| The strength and toughness of the materials are the two kinds of properties that are mutually exclusive in traditional metal matrix composites. The preparation of well obdurability materials has been the focus of research on metal matrix composite. Preparing composites with good strength and toughness by the application of bionics principle has become an inevitable trend. Therefore, the development of layered composites of imitation pearl shell structure has attracted great attention. A new possibility of fabricating metal/ceramic composites having an interpenetrating lamellar structure has recently been opened by the availability of ceramic preforms processed by freeze-casting of ceramic suspensions. Therefore, in this paper, we produced the innovative Al2O3(-Ti C)/Al alloy composites by melt infiltration of ceramic preforms prepared by freeze-casting. During the process, the microstructure of porous ceramic preforms was well controlled by initial solid loading, freezing temperature and sintering aids, consequently, the content and architecture of ceramic reinforcement in the final composites and its mechanical property was precisely tailored. The main results obtained, in this paper, are as follows:(1) The Al2O3 scaffolds prepared by freeze casting shows a gradient change with the increase in the distance from the bottom surface. And the compressive strength increased while the microstructure got finer with increasing initial solid loading and decreasing freezing temperature. The introduction of sintering aids significantly reduced sintering temperature, promoted densification and increased the strength of porous Al2O3 scaffolds. In comparison, the Cu O-Ti O2 sintering aids was more effective and the resultant scaffolds(30 vol.%) exhibited high compressive strength(97-197 MPa) and relatively large porosity(51-45%). While the Al2O3-Ti C multiple-ceramic performs poorly in compressive property.(2) The Al2O3/Al-10Mg-12 Si composites with lamellar structures were prepared by pressureless infiltration and freeze casting successfully. The structure of the composites inherited the lamellar structure from the ceramic scaffold. However, the uneven distribution of elements in the alloy layer and incomplete infiltration in the final composite made the comprehensive performance of the composites sill poor.(3) In the Al2O3(-Ti C)/Al composites, prepared by vacuum-gas pressure infiltration, we found that:(a) The introduction of sintering aids brings a lot of closed pores in the final composites. Although the compressive strength of the corresponding composites significantly increased, it is bad for the improvement of the comprehensive performance. For instance, the bending strength of the composites without sintering aids is better.(b) Concerning the Al2O3(-Ti C)/ZL107 composites without sintering aids, the addition of Ti C have a remarkable effect on the compressive strength of them. However, the corresponding bending strength of the composites fell down, due to the segregation of Si in the matrix alloy and the formation of intermetallic compounds Ti Alx Siy.(c) In comparison, the Al2O3(-Ti C)/ZL205 A composites without sintering aids has the best comprehensive performance: The maximum compressive strength and strain were exhibited in the longitudinal direction of the composites of 30 vol.% initial solid loading with 30 wt.% Ti C, which reached 809±5 MPa and 19.46±1.06%, respectively. And the maximum bending strength was 871± 8 MPa. Corresponding, the bending strength, fracture toughness and work of fracture of the composites with 20 vol.% initial solid loading were 759± 5 MPa, 17±1 MPa·m1/2 and 1894±140 J·m-2, respectively. And with the increase of ceramic initial solid loading, the compressive strength gradually increased while the plasticity and toughness were on the decline.(4) This article gave a summary of toughening and failure mechanisms, according to Al2O3/Al-10Mg-12 Si ? Al2O3(-Ti C)/ZL107 and Al2O3(-Ti C)/ZL205 A composites with lamellar structure.(a) It was concluded that the interfacial debonding, interlaminar fracture and delamination, crack deflection and bridging of alloy layer were the dominant toughening mechanisms of the multilayer toughening conch nacre structure bio-inspired Al2O3(-Ti C)/Al composites.(b) The micro bending of the compound layer and the shear instability of the alloy substrate were the two main failure mechanisms in the layered composites under the horizontal loads. |
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