Effects of shock loading and cold rolling on the structure and high temperature creep properties of γ' strengthened Ni-18.6 pct Cr-4.3 pct Al
Abstract
The effects of shock loading and cold rolling on the structure and high temperature creep properties of precipitation strengthened Ni-18.6 pct Cr-4.3 pct Al have been investigated. The creep properties of this alloy depend on whether the testing is conducted in forming gas (90 pct N2 + 10 pct H2) or in vacuum. It is found that cold rolling invariably increases the creep rate and decreases the creep life when testing is conducted in forming gas. This unexpected result is believed to be caused by strain concentrations at grain boundaries which are associated with cold rolling and which contribute to creep by promoting premature intergranular fracture. In order to minimize the effects of intergranular fracture and to determine the intrinsic effects of prestraining it is necessary to conduct creep tests in vacuum. Taking this precaution, we find that the creep strength of this alloy can be enhanced only slightly by cold rolling a few percent. Cold rolling by a greater amount or shock loading to about 70 kbar (6.99 × 109 Pa) results in higher creep rates than the asaged condition. It is shown that these unexpected weakening effects can be correlated with, and are probably caused by, the presence of misshaped γ' precipitate particles. The irregular shapes of these precipitates are believed to be caused by the line tension effects of surrounding dislocations.
- Publication:
-
Metallurgical Transactions
- Pub Date:
- January 1974
- DOI:
- 10.1007/BF02642944
- Bibcode:
- 1974MT......5..205H