Preparation Of Al Alloy/TiC Lamellar Composites By Freeze Casting And Melt Infiltration Techniques

Through precise combination of organic and inorganic components,natural biological materials such as nacre developed highly ordered hierarchical structure at nanoscale by alternative stacked arrangement of the soft and hard phases,and thus exhibited excellent toughness performance that traditional artificial synthesis materials cannot be reached.Inspired by the nacre,in this study we prepared laminated Al alloy/TiC hybrid materials by using directional freezing of water-based TiC ceramic slurries and then infiltrating molten Al alloy into the scaffolds.By controlling the processing parameters,we can realize the regulation of the laminated structure of the composites.The Al alloy/TiC composite materials inherited the original lamellar structure of the porous ceramic scaffolds.The metal phase and the ceramic phase were alternately arranged.The A1 alloy/TiC biomimetic composites with high performance were prepared.In this paper,the main research results are as follows:(1)The preforms prepared by freeze casting can be divided into three distinct regions from bottom to top,i.e."dense zone","cellular zone" and "lamellar zone" The "lamellar zone" had the largest proportion in the area of the preform.The thickness of the lamellae increased while the porosities decreased with increasing ceramic content.The protruding dendrite structure formed at one side of the lamellae and "ceramic bridge" between lamellae were similar to the surface micro-roughness topography of the nacre layers.The longitudinal compressive strength of the preform increased with increasing ceramic content.The maximum compressive strength was 19 MPa for the scaffold with a 35 vol.%initial solid loading after sintered at 1500 ℃ for 2 h.(2)Al-Mg-Si/TiC composites were prepared by pressureless infiltration.Mg2Si enhanced the strength of the Al-Mg-Si alloy and the Ti-Si-C intermetallics formed through interfacial reaction enhanced the bonding strength at the interface.Therefore,the composites exhibited high compressive strength and elastic modulus.The maximum compressive strength of the composites reached 1628 ± 47 MPa,which was about 4。6 times as large as that of the matrix alloy and the maximum elastic modulus was 230.6 GPa for the composites with an initial ceramic content of 35 vol.%.The bending strength of the composites was relatively low due to the presence of void defects and very low bending strength of the alloy.The maximum bending strength was 288 ± 12 MPa for the composite with an initial ceramic content of 35 vol.%.(3)ZL205A/TiC composites were prepared by vacuum-gas pressure infiltration technique.The bonding strength at the interface was weak because of insignificant interfacial reaction between the TiC reinforcement and the ZL205A alloy.The maximum compressive strength and elastic modulus were exhibited in the longitudinal direction,which reached 767 ± 31 MPa and 150.6 GPa,respectively,for the composites with an initial ceramic content of 35 vol.%.With the increase of the ceramic content,however,the bending strength and fracture toughness decreased gradually.The maximum bending strength and the fracture toughness KIc were 598 ± 21 MPa and 12 MPa·m1/2,respectively,for the composites with an initial ceramic content of 25 vol.%.(4)The influencing laws of the ceramic content,microstructure and interfacial bonding strength on the properties of the composites were obtained.The compressive strength and elastic modulus of the composites increased with increasing ceramic content,the compressive strength of the matrix alloy and the bonding strength of the interface.The compressive strength and elastic modulus of the composites in the direction parallel to the lamellar were higher than that perpendicular to it.The lamellar structure can significantly improve the compressive strength of the composites.The bending strength of the composites increased with increasing bending strength of the matrix alloy.(5)The bending fracture mode and the crack propagation path for the lamellar composites with weak interfacial bonding were revealed.The bending fracture mode was interfacial debonding between the ceramic particles and the matrix alloy at the interface and the brittle fracture of the ceramic layers.There are two paths for the crack propagation when the composite was subjected to stress:(a)The crack extended along the interfaces between the lamellae,which can be passivated and deflected when encountered the ceramic particles;(b)The crack extended through the layers but then the crack deflection occurred and the speed of the crack propagation was reduced as the metal layers consumed and absorbed a lot of crack propagation energy by plastic deformation.