The effects of Mg microaddition on the mechanical behavior and fracture mechanism of MAR-M247 superalloy at elevated temperatures

摘要

The effects of microadditions of Mg onthe mechanical behavior and fracture mechanism ofMARM247 superalloy were investigated in this study.The microstructural observations and imageanalysis showed that a Mg microaddition rangingfrom 30 to 80 ppm significantly changed theprimary MC carbide characteristics and inhibitedthe scriptlike carbide formation. After a 80 ppmMg addition, the elongation measured at 1172Kincreased over 3 times found that for the Mg-freeMAR-M247 superalloy. The creep life and ruptureelongation of the MAR-M247 superalloy with 80 ppmMg was also improved up to 3 to 5 times that ofthe alloy without Mg during a 1033 K/724 Mpa creeptest. The fracture analyses demonstrated thatcracks were mainly initiated and propagated at theinterface of scriptlike MC carbides in the Mg-freeMAR-M274 superalloy at elevated temperatures. TheMg microaddition effectively refined andspheroidized these coarse carbides so that achange in the crack initiation occurred from thecarbide/matrix interface to that along the r-r'eutectic. Interfacial analysis using Augerelectron spectroscopy illustrated that Mg segregated to the interface of the MCcarbide/matrix, causing a change in the morphologyand interfacial behavior of the carbides. Thisimprovement contributed to a prolonged rupturelife and upgraded the moderate temperature ductility of the MAR-M247 superalloy.