| For improving the properties and efficiency of modern are-engine and gas engine, the inlet temperature of gas before turbine now is approaching to 1300 °C. The ability of affording high temperature for the turbine blade is increasing continuously. Nowadays, the main technique for strengthening the nickel based single crystal(SC) superalloy is adding mass of refractory elements and costly rare earth elements like Re and Ru. However, adding these exorbitant solutes gives rise to lots of negative effects such as receding stability of microstructures, higher density and unmanageable cost. These defects strongly restrict the services of these high-performance SC superalloys. Hence, decreasing the accession of theses costly elements is becoming an important way for nowadays developing of SC superalloy. So it is very meaningful to finding out the effective way for ascending the properties of SC superalloy without dependent of refractory rare elements and dig out the properties of active SC alloys. To achieving this purpose, it is necessary to research the high temperature properties and corresponding deformation behaviors for these SC superalloys under different environments.In this paper, a low rhenium-containing nickel based single crystal nickel-based superalloys directionally casted along [001] orientation was selected. Several different γ’ morphologies of this alloy were obtained by discrepant heat treatments. The samples respectively first aged at 1000 °C, 1180 °C+1150 °C and 1100 °C(standard) are selected and high temperature creep experiments, high temperature compressive tests and long time exposure tests were carried out on them. Analysis was processed on the high-temperature properties and microstructure stabilities of these specimens. Based on the results of the experiments and analysis, the way for improving the properties of SC superalloy by adjusting microstructures was verified.The TEM and SEM observations were used to analysis the evolution of dislocation configurations and microstructures of these SC specimens during the creep tests and compressive tests.For creep at 1100 oC /137 MPa, the creep processes of those SC samples are dominated by γ/γ’ interracial dislocation structures: at the first creep stage, the creep was controlled by the motions of a/2 <011>, a/2 <101> dislocations emerged in the γ channel. The sample first aged at 1000 °C had a minimum creep strain due to its lowest density of matrix dislocations. The other samples had higher densities of matrix dislocations and some of those dislocations were forming interfacial dislocation networks on γ/γ’ interfaces; at the second creep stage, the creep was dominated by the formation and density of those dislocation networks. The sample first aged at 1180 °C+1150 °C got the most contact dislocation networks while there were looser networks on the γ/γ’ interfaces of the sample first aged at 1000 °C; at the third creep stage, some a/2 <101> and a/2 <011> superlattice dislocation pairs were found to cut the γ’ phases in all three samples, the impediment to these superlattice dislocations by γ/γ’ interfacial dislocation networks dominates the creep behavior. The sample first aged at 1180 °C+1150 °C which got 0.5um cubic γ’ phases obtained the longest third creep stage due to the most effective impediment to the motions of superlattice dislocations by contact dislocation networks. So, this SC sample owned the highest rupture time compared to the others under this creep environment. Its rupture time was 89 h longer than that of the 1100 °C aged SC which was a standard heat-treated sample.Directional rafts of γ’ phases perpendicular to the external stress were found in all the three SC samples during creep at 1100 °C/137 MPa. Although the preliminary raft of γ’ of the sample first aged at 1180 °C+1150 °C was faster than the others due to its highest original interfacial misfit, the ultimate rafted structures were similar for the three SC samples.For creeping at 850 oC /660 MPa, the main creep mechanisms of the samples first aged at 1000 °C and 1100 °C(standard) were the super intrinsic stacking faults(SISF) formed by the cutting a/6 <112> super partial dislocations in γ’. The creep mechanism of the sample first aged at 1180 °C+1150 °C was still dominated by the motions of matrix dislocations. TEM observations proved that the multiple slip systems were actuated in the sample first aged at 1000 °C which got irregular γ’ phases with an average size of 0.34 um and there only single <112> {111} slip system existed in the sample first aged at 1100 °C(standard) which got 0.45 um cubic γ’ phases. The multiple slips of SISF decreased creep rate and resulted in prolonging the rupture life. Although the tangled matrix dislocations were found in the sample first aged at 1180 °C+1150 °C, no regular dislocation networks formed on γ/γ’ interfaces which can decrease the creep rate. So, the sample first aged at 1000 °C obtained the longest rupture life which was 49 h longer than that of the sample first aged at 1100 °C.The degree of rafts of γ’ of the three samples during at 850 °C/660 MPa was lower than those during at 1100 °C/137 MPa. The sample first aged at 1180 °C+1150 °C got the fastest raft process and most obvious raft structure.For high temperature compressive experiments, all the three SC samples with different γ’ morphologies exhibit anomalous yield strengths compressed at high temperatures and the TEM was employed to research the deformation behaviors of these specimens. For compression at 600 °C(below the peak temperature), the anti-phase boundary defects(APB) formed by cutting superlattice dislocation pairs were found in all the three samples. The sample first aged at 1180 °C+1150 °C got not only the highest APB densities but the highest γ111/γ001 ratio of APB energies that gave the highest probability of K-W(Kear-Wilsdorf) locking of dislocation pairs and resulted in the broadest anomalous temperature domain and highest yield strengths of this sample. For compression at 1000 °C(above the peak stress temperature), the deformation mechanism of the three samples become to the multiple SISF shearing modes. The sample first aged at 1180 °C+1150 °C have the highest SISF energy of γ’ phase which favors its yield strength. Thus, this sample also got highest yield stresses compressed at those temperatures. The peak stress temperatures of these specimens are also different. For the sample first aged at lower temperatures, the compressive peak stresses are located at around 850 °C, and it is located at around 800 °C for the sample first aged at 1180°C+1150 °C.The stabilities of microstructures of different aged samples were performed under long-time exposure at high temperature. The stability of microstructure of this SC superalloy was dominated by temperature and γ/γ’ interfacial energy. The SEM was employed to analysis the evolution of their γ’ morphologies and it is found that the raft of the γ’ depends on the temperature-controlled diffusions of elements at 1100 °C, while it depends on the interfacial-controlled diffusions of elements at 850 °C temperature. It is most unstable of γ’ at both temperature exposures for the sample first aged at 1180 °C+1150 °C. |
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