Contents lists available at ScienceDirect Ceramics International journal homepage: www.elsevier.com/locate/ceramint Microstructure, mechanical properties and bio-corrosion properties of Mg- HA bionanocomposites fabricated by a novel severe plastic deformation process H. Torabi, M. Hoseini, M. Sadrkhah, G. Faraji ∗ , A. Masoumi School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, 11155-4563, Iran ARTICLE INFO Keywords: Corrosion Mechanical properties Mg-HA bionanocomposites Severe plastic deformation Microstructure ABSTRACT This research investigates the alterations in microstructure, mechanical properties, and corrosion behavior of binary magnesium-hydroxyapatite bionanocomposites with 2, 5, and 10 wt%HA. By mixing Mg and HA powders with diferent percentages of HA contents, a combined method of cyclic extrusion compression (CEC), equal channel angular pressing (ECAP) and conventional extrusion were employed to consolidate the mixture of powders. All composites were examined. The results indicate that the addition of hydroxyapatite to magnesium improves the mechanical properties, but these properties are deteriorated with the hydroxyapatite content of over 5 wt%. The corrosion behavior of the composites was examined by immersion test, mass loss and polar- ization tests in Hank’s solution. The results indicate that Mg-5HA exhibits the best corrosion resistance and the corrosion rate increases when the HA content rises to more than 5 wt%. In addition, the specimen produced through the proposed method in this work indicates better corrosion resistance in comparison with cast and extruded pure Mg. 1. Introduction Nowadays, magnesium and magnesium alloys have attracted a great thought as a useful material to be employed in biodegradable bone implants, taking into consideration their mechanical properties. The Young modulus of magnesium is actually near to that of bone, and it is the least dense among other structural metals. Also, when putting into an environment of living cells, it shows a degradable nature [1–3]. Selecting an alloying element for magnesium to allocate its unique properties has been widely studied [4–10]. Nevertheless, rapid corro- sion, low strength, and toxic ions imposed by aluminum and other heavy elements in some magnesium alloys constrained its usage. In order to use this metal for medical applications, these problems should be solved [6]. HA (hydroxyapatite) has received an increasing consideration to be used in making bone grafting materials and also dental prosthetics. Comparing all calcium phosphate bioceramics, HA is the one which is the most applied for medical uses due to its biocompatibility with a living body and its chemical composition, which resembles that of the bone. In fact, biocomposite materials could be permissible to achieve a variety of mechanical and biological characteristics [11,12]. Further- more, the contact between biocomposite and the surrounding tissue could be as a function of constituents [13,14]. Therefore, HA can be an appropriate selection to manufacture Mg-HA nanocomposites in order to have the properties of Mg and HA, simultaneously. Preparation of metal matrix composite AZ91D/HA (20% wt.) by powder metallurgy (PM) process done by researchers proved an amelioration in corrosion resistance compared to AZ91D [15]. In reality, for AZ magnesium al- loys, one primary concern to use them is their biocompatibility because of aluminum presence in this kind of alloys which is toxic and may cause disorders such as dementia and Alzheimer [16]. Therefore, it could not be an adequate material for biocomposites. Adding alloying elements such as Zn, Ca, Mn, Zr, Sn, Ag [17–21] and coatings such as HA has been the matter of interest for most of the researchers [22–25]. Recent researches have shown that severe plastic deformation (SPD) methods have a signifcant impact on grain refne- ment and mechanical properties of Mg alloys [26], such as equal channel angular pressing (ECAP) [27], high-pressure torsion (HPT) [28] and cyclic extrusion and compression (CEC) [29]. Furthermore, investigations have been performed to characterize the efect of plastic deformation methods on the corrosion resistance. To this end, sig- nifcant attention was paid to the efect of grain refnement. Re- searchers proved that the tendency of corrosion develop while the grain size decreased, and this phenomenon could be explained by a relation https://doi.org/10.1016/j.ceramint.2019.09.276 Received 12 August 2019; Received in revised form 26 September 2019; Accepted 27 September 2019 ∗ Corresponding author. E-mail address: ghfaraji@ut.ac.ir (G. Faraji). Ceramics International xxx (xxxx) xxx–xxx 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Please cite this article as: H. Torabi, et al., Ceramics International, https://doi.org/10.1016/j.ceramint.2019.09.276