Elevated temperature mechanical properties of the iron base oxide dispersion strengthened alloy ma 956 bar
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Recentwork 1,2has shown that the oxide dispersion strengthened (ODS) iron-base alloy MA 956, nominally Fe-20Cr-4.5A1-0,5Ti-0.5Y203, deforms in an unusual manner at 1366 K. In general, it appears that under conditions designed to promote slow plastic deformation in tension, MA 956 deforms by the nucleation and growth of cracks. Such cracks slowly grow until the remaining cross sectional area in front of one of the cracks is reduced to the point where the tensile strength is exceeded. When this occurs, fracture is immediate. In addition, Lin, Whittenberger, and Sherby 3 have tested MA 956 in compression at 1366 K. They found that during slow straining the MA 956 exhibited severe deformation in a narrow band. Within this band cavities could nucleate, grow, and agglomerate, leading to physical separation after relatively low strain ( ~ 2 pct). Due to the interest in using MA 956 type alloys under very demanding conditions, such as those found in the hot sections of gas turbine engines: and in view of the abnormal deformation mode at elevated temperature, further studies of the mechanical properties were warranted. This paper presents the results of conventional elevated temperature tensile, stress rupture, and creep tests as well as the residual room temperature tensile properties after creep exposure for MA 956. This work was part of an effort at the Lewis Research Center to compare the behavior after elevated temperature creep testing of Ni- and Co-base superalloys with advanced ODS alloys: EXPERIMENTAL PROCEDURES Four pieces of hot-finished MA 956 bar, nominally 8 by 3 cm in cross section and 80 cm in length, were procured from Huntington Alloys, Inc. All pieces were from the same heat of material, heat DH0001F3, with the following certified chemistry (wt pct) provided by the vendor: 20.7 Cr, 5.09 A1, 0.32 Ti, 0.02 C, 0.017 S, 73.1 Fe and 0.76 yttria. This alloy possessed an exJ. DANIEL WHITTENBERGER is Materials Engineer at NASA-Lewis Research Center, Cleveland, OH 44135. Manuscript submitted June 24, 1980. METALLURGICAL TRANSACTIONS A
tremely large elongated grain structure consisting of grains on the order of a cm in diameter by tens of cm long in the extrusion direction. The structure is highly oriented with [i-13] parallel to the extrusion direction and [332] and [110] parallel to the short transverse and long transverse directions respectively. This heat of material was also used in the previously reported studies of the slow strain rate properties) ,3 All machining of test specimens, tensile testing, creep testing and most residual property testing were accomplished by Metcut Research Associates, Inc., under NASA contract. Stress rupture testing and a few residual property tests of specimens with damaged grip ends were conducted at the Lewis Research Center. Most MA 956 specimens with gage length parallel to the longitudinal (extrusion) direction were machined with a 5.7 cm long reduced section. Long transverse and some longitudinal specimens had either a 3.2 or 2.5 cm long reduced section due to limitation
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