Review—(Mn,Co)3O4-Based Spinels for SOFC Interconnect Coating Application

With the reduction of solid oxide fuel cell (SOFC) operating temperature to the range of 600 − 800℃, Cr-containing ferritic alloys have become the preferred interconnect material, which unfortunately are susceptible to continuous scale growth and Cr volatility at the SOFC operating temperatures. The (Mn,Co)3O4 spinel system is widely regarded as the most effective coating for SOFC interconnect protection, due to its high thermal and electrical conductivity, adequate coefficient of thermal expansion, and excellent Cr blocking capability. This article reviews the physical and chemical properties of the (Mn,Co)3O4-based spinels; different types of coating precursors and deposition techniques; and the effects of spinel composition, quality and thickness on the coating performance. It is concluded that the spinel coating composition, quality, and thickness are more critical than the coating process in affecting the overall coating performance.

A study on mechanical properties of ferritic alloy by physical testing for nuclear power fusion reactors

The ferrite plays an important role in key component materials for nuclear power plant. The study was performed on ferritic alloys with various Cr content ranging from 10 to 38wt%. The Vickers-hardness and mechanical test results indicate that the high Cr content will cause a hardening and strengthening effect on the ferrite steel. Meanwhile, it can be concluded that the ferritic alloy suffers a reduction of toughness and a failure mode transition from ductile to brittle fracture with the increasing Cr content from the SEM fractography analysis.

The Corrosion Propagation Stage of Stainless-Steel Reinforced Concrete: A Review

Stainless steel (SS) reinforcement is increasingly used to control corrosion of reinforced concrete in aggressive marine and deicing salt service. It is well established that the chloride threshold of SS is greater than that of plain steel (PS) rebar, yielding substantially increased duration of the corrosion initiation stage. Much less known, however, is if there is a similar benefit to the duration of the corrosion propagation stage (tp). Thus, credit for increased tp in durability forecasts for SS use tends to be conservatively limited. To reduce that uncertainty the literature was gleaned for the few instances where SS reinforcement had reached, and preferably completed, the corrosion propagation stage. Particular attention was given to actual structural service experience, outdoor tests, and realistic laboratory conditions. Only a single case of actual service in a structure was found for which tp could be estimated, albeit indirectly. The result suggests a tp of several decades for the case of austenitic Cr-Ni rebar in marine service. Outdoor tests without unnatural acceleration showed a few cases where tp was reached, but only for straight Cr ferritic alloys which showed some limited improvement over tp for PS. With the additional insight from laboratory tests, it was concluded that SS rebar made with high pitting resistant grades, and thoroughly descaled, had a positive outlook for propagation stage durations that substantially exceed those of PS rebar. Quantification of that improvement is much in need of further field and laboratory assessment.

Effect of Different Precipitation Routes of Fe2Hf Laves Phase on the Creep Rate of 9Cr-Based Ferritic Alloys

We performed creep tests for three types of Fe-9Cr-Hf alloys with a ferritic matrix w/o Fe2Hf Laves phase particles formed by two precipitation routes: (1) with fine Fe2Hf particles formed by the conventional precipitation route (hereafter the particles are called CP particles), namely formed in the α-ferrite matrix after γ-austenite ® α-ferrite phase transformation; (2) with fine Fe2Hf particles formed by interphase precipitation (hereafter called IP particles) during δ-ferrite ® γ-austenite phase transformation before γ ® α phase transformation and (3) without Laves phase particles. CP particles were found to be effective in reducing the creep rates from the transient creep regime to the early stage of a slowly accelerating creep regime but were coarsened after the creep tests. IP particles were less effective in reducing the creep rate in the early creep stages but showed a higher stability against particle coarsening than CP particles in the creep tests, suggesting their effectiveness in delaying the recovery and recrystallization processes in the matrix and thereby retarding the onset of a rapid creep acceleration and creep rupture. The effects of the different precipitation routes are discussed based on the results obtained.