Cu addition to the base alloy reduces the total amount of deleterious phases such as chromium nitride and sigma and chi phases. In particular, Cu addition to the base alloy results in pronounced suppression of the amount of sigma phase whereas it slightly facilitates the precipitation of chromium nitride and chi phase along the phase boundaries and within ferrite grains. During the initial stage of aging, the preferential precipitation of chromium nitride and chi phase seems to be closely associated with the retardation of the precipitation of the sigma phase. The preferential precipitation of chromium nitride and the chi phase inhibits the nucleation and growth of the sigma phase by depleting the Cr adjacent to the chromium nitride particles and depleting the Mo and W adjacent to the chi phase. Thus, the addition of Cu to the base alloy reduces its embrittlement owing to the delayed precipitation of these deleterious phases.

The effects of Cu addition on the microstructure and localized corrosion of hyper duplex stainless steels aged at 748 K were investigated using TEM analysis and electrochemical test. The addition of Cu to the base alloy facilitated the precipitation of a Cr-enriched ¡A-phase due to an increase in the Cr activity, thereby reducing the localized corrosion resistance. The localized corrosion was initiated at the Cr-depleted regions around the Cr-enriched ¡A-phase.

The effect of Zr addition on the corrosion behavior of an extruded Mg-10Gd-1Zn alloy (GZ101) in 3.5 mass% NaCl solution was investigated by electrochemical and immersion tests in 3.5% NaCl solution. The addition of 1 mass% Zr to GZ101 (to afford GZ101-1Zr) decreased the fraction of 14H (number of stacking layers and H-Hexahedral structure) and lamellar long period stacking ordered (LPSO) phases across the α-Mg matrix and increased the fraction of the X-phase (Mg 12 GdZn) formed at grain boundaries. Extruded GZ101-1Zr exhibited a signi cantly smaller corrosion rate than extruded GZ101 (0.13 vs. 2.11 mm year −1 ) due to containing less 14H/lamellar LPSO phases (detrimental to corrosion resistance) and featuring a noble {1010} prismatic texture in the extrusion direction. [

Influence of annealing temperature on the microstructure and resistance to pitting corrosion of the hyper duplex stainless steel was investigated in acid and neutral chloride environments. The pitting corrosion resistance is strongly dependent on the microstructure, especially the presence of chromium nitrides (Cr 2 N), elemental partitioning behavior and volume fraction of ferrite phase and austenite phase. Precipitation of deleterious chromium nitrides reduces the resistance to pitting corrosion due to the formation of Cr-depleted zone. The difference of PREN (Pitting Resistance Equivalent Number) values between the ferrite and austenite phases was the smallest when solution heat-treated at 1060 o C. Based on the results of electrochemical tests and critical crevice temperature tests, the optimal annealing temperature is determined as 1060 o C.