Boron nitride nanotube reinforced titanium metal matrix composites with excellent high-temperature performance
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Arvind Agarwal Advanced Materials Engineering Research Institute (AMERI), Florida International University, Miami, Florida 33174, USA
Ma Qian Centre for Additive Manufacturing, School of Engineering, RMIT University, Melbourne VIC 3000, Australia
Ying Chena) Institute for Frontier Materials, Deakin University, Waurn Ponds, VIC 3216, Australia (Received 3 May 2017; accepted 4 August 2017)
Boron nitride nanotube (BNNT) reinforced titanium (Ti) matrix composites were prepared using the cold press-and-sinter method. In the composite sintered at 800 °C for 1 h, BNNTs were homogeneously distributed in the Ti matrix and restricted the growth of Ti grains. The compressive strength of the as-sintered Ti–4 vol% BNNT composite achieved 985 MPa at room temperature versus 678 MPa without the BNNT reinforcements. The highest compressive strength of 277 MPa at 500 °C was obtained from the Ti–5 vol% BNNT composite. When sintered at 1000 °C, chemical reactions occurred between Ti and BNNTs leading to the formation of the interfacial TiB phase, which serves as a strong binding between BNNTs and the Ti matrix. The reinforcements were attributed by a mixture of BNNTs and TiB after sintering at 1000 °C for 3 h. However, no BNNT was observed in the microstructure after sintering at 1100 °C for 3 h due to complete transformation into TiB whiskers.
I. INTRODUCTION
Titanium (Ti) is an attractive material because of its high strength to weight ratio compared to aluminum and steel.1,2 It also possesses high corrosion resistance and good chemical inertness, a desirable feature for structural materials.3,4 To increase the fuel efficiency, a number of Ti alloys and composites have been developed over the decades for manufacturing specific components in aerospace and other industries.5–10 The adoption of TiB reinforced Ti metal matrix composites (TMMCs) by Toyota Motors for the intake and exhaust valves11,12 was a milestone development in TMMCs. The reduced weight and improved performance of TMMCs at both room and high temperatures can mitigate the concern over the cost issue and make Ti materials more acceptable to the automotive industry. Therefore, a number of reinforcements, such as WC, Al2O3, SiC, TiB, TiC, and CNT, in the form of particles, whiskers, rods, wafers or thin plates (,150 nm thick), and nanotubes have been explored
Contributing Editor: Yang-T. Cheng a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.345
previously for the fabrication of TMMCs.13–17 In particular, ultrahigh compressive strengths (.2.5 GPa) and ductility (.40%) have been obtained for Ti–TiC MMCs fabricated by the simple press-andsinter approach.18 Boron nitride nanotubes (BNNTs) have excellent physical, mechanical, and chemical properties that are comparable to carbon nanotubes.19 They possess very high elastic modulus (750–1200 GPa)20,21 and tensile strength (;24 GPa),22 in addition to their high melting point (;3000 °C), high oxidation resistance over the temperature range of 700–950 °C, and good thermal and
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