[en] Single crystals of the commercial nickel-base superalloy NIMONIC 105 with four different orientations have been compression tested in the temperature range 600-1150 K. NIMONIC 105 is strengthened by fine, coherent, shearable, homogeneously distributed precipitates of the L1₂-long-range ordered γ'-phase (47 vol.%). The same investigations were undertaken for single crystals of the two constituent phases: L1₂-ordered, intermetallic single-phase γ' and disordered single-phase f.c.c. γ-matrix. Their compositions were those of the two equilibrium phases of NIMONIC 105. The CRSS of NIMONIC 105 and of the γ'-phase were anisotropic in the whole temperature range. The CRSS of the γ-matrix was isotropic. The interpretation of the anisotropy of NIMONIC 105 follows that of single-phase L1₂-ordered γ'. (orig.)

[en] Earlier experimental data on the hardening of the NIMONIC alloy PE 16 by ordered γ'-particles are reevaluated in accordance with a recently published model for strengthening by ordered particles; moreover allowance is made for the fact that solid solution and particle hardening superimpose Pythagorean. The following results are obtained: For single crystals of PE 16 in the underaged state, this new model describes the dependence of the critical resolved shear stress on the γ'-particles' size and volume fraction qualitatively quite well, but the quantitative agreement is not adequate. The yield stress of an overaged polycrystal which contains two classes of particles - one fine, one coarse - equals (sigma²₁ + sigma²₂)sup(1/2), where sigmasub(i), 1 <= i <= 2, are the individual yield stress contributions of the two particle classes. (orig.)

[en] Single crystal samples of quaternary alloy Ni₆₉Co₉Al₁₈Ti₄ were in situ strained in a transmission electron microscope. The alloy consists of an L1₂-long-range ordered γ'matrix strengthened by particles of the disordered γ-phase. During in situ straining the interaction of the dislocations with the γ-particles was investigated under stress. Microscopic features such as the dissociation width of the superpartial dislocations, bending of the dislocations between the γ-particles and the pinning of the dislocations at the departure side of the γ-particles are in excellent agreement with computer simulations performed recently

No abstract available

[en] The critical resolved shear stress τ_0NIM^γ' of the multicomponent nickel-rich L1₂-long-range ordered γ'-phase γ'_NIM has been measured in tension (t) and compression (c) tests. Precipitates of γ'_NIM strengthen the commercial nickel-base superalloy NIMONIC 105. The nominal orientations [hkl] of the single crystal axes were: [001], [011], [111], and [123]; the deformation temperatures (T) ranged from 283 to 1150 K. The results τ_0NIM^γ'([hkl],T,t/c) show the following anomalies: (1) positive slope ∂ τ₀^γ'/∂ T; (2) anisotropy; (3) t/c-asymmetry. The experimental data τ_0NIM^γ'([hkl],T,t/c) are discussed in the light of current models. (orig.)

[en] Analytical models of the critical resolved shear stress (CRSS) of a crystal always involve the assumption of a line tension. This variable - even though helpful for general considerations - is only a rough approximation for the elastic self interaction of a dislocation. Moreover, it strongly depends on the dislocation character, leading to different predictions for the CRSS. For a real material of course the CRSS is unequivocal. By means of computer simulations some light is shed on the question which dislocation character governs the CRSS in case of the γ'-strengthened nickel base superalloy NIMONIC PE16. (orig.)

[en] Carbide particles contribute to the high strength of nickel-base superalloys. It is a long standing question whether these carbide particles contain nitrogen. Here we examine the nitrogen content of the titanium–molybdenum-carbide in the commercial superalloy NIMONIC PE16 using a combination of electron energy loss spectroscopy (EELS) with energy dispersive X-ray (EDX) analysis. Careful examination of the molybdenum M_3- and M_2-edges, which overlap with the nitrogen K-edge, leads to an upper limit for the nitrogen content of the carbide: 1.8 at.%

[en] A new method for the investigation of Fermi surfaces by positron annihilation is introduced. In spite of its high resolution of 1.6 x 1.1 mrad² the counting rates are sufficient. The 'rotating specimen method' is applied. Instead of crossed slits thin grooves which are engraved in steelplates, are used. Since external ⁶⁴Cu-sources produce the positrons, all solids can be studied. The results of test measurements of copper single crystals are presented. (author)

[en] Coarsening of γ'-precipitates in nickel-base superalloys and of δ'-precipitates in aluminium-rich aluminium-lithium alloys is investigated by analytical transmission electron microscopy. The growth rate of the particles increases with their volume fraction. This increase is described best by Ardell's model. The γ'-volume fractions of the superalloys are independent of the annealing time t. In the case of the Al-Li alloys the analogous statement holds only if t is long enough to yield average δ'-particle radii of 9.4 nm or more. For shorter heat-treatments the δ'-volume fraction increases strongly with t. (orig.)

[en] γ'-precipitates have been grown in the nickel-base superalloy NIMONIC 105 by an Oswald ripening treatment. After that their and the γ-matrix' compositions have been determined by energy dispersive X-ray analyses. Strong concentration gradients were found next to the γ-γ'-phase-boundary. Their major part was within the γ'-particles, whose outer layers were relatively rich in Co and Cr and too poor in Ni and Al. The concentration gradients observed within the γ'-particles are interpreted on the basis of the diffusion processes controlling their growth. (orig.)