Influence Of Niobium On The Control Structur And Properties Of Ti/Al₂o₃ Composites

It was necessary to fabricate the Ti/Al₂O₃ composites on applying to graded flier- plate, reamer and engine parts because Ti and Al₂O₃ had high strength with light mass, well thermal stability and high the module of elasticity, and what's more, it can also stand high temperature and wear.The full dense and excellent composites were obtained by spark plasma sintering on the base of controlling interfacial reaction by means of suitable metal elements. Studying on Ti/Al₂O₃ interfacial reaction by XRD, EDS and EPMA showed that alumina decomposed firstly and then aluminum atom reacted with titanium forming Ti₃Al in the further titanium and poor aluminum and TiAl in the titanium and further aluminum, and O dissolved into titanium, niobium, however, not only hold back interfacial reaction and forming Ti₃Al, but also decreased aluminium diffusing from Al₂O₃ to Ti, at the same time, reduced the ability of O into titanium.The acoustics and mechanical properties of Ti/Al₂O₃ by ultrasonic pulse-echo method were measured and results indicated that wave impedance was 25～30(×109 g/m2s) between W, Mo and Al, Mg. The Mo-Ti/Al₂O₃ flier-plate with good parallelism, planeness and high densification was prepared by using diffusion welding method (under certain welding parameters such as temperature, pressure, time and atmosphere, etc). The microstructure showed that Ti₃Al was major reason resulting in decreasing the mechanical of Ti/Al₂O₃ composite.Influencing of niobium on properties disciplinarian of Ti/Al₂O₃ composites indicated that the relative density, bending strength, fracture toughness and micro- hardness of 20vol% Ti/Al₂O₃ and 40vol%Ti/Al₂O₃ composites were best adding 1.5vol%Nb. 60vol%Ti/Al₂O₃ composites, however, required 2.0vol%Nb and 80vol%Ti /Al₂O₃ composite increased with niobium increasing. Based on niobium controlling interfacial reaction, the fracture mode of the Ti/Al₂O₃ composites changed from interganular to a mixing fracture of interganular and transgranular, and simultaneously dislocation strengthened the mechanical properties. The crack propagating was mainly deflection and bridging the prolonged the crack propagating path and advanced the fracture critical stress which was main cause of enhancing toughness of composites.