The effect of aging on the fracture behavior of Cu-AI-Ni jo phase alloys
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I.
Table I.
INTRODUCTION
CU-A1-Ni/3 phase alloys are potentially very attractive because of their shape memory effect, ~ll The shape memory effect has been observed in alloys with aluminum content close to 14 wt. pct and with a varying nickel content. Figure 1, after Alexander, I21shows a relevant portion of the Cu-A1-Ni ternary phase diagram sectioned at 14 wt. pct A1. The phases which appear in the/3 phase region are described in Table I. Unfortunately, the application of these
Phases o~
/3 /3, 3/2 Martensite NiAI
1200
Description Primary solid solution of A1 and Ni in Cu, fcc structure High temperature disordered phase based on Cu3A1, bcc structurepl Low temperature ordered phase based on Cu3A1, DO3 structureI41 Complex cubic structureth} Ordered phase with orthorhombic structuret61 Ordered bcc structuret7]
alloys is seriously limited because of their poor impact strength associated with intergranular fracture. It is observed that the intergranular embrittlement increases with increasing nickel content. I8] Alloys with 10 wt. pct Ni are so brittle that they sustain intergranular cracking on quenching in cold water from the homogenization temperature. A detailed study has been carried out to investigate the causes of the intergranular embrittlement in these alloys and to find remedial measures. [9] This paper reports the beneficial effects of aging on the fracture behavior of Cu-14 wt. pct All0 wt. pct Ni. This composition was selected because it was found that the samples of this alloy were extremely brittle, showing 100 pct intergranular fracture.
1100
1000
I l l 900 rr" ~-< 800 n~ L~ EL
i,t 700 I--
II. /
600
/
~1* NiAI ~162
f
a*Y~ 500
Phases Present in the/] Phase Region
/
ca* ~*NiAI
/
0
5
10 15 NICKEL (wt 7.)
2.0
Fig. 1--Cu-AI-Ni phase diagram, section taken at 14 wt pct A1, after Alexander. t21 (Note: Alexander used the symbol 8 instead of ~/2 used in
Metals Handbook. [5])
S.W. I-IUSAIN, formerly with The University of Connecticut, Storrs, CT 06268, is with Dr. A.Q. Khan Research Labs, G.P.O. Box 502, Rawalpindi, Pakistan. P.C. CLAPP is Professor, Department of Metallurgy and Institute of Materials Science, The University of Connecticut, Storrs, CT 062689 Manuscript submitted March 14, 1986. METALLURGICALTRANSACTIONS A
EXPERIMENTAL PROCEDURES
The samples were melted in an induction furnace using copper (99.99 pct), aluminum (99.999 pct), and nickel (99.99 + pct). The melting was carried out in an argon gas atmosphere and the metal was poured into a copper mold. After homogenization for 4 hours at 950 ~ samples were cut to sizes of 5 • 5 • 20 mm, heated at 950 ~ for 45 minutes, and quenched in boiling water. Boiling water was used since quenching in cold water always resulted in quench cracks. Nondestructive techniques such as X-radiography, ultrasonic, and eddy current testing were employed to make sure that the specimens quenched in boiling water did not have any cracks. This was further confirmed by the fracture behavior. When the notched samples were broken by impact, the sa
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