Elsevier

Intermetallics

Volume 121, June 2020, 106774
Intermetallics

Nature-inspired nacre-like Ti6Al4V-(Ti2AlC/TiAl) laminate composites combining appropriate strength and toughness with synergy effects

https://doi.org/10.1016/j.intermet.2020.106774Get rights and content

Highlights

  • Nacre-like Ti2AlC/TiAl–Ti6Al4V laminated composite sheets were obtained.

  • Bio-inspired design achieved extrinsic toughening via synergistic effects.

Abstract

Nacre, a biomimetic model system with multiscale architectures and adjustable components, has always inspired researchers to create novel materials with advantages such as light-weight, exceptional strength and toughness. Inspired by nature, nacre-like bionic Ti2AlC/TiAl–Ti6Al4V laminated composite sheets had been designed and fabricated by spark plasma sintering technology using commercial Ti6Al4V as the toughening layers and Ti–Al–TiC reaction system as the composite layers. The phase compositions and structural characteristics of the composite sheets were characterized by XRD, SEM and EDS. In addition, the mechanical properties at room temperature were also measured. The results indicated that a Ti3Al interfacial layer was formed between the composite layer and the toughening layer, meanwhile the compositions of the composite layer were composed of TiAl, Ti3Al, Ti2AlC and a small amount of TiC. It's noteworthy that the Ti2AlC/TiAl–Ti6Al4V laminated composite sheets showed a significant increase in toughness while maintaining or improving strength even with holes in the sheets, in comparison with monolithic TiAl. When the loading direction was perpendicular to the laminated structure, the flexural strength and fracture toughness of the composite sheet with 20 wt% Ti2AlC reached good comprehensive values, which were up to 564.86 MPa and 39.15 MPa m1/2, respectively. The particles-reinforced composite layers and laminated structure design not only affected the crack propagation, but also cooperated with each other leading to a complex deflection and expansion behavior, which consumed the fracture energy and improved the overall mechanical properties of the composite sheets.

Introduction

TiAl intermetallic compounds possessing many advantages, including corrosion resistance, oxidation resistance, high specific strength and specific stiffness, have been widely used in the aerospace, automotive, marine, and other industrial fields [[1], [2], [3], [4]]. However, the extensive application of TiAl intermetallic compound has been restricted by some key scientific problems, such as intrinsic brittleness and difficulties in forming and processing [[5], [6], [7]]. Researchers worldwide have been striving to develop new composite technologies to solve the problems mentioned above. Wang et al. [8] successfully fabricated two-scale Ti6Al4V-(TiBw/Ti6Al4V) laminate-network structured composites. They found that the ultimate strain of two-scale composite doubled while bending strength was similar in comparison with TiBw/Ti6Al4V composites. The impact toughness of two-scale composites was nearly fivefold enhanced compared with monolithic TiBw/Ti6Al4V composites, implying a strength-ductile balance was achieved. Han et al. [9] fabricated continuous Al2O3 ceramic fiber reinforced Ti/Al3Ti metal-intermetallic laminated (CCFR-MIL) composite. It was found that compared to Ti/Al3Ti MIL composite, without fiber reinforcement, both the strength and failure strain of CCFR-MIL composite increased under both compressive and tensile stress states due to the contribution of the continuous ceramic Al2O3 fiber. It's indicated that the composite technology could effectively improve the overall performance of TiAl-based alloys.

Hitherto, the introduction of composite structure seems to be a useful way to improve the performance. As an important component for the composites, the reinforcements play an important role in enhancing the performance of the composites. In recent years, Ti2AlC ternary carbide as a particular reinforcement has been widely recognized [[10], [11], [12], [13], [14], [15]]. The thermal expansion coefficient of Ti2AlC is close to TiAl, which prevents ceramic particles segregation and reduces the internal stress between the ceramic and matrix during the preparation process [[10], [11], [12]]. Song et al. [13] successfully synthesized Ti2AlC/TiAl composites by vacuum arc melting technique. It is noteworthy that as the amount of Ti2AlC ceramic increased, the microhardness and compressive strength of the TiAl/Ti2AlC composites improved linearly, and crimping of Ti2AlC played a key role in the improvement of the strength and plasticity of the composites. Moreover, as reported by Chen et al. [14], in-situ Ti2AlC/TiAl composites were produced by metallurgical method, and the compressive strength increased up to 1678.68 MPa as Al content was 46 at.%. Compressive strength enhanced 1.39 times and strain increased 2.21 times due to the Ti2AlC phase and the fully lamellar structure. Li et al. [15] fabricated Ti2AlC/TiAl composites by powder metallurgy. They found that the tensile property of as-forged composites was improved simultaneously, with elongation (δ) increasing from 12.10% to 30.87%. In particular, at 1000 °C, the engineering strain was up to 176%, exhibiting superplasticity. Microstructure analysis indicated that the inhomogeneous microstructure and dispersed Ti2AlC particles played an important role in improving the performance of the composites. However, the inverse relationship between strength and toughness continues to be a prominent problem in current research.

