S. Aravindan

Joining of ceramic composites by microwave heating

Abstract Ceramic matrix composites find increasing use in high technology applications because of their enhanced toughness and wear resistance. Reliable joining techniques are however needed for the development of intricate shapes made of ceramic composites. In this present work, sintered alumina–30% zirconia ceramic composites were joined by hybrid heating using microwave radiation (2.45 GHz, 700 W), along with sodium silicate glass powder as an interlayer. The joints/welds were studied using XRD, SEM, EPMA, microhardness, and 3 point bend tests.

Machining of Hard-Brittle Materials by a Single Point Tool Under External Hydrostatic Pressure

This paper reports on the development of a machining device which is capable of carrying out precision machining experiments under external hydrostatic pressure. Machining trials were conducted on hard-brittle materials such as soda glass, quartz glass, silicon and quartz wafers using the newly developed machining device under the externally applied hydrostatic pressures of zero and 400 MPa. The machined traces were analyzed by laser microscope. From the trace profiles, crack ratio and area of cross section of the trace were estimated. The applied hydrostatic pressure enhanced the critical cross sectional area and reduced the cracks and chippings of all the tested materials. Effects of hydrostatic pressure on the machining characteristics of the crystalline and glassy materials are discussed in detail. The mechanism behind the enhancement of ductile-brittle transition by the externally applied hydrostatic pressure is also elucidated by a theoretical model.

Nanosurface Fabrication of Hard Brittle Materials by Structured Tool Imprinting

This paper reports on nanosurface fabrication of hard brittle materials by structured diamond tool imprinting. Ultrafine structured surfaces were fabricated on soda glass, firelite glass, quartz glass, quartz wafer, and silicon. A specially designed and developed nanoindentation tester and a structured diamond tool machined by Focused Ion Beam (FIB) are used for the generation of such surfaces. Imprinted marks and the ultrafine structures are analyzed for their geometrical shape and accuracy. Load-depth analysis on the formed surfaces was carried out. Critical depth, at which ductile-to-brittle transition in deformation occurs, was assessed for the hard brittle materials. Limits of ductile mode indentation for hard brittle materials were discussed in detail. Variation in the depth of structures in an imprinted mark was studied.

Machinability Study of Cemented Carbide Using Focused Ion Beam (FIB) Milling

Focused ion beam (FIB) milling is one of the fastest and accurate processes for the micro- and nanofabrication of devices. There is a need of making micro- and nanoscale components from cemented carbide material due to its favorable properties of high hot hardness and wear resistance. These are the required properties of a microtool during micromachining. Efforts have been put forward to investigate the machinability aspects of cemented carbide by the FIB milling process. Beam current was observed as the significant process parameters of FIB milling process to affect the material removal rate (MRR) and surface roughness on the machined surface of cemented carbide. In addition, extraction voltage, angle of beam incidence, and percentage overlap between beam diameters of adjacent pixels were taken into account to analyze the machinability aspects of cemented carbide by FIB milling. Dwell time was observed as a less significant parameter to affect MRR and surface roughness of cemented carbide.

Influence of Y2O3 particles on mechanical properties of magnesium and magnesium alloy (AZ91D)

Nowadays, research studies and industrial requirements are directed toward the goals of achieving environmental friendliness, energy savings, and reduced weight. Magnesium and magnesium alloys are well suited for structural and automotive applications owing to their lightweight. However, the reduced hardness and strength of these alloys do pose problems in exploiting their usage. These impediments of lightweight metal matrix can be alleviated by reinforcing hard-phase particles. Different volume percentages of Y2O3 particles (average grain size 5 µm) were added as reinforcements in pure magnesium and magnesium alloy (AZ91D) and the composites were processed through the two-step stir-casting technique. Mechanical and metallurgical characterization studies were carried out on the stir-cast composites under as-cast and heat-treated conditions. Uniform distribution of yttria particles in magnesium and magnesium alloy matrix was observed through scanning electron micrographs. Macro and microhardness tests revealed the increased hardness with the increased amount of yttria reinforcement.

