東華大學圖書館 |

Microstructure Heterogeneity in Additive Manufactured Ti-6Al-4V.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Microstructure Heterogeneity in Additive Manufactured Ti-6Al-4V./
作者:	Zhao, Hao.
面頁冊數:	1 online resource (271 pages)
附註:	Source: Dissertations Abstracts International, Volume: 80-05, Section: C.
Contained By:	Dissertations Abstracts International80-05C.
標題:	Materials science. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10755565click for full text (PQDT)
ISBN:	9781073934119

Microstructure Heterogeneity in Additive Manufactured Ti-6Al-4V.
Zhao, Hao.

Microstructure Heterogeneity in Additive Manufactured Ti-6Al-4V. - 1 online resource (271 pages)

Source: Dissertations Abstracts International, Volume: 80-05, Section: C.

Thesis (Ph.D.)--The University of Manchester (United Kingdom), 2017.

Includes bibliographical references

Additive manufacturing (AM) is a novel near-net-shape manufacturing technology which deposited a component layer by layer directly from 3D CAD files. This rapid and complex weld pool process may introduce short and long range microstructure heterogeneities, which can potentially impact on the local mechanical properties of AM components. The present research thus focuses on the quantitatively analysing the microstructural heterogeneity, by the development and application of methods for the SEBM and WAAM Ti-6Al-4V parts.An additive manufacturing microstructure quantification tool, 'AMMQ', has been developed that combines automatic high resolution SEM image mapping with batch image analysis, to enable efficient quantification over large areas at the required resolution. It was found that the microstructural variation could be described by two key parameters, namely: the mean alpha plate spacing and mean β circularity of the retained β phase. The former corresponds to the combined effect of the rate of solid-state phase transformation upon cooling through the β transus in the first sub-Tβ thermal cycles followed by coarsening, whereas the latter attributes to a spheroidisation effect during subsequent re-heating and annealing below the β transus. The microstructure analysis algorithms showed adequate consistency for the possible varying imaging conditions, and for the different AM Ti-6Al-4V microstructure morphologies.In the SEBM specimens, a layer-scale periodicity in β phase circularity was detected, and a systematic drift of 'hot/cold regions was seen in the geometric specimens. Numerical modelling using a Rosenthal's model showed that the varied cooling conditions with respect to layer depth could be responsible for the layer-wise heterogeneity. Moreover, it has been shown that there is a direct linkage between thermal input, microstructure, and porosity density, as lack of fusion defects were detected in regions of low heat input, as inferred from local alpha plate measurements. This heterogeneity can firstly attribute to the SEBM control themes which were not optimised. Secondly, the heat dissipation condition for each geometry could also have affected the accumulated heat received for each volume of a part.In the WAAM specimens, a periodic microstructure pattern was consistently seen in the steady-state regions, where three typical microstructure morphologies were present: fine basketweave, colony alpha, and coarse basketweave. Micro-hardness mapping and in-situ tensile strain analysis were performed to investigate the microstructural influence on mechanical properties. It was found that both the hardness distribution and the tensile strain distribution was a function of the microstructural heterogeneity and that thin bands within each deposited layer with a colony alpha morphology appeared to be the main region of weakness within the deposited microstructures. Otherwise, the local hardness and tensile strength varied inversely to the local mean alpha plate spacing as expected. Finally, two important microstructure evolution mechanisms were proposed: i) alpha plate coarsening by the joining of neighbouring β layer as β phase volume fraction increases as the temperature approaches Tβ; ii) formation of the colony alpha by regrowth from a small fraction of alpha remnants at temperatures very close to Tβ.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2023

Mode of access: World Wide Web

ISBN: 9781073934119Subjects--Topical Terms:

543314
Materials science.
Index Terms--Genre/Form:

542853
Electronic books.

Microstructure Heterogeneity in Additive Manufactured Ti-6Al-4V.
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500 $a Source: Dissertations Abstracts International, Volume: 80-05, Section: C.
500 $a Publisher info.: Dissertation/Thesis.
500 $a Advisor: Prangnell, Philip; Lee, Peter.
502 $a Thesis (Ph.D.)--The University of Manchester (United Kingdom), 2017.
504 $a Includes bibliographical references
520 $a Additive manufacturing (AM) is a novel near-net-shape manufacturing technology which deposited a component layer by layer directly from 3D CAD files. This rapid and complex weld pool process may introduce short and long range microstructure heterogeneities, which can potentially impact on the local mechanical properties of AM components. The present research thus focuses on the quantitatively analysing the microstructural heterogeneity, by the development and application of methods for the SEBM and WAAM Ti-6Al-4V parts.An additive manufacturing microstructure quantification tool, 'AMMQ', has been developed that combines automatic high resolution SEM image mapping with batch image analysis, to enable efficient quantification over large areas at the required resolution. It was found that the microstructural variation could be described by two key parameters, namely: the mean alpha plate spacing and mean β circularity of the retained β phase. The former corresponds to the combined effect of the rate of solid-state phase transformation upon cooling through the β transus in the first sub-Tβ thermal cycles followed by coarsening, whereas the latter attributes to a spheroidisation effect during subsequent re-heating and annealing below the β transus. The microstructure analysis algorithms showed adequate consistency for the possible varying imaging conditions, and for the different AM Ti-6Al-4V microstructure morphologies.In the SEBM specimens, a layer-scale periodicity in β phase circularity was detected, and a systematic drift of 'hot/cold regions was seen in the geometric specimens. Numerical modelling using a Rosenthal's model showed that the varied cooling conditions with respect to layer depth could be responsible for the layer-wise heterogeneity. Moreover, it has been shown that there is a direct linkage between thermal input, microstructure, and porosity density, as lack of fusion defects were detected in regions of low heat input, as inferred from local alpha plate measurements. This heterogeneity can firstly attribute to the SEBM control themes which were not optimised. Secondly, the heat dissipation condition for each geometry could also have affected the accumulated heat received for each volume of a part.In the WAAM specimens, a periodic microstructure pattern was consistently seen in the steady-state regions, where three typical microstructure morphologies were present: fine basketweave, colony alpha, and coarse basketweave. Micro-hardness mapping and in-situ tensile strain analysis were performed to investigate the microstructural influence on mechanical properties. It was found that both the hardness distribution and the tensile strain distribution was a function of the microstructural heterogeneity and that thin bands within each deposited layer with a colony alpha morphology appeared to be the main region of weakness within the deposited microstructures. Otherwise, the local hardness and tensile strength varied inversely to the local mean alpha plate spacing as expected. Finally, two important microstructure evolution mechanisms were proposed: i) alpha plate coarsening by the joining of neighbouring β layer as β phase volume fraction increases as the temperature approaches Tβ; ii) formation of the colony alpha by regrowth from a small fraction of alpha remnants at temperatures very close to Tβ.
533 $a Electronic reproduction. $b Ann Arbor, Mich. : $c ProQuest, $d 2023
538 $a Mode of access: World Wide Web
650 4 $a Materials science. $3 543314
650 4 $a Mechanical properties. $3 3549505
650 4 $a Microstructure. $3 555179
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773 0 $t Dissertations Abstracts International $g 80-05C.
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10755565 $z click for full text (PQDT)