Mechanical and Microstructural Analysis on the High Temperature Deformation of Gamma TiAl Alloy PDF Download
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Languages : en
Pages : 0
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Book Description
It is aimed in this study to investigate the high temperature deformation mechanisms of two-phase gamma titanium-aluminum alloy in view of the inelastic deformation theory and to quantify the relative contribution of each mechanism to the overall deformation. The influence of y/a2 volume fraction on high temperature deformation behavior and the preferable cavity initiation sites have also been studied. For this purpose, a series of load relaxation tests and tensile tests have been conducted at temperatures ranging from 800 to l050 deg C. In the early stage of the deformation, (as in the load relaxation test) flow curves of the fine-grained titanium-aluminum alloy are well fitted with the combined curves of grain matrix deformation and dislocation climb. The evidence of grain boundary sliding has not been observed. However, when the amount of deformation is large (exceeding 80%), flow curves change its shape indicating that other deformation mechanism operate at this stage. It is identified as grain boundary sliding resulted from dynamic recrystallization. The activation energy values for grain matrix deformation and dislocation climb have been obtained from constitutive parameters analysis. Calculated values for QGMD and Qdisl. climb are 3l9kJ/mol, and 386 kJ/mol, respectively Qdisl.climb is found to be similar to that for self-diffusion of Aluminum in titanium-aluminum or in Ti3Al. With the increase in the volume fraction of a sub 2-phase, the flow stress for grain matrix deformation increase because a sub 2-phase is considered as hard phase which acts as barrier for dislocation movement. The fact that the frequency of cavity initiation at a sub 2 phase is 8 times as high as that of a sub 2/y supports the above interpretation.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
It is aimed in this study to investigate the high temperature deformation mechanisms of two-phase gamma titanium-aluminum alloy in view of the inelastic deformation theory and to quantify the relative contribution of each mechanism to the overall deformation. The influence of y/a2 volume fraction on high temperature deformation behavior and the preferable cavity initiation sites have also been studied. For this purpose, a series of load relaxation tests and tensile tests have been conducted at temperatures ranging from 800 to l050 deg C. In the early stage of the deformation, (as in the load relaxation test) flow curves of the fine-grained titanium-aluminum alloy are well fitted with the combined curves of grain matrix deformation and dislocation climb. The evidence of grain boundary sliding has not been observed. However, when the amount of deformation is large (exceeding 80%), flow curves change its shape indicating that other deformation mechanism operate at this stage. It is identified as grain boundary sliding resulted from dynamic recrystallization. The activation energy values for grain matrix deformation and dislocation climb have been obtained from constitutive parameters analysis. Calculated values for QGMD and Qdisl. climb are 3l9kJ/mol, and 386 kJ/mol, respectively Qdisl.climb is found to be similar to that for self-diffusion of Aluminum in titanium-aluminum or in Ti3Al. With the increase in the volume fraction of a sub 2-phase, the flow stress for grain matrix deformation increase because a sub 2-phase is considered as hard phase which acts as barrier for dislocation movement. The fact that the frequency of cavity initiation at a sub 2 phase is 8 times as high as that of a sub 2/y supports the above interpretation.
Author: Karthikeyan Subramanian
Publisher:
ISBN:
Category : Aluminum alloys
Languages : en
Pages :
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Book Description
Abstract: Despite the large body of work done in the area of high-temperature creep, the present understanding of creep mechanisms and the effect of alloying and microstructure is limited. The first part of this investigation concentrates on the creep behavior in the equiaxed microstructure of gamma-TiAl alloys, to understand the mechanisms and develop a physically-based model for creep in the gamma phase. A modification of the classic jogged-screw model has been previously adopted to explain observations of 1/2[110]-type jogged-screw dislocations in equiaxed Ti-48Al under creep conditions. The goal of this study is to verify and validate the parameters and functional dependencies that have been assumed in that model. The original solution has been reformulated with the aid of analytical modeling, numerical simulations and Transmission Electron Microscopy. Both experiment and theory lead to an excellent prediction of creep rates and stress exponents. In the second part of this study creep behavior of the fully lamellar TiAl alloys is investigated. Dislocation structures similar to those observed in the equiaxed alloys suggests that the jogged-screw model can be adapted for lamellar alloys. The aim of the model is to predict the unique creep phenomenology of fully lamellar alloys. The strengths and shortcomings of the model are discussed. Probable low stress creep mechanisms are also suggested. The origin of fully lamellar alloys' superior creep properties stems from the constrained nature of deformation in the lamellae. The results from stress drop experiments are analysed to explore the origin of the large back stresses associated with the fully lamellar alloys. Reduction of the lamellar spacing is proposed as the best way to lower creep rates. In the final part of this study, the microstructural stability of lamellar alloys during exposure to creep conditions is investigated. A detailed investigation of the creep behavior of the aged (stabilized) and unaged (unstabilized) alloys was carried out and subsequent TEM studies were done to characterize the microstructural changes during creep. Continued loss of metastable alpha-2 is proposed as the reason for the larger strain rates in all stages of creep for the alloy in the unaged condition. Dynamic recrystallization and the formation of equiaxed gamma grains are discussed. These results suggest that microstructural stability is critically important in order to achieve the highest possible creep strengths. The effect of microalloying and the role of precipitation hardening in creep are investigated. The probable mechanisms of primary, secondary and tertiary creep are discussed and methods for improving the creep properties are suggested.
