Effect of Varying Wt% of TiC on Mechanical and Wear Properties of RZ5-TiC In-Situ Composite

Introduction

Magnesium is one of the lightest metallic materials (35% lighter than aluminum and 78% lighter than steel) available for engineering application (Wang, Jiang, Li, & Wang, 2003; Guan, Wang, Li, & Jiang, 2004). Due to the light weight and adequate structural strength, magnesium alloys are considered as the potential materials for reducing the specific weight of the engineering components, especially in aerospace industries by replacing heavier materials such as steel and aluminum alloys (Sohn, Euh, Lee, & Park, 1998; Natarajan, Krishnaraj, & Davim, 2015). Over the years, the magnesium matrix composites (MMC) have been produced through various routes such as stir casting, powder metallurgy and squeeze casting (Gui, Li, & Han, 2003; Luo, 1995; Zhang, Fan, Wang, & Zhou, 2000). The stir casting route of composite synthetization is preferred by many because of low cost and high production rate (Ray, 1993).

In ex-situ fabrication of magnesium based MMC, many investigators have utilised SiC as reinforcement. Based on scanning electron microscopy (SEM) results, Saravanan et al. (2000). opined that no reactions took place between pure Mg and SiC during stir casting at 700ºC. It has been reported that, during the synthesis, magnesium does not react with SiC. The properties of the composite degraded due to the phase Mg₁₇Al₁₂. The ultimate tensile strength increased from 175 MPa to 203.1 MPa has been observed (Contreras, Angeles-Chávez, Flores, & Perez, 2007). Moreover, it has also been reported that at a temperature higher than 680 ºC the MgC₂ phase is not stable. It is well known that wetting characteristics of reinforcement and matrix during synthesis of MMC play an important role in overall quality characteristics. The aluminum as a matrix material generally has exhibited better wetting characteristics than magnesium for ceramic reinforcements such as TiC and SiC (Contreras et al., 2007).

Chen et al. (2005) synthesized AZ91-TiC composite using a preform prepared from titanium and carbon at 800ºC. This method confirmed the formation of the TiC by XRD. The Cao et al. (2008) and Wang et al. (2006) achieved in-situ reaction of titanium and carbon in molten magnesium at 800 ºC. More recently, Shamekh et al. (2012) used infiltrated preform of Ti-B₄C powder with AZ91 in order to fabricate magnesium MMC reinforced with TiC-TiB. Although, different reaction products of Mg-B and Ti-B such as MgB₂, TiB₂, TiB, Ti₃B₄ and even TiC and Ti₂AlC were detected, no evidence of reaction of magnesium and titanium or carbon was observed. Contreras et al. (2004) processed 56 vol.% TiC-Mg MMC through mechanical alloying route by infiltrating molten magnesium into porous TiC preforms at temperatures of 850 ºC to 950 ºC under argon shielding atmosphere. The reaction forms TiC, TiB2 and third form Ti₂AlC. They observed that the ultimate tensile strength increased from 175 MPa to 200 MPa and hardness from 183 to 194 VHN. Among all the Mg alloys, the ZE41 is a established alloy that contains Zn, rare earth such as Zr, has decent mechanical properties at room and elevated temperatures due to the solution and precipitation hardening. It has been widely used in aircraft gearbox and generator housings, and military helicopter components (López, Torres, Taltavull, & Rams, 2013; Trojanová, Gärtnerová, Lukáč, & Drozd, 2004).