We report on investigations of gas metal arc welding plasma operated in pure argon and in a mixture of argon and CO 2 at a dc current of 326 A. The spatially resolved electron densities and temperatures were directly obtained by measuring the Stark widths of the Ar I 695.5 nm and Fe I 538.3 nm spectral lines. Our experimental results show a reduction of the plasma conductivity and transfer from spray arc to globular arc operation with increasing CO 2 concentration. Although the electron density n e increases while approaching the core of the plasma in the spray-arc mode, a drop in the electron temperature T e is observed. Moreover, the maximum T e that we measure is about 13 000 K. Our experimental results differ from the Haidar model where T e is always maximum on the arc axis and its values exceed 20 000 K. These discrepancies can be explained as a result of underestimation of the amount of metal vapours in the plasma core and of the assumption of local thermal equilibrium plasma in the model.

Abstract. For the UV OH band at 306.357 nm (transition A 2 , ν = 0 → X 2 , ν = 0) that is frequently observed in hot gases containing oxygen and hydrogen (flames, arc plasmas), a very sensitive variation of two groups of unresolved rotational lines as a function of the temperature has been found. Using a numerical simulation, this variation has been calibrated as a function of the temperature and of the optical apparatus function. This calibration allows us to easily determine the rotational temperature without computing any line intensity.

For testing the determination of the reactivity of aluminum powders it is proposed to use the following parameters: temperature of the beginning of oxidation, maximal oxidation rate, degree of transformation (degree of oxidation) of aluminum, relative thermal effect. Parameters for an evaluation of the reactivity of powders were chosen following the analysis of results of a non‐isothermal oxidation of powders of different grain size under conditions of programmed heating (the oxidizer being air). According to the proposed method of testing, the sample of ultrafine powder UFAP‐4 produced by the electrical explosion of wires has the highest reactivity among the studied powders.

This work was aimed at studying the tribological properties of nanolamellar tungsten and molybdenum disulfides produced from nanosized W and Mo nanopowders by self-propagating high-temperature synthesis. The prepared WS2and MoS2powders were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), and differential thermal analysis (DTA). For tribological tests, oil-based lubricants added with nanolamellar tungsten and molybdenum disulfides were prepared. The tribological tests show that the friction coefficient of the nanolamellar powders is lower than that of commercial powder(μmin=0.024and 0.064, resp.). It is also found that the oil-based lubricants with nanolamellar disulfide additives display higher antifriction and antiwear properties compared to commercial powder.

Composition of the applied shielding gas has a strong influence on physical properties of the plasma and parameters of the welding process. In particular, increase of the percentage of carbon dioxide in argon results in an increase of the transition current value while changing from the globular to spray mode of metal transfer during the welding process. In order to explain this phenomenon, the MIG/MAG welding arc plasma was investigated for different mixtures of argon and carbon dioxide in the shielding gas. Applying a fast camera, recording distribution of spectral lines of the plasma components, we noticed some phenomena not described yet in the literature. Especially, there is a limit in the percentage of relative concentration CO2/Ar beyond which the arc shape is significantly modified.