Non-conventional methods of machining are used for many engineering applications where the traditional processes fail to be cost-effective. Such processes include Ion Beam Machining (IBM), focused ...ion beam (FIB) machining and plasma discharge machining. The mechanisms of material removal and associated hardware and software developed for industrial applications of these fascinating electro-physical and chemical machining processes are reviewed together with the latest research findings.
A previous paper reported some features of atmospheric Tungsten inert gas arc plasmas obtained with Langmuir probes operating in floating conditions and results on averaged quantities were given. ...This paper develops the method for probes in biased conditions. Because in the available literature sources, the construction of characteristic curves (V-I) in arcs is not discussed, a description of directly observed quantities is presented and some constructive methods are shown for a range of arc currents (50 to 200 A) and probe positions with considerable detail. The main result of this work is that these curves are incomplete in the column of atmospheric pressure arcs so that the traditional methods to extract plasma parameters are of little use. In contrast to previous works dealing with the anode region of the arc, it is found that the only useful portion of the V-I curve is the ion saturation part for all the arc currents investigated. Also, it is not possible to identify the plasma potential from the V-I curve. Ion saturation occurs for all probe locations at the lowest arc currents, whereas saturation is uncertain for probes closer to the cathode at higher arc currents. When saturation does occur, it is characterized by the flatness of the curve with respect to the potential: no power law dependencies on the voltage are found. Also, for the higher arc currents, an inner arc region can be identified where ion saturation is uncertain or does not occur. An accompanying paper exploits the ion saturation part of the characteristics to estimate the arc plasma temperature.
In a previous paper, it was shown that only the ion portion of the probe characteristics curve (V-I) can be used to estimate the temperature from probes sweeping in the column of a flowing ...atmospheric pressure arc plasma. Methods relating the measured ion current directly to the temperature can be used, if a particle density-temperature relationship is available. However, several sources of "disturbance" need to be considered in the application of these methods. The main focus of this paper is in establishing how the experimental data permit an identification of the correct model taking into account these limitations. It is shown that some previously published criteria for the establishment of cooling induced by probes in atmospheric pressure arc plasmas and of recombination in the perturbed region are inadequate and their modification is consistent with the gathered data. Because of the thin and collisionless sheath, the temperatures reconstructed by probes belong to the edge of a sheath which is fully embedded in a perturbation region (PR) and not to the bulk of the plasma. A range of arc currents is studied and comparison with data from emission spectroscopy is used to assess and quantify the degree of depression shown by the probe determined temperatures. The consideration of flow velocity within the expressions for the probe currents shows that ad hoc corrections, in absence of direct experimental evidence on flow velocity distributions, do not lead to substantial benefit for the temperature corrections. "Cooling" mechanisms are considered and between ion energy loss and ion-electron recombination, the first dominates at temperatures below about 7500 K, whereas the latter dominates within the PR in the temperature range 9-13 000 K. For higher temperatures, the two contributions are very close to each other. Despite the severe interpretation difficulties, the practical reproducibility of the results and their empirical relationships with spectroscopic values assumed "exact," permits the reconstruction of reasonable electron temperature by the probe method in these plasmas even if experimental data on flow velocity distribution are not available.
The Ti-10Nb-10Zr-5Ta alloy, prepared in a levitation melting furnace, was investigated as a possible candidate for replacing Ti6Al4V alloy in medical applications. The sessile drop method, ...pin-on-disc and in vitro tests were used to analyze wettability, wear resistance, and biocompatibility of the new alloy. The characteristics of the Ti-10Nb-10Zr-5Ta alloy were assessed in comparison to those of the Ti6Al4V alloy. The Ti-10Nb-10Zr-5Ta system was found to have hydrophilic characteristics with similar contact angle as the Ti6Al4V alloy. In all environments (deionized water, simulated body fluid and Fusayama Meyer artificial saliva), the friction coefficient showed a stable evolution versus sliding distance, being similar for both alloys. On overall, the wear resistance of Ti-10Nb-10Zr-5Ta alloy was lower than that of Ti6Al4V for all testing environments. The Ti-10Nb-10Zr-5Ta alloy exhibited good biocompatibility characteristics at in vitro test compared to Ti6Al4V alloy. The cell viability on Ti-10Nb-10Zr-5Ta surfaces was higher than the one observed on Ti6Al4V samples, regardless the number of days spent in osteoblast-like cells culture. A high degree of cell attachment and spreading was observed on both alloys.
