W-25%Re-HfC composite materials for Pin tool material applications: Synthesis and consolidation Zafar Iqbal a , Nouari Saheb a, b, * , Abdel Rahman Shuaib a a Department of Mechanical Engineering, King Fahd University of Petroleum and Minerals, Dhahran, 31261, Saudi Arabia b Centre of Research Excellence in Nanotechnology, King Fahd University of Petroleum and Minerals, Dhahran, 31261, Saudi Arabia article info Article history: Received 26 January 2016 Received in revised form 3 March 2016 Accepted 5 March 2016 Available online 10 March 2016 Keywords: Mechanical alloying Spark plasma sintering Hard metals Composites Microstructure Density Hardness abstract The development of tool materials for high temperature applications such as friction stir welding of steels and high strength materials remain a key challenge because these materials are difficult to syn- thesize and consolidate by conventional means. In this work, nanostructured W-25 wt.%Re alloy and W- 25Re-HfC composites of uniform microstructure containing 5 and 10 vol.% of HfC particles, were developed by mechanical alloying (MA) and spark plasma sintering (SPS) techniques. The effect of processing parameters and reinforcement content on the microstructure, densification, and properties of the developed materials was investigated. Mechanical alloying of the as-received and partially alloyed W-25 wt.%Re powder for 25 h yielded a single nanostructured solid solution with a crystallite size of 13 nm and increased its lattice strain to 0.75%. The fully alloyed powder was reinforced with 5 and 10 vol.% of HfC particles and further milled for 15 h, this led to the formation of composite powders with a uniform distribution of particles in the matrix. The uniform distribution of HfC particles, obtained by mechanical alloying, was maintained in the consolidated samples. Crystallite size of the matrix phase in the sintered composites remained in the nanometer range and did not exceed 100 nm. Partially and fully alloyed monolithic W-25 wt.%Re alloys, spark plasma sintered at 1800  C for 10 min, had relative density values of 98.2 and 97.8%, respectively. W-25Re-HfC composites containing 5 and 10 vol.% HfC, spark plasma sintered at 1800  C for 10 min, had relative density values of 96.9 and 96.2%, respectively. The composite containing 10 vol.% of HfC possessed the highest Vickers hardness value of 495. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Friction stir welding (FSW) is a relatively new solid-state joining process developed at the Welding Institute in the united kingdom in 1991 [1]. The process is energy efficient, environment friendly, and versatile [2]. It uses a spinning tool to produce frictional heat in the work piece. This tool is pressed into contact with a seam to be welded, the base metal heats up to around 80% of its melting temperature and softens which assists in deforming the metal to achieve joining. The FSW process was initially applied to aluminum alloys [3,4], and has been extended to harder and higher melting point materials such as steels [5], titanium alloys [6], and copper [7]. However, the development of tool materials [8] for high tem- perature applications such as friction stir welding of steels remains a key challenge as these materials are difficult to synthesize by conventional means. Successful friction stir welding of these ma- terials mainly depends on the appropriate selection of material, processing, and design of the tool. The two major groups of tool materials for FSW of steels and high temperature materials are superabrasives and refractory metal alloys. Superabrasives include polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (PCBN), which are relatively expensive for average commercial use. The refractory metal alloys include tungsten, molybdenum, and tungsten-rhenium alloys. Tungsten based materials [9] have been successfully used as tools for FSW of hard metals such as steel and titanium. They showed maximum tool life and high resistance to degradation. Tungsten- rhenium alloys and their composites have been developed and introduced on a limited scale. Commercial pure tungsten has high strength at elevated tem- peratures but it has low toughness at room temperature. It possess high wear resistance when used for FSW of steels and titanium alloys. When pure tungsten is cooled from temperatures higher * Corresponding author. Department of Mechanical Engineering, King Fahd University of Petroleum and Minerals, Dhahran, 31261, Saudi Arabia. E-mail address: nouari@kfupm.edu.sa (N. Saheb). Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom http://dx.doi.org/10.1016/j.jallcom.2016.03.030 0925-8388/© 2016 Elsevier B.V. All rights reserved. Journal of Alloys and Compounds 674 (2016) 189e199