Introduction Characterization of selectively laser melted Ti-6Al-4 V micro-lattice struts.

Available online at www.sciencedirect.com Corresponding author. Tel.: +44-0-151-794-4819; fax: +44-0-151-794-4819. E-mail address: r.minesliv.ac.uk ICM11 Characterization of selectively laser melted Ti-6Al-4V micro- lattice struts Rafidah Hasan a,b , Robert Mines a , Peter Fox a a Department of Engineering, University of Liverpool, The Quadrangle, Liverpool L69 3GH, UK b Faculty of Mechanical Engineering, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia Abstract This paper presents a characterization study of titanium alloy Ti-6Al-4V micro-struts manufactured using selective laser melting SLM. Previous test results from sandwich structures with titanium alloy micro-lattice cores showed that the material experienced brittle fracture failure, although it had a reasonable specific strength. Therefore, the microstructure present in the struts has been investigated in order to understand its influence on the mechanical behaviour. Conclusions on the way forward for improved mechanical behaviour, by the use of subsequent heat treatment and careful control of the manufacturing process can then be identified. © 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of ICM11 Keywords: selective laser melting; titanium alloy; micro-lattice; sandwich structure

1. Introduction

The University of Liverpool has investigated the use of selectively laser melted SLM micro-lattice structures within a number of engineering areas including medical devices and aerospace mechanical structures, such as lightweight sandwich constructions [1, 2]. Previous work reported that the specific strength of titanium alloy Ti-6Al-4V micro-lattice structures is competitive with that of aluminum honeycomb [3] and this is especially true if the energy density is high higher laser powers and long exposure times during the SLM process, with optimum results being obtained with a laser power of 200 Watts and an exposure time of 1000 —s. This combination of parameters for the Ti-6Al-4V micro-lattice structure core resulted in a more localized impact area in the sandwich constructions as compared to aluminum honeycomb core [4]. A more localized impact area means that a smaller area is affected by 1877-7058 © 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of ICM11 doi:10.1016j.proeng.2011.04.090 Procedia Engineering 10 2011 536–541 Rafi dah Hasan et al. Procedia Engineering 10 2011 536–541 537 im th sh lo 4 b fa b n 1 [ la st th S st F un F n p th mpact damage he impacted a howing almos oad bearing s 4V micro-lattic behavior of th failure of the m brittle fracture need to be dete 1.1. Micro-latt The micro-p 1] from their attice block w truts protrudin hat fracture oc SLM Ti-6Al-4 trut ends can b Fig. 1. a side vie nit cell with 8 str Fig. 2. SEM image ode area [7] Previous w possibility that hat a similar p e, and this is p area of the T st flat fracture tructure perfo ce structures n he basic micro micro-struts i e failure obser ermined by th tice strut plastic and -e basic buildin with 2.5 mm u ng from a nod ccurred in the 4V micro-latti be clearly obs ew of 20 mm X 2 ruts [2] e of 200W X 100 work on the SL t the ‘cast’ mi problem may preferred by t Ti-6Al-4V mic e surfaces. Sin ormance, espe needs to be fu o-strut build is thought to rved needs to e use of a reli lastic properti ng block whic unit cell size, w de at the centr e end part of c ice block fails served in the s 20 mm X 20 mm 00 —s SLM Ti-6Al LM processin icrostructure m occur with Ti the aircraft ma cro-lattice str nce plasticity ecially in aero urther studied is an importa predict the be be found, and able micro-str ies of SLM T ch is the micr while Fig 1b re. When subj certain struts, s on a 45° dia scanning elect m BCC Ti 6Al 4V l-4V micro-lattice ng of stainles may contribut i-6Al-4V and a anufacturer [5 ructure core e is an importa ospace applica d and analyzed ant part of cu ehavior of the d in parallel, rut test. Ti-6Al-4V mic ro-strut. Fig 1 b graphically jected to impa near the node agonal plane tron microscop V micro-lattice str e block which sho ss steel micro e to the less d that this issu 5]. However, i experienced b ant criterion f ations [6], the d. Therefore, t urrent researc e micro-lattice the elastic pro cro-lattice stru 1a shows a shows a BCC act or compre e region. As r as shown in F py SEM ima ructure block; b ows failure at cer -lattice struct ductile behavio ue could be cla it has been ob brittle failure, for energy abs e failure of the the investigati ch, as the pro e. An explana operties of th uctures can be BCC Ti-6Al- C unit cell wit ession load, it reported by Sh Fig 2. The fai age in the figu graphic illustrat rtain point in the tures [1] high or. It has been arified by exa b bserved that with struts sorbency in ese Ti-6Al- ion into the operties and ation of the e structures e quantified -4V micro- th 8 micro- was found hen [7], the ilure of the ure. tion of a BCC strut, near hlighted the n suggested amining the 538 Rafi dah Hasan et al. Procedia Engineering 10 2011 536–541 m [8 p su st h 2 st T a le m m w o a F 3 3 lo s to w F m microstructure 8, 9], where phases presen ubsequent he tudied and rep have not been

2. Material