Last modified: 2018-07-27
Abstract
Abstract
Hot isostatic pressing (HIP) is known to be a process which permits to elaborate totally dense cemented carbide with perfect homogenous structure. It also offers the possibility to totally consolidate the powders mixtures WC-Co without reaching the fusion temperature of the binding cobalt. The HIP process was used in this work to produce three cemented carbide simples with 11% mass cobalt. The temperatures of treatment are 1350C to 1400C. The pressure of HIP cycle used is 1950 Bars.. The conditioning of powders mixtures of tungsten carbide and cobalt is realized in a titanium and mild steel containers. Within the context of this work we studied the reactivity of the material of the container with the components of mixtures of base powders densified by HIP. Observations by scanning electronic microscope revealed that the hipped sample obtained, is composed of a cobalt and tungsten carbide dispersed homogeneously. However, there is an inhomogenous distribution of both WC and Co phases at the interface steel container-compressed. Analysis by X-ray diffraction and energy dispersion reveals zones very rich in iron at the interface steel container-compressed. This results in the formation of mixed carbides FeW3C, which generates an alteration of mechanical properties in zones close to the container. The transmission electron microscopy observations show that the WC-Co interfaces appear without any secondary phases and are parallel to the single crystallography planes of the WC lattice. On the other hand, the interfaces WC-WC appear in a form of a strong thin soldered joints of cobalt between a tungsten carbide grains. The densification by hot isostatic pressing induces a specific microstructure which is different of that observed in tungsten carbides elaborate by sintering. This change allows an improvement in the hardness of the products elaborated by the HIP process. It is noted that the improvement in mechanical properties is weakened by the use of steel container to encapsulate the powder mixtures of tungsten carbide and cobalt.