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The hierarchy of microstructure parameters affecting the tensile ductility in centrifugally cast and forged Ti-834 alloy during high temperature exposure in air

Pete Davies, R. Pederson, Mark Coleman Orcid Logo, Soran Birosca Orcid Logo

Acta Materialia, Volume: 117, Pages: 51 - 67

Swansea University Authors: Pete Davies, Mark Coleman Orcid Logo, Soran Birosca Orcid Logo

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Abstract

Ductility regression is the main concern in using Ti-834 titanium alloy at temperatures above 500ºC for aerospace applications. The reduction of ductility in titanium alloys at high temperatures is strongly correlated to the exposure time. In the current study the effect of prolonged exposure at 500...

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Published in: Acta Materialia
ISSN: 1359-6454
Published: 2016
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URI: https://cronfa.swan.ac.uk/Record/cronfa29194
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The reduction of ductility in titanium alloys at high temperatures is strongly correlated to the exposure time. In the current study the effect of prolonged exposure at 500oC on the tensile ductility of two differently processed Ti-834 alloys was investigated. In order to simulate actual Ti-834 processing routes, forged and centrifugally cast materials were used. The tensile tests were conducted on various specimens exposed at 500&#xBA;C for 100, 200 and 500 hours to observe microstructure feature changes. Moreover, the effect of microstructure, microtexture, &#x3B1;-case, &#x3B1;2 and silicide precipitate coarsening during high temperature exposure was studied thoroughly. The cast alloy was found to have a minimum ductility and failed at 1.8% strain after exposure at 500oC/500 hour when the &#x3B1;-case layer was retained during testing, whilst, the ductility of the forged alloy was unaffected. The effects of individual microstructural parameters on the ductility regression in Ti-834 alloy were quantified. The results showed that 7.1% strain differences between the cast and forged alloy are related to microstructural variations including; morphology, lath widths, grain size and shape, grain orientations and microtexture. A total of 9.6 % strain loss was observed in centrifugally cast Ti-834 after aging at 500&#xBA;C/500h and quantified as follow; 3.6% due to &#x3B1;-case formation during high temperature exposure, 0.2% due to &#x3B1;2-precipitates coarsening, 4.4% due to further silicide formation and coarsening, 1.4% due to additional microstructure changes during high temperature exposure. Furthermore, silicide coarsening on &#x3B1;/&#x3B2; phase boundaries caused large void formation around the precipitates. A theoretical model supported by experimental observations for silicide precipitation in fully colony and duplex microstructures was established. The element partitioning during exposure caused Al and Ti depletion in the vicinity of the &#x3B2; phase in the lamellae, i.e., &#x3B1;s area. This resulted in lowering the strength of the alloy and facilitated the formation of Ti3(SiZr)2 precipitates. The Al depletion and nano-scale partitioning observed at the &#x3B1;s/&#x3B2; boundaries resulted in easy crack initiation and promoted propagation in the centrifugally cast colony microstructure and reduced the basal slip &#x3C4;crss. 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spelling 2021-01-14T13:27:28.6755688 v2 29194 2016-07-12 The hierarchy of microstructure parameters affecting the tensile ductility in centrifugally cast and forged Ti-834 alloy during high temperature exposure in air 38c85534a35a03aac99b687029078831 Pete Davies Pete Davies true false 73c5735de19c8a70acb41ab788081b67 0000-0002-4628-1077 Mark Coleman Mark Coleman true false 3445603fcc2ff9d27b476a73b223a507 0000-0002-8380-771X Soran Birosca Soran Birosca true false 2016-07-12 FGSEN Ductility regression is the main concern in using Ti-834 titanium alloy at temperatures above 500ºC for aerospace applications. The reduction of ductility in titanium alloys at high temperatures is strongly correlated to the exposure time. In the current study the effect of prolonged exposure at 500oC on the tensile ductility of two differently processed Ti-834 alloys was investigated. In order to simulate actual Ti-834 processing routes, forged and centrifugally cast materials were used. The tensile tests were conducted on various specimens exposed at 500ºC for 100, 200 and 500 hours to observe microstructure feature changes. Moreover, the effect of microstructure, microtexture, α-case, α2 and silicide precipitate coarsening during high temperature exposure was studied thoroughly. The cast alloy was found to have a minimum ductility and failed at 1.8% strain after exposure at 500oC/500 hour when the α-case layer was retained during testing, whilst, the ductility of the forged alloy was unaffected. The effects of individual microstructural parameters on the ductility regression in Ti-834 alloy were quantified. The results showed that 7.1% strain differences between the cast and forged alloy are related to microstructural variations including; morphology, lath widths, grain size and shape, grain orientations and microtexture. A total of 9.6 % strain loss was observed in centrifugally cast Ti-834 after aging at 500ºC/500h and quantified as follow; 3.6% due to α-case formation during high temperature exposure, 0.2% due to α2-precipitates coarsening, 4.4% due to further silicide formation and coarsening, 1.4% due to additional microstructure changes during high temperature exposure. Furthermore, silicide coarsening on α/β phase boundaries caused large void formation around the precipitates. A theoretical model supported by experimental observations for silicide precipitation in fully colony and duplex microstructures was established. The element partitioning during exposure caused Al and Ti depletion in the vicinity of the β phase in the lamellae, i.e., αs area. This resulted in lowering the strength of the alloy and