Densification kinetics of a copper-tin powder composite during electric-discharge sintering

Conclusions In the electric-discharge sintering of a copper-tin composite raising the prepressing pressure from 4.17 to 12.5 MPa decreased the extent and rate of shrinkage by more than half. To attain the same hardness in the sintered copper-tin powder composite on passing from a low (4.17 MPa) to a higher prepressing pressure (12.5 MPa), it was necessary to resort to increasing the current density by 100 A/cm² (from 595 to 695 A/cm²).Translated from Poroshkovaya Metallurgiya, No. 7(295), pp. 19–21, July, 1987.     

Infiltration of graphite by aluminum during electric-discharge sintering

Conclusions During the electric-discharge sintering of an aluminum powder in contact with graphite, infiltration of the latter by molten aluminum takes place. A similar phenomenon is observed during sintering in a graphite-bronze system. The intensity of infiltration growswith increasing effective current density and with rising external mechanical pressure. Infiltration by aluminum increases the strength and wear resistance of graphite and decreases its coefficient of friction on steel.Translated from Poroshkovaya Metallurgiya, No. 3(231), pp. 26–28, March, 1982.     

Reactive electric-discharge sintering of TiN-TiB2

Powder mixtures based on titanium and its dihydrides are sintered by electric discharge in a certain current mode to produce TiN + TiB₂ composites. It is established that the use of tetragonal titanium hydride as the starting material results in the complete synthesis leading to a TiN + TiB₂ composite. The higher shrinkage rate results from the higher purity of titanium dihydride, which, in its turn, increases the partial pressure of hydrogen in the reaction area and the reaction rate. Tetragonal titanium hydride is more preferable than cubic hydride and metal titanium. The microstructure of alloys resulting from the sintering of hydride-based mixtures is more homogenous: it includes equiaxial grains with the mean size of about 1 µm.     

Activated sintering of W-HfC composite materials

The features of consolidation of the particles during the activated sintering of tungsten powders with different values of dispersity (d _av = 2–3 and 0.8–1.0 μm) are investigated. Sintering was activated by introducing nickel additives (up to 0.5 wt %), tungsten nanoparticles (up to 30 wt %), and finely dispersed hafnium carbide (5–30 vol %) with subsequent milling in a vibrating mill. The uniaxial compaction of the samples has been performed under pressures from 50 to 1000 MPa, and sintering was performed in vacuum at 1850°C with holding for 1 h. It is shown that the additives of tungsten carbide increase the density of sintered billets and, in combination with dispersed hafnium carbide, tungsten-based composite materials with a grain size up to 2 μm can be obtained.     

Wear-resistant coatings produced by shock-wave compaction of powders

Wear-resistant metal-matrix composite coatings with a thickness of 1.5 mm were fabricated on low-alloy steel substrates by explosively generated shock waves. Starting materials were equivolume mixtures of WC or Cr₃C₂ powder mixed with either titanium or cobalt powder as a binder phase. Three different planar geometries were used, with powder layer thicknesses varying from 1 to 3 mm. Microstructural examination showed that fully dense, crack-free coatings could be produced with a uniform distribution of the carbides within the metallic binder phase. Shear strengths in excess of 40 MPa were measured for coatings composed of equivolume powder mixtures of (Cr₃C₂ + Ti) and (WC + Ti). The weight loss of a coating produced from an equivolume (WC + Co) powder mixture measured from a two-body abrasive wear test was significantly lower than that measured for a wear-resistant tool steel used as a reference material.     

Thermal treatment of steel-TiC composite materials produced by laser surfacing

The effect of heat treatment (ageing) on the microstructure and properties of SPN14A7M5/TiC materials produced by laser surfacing is studied. The optimum ageing conditions are found.     

Influence of specific energy expenditures in electric-discharge sintering on the structure and properties of a copper-tin-abrasive composite

Conclusions It has been experimentally established that an increase in the specific energy expenditure caused by an increase in the strength of the dc leads to an increase in process temperature in electric discharge sintering of a copper-tin-abrasive composite. By changing the specific energy consumption parts with different structures and properties are obtained from this composite by electric discharge sintering.Translated from Poroshkovaya Metallurgiya, No. 8(284), pp. 67–70, August, 1986.     

Wear-resistant Ti-Al-Si-C-N coatings produced by magnetron sputtering of SHS targets

The results of an investigation into hard wear-resistant nanostructured coatings in the Ti-Al-Si-C-N system produced by the magnetron sputtering of multicomponent composite targets with various ratios of metallic and nonmetallic elements are presented. Coatings are deposited in the reaction gas mixture with constant values of the substrate temperature and bias voltage. The structure of coatings is investigated using X-ray diffraction, glow-discharge optical emission spectroscopy, scanning and transmission electron microscopy. The mechanical and tribological properties are determined using the nanoindentation and scratch-testing methods, as well as using tribological tests according to the “pin-on-disc” scheme. The results of investigations show that the coatings are based on the fcc phase consisted of titanium carbonitride with an average crystallite size of 2–20 nm; the crystallites are arranged in an amorphous matrix. The coatings of optimal composition possess hardness of 40–50 GPa, a stable friction coefficient of <0.55, an adhesion strength of ≥50 N, and a wear rate of <1 × 10^?5 mm³/(N m).     

Structure and properties of tungsten carbide obtained by electric-discharge sintering of a disperse powder

Samples of highly dispersed tungsten carbide powders of various origins were obtained by electrical-discharge sintering. The specimens were 8 mm in diameter, 5 mm in height and had a grain size of 1 µm, density 15.5–15.8 g/cm³, hardness 92–93 HRA, and cracking resistance 6–8 MPa·m^1/2. The structure and phase composition of the sintered samples was not observed to change appreciably from those of the initial powder. The salient features of electrical-discharge sintering of tungsten carbide power are described.