Synthesis and Fracture Characteristics of TiB 2 -TiAl Composites with a Unique Microlaminated Architecture

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INTRODUCTION

TITANIUM aluminide (TiAl)-based alloys are considered one of the most promising candidates in the fields of aerospace and high-performance automobiles because of their attractive properties, which combine low density, good oxidation/ignition resistance, and excellent high-temperature strength.[1–3] However, TiAl-based alloys suffer from weak ductility at ambient temperature and poor formability, limiting their practical application.[4–7] Although the plasticity of TiAlbased alloys can be improved by the addition of Cr,[8,9] Nb,[10–12] Mo,[9] Zr,[13] and V,[12] to a certain extent,

XIPING CUI, YUANYUAN ZHANG, YAO YAO, HAO DING, LIN GENG, and LUJUN HUANG are with the School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, P.R. China. Contact emails: [email protected], [email protected] YUAN SUN is with the Department of Superalloys, IMR, CAS, Shenyang 110016, P.R. China. Contact e-mail: [email protected] Xiping Cui and Yuanyuan Zhang have contributed equally to this work. Manuscript submitted May 13, 2019. Article published online October 18, 2019 METALLURGICAL AND MATERIALS TRANSACTIONS A

unfortunately, the plasticity enhanced by alloying is far from enough for the traditional plastic deformation and forming. Thereby, it is essential to exploit an effective processing method. For this purpose, some researchers have proposed elemental foil metallurgy for the fabrication of titanium aluminide (TiAl)-based alloy sheets by rolling and subsequent reaction annealing of alternately stacked Ti foils and Al foils,[14–17] which can avoid the direct deformation of brittle TiAl-based alloys and is commonly regarded as a near-net-shape process. However, this method poses several challenges. (1) Due to the poor deformation resistance of Al compared with Ti, Al is commonly squeezed out during plastic deformation, resulting in the loss of Al, so the chemical composition and microstructure of the resulting TiAl intermetallic compound are difficult control. (2) The low high-temperature strength (ultimate tensile strength at 750 C £ 250 MPa[18]) still cannot satisfy the requirements for lightweight, heat-resistant structural materials applied in the aerospace industry. (3) Kirkendall voids are formed during reaction annealing, resulting in the relatively low specific density of the resulting TiAl intermetallic compound. In view of the preceding problems, previously published studies reported that

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the mechanical properties of Al could be improved by introducing reinforcement (SiC,[19–21] TiB2,[21,22] Ti5Si3,[23] etc.); namely, Al matrix composites showed similar mechanical properties in comparison with pure Ti, thus avoiding the loss of Al during plastic deformation. Therefore, in our previous publications,[22,24] TiB2/ Al foils and Ti foils were used as raw materials and the (TiB2/Al)-Ti laminates showed excellent deformation compatibility during hot rolling. Subsequently, the as-rolled (TiB2/Al)-Ti laminates were subjected to reaction annealing and