Development of processing map and constitutive relationship for thermomechanical processing of Aluminum Alloy AA201

Isothermal hot compression tests were performed on aluminum alloy 2014 (AA2014) to study the evolution of microstructure over a wide range of temperatures (300°C–500°C) and strain rates (0.001–100 s−1). The true stress–true strain curves obtained at all deformation temperatures and strain rates showed gradual flow softening, which is typical of a dynamic recovery-type material such as aluminum. Processing maps that delineate the stable and unstable regions during hot working were developed and validated by comparing the microstructures recorded in the deformed specimens. Optimum processing conditions (temperature > 450°C, strain rate < 0.1 s−1) for the hot deformation of AA2014 were proposed based on contour maps of efficiency of power dissipation and strain-rate sensitivity parameter. The activation energy value (Qavg) for the hot working of AA2014 was calculated to be 181 kJ/mol−1. Finally, the constitutive equation for the hot working of AA2014 was established.by S. V. S. Narayana Murty, Aditya Sarkar and P. Ramesh Narayana

A failure mechanism based failure theory for laminated composites including the effect of shear stress

In this paper, a new failure theory for laminated composite based on initiating failure mechanism is presented. Unlike the existing failure theories, the present theory is based on biaxial state of normal stresses with and without shear stress. The approach is based on micromechanical analysis of composites, wherein a representative volume consists of a fiber surrounded by matrix in appropriate volume fraction and modelled using 3-D finite elements to predict the strengths. In this paper, different failure envelopes are developed by varying shear stress say from 0% of shear strength to 50% of shear strength in steps of 25% of shear strength. Results obtained from this approach are compared with Tsai-Wu and maximum stress failure theories. The results show that the predicted strengths match more closely with maximum stress theory. Hence, it can be concluded that influence of shear stress on the failure of the lamina is of little consequence as far as the prediction of strengths in laminates

Cryogenic Mechanical Properties of Warm Multi-Pass Caliber-Rolled Fine-Grained Titanium Alloys: Ti-6Al-4V (Normal and ELI Grades) and VT14

The effect of microstructural refinement and the beta phase fraction, V (beta), on the mechanical properties at cryogenic temperatures (up to 20 K) of two commercially important aerospace titanium alloys: Ti-6Al-4V (normal as well as extra low interstitial grades) and VT14 was examined. Multi-pass caliber rolling in the temperature range of 973 K to 1223 K (700 A degrees C to 950 A degrees C) was employed to refine the microstructure, as V (beta) was found to increase nonlinearly with the rolling temperature. Detailed microstructural characterization of the alloys after caliber rolling was carried out using optical microscopy (OM), scanning electron microscopy (SEM), electron back-scatter diffraction (EBSD), and transmission electron microscopy (TEM). Complete spheroidization of the primary alpha laths along with formation of bimodal microstructure occurred when the alloys are rolled at temperatures above 1123 K (850 A degrees C). For rolling temperatures less than 1123 K (850 A degrees C), complete fragmentation of the beta phase with limited spheroidization of alpha laths was observed. The microstructural refinement due to caliber rolling was found to significantly enhance the strength with no penalty on ductility both at room and cryogenic temperatures. This was attributed to a complex interplay between microstructural refinement and reduced transformed beta phase fraction. TEM suggests that the serrated stress-strain responses observed in the post-yield deformation regime of specimens tested at 20 K were due to the activation of tensile twins. (C) The Minerals, Metals & Materials Society and ASM International 201

Development of processing maps and constitutive relationship for thermomechanical processing of Aluminum Alloy AA2219

Isothermal uniaxial compression tests were conducted on aluminum alloy AA2219 to study the evolution of microstructure over a wide range of temperatures (300-500 °C) and strain rates (0.001-100 s−1) with a view to study the flow behavior and concurrent microstructural evolution. True stress-true strain curves showed only a gradual flow softening at all temperatures except at 300 °C where strain hardening was followed by severe flow softening. Processing map delineating the stable ‘safe’ and unstable ‘unsafe’ regions during hot working is developed and validated by comparing the microstructures observed in the deformed compression specimens. Optimum processing parameters (temperature 450 °C and strain rate 0.001 s−1) for hot deformation of AA2219 were proposed based on contour maps of efficiency of power dissipation and strain rate sensitivity parameter. The activation energy value (Qavg) of AA2219 for hot working was computed to be 169 kJ/mol. Finally, a constitutive equation for hot working of AA2219 was established as: ε˙=4.99×109⋅exp(0.06149σ)⋅exp(−168.958/RT)ε˙=4.99×109⋅exp⁡(0.06149σ)⋅exp⁡(−168.958/RT).by S. V. S. Narayana Murty, Aditya Sarkar, P. Ramesh Narayanan, P. V. Venkitakrishnan and Jyoti Mukhopadhya

Microstructure-texture-mechanical properties relationship in multi-pass warm rolled Ti-6Al-4V Alloy

In the present study, high strength bulk ultrafine-grained titanium alloy Ti-6Al-4V bars were successfully processed using multi-pass warm rolling. Ti-6Al-4V bars of 12 mm diameter and several metres long were processed by multi-pass warm rolling at 650 degrees C, 700 degrees C and 750 degrees C. The highest achieved mechanical properties for Ti-6Al-4V in as rolled condition were yield strength 1191 MPa, ultimate tensile strength of 1299 MPa having an elongation of 10% when the rolling temperature was 650 degrees C. The concurrent evolution of microstructure and texture has been studied using optical microscopy, electron back scattered diffraction and x-ray diffraction. The significant improvement in mechanical properties has been attributed to the ultrafine-grained microstructure as well as the morphology of alpha and beta phases in the warm rolled specimens. The warm rolling of Ti-6Al-4V leads to formation of < 10 (1) over bar0 >alpha//RD fibre texture. This study shows that multi-pass warm rolling has potential to eliminate the costly and time consuming heat treatment steps for small diameter bar products, as the solution treated and aged (STA) properties are achievable in the as rolled condition itself. (C) 2013 Elsevier B.V. All rights reserved