Microstructure And Mechanical Properties Of Multi-scale (TiB₂+TiC)/Al Layered Composite

To solve the“inverted”relationship of strength and toughness of the particle-reinforced aluminum matrix composites,based on the idea of the bionic shell layer structure,the layered green bodies were prepared according to frozen casting by adding（TiAl+TiC）or Ti₃AlC₂ into TiB₂ particles.Then multi-scale（TiB₂+TiC）/Allayer composites were fabricated when the melting Al-Mg alloys were processed into the green bodies using pressure infiltration.The effects of（TiAl+TiC）and Ti₃AlC₂ content on the microstructures,mechanical properties,and dry friction and wear performance of the multi-scale（TiB₂+TiC）/Allayered composites were studied.The strengthening and toughening mechanism and friction,and wear mechanism of the multi-scale（TiB₂+TiC）/Allayered composites were analyzed,which provides a certain technical reference for developing aluminum metal matrix composites with lightweight,high strength and toughness.The main research results of this thesis are as follows:（1）The effect of（TiAl+TiC）content on the microstructures and mechanical properties of the multi-scale（TiB₂+TiC）/Allayered composites were studied.It was found that the TiAland TiC were synthesized in situ and then decomposed into nano-TiC particles during sintering.However,some ceramic particles existed in the form of a ring or non-continuous block due to agglomeration.According to the results of mechanical properties,the highest compressive strength,585 MPa,was the composites with 0 vol.%（TiAl+TiC）;the highest bending strength,586 MPa,was the composites with 10 vol.%（TiAl+TiC）,while the highest crack-initiation fracture toughness(K_IC)and crack-growth toughness(K_JC),18.32 MPa·m^1/2 and 38.22 MPa·m^1/2 respectively,was the composites with 20 vol.%（TiAl+TiC）.（2）The effects of Ti₃AlC₂ content on the microstructures and mechanical properties of the multi-scale（TiB₂+TiC）/Allayered composites were studied.It was found that Ti₃AlC₂ particles were decomposed into nano-TiC particles and a small amount of Ti₃AlC during sintering.The infiltration was completed while the agglomeration was produced,and some larger blocks were broken under pressure.The mechanical properties showed that the composites with 10 vol.%Ti₃AlC₂ possessed excellent compressive and bending strength,625 MPa and 631 MPa,respectively;the K_IC and K_JC of the composites with 20 vol.%Ti₃AlC₂ were the highest,21.27 MPa·m^1/2 and 55.52 MPa·m^1/2,respectively.（3）The excellent fracture toughness of the multi-scale（TiB₂+TiC）/Allayered composites is mainly due to several fracture mechanisms,such as cracks blunted,cracks branches,cracks deflection,multi-crack expansion,bridging of the unbroken process area,the pull-out behavior and the plastic deformation of the Al-Mg matrix,and the“mixed enhancement”effect of nano-TiC particles and micron-TiB₂ particles.（4）The effects of（TiAl+TiC）and Ti₃AlC₂ content on the dry friction and wear performance of the multi-scale（TiB₂+TiC）/Allayered composites were studied.It was found that the abrasion resistance of the composites with 10 vol.%（TiAl+TiC）and the composites with 20 vol.%Ti₃AlC₂ under different loads is better than other composites of the same system.The multi-scale（TiB₂+TiC）/Allayered composites possess better abrasion resistance under 10 N loads as compared with 5 N loads.The friction and wear mechanisms of the multi-scale（TiB₂+TiC）/Allayered composites are fatigue wear,abrasive wear,and adhesive wear.The nano-TiC particles play the role of“supporting protection”,which is conducive to the improvement of abrasion resistance.