Machining of plastics with magnetoabrasive powders

Conclusions Magnetoabrasive machining can be successfully employed as the finishing operation in the manufacture of plastics articles. The effects of magnetoabrasive machining time, powder particle size, and peripheral speed of rotation on the surface roughness of plastics and the amount of material removed from them have been determined. Considerable differences in response to machining have been found between homogeneous and heterogeneous plastics.Translated from Poroshkovaya Metallurgiya, No. 5(269), pp. 70–74, May, 1985.     

Composite powders for controlled abradability applications

Abstract

The use of composite powders for abradable seals is increasing and is a unique solution to the problem of maintaining pressure differentials in the flow of hot gases in high-performance turbine engines. This paper reviews the powder production methods and the properties of various commercial composite powders. The methods used to form these powders into abradable structures are outlined and the properties of these structures are discussed. Specific engine applications are detailed and the use of advanced composite powders in future turbine engines is outlined.

Résumé

Il y a accroissement de l'utilisation de composites frittés pour des joints d'étanchéité usables par abrasion; ceux-ci sont une solution unique au problème du maintien de différences de pression des gaz chauds dans les diverses sections des moteurs à turbine à haute performance. Les méthodes de production de poudre et les propriétés des divers composites frittés commerciaux sont pas sées en revue dans cet article. Les grandes lignes des méthodes utilisées pour transformer les poudres en structures usables par abrasion sont présentées et les propriétés de ces structures sont discutées. On présente en détail des applications à des moteurs particuliers et on esquisse l'utilisation de composites frittés plus avancés dans les moteurs à turbine de l'avenir.     

Composite materials based on polymer binders and very fine silver and graphite powders

Conclusions An investigation was carried out into the effect of various factors on the electrophysical properties of coatings formulated from a polymer binder and very finely divided silver and graphite. It has been established that for silver-base systems the greatest increase in conductivity is achieved by the application of ultrasonic vibration during the preparation of the silver powder and its subsequent polishing, and for graphite-base systems, by comminution of the graphite. The electrical conductivity of finished coatings is increased by calendering, which leads to the formation of additional contact points as a result of denser packing and the breaking up of surface particle agglomerates. The properties of such paste coatings are strongly affected by the rheological characteristics of the pastes. Optimum relative amounts of the paste components (polymer, diluent, and filler) have been established, and the rheological characteristics determined. Compositions of current-conducting pastes of low annealing temperature have been developed which can be applied to base materials of low heat resistance.Translated from Poroshkovaya Metallurgiya, No. 12(228), pp. 60–65, December, 1981.     

Structure formation in magnetoabrasive materials from iron-carbon melts alloyed with carbide-forming elements

Conclusions The structures of magnetoabrasive powders from iron-carbon melts alloyed with carbideforming elements constitute disperse systems which can arbitrarily be divided into two groups: 1) structures characterized by the presence of two distinct types of components — a monocarbide (TiC, Nb₄,C₃, ZrC, or VC), which possesses abrasive qualities, and a ferromagnetic (Fe-Si) matrix, which ensures the necessary magnetic properties, and 2) structures characterized by the fact that abrasive functions are performed by all their structural constituents — a double carbide formed by iron together with an alloying element (Si, Mo, W, or Cr) and a martensitic (bainitic) matrix. The particles of an atomized magnetoabrasive powder from any given alloyed melt have structures differing in macromorphology, which is a result of differences in conditions of solidification of metal drops during melt disintegration. In the presence of carbide-forming elements silicon in an iron-carbon melt dissolves mainly in ferrite, without significantly affecting the morphology of structure of the atomized particles. The effectiveness of magnetoabrasive machining (polishing) depends to a large extent on the choice of abrasive and work materials.Translated from Poroshkovaya Metallurgiya, No. 2(242), pp. 76–84, February, 1983.     

Formation of TiN/TiC-Fe composites from ilmenite (FeTiO3) concentrate

The production of a ceramic hard material-metal composite directly from a mineral concentrate has great potential application. An homogenizing pretreatment of a mixture of ilmenite (FeTiO₃) and graphite, followed by annealing under an argon ambient, showed the formation of titanium carbide and elemental iron. Annealing of the same powder in nitrogen resulted in the formation of a composite of elemental iron and titanium nitride. The nitride was formed at a lower temperature than the carbide with almost complete conversion after 1 hour at 1000 °C. The rate of carbide formation was controlled by carbon diffusion, whereas the nitridation reaction was controlled by either oxygen or nitrogen diffusion. The TiC was found to form via TiC_0.5, which slowly increased its carbon content until near stoichiometric TiC was formed; stoichiometric TiN formed directly with no intermediate phases. Titanium carbide showed the presence of a second phase with a slightly smaller unit cell size; this was due to interdiffusion between the iron and TiC. The titanium carbide composite was found to be composed of 3 to 4 μm anhedral iron grains dispersed in the titanium-rich matrix. There was no segregation in the iron/titanium nitride composite with apparently submicron distribution.     

Morphology,microhardness, and grinding ability of single-crystal powders

Conclusions A study was made of the variation of the morphology and size of TiC and TaC crystals as functions of cooling rate of solutions of these carbides in molten Al (in the mass crystallization process). TiC and TaC were found for the first time to be characterized by polar as well as by reticular anisotropy of microhardness on their (111) faces. It was confirmed that the slip systems in TiC and TaC are {110} [110] and {111} [110], respectively. It is shown that TiC and TaC single crystals surpass corundum and fused carbides (TiC) in grinding ability and strength of individual grains.Translated from Poroshkovaya Metallurgiya, No. 8(224), pp. 76–80, August, 1981.