Direct metal laser sintering synthesis of carbon nanotube reinforced Ti matrix composites: Densification, distribution c
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on nanotubes (CNTs) reinforced Ti matrix composites with tailored microstructures and properties were fabricated by direct metal laser sintering (DMLS). A relationship of processing conditions, distribution characteristics of CNTs, and properties was established. The appearance of balling phenomenon and micropores at relatively low laser energy input reduced the densification level of DMLS CNTs/Ti composites. As a g of 700 J/m was properly settled, the composite part with a near-full 96.8% density was obtained. On increasing the laser energy input, the distribution states of CNTs in Ti matrix changed markedly from agglomeration to homodisperse. The optimally prepared fully dense CNTs/Ti composite with uniform distribution of CNTs had significantly enhanced Hd of 9.4 GPa and Er of 328 GPa, which showed respectively ;2.5- and ;3.4-fold increase upon that of unreinforced Ti, and resultant a relatively low friction coefficient of 0.23 and reduced wear rate of 3.8 105 mm3/(N m).
I. INTRODUCTION
With many unique characteristics, such as low density, high specific strength, and good corrosion resistance, Ti can be used as high strength and lightweight structure materials for improving energy efficiency in airplane and automotive industries.1–3 Nevertheless, the relatively low hardness and resultant poor wear performance limit its wide application in load and abrasion environments.1 The addition of rare earth elements in Ti alloys has also restricted their use in industrial applications owing to the high-cost and shortage of resources. Therefore, the promising reinforcements are needed to fabricate Ti matrix composites (TMCs) to meet the growing demands in aerospace, automotive, and other engineering areas. The volume fraction, size, shape, and orientation of reinforcements in TMCs play a crucial role in determining the final mechanical properties. For particles reinforced TMCs, the micrometer scale ceramic particles, such as TiC,2 SiC,4 TiB,5 and TiN,6 are commonly applied. Generally, the size of these particle reinforcements ranges from a few micrometers to several tens of micrometers. These relatively large-sized ceramic particles are normally difficult to be melted during processing due to the relatively high
Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.403 J. Mater. Res., Vol. 31, No. 2, Jan 28, 2016
melting points. Accordingly, the interfacial bonding ability between ceramic reinforcing particles and metal matrix is limited because of the poor wettability between metals and ceramics. On the other hand, the densities and thermal expansion coefficients of ceramic particles and metal matrix are generally great deal of difference. Therefore, the cracks are normally generated during processing or mechanical loading, resulting in a premature failure of TMCs. Carbon fibers are considered to be the innovative reinforcements for metal matrix composites. In particular, carbon nanotubes (CNTs) regarded as “ultimate fibers” have inspired great re
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