Research On MAX Phases As Super-hard Material Binders

MAX phases （with titanium silicon carbide and titanium aluminum carbon asrepresentatives） are machinable ceramics with excellent properties of both metal andceramic. It not only possesses good thermal and electric conductivities, plasticity andmachinable, but also has high strength, excellent oxidation resistance, thermostability.Du to the unique properties, MAX phases are ideal candidates as the binders ofsuperhard materials. For this application, this thesis researched a cheap way to makeMAX phases powders, researched the making of MAX bond superhard compositematerials and researched the properties of these new superhard composites. In this thesis,in the aspects of material synthesis, mechanism analysis, microstructure and interfacebonding, we got following achievments:Some MAX phases, such as Ti₃SiC₂and Ti₃AlC₂, can be synthesized at1400¹500°C and1350¹500°C for60¹80min from TiH₂as Ti source by pressurelesssintering （PLS） without preliminary dehydrogenation, respectively. Choosing TiH₂replaced Ti as Ti source researchs the Ti-A-C （A=Si, Al） system thermal change, theinfluence of sintering temperature and holding time for the composition, purity andmicrostructure of sintering product.Polycrystalline cubic boron nitrides （PCBN） bonded by Ti₃SiC₂can be fabricatedunder4.5GPa from the mixture of cBN particles and Ti₃SiC₂synthesized in ourlaboratory. The interface between Ti₃SiC₂and cBN particles is strong. Ti₃AlC₂wassynthesized and cBN-Ti₃AlC₂composites were prepared at4.5GPa and1100¹250°Cfrom Ti, TiC, Al powders and cBN particles. The as-prepared composites showexcellent mechanical properties as a kind of promising novel superhard materials.We successfully fabricated Ti₃SiC₂bonded ploycrystalline diamond compositematerials by two-step method from Ti₃SiC₂powders and diamond powders andresearched the stable phase area of Ti₃SiC₂under high pressure. If the sinteringcondition passed Ti₃SiC₂stable phase, TiC appeared in the matrix. Ti₃SiC₂-Diamondcomposites were first reported to be in-situ synthesized under high pressure （4GPa） andat high temperature （1100°C）（HPHT） from the mixtures of Ti, Si, graphite and diamondpowders or the mixture of Ti, SiC, graphite and diamond powders. For as-synthesized composites, diamond particles were evenly distributed in matrix. The diamond particlesare bonded well with the matrix by three types of interface.MAX phase, such as Ti₃SiC₂or Ti₃AlC₂, was utilized in superhard field, and then itis possible to be a new and novel binder for high proformance superhard materials.