Materials Science and Engineering A 485 (2008) 703–710 Mechanical properties of Ti–W alloys reinforced with TiC particles Heeman Choe a,∗ , Susan Abkowitz b , Stanley M. Abkowitz b , David C. Dunand c a School of Advanced Materials Engineering, Kookmin University, Chungneung-dong, Songbuk-ku, Seoul 136-702, South Korea b Dynamet Technology Inc., Eight A Street, Burlington, MA 01803, USA c Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA Received 23 August 2007; received in revised form 14 January 2008; accepted 24 January 2008 Abstract Composites consisting of a Ti–W solid-solution-strengthened matrix reinforced with TiC particles are produced by powder metallurgy. TiC additions increase strength but reduce ductility and matrix microhardness. Composites with 7.5 wt.% TiC show some tensile ductility (3–7%) but those with 15 wt.% TiC are brittle in tension. They are however strong and ductile in compression: Ti–15W/15TiC (wt.%) has a compressive yield strength exceeding 1200 MPa. This composite also shows tensile crack growth rates which are considerably faster than for pure titanium (by a factor 2) or Ti–15W (by a factor 2–6) and a fracture toughness which remains relatively high as compared to Ti–15W (21 vs. 34MPa √ m). © 2008 Elsevier B.V. All rights reserved. Keywords: Titanium alloy; Composite; Orthopedic; Powder metallurgy; Mechanical properties; Titanium carbide 1. Introduction Titanium and its alloys are used extensively for biomedical implants due to their excellent mechanical properties, corrosion resistance and biocompatibility [1–4]. Moreover, their stiffness (∼80–130 GPa [5]) is substantially lower than that of other conventional metallic implant materials such as stainless steel (∼190–200 GPa [5]) or Co alloys (∼200–248 GPa [5]), thus reducing the stress shielding effect arising from differences in compliance between bone (∼10–40 GPa [6]) and implant [7,8]. While used for some low-stress bone implants [9,10], com- mercially pure titanium (CP-Ti) suffers from a relatively low strength and poor wear resistance, making it inadequate for highly stressed bone implants or wear-prone prostheses [11]. Hardness and wear resistance, and to a lesser extent strength, can be improved by the addition of TiC particles to CP-Ti [12–20]; however, these Ti–TiC composites, in line with other metal matrix composites [21], show reduced ductility and fracture toughness [12–14,22]. Recently, the use of tungsten as a solid-solution strengthener in CP-Ti has been found to result in large increases in strength and hardness with only moderate decrease in ductility [23,24]. For the two alloys studied to date, Ti–10 wt.% W exhibits ∗ Corresponding author. Tel.: +82 2 910 4417; fax: +82 2 910 4320. E-mail address: heeman@kookmin.ac.kr (H. Choe). a stress–strain curve similar to Ti–6Al–4V (yield strength σ y = 770–800 MPa and ductility ε f = 14.1–18.5% [23,24]) while Ti–15 wt.% W is stronger but less ductile (σ y = ∼1000 MPa and ε f = ∼9%). While Ti–W alloys are also harder than CP-Ti, they are not expected to achieve the high levels of hardness and wear resistance needed for some of the above implant applications [25]. Here, we investigate the effect of adding TiC particles to Ti–W alloys, with the goal of striking a balance between the gain in hardness and wear resistance and the penalty in ductility and toughness provided by the ceramic reinforcement. We report on the microstructure and room-temperature mechanical properties of five composites consisting of Ti matrices alloyed with 0, 7.5 or 15 wt.% W and containing 7.5 or 15 wt.% TiC particles. 2. Experimental procedures 2.1. Processing and microstructure As summarized in Table 1, five TiC-containing compos- ites with Ti–7.5W or Ti–15W matrix and two TiC-free control alloys CP-Ti and Ti–15W (all compositions are given in wt.% in the following) were created by the combined cold and hot isostatic pressing (CHIP) process [26]. Ti powders (<150 m), W powders and TiC powders (both <10 m) were blended and compacted into billets by cold isostatic pressing at a pressure of 0921-5093/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2008.01.069