S. Jayalakshmi

Aluminum and Magnesium Metal Matrix Nanocomposites

The book looks into the recent advances in the ex-situ production routes and properties of aluminum and magnesium based metal matrix nanocomposites (MMNCs), produced either by liquid or semi-solid ...

Microstructure and damping characteristics of Mg and its composites containing metastable Al85Ti15 particle

This paper reports for the first time the damping behavior of Mg-Al85Ti15 metastable composites synthesized using near dense blend-press-microwave sinter-hot extrusion methodology. Optical microscopy results show that the metastable particles were located along the grain boundaries and the formation of twins within the grains. In addition, scanning electron microscopy reveals reasonable distribution of particles, good matrix-particle interfacial bonding and minimal presence of microvoids. The damping test results show an increment in damping capacity and damping loss rate with the presence and increasing amount of particles. The effect of microstructure on damping characteristics of magnesium and damping mechanisms are discussed.

Ex Situ Production Routes for Metal Matrix Nanocomposites

Among different production routes hitherto developed for the manufacturing of metal matrix nanocomposites, a distinction can be done depending upon the matrix state during the production process, which can be molten, solid or semi-solid. In this Chapter, an overview of ex situ production routes is given, highlighting their general potential and shortcomings. Relevant case studies on the most promising and widespread casting production routes will be discussed more in detail in Chap. 3.

Mechanical Behavior of Al and Mg Based Nanocomposites

This chapter provides an insight into the mechanical properties of Al and Mg based nanocomposites. Tensile and compression properties, ductility and the influence of heat treatment on mechanical behavior of both aluminum and magnesium based nanocomposites are discussed. Experimental data (hardness, tensile/compression strength, ductility) reported in recent literature works is presented and compared, to highlight the effect of different processing techniques on the mechanical response of nanocomposites.

Metal Matrix Nanocomposites: An Overview

In this chapter, an overview on both Al and Mg based nanocomposites is given, emphasizing particularly on the importance of using reinforcements at nano length scale. The strengthening mechanisms at the basis of the reinforcing action exerted by nanoparticles (Orowan mechanism, enhanced dislocation density, grain refinement and load bearing effect) is described and their contribution discussed; modelling of the above mentioned mechanisms is also presented.

Casting Routes for the Production of Al and Mg Based Nanocomposites

As previously described in Chap. 2, the different production techniques for metal matrix nanocomposites (MMNCs) may be classified depending on the matrix state: liquid, solid or semi-solid. In comparison to other methods, liquid and semi-solid state MMNCs processing techniques are particularly attractive since they are potentially scalable to industrial level for the high volume production of near-net shape components. Nevertheless, such methods pose critical issues related to the low wettability of nanosized particles, generally leading to clusterization and high casting defects content. In this chapter, the main liquid and semi-solid casting routes (stir casting, compocasting, ultrasonic assisted casting and disintegrated melt deposition, DMD) will be described; the results of recent and relevant case studies on Al and Mg based nanocomposites will be summarized and discussed, by highlighting the main drawbacks of such processes.

Tribological Characteristics of Al and Mg Nanocomposites

Al and Mg nanocomposites have good mechanical properties and are potential tribological candidates for applications where weight-reduction is a critical factor, such as in automotive, aerospace and sports. This chapter presents the tribological characteristics of various Al and Mg nanocomposites. The tribological properties of wear and friction of the light-metals nanocomposites are influenced by several factors such as: process and process parameters, composition and microstructure, mechanical properties, heat treatment to enhance mechanical properties, applied external parameters of velocity and load, and formation of in situ protective films/layers. Examples of tribological investigations of nanocomposites that highlight these influencing factors are presented in the view of providing a comprehensive outlook on the tribology of light-metals nanocomposites. Some suggestions for future work are also mentioned.

Solutions for friction reduction at nano/microscale for MEMS actuators-based devices

Micro-Electro-Mechanical Systems (MEMS) are miniaturized devices built at nano/micro-scale. MEMS are fabricated from semiconductor silicon. At nano/micro-scale, capillary force along with asperity deformation induces friction at the surfaces of moving elements of actuators-based devices. The magnitude of friction force so generated is of the same order as that of the forces driving the moving elements. Friction therefore resists the relative mechanical motion between moving elements and reduces the useful operating lifetime of actuator devices. Solutions to reduce friction at nano/micro-scale in silicon by surface modification include: (i) chemical modification i.e. thin lubricant films/coatings, (ii) topographical modification i.e. surface patterning and (iii) hybrid modification, i.e. combination of topographical and chemical modifications. Friction behavior at nano/micro-scale of silicon and modified silicon surfaces is presented and discussed in this paper. Amongst the different surface modification approaches, the hybrid modification shows the best results in terms of friction reduction.

Microwave sintered aluminium composite with metallic glass reinforcement

Incorporation of light metal matrices with amorphous alloy/metallic glass particles as reinforcements is an emerging research topic. In the present work, pure Al has been reinforced with amorphous Ni60Nb40 particles. The microwave-assisted two-directional rapid sintering technique has been used to produce these novel composites. By using microwave sintering, Al-materials can be sintered at high temperatures in a relatively shorter period of time. The sintered composites are then hot extruded, and studied for their mechanical and wear properties. The property evaluation of the extruded composite reveal that when compared to pure Al, microhardness, tensile, compressive and wear properties improve significantly. The results of the present work highlight: (i) the effectiveness of amorphous particles as promising reinforcement material, by which the advantage of the light-metal matrix and also those of the amorphous alloy/glassy particles has been utilized and, (ii) microwave sintering as a successful method to produce these composites, wherein in retention of the amorphous structure of reinforcement has been achieved due to effective sintering.

Impression Creep Characteristics of Mg-Sn-Ag Alloy

Magnesium alloys with enhanced thermal stability are being developed for automobile engine applications. The available commercial Mg-alloys are usually alloyed with aluminum that are thermally stable only for T < 150o C. Development of new Mg-alloys is underway and Mg-Sn alloys are a promising option. In Mg-Sn alloy, the Mg2Sn phase has high thermal stability and is expected to enhance the high temperature properties. In this study, Mg-5Sn alloy is incorporated with Ag as a minor alloying element (0.175 wt. %). The creep behavior of the Mg-Sn-Ag alloy is investigated using the impression creep technique. The impression creep tests were carried out under punching stress in the range of 80-320 MPa and temperature of 373-573 K, for dwell times up to 5 hours. The results highlight that creep of the alloy was load and temperature dependent, i.e. increasing the load and temperature resulted in higher creep rates.