Influence of matrix property and interfacial reaction on the mechanical performance and fracture mechanism of TiC reinforced Al matrix lamellar composites

Abstract

Freeze casting is a versatile approach for the design of lamellar metal−ceramic composites with unique combination of strength and toughness. However, previous studies mainly focused on ceramic factors such as content and lamellae structure, seldom concerning the effects of metal property and interfacial structures, which, in practice, are key factors in determining the mechanical performances of the composites. In this work, we prepared three kinds of Al/TiC lamellar-interpenetrated composites with different matrix compositions (pure Al, 6061Al (Al−0.4Cu−1.0Mg−0.6Si) and ZL107 (Al–7Si–5Cu)) via freeze casting and pressure infiltration, aiming at clarifying the roles of matrix property and interfacial reaction on the mechanical properties and fracture mechanisms of the composites. The flexural strengths of pure Al/TiC, 6061Al/TiC and ZL107/TiC composites reached 355 ± 10, 415 ± 15 and 459 ± 18 MPa, while the toughness values (characterized by crack-growth toughness) were 81.0 ± 2.0, 57.6 ± 1.2 and 43.4 ± 1.5 MPa m^1/2, respectively. The exceptional damage tolerance of these lamellar composites was attributed to multiple toughening mechanisms such as crack deflection, uncracked-ligament bridging of ductile layers and plastic deformation of the metal matrix. However, the presence of Si in the 6061Al and ZL107 alloys weakened the stability of TiC and promoted interfacial reaction, leading to the formation of a certain number of (Al_1-m, Si_m)₃Ti and Al₄C₃, which greatly weakened the toughness of the composites. Due to the combined effects of alloy plasticity, lamellar-interpenetrated structure and interfacial reaction, the fracture of the materials changed from a multiple cracking mode in the Al/TiC composite to a single crack propagating mode in the 6061Al/TiC and ZL107/TiC composites.

Introduction

The quest for engineering applications necessitates the development of lightweight metal−ceramic composites with exceptional strength and toughness [1]. However, in most traditional structural materials, these two properties are mutually exclusive [2], thereby requiring an optimization. In recent decades, it has been demonstrated that materials can be enhanced by tailoring their microstructures and reinforcement distribution to form bicontinuous, gradient or lamellar structures [[2], [3], [4]]. In particular, lamellar structures are very attractive due to their great potential in achieving high damage tolerance capacity [5,6].

To prepare lamellar composites, many approaches, such as layer-by-layer deposition [7], evaporation-induced self-assembly [8] and tape deposition [9], have been developed. However, these methods are generally restricted to the fabrication of 2D submillimeter-thick films that are not suitable for structural applications. As a promising alternative, a combination of freeze-casting and infiltration techniques was recently exploited to prepare 3D bulk lamellar composites [10]. This process consists of preparing a suspension of ceramic powders in a suitable solvent, freezing the suspension, and subliming the solidified liquid medium under vacuum to generate a porous body which is an exact replica of the initial frozen structure. The green body is subsequently sintered to enhance its strength, and the spaces between the ceramic lamellae are later filled with a compliant phase (either polymer or metal) using an infiltration technique to form a lamellar composite [[11], [12], [13], [14]]. For instance, in our prior work, we fabricated ZL205A/SiC lamellar composites with an interpenetrated structure and examined their mechanical properties [14]. The maximum flexural strength and crack-growth toughness (K_JC) reached 760 MPa and 33 MPa m^1/2, respectively, in the composite with 20 vol% SiC, exhibiting exceptional damage tolerance. To date, although great efforts have been devoted to prepare various lamellar composites via the similar routes, most investigations have focused on ceramic factors such as content and lamellae structure, seldom concerning the influences of metal matrix and interface properties. In practice, these two factors play a significant role in the determination of the mechanical properties of the composites [[15], [16], [17], [18], [19]].

In this work, we prepared three kinds of Al/TiC composites via pressure infiltration of pure Al, 6061Al (Al−0.4Cu−1.0Mg−0.6Si) and ZL107 (Al–7Si–5Cu) alloys into freeze-cast TiC lamellar scaffolds with a primary purpose to clarify the effects of matrix property and interfacial reaction on the mechanical properties and fracture behavior of the composites. We expect that such knowledge would provide helpful guidance for the development of lightweight, high-performance composites.