Ti-10Nb-10Zr-5Ta alloy was investigated as possible material candidate for replacing Ti6Al4V in medical applications. The alloy was prepared in a levitation melting furnace and characterized in terms ...of elemental and phase composition, microstructure, mechanical properties, and corrosion resistance in simulated body fluid and Fusayama Meyer artificial saliva solutions. The characteristics of the new alloy were compared to those of the Ti6Al4V alloy. The Ti-10Nb-10Zr-5Ta system was found to posses of a polyhedral structure consisting in α′ and β phases. X-ray structural analysis revealed a mixture of hexagonal α′ martensite (main phase, with grain size of about 21 nm) and β bcc phase. The Ti-10Nb-10Zr-5Ta alloy exhibited some better mechanical properties (Young modulus, tensile properties) and corrosion resistance (polarization resistance, corrosion current density, and corrosion rate), as compared to Ti6Al4V alloy.
The determination of residual stress (RS) in case-hardened steel gear truck synchronisers coated with thermal sprayed molybdenum was carried out using neutron and synchrotron X-ray diffraction. Two ...samples with different coating thicknesses (about 120 μm and 1.4 mm) and different steel substrates (16MnCr5 and SAE4140, respectively) were investigated. Microanalysis revealed substantial porosity in both samples and some debonding was observed between the thin coating and the substrate. The bulk hardness of the SAE 4140 proved to be much higher than the 16MnCr5 and the surface case-hardening increased it by a further 20%. The full three-dimensional stress depth-profile was determined by neutron diffraction (ND) in both the coatings and the substrates, while synchrotron radiation allowed a depth strain scan in the thinner sample. Corrections were applied to the ND data to overcome the surface effect and data reduction was performed to coherently interpret the results, including the determination of the centre-of-mass of the diffracting volume. The results show how thermal stresses play an eminent role in this system, especially in the case of the thicker coating. Quenching stresses mitigate their effect in the thinner coating. Stresses as high as 800 MPa are reached in the sample with the thicker coating, while they are limited to 250 MPa in the sample with the thinner coating. This can be explained by the radically different yield strength of the two steels and by the different coating characteristics.
Hyperon production in the threshold region was studied in the reaction pp→K+Λp using the time-of-flight spectrometer COSY-TOF. Exclusive data, covering the full phase-space, were taken at three ...different beam momenta pbeam=2.59, 2.68 and 2.85 GeV/c (corresponding to excess energies of ɛ=85, 115 and 171 MeV). Total cross-sections were deduced to be 7.4±0.5 μb, 8.6±0.6 μb and 16.5±0.4 μb, respectively. Differential observables including Dalitz plots were obtained. From the investigation of the Dalitz plot at pbeam=2.85 GeV/c a dominant contribution of the N∗(1650)-resonance to the reaction mechanism was found. In addition the pΛ-final-state interaction turned out to have a significant influence on the Dalitz plot distribution even 171 MeV above threshold.
The atmospheric pressure Tungsten Inert Gas (TIG) arc plasma in argon is studied combining results from emission spectroscopy temperature maps with composition data and transport parameters available ...from literature. Two arc currents are considered and maps are obtained for the Debye number, the number of particle in the Debye sphere, which shows values of the order of 10 or less in the core region of these arcs. This low number puts into serious question the plasma quasi-neutrality. It is striking that this circumstance occurs where Local Thermodynamical Equilibrium (LTE) is usually assumed in these discharges. It is shown that TIG arcs violate the quasi-neutrality requirements and, as such, these discharges are called 'plasma' quite improperly. Differently from previously published works, the starting point of the discussion is the experimental two-dimensional temperature maps.
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