High-strength binary Ti-Fe bulk alloys with enhanced ductility
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Larissa V. Louzguinab) Research and Development Project, CREST, Japan Science and Technology Agency, Sendai 985-8577, Japan
Akihisa Inoue Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan (Received 4 June 2004; accepted 15 September 2004)
The structure of hypoeutectic, hypereutectic, and eutectic Ti–Fe alloys produced in the shape of arc-melted ingots was found to consist of the ordered Pm-3m TiFe and disordered BCC Im3¯m –Ti solid solution phase. The dimensions of the ingots were about 25–40 mm in diameter and 10–15 mm in height, and their structure was studied by x-ray diffractometry and scanning electron microscopy. The rectangular parallelepiped-shaped samples 2.5 × 2.5 × 5 mm in size cut from the central part of the ingots exhibit a high strength of about 2000 MPa, except for Ti60Fe40, and a certain ductility. The relatively low density of Ti (4.5 Mg/m3) implies high strength/density ratio for the studied alloys. These alloys are characterized by the low cost of the alloying element Fe and, compared to most of the high-strength non-equilibrium materials, do not require additional injection mold casting or rapid solidification procedures.
I. INTRODUCTION
Typical commercial structural Ti-based alloys have an ultimate tensile strength slightly exceeding 1000 MPa and show plastic elongation of 10–15 % to failure.1 However, Ti alloys exhibit capability for further strengthening. For example, rapid solidification or fast cooling using mold casting allow Ti-based bulk glassy alloys to be produced2,3 with high tensile strength, for example 1800 MPa in the case of the Ti50Ni25Cu25 alloy (alloys’ compositions are given in atomic percents).4 Even higher tensile strength of 2200 MPa is obtained for the Ti50Ni20Cu23Sn7 bulk glassy alloy as a result of Sn addition.5 One should also mention relatively high corrosion resistance of Ti and its alloys at room temperature.6 The relatively low density of the main alloying element Ti (4.5 Mg/m3) implies higher strength/density ratio compared to Fe- or Zr-based bulk amorphous alloys. a)
Address all correspondence to this author. e-mail: [email protected] Spelling of the family names. a) Louzguine is official French spelling. English spelling is Luzgin. b) Louzguina is official French spelling. English spelling is Luzgina. DOI: 10.1557/JMR.2004.0462 3600
J. Mater. Res., Vol. 19, No. 12, Dec 2004
However, small critical size of the Ti-based bulk glassy alloys4,7 attained so far and low ductility restrict their applications. Recently, it also has been shown that a 3-mm-diameter cylindrical rod of cast Ti60Cu14Ni12Sn4Nb10 alloy consisting of micron-sized –Ti dendrites exhibits high ultimate compressive strength of 2.4 GPa and 14.5 % plastic strain to failure.8 Nb acts as a body-centered-cubic (bcc) Im3¯m –Ti stabilizer. This phase exhibits better ductility than hexagonal close-packed (hcp) ␣–Ti. The bcc -Zr phase is also known to be useful for ductilization of bulk glassy alloys.9 However, one can notice that all 3-d transition metals, except for Sc, are als
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