Slip band characteristics in the presence of grain boundaries in nickel-based superalloy

Abstract

Shear strain profiles along slip bands in a modified Rolls-Royce nickel superalloy (RR1000) were analyzed for a tensile sample deformed by 2%. The strain increased with distance away from a grain boundary (GB), with maximum shear strain towards the center of the grain, indicating that dislocation nucleation generally occurred in the grain interior. The strain gradients in the neighborhood of the GBs were quantified and generally correlated with rotation about the active slip system line direction. This leads to an ability to determine the active slip system in these regions. The dislocation spacing and pileup stresses were inferred. The dislocation spacing closely follows an Eshelby analytical solution for a single ended pileup of dislocations under an applied stress. The distribution of pileup stress values for GBs of a given misorientation angle follows a log-normal distribution, with no correlation between the pileup stress and the GB misorientation angle. Furthermore, there is no observed correlation between various transmissivity factors and slip band pileup stress. Hence it appears that the obstacle strength of any of the observed GBs is adequate to facilitate the dislocation pileups present in the slip bands. However, slip band transmission does correlate with transmissivity factors, with the current study focusing on the Luster and Morris m'-factor. Observation of strain profiles of transmitted bands indicate dislocation nucleation locations.

Slip band interactions and GND latent hardening in a galling resistant stainless steel

“…stress follows a r -1/2 relationship where r is the distance from the start of the pile-up). This has been experimentally verified in hexagon [16,17] and cubic [54] alloys An attempt to calculate the strain and stress fields directly adjacent to blocked slip bands observed in this work was made, using the HR-EBSD elastic strain measurements. However, it was difficult to extract any useful information due to both the spatial resolution at which the HR-EBSD measurements were taken and the more complex slip behaviour than the simple slip band to grain boundary behaviour observed in the studies in titanium [16,17] or nickel [54].…”

“…This has been experimentally verified in hexagon [16,17] and cubic [54] alloys An attempt to calculate the strain and stress fields directly adjacent to blocked slip bands observed in this work was made, using the HR-EBSD elastic strain measurements. However, it was difficult to extract any useful information due to both the spatial resolution at which the HR-EBSD measurements were taken and the more complex slip behaviour than the simple slip band to grain boundary behaviour observed in the studies in titanium [16,17] or nickel [54]. The spatial resolution of the HR-EBSD in this work was optimised to cover a large area in order to capture a range of slip behaviour, using a step size of 0.5 μm, larger than the 0.2 μm used in [16,17] but in keeping with the work of others [14,31,55].…”

Criteria for slip transfer across grain and twin boundaries in pure Ni

“…Once the two active slip systems across the GB or TB were identified, different metrics can be determined to assess whether they are able to predict slip transfer or blocking. Among them, the Luster-Morris parameter m and the residual Burgers vector ∆b have been used previously [11,13,16,17] in metallic polycrystals. It should be noted that If slip traces were only visible only in one grain across the boundary but not in the other, these GB or TB were not included in the analysis because it was not possible to identify the active slip plane in the latter grain.…”

“…They could not, however, provide a criteria because of the experimental scatter, which was attributed to the influence of the twist angle θ which cannot be determined from the EBSD information for regular GB. Finally, Sperry et al [17] also combined EBSD with high resolution digital image correlation to study slip transfer in another Ni-based superalloy. They concluded that slip transfer in regular GB was associated with low misorientation angles and it was maximum when m = 0.78 in twin boundaries.…”

Review of Microstructure–Mechanical Property Relationships in Cast and Wrought Ni‐Based Superalloys with Boron, Carbon, and Zirconium Microalloying Additions

“…The interaction of dislocations with GBs as well as GB sliding, e.g., during creep, can be assessed using molecular dynamics. [90][91][92][93][94] Cleavage energy and (partial) cohesive energy are calculated to gauge the resistance against GB decohesion. [36][37][38]43] Table 1 provides a brief summary of first-principles calculations on B in Ni.…”