Department of Metallurgical & Materials Engineering

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Flow properties of aluminum and aluminum-boron carbide (Al-B4C) composites, containing 5, 10 and 15wt% B4C, were investigated by compression tests at strain rates of 10-4, 10-3 and 10-2 s-1 over the temperature range 25 to 500. The nature of stress-strain curves as a function of reinforcement, temperature and strain rate revealed that (1) flow stress initially increases as the reinforcement increases, but it decreases for Al-15% B4C composite, (2) flow stress increases with the increase in strain rate, with the strain rate sensitivity index varying from 0.01 for aluminum at 200 to 0.30 for Al-5% B4C composite. The activation energy for deformation is found to vary from 124 to 187kJ/mol for Al-15% B4C and Al-5% B4C composites, respectively. © The Author(s) 2013 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

World University root node

Journal of Composite Materials

Effects of temperature and strain rate on compressive flow behavior of aluminum-boron carbide composites

Caliber rolling process, useful for mass production of high precision and high strength material, was employed to process Mg-3Al-1Zn (AZ31) alloy at 250, 300, 350, 400 and 450 °C. The effects of caliber rolling temperature on the microstructure and tensile properties at room temperature were investigated at a strain rate of 1 × 10-4 s-1. The nature of stress-strain curves obtained was found to vary with the temperature employed in caliber rolling. Grain size is refined from 33 μm in mill-rolled condition to 3.6 μm upon caliber rolling at 300 °C. This condition results in ultimate tensile strength of 290 MPa and total elongation of 22% in comparison to 188 MPa and 18% respectively for mill-rolled condition. © (2014) Trans Tech Publications, Switzerland.

Solid State Phenomena

Effect of high temperature caliber rolling on microstructure and room temperature tensile properties of Mg-3Al-1Zn (AZ31) alloy

Stainless steels such as ferrritic, austenitic, martensitic and duplex stainless steels are well known for their corrosion resistance to varying extents. Among these, austenitic stainless steels exhibit superior corrosion resistance and better ductility. Therefore, the ability to give simple to intricate shapes in this grade of steel brings their potential for a wide range of applications. However, the austenitic stainless steel e.g. AISI 304 is known to undergo a strain induced martensitic (SIM) transformation during conventional cold rolling at room temperature. This strain induced martensite causes reduction in ductility and limits formability of stainless steel. Therefore, wavy rolling technique was developed to strengthen the stainless steel through microstructural refinement. In the current study, wavy rolling with 1.5 mm amplitude was conducted on 1 mm thick stainless steel sheet to different cycles ranging from 1-4. These rolled samples were characterized by optical and atomic force microscopy (AFM) for high resolution features in the material. This AFM examination bring out the details of grain refinement and topographical roughness emerging from crystalline and microstructural properties like orientation by color contrast after etching, precipitation, deformation bands, slip lines and shear bands with progress in rolling as referred by the number of rolling cycles here. The structural development is semi-quantitatively related to the degree of deformation and its effect on tensile properties during wavy rolling cycle. © (2013) Trans Tech Publications, Switzerland.

Advanced Materials Research

AFM characterization of structural evolution and roughness of AISI 304 austenitic stainless steel under severe deformation by wavy rolling

Mg-3Al-1Zn (AZ31) alloy was caliber rolled isothermally in the temperature range of 250-450 °C to develop fine grains of 3.6-12.5 μm. The stress-strain curves obtained from tensile tests at room temperature were found to vary with the temperature employed in caliber rolling. Maximum tensile strength of 290 MPa and ductility of 13.5% were obtained upon caliber rolling at 300 °C as compared to 188 MPa and 15.2%, respectively, in the mill-rolled condition. The variations in tensile properties are explained by the concomitant grain size, texture and twins obtained as a function of caliber rolling temperature. © 2013 National Engineering Research Center for Magnesium Alloys of China, Chongqing University.

