Effects of alloy and solution chemistry on the fracture of anodic films formed at metastable pitting potentials

Abstract

The Taguchi analysis method along with a nanoindentation technique were used to study the effects of alloy chemistry, pH and halide ion concentrations on the mechanical fracture of electrochemically grown passive films formed at a metastable pitting potential. Three austenitic stainless steels, 304L, 316L and 904L, were potentiostatically polarised in hydrochloric acid solutions. The load at film fracture during nanoindentation was primarily dominated by both alloy chemistry and the salt concentration. Passive films mechanically weakened as the ratio of iron to the total metallic atoms increased in the film; an estimate of the applied tensile stress that caused fracture increased from 0 . 8 GPa to 1 . 18 GPa as the alloy was changed from 304L to 904L. Increasing the salt concentration present during film growth from 0 . 01M to 0 . 2M reduced the applied stress for fracture by a factor of two. Prolonged anodic aging times at 40uC decreased the fracture load of these passive films.

Pitting corrosion transformation of SUS304 stainless steel in lithium bromide solution at high temperature

“…The Taguchi method was chosen to investigate the effects of multiple variables on the corrosion of austenitic stainless steels at higher temperature. This method provides the ability to study the effect of multiple variables simultaneously, to investigate the influence of individual factors on the corrosion, and to determine which factor has the most significant influence 24. The matrix in this study consists of three controllable factors and each factor has four levels.…”

Development of experimental verification techniques for non-linear deformation and fracture on the nanometer scale.

“…[37,38] . In summary, an EG&G 173 and 175 potentiostat and controller were used to grow the passive films .…”

“…In our previous studies [37,38], ex-situ nanoindentation tests were made to investigate the influences of alloy and solution chemistries on the load required to fracture the passive film formed on austenitic stainless steel alloys at anodic potentials where the passive film is stable and metastable . For the passive film formed at a stable passive potential, the substrate on which the film was grown was the most significant factor affecting the load at fracture .…”

“…The loads at fracture for the film tested in-situ and ex-situ [37,38] were used to roughly compute and compare the tensile stress applied needed to fracture the passive film using Hertzian contact mechanics.…”