• PDF / 2,790,982 Bytes
• 11 Pages / 593.972 x 792 pts Page_size
• 15 Downloads / 240 Views

DOWNLOAD

REPORT

---

TRODUCTION

INTERMETALLIC alloys with multi-phase microstructures,[1,2] e.g., TiAl-[3] and MoSi-[4]-based alloys, are recently receiving increased attention because drawbacks such as low tensile ductility at ambient temperature and insufficient strength at elevated temperature have been overcome by refining the microstructure or making use of high-temperature melting compounds. Ni-based dual two-phase intermetallic alloys have been developed, based on Ni3Al (c ‘: L12) and Ni3V (c ‘‘: D022) pseudo-binary alloy system shown in Figure 1.[5] Both phases are crystallographically similar: the a parameter of the D022 structure is close to that of the L12 structure but the c parameter of the HIKARU KATO, YASUYUKI KANENO, and TAKAYUKI TAKASUGI are with the Department of Materials Science, Osaka Prefecture University, Gakuen-cho 1-1, Naka-ku, Sakai, Osaka 5998531, Japan. Contact e-mail: [email protected] SATOSHI SEMBOSHI is with the Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai, Miyagi 980-8577, Japan. Manuscript submitted July 17, 2019. Article published online February 14, 2020 METALLURGICAL AND MATERIALS TRANSACTIONS A

D022 structure is roughly doubled with a slight extension. Hyper-eutectoid alloy compositions in Figure 1 have been used as the dual two-phase intermetallic alloys. At high temperatures above the eutectoid temperature, 1000 C (1273 K), the alloys exhibit microstructures comprised of primary Ni3Al phase precipitated from A1(c) phase matrix. At low temperatures below the eutectoid temperature, the A1 phase in the channel region is transformed into a lamellar-like microstructure consisting of the Ni3Al and Ni3V phases with a submicron size.[6–8] The dual two-phase intermetallic alloys having crystallographic coherency between the constituent phases are stable at elevated temperatures and accordingly considered to be used as high-temperature structural materials.[9] To enhance the performance of the dual two-phase intermetallic alloys as high-temperature structural materials, the addition of some transition metals has been conducted so far. It was shown that Ti, Nb, and Ta (groups IV and V in a periodic table) enhanced the microstructural stability and acted as effective solid solution strengtheners[10–13] while W, Mo, and Re (groups VI and VII) resulted in the precipitation in the

VOLUME 51A, MAY 2020—2469

Table I.

Nominal Chemical Compositions of the Alloys Used in this Study Chemical Composition Ni

Al V At. Pct

Fe

B Wt Pct

75 73 71 69 75 75 75 75 75 75 73.6 72.2 70.9

9 9 9 9 7 5 3 9 9 9 8.8 8.7 8.5

— 2 4 6 2 4 6 2 4 6 1.9 3.8 5.5

0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005

Alloy Designation Base 2Fe(Ni) 4Fe(Ni) 6Fe(Ni) 2Fe(Al) 4Fe(Al) 6Fe(Al) 2Fe(V) 4Fe(V) 6Fe(V) 2Fe(Ni/Al/V) 4Fe(Ni/Al/V) 6Fe(Ni/Al/V)

Fig. 1—Longitudinal Ni3Al and Ni3V pseudo-binary phase diagram. The hyper-eutectoid compositions have been used for the development of so-called Ni-based dual two-phase intermetallic alloys.

channel region and led to t