Fulltext

Journal of Magnesium and Alloys

Effects of caliber rolling on microstructure and room temperature tensile properties of Mg-3Al-1Zn alloy

Co vacancy (VCo) induced robust room temperature ferromagnetism (Ms ∼ 60 emu/cm3 and coercivity ∼ 603 Oe) is experimentally realized in rock-salt CoO epitaxial thin film (∼110 nm) grown by pulsed laser deposition. Co charge state is found to be higher ∼+3.2 (from Co L3/L2 white line ratio) and this is due to the V Co induced charge transfer from the neighboring Co-3d to O-2p states in order to compensate for the hole formation. O-K and cathodoluminescence spectra corroborate the existence of VCo and higher charge state. Temperature dependent magnetization and exchange bias experiments confirm the coexistence of ferromagnetic and antiferromagnetic phases. © 2013 AIP Publishing LLC.

Applied Physics Letters

Robust room temperature ferromagnetism in epitaxial CoO thin film

The hot working behaviour of Ti-modified 15Cr-15Ni-2Mo austenitic stainless steel (Alloy D9) was studied by hot compression test at temperatures of 900-1200 °C and at strain rates of 0.002-1 s-1. The progress of dynamic recrystallization (DRX) was modelled by the Avarmi kinetics equation. The flow softening was directly related to the DRX volume fraction and the DRX time was determined by strain rate. For quantification of recrystallization rate, the time corresponding to the DRX fraction of 50% was used. Analysis of the sigmoid-shaped recrystallization curves revealed that the rate of DRX increases with increasing deformation temperature and strain rate. Results of the Avrami analysis were used to predict the DRX flow curves. © 2012 Elsevier B.V. All rights reserved.

Journal of Nuclear Materials

Kinetics of dynamic recrystallization in Ti-modified 15Cr-15Ni-2Mo austenitic stainless steel

Blending of elemental powders is a common powder metallurgical processing route to produce titanium alloys designed to meet the required properties. An alternative to blending is coating the base titanium powders with specific metal ions by an electroless route to maximise advantages associated with homogeneous coating. In this work, Ni-P is being used as the coating material, to coat hydrogenated/dehydrogenated titanium powders. The particle size distribution of uncoated and coated powders was used to explain the change in tap density. A diametrical compression test was carried out to evaluate green strength of the particles when consolidated before and after coating. © W. S. Maney & Son Ltd. 2013.

Materials Research Innovations

Effect of plating on consolidation of commercially pure titanium powders

A metal-ceramic bonding process was developed to produce vacuum tight alumina-Inconel 600 joints using an Ag-based active metal brazing alloy that can withstand continuous operating temperature up to 560 °C. The microstructure and microchemistry of the braze zone was examined using extensive microanalysis of the constituent phases and a mechanism for the interfacial reactions responsible for the bonding is proposed. Prolonged heat treatment at 400 and 560 °C under simulated in-service conditions revealed that the microstructure of braze zone of the joints was stable and maintained leak-tightness and strength. The bond strength of the interface was high enough to cause failure in the alumina side of the joints. Failure of the joints was caused by initiation of crack on the surface of alumina as a result of high tensile residual stress adjacent to the metal-ceramic interface. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Acta Materialia

Microstructural evolution during reactive brazing of alumina to Inconel 600 using Ag-based alloy

Fine grains were developed in Mg-3Al-1Zn (AZ31) alloy by isothermal Caliber Rolling (CR) at five different temperatures in the range of 250-450°C. The samples of different grain sizes were deformed by constant strain rate (CSR) and differential strain rate (DSR) test techniques over the temperature range of 220-450 °C and strain rate range of 10-5 to 10-1 s-1. The effects of grain size, test temperature and strain rate on flow stress were analysed to develop the constitutive relationship for superplastic deformation. © (2013) Trans Tech Publications, Switzerland.

Materials Science Forum

Effect of severe caliber rolling on superplastic properties of Mg-3Al-1Zn (AZ31) alloy

Oxygen Free High Conductivity (OFHC) copper was subjected to severe plastic deformation using Repetitive Upsetting-Extrusion (RUE) process at room temperature. Numerical simulation up to 10 cycles of RUE was carried out to estimate the strain distribution across the cross-section of the RUE processed samples. The strain obtained from the finite element analysis (FEA) was correlated with the microstructure and microhardness obtained by carrying out RUE experiments up to 10 cycles. The microhardness of the material initially increases sharply with strain, reaches a peak and thereafter decreases rapidly to finally attain a steady state. The decrease in hardness after a peak is attributed to the decrease in the output of Frank-Reed sources as discussed in the modified ETMB or Kinetic model. © 2013 Elsevier B.V.