Problems and prospects of selective layer-by-layer laser sintering of powders

The present state, problems, and prospects for the development of a new powder metallurgy technique, called selective layer-by-layer laser sintering, are considered. With this technique three-dimensional powder products can be obtained without resorting to traditional forming methods. The results of experiments in which one-component and multicomponent mixtures based on metals, ceramics, and polymers were sintered in the solid and liquid phase by this technique are discussed.Vitebsk Branch of the Institute of Solid-State and Semiconductor Physics, Belorussian Academy of Sciences. Translated from Poroshkovaya Metallurgiya, Nos. 3/4, pp. 32–37, March–April, 1995.     

Thermodynamic Assessment of the Reduction of WO<Subscript>3</Subscript> by Carbon and Silicon

An interesting process in terms of resource conservation is the arc surfacing of worn components by means of powder wire in which the filler contains tungsten oxide WO₃ and a reducing agent (carbon and silicon). Thermodynamic assessment of the probability of 21 reactions in standard conditions is based on tabular data for the reagents in the range 1500–3500 K. This range includes the temperatures at the periphery of the arc and in the upper layers of the surfacing bath. The reactions assessed include direct reduction of WO₃ by carbon and silicon, indirect reduction of WO₃ by carbon, and reaction of tungsten compounds with carbon and silicon to form tungsten carbides and silicides. The possible reaction products considered are W, WC, W₂C, WSi₂, W₅Si₃, CO, CO₂, SiO, and SiO₂. The reduction of the oxide is written for 1 mole of O₂, while the reactions of tungsten compounds with carbon and silicon compounds are written for 2/3 mole of tungsten W. The probability of the reactions is estimated in terms of the standard Gibbs energy. In the range 1500–3500 K, the standard states of the reagents are assumed to be as follows: W(so); WO₃(so, li), with phase transition at 1745 K; WC(so); W₂C(so); C(so); CO(g); CO₂(g); WSi₂(so, li), with phase transition at 2433 K; W₅Si₃(so, li), with phase transition at 2623 K; Si(so,li), with phase transition at 1690 K; SiO(g) and SiO₂(so, li), with phase transition at 1996 K. To assess the influence of the possible evaporation of tungsten oxide WO₃ in the arc (T_b = 1943 K) on the thermodynamic properties, the thermodynamic characteristics of two reactions are considered; the standard state in this temperature range is assumed to be WO₃(g). Thermodynamic analysis of the reduction of tungsten oxide WO₃ shows that the temperature of the melt and the composition of the powder wire may affect the composition and properties of the layer applied. At high melt temperatures (>2500 K), the formation of tungsten and also tungsten carbides and silicides is likely. These reactions significantly change the composition of the gas phase, but not that of the slag phase in the surfacing bath. Below 1500 K, the most likely processes are the formation of tungsten silicides and tungsten on account of the reduction of WO₃ by silicon. In that case, the slag phase becomes more acidic on account of the silicon dioxide SiO₂ formed. However, this temperature range is below the melting point of WO₃ (1745 K). In the range 1500–2500, numerous competing reduction processes result in the formation of tungsten and also tungsten carbides and silicides in the melt. The reaction of tungsten compounds with carbon and silicon to form carbides and silicides is less likely than reduction processes. Evaporation of tungsten oxide WO₃ in the arc increases the thermodynamic probability of reduction; this effect is greatest at low temperatures.     

Surface layer of commercially pure VT1-0 titanium after electric-explosion alloying and subsequent treatment by a high-intensity pulsed electron beam

The structure, phase composition, and mechanical, tribological, and corrosional properties of commercially pure VT1-0 titanium are investigated after electric-explosion alloying and subsequent treatment by a high-intensity pulsed electron beam. Treatment conditions that greatly increase the properties of the titanium are identified. The physical factors at work here are considered.     

Areas of Application of Clays of the Latnenskoe Deposit

A detailed characterization of clays recovered at the Belyi Kolodets, Strelitsa Blizhnyaya, and Srednii quarries of the Latnenskoe deposit is given. Industrial and commercial uses of these clays are discussed.     

Ceramic clays from Voronezh oblast

The Latnensk deposit of refractory clays and the Shramovsk deposit of refractory clays suitable for production of ceramics ware are examined.     

A two-wave 1064/532-nm diode-pumped pulse-periodic YAG:Nd laser

A compact 1064/532-nm diode-pumped pulse-periodic YAG:Nd laser is described. Its parameters are as follows: the wavelength is 1064 nm, the pulse energy is 1.2 J, the pulse duration is 5 ns, the pulse repetition rate is 100 Hz, and the beam divergence is ≤1.6 mrad. The laser light efficiency is 12%, and the full efficiency of the laser system is 4%. Two lasing modes are realized in the laser: at the fundamental frequency and with the frequency conversion into the second harmonic at a wavelength of 532 nm and a pulse energy of 0.3 J.     

Features of structure formation of the surface layer in the course of electroexplosive alloying tungsten carbide hard alloy

The surface of the VK10KS hard alloy is hardened to 25 GPa; it is affected by pulsed plasma jets formed by the electric explosion of coal-graphite fibers and aluminum or titanium foil. It is established that intense hardening is inherent in alloys after electroexplosive alloying with titanium due to the formation of TiC and (Ti, W)C carbides in the surface layer.     

Integrated Development of the Overburden Rock at the Latnenskoe Refractory Clay Deposit

Overburden rocks at the Latnenskoe Clay Deposit are examined with a view for their potential use. Chemical, mineral, and granulometric compositions, ceramic properties, and processing characteristics of loam, chalk, sand, sandstone, phosphorite, and substandard refractory clay are given. It is concluded that an integrated approach to the utilization of auxiliary minerals will improve the cost-effectiveness of mining operations of the quarry in service at the Latnenskoe Deposit.