Papers by Keyword: V

Abstract: (W,Ti)C-10%Co system cermets doped with Ta, Nb or V grain growth inhibitor were prepared in this work. The effect of Ta, Nb and V on the microstructure and mechanical properties of (W0.8783Ti0.0976VB0.0242)C-10%Co systems was investigated. The results show that the three elements play an important role on the WC grain growth and shape; the cermets appeared uniformly distributed as whiskers or thin platelets. V results in the hardest material, Ta causes the material to become harder compared with (W0.9Ti0.1)C-10%Co cermets. But the hardness of cermets with Nb addition decrease because of the increasing of porosity.

Abstract: From the viewpoint of oxide metallurgy and the impact of V on Steel organization, the morphology, size, distribution and composition of the inclusions in Steel after V deoxidation were studied by using optical microscopy and SEM, and organization changes of steel after adding V were investigated. The results of the experiment were showed that acicular ferrite was radially appeared at the core of small inclusions after adding V. Carbon, nitrides (VN, V3C4) of V can become nucleation of intragranular ferrite, which were small and dispersed. V could also refine the organization of steel.

Abstract: A series of V-Cr/SBA-15/Al₂O₃/FeCrAl metal monolithic catalysts with V content of 10wt% and Cr contents from 0 to 12.5wt% were prepared. The structure of the catalysts was characterized using XRD, XPS and TPR techniques. The catalytic activity for oxidative dehydrogenation (ODH) of propane with CO₂ was evaluated. The results indicate that the mesoporous structure of SBA-15 was retained after vanadium and chromium incorporation and the vanadium species were well dispersed. The V-Cr/SBA-15/Al₂O₃/FeCrAl catalyst with 10wt% V and 10 wt% Cr exhibited the best activity with a propane conversion of 49.9% and a propylene selectivity of 86.5% at 650 °C.

Abstract: Pt-IrOx and Au-V2O5 thin films were created by magnetron co-sputtering from multiple targets in an Ar-O2 mixture. Successful Pt-IrOx production required high O2 partial pressure and slow deposition rate followed by post-annealing in pure O2. In contrast, deposition of Au-V2O5 films required relatively low O2 partial pressure, and did not need any post-anneal. These different strategies for forming oxide dispersion strengthened films in a multi-target reactive sputtering configuration are directly related to the thermodynamic characteristics of the two materials systems. The most important characteristics are the low equilibrium oxygen solubility in Pt and Au, and the different degrees of oxygen affinity by Ir and V.

Abstract: The effect of interpass time during thermomechanical processing of AA61111 on flow behaviour and microstructure evolution has been investigated. This was achieved using plane strain compression testing undertaken on the Sheffield thermomechanical compression (TMC) facility, using the hit-hold-hit-quench approach. Following solution treatment at 560°C for 1200s, samples were water mist quenched to 320°C and deformed at a constant strain rate of 85s-1 to an initial strain of 0.5, unloaded and held for delay times of 0.019, 6, 60, 600 and 6000s and then given a second deformation for a further strain of 0.5, followed by a water quench to room temperature. Hardening of the alloy was observed, the extent of which was dependent on the hold time. The microstructure of the samples was quantified by TEM in order to determine the extent of strain induced precipitation. TEM identified precipitation, predominantly β and Q phases, on dislocation lines, the size and volume fraction of which were a function of the hold time. The coarsening rate during the hold period of the precipitates was considerably faster than for coarsening following a conventional precipitation treatment. The size of the microband structure at the end of the double deformation was a function of the hold time, suggesting that coarsening of the precipitates during the hold had altered the Zener pinning potential. The implication of these observations on the thermomechanical processing of 6xxx alloys is discussed.

Abstract: The application of 6000 series alloys is widespread and of particular importance to the automotive sector. Their functionality depends on the detailed behaviour of the strengthening phases. In this study, transmission electron microscopy (TEM) supplemented with a variety of mechanical tests were used to examine the precipitates and their role in aspects such as the Bauschinger effect, damage and fracture events, and in recovery and recrystallization processes.

Abstract: In dynamic dislocation-defect analysis, the thermodynamic deformation-mode signatures are examined as the ageing proceeds. In this method, the activation volume (ν) and the mean slip distance (λ) is simultaneously determined with the flow stress (τ) such that the inverse workhardening slope (1/θ) can be plotted versus b2λ/ν where b is the Burgers vector. The slope of this almost linear locus is directly proportional to the activation distance (d). Calibration with a model alumina-dispersed high conductivity copper reveals that punched-out loops are produced up to failure and is represented by a linear locus from 0.1 to 11 % strain. Artificial ageing of AA6111 at 180°C follows this pattern but the naturally-aged specimen manifest a distinctly different signature which shows a transition as the GP zone-type precipitates are sheared. Furthermore by selecting a suitable tensile-test temperature below 250K, the particle size and volume fraction can be determined if particle shearing does not take place. The optimum size and volume fraction necessary for sufficient strength and ductility can be assessed using this method.

Abstract: AA6111 sheet alloy has been used in automotive panel applications in North America and Europe for several years. This alloy exhibits an excellent combination of strength, formability, ageing response and surface appearance following forming and painting operations. Such a combination of properties is obtained by carefully tailoring the processing route to obtain the desired microstructure of the alloy. In recent years, the ability to predict the phase stability in different alloys has improved significantly, and it is now relatively easy to predict the particles that could form in complex multi component alloys during different processing steps. The accuracy of the predictions is dependent on whether or not the free energy expressions used in the calculations are correct. In this study, the AA6111 alloy was subjected to various annealing treatments that are reflective of different phase fields computed by the Thermo-Calc software. The particles were extracted using the phenol extraction technique and were identified using energy dispersive analysis. The interrelation of the particle analyses with the computed phase stability in AA6111 is presented.

Abstract: This paper presents results from quasi-static and high rate tensile testing of three aluminum sheet alloys, AA5754, AA5182 and AA6111, all of which are candidates for replacing mild steel in automotive bodies. Tests were performed at quasi-static rates using an Instron apparatus and at strain rates of 600 to 1500 s-1 using a tensile split Hopkinson bar. Additionally, an in-depth investigation was performed to determine the levels of damage within the materials and its sensitivity to strain rate. The constitutive response of all of the aluminum alloys tested showed only mild strain rate sensitivity. Dramatic increases in the elongation to failure were observed with increases in strain rate as well as greater reduction in area. Additionally, the level of damage was seen to increase with strain rate.

Abstract: Nonempirical study of the site preference occupation for Ni and V substituting in Fe3Al has been carried out in the framework of the coherent potential approximation. Obtained values of total energies show in a full agreement with experiments that Ni atoms in the equilibrium configuration occupy the iron sub-lattice for alloying with 5 at % of Ni in the Fe3Al-based alloy. Calculations of alloys with the V-doped iron aluminide in the D03 phase show differences in bonding and site occupation preferences in comparison with Ni doping. V atoms occupy aluminum sublattice.