Microstructure and Mechanical Behavior of ODS Stainless Steel Fabricated Using Cryomilling
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THE demand to limit global exhaust gas emissions and fuel consumption has prompted the need to build smaller engines with optimal engine power output for transportation purposes.[1] A turbocharger is an effective approach to decrease the size of high-output engines. However, in order to achieve better combustion efficiency, the temperature of the exhaust gas from a turbocharger engine must be significantly raised compared to that of conventional piston engines; and this requires the timely development of compatible materials for turbochargers that operate efficiently at
CHEN DAI and LILIA KURMANAEVA are with the Department of Chemical Engineering and Material Science, University of California, Davis, Davis, CA 95616. CHRIS SCHADE is with the Hoeganaes Corporation, Cinnaminson, NJ 08077. ENRIQUE LAVERNIA is with the Department of Chemical Engineering and Material Science, University of California, Davis and also with the Department of Chemical Engineering and Material Science, University of California, Irvine, Irvine, CA 92697. Contact e-mail: [email protected] DIRAN APELIAN is with the Material Processing Institute, Worcester Polytechnic Institute, Worcester, MA 01609. Manuscript submitted March 28, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
temperatures as high as 1323 K (1050 C). A candidate material currently being explored for this particular application is oxide-dispersion-strengthened (ODS) steel, which can be much more cost effective than the Inconel family of alloys that have been commonly used.[2] ODS steels contain submicron or nanoscale oxides which are dispersed evenly throughout the steel matrix to pin on dislocations and grain boundaries in order to retain the strength at elevated temperatures.[3] In this manner, ODS steels are also suitable for other extremely severe environmental applications, such as those in the nuclear and aerospace industries.[4] A commercially viable method to fabricate ODS steels involves mechanical milling, followed by pressing and sintering. Compared to fabrication methods involving precipitation reactions[5] or oxidation reactions on either the surface[6] or in the interior,[7] mechanical alloying is considered to be a versatile technique for producing ODS steels because of the simplicity of the process, the associated economic benefits, and its ability to generate nonequilibrium phases (such as oxides) in the system.[8] In this study, cryogenic ball milling (cryomilling) is used to blend oxide particles into a stainless steel matrix. Cryomilling is essentially mechanical attrition under a liquid cryogenic environment. By utilizing cryomilling, it is expected that oxides will be effectively dispersed, while
recovery and recrystallization are suppressed by the cryogenic temperatures, thereby leading to an increase in the kinetics of grain refinement[9,10] A high concentration of dislocations is introduced into the microstructure during cryomilling process from the impacts of the powder with the milling media. Within the material, the localization of deformation resu
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