Strength-Toughness Modulation and Interfacial Microstructure of Bionic Bamboo Fiber-like Aluminum-Based Composite Structures(Invited)
Objective Aluminum matrix composites(AMCs)are widely used in the aerospace industry,transportation,electronics,and other fields because of their high specific strength,low cost,good corrosion resistance,and easy recyclability,which puts higher demands on their comprehensive performance to meet the damage tolerance design criteria.However,AMCs prepared by traditional methods are costly and complex,and the formed materials are prone to the phenomenon of mutual exclusion of strength and fracture toughness.To further improve the strength and toughness of AMCs and overcome the inverse relationship between them,in addition to the selection of the reinforcement material for the matrix,the preparation method and design of the spatial structure also play a crucial role in the construction of high-strength and high-toughness AMCs.The additive manufacturing method differs from the traditional preparation method in that it stacks layers of material onto a substrate and can obtain a free form by precisely regulating the phase evolution as well as the distribution of components and structures.Thus,as it can customize the structure and synthesize a variety of materials,this process is more suitable for developing heterogeneous structures.At the same time,bionic structures provide a new way of thinking for realizing high-performance materials by mimicking the regulation of existing microstructures in nature.Methods By adding titanium alloy skeleton structures with different volume fractions and sizes to the aluminum matrix,strength-and toughness-adjustable bamboo fiber-like Al-Ti composite structures were prepared.The micro/macro interfacial organization of the composite structure was observed,the chemical composition and elemental distribution of each phase were analyzed,the coordinated deformation ability of the composite structure under compressive stress was studied,and the deformation and interfacial toughening mechanisms of the composite structure were elucidated.Results and Discussions It is found that a diffusion reaction occurs in the interface of the titanium-alloy reinforcement skeleton and aluminum alloy matrix,forming a dense metallurgical bond,and the precipitated phases at the interface are Ti-Al intermetallic compounds(Fig.3).Compared with traditional aluminum-matrix composite materials,this composite structure has a compressive strength as high as 380-1085 MPa and forms an integrated micro/macro"high strength-high toughness"fiber-like composite structure(Fig.4).The study of the micro-deformation mechanism reveals that the precipitation of high-strength compounds effectively prevents cracks from sprouting and expanding in the heterogeneous interface(Fig.5).Meanwhile,high-resolution observation shows that the Ti3Al phase precipitated at the interface forms effective deformation twins inside the grains after deformation(Fig.7)and improves the coordinated deformation ability between the high-and low-modulus phases precipitated at the interface.This is the main mechanism for the enhancement and toughening of the composite structure.Conclusions By adjusting the vacuum melting temperature,an aluminum/titanium composite structure can be obtained with a dense combination of the interface.The thickness of the reaction-generated interface is approximately 600 μm,and the phase precipitated within the interface is a Ti-Al intermetallic compound with high hardness.The aluminum/titanium composite structure has good strength and toughness,and by adjusting the volume fraction of the titanium alloy skeleton,the macro-strength/toughness of the composite structure can be adapted.The achieved compressive strength varies in the range of 380-1085 MPa,which is 1.4-4 times that of the aluminum matrix(270 MPa).Regarding the pre-fracture elastic deformation,the strain of the composite structure is3.3％-7.2％,which is 0.6-2.4 times that of the aluminum matrix(2.1％),and a bidirectional prediction model of structure-property is established.The main reasons for the enhanced toughening of the Al-Ti composite structure are as follows:First,by controlling the reaction temperature,a soft phase and hard phase spatially interpenetrating phase structure is formed in the interface,and this soft/hard zone induces the hetero-deformation induced(HDI)strengthening mechanism under the action of the stress.The Ti3Al twins in the interface have certain deformation ability,which further forms a micro/macroscopic interface with a very good match of strength and toughness.Second,geometrically necessary dislocations are formed around the phases with higher modulus precipitated in the interface,which is favorable for the coordinated deformation between the soft and hard phases.It is worth mentioning that the processing method presented in this study can be extended to any metal system with compositions having different melting points,which can provide a theoretical basis for more accurate and efficient design and construction of multimetallic systems.
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