Influence of Cutting Force on Bimetallic Piston Machining by a Cubic Boron Nitride (CBN) Tool

Bimetallic pistons are most widely used in diesel engine vehicles for weight reduction and enhanced performance with long life. Aluminum alloy is reinforced with cast iron insert to realize the bimetallic pistons. The bonding between aluminum and cast iron is achieved through a patented process named the Al-Fin process. To ensure better bonding, the insert is dipped in the molten aluminum bath, this dipping time playing a vital role. The present study focuses on varying the dipping time from 90 s to 5 min to find the optimum dipping time. Achieving the near net shape of the bimetallic pistons without damaging the bonding between the aluminum and cast iron is the major challenge. This investigation also obtains optimal cutting parameters in turning off such pistons with cubic boron nitride as a single tool to machine the metal. The bond integrity after machining is primarily related to the magnitude of the cutting forces. Taguchi design of experiment analysis was conducted on the inserts which are subjected to various dipping time. The optimal cutting parameters for minimized cutting forces were identified. The extent of deboning and the surface finish were measured after machining to ensure the minimum cutting force condition to satisfy the requirements.

Grinding of magnesium /Y2O3 metal matrix composites

The advanced metal matrix composites are finding high technology applications in aerospace and automotive industries because of their light weight coupled with high specific strength. Although advances have been made in near-net-shape technology, a finishing operation is needed to achieve the required dimensional tolerance and good surface finish. Magnesium especially experiences problems during grinding owing to its ductility and fire hazardous nature. Though grinding is not preferred for a pure magnesium matrix composite, owing to their increased hardness necessitate grinding, an attempt was made to perform grinding on the magnesium yttria composites with commercially available alumina and silicon carbide wheels. Grinding of magnesium composite was carried out by varying process parameters, such as wheel peripheral speed, workpiece velocity, and depth of cut. During the process the forces were monitored by a piezoelectric dynamometer. The performance of the grinding was studied by analyzing and comparing the grinding forces, specific grinding energy, and the average surface roughness. The ground surface was analyzed using optical and scanning electron microscopy. The grinding forces were observed to be decreasing with the increase in hardness, which in turn resulted in smooth surfaces. The obtained surface roughness (Ra) values were in the range of 0.6–1.3 µm.

Optimizing the weld bead characteristics of super austenitic stainless steel (904L) through grey‐based Taguchi method

Purpose – The purpose of this paper is to optimize the gas metal arc welding (GMAW) process input parameters simultaneously considering the multiple output variables (bead width (BW), bead height (BH) and depth of penetration (DP)).Design/methodology/approach – Grey‐based Taguchi approach was used for designing the experiment, L27 orthogonal array was used which composed of three levels and 27 rows, which means that 27 experiments were carried out. Design of experiments was selected based on a four welding parameters with three levels each. The selected welding parameters for this paper are gas flow rate, voltage, travel speed and wire feed rate. The bead‐on‐plate welding trials are carried out on AISI 904L super austenitic stainless steel (SASS) sheets and evaluate the shape of the fusion zone depends upon a number of input parameters.Findings – Bead‐on‐plate welding of 904L SASS sheet is successfully performed (without any cracks and discontinuity) by GMAW process and the bead profiles are measured. The...

Multi-objective Optimization of Continuous Drive Friction Welding Process Parameters Using Response Surface Methodology with Intelligent Optimization Algorithm

The optimum friction welding (FW) parameters of duplex stainless steel (DSS) UNS S32205 joint was determined. The experiment was carried out as the central composite array of 30 experiments. The selected input parameters were friction pressure (F), upset pressure (U), speed (S) and burn-off length (B), and responses were hardness and ultimate tensile strength. To achieve the quality of the welded joint, the ultimate tensile strength and hardness were maximized, and response surface methodology (RSM) was applied to create separate regression equations of tensile strength and hardness. Intelligent optimization technique such as genetic algorithm was used to predict the Pareto optimal solutions. Depending upon the application, preferred suitable welding parameters were selected. It was inferred that the changing hardness and tensile strength of the friction welded joint influenced the upset pressure, friction pressure and speed of rotation.

Experimental investigation on machining of filament wound GFRP pipe by cemented carbide (K20) cutting tool

Near nett shaped GFRP pipes, with the required surface finish can be obtained by machining. Experiments were conducted through the established Taguchis orthogonal array and design of experiments. This work is an attempt to investigate the performance of K20 grade cemented carbide tools on machining of filament wound GFRP pipes. Effect of machining parameters on tool wear is studied. Also, the influence of cutting forces and their effects are studied. The machined surface exhibited a better surface finish of two to four microns whereas the surface roughness of unmachined surface varies from 60 to 80 microns. The machining parameters are also optimised through simple regression and cross product regression methods.