ABSTRACT
FIGURE 4.1 IN718 nickel-based superalloy held for 1min at 850C. Reflected light microscope, cross-polarized, with Nomarski filter. The micrograph shows that no precipitation has occurred. (From [1]. With permission.)
FIGURE 4.2 IN718 nickel-based superalloy held for 20min at 850C. Reflected light microscope, cross-polarized, with Nomarski filter. The micrograph shows that no precipitation has occurred. It can be seen that small 00 precipitates have precipitated out within the matrix. (From [1]. With permission.)
FIGURE 4.4 IN718 nickel-based superalloy held for 3 h at 850C. Reflected light microscope, crosspolarized, with Nomarski filter. The micrograph shows that the volume fraction of d is greater than when held for shorter periods of time. (From [1]. With permission.)
FIGURE 4.3 IN718 nickel-based superalloy held for 1 h at 850C. Reflected light microscope, cross-polarized, with Nomarski filter. Platelets of d are seen to have precipitated out at the grain boundaries. (From [1]. With permission.)
Characterization of Aluminum, Steel, and
FIGURE 4.6 IN718 nickel-based superalloy held for 24 h at 850C. Reflected light microscope, crosspolarized, with Nomarski filter. Here, the highest volume fraction of d has formed. (From [1]. With permission.)
FIGURE 4.5 IN718 nickel-based superalloy held for 6 h at 850C. Reflected light microscope, crosspolarized, with Nomarski filter. The volume fraction of d is greater than when held for shorter periods of time. (From [1]. With permission.)
FIGURE 4.8 IN718 nickel-based superalloy held for 72 h at 850C. Reflected light microscope, crosspolarized, with Nomarski filter. The long precipitates are seen to have become more spheroidal than after shorter periods. (From [1]. With permission.)
FIGURE 4.7 IN718 nickel-based superalloy held for 48 h at 850C. Reflected light microscope, crosspolarized, with Nomarski filter. The long precipitates are seen to have become more spheroidal than after shorter periods. This occurs because the spherical shapes have a lower surface area to volume ratio than the needles and are, therefore, more thermodynamically stable. (From [1]. With permission.)
Characterization of Aluminum, Steel, and
FIGURE 4.10 An as-cast alloy 718 ESR ingot showing dendritic structures. (From [2]. With permission.)
FIGURE 4.9 An as-cast alloy 718 Electronic Slag Remelt (ESR) ingot prior to homogenization. (From [2]. With permission.)
FIGURE 4.11 An as-cast alloy 718 ESR ingot showing (b) interdendritic segregation. (From [2]. With permission.)
FIGURE 4.12 The microstructure of homogenized alloy 718 ESR ingot. (From [2]. With permission.)
FIGURE 4.13 Transverse ingot sections showing the effect of homogenization on the as-cast macrostructure of alloy 718. (From [2]. With permission.)
Characterization of Aluminum, Steel, and
FIGURE 4.15 Micrographs of hot-worked alloy 718 showing the start of recrystallization after reheating the material at 1,107C. (From [2]. With permission.)
FIGURE 4.16 Micrographs of hot-worked alloy 718 showing extensive recrystallization, less recrystallization near the billet surface after reheating the material at 1,107C. (From [2]. With permission.)
FIGURE 4.14 Transverse ingot sections showing the effect of homogenization on the macrostructure of alloy 718 after homogenization. (From [2]. With permission.)
FIGURE 4.17 Micrographs of hot-worked alloy 718 showing less recrystallization near the billet surface because of lower billet surface temperature due to cooling after reheating the material at 1,107C. (From [2]. With permission.)
FIGURE 4.18 Micrographs of hot-worked alloy 718 showing complete recrystallization after reheating the material at 1,107C. (From [2]. With permission.)
Characterization of Aluminum, Steel, and
FIGURE 4.20 Micrographs showing the structure of d-phase-processed alloy 718 during the acicular d-phase after heating at 900C for approximately 24 h. (From [2]. With permission.)
FIGURE 4.19 A micrograph of conventional-forged alloy 718 billet (254mm diameter) showing a uniform grain structure. (From [2]. With permission.)
FIGURE 4.21 Micrographs showing the finished product structure of d-phase-processed alloy 718 after heating at 900C, showing very fine grain size. (From [2]. With permission.)
FIGURE 4.22 The microstructure of spray-formed 718. (From [2]. With permission.)
Characterization of Aluminum, Steel, and
FIGURE 4.24 The typical appearance of carbides in alloy 718 in hot-worked 254mm diameter billet. (From [2]. With permission.)
FIGURE 4.23 The typical appearance of carbides in alloy 718 in cast 500mm diameter ingot. (From [2]. With permission.)
FIGURE 4.26 Typical microstructures of alloy 720 at various points in processing the ingot to a semi-finished product showing an irregular g0 structure during intermediate processing in forged billet. (From [2]. With permission.)
FIGURE 4.25 The typical appearance of carbides in alloy 718 in hot-worked 127mm diameter billet. (From [2]. With permission.)
