Special features of manufacturing highly porous materials from silicon nitride,silicon oxynitride,and sialons

Results obtained in a study of factors that affect shaping and sintering of highly porous materials are presented. A technology providing highly porous silicon nitride materials that is based on shaping preliminarily fabricated pieces of thermoplastic slip makes it possible to use initial silicon powders of different dispersities. Highly porous materials can also be produced on the basis of sialons and exhibit a diminished thermal conductivity and a heat resistance at the level of similar silicon nitride materials.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 11, pp. 8 – 13, November, 1996.     

Stabilization of water suspensions of metal powders

Sedimentation stability of water suspensions of dispersed metal powders with water-soluble high-molecular compounds (HMC) added is investigated by a method of analyzing the kinetics of their sedimentation. When stabilizing by polyvinyl alcohol (PVA) the concentration regions of sedimentation stability for the suspensions are determined. The stabilization is explained according to the model of formation of coagulation HMC layers on metal particles. The dependence of the coagulation layer thickness on the concentration of PVA in the solution is estimated.Republican Engineering-and-Technical Center of Powder Metallurgy, Perm'. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 64, No. 5, pp. 583–587, May, 1993.     

Experimental study of the structure of multicomponent nanostructured coatings on the basis of Ti-Zr-N alloys formed by ionic plasma methods

The stabilization and interpretation of properties of ion-plasma-produced multicomponent nanostructured coatings (MNCs) is a fairly complicated problem because of a great variety of factors which influence their characteristics. This work is aimed at the establishment of a correlation between the processes of the production (using vacuum-arc evaporation or a special combined method) of nanodimensional coatings on the basis of the Ti-Zr-N system and the processes proceeding in the near-surface layers of the material of the sputtered and evaporated targets. The coatings were obtained using a modernized URMZ.279.048 setup equipped with two electric-arc vaporizers and four dc magnetrons. The structure, properties, and morphological features of MNCs and the relief of the target surfaces were investigated using a Nanoskan atomic-force microscope, a CARL ZEISS LEO 1430 VP scanning electron microscope, and an Umka scanning tunneling microscope. A difference in the processes that take place on the surface of the evaporated and sputtered targets has been established and their analogy with the processes of MNC formation was revealed for the first time.     

Special features of the α → γ transformation in powder carbon steels

The structural state of powder steels after sintering depends on the technological regimes of their production and can markedly affect the transformations in subsequent heat treatment. The effect of the technological regimes on the nature of the transformation is investigated.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 14–16, March, 1996.     

Role of bulk and mass effects of reactions in reaction sintering processes

Peculiarities of the fabrication of ceramic porous and dense composite materials based on compounds of the Si–C–O–N system with the participation of chemical reactions and the formation of new phases are discussed. An analysis of comparatively new technologies is attempted in terms developed in earlier studies on the reaction sintering of silicon nitride, carbide, and oxynitride. It is shown that the approach to reaction sintering that includes the selection of promising reaction systems allowing for the bulk effect of reactions accompanying material formation can be extended to the fabrication of porous and highly porous materials. In contrast to the fabrication of dense materials, when reaction systems with positive bulk effects are used, the reaction systems with negative bulk effects can be used in the fabrication of highly porous materials.     

Structure-phase composition and properties of mechanically alloyed high-nitrogen powder steels

The structure and properties of the Fe-21% Cr-N and Fe-18% Cr-7% Ni-0.8% Mn-0.5% C-N powder systems mechanically alloyed in nitrogen atmosphere and steels sintered from the powders in dissociated ammonia at t = 1170°C have been investigated. The thermodynamic calculations of the phase compositions of the steels are carried on the basis of searching the Gibbs integral energy minimum for the system. In comparing the obtained experimental data with the results of thermodynamic calculations for the Fe-Cr-C-N and Fe-Cr-N systems, it is found that the equilibrium phase composition is not reached. The resulted steels contain increased nitrogen quantity (1.6 to 2.1%) distributed in austenite and/or nitrides. The steels have high strength, wear and corrosion resistance.