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You searched for subject:(Near Ti Alloy). Showing records 1 – 2 of 2 total matches.

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Indian Institute of Science

1. Kantibhai, Agrawal Priyanka. Dynamic Strain Aging and Creep in nearTi Alloy, IMI834.

Degree: PhD, Engineering, 2018, Indian Institute of Science

IMI 834 is a near- Ti alloy used in high temperature applications such as compressor discs and blades of aero engines. Titanium alloys including IMI 834 are known to exhibit dynamic strain aging (DSA) over the temperature range of 623-773K. However, the interplay between DSA and creep has not been previously studied in detail in titanium alloys. The objective of the present study is to probe creep mechanisms and phenomenology at intermediate temperatures in IMI 834 where DSA is expected to play a prominent role. Coupons of IMI834, cut from a hot rolled rod, were heat treated to obtain a microstructure of 80% equated , 15% of lamellar and 5% . The heat treatment was optimized to ensure Si retention in the solution as it is known to affect DSA in titanium alloys. Constant strain rate tests carried out in tension over a range of temperatures and strain rates identified the DSA regime in the temperature range of 623-823K as determined by serrated behavior in stress-strain curves and negative strain rate sensitivity. The dislocation structure in this domain is dominated by jogged screw dislocations in slip bands. Strain accumulation is shown to depend on conservative jog glide along the length of screw dislocations due to line tension forces. We have tried to predict this domain of DSA using Friedel’s model for breakaway stress, i.e. the stress required to break free the dislocations from solute atmosphere, using estimates of solute concentration accumulating at the edge jogs on arrest during thermally activated glide of the jogs at static solute obstacles. There is a good agreement between model and experimental data showing a DSA peak in the temperature range of 673-723K. The solute species responsible for DSA is estimated to be Si and C, but dominated by C in this temperature and strain rate regime. Creep behavior of the alloy was explored over similar temperature regime in tension. Over this temperature range, especially at lower temperatures, very low strain rates below the resolution limits of the strain gauge were reached before the onset of steady state and therefore current work is primarily focused on primary creep behavior. Different types of primary creep behavior were observed with temperature and stress. Anomalous primary creep behavior has been observed in the form of an abrupt decrease in strain rate beyond certain critical strains, as well as in a stress insensitivity of instantaneous strain rates on loading at 673K. At higher temperatures of 773K, conventional behavior showed strain rates approaching a steady state value. Dislocation structure in primary creep was again dominated by jogged screw dislocations. At the strain rates associated with creep, our model shows that transitions occur in jog glide from solute breakaway controlled glide to solute drag controlled glide and then again to thermally activated glide over static solutes with increasing temperature. However, in contrast to high strain rate behavior, Si solutes dominates the mechanisms of jog glide in creep. The work of this thesis… Advisors/Committee Members: Banerjee, Dipankar (advisor).

Subjects/Keywords: Dynamic Strain Aging (DSA); IMI 834; Steady State Creep Models; α-Titanium; Creep; Near-α Ti Alloy; Friedel’s Model; Titanium Alloys; Portevin-Le Chatelier (PLC) Effect; Materials Engineering

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Kantibhai, A. P. (2018). Dynamic Strain Aging and Creep in near-α Ti Alloy, IMI834. (Doctoral Dissertation). Indian Institute of Science. Retrieved from http://etd.iisc.ac.in/handle/2005/4036

Chicago Manual of Style (16th Edition):

Kantibhai, Agrawal Priyanka. “Dynamic Strain Aging and Creep in near-α Ti Alloy, IMI834.” 2018. Doctoral Dissertation, Indian Institute of Science. Accessed January 23, 2021. http://etd.iisc.ac.in/handle/2005/4036.

MLA Handbook (7th Edition):

Kantibhai, Agrawal Priyanka. “Dynamic Strain Aging and Creep in near-α Ti Alloy, IMI834.” 2018. Web. 23 Jan 2021.

Vancouver:

Kantibhai AP. Dynamic Strain Aging and Creep in near-α Ti Alloy, IMI834. [Internet] [Doctoral dissertation]. Indian Institute of Science; 2018. [cited 2021 Jan 23]. Available from: http://etd.iisc.ac.in/handle/2005/4036.

