Browsing by Author "Koch, CC"

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    Effect of Cr and Zr addition on oxidation resistance of nanocrystalline Fe-Cr-Ni-Zr
    (Curran Associates, Inc., 2011-11-20) Venkataraman, MB; Singh, R; Atanacio, AJ; Fu, J; Koch, CC
    The effect of nanocrystalline grain size and alloying additions of Cr, Ni and Zr on the oxidation resistance of nanocrystalline Fe-based alloys has been investigated. Bulk nanocrystalline alloy pellets, having composition Fe-xCr-5Ni-2Zr and Fe-xCr-5Ni {x = 7, 10} were prepared by a mechanical alloying and compaction route. A novel multi-step hot-compaction process has been investigated for the consolidation of powders into close-to-100% dense nc pellets (grain size 60-70 nm). The pellets showed high hardness (7.5-8.0 GPa) and reasonable ductility under shear stress condition. The high temperature oxidation resistance of these alloys, at 550 °C, has been compared with conventional microcrystalline stainless steel alloy. Nanocrystalline grain size was found to improve the oxidation resistance particularly in the alloys with lower Cr content. This behaviour is attributed to the greater grain boundary diffusivity of Cr in the nanocrystalline alloys. Zr addition was found to improve the thermal stability and insignificantly influence the oxidation resistance. © 2011 Australasian Corrosion Association
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    Role of micro-/nanocrystalline structure in oxidation of Fe-Cr alloys
    (Curran Associates, Inc., 2008-11-16) Singh, R; Gupta, RK; Atanacio, AJ; Koch, CC
    A simplistic approach would suggest a greater corrosion rate of an alloy in its nanocrystalline state than in microcrystalline state, due to a larger fraction of grain boundaries (i.e., high energy area) in the former. However, the nature of influence of nanostructure on corrosion does not seem to be similar in all cases. The nature of the influence can be opposite, depending on the type of corrosion and environment-material system. A considerably improved corrosion resistance of an Fe-C alloy in the nanocrystalline state (as opposed that in the microcrystalline state) has been established.Copyright© (2008) by the Australasian Corrosion Association
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    Secondary ion mass spectrometry for establishing role of nanocrystalline structure in extraordinary oxidation resistance of Fe-Cr alloys
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2009-11-25) Gupta, RK; Singh Raman, RK; Atanacio, AJ; Prince, KE; Koch, CC
    The last decade has witnessed a great surge in the materials science and engineering research on the development of nano-crystalline and sub-microcrystalline materials. A great deal of these studies has focused on the fundamental characterisation of the structures and their bearing on the physical and mechanical properties of nano-size and ultrafine grain materials. However, corrosion behaviour of nanocrystalline materials has received a very limited research attention. Rather, a simplistic approach to understanding the role of nanostructure in corrosion as compared to the microcrystalline material of same composition may suggest an increase in corrosion rate of the nanostructured material due to a large fraction of grain boundaries (i.e., high energy areas). However, the nature of influence of the nanostructure per se on corrosion does not seem to be similar in all cases. In fact, the nature of such influence can be contradictory, depending on the type of corrosion and environment-material system. For example, nanocrystalline structure is reported to improve the resistance of an iron aluminide system in a corrosive gas, whereas the dissolution rate of a nanocrystalline copper is reported to be greater than the conventional polycrystalline copper. It was hypothesised that it may be much easier to develop a protective film on nanocrystalline Fe-Cr alloys. Nanocrystalline (nc) and microcrystalline (mc) Fe-10Cr alloys were produced at North Carolina State University. During oxidation in air at 350 degrees C oxidised, oxidation kinetics of the nc alloy was found to be an order magnitude slower than the mc counterpart. Oxide scales on both alloys were characterised by depth profiling chromium, oxygen and iron using secondary ion mass spectrometer (SIMS) at ANSTO. SIMS results established that an Fe-Cr nanocrystalline alloy with only 10wt% Cr can provide as much or better corrosion resistance as/than an Fe-20Cr alloy, suggesting possibility of developing sufficient oxidation resistance at much lower Cr contents. © 2009 AINSE