Devinder Yadav

Development of Cu particles and Cu core-shell particles reinforced Al composite

Abstract Copper particles were incorporated and retained in elemental state in an aluminium matrix by friction stir processing thereby producing a non-equilibrium particulate composite. The processed Al–Cup composite exhibited improved strength with significantly high ductility. The composite was stable up to a temperature of more than 300°C. Thermal exposure at 350°C for more than 10 min led to diffusion of Cu atoms into the Al matrix forming a core-shell type structure in the Cu particles and thus producing an Al–Cu core-shell composite. The shell consists of multiple layers, the thickness of which was controllable.

Densification mechanisms during reactive spark plasma sintering of Titanium diboride and Zirconium diboride

Abstract In this study, dense fine-grained ZrB2 and TiB2 were fabricated using reactive spark plasma sintering (RSPS) of ball-milled Zr/B and Ti/B mixtures. Systematic investigations were carried out to understand the mechanisms of reactive sintering. Two densification mechanisms were found to be operating during RSPS. The first stage of densification was due to self-propagating high temperature synthesis reaction leading to formation of ZrB2 and TiB2 compacts having relative density of ~48 and ~65%, respectively. The second stage of densification occurred at temperatures more than 1100 °C and resulted in final relative density of more than 98%. Electron backscatter diffraction and electron microscopy studies on interrupted RSPS samples as well as dense samples showed deformed grains and presence of slip steps while grain orientation spread map and pole figure analysis confirmed plastic flow. Plastic flow-aided pore closure is shown as major mechanism during reactive sintering.

Microstructure Development in Single and Double-Pass Friction Stir Processing of Aluminium

Single pass and double-pass friction stir processing was carried out on commercially pure aluminium at a rotation speed of 640 rpm and traverse speed of 150 mm/min and a detailed electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) analysis was carried out to understand the microstructure developed. The grain size was refined substantially after the first pass whereas there was no significant change in the grain size after the second pass. This indicates that the final grain size after friction stir processing does not depend on the starting grain size. The equiaxed fine grains were formed by dynamic recrystallization process as revealed by EBSD analysis. TEM observations showed banded contrast across the grain boundaries indicating grain boundaries to be in equilibrium. Free dislocations observed inside grains after the first pass were well arranged into subgrain boundaries after the second pass. EBSD also revealed some variation in microstructural features such as grain size, texture index, grain orientation spread and grain average misorientation across the surface and also in the cross section of the stir zone both after single and double pass.

Surface Composites by FSP

Surface engineering is becoming increasingly important for engineering components which involve surface interactions. The surface of such components is either protected, for example by protective coatings, or modified in a manner that suits the interactions at the surface. Surface hardening of components that are subjected to friction and consequent wear is a common industrial practice. While there are many surface hardening techniques in use they have their own limitations. Surface composites have been emerging as an attractive way to enhance the surface hardness and protect it against wear and tear. Friction stir processing (FSP) has emerged as an effective technique for surface modification and hardening. The technique also allows incorporation of hard ceramic reinforcement into the modified surface to further enhance the hardness. This chapter will deal with such surface composites made by FSP. It should be however, remembered that unless otherwise mentioned specifically, the distinction between surface and bulk composites made by FSP is not absolute and depends on how one perceives the depth to which particles are distributed and the intended application. The processing approaches for making bulk and surface composite by FSP, therefore, also remain the same. These approaches are detailed in Chapter 3, Processing Metal Matrix Composite (MMC) by FSP, and hence, the processing methods of surface composites will be briefly described here.

Optimized process parameters for fabricating metal particles reinforced 5083 Al composite by friction stir processing.

