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Fast densification and deformation of titanium powder
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
2005 (English)In: Powder Metallurgy, ISSN 0032-5899, Vol. 48, no 3, 231-236 p.Article in journal (Refereed) Published
Abstract [en]

 A coarse titanium powder containing 0.2 wt-% oxygen with an average particle size of 45 micrometers was rapidly densified using the spark plasma sintering (SPS) technique. The fully consolidated specimens were also deformed in compression in the SPS unit and in a conventional hot pressing (HP) furnace. The densification and deformation behaviours were investigated by microstructural observation and examining the shrinkage and shrinkage rate recorded in real time. The efforts were focused on clarifying to what extent the possible spark discharging and intensive Joule heating at the particle contact points contribute to the densification, and what effect if any the pulsed electrical heating has on the densification. The results showed that what contributed to the densification were neither spark discharging nor anisotropic heating, but the particle deformation. Deformation occurs throughout the entire particle both in SPS and HP conditions, with a higher strain rate under SPS condition especially in the a phase region.

Place, publisher, year, edition, pages
Maney Publishing , 2005. Vol. 48, no 3, 231-236 p.
Keyword [en]
Spark Plasma Sintering, Electrical Field, Densification, Deformation, Titanium
National Category
Environmental Sciences
Identifiers
URN: urn:nbn:se:su:diva-26119DOI: 10.1179/174329005X71939OAI: oai:DiVA.org:su-26119DiVA: diva2:202496
Available from: 2009-03-10 Created: 2009-03-10 Last updated: 2010-04-27Bibliographically approved
In thesis
1. Spark plasma sintering and deformation behaviour of Titanium and Titanium/TiB2Spark plasma sintering and deformation behaviour of Titanium and Titanium/TiB2 composites
Open this publication in new window or tab >>Spark plasma sintering and deformation behaviour of Titanium and Titanium/TiB2Spark plasma sintering and deformation behaviour of Titanium and Titanium/TiB2 composites
2007 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Titanium has been used as a model substance to study how it behaves in a SPS apparatus when heating rate and/or pressure were varied during the sintering and deformation process. The sintering and deformation of Ti in SPS were compared with that occurring in the conventional hot pressing (HP) in order to reveal if there are any positive effects added by the use of SPS. The ductility of Ti was explored in order to understand the sintering and deformation of (Ti) x (TiB2)1-x composites with x = 0.05, 0.1, and 0.2, respectively, expressed in mol ratio. The temperature difference (DT) between the monitored and the temperature that the samples are exposed to was evaluated.

It was noticed that Ti can be sintered at relatively low temperatures. High heating rate implied that the onset temperatures of the sintering and deformation processes decreased. Increasing pressure did not affect the onset temperature but revealed that the deformation of Ti is different if the experiments are conducted within the stability region of the a -phase region of Ti or if the deformation takes place in a temperature region that covers both a-and b-phase areas, i. e. the use of high pressures implied a one step deformation process while the use of low implied that the main part of the deformation took place in the b-phase region.

(Ti) x (TiB2)1-x composites were prepared to full densities at 1500 °C using a holding time of 3 min and pressure of 50 MPa. During the SPS sintering the composite with x= 0.2 revealed the presence of TiB due to the reaction Ti + TiB 2 -> 2TiB while the composites with low x values did not show any formation of TiB. The formation of TiB impaired the mechanical properties. The deformation of composites was very difficult. Their deformability increased with increasing x and temperature as well as pressure. During the deformations of pre-sintered samples TiB was formed in all of the composites.

Publisher
33 p.
Research subject
Materials Science
Identifiers
urn:nbn:se:su:diva-26122 (URN)
Presentation
(English)
Opponent
Supervisors
Available from: 2010-01-20 Created: 2009-03-10 Last updated: 2010-04-27Bibliographically approved
2. Spark Plasma Sintering Enhancing Grain Sliding, Deformation and Grain Size Control: Studies of the Systems Ti, Ti/TiB2, Na0.5 K0.5 NbO3, and Hydroxyapatite
Open this publication in new window or tab >>Spark Plasma Sintering Enhancing Grain Sliding, Deformation and Grain Size Control: Studies of the Systems Ti, Ti/TiB2, Na0.5 K0.5 NbO3, and Hydroxyapatite
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The unique features of the Spark plasma sintering (SPS) were used to investigate the sintering and deformation behaviour of titanium and titanium–titanium diboride composites, and to control the sintering and grain growth of ferroelectric Na0.5K0.5NbO3 (NKN) and of hydroxyapatite (HAp). In the SPS the samples experience a temperature different from that recorded by the thermocouple (pyrometer) used and this temperature difference has been estimated for Ti and NKN.

 

Sintering and deformation of titanium was investigated. Increasing heating rate and/or pressure shifted the sintering to lower temperatures, and the sintering and deformation rates changed when the α→β phase transition temperature was passed. Fully dense Ti/TiB2 composites were prepared. The Ti/TiB2 composites could be deformed at high temperatures, but the hardness decreased due to the formation of TiB. 

 

The kinetic windows within which it is possible to obtain fully dense NKN and HAp ceramics and simultaneously avoid grain growth are defined. Materials have a threshold temperature above which rapid and abnormal grain growth takes place. The abnormal grain growth of NKN is due to a small shift in the stoichiometry, which in turn impairs the ferroelectric properties. Fully transparent HAp nanoceramics was prepared, and between 900 and 1050 oC elongated grains are formed, while above 1050 oC abnormal grain growth takes place.NKN samples containing grains of the sizes 0.35–0.6 µm yielded optimum ferroelectric properties, i.e. a high remanent polarization (Pr = 30 µC/cm2) and high piezoelectric constant (d33= 160 pC/N). The ferroelectric domain structure was studied, and all grains exhibited a multi-domain type of structure.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry, Stockholm University, 2010. 81 p.
Keyword
Spark plasma sintering, plastic deformation, grain growth, titanium, TiB2, hydroxyapatite, Na0.5K0.5NbO3, ferroelectric, transparent
National Category
Materials Chemistry
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-38681 (URN)978-91-7447-072-7 (ISBN)
Public defence
2010-05-25, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of doctoral defense the following articles were unpublished and had a status as follows: Article 4: Manuscript; Article 5 : Manuscript Available from: 2010-05-04 Created: 2010-04-26 Last updated: 2010-04-27Bibliographically approved

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