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Constant extension rate tests have been conducted on Type 304 stainless steel base metal specimens and on stainless steel weld metal specimens with ferrite contents of Ferrite Number 1, 3, 6, 11, 16, and 24, at room temperature in deaerated, 1 N HCI. Stress corrosion cracking in wholly austenitic Type 304 base metal occurs transgranularly, while cracking in duplex weld metal occurs either by the combined action of stress assisted ferrite dissolution and stress corrosion cracking (SCC) in the austenite or entirely by stress assisted dissolution of the ferrite. Ferrite content and distribution are important in determining both the stress corrosion susceptibility and crack morphology of duplex weld metals. The most susceptible duplex weld metals are those which exhibit a continuous or nearly continuous vermicular ferrite structure.

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During the manufacturing and the service life of Au-Al wire bonded electronic packages, the ball bonds experience elevated temperatures and hence accelerated interdiffusion reactions that promote the transformation of the Au-Al phases and the growth of creep cavities. In the current study, these service conditions were simulated by thermally exposing Au-Al ball bonds at 175 and 250°C for up to 1000 h. The Au-Al phase transformations and the growth of cavities were characterized by scanning electron microscopy. The volume changes associated with the transformation of the intermetallic phases were theoretically calculated, and the effect of the phase transformations on the growth of cavities was studied. The as-bonded microstructure of a Au-Al ball bond typically consisted of an alloyed zone and a line of discontinuous voids (void line) between the Au bump and the bonded Al metallization. Thermal exposure resulted in the nucleation, growth, and the transformation of the Au-Al phases and the growth of cavities along the void line. Theoretical analysis showed that the phase transformations across and lateral to the ball bond result in significant volumetric shrinkage. The volumetric shrinkage results in tensile stresses and promotes the growth of creep cavities at the void line. Cavity growth is higher at the crack front due to stress concentration, which was initially at the edge of the void line. The crack propagation occurs laterally by the coalescence of sufficiently grown cavities at the void line resulting in the failure of the Au-Al ball bonds.