Abstract
The stress corrosion susceptibility of the alloy system is determined by means of a constant strain rate test, the degree of susceptibility being assessed from mechanical properties and fractographic examination. The effect of alloy composition, ageing treatment and environment is investigated.
A change in fracture morphology is demonstrated for the cobalt-tin free alloy when tested in high pH solutions (≍ 12) and this is attributed to a strain-generated activepath mechanism.
Additional changes are demonstrated for the cobalt-tin alloy when tested in sea water, the observed features being related via composition, percentage prior cold work and heat treatment time at ageing temperature to its ageing curve. The sensitivity to stress corrosion cracking in this environment is attributed to a pre-existing active path mechanism resulting from precipitation at stacking faults.The mechanical properties recorded from the tests are shown to be similar to those achieved from tensile tests in air which indicates a high threshold stress is necessary to promote stress corrosion.
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