Effect of mechanical alloying and consolidation process on microstructure and hardness of nanostructured Fe–Cr–Al ODS alloys

Nanostructured ferritic oxide dispersion strengthened (ODS) alloys are promising materials for both high temperature creep properties and irradiation resistance. These alloys were produced by mechanical alloying (MA) which is a complex process and a number of process variables need to be controlled to achieve the desired properties. In this study, the effect of mechanical alloying and consolidation processes on the microstructure and properties of nanostructured ferritic ODS alloy were investigated. The powder mixtures were milled in Spex mill for different milling times (1 h, 3 h, 8 h, and 15 h). The effect of process control agents (PCAs) and ball to power ratio (BPR) were studied. Two-stage sintering and canning-HIP processes were introduced as new consolidation methods to produce ODS alloys with improved mechanical properties. The results showed that crystallite size during milling decrease with milling time and higher BRP has a significant influence on the rate of decrease of the crystallite size. The use of stearic acid as PCA led to fine, uniform and spherical particles during the ball milling. Additionally, the samples sintered at the elevated temperatures over long periods resulted in a reduction in porosity; however, the microstructure became coarser, accompanied by a decrease in the hardness. The canning-HIP technique can effectively minimize the content of oxygen and carbon impurities to achieve high relative density and high hardness.

► The particle size progressively decreases with increase in milling time.
► The use of stearic acid can was found to achieve fine uniform spherical powders.
► High BPR has a significant influence on the rate of decrease of crystallite size.
► High-temperature sintering leads to relative density increase and grain growth.
► Canning-HIP technique has a significant improvement in mechanical properties.