Research On The Manufacturing Process And Oxidation Resistance Of Cr₃C₂-based Cermets At High Temperature

In this thesis, the relationship among composition, manufacturing process, microstructure and properties of Cr3C2-based cermet has been systematically investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscope (EDS) and so on. And then the oxidation behavior and oxidation mechanism at high temperature of Cr3C2-based and Ti(C, N)-based cermets have been studied.An overview on the research advance of manufacturing process of cermets and sintering theories is presented in the first part of this thesis. The effects of composition and additive on the microstructure and properties of cermets are described briefly. Especially, the research progress of chromium carbide based cermet is reviewed. In addition, high temperature oxidation of materials and research test methods are summarized. Based on above work, the purpose and significance of the thesis have been pointed out.The effect of main sintering process parameters on the microstructure and properties of cermet has been studied. The results showed that the sintering body prepared at the sintering temperature of 1250℃and for the soaking duration of 60min had better microstructure and higher properties.Transvers rupture strength (TRS) and hardness (HRA) of the cermet were up to 1426MPa and 91.5HRA, respectively. The optimized sintering process has been achieved.The effect of chemical compositions on the microstructure and properties of cermets has been further studied by optimized sintering process. The experiments results indicated that when the mass ratio of Ni to Cr is 4:1, the materials had better microstructure and higher strength and toughness with the amount of 75wt%Cr3C2 and additions of 0.3wt%C.The oxidation behavior and oxidation mechanism at high temperature of Cr3C2-based cermet have been studied. After 100 hour oxidation, the oxidation weight grain in unit area of Cr3C2-based cermet was 15.69×10-4g·cm-2, and the oxidation rate constant was 3.67×10-5mg2·cm-4h-1 at the temperature of 750℃in the air. The high temperature oxidation behavior of cermets follows the logarithmic law, approximately. During the later stage of oxidation, the oxidation rate is controlled by the diffusion rate of Cr3+ ions in the oxidation film.In addition, the oxidation behavior and oxidation mechanism at high temperature of Ti(C, N)-based cermet have also been investigated. At temperature of 750℃in the air, the oxidation weight grain in unit area of Ti(C, N)-based cermet was 33.52×10-4g·cm-2, and the oxidation rate constant was 11.21×10-5 mg2·cm-4h-1 after 100 hour oxidation. The high temperature oxidation behavior of cermet follows the parabolic law. The oxidation rate is controlled by the diffusion of external oxygen ions from oxide layer to reaction interface at the final stage.By comparing Cr3C2-based cermet with Ti(C, N)-based cermet on properties, the conclusions were obtained as follows: The difference between the mechanical properties of two kinds of materials was slight. The Cr3C2-based cermet showed better high temperature oxidation resistance. A series of results obtained from a great deal of applications showed that the Cr3C2-based cermet possessed perfect conductivity, better wear resistance, higher strengths and toughness and excellent high temperature oxidation resistance.