Thermal-fatigue tests were performed on corset samples made from five single-crystal nickel-based superalloys with various crystallographic orientations (〈 〉 001 ,〈 〉 011 ,〈 〉 111 ) at different temperatures and cycle durations. The proposed criteria for the thermal-fatigue crack initiation and crack propagation are discussed and compared with experimental results. The sensitivity of durability to the crystallographic orientation and to thermal-cycle parameters is analyzed experimentally and by means of the corresponding finite-element simulations. Keywords: nickel-based superalloy, single crystal, thermal fatigue, crack initiation, crack propagation Preizkusi toplotnega utrujanja so bili izvr{eni na vzorcih korzetne oblike. Vzorci so bili izdelani iz petih monokristalnih nikljevih superzlitin z razli~no kristalografsko orientacijo (〈 〉 001 ,〈 〉 011 ,〈 〉 111 ), preizkusi pa so bili narejeni pri razli~nih temperaturah trajanja ciklov. Predlagana merila za nastanek razpok in njihovo napredovanje pri toplotnem utrujanju so opisana in primerjana z eksperimentalnimi rezultati. Odvisnost zdr`ljivosti od kristalografske orientacije in parametrov toplotnih ciklov je eksperimentalno analizirana in ugotovljena z ustrezno simulacijo s kon~nimi elementi. Klju~ne besede: superzlitina na osnovi niklja, monokristal, toplotno utrujanje, nastanek razpok, napredovanje razpoke
EXPERIMENTAL DATAThe durability of the single-crystal blades of modern gas turbines is mainly determined by their ability to resist the thermal-cycling stress. In Russia, the testing of the thermal fatigue of corset samples (Figure 1) in vacuum conditions, with and without lateral thermal-barrier coatings is widespread. During the test, the shearband formation, the conditions of crack nucleation and the rate of crack propagation are investigated.Experimental studies were performed on five singlecrystal alloys (ZhS32, ZhS36 and others) developed by the VIAM research centre, with different alloying and, most importantly, different carbon contents. The chemical compositions of the alloys are given in Table 1.The tests of the thermal-fatigue resistance were carried out for different crystallographic orientations (CGOs) of the specimens, various minimum (T min ) and maximum temperatures (T max ) of the cycle, with and without a dwell time at T max . 1,2 The test results were characterized with the number of cycles to the macrocrack initiation and to the failure of the samples and the in-plane and out-of-plane residual strains (e in , e out ) in the central parts of the specimens. The changing of T max and CGO has a significant influence on the thermal-cycling durability ( Table 2).The results of a comparative analysis of the thermalfatigue durabilities of the five considered alloys are given in Figure 2, for a thermal cycle of 150«900°C (Figures 2a and 2c) and for a cycle of 500«1050°C (Figures 2b and 2d).