Microwave Sintering Yg8 Hard Decarburization Behavior And Its Control

WC-Co cemented tungsten carbide is a typical powder metallurgy (P/M) material fabricated by liquid phase sintering (LPS), having a broad application in ordnance and civilian, such as tool materials, wear-resisting materials. Microwave sintering has gained a lot of acceptance in resent decades because of its dramatic advantages such as a rapid heating rate, energy efficiency, a reduced fabricating cycle, rapid densification, a homogeneous microstructure and enhancing mechanical properties. Based on the great significance of hardmetals and the numerous advantages of microwave sintering, our experiment focuses on microwave sintering of WC-8Co alloys in terms of microstructure, densification behaviors and a decarburization of the YG8 alloys. And the methods for resolving the decarburization are suggested. The major conclusions of this paper are summarized as following:(1)The resulted evidence shows that the WC-8Co alloys with a full density and a fine microstructure are obtained by microwave processing. In contrast to conventional sintering, microwave enhances the densification behavior. A relative density of 99.25%is achieved under microwave sintering at 1400℃for 0 min. For the same temperature and soaking time, conventional sintered alloy is 85.97%. A full density can be attained after sintering conventionally at 1400℃for 20 min. In addition, for conventionally sintered technique, holding time promotes the growth of the WC grain size. However, microwave sintered samples do not show obvious grain growth.(2) It is evident that the decarburization occurs in microwave sintered YG8 hardmetals. Decarburization layers appear on the surface of the samples. The microstructure of the layers can be distinguished as (W and a little Co7W6 phase), (r) phase and WC phase), (WC phase and a littleηphase), respectively. Higher sintering temperature, longer holding time, N2 and H2 mixed atmosphere could exacerbate the decarburization of the alloys prepared by microwave sintering, and the environmental carbon potential also effects on it. Additional, it is found that the microwave heated WC powder decarburizes as well. (3)To suppress the decarburization and improve the mechanical properties of YG8 hardmetals, we designed two groups of experiments of adding activated carbon powder into the initial powder (C content in total of 8.84 wt%,9.28 wt%,9.71 wt%,10.14 wt%, respectively) and elevating sintering carbon potential. In the first case, both microstructure and performance of alloys is inadvisable. While the second way could get alloys with a uniform microstructure, noηphase. Therefore, the mechanical properties (bending strength:2053.43 Mpa, hardness:90.4 HRA) is improving.