Sequence of distinct microyielding stages of the monocrystalline nickel-base superalloy CMSX-6 at high temperatures

Abstract

The microyielding behaviour of the monocrystalline nickel-base superalloy CMSX-6 has been studied experimentally in tensile tests up to small strains at 900 °C, 1000 °C and 1100 °C and by transmission electron microscopy of the deformed specimens. Inspection of the microyielding stress-strain curve with highly resolved plastic strain showed four distinct stages of deformation at the lowest temperature (900 °C) but not at the two higher temperatures. By considering the superposition of the external stress with the original coherency stresses and with the deformation-induced internal stresses and by inspection of the electron micrographs, these deformation stages could be assigned to successive dislocation glide processes in the horizontal and vertical -channels and, finally, in the ′-particles.

Microstructural aspects of high temperature deformation of monocrystalline nickel base superalloys: Some open problems

“…3-16 and 20-29), which is known to occur in the form of c/c9 plates lying roughly perpendicular to the stress axis in the case of superalloys with negative c/c9 lattice misfit d. At the temperature of 1100uC, the observations show no evidence of cutting of c9 particles but indicate that the particles are circumvented by climb. According to a simple estimate of the climb velocity, 19 this appears reasonable. One minor point should be noted.…”

“…Subtle effects of the temperature dependence and its effects on the highly resolved stress-strain curves have not previously been investigated in sufficient detail. In a more detailed so far unpublished study, Reichstein et al 18,19 investigated the microyielding behaviour of single crystals of the superalloy CMSX-6 which had been deformed in tension at a total strain rate : e t 5 6?67610 25 s 21 up to total strains e t of 3% at temperatures of 900, 1000 and 1100uC respectively. Figure 2 shows the stress-strain curves in the forms stress s versus total strain e t (Fig.…”

“…Stage 1 dislocation glide occurs in the horizontal c channels, accompanied by strain hardening, interfacial dislocations accumulate at the c/c9 interfaces. This leads to the a initial coherency stresses; b superposition of coherency stresses with small external elastic tensile stress s; c as b, for larger external stress s, after small plastic deformation 1 Schematic illustration of stresses acting in superalloy with cuboidal c9 particles embedded in c matrix channels: sizes of arrows indicate qualitatively magnitude of locally acting stresses (after Reichstein et al 18,19 ) building up of deformation induced transverse internal back (tensile) stresses in the c channels and transverse internal 'forward' (i.e. compressive) stresses in the c9 particles Stage 2 dislocation glide now occurs also in the vertical c channels.…”

“…In their study on a model monocrystalline superalloy and the superalloy NASAIR 100, Gabb a plot of s versus e t ; b plot of s versus e pl 2 Microyielding stress-strain curves of CMCX-6 monocrystals deformed in tension at total strain rate ėt 56?67610 25 s 21 at temperatures of 900, 1000 and 1100uC up to total strains e t 50?03 (courtesy Reichstein et al) 18,19 3 Images (TEM) showing dislocation distributions in (010) sections of CMSX-6 single crystals after tensile deformations at temperatures of a 900uC, b 1000uC and c 1100uC to total strains e t 50?03: cutting of c9 particles and rounding-off of corners at 1000uC and coarsening and coalescence at 1100uC should be noted. The stress axis and the direction of the diffraction vector g lie in the verticle direction, as indicated (courtesy Reichstein et al 18,19 ) et al found that 'dislocations were not required at the c9 interfaces which coalesced to produce rafts'. 10 While this finding differs from that of Reichstein et al, it probably indicates that such details depend on the particular alloy investigated.…”

Effects of Temperature and Pressure on Elastic Properties of Single Crystal Aluminum in Different Crystal Orientations

“…[ 31 ] However, at higher temperature, the accuracy of the static method decreases, and in this case, the dynamic method is recommended by MMPDS. [ 32 ] Compared with the static method, the dynamic method has higher accuracy, but there are also obvious deficiencies: The measured value of the elastic modulus is lower than the true value [ 33 ] ; the axis of the specimen does not completely coincide with the crystal orientation; and the loading direction generally has a certain deflection angle with a specific orientation (such as [011]), resulting in excessive deviation of test results. [ 31 ] Therefore, the influence of the deviation of crystal orientation on elastic modulus, shear modulus, and Poisson's ratio must be considered.…”