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Home  >  Journal list  >  MATERIALS TRANSACTIONS  >  Vol.54  No.2 (2013)  >  pp.169-175

MATERIALS TRANSACTIONS
<<Previous article Vol.54  No.2 (2013)   pp.169 - 175 Next article>>

Tensile and Fatigue Properties of Carbon-Solute-Strengthened (α+β)-Type Titanium Alloy

Masaaki Nakai1), Mitsuo Niinomi1), Junko Hieda1), Ken Cho1), Toshikazu Akahori2), Kazuhiro Hayashi3), Yoshio Itsumi4), Shogo Murakami5), Hideto Oyama4)
1) Institute for Materials Research, Tohoku University 2) Faculty of Science and Technology, Meijo University 3) Graduate School of Engineering, Tohoku University 4) Titanium Research and Development Section, Kobe Steel, Ltd. 5) Materials Research Laboratory, Kobe Steel, Ltd.

The effects of interstitial carbon solute and titanium carbide on the tensile and fatigue properties of an (α+β)-type titanium alloy, Ti–4.5Al–2.5Cr–1.2Fe–0.1C (KS Ti-531C), with bimodal and Widmanstätten α structures were investigated. In order to control the microstructures, this alloy was subjected to annealing at temperatures just below and just above the β-transus (531C-α+β annealed and 531C-β annealed, respectively). The microstructure of 531C-α+β annealed shows a bimodal structure and any titanium carbide is not observed, whereas that of 531C-β annealed shows a Widmanstätten α structure and some titanium carbides, which are considered to be Ti2C, are observed. The tensile strength and elongation of 531C-α+β annealed and 531C-β annealed are similar, but 0.2% proof stress is higher and further the reduction of area is much larger for 531C-α+β annealed than 531C-β annealed. Their tensile properties depend mainly on the type of microstructure and interstitial element partitioning because the titanium carbide is not observed on the fractured surfaces of both the alloys after tensile tests. Also, the fatigue properties of 531C-α+β annealed are better than those of 531C-β annealed. The titanium carbide is observed on the fractured surface of 531C-β annealed, but not observed on that of 531C-α+β annealed, after fatigue tests. Therefore, titanium carbide is considered to cause deterioration in the fatigue properties of 531C-β annealed compared to those of 531C-α+β annealed.


Keyword:
(α+β)-type titanium alloy, bimodal structure, Widmanstätten α structure, tensile properties, fatigue properties

Received: May 14, 2012
Accepted: September 07, 2012 , Published online: January 25, 2013
Copyright © 2013 The Japan Institute of Metals

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