facilitated the formation of Ti3(SiZr)2 precipitates. The Al depletion and nano-scale partitioning observed at the αs/β boundaries resulted in easy crack initiation and promoted propagation in the centrifugally cast colony microstructure and reduced the basal slip τcrss. Furthermore, silicides were not formed in αp (high Al, Ti and low Zr areas) in the forged duplex microstructure that promoted superior mechanical performance and ductility over the cast alloy. Journal Article Acta Materialia 117 51 67 1359-6454 Ti-834 Alloy, Ductility, Microstructure, Silicide, Alpha Case 15 9 2016 2016-09-15 10.1016/j.actamat.2016.07.015 COLLEGE NANME Science and Engineering - Faculty COLLEGE CODE FGSEN Swansea University 2021-01-14T13:27:28.6755688 2016-07-12T13:14:10.9299874 College of Engineering Engineering Pete Davies 1 R. Pederson 2 Mark Coleman 0000-0002-4628-1077 3 Soran Birosca 0000-0002-8380-771X 4 0029194-12072016131607.pdf Acta.pdf 2016-07-12T13:16:07.5870000 Output 2068863 application/pdf Accepted Manuscript true 2017-07-14T00:00:00.0000000 Released under the terms of a Creative Commons Attribution Non-Commercial No Derivatives License (CC-BY-NC-ND). true eng
title The hierarchy of microstructure parameters affecting the tensile ductility in centrifugally cast and forged Ti-834 alloy during high temperature exposure in air
spellingShingle The hierarchy of microstructure parameters affecting the tensile ductility in centrifugally cast and forged Ti-834 alloy during high temperature exposure in air
Pete Davies
Mark Coleman
Soran Birosca
title_short The hierarchy of microstructure parameters affecting the tensile ductility in centrifugally cast and forged Ti-834 alloy during high temperature exposure in air
title_full The hierarchy of microstructure parameters affecting the tensile ductility in centrifugally cast and forged Ti-834 alloy during high temperature exposure in air
title_fullStr The hierarchy of microstructure parameters affecting the tensile ductility in centrifugally cast and forged Ti-834 alloy during high temperature exposure in air
title_full_unstemmed The hierarchy of microstructure parameters affecting the tensile ductility in centrifugally cast and forged Ti-834 alloy during high temperature exposure in air
title_sort The hierarchy of microstructure parameters affecting the tensile ductility in centrifugally cast and forged Ti-834 alloy during high temperature exposure in air
author_id_str_mv 38c85534a35a03aac99b687029078831
73c5735de19c8a70acb41ab788081b67
3445603fcc2ff9d27b476a73b223a507
author_id_fullname_str_mv 38c85534a35a03aac99b687029078831_***_Pete Davies
73c5735de19c8a70acb41ab788081b67_***_Mark Coleman
3445603fcc2ff9d27b476a73b223a507_***_Soran Birosca
author Pete Davies
Mark Coleman
Soran Birosca
author2 Pete Davies
R. Pederson
Mark Coleman
Soran Birosca
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container_title Acta Materialia
container_volume 117
container_start_page 51
publishDate 2016
institution Swansea University
issn 1359-6454
doi_str_mv 10.1016/j.actamat.2016.07.015
college_str College of Engineering
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hierarchy_top_title College of Engineering
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hierarchy_parent_title College of Engineering
department_str Engineering{{{_:::_}}}College of Engineering{{{_:::_}}}Engineering
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description Ductility regression is the main concern in using Ti-834 titanium alloy at temperatures above 500ºC for aerospace applications. The reduction of ductility in titanium alloys at high temperatures is strongly correlated to the exposure time. In the current study the effect of prolonged exposure at 500oC on the tensile ductility of two differently processed Ti-834 alloys was investigated. In order to simulate actual Ti-834 processing routes, forged and centrifugally cast materials were used. The tensile tests were conducted on various specimens exposed at 500ºC for 100, 200 and 500 hours to observe microstructure feature changes. Moreover, the effect of microstructure, microtexture, α-case, α2 and silicide precipitate coarsening during high temperature exposure was studied thoroughly. The cast alloy was found to have a minimum ductility and failed at 1.8% strain after exposure at 500oC/500 hour when the α-case layer was retained during testing, whilst, the ductility of the forged alloy was unaffected. The effects of individual microstructural parameters on the ductility regression in Ti-834 alloy were quantified. The results showed that 7.1% strain differences between the cast and forged alloy are related to microstructural variations including; morphology, lath widths, grain size and shape, grain orientations and microtexture. A total of 9.6 % strain loss was observed in centrifugally cast Ti-834 after aging at 500ºC/500h and quantified as follow; 3.6% due to α-case formation during high temperature exposure, 0.2% due to α2-precipitates coarsening, 4.4% due to further silicide formation and coarsening, 1.4% due to additional microstructure changes during high temperature exposure. Furthermore, silicide coarsening on α/β phase boundaries caused large void formation around the precipitates. A theoretical model supported by experimental observations for silicide precipitation in fully colony and duplex microstructures was established. The element partitioning during exposure caused Al and Ti depletion in the vicinity of the β phase in the lamellae, i.e., αs area. This resulted in lowering the strength of the alloy and facilitated the formation of Ti3(SiZr)2 precipitates. The Al depletion and nano-scale partitioning observed at the αs/β boundaries resulted in easy crack initiation and promoted propagation in the centrifugally cast colony microstructure and reduced the basal slip τcrss. Furthermore, silicides were not formed in αp (high Al, Ti and low Zr areas) in the forged duplex microstructure that promoted superior mechanical performance and ductility over the cast alloy.
published_date 2016-09-15T03:40:47Z
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