VHCF life evolution after microstructure degradation of a Ni-based single crystal superalloy

Very High Cycle Fatigue of Ni-Based Single-Crystal Superalloys at High Temperature

“…These results are in agreement with previous results from the authors using the same experimental conditions on CMSX-4 material. [9] In the specific case of MAR-M200+Hf and DS200+Hf alloys, small cracked carbides are present inside casting pores serving as crack initiation sites. Dimension ranges of casting pores that acted as crack initiation site can be found in Table I.…”

“…A previous work from the authors [9] has shown that under fully reversed conditions (R = À 1), casting pores are the main crack initiation sites in VHCF at 1000°C in CMSX-4 alloy cast using a standard Bridgman solidification process. Microstructure degradation (c¢ coarsening or N-type c¢ pre-rafting) has a minor impact on the VHCF life and rupture mechanisms.…”

“…[22] First results in VHCF at high temperature on Ni-based SX alloys have shown the predominant role of pores, [9] and also carbides [7] and eutectics on crack initiation for lifetimes in excess of 10 9 cycles. [9] However, no material containing both defects have been studied, and the role of eutectics is still not clearly understood. To better understand the role of these inclusions, two sub-groups of SX alloys have been tested to investigate the impact of eutectics and carbides on the VHCF life.…”

“…[24][25][26][27] A detailed description of the experimental procedure used during this study can be found in a previous work from the authors. [9] Briefly, a continuous excitation is applied on the specimen to solicit at a strain ratio of R = À 1. Over self-heating of the specimen is avoided using a closed-loop control of the specimen's temperature in the middle of its gage length.…”

“…Specimens have been designed so that their first tension mode frequency is of 20 ± 0.5 kHz. Specimen dimensions have been determined previously [9] for tests done using CMSX-4 material at 1000°C. Since at this temperature, the Young's modulus between different h001i SX and DS superalloys is similar according to literature, [28][29][30][31][32][33] a same geometry of specimen has been used during this study, whatever the alloy.…”