Author: Fritz Appel
Publisher: John Wiley & Sons
ISBN: 352731525X
Category : Technology & Engineering
Languages : en
Pages : 763
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Book Description
The first book entirely dedicated to the topic emphasizes the relation between basic research and actual processing technologies. As such, it covers complex microstructures down to the nanometer scale, structure/property relationships and potential applications in key industries. From the contents: * Constitution * Thermophysical Constants * Phase Transformations and Microstructures * Deformation Behaviour * Strengthening Mechanisms * Creep * Fracture Behaviour * Fatigue * Oxidation Resistance and Related Issues * Alloy Design * Ingot Production and Component Casting * Powder Metallurgy * Wrought Processing * Joining * Surface Hardening * Applications and Component Assessment
Author: Young-Won Kim
Publisher: John Wiley & Sons
ISBN: 1119017165
Category : Technology & Engineering
Languages : en
Pages : 468
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Book Description
This book is a collection of papers presented at the 4th International Symposium on Gamma TiAl Alloys (ISGTA 2014) that was held in conjunction with the 2014 Annual Meeting of The Minerals, Metals & Materials Society. Papers discuss and assess advances in application and implementation experience in current alloys, fundamental aspects in current gamma alloy materials technology, new processes development and assessment, and emerging new alloys, their potentials and limitations, and breakthroughs. Papers that originated in the panel discussion of the symposium are intended to help the scientific community realize the limitations of current alloys materials and processes and discuss possible solutions. Six topic areas selected for this purpose included: Wrought-processed alloys: status, dilemmas and pathways to future Cast alloys for aero engine applications: status, issues, and barriers to advances Cast alloys for turbocharger wheels: status and barriers to widespread applications Emerging new alloys: justification, potentials, status, and future Novel processes: justification, potential vs. realization issues, and future Future applications and realistic pathways to them
Author: Young-Won Kim
Publisher: Minerals, Metals, & Materials Society
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 1036
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Book Description
This two-volume publication is a comprehensive update of the fundamental and practical issues confronting the research, development and application of gamma titanium aluminides.
Author: Vasisht Venkatesh
Publisher: John Wiley & Sons
ISBN: 1119296099
Category : Technology & Engineering
Languages : en
Pages : 2004
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Book Description
This book contains the Proceedings of the 13th World Conference on Titanium.
Author: Roberto Montanari
Publisher: MDPI
ISBN: 3036510125
Category : Science
Languages : en
Pages : 146
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Book Description
This collection covers the physical and chemical phenomena of metal surfaces, including surface modifications and treatments. It is targeted at researchers working in materials science and also at newcomers to the research field of metal surfaces and surface analysis.
Author: Srikumar Banerjee
Publisher: Elsevier
ISBN: 0080548792
Category : Technology & Engineering
Languages : en
Pages : 837
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Book Description
The terms phase transitions and phase transformations are often used in an interchangeable manner in the metallurgical literature. In Phase Transformations, transformations driven by pressure changes, radiation and deformation and those occurring in nanoscale multilayers are brought to the fore. Order-disorder transformations, many of which constitute very good examples of continuous transformations, are dealt with in a comprehensive manner. Almost all types of phase transformations and reactions that are commonly encountered in inorganic materials are covered and the underlying thermodynamic, kinetic and crystallographic aspects elucidated. - Shows readers the advancements in the field - due to enhanced computing power and superior experimental capability - Drawing upon the background and the research experience of the authors, bringing together a wealth of experience - Written essentially from a physical metallurgists view point
Author: Christoph Leyens
Publisher: John Wiley & Sons
ISBN: 3527605207
Category : Technology & Engineering
Languages : de
Pages : 532
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Book Description
This handbook is an excellent reference for materials scientists and engineers needing to gain more knowledge about these engineering materials. Following introductory chapters on the fundamental materials properties of titanium, readers will find comprehensive descriptions of the development, processing and properties of modern titanium alloys. There then follows detailed discussion of the applications of titanium and its alloys in aerospace, medicine, energy and automotive technology.
Author: Sonia Luisa dos Santos Simoes
Publisher: CRC Press
ISBN: 1351647415
Category : Science
Languages : en
Pages : 248
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Book Description
The book covers the development of new technologies for the joining of TiAl alloys that result in sound bonds obtained in less demanding conditions. It discusses joint processing, microstructural and mechanical characterization, and summarizes developments in new approaches to the joining of TiAl alloys using advanced characterization techniques.
