| Ti6Al4V spherical particles with the average size of 150?m and Ti B2 powders with 3?m of average size were used as raw material in this experiment.A kind of double-structure TC4-(Ti Bw/TC4)composites with laminated and network structure was successfully fabricated adopting the process of ball milling,stacking and hot pressing by the way of spreading powder-powder metallurgy.The toughening mechanism of this kind of composites in different load modes were investigated by adjusting volume fraction of reinforcement in the composites layer,sample structure and rolling reduction,and testing the room temperature tensile property,threes point bending property and impact toughness test at room temperature.Scanning electron microscope,electron backscatter diffraction system and transmission electron microscope were used to characterize the microstructure and analyze fracture.Combining mechanical testing results and microstructure characterization,the toughening of this kind of laminate structure was achieved via interface cracks and introducing alloy layer under the condition of bending(especially notch-bending)and impact.The strength,elongation and toughness of this kind of composites can be significantly improved via hot rolling process,mechanical properties of samples in TD direction was better than the samples in RD direction.A kind of TC4-(Ti Bw/TC4)composites with controllable layer thickness and high interfacial bonding strength was fabricated via direct spread powder way after a series of explorations,and grain size refiner phenomenon was observed in the composites layer.The titanium alloy layers and titanium matrix composites layers constituted the primary laminate structure of the double-structure composites,and a kind of network microstructure was introduced in titanium matrix composites layers to form the secondary structure.The layer thickness of primary laminate structure was controllable and the transition of adjacent layers was good.The result of room temperature tensile test shows that the TC4-(Ti Bw/TC4)composites exhibit no toughening effect,which is related to deformation incompatibility caused by strong interface.The result of three point bending test shows that this kind of composites has good toughening effect when the outer layer is TC4 alloy,and the location of notch has great effect on the mechanical property of composites.The energy absorbed during crack propagating in three point bending of TC4-(Ti Bw/TC4)composites shows an improvement of 300% compared with Ti Bw/TC4 composites with network microstructure at the same case of volume fraction of reinforcement,which suggests that TC4-(Ti Bw/TC4)composites have good effect on inhibiting crack growth.The result of impact toughness test at room temperature shows the impact energy of TC4-(Ti Bw/TC4)composites is more than 4 times higher than this value of Ti Bw/TC4 composite with network microstructure,which is closely related to the introduction of alloy layer.The analysis of impact load-displacement curve and microstructure suggests that with the increase of volume fraction of reinforcement in composite layer,the impact property of TC4-(Ti Bw/TC4)composite will improve because of the appearance of interface crack.Hot rolling process can reduce layer thickness of TC4-(Ti Bw/TC4)composites.The texture intensity will increase with the increase of rolling reduction.After deformation,large quantity of dislocations was observed in matrix,and Ti B whiskers deflected its direction and distributed along the rolling RD direction.The strength,elongation and toughness of TC4-(Ti Bw/TC4)composites improved a lot after hot rolling.Composites with 40% rolling reduction exhibited the tensile strength of 1000 MPa and elongation of 7%.This phenomenon suggests that hot rolling process can improve mechanical properties of this kind of composites. |
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