All-Russian Research and Design Institute of Hard Alloys and Refractory Metals

The processes of structure and phase formation during the formation of combined physical deposition (PVD)/chemical deposition (CVD) coatings on a hard-alloy tool are investigated. It is shown that the formation of the Cr PVD barrier layer prevents the formation of the η phase with the subsequent deposition of the TiC-Ti(C,N)-TiN CVD coating. Treatment of the CVD coating with the ion-plasma flow and deposition of the finishing TiN PVD layer lead to the formation of the texture {111} in the coating and the diminishment of its subgrains to ∼30 nm. Upon going from articles with CVD coatings to combined PVD-CVD-PVD coatings, the strength and hardness of hard-alloy blades increase. This is explained by the effect that the corresponding phase and structural transformations that occur in the coating and at the phase interfaces during their formation have on these characteristics. The results of certification tests of cutter tools for continuous and intermittent cutting indicate the efficiency of these coatings both for turning work and, especially, for mill operation, when high toughness, along with hardness, is the most important characteristic.

The cracking resistance of the TiC-steel alloys with 40 and 50% TiC decreases with the increase of the carbon content of martensite and with the appearance of excess MxCy carbides in the structure. The permissible volume of the MxCy phase is not higher than 2%.

This work is devoted to a study of the influence of tantalum on the structure and properties of three-phase alloys. The investigations were made with a constant weight ratio of Ti:WC = 35:65% and an unchanged carbon content. The alloys were prepared by mixing of the (T, W, Ta)C carbides with cobalt and tungsten carbide. The pressed specimens were given a preliminary sinter in hydrogen at 923-973 K and a final one in a vacuum furnace at 1773 K. The microstructure, density, and bend and compressive strengths at room and increased temperatures, coeffiecients of cutting life and strength (in comparison with a standard taken as unity), and adhesion interaction were determined. The coefficient of cutting life was determined by transverse machining of steel. The coefficient of strength was determined by the method of breaking feed in milling of 50 steel with a single-tooth cutter. The adhesion interaction of TiC-WC-TaC-Co alloys with the material being machined (50 steel) was determined in vacuum (which eliminated the additional influence of oxidation of the alloy) at 873 K with a load of 1000N. Tantalum carbide additions have a favorable influence on the physicomechanical and service properties of TiC-WC-Co alloys. Their bend strength at roommore » and increased temperatures increases and there is an increase in the total deformation and the work for deformation at increased temperatures, a reduction in oxidation and adhesion interaction with the material being machined, and a significant increase in wear resistance in cutting. Graphs and tables are included.« less

In this work an investigation was made of the wettability of titanium and tungsten carbides and also of (Ti, W)C solid solutions by the molten intermetallic compound Ni/sub 3/Al, which has been used for some time as a binder for sintered carbides. The wetting process was investigated using the stationary variation of the sessile drop method in vacuum on a special induction unit with an Alundum tube enveloping a graphite fabric one, which serves as the heating body. The carbide-intermetallide contact zone was investigated by optical microscopy and micro-x-ray spectral analysis. The investigations conducted showed the possibility in principle of creation of compact TiC-WC pseudobinary system carbide-Ni/sub 3/Al intermetallide composites produced by liquid-phase sintering. Diagrams and table are included.

In order to study the effect of tantalum on the structure and properties of the complex carbides (Ti, W, Ta) C, the authors prepared solid solutions (Ti, W, Ta) C with the molar concentration ration TiC: WC = 64:36 (35:65 by weight). It is shown that the electrical resistivity of the alloys decreases with increasing amount of tantalum carbide, i.e., the electrical conductivity increases. This is caused by the increased concentration of the conducting (free) electrons and the increased Me-Me bond strength. Alloying with tantalum considerably changes the physicomechanical properties of the carbide constituent of th hard metals, viz., the (Ti, W, Ta) C solid solution. The concentration of the dissolved tungsten and titanium in the cobalt phase is determined by the carbon content in the alloy.