Characterization of Aluminum, Steel, and
FIGURE 4.28 Typical microstructures of alloy 720 at various points in processing the ingot to a semi-finished product showing unrecrystallized isolated grain in forged billet. (From [2]. With permission.)
FIGURE 4.27 Typical microstructures of alloy 720 at various points in processing the ingot to a semi-finished forged billet (165mm in diameter). (From [2]. With permission.)
FIGURE 4.29 Fatigue crack propagation in UdimetTM 720. (From [3]. With permission.)
FIGURE 4.30 Fatigue crack propagation in UdimetTM 720. (From [3]. With permission.)
FIGURE 4.31 Fatigue crack propagation in UdimetTM 720. (From [3]. With permission.)
Characterization of Aluminum, Steel, and
FIGURE 4.32 Ni-based superalloy containing Al, Re, W, Ta, Cr, Co, and Ru. Field emission gun scanning electron microscope (FEGSEM) in secondary electron imaging (SEI) mode. This image shows a secondary electron image of a solutioned Ni-base superalloy. The microstructure consists of g/g0, the darker phase is g0, and the brighter phase is the g. (From [4]. With permission.)
FIGURE 4.33 Ni-based superalloy containing Al, Re, W, Ta, Cr, Co, and Ru. Solution heat-treated, creep test. The single crystal superalloy can undergo microstructural changes when it is stressed at high temperature. The phenomenon is called ‘‘rafting,’’ which can be good for high temperature (above 1050C) and low stress (100MPa) conditions. The g0 phase has rafted. (From [4]. With permission.)
FIGURE 4.34 Ni-based superalloy containing Al, Re, W, Ta, Cr, Co, and Ru. Solution heat-treated, creep test. TEM image. (TBBF) two-beam condition was set near 50014 to observe the dislocation structure in the crept Ni-base superalloy. (From [4]. With permission.)
FIGURE 4.35 Ni-based superalloy (composition (wt%): Ni, Cr 14.4-15.2, Co 13-18, Mo 3.5-4.5, Al 3.0-3.3, Ti 4.2-4.8, Ta 2.5, Zr 0.05-0.07, C 0.05, B 0.01-0.03). Extruded at 1100C with a 5.5:1 reduction in area. Scanning electron microscope (SEM) in backscattered electron-imaging (BEI) mode. Micrograph shows a fully recrystallized microstructure containing many equiaxed grains and g0
precipitates. In addition to this there are also several carbides and borides (seen as white). There is
evidence of mis-orientation between adjacent grains, demonstrated by the large degree of contrast. (From [5]. With permission.)
Characterization of Aluminum, Steel, and
FIGURE 4.37 Ni-based superalloy (composition (wt%): Ni, Cr 14.4-15.2, Co 13-18, Mo 3.5-4.5, Al 3.0-3.3, Ti 4.2-4.8, Ta 2.5, Zr 0.05-0.07, C 0.05, B 0.01-0.03). Extruded at 1100C with a 5.5:1 reduction in area. TEM carbon replica. Ground to 4000 Grade SiC paper and then polished at 6mm 3min, 1mm 5min, colloidal silica 10min; etched in 10% phosphoric acid in water for 5 s at 10V; carbon film
deposited under high vacuum; carbon film removed by etching in 20% perchloric acid in ethanol at 5V for 10 s; carbon replica then ‘‘floated’’ onto copper TEM grid. The micrograph shows the three distinct phases of g0 present in polycrystalline superalloys. These are primary, secondary, and tertiary, defined by their sizes (primary 0.5-1mm, secondary 30-200 nm, tertiary 1-25 nm) and their locations within the microstructure. Primary g0 segregates on the grain boundaries whereas the other forms are more uniformly distributed throughout the matrix. A grain boundary is clearly visible running from top right to bottom left. Due to the technique used, some g0 remains on the surface of the specimen and these ‘‘echoes’’ can be seen in the replica – principally the primary g0 shapes on the grain boundary. There is also an increased density of tertiary g0 present alongside the grain boundary. (From [5]. With permission.)
FIGURE 4.36 Ni-based superalloy (composition (wt%): Ni, Cr 14.4-15.2, Co 13-18, Mo 3.5-4.5, Al 3.0-3.3, Ti 4.2-4.8, Ta 2.5, Zr 0.05-0.07, C 0.05, B 0.01-0.03). Extruded at 1100C with a 5.5:1 reduction in area. Scanning electron microscope (SEM) in backscattered electron-imaging (BEI) mode. Ground to 4000 Grade SiC paper and then polished at 6mm 3min, 1mm 5min, colloidal silica 10min.
Etched using a ‘‘Nimonic’’ etch which preferentially attacks g0. Micrograph shows a fully recrystallized microstructure containing many equiaxed grains and g0 precipitates. In addition to this there are also several carbides and borides (seen as white). There is evidence of mis-orientation between adjacent grains, demonstrated by the large degree of contrast. (From [5]. With permission.)
