The critical resolved shear stress of a superalloy as a combination of those of its γ matrix and γ′ precipitates

The critical resolved shear stress (CRSS), τ ₀, of peak-aged single crystals of the γ′-hardened commercial nickel-base superalloy NIMONIC 105 has been measured as a function of temperature T and orientation [hkl] of the compression axis. The same measurements have been carried out for the two constituent phases of NIMONIC 105: for the single-phase γ matrix and for the single-phase L1₂-long-range ordered γ′ phase. The value of T ranged from 283 to 1150 K, and the following orientations were studied: [001], [011], , and . The specimens were compression tested. The τ ₀ values of NIMONIC 105 and of the γ′ phase are anisotropic; the anisotropy of NIMONIC 105 is similar to that of the γ′ phase, but less pronounced. The τ ₀ of the γ phase is isotropic. The τ ₀ values of the γ and of the γ′ phase vary with T, whereas the τ ₀ of NIMONIC 105 is nearly independent of T for 400 K≤T≤1000 K. A model is presented that relates the function τ ₀ ([h, k, l], T) of NIMONIC 105 to the analogous functions of its constituent γ and γ′ phase.     

Tem analysis of square-shaped dislocation configurations in the γ′ phase of a Ni-based superalloy

Straight sessile dislocations are observed in the γ' phase of a Ni-base superalloy deformed at 975°C. They are shown to be prismatic pure edge dislocations, lying along 〈110〉 directions, with a Burgers vector $\text{b}\text{= 2a〈001〉}$. We propose a formation mechanism and a non-planar core structure which accounts for the observations.     

TEM-in situ deformation of beryllium single crystals—a new explanation for the anomalous temperature dependence of the critical resolved shear stress for prismatic slip

The critical resolved shear stress for prismatic slip within beryllium single crystals passes through a maximum in the temperature range of 170–450 K. A valid explanation has not been found till now. In the present paper the experimental results of TEM-in situ deformation of single crystal beryllium are presented. Although the samples were oriented to promote prismatic slip, combined slip mechanisms on prismatic and basal planes were observed at room temperature. However, at 170 K plastic deformation only occurred by prismatic slip. A new model explaining the anomaly of the critical resolved shear stress is proposed which is based on elementary dislocation processes, i.e. formation and motion of salient points on dislocation lines. The same mechanisms might also result for other hexagoanl metals in a comparable anomaly of the plastic behavior.