B. Reppich

Order strengthening in the cast nickel-based superalloy IN 100 at room temperature

Abstract The isothermal aging behavior of the cuboidal ordered γ′ precipitates of the cast nickel-based superalloy IN 100 was investigated at temperatures between 800 and 1000°C. Despite the complication connected with morphological changes of the γ′ particle microstructure due to coarsening and raft formation a classical Ostwald ripening law was confirmed. Comparing the calculated critical resolved shear stress (CRSS) increase with the experimental data exhibits the functional dependencies on the mean γ′ size as predicted by theory [B. Reppich, in: R.W. Cahn et al. (Eds.), Materials Science and Technology, vol. 6, in: H. Mughrabi (Ed.), Plastic Deformation and Fracture of Materials, Wiley-VCH, Weinheim, Germany, 1993, pp. 311–357]: (a) a parabolic increase of the CRSS for cutting of fine under-aged γ′ particles (weak pair-coupling); (b) a transition to cutting by strongly pair-coupled dislocations for increasing particle sizes; and (c) a deviation from the hyperbolic CRSS decrease due to strong pair-coupled cutting towards Orowan by-passing for non-coupled single dislocations at over-aged particles.

Strengthening mechanisms in mgo containing coherent stress-free precipitation particles—I. Theory

Abstract A simple hardening model is proposed describing the increase of the critical resolved shear stress (CRSS) of MgO caused by coherent, stress-free magnesia ferrite particles. The calculation is based on the following assumptions: 1. (i) The particles are cut by dislocation pairs which are coupled by the antiphase boundary (APB) created in the spinel lattice of the sheared particles. The pair-coupling of the dislocations depends on particle size and determines the CRSS as predicted by Gleiter and Hornbogen. 2. (ii) In addition, the cutting dislocations create ledges of new matrix-particle interface. This chemical hardening gives a marked contribution to CRSS for small particle sizes. The comparison with experiments is presented in the subsequent paper (part II).

Electron microscopy of γ′ particles in nickel-based superalloys

Experimental results of extensive transmission and scanning electron microscopy investigations on a range of commercial two-phase superalloys (Nimonic PE 16, Nimonic 80 A, Nimonic 90, Nimonic 105 and IN-100) are reported. The growth of the unimodal size-distributed ordered γ′ (Ni3Al, Ti) precipitates during one-stage isothermal aging obeys strictly the common t13 law independent of the degree of misfit, volume fraction and particle shape (spheres, cuboids and cuboidal arrays). Deviations from the t13 behaviour are observed only in the final overaging stage because of drastic changes in the γ′ morphology γ′ volume fractions increase monotonically with increasing aging time, and the particle number densities decrease monotonically with increasing particle size, suggesting that the morphological development is governed by the combined decomposition and Ostwald ripening.

Creep lifetime prediction of oxide-dispersion-strengthened nickel-base superalloys: A micromechanically based approach

AbstractThe high-temperature creep behavior of the oxide-dispersion-strengthened (ODS) nickel-base superalloys MA 754 and MA 6000 has been investigated at temperatures up to 1273 K and lifetimes of approximately 4000 hours using monotonic creep tests at constant true stressσ, as well as true constant extension rate tests (CERTs) at

Strengthening mechanisms in mgo containing coherent stressfree precipitation particles—II. Experiments and comparison with theory

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Application of the HAI-model to the creep behaviour of particle hardened nickel-base superalloys

. The derivation of creep rupture-lifetime diagrams is usually performed with conventional engineering parametric methods, according to Sherby and Dorn or Larson and Miller. In contrast, an alternative method is presented that is based on a more microstructural approach. In order to describe creep, the effective stress model takes into account the hardening contributionσp caused by the presence of second-phase particles, as well as the classical Taylor back-stressσp caused by dislocations. The modeled strain rate-stress dependence can be transferred directly into creep-rupture stress-lifetime diagrams using a modified Monkman-Grant (MG) relationship, which adequately describes the interrelation between

Some new aspects concerning particle hardening mechanisms in γ' precipitating Ni-base alloys—I. Theoretical concept

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