Creep and stress rupture of oxide dispersion strengthened mechanically alloyed inconel alloy MA 754
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NEW oxide dispersion strengthened (ODS) materials for use at high temperatures are being made by mechanical alloying, 1,2 a process which allows the ODS alloy designer to incorporate dispersed oxide phases into a matrix of virtually any composition. One of the first commercially available mechanical alloys, I N C O N E L * alloy MA 754, is a nickel-base solid * Trademark of the INCO family of companies.
solution containing a low volume fraction of yttrium oxides. Little work has been reported in the literature on the creep and stress rupture behavior of MA 754 at different temperatures and stresses. Although several brief descriptions of the structures and elevated temperature strengths of MA 754 and other ODS mechanical alloys are available, most of these descriptions contain little more than minimum engineering data (e.g., see Refs. 2 to 4). One more in-depth study was done by Whittenberger, who reported tensile creep data for MA 754 at 1093 ~ and low stresses in a study of the creep and tensile properties of several ODS nickel-base alloys? That study found an apparent threshold stress for creep at 1093 ~ in MA 754 and linked that threshold stress with a diffusional creep mechanism. Evidence of diffusion creep in a specimen crept for 100 h, in the form of dispersoid free bands at grain boundaries was given. In another study by Whittenberger, the residual room temperature tensile properties of several ODS nickel-base alloys, including MA 754, were studied after creep testing. 6 Degradation of the tensile properties of MA 754 was found after small amounts of creep at 1093 ~ This degradation T. E. HOWSON and J. K. TIEN are Research Associate and Professor, respectively, Henry Krumb School of Mines, Columbia University, New York, NY 10027. J. E. STULGA, formerly at Columbia University, is now with Crucible Research Center, Pittsburgh, PA 15230. Manuscript submitted June 8, 1979.
was again attributed to microstructural changes (dispersoid free bands at grain boundaries) produced by diffusional creep. The present investigation of MA 754 was undertaken to determine the stress and temperature dependence of the creep rate over a range of applied stresses and temperatures, and to examine the stress rupture behavior with attention given to the effect of stress, temperature, heterogeneities and dispersoid free bands, if any. EXPERIMENTAL PROCEDURE AND MATERIAL CHARACTERIZATION Creep testing was conducted in air, under constant tensile load, at 760, 982, and 1093 ~ A direct load tester was used for tests at 1093 ~ all tests at 760 ~ were done in lever arm creep machines with both manual or automatic re-alignment capability and Universal joints in the load trains to minimize bending moments. The maximum bending stresses were always less than 0.1 MPa. Test temperatures were maintained to within _+ 1 ~ over the full gage length of the specimens. Creep strain was monitored on the lever arm machines by measuring the displacement of the grip linkage outside the furnace as a function of time with an L V D T linked to a strip chart
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