Grain Structure Of Material Research Articles

3D FEM simulation of Al-Zn-Mg-Cu alloy during multi-pass ECAP with varying processing routes

Equal channel angular pressing (ECAP) is one of the efficient metal fabricating processes to produce very fine grain structure in materials. In the present investigation, 3D finite element method has been adopted to understand the deformation response for Al-Zn-Mg-Cu alloy with three different ECAP processing routes, namely, A, BC, and C. The simulation results revealed enormous improvement in effective plastic strain with ECAP passes for all routes; however, route BC has the edge over the other routes. In the current investigation, homogenous deformation is mainly observed across the main deformation zone (MDZ). Even after three passes, BC is found to be consistent in offering higher and relatively uniform plastic strain along with the sample thickness compared to the other routes of the same deformation level. Microstructure analysis revealed a considerable amount of grain refinement (from 74 ± 5 μm to 570 ± 7 nm) after the third ECAP pass following BC route. Also, the microstructure is featured with a high fraction of deformation bands and a high density of dislocations. The hardness, yield strength, and ultimate strength have increased to 94 %, 126 %, 53 %, respectively, compared to the initial annealed condition. The enrichment of mechanical properties can be substantiated by a significant amount of grain refinement and dislocation strengthening.

Suppression of Hopf bifurcation in metal cutting by extrusion machining

Hopf bifurcation is a common phenomenon during the metal cutting process, which results in poor surface finish of the workpiece and inhomogeneous grain structure in materials. Therefore, understanding and controlling Hopf bifurcation in metal cutting are necessary. In this work, the systematic low-speed extrusion machining experiments were conducted to suppress Hopf bifurcation phenomenon. It is found that the suppression of Hopf bifurcation is achieved with the increasing constraint extrusion degree. In order to reveal the mechanism of the suppression of Hopf bifurcation, a new nonlinear dynamic model for extrusion machining is developed where the convection, the diffusion, the extrusion of constraint, the thermal-softening deformation and the fracture-type damage are included. The theoretical predictions are in agreement with the experimental results; therefore, the present theoretical model is effective to characterize the suppression of Hopf bifurcation in metal cutting. Based on the numerical calculation of the theoretical model, the mechanisms underlying in extrusion machining are further revealed: Fracture-type deformation is more important than the thermal-softening-type deformation in low-speed extrusion machining; however, the thermal-softening-type deformation is the primary deformation mode for high-speed extrusion machining.

Spatially resolved acoustic spectroscopy for rapid imaging of material microstructure and grain orientation

Measuring the grain structure of aerospace materials is very important to understand their mechanical properties and in-service performance. Spatially resolved acoustic spectroscopy is an acoustic technique utilizing surface acoustic waves to map the grain structure of a material. When combined with measurements in multiple acoustic propagation directions, the grain orientation can be obtained by fitting the velocity surface to a model. The new instrument presented here can take thousands of acoustic velocity measurements per second. The spatial and velocity resolution can be adjusted by simple modification to the system; this is discussed in detail by comparison of theoretical expectations with experimental data.

Taguchi Method Approach for Recyling Chip Waste from Machining Aluminum (AA6061) Using Hot Press Forging Process

This paper investigates the recycling waste aluminum alloy 6061 from high speed machine (HSM) machine using hot forging process. Hot forging process able to recover the grain structure of material by controlling certain pressure and temperature. The experiments conducted by Taguchi method design. Three factors selected are chip size, operating temperature and operating pressure with three levels for each factor. Both factors for operating temperature and pressure direct control from hot forging machine. The chip sizes are prepared from HSM machine using by three machine parameters, which are constant cutting speed and manipulate three levels for each parameter for feed rate and depth of cut. The final result between reference and experiment specimen shows the close gap in the tensile test. The main effect, signal noise ratio and analysis of variance were employed to investigate the results and the optimum parameters for hot forging process can be established. It can be concluded that the hot forging process able to recycle waste (chip) aluminum compared to the current recycling aluminum process.

Bioactive Grain Refined Magnesium by Friction Stir Processing

Magnesium and its alloys are promising candidates for temporary implant applications due to their combination of mechanical properties, biocompatibility and biodegradation. But higher degradation rate restricts their wider applications. Recently friction stir processing (FSP) has emerged as a promising tool to attain near surface fine grain structure in materials. In the present work commercial purity magnesium was processed by FSP to obtain fine grain structure and the effect of the grain refinement on the bioactivity was investigated. The microstructural observations were carried out at different locations of the processed regions, from an original grain size of 1500μm, grain refinement was achieved to a level of 6.2μm at the nugget zone. Microhardness was measured across the processed regions and improvement was observed at the nugget zone. Contact angle measurements were carried out to estimate the wettability of the material and the measurements indicate increased wettability due to the increased surface energy induced by grain refinement. For studying the bioactivity the FSPed samples were immersed in simulated body fluids (SBF 5X) for different intervals of time. The phases formed on the samples were investigated by X-ray diffraction (XRD) method, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. The phases on the samples after 72hr of immersion were confirmed as magnesium hydroxide, hydroxyapatite and magnesium phosphate by XRD. Controlled degradation due to formation of these phases was observed. FSPed samples have more deposition of Ca/P than non FSP samples which implies better control over the degradation. Hence grain refinement by FSP can be a simple technique to control the degradation of magnesium for temporary implant applications.

Mechanical Properties of Aluminium Wires Produced by Plastic Consolidation of Fine Grained Powders

The paper presents results of mechanical tests and grain structure investigation of aluminium wires obtained by plastic consolidation of aluminium powders produced by atomisation from liquid state. The powders produced by this method could be potentially adopted to obtain ultra fine/nano structured materials by rapid solidification. Conversion of material from powder to bulk state with retaining of powders fine structure and minimizing of porosity are crucial for technological route of sub-micron grained materials production. An influence of condition of plastic consolidation by hot extrusion on mechanical properties of consolidated products is a main target of presented investigation. The standard mechanical properties of extrusion products have been determined and grain structure has been inspected. The results have been compared to extrusion products of conventional bulk aluminium. It has been stated substantial increase of properties and refining of grain structure in materials consolidated from powders.

Multi-stage adaptive noise cancellation for ultrasonic NDE

Adaptive noise cancellation techniques are ideally suited for reducing spatially varying noise due to the grain structure of material in ultrasonic nondestructive evaluation. Since grain noise is generally uncorrelated, in contrast to the correlated flaw echoes, adaptive filtering algorithms exploit the correlation properties of signals in a C-scan image to enhance the signal-to-noise ratio of the output signal. In this paper, a multi-stage adaptive noise cancellation method is proposed for enhancing flaw detection in ultrasonic signals. The overall method is based on the use of an adaptive least mean square error filter with primary and reference signals derived from two adjacent positions of the transducers. Results of implementing the proposed algorithm on ultrasonic signals obtained from hard-α inclusions in titanium will be presented.

Relationships Between Grain Boundary Structure and Material Properties

This brief review seeks to summarize some of the main property changes which may be induced by altering the grain structure of materials. Where appropriate an interpretation is given of these changes in terms of current theories of grain boundary structure, and some examples from current studies are presented at the end of this paper.