Processing and properties of topologically optimised biomedical Ti–24Nb–4Zr–8Sn scaffolds manufactured by selective laser melting Y.J. Liu a , X.P. Li b , L.C. Zhang a,nn , T.B. Sercombe b,n a School of Engineering, Edith Cowan University, 270 Joondalup Drive, Joondalup, Perth, WA 6027, Australia b School of Mechanical and Chemical Engineering, The University of Western Australia, 35 Stirling Highway, Crawley, Perth, WA 6009, Australia article info Article history: Received 7 May 2015 Received in revised form 23 June 2015 Accepted 26 June 2015 Available online 30 June 2015 Keywords: Selective laser melting Ti–24Nb–4Zr–8Sn Mechanical behaviours Porous materials abstract This study investigated the effect of the processing parameters on the quality and mechanical properties of a biomedical titanium alloy (Ti–24Nb–4Zr–8Sn) scaffolds fabricated by selective laser melting. Optimal manufacturing parameters were then determined through analysing the pores distribution, geometrical accuracy and the mechanical properties of the produced components. The evaporation of tin during the process is thought to be the main cause of pore generation at higher incident energy densities. Using the optimal processing conditions, the strength of the scaffold reached 51 MPa at a scaffold density of o1 g/cm 3 and a high solid strut relative density of 99.3%. Fracture surface analysis found that the main reason for strut early failure was the weaknesses of struts caused by the presence of pores as well the thickness of strut and internal unmelted powders. **Co-corresponding author. Crown Copyright & 2015 Published by Elsevier B.V. All rights reserved. 1. Introduction Driven by the increasing number of joint diseases related to an aging population and obesity, it has been estimated that the re- quired number of total hip replacements and total knee ar- throplasties will increase by 174% and 673% by 2030, respectively [1]. These artificial joints have been employed to reduce the suf- fering and improve the patient's quality of life. The material from which the implant is fabricated from should have sufficient me- chanical strength to sustain the loads to which they are exposed [2], so that the risk of failure and consequential painful revision surgery is minimised [3]. Excellent biocompatibility, as well as a low modulus and no cytotoxicity, are key requirements, especially in load-bearing applications [4–7]. Currently, the three most commonly used load-bearing implant materials are stainless steel, CoCr alloys and titanium [8–10]. With some unique properties, such as high strength and corrosion resistance and low modulus [11], titanium alloys are more preferable than CoCr alloys and stainless steel in orthopaedic applications. Mismatch in stiffness between an implant and the surrounding bone can cause stress shielding, which often results in implant loosening and the need for revision surgery [12]. Ti–24Nb–4Zr–8Sn (abbreviated hereafter as Ti2448), with a nominal chemical composition of 24% niobium, 4% zirconium and 8% (all in weight percent) [11], has a significantly lower modulus of  42–50 GPa compared with other conventional titanium alloys (  100–120 GPa) [5]. It has the potential to im- prove the performance of implant with its low modulus, high biocompatibility, strength and corrosion resistance [13–15]. However, the modulus of Ti2448 alloy (42–50 GPa) must be reduced further if it is to match the modulus of bone (4–30 GPa) [16,17]. One common method to reduce the modulus of a material is to introduce porosity into the structure [18–20]. Porous mate- rials play a key role in bone tissue engineering applications, due to their low modulus coupled with the possibility of enhanced bio- logical fixation through bone cell in-growth [21]. The geometric freedom offered by additive manufacturing technologies such as Selective Laser Melting (SLM) are being considered as one of the most advantageous methods for fabri- cating the complicated porosity structure of an artificial bone implant [22–24]. During SLM process, a high-intensity laser beam selectively scans a thin powder bed, melting the metal particles, which solidify to form a solid layer. The build platform then moves down by the thickness of one layer (typically 50–100 μm), a new layer of powder is deposited on top and the process continues until the part is complete. One of the key advantages of selective laser melting is its ability to produce near-full density metallic parts [25–27] with a high degree of geometrical complexity without the need for any tooling or machining [28]. Recent work has coupled topology optimisation with SLM to produce light- weight scaffolds with high specific strength and stiffness [29]. However, this work was performed with Ti–6Al–4V, which has Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/msea Materials Science & Engineering A http://dx.doi.org/10.1016/j.msea.2015.06.088 0921-5093/Crown Copyright & 2015 Published by Elsevier B.V. All rights reserved. n Corresponding author. nn Co-corresponding author. E-mail addresses: l.zhang@ecu.edu.au, lczhangimr@gmail.com (L.C. Zhang), tim.sercombe@uwa.edu.au (T.B. Sercombe). Materials Science & Engineering A 642 (2015) 268–278