Laser shock surface treatment was applied to CMSX-2, AM1, and Astaloy nickel superalloys. Both deformation mechanism and the laser beam optical phenomena were studied. TEM and XRD were used to analyze microstructural features. A surface release wave mechanism model was developed to describe the formation of residual stresses.
The various models proposed in the literature in order to interpret the Hal-Petch relation are critically reviewed by comparison with experimental data. The pile-up models and the work hardening theories must include the inner structure of the grain in the case of alloys hardened by a second phase. Similarly, the properties and structure of the grain boundaries are influenced by impurities or the presence of particles. Ultra-fine grain sizes can ...
Single crystals of gamma prime hardened nickel base superalloys of several compositions were grown along the direction. Controlled thermal treatments led to a fairly regular distribution of oriented gamma prime cuboidal precipitates of about 0.4 microns in size prior to creep tests at 1050 C under uniaixal tensile stress along the growth axis. Other specimens were aged for several hundred hours at 1050 C under no stress. The lattice misfit ...
The first part of the present study describes the comparative creep properties of homogeneous and finely dendritic single-crystals of MAR M200 at high temperature (980 C). The results and observations of the microstructures after deformation reveal that this industrial alloy has the same elementary deformation mechanisms as those found for an experimental alloy containing a smaller proportion of hardening phase. The second part of this study deals with creep of ...
Two modifications of Udimet 700 were formed into cylinders from HIPed bars and were thermomechanically treated prior to compression testing. The treatment was designed to simulate forging sequences, and extensive twinning and stacking faults were observed in tests up to 1080C. One of the alloys tested was a low carbon version of Udimet 700. The other contained a higher volume fraction of gamma prime and additions of Cb, W and ...
Low cycle fatigue of Ni base alloy Rene 80 was studied at 871 C. Prior to testing, specimens were exposed for 100 h at 982 C either stress-free at 97 MPa (1/3 the yield), The LCF studies were supplemented by tensile and creep tests. The prior exposure caused significant microstructural changes and life reductions which were most pronounced for stress exposed specimens tested at high rates. Dislocation substructures were extensively ...
direct observation of the dislocation structures in connection with the values of the effective parameters leads to suggest a creep model for that particular creep stage observed in superalloys. the incubation period may be described as a steady state creep rate when deformation is produced by the glide of a low density of mobile screw dislocations (rho(sub m) approximately 10(super 5)cm(super minus 2)) bowing out between gamma prime precipitates. the ...
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