Influence of Cr and Y Addition on Microstructure, Mechanical Properties, and Corrosion Resistance of SPSed Fe-Based Allo
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FE-CR based alloys are extensively useful in many applications including nuclear power plants, petrochemical industries, hot acid container, heat exchanger and construction industry[1,2] due to their attractive corrosion, wear and oxidation resistance and appreciable mechanical strength as well as good formability.[3–5] The yield strength and other mechanical properties increase significantly due to the grain size reduction (to ultrafine range) as per the Hall–Petch relationship.[6,7] Bulk metals and alloys with nanocrystalline/ultrafine grains could be produced by various severe plastic deformation (SPD) techniques such as cryorolling, ECAP, ARB, multiaxial forging, and high pressure torsion.[8] But, for immiscible alloy systems, such as Fe-Cr-Y, the SPD techniques cannot be useful to produce homogeneous nanocrystalline solid solutions/alloys. Therefore, non-equilibrium processing routes must be followed to
V.M. SUNTHARAVEL MUTHAIAH and SUHRIT MULA are with the Metallurgical and Materials Engineering Department, Indian Institute of Technology, Roorkee, Roorkee 247667, India. Contact e-mail: [email protected] Manuscript submitted June 10, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
prepare such alloys. Among the non-equilibrium routes, mechanical alloying (MA) followed by consolidation using spark plasma sintering (SPS) seems to be an efficient method in producing such ultrafine grained/nanocrystalline structures.[9,10] Among the other non-equilibrium processes, the MA is preferred due to its effectiveness in preparing highly supersaturated solid solutions easily in large quantities.[10] Although, the SPS technique primarily was developed for producing bulk ceramic materials, recently many researchers have reported that it is possible to produce bulk nanostructured metallic materials such as Cu,[11] Ni,[12] Al[13], and Fe-based alloys through SPS.[14,15] The major challenge in processing such nanostructured material is to obtain fully dense bulk size components retaining its nanocrystalline features. Groza[16] reported to compact nanocrystalline materials by many techniques including hot pressing (HP)/hot isostatic pressing (HIP) and explosive compaction. The compaction of nanocrystalline Fe-Cr alloys is very difficult due to their body-centered cubic structure and associated high hardness values which require a very high compaction pressure and high temperature for consolidation. Gupta et al.[5] reported that the annealing treatment of the ball-milled nanocrystalline Fe-10 wt pct Cr alloy was helpful for densification by conventional pressing using a pressure of 2.7 GPa. The
high hardness value of ~10 GPa was reported for pure nanocrystalline iron (grain size 10 nm).[17] It is reported that at least a pressure of ‡1/3rd of the hardness (i.e., 3.5 GPa) of the material is essential for proper compaction.[17] Moreover, consolidation at high temperatures, the material loses their nanocrystalline structures leading to produce microcrystalline grains. Therefore, in order to optimize the compaction process, more
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