

Interfacial microstructures and mechanical integrity of synthetic diamond brazed by a low-temperature Cu-Sn-Cr filler alloy

To ensure the formation of metallurgical bonding of diamond abrasive grits, active brazing using the Cr-containing Ni-based filler alloys has been employed for decades. However, the high brazing temperature of Ni-based filler alloy inevitably induces intense thermal damage and impairs the mechanical properties of brazed diamond grits. In this study, a Cr-containing Ni-free CuSn filler alloy of melting point lower than that of Ni-based alloy was developed based on our previous wettability study. Interfacial microstructures and mechanical properties of diamond grits brazed using this newly developed Cu-Sn-Cr alloy and the commercial Ni-Cr-P alloy were investigated and comparatively analyzed. By using FIB-TEM, Raman spectroscopy and XRD techniques, a thin and uniform interfacial Cr7C3 chromium carbide was observed at interface between synthetic diamond grits and the Cu-Sn-Cr alloy brazed at 750 and 950 °C. The impact toughness (TI) of diamond grits brazed using Cu-Sn-Cr alloy was significantly improved as compared with the diamond grits brazed by commercial Ni-Cr-P filler alloy at 950 °C. It was found that the alloy composition played a more significant role in the interfacial carbide formation than brazing temperature. In particular, the decrease of C solubility in Cu-Sn-Cr alloy was the main reason for the refinement of interfacial chromium carbide and the improvement of mechanical properties. Experimental results obtained in this work lay a foundation for the further development of Cr-containing filler alloys for diamond brazing application.

Reactive wetting of binary Sn[sbnd]Cr alloy on polycrystalline chemical vapour deposited diamond at relatively low temperatures

Synthetic diamond has excellent mechanical, thermal, and electrical properties, which makes it an ideal material in a wide range applications from abrasive grinding tools to modern electronic devices. Hence, understanding the wettability of metals on the synthetic diamond is of great importance for the development of diamond-related materials and devices. In this study, the wettability and spreading kinetics of binary SnCr alloy on chemical vapour deposed (CVD) polycrystalline diamond compacts were investigated using a sessile drop method. In situ observation of contact angle at elevating temperatures indicated trace addition of Cr dramatically improved the wettability of Sn on CVD diamond, and the SnCr alloy started to wet CVD diamond at approximately 750 °C. Isothermal spreading kinetic analysis revealed that the spreading of SnCr alloy on CVD diamond was controlled by the kinetics of chemical reaction at advancing triple line. Microstructure characterization indicated that the formation of nano-sized scallop-like Cr7C3 grains was responsible for the improved wettability of SnCr alloy on CVD diamond substrate. The wetting temperature was found to play a determinant role in the interfacial carbide formation, and hence the reactive wetting of SnCr alloy on CVD diamond at temperatures from 700 to 900 °C.

Microstructural evolution and high temperature failure of ferritic to austenitic dissimilar welds

Dissimilar metal welds between ferritic and austenitic alloys are used extensively in power plants. Premature failure of such welds can occur below the expected creep life of either base metal. This article reviews microstructural evolution in dissimilar welds and describes factors that contribute to premature failure. The microstructure in the as welded condition consists of a sharp chemical concentration gradient across the fusion line. Martensite forms within this gradient due to high hardenability and rapid cooling rates from welding. Upon aging, carbon diffuses down the chemical potential gradient from the ferritic steel toward the austenitic alloy. This can lead to formation of a soft carbon denuded zone in the ferritic steel, and nucleation and growth of carbides in the austenitic steel that produce high hardness. These differences in microstructure and hardness occur over distances of about 50–100 μm. Failure is attributed to the steep microstructural and mechanical property gradients, the large difference in coefficient of thermal expansion, formation of interfacial carbides that promote creep cavity formation, and preferential oxidation of the ferritic steel. Information is also provided on available creep rupture properties, remaining life estimation techniques, current best practices and research in progress.

Interfacial reactions in chromium-carbon multilayers

Thermal modifications due to interfacial compound formation in magnetron sputtered Cr-C multilayers have been investigated in the temperature range between 450° C and 580° C and the formation of interfacial carbides has been discussed on the basis of thermodynamic and kinetic considerations. Grain boundary diffusion accompanied by grain growth proportional to the reacted layer thickness has been assumed to account for the observed t1/3 time dependence of the growth rate. The compound layer growth has been thermally activated with an activation energy of QG=0.85 eV.

On the formation of interfacial carbides in a carbon fibre-reinforced aluminium composite

The precipitation of interfacial carbides in a carbon fibre-reinforced aluminium alloy produced by liquid metal infiltration has been investigated. Lath-like aluminium carbides of the type Al 4C 3 nucleate heterogeneously at the fibre surface and cause formation of deleterious surface notches. Transmission Electron Microscopy (TEM) studies showed that (0001) basal planes of the carbide phase preferentially form at surface defects constituted by small clusters of carbon layers inclined to the fibre surface, which locally expose their reactive basal plane edges. A crystallographic relationship in the form (0001)Al 4C 3  (001)C is locally established with the fibre structure, and subsequent growth of carbides is fast into the molten aluminium matrix along preferential [ 2 110] direction. It is suggested that carbides develop lath-like in shape mainly because their thickening at the fibre surface-is limited by the different orientation and lower reactivity of adjacent fibre surface regions.