Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys Corrosion behavior and in-vitro bioactivity of porous Mg/Al 2 O 3 and Mg/ Si 3 N 4 metal matrix composites fabricated using microwave sintering process Ehsan Ghasali a,* , Aidin Bordbar-Khiabani b , Masoud Alizadeh a , Masoud Mozafari b , Morteza Niazmand a , Houman Kazemzadeh c , Touradj Ebadzadeh a a Ceramic Dept., Materials and Energy Research Center, Alborz, Iran b Nanotechnology and Advanced Materials Dept., Materials and Energy Research Center, Alborz, Iran c Tehran University of Medical Sciences, Tehran, Iran HIGHLIGHTS • Porous Mg composites have been prepared successfully through microwave heating. • Reaction between reinforcements and Mg matrix leads to for intermetallic products. • The corrosion behavior of porous Mg composites can be changed by formation reaction products. ARTICLE INFO Keywords: Magnesium Microwave sintering Porous Composite Bioactivity ABSTRACT In the present work the corrosion behavior and in-vitro bioactivity of two kinds of porous Mg-metal matrix nano- composites separately reinforced with Al 2 O 3 whiskers and Si 3 N 4 particles were reported. 10 wt% of reinforce- ment was mixed with magnesium using high-energy ball milling and ethanol media for 10 min. After that, 10 ml ethylene glycol was added to milled mixture at the final stage of drying on a heater/stirrer at 70 °C. After stirring for 12 h, the powder mixtures were uniaxially pressed at 300 MPa to produce bar-shaped green specimens. The microwave sintering was performed at 650 °C without soaking time in a graphite bed. Porosity of about 50% was measured for both sintered composites using Archimedes principle. The XRD investigations revealed Mg 2 Al 3 and MgO phases as the result of reaction between Mg and Al 2 O 3 . Moreover, the reaction products in Mg- Si 3 N 4 composite were Mg 2 Si, Mg 3 N 2 and Si. The corrosion tests showed that the polarization resistance of both pre- pared composites is higher than that of pure Mg. Mg-Al 2 O 3 composite also showed lower corrosion current density compared to Mg- Si 3 N 4 composite (1.42E -4 and 1.36E -3 A cm -2 , respectively). In-vitro bioactivity analysis of composites showed high level of needle-shaped CA-P inside porosities of Mg-Si 3 N 4 composite; while in the case of Mg-Al 2 O 3 composite a lower amount and smaller needle-shaped particles were found. 1. Introduction Pure magnesium and its metal matrix composites (MMCs) have re- markable properties especially in the case of specific strength which normally feature is related to the lowest density of Mg among con- structive metals [1–3]. The unique advantage of Mg-MMCs results in the use of these composites in specific positions in aerospace and au- tomotive industries as lightweight products [4,5]. Moreover, the ap- plication of Mg-MMCs has not been limited to above-mentioned ap- plications and they are also being used as biomaterials [6–8]. The porous structures can be used to enhance the unique properties of Mg-MMCs as biocompatibility and also lightweight materials that increase the specific surface area with the formation of pore structure [9–11]. Many novel processes have been used to produce pore structure of Mg alloys such as titanium wire space holder [12], negative salt pattern molding [13], powder metallurgy [14], hydrogen injection [15] and etc. Each of the above mentioned processes has promising effect on the properties of product besides their cost and limitations [16]. Powder metallurgy route can be applied as promised candidate to produce porous structure by using space holder agent and burning this agent to form porosities [17]. Normally, two steps are necessary to produce porous structure in powder metallurgy process by conventional heating. The first step is an effort to remove of space holder agent at low temperatures and the second step is the sintering of samples around https://doi.org/10.1016/j.matchemphys.2019.01.007 Received 1 October 2018; Received in revised form 30 December 2018; Accepted 2 January 2019 * Corresponding author. E-mail addresses: Ehsan_ghasali@yahoo.com, e.ghasali@merc.ac.ir (E. Ghasali). Materials Chemistry and Physics 225 (2019) 331–339 Available online 04 January 2019 0254-0584/ © 2019 Elsevier B.V. All rights reserved. T