The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Department of Defense, Washington Headquarters Services, Directorate for Information AFRL-RX-WP-TP-2012-0394 SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)Air Force Research Laboratory SPONSORING/MONITORING AGENCY ACRONYM(S)Materials SPONSORING/MONITORING AGENCY REPORT NUMBER(S) AFRL-RX-WP-TP-2012-0394 DISTRIBUTION/AVAILABILITY STATEMENTApproved for public release; distribution unlimited. Preprint to be submitted to Acta Materialia. SUPPLEMENTARY NOTESThis work was funded in whole or in part by Department of the Air Force contract FA8650-08-C-5226. The U.S. Government has for itself and others acting on its behalf an unlimited, paid-up, nonexclusive, irrevocable worldwide license to use, modify, reproduce, release, perform, display, or disclose the work by or on behalf of the U.S. Government. PA Case Number and clearance date: 88ABW-2012-2171, 11 April 2012. This document contains color. ABSTRACTCreep tests on Ni-based single crystal superalloy sheet specimens typically show greater creep strain rates and/or reduced strain or time to creep rupture for thinner specimens than predicted by current theories which predict a size independent creep strain rate and creep rupture strain. This size dependent creep response is termed the thickness debit effect. To investigate the mechanism of the thickness debit effect, isothermal, constant nominal stress creep tests were performed on uncoated PWA1484 Ni-based single crystal superalloy sheet specimens of thicknesses 3.18mm and 0.51mm under two test conditions: 760•C/758MPa and 982•C/248MPa. The specimens contained initial micro-voids formed during the solidification and homogenization processes. The dependence of the creep response on specimen thickness differed under the two test conditions: at 760•C/758MPa there was a reduction in the creep strain and the time to rupture with decreasing section thickness while at 982•C/248MPa a decreased thickness resulted in an increased creep rate even at low strain levels and a decreased time to rupture but with no systematic dependence of the creep... SUBJECT TERMS AbstractCreep tests on Ni-based single crystal superalloy sheet specimens typically show greater creep strain rates and/or reduced strain or time to creep rupture for thinner specimens than predicted by current theories which predict a size independent creep strain rate and creep rupture strain. This size dependent creep response is termed the thickness debit effect. To investigate the mechanism of the thickness debit effect, isothermal, constant nominal stress creep tests were performed on uncoate...