Two-step Sintering Study Of TiB_w/TC4 Composite With A Quasicontinuous Network Reinforcement Distribution

Titanium matrix composites which have the advantages of high specific stiffness,high specific strength,good high temperature performances,high wear resistance and low thermal expansion,will be widely applied in aerospace,automobile manufacturing and other fields in the future.In traditional titanium matrix composites,reinforcements usually distribute in matrix evenly,and the strength of composite is greatly improved,but the toughness is declined due to the destruction of the connection of matrices.The inhomogeneous composite can solve this problem to some extent.In all kinds of inhomogeneous composite,the microstructure of composite with a quasi-continuous network is that reinforcement distribute uniformly along the matrix particle boundary.While bearing capacity of the material is improved,the quasi-continuous network structure can maintain integrity and connection of matrix,and reduce the stress concentration at the crack tip effectively,there by improving the toughness of the composites.In the Ti B_w/TC4 composite with a quasi-continuous network reinforcement distribution,TiB_w whose shapes are needles,brunches,and claws are rolled into the matrix,which is to increase the strength and maintain the connectivity and integrity between matrix.And the composite have a good overall performance.However,the TiB_w structure was destroyed and the interface bonding strength was low in the subsequent deformation process,so the material properties decreased.Therefore,we use different processes to solve the defects in the microstructure of the material.In this thesis,a method called two-step sintering was used to prepare TiB_w/TC4 composite with quasi-continuous network reinforcement distribution.In the first step of pre-sintering,TMCs were prepared and the in-suit process by controlling the temperature.After hot rolling,the distribution of reinforcement around the matrix will be improved and the density will be increased.TiB₂ reacts with Ti in the second step of sintering,TiB_w will be rolled into the matrix,and the microstructure and properties were improved.In the first step of pre-sintering,three sintering temperatures,1000°C,1100°C,1200°C were adopted,the sintering time of the first step was1 hour and the temperature cooled with the furnace cooling to room temperature.The density of TiB_w/TC4 composites at different temperatures is about 85%.Then the composites obtained in the 1000°C and 1200°C were chosen to take multi-pass rolling at 900°C with 50%deformation.The densities of all the composites were about 91%.In the second step of sintering,the composite was sintered at1200°C for 2 hours.The TiB_w/TC4 composite with quasi-continuous network reinforcement distribution was prepared.Composite density slightly increased,was still around 92%.In the TiB_w/TC4 composites of pre-sintering,the structure was relatively loose,and the distribution of TiB₂ particles is uneven and has agglomeration phenomenon.Theα-phase andβ-phase of the matrix were distributed lamellarly,and the reinforcing phase was distributed in a network around the matrix.As the temperature rised,the size and content of TiB_w obtained by in-situ reactive sintering increased.After hot rolling,the structure of composite was relatively dense,the TiB₂ particle agglomeration phenomenon was obviously improved,and the voids were obviously reduced.In the TiB_w/TC4 composites of secondary sintering,the TiB_w is distributed in a quasi-continuous network around the matrix.It acted as a pin-roll at the interface and increased the interfacial strength.The matrix was equiaxedα-phase.The composite with pre-sintering temperaturethat is 1000°C-hot rolling-secondary sintering was better,which maintained integrity and connection of matrix,and the hardness of matrix is 618 HV.