Microstructure characterisation and stress analysis of the Ti48Al2Ag coating on the near-α titanium alloy

The microstructure and phase composition of the protective Ti48Al2Ag coating produced on Timetal 834 by magnetron sputtering have been examined by scanning and analytical transmission electron microscopy (SEM, TEM). TEM investigations revealed that Ti48Al2Ag coating consists of two sublayers: outer columnar γ-TiAl and amorphous Ti₅Al₃O₂. Energy-dispersive synchrotron radiation diffraction was applied for stress analysis. The results show that there are tensile residual stresses present within the Timetal 834 substrate and compressive residual stresses within the γ-TiAl sublayer.     

Synthesis, characterization and densification of WCu nanocomposite powders

In the present investigation, W20-40wt.% Cu nanocomposite powders with average sizes ranging between 25 and 30 nm were synthesized by a soft chemical approach using tungsten hexacarbonyl [W(CO)₆] and copper acetonyl acetonate [Cu(acac)₂] as metal precursors. Particle size, morphology and distribution were measured using transmission electron microscope (TEM) and small angle X-ray scattering (SAXS). Surfactant coating on WCu composite powders was removed on heat treatment of powders at 450 °C in hydrogen atmosphere for 1 h. Elemental analyses of as-synthesized and annealed (at 450 °C) WCu nanocomposite powders were carried out using inductively coupled plasma-optical emission spectrometer (ICP-OES) and Leco gas analyzers. X-ray diffraction studies showed that the tungsten phase is amorphous while the crystal structure of copper phase is fcc in as-synthesized WCu nanocomposite powders. After annealing at 700 °C peaks corresponding to bcc tungsten are observed and peaks corresponding to fcc copper become sharper. Relative densities of 98.2%, 98.8% and 99.2% were achieved for W20wt.% Cu, W30wt.% Cu, and W40wt.% Cu composite powders respectively when sintered at 1000 °C.     

Influence of rare earth metals on the characteristics of anodic oxide films on aluminium and their dissolution behaviour in NaOH solution

The characteristics of oxide films on Al and Al1R alloys (R = rare earth metal = Ce, Y) galvanostatically formed (at a current density of 100 μA cm⁻²) in borate buffer solution (0.5 M H₃BO₃ + 0.05 M Na₂B₄O₇·10H₂O; pH = 7.8) were investigated by means of electrochemical impedance spectroscopy. EIS spectra were interpreted in terms of an “equivalent circuit” that completely illustrate the Al(Al1R alloy)/oxide film/electrolyte systems examined. The resistance of the oxide films was found to increase on passing from Al to Al1R alloys while the capacitance showed an opposite trend. The stability of the anodic oxide films grown in the borate buffer solution on Al and Al1R alloys was investigated by simultaneously measuring the electrode capacitance and resistance at a working frequency of 1 kHz as a function of exposure over a period of time to naturally aerated 0.01 M NaOH solution. Analyses of the electrode capacitance and resistance values indicated a decrease in chemical dissolution rate of the oxide films on passing from Al to Al1R alloys.     

Cutting simulation capabilities based on crystal plasticity theory and discrete cohesive elements

A material microstructure-level (MML) cutting model based on the crystal plasticity theory is adopted for modelling the material removal by orthogonal cutting of the Titanium alloy Ti6Al4V. In this model, the grains are explicitly taken into account, and their orientation angles and slip system strength anisotropy are considered as the main source of the microstructure heterogeneity in the machined material. To obtain the material degradation process, the continuum intra-granular damage model and the discrete cohesive zone inter-granular damage model have been implemented. Zero thickness cohesive elements are introduced to simulate the bond between grain interfaces. The material model is validated by the simulation of a compression test and results are compared with experimental data from the literature. Simulation results demonstrate the ability of the MML cutting model to capture the influence of the material microstructure, in terms of initial grain orientation angles (GOA), on chip formation and machined surface integrity.     

Fracture properties of hydrogenated amorphous silicon carbide thin films

The cohesive fracture properties of hydrogenated amorphous silicon carbide (a-SiC:H) thin films in moist environments are reported. Films with stoichiometric compositions (C/Si ≈ 1) exhibited a decreasing cohesive fracture energy with decreasing film density similar to other silica-based hybrid organic-inorganic films. However, lower density a-SiC:H films with non-stoichiometric compositions (C/Si ≈ 5) exhibited much higher cohesive fracture energy than the films with higher density stoichiometric compositions. One of the non-stoichiometric films exhibited fracture energy (∼9.5 J m⁻²) greater than that of dense silica glasses. The increased fracture energy was due to crack-tip plasticity, as demonstrated by significant pileup formation during nanoindentation and a fracture energy dependence on film thickness. The a-SiC:H films also exhibited a very low sensitivity to moisture-assisted cracking compared with other silica-based hybrid films. A new atomistic fracture model is presented to describe the observed moisture-assisted cracking in terms of the limited SiOSi suboxide bond formation that occurs in the films.     

Improvement of grain refining efficiency for Mg–Al alloy modified by the combination of carbon and calcium

The effects of carbon and/or Ca on the grain refinement of the Mg–3Al alloy have been investigated in the present study. The grain size of the Mg–3Al alloy decreased steeply with increasing the Ca content when it was lower than 0.2%. And then, the grain size decreased slightly when the Ca content was increased to 0.5%. A remarkable grain refining efficiency could be obtained for the Mg–3Al alloy treated with only carbon. Further high grain refining efficiency could be obtained by the combination of 0.2%C and the optimal content (0.2%) of Ca. Therefore, Ca is an effective element to improve the grain refining efficiency for the Mg–Al alloys refined by carbon. The AlCO particles were observed in the samples refined whether by only 0.2%C or by the combination of 0.2%C and a little (less than 0.2%) Ca addition. These AlCO particles should be the potent nuclei for the Mg grains. However, the AlCOCa intermetallic particles were observed when Ca content was increased to 0.5%. Peculiar particles with duplex phases were found in this sample in such a state that AlCO coating film was formed on the surface of Al–Ca compounds. These particles should also be the potent nuclei for the Mg grains.     

Manufacture of a new kind diamond grinding wheel with Al-based bonding agent

A new kind diamond grinding wheel with Al-based bonding agent was prepared in this paper. The influence of sintering temperature to the relative density (R.D.), hardness and service life of diamond grinding wheels with AlSnTi, AlSnTiNiCo, AlSnTiNi and AlSnNiCo bonding agent was studied. The microstructure of different bonding agent sintered at different temperature was observed. The service life of the Al-based grinding wheels was compared with Cu-based or resin-based ones. The results showed that the AlSnTiNiCo is the best composition system in this research. The best sintering temperature is 300 °C. The sample has a high relative density after sintered at 300 °C. The retention of Al-based bonding agent to diamond grit is strong. The service life of this Al-based diamond grinding wheel is about three times as long as that of resin-bonded grinding wheel.