熱均壓處理及燒結參數對WC-12 wt%Co的機械性質之影響

Abstract

Tungsten carbide (WC-Co) composites are widely used in industry such as machining tools, mining tools, and wear-resistant parts operated in critical condition which with superior mechanical properties, cutting performance and wear-resistant abilities. Because of the high melting point, this kind of hard metal is mostly manufactured by powder metallurgy method. Hot isostatic pressing (HIP) technique is a heat treatment method which combines high temperature and high pressure. Furthermore, the pressure medium is used inert gas, and it exerted on the work-piece in all direction are equal. Recently HIP technique has been wildly used in powder metallurgy industry to eliminate the isolated pores and defects inside the work-piece. Therefore, the mechanical and physical properties of materials can be improved. The experimental result indicated that the specimen of WC-12wt% Co contained few pores and showed the excellent mechanical properties, because the well liquid phase sintering was occurred during sintering progress. The specimen of G5 sintered at 1400℃ for one hour achieved 98% of relative density, and hardness was HRA 88, TRS increased to 2398 MPa, respectively. Moreover, all the specimens of F12 sintered at 1350℃ and 1400℃ for one hour achieved 99% of relative density, and hardness was HRA 92, TRS also enhanced to 2200 MPa. In this study, a large amount of η phase (Co3W3C) precipitations at high sintering temperature. The precipitations were generated by liquid phase (mainly contain was cobalt) particularly gathered in some special region of specimen, and then reacted with the WC particles. The phenomenon also could be obviously found in the specimens by HIP treated parameters, therefore the TRS of specimens were decreased. When a large amount of Co3W3C phase has been generated, the thickness of average binder’s phase between WC particles was decrease. Furthermore, Co3W3C was a hard and brittle phase, it will result in the lower TRS of specimens.