Nature, however, is particularly adept at developing damage-tolerant materials that are both strong and ductile through the creation of hierarchical architectures. For example, shells in nature are composed of nacre and special proteins, which have high strength and toughness, and have been widely used by researchers for bionic designs [16,18,19]. Accordingly, natural and biological materials have provided much inspiration over the past decade in the quest for new and improved structural materials [17]. Inspired by nature, Ti–Al based laminated composites with the micro-scale sandwiched architecture designing, to benefit from the creation of critical structural features over multiple length-scales, have been becoming more attractive. Because they can not only retain the high stiffness and low density of intermetallic, but also possess the high strength and fracture toughness [16,18,19]. Fei et al. [16] prepared a TC4/TiAl-based composite sheet by spark plasma sintering. When the stress was perpendicular to the laminate structure, the flexural strength and fracture toughness of the composite sheet with 20 wt% Ti2AlC reached maximum values of 1428.79 MPa and 64.08 MPa m1/2, respectively. Lyu et al. [18] proposed a new strength calculation formula for the influence of the sequence on the mechanical properties of Ti/TiAl laminate composites. The experimental measurements were in good agreement with the theoretical predictions and the optimal fracture toughness of the sample was 48 MPa m1/2. Ai et al. [19] payed much attention on TC4/Ti2AlC–TiAl composite sheets and found that when the theoretical content of Ti2AlC reached to 10 wt%, the flexural strength and fracture toughness were as high as 1346.98 MPa and 67.72 MPa m1/2, respectively. However, during designing the biomimetic laminated structure, it's found that when the interfacial bonding strength between the layers was unsatisfactory, the tearing phenomena were easy to occur, and resulted in the decrease in the mechanical properties of the overall composite sheet.

In our present work, Ti2AlC/TiAl–Ti6Al4V laminated composite sheets were fabricated from commercial Ti6Al4V as the toughening layers and Ti–Al–TiC reaction system as the composite layers by spark plasma sintering technology, which was an excellent strategy to produce a bionic laminated structure and particles-coupled reinforced structure with the improvement of the mechanical properties of composite sheets. The phase compositions, microstructure and mechanical behavior of the composite sheets were studied in detail.

Section snippets

Preparation of Ti2AlC/TiAl–Ti6Al4V laminated composite sheets

Commercial Ti powder (purity ≥ 99.5%, average particle size < 35 μm), Al powder (purity ≥ 99.5%, average particle size < 55 μm), and TiC powder (purity ≥ 99.5%, average particle size < 20 μm) were used as raw materials. Ti–Al–TiC mixed powders served as the composite layers, and according to the formula (1 + n)Ti+(1 + n)Al + TiC = nTiAl + Ti2AlC, as illustrated in Table 1, Table 2, were ball-milled for 4 h with rotate speed of 150 r/min to obtain the homogeneous powders. Commercial TC4 titanium

Phase composition analysis

Fig. 2 is XRD patterns of the Ti2AlC/TiAl-TC4 laminated composite sheets corresponding to different content of Ti2AlC. As shown in Fig. 2, it is found that the composite layers are mainly composed of TiAl, Ti3Al, Ti2AlC and TiC phases. Without TiC additive, the main products of the composite layer are composed of γ-TiAl and α2-Ti3Al. No other phases are formed during the hot-pressing processing. Ti2AlC content increases with increasing of TiC additive. Thus, in-situ reaction process can be

Conclusion

In summary, bionic nacre-like Ti2AlC/TiAl-TC4 laminated composite sheets were successfully prepared by spark plasma technology, and the microstructure and mechanical properties were studied. And the main conclusions were presented as follows:

  • (1)

    The composite layer of the Ti2AlC/TiAl-TC4 laminated composite sheets consisted of TiAl, Ti3Al, Ti2AlC and a small amount of TiC. Kirkendall effect was eliminated gradually with increase of Ti2AlC content. The interface layer was divided into two regions

CRediT authorship contribution statement

Ai Taotao: Writing - original draft, Supervision. Niu Qunfei: Writing - original draft, Formal analysis, Data curation. Deng Zhifeng: Supervision. Li Wenhu: Data curation. Dong Hongfeng: Formal analysis. Jing Ran: Formal analysis. Zou Xiangyu: Data curation, Formal analysis.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grant No. 51671116), and the Scientific Research Startup Program for Introduced Talents of Shaanxi University of Technology, China (Grant No. SLGQD1801).

References (26)

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