Council of Science Editors:

Kantibhai AP. Dynamic Strain Aging and Creep in near-α Ti Alloy, IMI834. [Doctoral Dissertation]. Indian Institute of Science; 2018. Available from: http://etd.iisc.ac.in/handle/2005/4036


Virginia Tech

2. Kelly, Shawn Michael. Thermal and Microstructure Modeling of Metal Deposition Processes with Application to Ti-6Al-4V.

Degree: PhD, Materials Science and Engineering, 2004, Virginia Tech

Laser metal deposition (LMD) offers a unique combination of process flexibility, time savings, and reduced cost in producing titanium alloy components. The current challenge in processing titanium alloys using LMD methods is understanding the complex microstructure evolution as a part is fabricated layer by layer. The current work focuses on the characterization, thermal, and microstructural modeling of multilayered Ti-6Al-4V deposits. A thermal model has been developed using finite difference techniques to predict the thermal history of LMD processes. A microstructure model that predicts the alpha phase fraction and morphology evolution was constructed to quantify the effect of thermal cycling on the as-deposited microstructure evolution. Alpha dissolution and growth are modeled assuming one-dimensional plate dissolution according to a parabolic rate law, and a Johnson-Mehl-Avrami-Kolmorgorov (JMAK) nucleation and growth model, respectively. Alpha morphology (colony-alpha and basketweave-alpha) evolution is tracked using a simplistic approach. Characterization of the deposit has shown that a complex microstructure evolves consisting of a two distinct regions: a transient region of undeveloped microstructure and a characteristic layer that is periodically repeated throughout the deposit. The transient region contains a fine basketweave and colony-alpha morphology. The characteristic layer contains a two phase mixture of alpha+beta, with the alpha phase exhibits regions of colony-alpha (layer band) and basketweave-alpha morphology. The different regions of microstructural contrast in the deposit are associated with thermal cycling. The thermal model results show that a heat affected zone defined by the beta transus extends approximately 3 layers into the deposit. The phase fraction model predicts the greatest variation in microstructural evolution to occur in a layer n after the deposition of layer n+3. The results of the morphology model show that increased amounts of colony-alpha form near the top of a characteristic layer. It follows that a layer band (colony-alpha region) forms as a result of heating a region of material to a peak temperature just below the beta transus, where a large amount of primary-alpha dissolves. Upon cooling, colony-alpha forms intragranularly. The coupled thermal and microstructure models offer a way to quantitatively map microstructure during LMD processing of Ti-6Al-4V. Advisors/Committee Members: Kampe, Stephen L. (committeechair), Reynolds, William T. Jr. (committee member), Aning, Alexander O. (committee member), David, Stan A. (committee member), Christodoulou, Leonitus (committee member), Babu, Sudarsanam Suresh (committeecochair).

Subjects/Keywords: microstructure model; heat treatment; ti-6al-4v; metal deposition; titanium alloy; additive manufacturing; near net shape; thermal model; rapid prototyping

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Kelly, S. M. (2004). Thermal and Microstructure Modeling of Metal Deposition Processes with Application to Ti-6Al-4V. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/29731

Chicago Manual of Style (16th Edition):

Kelly, Shawn Michael. “Thermal and Microstructure Modeling of Metal Deposition Processes with Application to Ti-6Al-4V.” 2004. Doctoral Dissertation, Virginia Tech. Accessed January 23, 2021. http://hdl.handle.net/10919/29731.

MLA Handbook (7th Edition):

Kelly, Shawn Michael. “Thermal and Microstructure Modeling of Metal Deposition Processes with Application to Ti-6Al-4V.” 2004. Web. 23 Jan 2021.

Vancouver:

Kelly SM. Thermal and Microstructure Modeling of Metal Deposition Processes with Application to Ti-6Al-4V. [Internet] [Doctoral dissertation]. Virginia Tech; 2004. [cited 2021 Jan 23]. Available from: http://hdl.handle.net/10919/29731.

Council of Science Editors:

Kelly SM. Thermal and Microstructure Modeling of Metal Deposition Processes with Application to Ti-6Al-4V. [Doctoral Dissertation]. Virginia Tech; 2004. Available from: http://hdl.handle.net/10919/29731

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