Contents lists available at ScienceDirect Ceramics International journal homepage: www.elsevier.com/locate/ceramint Short communication Microstructure and anti-penetration performance of continuous gradient Ti/ TiB–TiB 2 composite fabricated by spark plasma sintering combined with tape casting Biao Zhang a,b,*,1 , Zhaoxin Zhong a,1 , Jian Ye a , Qiang Liu a , Zhaoping Hou c , Yicheng Jin a , Haoqian Zhang a , Yang Wang a , Zhiguo Zhang b , Feng Ye a,** a Institute for Advanced Ceramics, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, 150080, PR China b Department of Physics, Harbin Institute of Technology, Harbin, 150001, PR China c College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan, 030024, PR China ARTICLE INFO Keywords: Ti/TiB–TiB 2 composite Continuous gradient Armor material Tape casting ABSTRACT Abrupt change of acoustic impedance at the interfaces of step gradient composites is the main reason which hinder their further improving of bulletproof performance. Eliminating these interfaces is an effective method to fundamentally solve this problem. In this study, continuous gradient Ti/TiB–TiB 2 composite was fabricated by spark plasma sintering (SPS) combined with tape casting. Interfaces between the different thin tape layers were successfully eliminated through the growth of rod-like TiB crystals during SPS sintering. High speed impact test indicates the continuous gradient Ti/TiB–TiB 2 composite not only possesses excellent anti-penetration perfor- mance, but also has the ability to resist a second strike. 1. Introduction Developing new armor materials with lightweight and high defen- sible performance is critical to improve the mobility and battlefield survivability for weapons [1,2]. Titanium alloys and their composites have become the hot spots in this field because of their low density, high specific strength as well as their adjustable toughness and hardness [3–5]. Common method used to enhance anti-strike capability of tita- nium-based armor materials is their multilayered design. In these la- minated structures, titanium alloys with high toughness and ductility are often selected as back sides, ceramics with high hardness are often selected as front sides, and several transition layers often exist between the back and front sides. These armor materials can be considered as one kind of step gradient composites [1,6]. Y.F. Zhang et al. [7] pre- pared a six-layered Ti/TiB–TiB 2 composite with total thickness of 10.63 mm by powder molding and spark plasma sintering (SPS). Thickness of each layer was 1.40 mm–2.20 mm, and the target volume fraction of TiB increased from 0 vol% to 100 vol%. A similar composite with five layers was also successfully prepared by M. Cirakoglu et al. using combustion synthesis technique [8]. Many existing reports have pointed out that this kind of step gradient structure possesses a great advantage in improving the protective ability for armor materials. However, composites mentioned above are hardly divided into much thinner layers, because the existing methods can only control the thickness of single layer at millimeter level [9]. Therefore, composition gradient of the step gradient composites in current reports was difficult to precisely control. Furthermore, obvious interfaces usually exist in the step gradient composites [7,8]. The adverse effects caused by the composition difference on both sides of the interfaces still cannot be ignored. One of the most representative negative effects is the mismatch of acoustic impedance between adjacent layers, due to the differences of elastic modulus and density [10]. The most serious consequence of acoustic impedance mismatch is stress-wave reflection at the interfaces, which results in the further damage of armor materials and decreasing their ability to resist multiple attacks [11]. In addition, damage caused by thermal mismatch between different layers is also a great challenge for the application of step gradient armor composites [12]. However, both the acoustic impedance and thermal expansion are depended on the composition of materials when the preparation processes are same. Therefore, eliminating interlayer interfaces to realize continuous gra- dual transition from titanium to TiB–TiB 2 ceramics (continuous gra- dient Ti/TiB–TiB 2 composites) is also realizing the continuous gradual https://doi.org/10.1016/j.ceramint.2019.12.125 Received 19 November 2019; Received in revised form 11 December 2019; Accepted 12 December 2019 * Corresponding author. Institute for Advanced Ceramics, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, 150080, PR China. ** Corresponding author. E-mail addresses: zhangbiao_nwpu@126.com (B. Zhang), yf306@hit.edu.cn (F. Ye). 1 Biao Zhang and Zhaoxin Zhong contributed equally. Ceramics International xxx (xxxx) xxx–xxx 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Please cite this article as: Biao Zhang, et al., Ceramics International, https://doi.org/10.1016/j.ceramint.2019.12.125