Contents lists available at ScienceDirect Journal of Manufacturing Processes journal homepage: www.elsevier.com/locate/manpro Machinablility of titanium matrix composites (TMC) reinforced with multi- walled carbon nanotubes Guangxian Li, Khurram Munir, Cuie Wen, Yuncang Li, Songlin Ding* School of Engineering, RMIT University, Bundoora,3083, Victoria, Australia ARTICLEINFO Keywords: Titainum matrix composite (TMC) Carbon nanotubes (CNTs) Dispersion Machinability Milling Electrical discharge machining (EDM) ABSTRACT Carbon nanotube (CNT) reinforced titanium matrix composite (TMC) is a type of new material with promising potentials in industry because of its superior properties such as low density and high elastic modulus. In this paper, the machinability of CNT-reinforced TMCs with diferent fabrication methods was studied experimen- tally. Multi-walled carbon nanotubes (MWCNTs) were dispersed in titanium (Ti) powder via diferent dispersive methods, and the Ti-MWCNTs powder mixtures were consolidated by spark plasma sintering (SPS) at diferent temperatures. The fabricated TMCs were machined by milling and electrical discharge machining (EDM), and their machinability was investigated by analysing the roughness, hardness, cutting forces and micro morphology of the machines surfaces. After milling, it was found that the machinability of the TMCs fabricated under dif- ferent processing conditions was diferent, which was refected by the diference in cutting force (values and frequecies), tool wear and facial morphology (roughness, hardness, faws and element distribution). The main causes of these variances in machinability were attributed to the CNT agglomeration and presence of in situ formed titanium carbide (TiC) particles in Ti matrices. Also, the CNT agglomeration and TiC particles infuenced the facial morphology of TMCs after EDM. The sizes and distribution of pores due to the erosion were diferent for the four TMCs. The results proved that the fabrication methods infuence the properties of the TMCs which signifcantally impact their machinability. 1. Introduction Titanium matrix composites (TMCs) have been gradually used in industry due to the outstanding properties including low density, high strength, and stifness [1]. Among diferent types of TMCs, the dis- continuously reinforced titanium matrix composites (DRTMCs) have been extensively investigated in diferent studies. The DRTMCs are fabricated by synthesising the mixtures of metal matrix and reinforce- ments powders. Depending on the fabrication routes, various methods for the synthesis of TMC can be classifed as ex-situ and in-situ methods. Compared with ex-situ methods, the in-situ methods including me- chanical alloying [2] and self-propagation high-temperature synthesis [3] are mostly adopted by industry due to cost-efectiveness. With the development of powder metallurgy technology, advanced synthesis methods such as reaction hot pressing and spark plasma sintering (SPS) are often adopted to manufacture high strength TMCs [4]. The princi- ples of these two synthesis methods are similar, both are used to con- solidate the mixed powders of reinforcements and metal matrix under elevated thermomechanical loads, e.g., temperature and pressure [5]. As for the materials of reinforcements, Table 1 lists some typical ma- terials which are normally used as the reinforcements in the fabrication of the TMCs. Generally, the reinforcements are hard ceramic particles or high-performance nano materials with low density and high elastic modulus. Previous studies on TMCs have elucidated that the mechan- ical properties of TMCs e.g. the elastic modulus, ultimate strength, yield strength, and hardness can be improved by reinforcing them with dif- ferent materials, as listed in Table 2. However, compared to Ti and its alloys, the machining of TMCs could be more difcult. Generally, Ti is considered as a difcult material to machine due to its high strength and low thermal conductivity. The reinforcements in Ti matrices further increase their strength and hardness which further afect the machin- ability of the TMCs [6]. Also, some internal pores and facial cracks in TMCs are inevitable because of the diference in the properties of re- inforcement materials and the metal matrices. This leads to the un- expected defects on the machined surfaces of TMCs. Therefore, it is important to investigate the machinability of TMCs and establish an in- depth understanding of the quality of their surfaces after the machining processes. https://doi.org/10.1016/j.jmapro.2020.04.008 Received 10 February 2020; Received in revised form 31 March 2020; Accepted 2 April 2020 ⁎ Corresponding author. E-mail addresses: guangxian.li@rmit.edu.au (G. Li), khurramshahzad.munir@rmit.edu.au (K. Munir), cuie.wen@rmit.edu.au (C. Wen), yuncang.li@rmit.edu.au (Y. Li), songlin.ding@rmit.edu.au (S. Ding). Journal of Manufacturing Processes 56 (2020) 131–146 1526-6125/ © 2020 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved. T