In-situ Fabrication Of ZrB₂-SiC Composite By Arc-melting Process

There are several limitations in the traditional solid-state sintering of ZrB2-SiCcomposite:1. The required fabrication conditions are very harsh;2. The status ofstarting powders can greatly influence the microstructures and properties of thecomposites, making the fabrication process unreliable.3. The sintering aids added inthe composite would deteriorate the composite’s high temperature properties;4. Themechanical property values of the fabricated composite are very limited. To solvethese problems, this research has proposed a novel method, In-situ Fabrication byArc-melting Process, to fabricate the ZrB2-SiC composite in order to improve themechanical properties of the composite by obtaining novel microstructures.The principle of In-situ Fabrication by Arc-melting Process is to fabricate thecomposite from ultrahigh temperature reactions in one step and to control themicrostructures of the composite by adjusting the composition and the heat diffusiondirection during the solidification process, in order to obtain fully dense compositewith unique high properties. In this research, the Zr, B4C and SiC were chosen to bestarting powders. Under the Argon Tungsten Arc Welding, ZrB2-SiC composite withnovel structures was successfully fabricated. The relationships between themicrostructures and mechanical properties of the ZrB2-SiC composite were carefullyanalyzed and revealed through different characterization methods and propertiesmeasurements.The compositions and microstructures on the cross section of the ZrB2–37mol%SiC composites have been characterized by XRD, SEM and EDS. The resultsindicated that two kinds of microstructures, textured and monolithic, are formed in theZrB2-SiC composite. The well-aligned ZrB2grains are firmly embedded in the SiCmatrix with well-combined interfaces. The mechanical properties of the compositeswere evaluated by the indentation method. Under the load of98N, the VickersHardness HV10of the composite was measured to be24.0±0.8GPa, the fracturetoughness KICof the composite calculated according to the Japanese IndustrialStandards (JIS R1607) is6.7±0.7MPa m1/2. Compared with the traditional solid-statesintering methods, the ZrB2-SiC composite fabricated from in-situ arc-melting processhas better mechanical properties. Under the analysis of ZrB2-SiC phase diagram, SEMand EDS, the formation of two microstructures was revealed. In the hypoeutecticcomposition of ZrB2–37mol%SiC composite, the textured phases with ZrB2and SiC are eutectic while the monolithic phases are primary ZrB2. The mechanical propertiesof different microstructures were evaluated by micro-indetation method. The resultshows that the textured microstructures play an important role in improving thestrength and toughness of the composite.To further research the relationships between the oriented microstructures andmechanical properties of the composite, ZrB2–48mol%SiC composite withanisotropic microstructures was fabricated. The anisotropic morphologies are shownon the different sections of the composite. On the section parallel with arc-meltedsurface, clusters of labyrinthine textures were observed while oriented textures werefound on the section perpendicular with the arc-melted surface. XRD results revealedthat the ZrB2grains grow in a preferred orientation along c–axis. The obviousmorphologies also provide the composite with excellent anisotropic mechanicalproperties. On the sections parallel and perpendicular with the arc-melted surface, theVickers Hardness values were measured to be22.4±1.8GPa and17.8±1.3GPa.Besides, the crack resistances on the two sections were also different. The anisotropicmechanical properties of the composite obtained from in-situ arc-melting process aremuch higher than those fabricated by other traditional methods.