Metal matrix composites (MMCs) exhibit improved strength but suffer from low ductility. Metal particles reinforcement can be an alternative to retain the ductility in MMCs (Bauri and Yadav, 2010; Thakur and Gupta, 2007) [1,2]. However, processing such composites by conventional routes is difficult. The data presented here relates to friction stir processing (FSP) that was used to process metal particles reinforced aluminum matrix composites. The data is the processing parameters, rotation and traverse speeds, which were optimized to incorporate Ni particles. A wide range of parameters covering tool rotation speeds from 1000 rpm to 1800 rpm and a range of traverse speeds from 6 mm/min to 24 mm/min were explored in order to get a defect free stir zone and uniform distribution of particles. The right combination of rotation and traverse speed was found from these experiments. Both as-received coarse particles (70 μm) and ball-milled finer particles (10 μm) were incorporated in the Al matrix using the optimized parameters.

Fabrication of Metal Particles Embedded Aluminum Matrix Composite by Friction Stir Processing (FSP)

Conventional metal matrix composites (MMCs) suffer from the disadvantage of low ductility. In order to overcome this, reinforcing the metal matrix with metal particles can be taken as an alternative approach. However, processing such composites can pose serious challenges as the metal particles can either go in to solution or form undesirable intermetallics during processing through conventional routes. Friction stir processing (FSP) is emerging as a versatile tool for processing and modification of variety of materials. In the present study, metal particulate reinforced aluminum matrix composite was processed by incorporating nickel particles through friction stir processing (FSP) in one step. The microstructure was characterized by scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). SEM observations revealed that particles are uniformly dispersed in the aluminum matrix with excellent interfacial bonding. FSP also lead to grain refinem...

Introduction to Friction Stir Processing (FSP)

This chapter presents an overview of the friction stir processing (FSP) technique. A brief introduction of the working principle of FSP and processing of light metals, particularly aluminum and magnesium, is presented. The microstructural aspects with emphasis on the microstructure evolution during the process have been also discussed.

Processing Nonequilibrium Composite (NMMC) by FSP

Metal matrix composites (MMCs) combine the properties of two different materials to produce a material with superior mechanical properties. Table 4.1 shows the mechanical properties of some of the Al based MMCs. One of the major shortcomings of MMCs, as can be seen in Table 4.1 as well, is the low ductility which arises out of various reasons related primarily to the hard and brittle reinforcement [1–5]. If the primary reason for this be the brittle ceramic particles, can there be alternative reinforcements that can prevent this embrittlement? Harder metallic particles may be the answer. However, the equilibrium phase diagrams say that the metallic particles will either dissolve to form solid solution or react with aluminum to form intermetallic compounds if they have low solubility. Metals can be classified into two groups based on their solid solubility in aluminum as shown in Table 4.2 [6]. Metals from the low solubility group have to be chosen as reinforcement particles as they do not dissolve in aluminum. Ni, Ti, and W are attractive choices as reinforcements because of their higher strength and stiffness compared to aluminum. However, owing to their low solubility such metals will react and form brittle intermetallics when processed in equilibrium conditions by conventional routes. Moreover, the reaction is exothermic in nature that leads to rapid reaction kinetics [7]. Therefore the conventional composite processing routes such as powder metallurgy (PM) and stir casting cannot be used to incorporate metallic particles in aluminum [8–10].

Introduction to Metal Matrix Composites

Materials with high specific strength and stiffness have seen an increasing demand for various applications that thrive on light weighting, better fuel efficiency, and higher pay load. This has necessitated the development of a class of materials known as composites. Composite materials have received wide acceptance owing to their greater potential for use as components/products with high specific strength, stiffness, enhanced wear resistance, and better high temperature properties compared to monolithic metals and alloys. Further, they can be tailor-made to satisfy specific design requirements in a variety of applications.

Processing Metal Matrix Composite (MMC) by FSP

Friction stir processing (FSP) uses the same principle as friction stir welding (FSW) [1]. In FSP a cylindrical tool that has a shoulder and a pin is rotated at high speed while a vertical force plunges the pin into the material. The frictional heat softens the material and as the tool is traversed forward the material is processed and consolidated. The process involves severe deformation and material mixing. The strain during FSP can go up to as high as 40 [2]. The temperature also rises significantly due to the frictional heating and the adiabatic heating arising from the deformation of the material [1]. The material mixing action and the thermomechanical aspect of the process thus offer the possibility of incorporating second phase particles in the stir zone (SZ) and make a composite.