Effect of Cu and Li Contents on the Serrated Flow Behavior of Al-Cu-Li Based Alloys
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e Portevin-Le Chatelier (PLC) effect, which occurs in the form of serrations in the stress–strain curve, is commonly observed in aluminum alloys during plastic deformation at low strain rates and over a range of temperatures.[1] Over the years, the PLC effect has been analyzed extensively and is attributed to several intrinsic (solutes, precipitates) and extrinsic (temperature, strain rate) factors.[2,3] Several modeling attempts (mostly
NIRAJ NAYAN is with the Vikram Sarabhai Space Centre, Indian Space Research Organization, Trivandrum, 695 022, India and also with the Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai, 400 076, India. A.K. MUKHOPADHYAY and RAJDEEP SARKAR are with the Defence Metallurgical Research Laboratory, Hyderabad, 500 058, India. S.V.S. NARAYANA MURTY is with the Vikram Sarabhai Space Centre, Indian Space Research Organization. Contact e-mail: [email protected] MANASIJ YADAVA is with the Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur, 208 016, India. M.J.N.V. PRASAD and I. SAMAJDAR are with the Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay. Manuscript submitted July 13, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
phenomenological and a few theoretical) have been made in the past to understand the basis of plastic instability in Al alloys.[4] In most of these models, the PLC effect is attributed to dynamic strain aging (DSA), where dislocations are temporarily pinned by the mobile solute elements while they are arrested at localized obstacles such as forest dislocations.[5] This mechanism is generally believed to be responsible for the negative strain rate sensitivity that is manifested as serrations in the stress–strain curves.[6] The second generation of Al-Li alloys with Li percentages > 2 wt pct had lower density than conventional aerospace alloys but suffered from problems such as strength anisotropy, lower short transverse toughness and ductility. The third generation of Al-Li alloys was designed to overcome the shortcomings of the second generation of Al-Li alloys. In the third generation of AlLi alloys, the lithium percentages ranged from 0.75 to 1.8 wt pct. The second and third generations of Al-Li alloys have been reported to show serration behavior in stress–strain curves. The micromechanisms responsible for these serrations were attributed to dislocation solute interaction and/or shearing of the coherent d¢ (metastable Al3Li) precipitates. In these alloys, the roles of major alloying elements and coherent phases were not discussed. Because the third-generation Al-Li alloys contain both types of compositions, i.e., with and without d¢ precipitates, it is very important to study the serration behavior of selected binary and ternary AlLi alloys under the condition of different strain rates. In view of this, a systematic study of the constituent binary and ternary alloys contained in third-generation Al-Li alloys needs
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