Papers by Keyword: Lattice Misfit

Abstract: Grain refinement tendency of pure Fe and Fe-X (X=5~10at%Al, 2~10at%Ti) alloys produced by laser powder bed fusion (LPBF) process was investigated. Pure Fe, Al, and Ti powders were dry mixed and cubic samples were built from the mixtures. The microstructure analysis revealed that (1) the microstructure of pure Fe consisted of equiaxed grains having an average diameter of 1.7 μm with fine iron oxide particles. (2) Fe-5 and 10at%Al alloys showed coarse columnar grains. (3) Fe-2at%Ti shows a mixture of fine equiaxed and columnar shape grains. (4) the microstructures of Fe-5at%Ti and 10at%Ti alloys are fully equiaxed, and grain refinement tendency was confirmed with increasing Ti content. Ti(N,O) oxi-nitrides are efficient in reducing the grain size because of the low lattice misfit with the ferrite matrix. Additionally, the effectiveness of Ti(N,O) particles as grain refiners was confirmed by building samples using TiN powder mixed with Fe-10at%Al and Fe-2at%Ti. While these alloys alone are coarse grained, a dispersion of Ti(N,O) particles achieved a fine-grained microstructure.

Abstract: The influence of minor Mo addition on the lattice misfit and creep rupture strength of a new single crystal superalloy have been investigated. It was shown that Mo can reduce the lattice misfit; increase the tendency of forming TCP phase; extend the time to material failure.

Abstract: The effects of applied tensile stress on the microstructural stability of a third generation single crystal superalloy DD10 have been investigated under stressed and un-stressed thermal exposure at 980 °C. The results indicated that μ phase precipitated in the dendrite core after both stressed and un-stressed thermal exposure at 980 °C for 450 h. The μ phase formation, γ′ coarsening and rafting processes were promoted by the applied tensile stress. However, the precipitation of μ phase was not sensitive to the magnitude of applied tensile stress. Meanwhile, the applied tensile stress did not affect the type and morphology of the topologically close packed (TCP) phase. It is suggested that the interaction of the applied tensile stress and the misfit stress decreased the lattice misfit between μ phase and γ matrix and promoted the formation of μ phase.

Abstract: The phase constituents of alloys from the (Ni,Co)85(Al,Ti)15 plane of the Ni-Co-Al-Ti quaternary system were investigated following prolonged exposure at 750°C. Microstructural investigations confirmed the existence of a continuous A1-L12 two-phase region in the Ni-Co-Al-Ti quaternary system between Ni-Ni3Al and Co-Co3Ti. The lattice misfits of alloys from this quaternary system were determined using neutron diffraction. With increasing contents of Ti the positive lattice misfit increases up to +0.79% in the Ti-containing alloys, which leads to an increasing tetragonal distortion of the  matrix phase due to the increasing coherency stresses.

Abstract: The influence of Ru, Co, Mo and W on the lattice misfit of eight highly alloyed Re containing single crystal nickel-base superalloys was investigated. High resolution X-ray diffraction (XRD) was used to relate the elemental partitioning behavior and the Vegard coefficients of the elements under investigation to the measured lattice parameter of the  and  phase. The residual chemical segregation and especially the coherency stress-induced tetragonal distortion of the  matrix lattice in the high Mo containing alloys results in the observation of two different lattice parameters for the  matrix phase. This leads to three overlapping, but clearly distinguishable {002} X-ray reflections.

Abstract: Phase separations of A1 (γ) supersaturated solid solution into γ, cubic-L12 (γ') and tetragonal-D022 (γ") phases were investigated in Ni-V-Ge alloys by means of transmission electron microscopy (TEM). When Ni-15.8at%V-9.0at%Ge alloy is aged at 1073 K, at the early stage of ageing γ" phases are observed in the γ matrix as triangle- or diamond-shaped precipitates. With further ageing, colonies of lamellar structure consisting of two variants of γ" phase are dispersedly formed in the γ matrix and then γ" plates grow along the <110> direction. When Ni-14.5at%V-8.8.at%Ge alloy is isothermally annealed at 1023 K, first spherical γ' particles precipitate homogeneously in the γ matrix, followed by the formation of lamellar structure of γ" phases. In the course of further ageing, the lamellar structure develops, and only γ' particles around the lamellar structure grow and others gradually fade out.

Abstract: Internal interfaces are decisive for many properties of materials. Both functional and structural properties of interfaces are briefly reviewed on selected examples. Approaches to the grain boundary classification are discussed in the context of the complex relationship between microstructure and material properties. Implications for grain boundary engineering are mentioned.

Abstract: Internal elastic strain, and its change accompanied with the raft formation during creep deformation in the Ni-based single crystal superalloy (TMS-26) have been investigated by X-ray diffractometry. The elastic strain caused by the lattice misfit between g and g' phases has markedly been changed by creep deformation especially in the directions perpendicular to the [001] tensile axis. The change in the elastic strain can be explained by the effect of creep dislocations stacked at g/g' interfaces. The evolution of the elastic stress field estimated from the elastic strain has explained well the transition from primary creep stage to the second one.