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An investigation was conducted into the influence of applying Pt Al bond-coat on the tensile deformation and fracture behavior of second-generation single crystal superalloy substrate with the temperature ranging between room temperature RT and 1100 °C. In the meantime, the development of a two-layer Pt Al bond-coat, consisting of an outer layer of single-phase β-(Ni,Pt)Al and an inter-diffusion zone of refractory metal precipitates, has also been discussed. As revealed by the results, the application of Pt Al bond-coat contributed to a noticeable deterioration in both yield strength and ultimate tensile strength of the superalloy substrate at elevated temperatures. Nevertheless, the elongation of coated superalloy was shown to be 17.2% (at RT) and 10.4% (at 750 °C) lower and 9.6% (at 1100 °C) higher compared to uncoated samples. Following tensile test, the TEM analyses indicated that there were onsets of various slip systems, the traditional superlattice stacking faults were retarded at intermediate temperature and the dislocation debris could be increased to develop dislocation networks at higher temperature in the region of superalloy near the bond-coat. As the temperature was on the rise, the fracture mechanism of coated superalloy shifted from tearing ridges and dimples to quasi-cleavage and then to micro-void coalescence. While that of Pt Al bond-coat was transformed from brittle to ductile rupture. Within the temperature range from RT up to 750 °C, a combination of long crack lengths and greater crack penetration depths into bond-coat caused more deterioration in the tensile properties of superalloy. When the temperature rose above 750 °C, the application of Pt Al bond-coat improved the ductility of the substrate, as a result of the ductile failure in the bond-coat which hindered the development of through-thickness cracks. • Pt Al coated superalloy tensile samples were tested at temperature between RT-1100 °C. • Dislocation density of superalloy nearby coating is higher than that of inner superalloy at all temperatures. • Presence of the coating reduces the tensile strength of the superalloy at all temperatures. • Above 750 °C, application of the coating does not have an adverse effect on the ductility of the superalloy. • Cracks density of failed Pt Al coating decreases with the tensile temperature increase. [ABSTRACT FROM AUTHOR]

A balance between the mechanical performance and castability of Ni-based single crystal superalloys is expected to be achieved by doping with appropriate carbon content. In this study, the influences of carbon content on the tensile properties of a novel low-cost 3rd-generation Ni-based single crystal superalloy at 760 °C and 1120 °C were investigated. Results showed that minor carbon addition could slightly increase the strength and plasticity of the experimental alloy at 760 °C, whereas it led to the decrease of strength and plasticity at an elevated temperature of 1120 °C. This variability was discussed in terms of the microscopic resistance for dislocation movement and the macroscopic deformation capacity associated with damage accumulation. It was found that the solid solution strength and interface strength were enhanced with increasing carbon content, however, the strength at high temperature was compromised by the enormous consumption of refractory elements, even though the precipitation of blocky M 6 C carbides provided additional hindrance. As for the macroscopic deformation capacity, interdendritic carbides could hinder the extension and/or trigger the activation of slip bands at 760 °C. Nonetheless, the initiation tendency and propagation behavior of microcracks at 1120 °C were facilitated due to the strong stress concentration and severe deformation incompatibility of interdendritic carbides. Overall, future compositional optimization should focus on reducing the formation of Ta-enriched MC carbides to minimize the loss of refractory element reinforcement and the reduction of deformability at high temperatures. • Primary MC carbides altered the extension and/or activation of slip bands at 760 °C. • Primary MC carbides caused the shift of local fracture from pure shear to cleavage fracture. • Interdendritic carbides promoted the generation and expansion of microcracks at 1120 °C. • This work guided future optimization of carbon content in Ni-based SX superalloys. [ABSTRACT FROM AUTHOR]

The effects of γ′ forming elements Ta + Al on the microstructural evolution of two Ru-containing single crystal (SX) superalloys deposited with γ′ + β NiAl coatings were investigated after thermal exposure at 1140 °C. TCP precipitation, recrystallization, and elemental interdiffusion were particularly investigated to illustrate the influence of Ta + Al on the compatibility between the coating and substrate. After exposure at 1140 °C, two distinct zones were formed under the IDZ, where the SRZ in the higher Ta + Al alloy contained a large number of rod-like and needle-like TCP phases. The other was the SDZ in the lower Ta + Al alloy, which possessed fewer and smaller granular TCP phases. Noteworthily, this discrepancy was attributed to the enhanced tendency of recrystallization in alloy with higher Ta + Al, since higher Ta + Al would result in more negative misfit of γ/γ′ and lower Al partitioning in γ phase, which provided more driving force for recrystallization. Meanwhile, the elemental distribution in the diffusion zone of the alloy with higher Ta + Al was more heterogeneous, and even the Ru Al phase was observed in the coating. As the thermal exposure time prolonged, the thickness of the SRZ exceeded that of the SDZ, which significantly reduced the effective load-bearing area of alloy with higher Ta + Al. It could be summarized that a worse compatibility between the coating and the substrate would be introduced with the increase of Ta + Al in the substrate. This study provided valuable insights into the design of coatings and alloy compositions, thereby facilitating the development and application of advanced Ru-containing SX superalloys as well as their corresponding coatings. • Microstructural evolutions below the coating/substrate interface were investigated. • The higher Ta + Al promoted the formation of SRZ with numerous rod-like TCP phases. • The mechanism of higher Ta + Al promoting recrystallization formation was analyzed. • The effect of different Ta + Al on elemental interdiffusion was discussed. [ABSTRACT FROM AUTHOR]