A study of new phase of elongated shape in granular structure of WС-(Ti,W)С-Со cemented carbide after its solid-phase annealing

Abstract

The results of the investigations by scanning electron microscopy, Auger spectroscopy and X-ray diffraction of the structure of Т5К10 cemented carbide (WC-(Ti,W)C-10Co group) sintered at 1520 °C before and after its additional heat treatment in vacuum at 1200 °C for 7 h are presented. It was shown that in addition to faceted WC grains, globular (Ti,W)C (γ-phase) grains of equilibrium (ratio Ti:W ~ 1:3) chemical composition for sintering temperature 1520 °C and Co-based layers, new inclusions of elongated shape up to 30 μm wide and up to 200 μm long were revealed in the structure. They are distributed stochastic both singly and in the form of clusters. The new phase contains the chemical elements W, Ti, C in the ratio (wt%) of the average values as 6.26:9.39:84.35, which is described by the stoichiometric formula W2.3TiС2.6. In contrast to the cubic cell of (Ti,W)C solid solution, the new phase has a hexagonal GaSe type crystal cell (quality H) with parameters a = 3.750 nm and c = 15.950 nm. On the surfaces of the new phase there are dispersed grains WС and (Ti,W)С solid solution, the sizes of which are 3–6 times smaller than the sizes of similar grains of the basic structure. The content (4.77%) of C in the dispersed grains of WC and in the same grains of the main structure is less than the calculated one. The cobalt phase in the adjacent surface of the new phase of the basic structure is superseded by W (3.57%) and C (0.85%).The formation of a new phase W2.3ТіС2.6 elongated shape in the structure of the T5K10 cemented carbide for the above annealing conditions cannot be explained by the basics of modern material science of its production.