12 research outputs found
Measurement of segregation and distribution coefficients in MAR-M200 and hafnium-modified MAR-M200 superalloys
Formation of Si-containing barrier in Al-Si coatings and Its effect on protective capability of superalloy
Effect of fluid flow and hafnium content on macrosegregation in the directional solidification of nickel base superalloys
The transition from columnar to equiaxed dendritic growth in proeutectic, low-volume fraction copper, Pb−Cu alloys
Oxidation Behavior and Structure Stability at 1250 °C of Chromium-Rich TaC-Containing Cast Alloys Based on Nickel and Cobalt
The effects of tantalum on the microstructure of two polycrystalline nickel-base superalloys: B-1900 + Hf and MAR-M247
Changes in the γ/γ\u27/carbide microstructure as a function of Ta content were studied in conventionally cast B-1900 + Hf and both conventionally cast and directionally solidified MAR-M247.* The effects of tantalum on the microstructure were found to be similar in both nickel-base superalloys. In particular, the γ\u27 and carbide volume fractions increased approximately linearly with tantalum additions in both alloys. The γ\u27 phase compositions did not change as tantalum additions were made with the exception of an increase in the tantalum level. Bulk tantalum additions increased the tantalum, chromium, and cobalt levels of the γ phase in both alloy series. The increase in the concentrations of the latter two elements was attributed to a decrease in the γ phase fraction with increasing bulk tantalum level and nearly constant γ\u27 /γ partitioning ratios. It was demonstrated that the large increase in the γ \u27 volume fraction was a result of tantalum not affecting the partitioning ratios of the other alloying elements. The addition of tantalum led to a partial replacement of the hafnium in the MC carbides, although the degree of replacement was reduced by the solutionizing and aging heat treat-ment. In addition, chromium-rich M23C6 carbides formed as a result of MC carbide decomposition during heat treatment
The effects of tantalum on the microstructure of two polycrystalline nickel-base superalloys: B-1900 + Hf and MAR-M247
Neutron and X-Ray diffraction study of internal stress in thermomechanically fatigued single-crystal superalloy
The relationship between internal stress and thermomechanical fatigue (TMF) in a Ni-based single-crystal superalloy is studied by neutron and X-ray diffraction. The extents of internal stress, deformation, lattice mismatch, and distortion during TMF are characterized by the determined deviatoric stress invariants and lattice parameters and compared with relevant microstructural information from scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that, in general, the macroscopic stress, plastic deformation, lattice mismatch, and distortion have all increased during TMF. The lattice mismatches of the TMF samples are at a high level, where the values along [100]/[010] are negative, but those along [001] are positive. The tetragonal lattice distortion of the γ matrix is slightly greater than that of the γ′ precipitates, where the c/a values of the γ matrix are smaller than 1, but that of the γ′ precipitate larger than 1. The γ matrix yields and becomes hardened at the initial TMF cycle and gradually loses most of its strength during the earlier TMF cycles, associated with stress relaxation and homogenous deformation. However, the γ′ precipitates yield and become hardened later, bearing the most stress up to the necking of the superalloy. This process is associated with a buildup of stress and significant concentrated and inhomogeneous distribution of deformation in the γ′ precipitate. The residual deformation states of the superalloy and its component phases at the earlier TMF are basically shearing, and only become stretched at a later stage of TMF. The microstructure of the TMF samples shows an initial stage of rafting, where the dislocations are accumulated at the γ/γ\ifmmode′\else\fi interfaces of the γ matrix channels, but both dislocation networks and stacking faults are inhomogeneously distributed in the γ′ precipitates