Corrosion Performance Of Alloys Research Articles

Effect of Gd addition on microstructure and corrosion behaviors of Mg–Zn–Y alloy

Abstract The Mg97-xZn1Y2Gdx alloys were prepared by as-casting method. Corrosion performance of alloys was evaluated by using potentiodynamic polarization, hydrogen evolution rate and mass loss measurements in 3% sodium chloride solution at room temperature. The results shown that the atomic rate of the long period stacking ordered (LPSO) with the composition of Mg12Zn1Y1. The microstructure of LPSO phases was lamellar structure. When the atomic fraction of Zn is 1% and the atomic ratio of Zn/RE (Y, Gd) is 2:5, the volume fraction of LPSO phase can reach the extreme value. The corrosion resistance of Mg–Zn–Y alloy improves with the increase of the volume fraction of LSPO phase. The Mg96.5Zn1Y2Gd0.5 (MG0.5) alloy had better corrosion resistance than those of other alloys. It meant that 0.5 at. % gadolinium (Gd) was a suitable addition to Mg97Zn2Y alloy about corrosion resistance.

Effects of molybdenum content on the wear/erosion and corrosion performance of low-carbon Stellite alloys

Abstract The strengthening agents of Stellite alloys are commonly various carbides, but intermetallic compounds may play a similar role to the carbides. In this research two low-carbon Stellite alloys with high molybdenum content are developed and studied, which are modified version of Stellite 21. This particular elemental content combination results in large amounts of Co3Mo intermetallic compound precipitated in these alloys. The microstructures of the alloys are analyzed using SEM/EDX/XRD and DSC. The dry sliding wear resistance and solid-particle erosion resistance of the alloys are evaluated experimentally. The corrosion performance of the alloys in 3.5 wt.% sodium chloride (NaCl) aqueous solution is investigated under electrochemical tests. It is shown that the intermetallic compounds enhance hardness and wear resistance as the carbides do in Stellite alloys, but do not favor solid-particle erosion resistance due to their brittleness. The presence of the intermetallic compounds does not worsen corrosion resistance, compared to Stellite 21.

The Long-Term Corrosion Performance of Alloy 22 in Heated Brine Solutions

Long-term corrosion experiments have been performed on Alloy 22 (UNS N06022), in a series of heated brines formulated to represent evaporatively concentrated ground water, to evaluate the long-term corrosion performance of the material. These solutions included 0.5 M NaCl, in addition to two simulated concentrated ground water solutions. Under conditions where Alloy 22 was anticipated to be passive, the corrosion rate was found to be vanishingly small (i.e., below the resolution of the weight-loss technique used to quantify corrosion in this study). However, under low pH conditions where Alloy 22 was anticipated to be active, or more specifically, where the chromium oxide passive film was not thermodynamically stable, the corrosion rate was appreciable. Furthermore, under such conditions the corrosion rate was observed to be a strong function of temperature, with an activation energy of 72.9±1.8 kJ/mol. Time of Flight-Secondary Ion Mass Spectroscopy analysis of the oxide layer revealed that, while sulfur was present within the oxide for all test conditions, no accumulation was observed at or near the metal/oxide interface. These observations confirm that inhibition of passive film formation via sulfur accumulation does not occur during the corrosion of Alloy 22.

Corrosion performance of alumina scales in coal gasification environments

Corrosion of metallic structural materials in complex gas environments of coal gasification is a potential problem. The corrosion process is dictated by concentrations of two key constituents: sulfur as H2S and Cl as HC1. This paper examines the corrosion performance of alumina scales that are thermally grown on Fe-base alloys during exposure to O/S mixed-gas environments. The results are compared with the performance of chromia-forming alloys in similar environments. The paper also discusses the available information on corrosion performance of alloys whose surfaces were enriched with Al by the pack-diffusion process, by the electrospark deposition process, or by weld overlay techniques.

Alloy corrosion in a coal gasification system

The corrosion performance of alloys in coal gasification systems is of increasing industrial interest as more advanced coal-fired power generating systems are developed. It is necessary to consider the performance of candidate materials under likely exposure conditions to ensure that components have adequate lifetimes. Materials performance can influence the economic feasibility of these systems. This paper reports the high temperature corrosion performance of a range of materials exposed in British Coal's air-blown, spouted fluidised bed coal gasification pilot plant. The exposures were carried out in the hot gas path of this plant for periods of up to 660 hours, in three distinct temperature ranges between 330 and 920 ° C (i.e. ranges representative of possible evaporator, superheater and ductwork conditions). By characterising the gasifier product gas using carefully selected elements and compounds, activity windows have been defined for sulphur and oxygen for this environment in the required temperature ranges. Standard metallurgical analyses were carried out on exposed alloys to determine their performance in the required temperature ranges. It was found that MA956 performed best in the higher temperature ranges, whilst alloys containing 22-28% chromium performed better in the lower temperature ranges.