Influence of mean grain size with ultrasonic velocity on microhardness of B 4 C–Fe–Ni composite Vildan Özkan a,⇑ , _ Ismail H. Sarpün b , Ayhan Erol c , Ahmet Yönetken d a Mus ß Alparslan University, Physics Dept., Mus ß, Turkey b Afyon Kocatepe University, Physics Dept., Afyonkarahisar, Turkey c Afyon Kocatepe University, Technology Faculty, Afyonkarahisar, Turkey d Afyon Kocatepe University, Electrical Engineering Dept., Afyonkarahisar, Turkey article info Article history: Received 20 March 2013 Received in revised form 10 May 2013 Accepted 15 May 2013 Available online 23 May 2013 Keywords: Ultrasonic velocity Attenuation Mean grain size Microhardness Compressive strength Composite materials abstract Composite samples were produced from boron carbide, iron and nickel matrix powders by using a pow- der metallurgy and electroless plating technique. Prepared samples were sintered at the temperature of ranging from 800 °C–1200 °C under Ar shroud. Ultrasonic velocity, ultrasonic attenuation and rate of screen heights of peaks were determined according to the pulse-echo method by using 2 MHz and 4 MHz probes. SEM (Scanning Electron Microscope), compressive testing and hardness measurements were employed to characterize the properties of the samples. Ultrasonic velocity, ultrasonic attenuation and rate of screen heights of successive peaks have showed a linear relation with mean grain size of sam- ples. The ultrasonic velocity has been correlated with the hardness and the compressive strength and sin- tering temperature. We see that the sharp decrease in the hardness and a rapid increase in the ultrasonic velocities versus sintering temperature are attributed to the increase in the amount of grain size. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Ultrasonic techniques can be used for qualitative or/and quan- titative evaluation of physical and elastic properties of materials [1]. Ultrasonic testing is used to detect cracks and other disconti- nuities in materials as a non-destructive testing [2–4]. Ultrasonic grain size determination of solid materials can be performed by several techniques which are dependent on ultrasonic quantities such as ultrasonic attenuation, ultrasonic backscattering, and velocity. Ultrasonic attenuation, velocity and their related parame- ters can be used to give insight into materials microstructure and associated physical properties [5,6]. In recent years, needs for light and superior materials to be used in aviation, space and automotive industries have increased depending on the new developments of technology. Materials used in space, aviation and automotive industries are exposed to high temperature, friction and high tension. Such needs encouraged the importance of production of composite materials and directed the studies on these materials using different meth- ods. Metal matrix composites (MMCs), produced by combining metallic matrix with ceramic reinforcements, have enhanced mechanical and physical properties such as high specific modulus, high strength, good wear, corrosion, higher stiffness, hardness, low thermal and electrical conductivity, and low sensitivity to temper- ature variation [7,8]. One of the commonly used industrial tech- niques for deposition of metal coatings is the electroless plating technique. Electroless deposition is a very simple process with the aid of a chemical reducing agent in solution, and without the application of external electrical power. The most important advantage of this process is to be obtaining the same metallic coat- ings of uniform thickness on metallic or non-metallic substrates. The ability to reinforce fine particulate matter such as hard ceramic or soft lubricious particles within metal matrix by electroless/auto- catalytic plating method has led to the development of composite coatings. These coatings exhibit superior properties compared to the plain electroless Ni–P coating [9]. Electroless nickel plating deposits a uniform coating regardless of the shape of the part or surface irregularities, allowing savings in material. The development and using of new wear resistant lightweight cermets on the base of boron carbide is actual because of their excellent properties such as low density, high wear resistance, elastic modulus and hardness [10]. Up to date, a wide range of rein- forcements have been used to produce (Fe, Ni, Al, Co, etc.)-based MMCs with mechanical alloying technique such as alloys, carbides (SiC, B 4 C, WC, TiC, Al 3 C 4 ), nitrides (AlN, Si 3 N 4 ), borides (TiB 2 ) and oxides (Al 2 O 3 , SiO 2 ) [11–15]. 0925-8388/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jallcom.2013.05.097 ⇑ Corresponding author. Tel.: +90 4362130013; fax: +90 4362130054. E-mail address: v.ozkan@alparslan.edu.tr (V. Özkan). Journal of Alloys and Compounds 574 (2013) 512–519 Contents lists available at SciVerse ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom