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1.
Three industrial gas turbine blades made of conventionally cast (CC) IN-738 and GTD-111 and directionally solidified GTD-111
Ni-base superalloys were examined after long-term exposures in service environments. All three blades exhibit similar, service-induced
microstructural changes (MCs) including γ′ coarsening and coalescence, excessive secondary M23C6 precipitation, and primary MC degeneration, regardless of the chemical composition and the grain size. Special attention
was paid to the primary MC decomposition. It is shown that the primary MC decomposition occurs by carbon diffusion out of
the carbide into the γ + γ′ matrix, resulting in the formation of Cr-rich M23C6 carbides near the initial carbide/matrix interface. A transition zone is shown to develop between the original MC core and
its perimeter, demonstrating the gradual outward diffusion of carbon and a slight inward increase in nickel concentration.
The hexagonal Ni3(TiTa) η-phase was also found in the MC transition zone and on the MC-γ/γ′ interface. The primary MC decomposition can be expressed by the reaction MC + γ/γ′ → M23C6 + η. Finally, it is shown that the grain-boundary (GB) MC decomposes more rapidly than that in the grain interiors. This is consistent
with the more rapid GB diffusion that leads to the acceleration of the MC diffusional decomposition processes. 相似文献
2.
Effect of phosphorus on the microstructure and stress rupture properties in an Fe-Ni-Cr base superalloy 总被引:2,自引:0,他引:2
W. R. Sun S. R. Guo D. Z. Lu Z. Q. Hu 《Metallurgical and Materials Transactions A》1997,28(3):649-654
This article describes the effect of phosphorus on the microstructure and stress rupture property at 650 °C in an Fe-Ni-Cr
base superalloy. The results showed that phosphorus markedly improved the intergranular precipitation in the range of 0.0005
to 0.016 wt pct, which facilitated M23C6 and M3B2 precipitation but inhibited the formation of MC carbide. A too high phosphorus addition (0.051 wt pct P) resulted in an excessive
precipitation at grain boundaries, while a too low phosphorus content (0.0005 wt pct P) led to many precipitate-free grain
boundaries. Phosphorus also enlarged the size of the γ′ particles and lowered its stability, that η-Ni3Ti preferred to form in the alloy with 0.051 wt pct P. Due to the improvement of the microstructure, appropriate amount of
P content significantly prolonged the rupture life of the alloys in the range of 0.0005 to 0.016 wt pct. The peak value was
660 hours at 0.016 wt pct, more than 4 times that of the alloy with 0.0005 wt pct phosphorus, but phosphorus reduced the fracture
elongation. The mechanism by which phosphorus influenced the alloy is discussed. 相似文献
3.
The influence of weld-simulated heat treatments of 9 to 12 pct steels is evaluated by a fundamental model for creep. The heat-affected
microstructure is predicted by considering particle coarsening, particle dissolution, and subgrain coarsening. Particle coarsening
is predicted for a multicomponent system, showing significant M23C6 coarsening in the bcc matrix. Dissolution simulations of MX and M23C6 are performed by considering a size distribution of particles, indicating that the smallest particles can be dissolved already
at relatively low welding temperatures. Recovery in dislocation networks will take place due to the coarser particles. Creep
rate modeling is performed based on the heat-affected microstructure, showing strength reduction of weld-simulated material
by 12 pct at 1123 K (850 °C) and 30 pct at 1173 K (900 °C). The main cause of this degradation is believed to be the loss
of the smallest carbonitrides. 相似文献
4.
Shingo Mineta Shigenobu Namba Takashi Yoneda Kyosuke Ueda Takayuki Narushima 《Metallurgical and Materials Transactions A》2010,41(8):2129-2138
The microstructures of as-cast and heat-treated biomedical Co-Cr-Mo (ASTM F75) alloys with four different carbon contents
were investigated. The as-cast alloys were solution treated at 1473 to 1548 K for 0 to 43.2 ks. The precipitates in the matrix
were electrolytically extracted from the as-cast and heat-treated alloys. An M23C6 type carbide and an intermetallic σ phase (Co(Cr,Mo)) were detected as precipitates in the as-cast Co-28Cr-6Mo-0.12C alloy;
an M23C6 type carbide, a σ phase, an η phase (M6C-M12C type carbide), and a π phase (M2T3X type carbide with a β-manganese structure) were detected in the as-cast Co-28Cr-6Mo-0.15C alloy; and an M23C6 type carbide and an η phase were detected in the as-cast Co-28Cr-6Mo-0.25C and Co-28Cr-6Mo-0.35C alloys. After solution treatment, complete precipitate
dissolution occurred in all four alloys. Under incomplete precipitate dissolution conditions, the phase and shape of precipitates
depended on the heat-treatment conditions and the carbon content in the alloys. The π phase was detected in the alloys with carbon contents of 0.15, 0.25, and 0.35 mass pct after heat treatment at high temperature
such as 1548 K for a short holding time of less than 1.8 ks. The presence of the π phase in the Co-Cr-Mo alloys has been revealed in this study for the first time. 相似文献
5.
The evolution of microstructural and mechanical properties of alloy 800 with respect to operating conditions of the steam
generator tubings of fast breeder reactors have been analyzed and presented. On the microstructural side two phenomena have
important influence on the mechanical properties, namely γ′ and carbide precipitation. Gamma prime precipitation occurs in
alloy compositions containing ≳0.50 pct Ti + Al, inducing mechanical property changes and, in particular, improving the long
term creep resistance. Its growth rate follows the exponential law which, when extrapolated, yields an overaging time beyond
4 × 104 h at ≲550°C. M23C6 carbide precipitation starts in early stages of exposure at 500 to 600°C, being of heterogeneous nature and forming mainly
on the grain boundaries. The M23C6 carbides advance perpendicular to the surface of one of the austenite grains, commonly having a <110>γ//<110>M23C8relationship, and occasionally develop into well defined cellular precipitates. On the mechanical side, a sharp creep ductility
decline is observed when either, or in particular both, strong γ′ strengthening and discontinuous precipitation develop in
the matrix. It is argued that this decline is principally due to the latter phenomenon and is accentuaged by matrix strengthening.
Formerly Associate Professor, Metallurgical Engineering Department, Arya Mehr University of Technology, Tehran, Iran. 相似文献
6.
Chuanyong Gui Akihiro Sato Yuefeng Gu Hiroshi Harada 《Metallurgical and Materials Transactions A》2005,36(11):2921-2927
We proposed a new method for developing Ni-base turbine disc alloy for application at temperatures above 700 °C by mixing
a Ni-base superalloy U720LI with a two-phase alloy Co-16.9 wt pct Ti in various contents. The microstructure and phase stability
of the alloys were analyzed using an optical microscope, a scanning electron microscope, energy-dispersive spectroscopy, and
an X-ray diffractometer. The yield strength was studied by compression tests at temperatures ranging from 25 °C to 1200 °C.
The results show that all the alloys had a dendritic structure. Ni3Ti (η) phase was formed in the interdendritic region in the alloys with the addition of Co-16.9 wt pct Ti, and its volume fraction
increased with the increase in the addition of Co-16.9 wt pct Ti. The results of exposure at 750 °C show that the addition
of Co-16.9 wt pct Ti to U720LI had a great effect on suppressing the formation of σ phase due to the reduced Cr content in the γ matrix. Compared to U720LI, the alloys with the addition of Co-16.9 wt pct Ti possessed higher yield strength. The solid-solution
strengthening of γ and γ′ and higher volume fraction of γ′ were assumed to cause this strength increase. 相似文献
7.
Hassan Ghassemi Armaki Ruiping Chen Kouichi Maruyama Masaaki Igarashi 《Metallurgical and Materials Transactions A》2011,42(10):3084-3094
Creep behavior and degradation of subgrain structures and precipitates of Gr. 122 type xCr-2W-0.4Mo-1Cu-VNb (x = 5, 7, 9, 10.5, and 12 pct) steels were evaluated during short-term and long-term static aging and creep with regard to
the Cr content of steel. Creep rupture life increased from 5 to 12 pct Cr in the short-term creep region, whereas in the long-term
creep region, it increased up to 9 pct Cr and then decreased with the addition of Cr from 9 to 12 pct. Behavior of creep rupture
life was attributed to the size of elongated subgrains. In the short-term creep region, subgrain size decreased from 5 to
12 pct Cr, corresponding to the longer creep strength. However, in the long-term creep region after 104 hours, subgrain size increased up to 9 pct Cr and then decreased from 9 to 12 pct, corresponding to the behavior of creep
rupture life. M23C6 and MX precipitates had the highest number fraction among all of the precipitates present in the studied steels. Cr concentration
dependence of spacing of M23C6 and MX precipitates exhibited a V-like shape during short-term as well as long-term aging at 923 K (650 °C), and the minimum
spacing of precipitates belonged to 9 pct Cr steel, corresponding to the lowest recovery speed of subgrain structures. In
the short-term creep region, subgrain coarsening during creep was controlled by strain and proceeded slower with the addition
of Cr, whereas in long-term creep region, subgrain coarsening was controlled by the stability of precipitates rather than
due to the creep plastic deformation and took place faster from 9 to 12 pct and 9 to 5 pct Cr. However, M23C6 precipitates played a more important role than MX precipitates in the control of subgrain coarsening, and there was a closer
correlation between spacing of M23C6 precipitates and subgrain size during static aging and long-term creep region. 相似文献
8.
Bikas C. Maji Madangopal Krishnan Gouthama R. K. Ray 《Metallurgical and Materials Transactions A》2011,42(8):2153-2165
The effect of Si addition on the microstructure and shape recovery of FeMnSiCrNi shape memory alloys has been studied. The
microstructural observations revealed that in these alloys the microstructure remains single-phase austenite (γ) up to 6 pct Si and, beyond that, becomes two-phase γ + δ ferrite. The Fe5Ni3Si2 type intermetallic phase starts appearing in the microstructure after 7 pct Si and makes these alloys brittle. Silicon addition
does not affect the transformation temperature and mechanical properties of the γ phase until 6 pct, though the amount of shape recovery is observed to increase monotonically. Alloys having more than 6 pct
Si show poor recovery due to the formation of δ-ferrite. The shape memory effect (SME) in these alloys is essentially due to the γ to stress-induced ε martensite transformation, and the extent of recovery is proportional to the amount of stress-induced ε martensite. Alloys containing less than 4 pct and more than 6 pct Si exhibit poor recovery due to the formation of stress-induced
α′ martensite through γ-ε-α′ transformation and the large volume fraction of δ-ferrite, respectively. Silicon addition decreases the stacking fault energy (SFE) and the shear modulus of these alloys and
results in easy nucleation of stress-induced ε martensite; consequently, the amount of shape recovery is enhanced. The amount of athermal ε martensite formed during cooling is also observed to decrease with the increase in Si. 相似文献
9.
M. Valsan P. Parameswaran K. Bhanu Sankara Rao M. Vijayalakshmi S.L. Mannan D.H. Shastry 《Metallurgical and Materials Transactions A》1992,23(6):1751-1761
Low-cycle fatigue (LCF) responses of NIMONIC PE-16 for various prior microstructures and strain amplitudes have been evaluated
and the fatigue behavior has been explained in terms of the operative deformation mechanisms. Total strain-controlled LCF
tests were performed at 923 K on samples possessing three different prior microstructures: alloy A in solution-annealed condition
(free of γ′ and carbides), alloy B with double aging treatment (spherical γ′ of 18-nm diameter and M23C6), and alloy C with another double aging treatment (γ′ of size 35 nm, MC and M23C6). All three microstructures exhibited an intial cyclic hardening followed by a period of gradual softening at 923 K. Coffin-Manson
plots describing the plastic strain amplitudevs number of reversals to failure showed that alloy A had maximum fatigue life while C showed the least. Alloy B exhibited a
two-slope behavior in the Coffin-Manson plot over the strain amplitudes investigated. This has been ascribed to the change
in the degree of homogeneity of deformation at high and low strain amplitudes. Transmission electron microscopic studies were
carried out to characterize the various deformation mechanisms and precipitation reactions occurring during fatigue testign.
Fresh precipitation of fine γ′ was confirmed by the development of “mottled contrast” in alloy C. Evidence for the shearing of the ordered γ′ precipitates was revealed by the presence of superdislocations in alloy C. Repeated shearing during cyclic loading led to
the reduction in the size of the γ′ and consequent softening. Coarser γ′ precipitates were associated with Orowan loops. The observed fatigue behavior has been rationalized based on the micromechanisms
stated above and on the degree of homogenization of slip assessed by slipband spacing measurements on tested samples. 相似文献
10.
M. J. Cieslak J. J. Stephens M. J. Carr 《Metallurgical and Materials Transactions A》1988,19(3):657-667
The weldability and weld metal microstructure of Cabot Alloy 214 have been investigated with a variety of experimental and
analytical techniques. These include Varestraint hot crack testing, hot ductility testing, pulsed Nd:YAG laser welding, scanning
and analytical electron microscopy, electron microprobe analysis, and X-ray diffraction. A heat of Alloy 214 containing intentionally
alloyed B (0.003 wt pct) and Zr (0.07 wt pct) was much more sensitive to both fusion zone hot cracking as quantified by the
Varestraint test and to simulated heat-affected-zone (HAZ) cracking as quantified by hot ductility testing than a heat of
Alloy 214 containing no intentionally added B (0.0002 wt pct) or Zr (0.02 wt pct). Scanning electron microscopy of the high
B and Zr alloy showed the presence of dendritically-shaped, Zr-rich constituents in interdendritic regions in the gas-tungsten-arc
(GTA) welds. Electron microprobe analysis of these welds revealed a segregation pattern of Cr, Al, Mn, and Zr enrichment in
interdendritic regions and Ni and Fe enrichment in dendrite core regions. Analytical electron microscopy revealed the presence
of ZrX (X = B, C, N, O), M23C6, andγ′ in the fusion zone of GTA weld specimens,γ′ was also found in the as-received base metal and in the GTA weld HAZ. X-ray diffraction analysis of extractions from the
high B and Zr GTA weld metal also indicated the presence of a ZrX-type constituent. The results of this study are in qualitative
agreement with earlier work performed on alloys such as NIMONIC 90 and INCONEL 718∗ relative to the detrimental effect of B and Zr additions on fusion zone and HAZ hot cracking susceptibility.
Formerly with Sandia National Laboratories, Albuquerque, NM 相似文献
11.
12.
The effects of carbon content and ausaging on austenite γ ↔ martensite (α′) transformation behavior and reverse-transformed
structure were investigated in Fe-32Ni-12Co-4Al and Fe-(26,28)Ni-12Co-4Al-0.4C (wt pct) alloys. TheM
s
temperature, the hardness of γ phase, and the tetragonality of α′ increase with increasing ausaging time, and these values
are higher in the carbon-bearing alloys in most cases. The γ → α′ transformation behavior is similar to that of thermoelastic
martensite; that is, the width of α′ plate increases with decreasing temperature in all alloys. The αt’ → γ reverse transformation
temperature is lower in the carbon-bearing alloys, which means that the shape memory effect is improved by the addition of
carbon. The maximum shape recovery of 84 pct is obtained in Fe-28Ni-12Co-4Al-0.4C alloy when the ausaged specimen is deformed
at theM
s
temperature and heated to 1120 K. There are two types of reverse-transformed austenites in the carbon-bearing alloy. One
type is the reversed y containing many dislocations which were formed when the γ/α′ interface moved reversibly. The plane
on which dislocations lie is (01 l)γ if the twin plane is (112)α′. The other type of reverse-transformed austenite exhibits γ islands nucleated within the α′ plates. 相似文献
13.
Liu Cheng A. Böttger E. J. Mittemeijer 《Metallurgical and Materials Transactions A》1992,23(4):1129-1145
The tempering behavior of ternary FeCN martensitic specimens, with a total amount of interstitials of about 5.5 at. pct and
carbon and nitrogen contents between about 1.5 and 3.9 at. pct, was investigated in the temperature range 110 to 830 K. Analysis
of the corresponding changes in crystalline structure (X-ray diffraction), volume (dilatometry), and hardness and enthalpy
(calorimetry) revealed that the following processes occurred: (a) martensitic transformation of retained austenite between
110 and 200 K; (b) redistribution of interstitials in martensite up to 370 K; (c) formation of nitrogen containing α′ precipitates
and carbon containing ε/η) precipitates between 370 and 450 K; (d) conversion of α′ nitride into γ′ nitride and coarsening
of ε/η carbide between 450 and 560 K; (e) decomposition of retained austenite above 540 K; and (f) conversion of ε/η carbide
into cementite above 570 K. Significant precipitation of carbon and nitrogen together, as nitrocarbides or carbonitrides,
was not observed. From a comparison with the tempering behavior of binary FeC and FeN alloys of similar interstitial content,
it was concluded for the ternary FeCN alloy that the transformation of the transition nitride (α′) into the “equilibrium”
nitride (γ′) was advanced and that the precipitation of the transition carbide(ε/η) and its conversion into the equilibrium carbide (cementite) and the decomposition of retained austenite were retarded.
Formerly Graduate Student, Laboratory of Metallurgy, Delft University of Technology. 相似文献
14.
Tatsuya Fukino Sadahiro Tsurekawa Yasuhiro Morizono 《Metallurgical and Materials Transactions A》2011,42(3):587-593
This article presents in-situ observation of ferrite (α)/austenite (γ) phase transformation in an Fe-8.5 at. pct Ni alloy deformed by rolling using an automated scanning electron microscopy/energy
backscattered diffraction (SEM/EBSD) system. During heating, recrystallization in α phase and α → γ phase transformation independently occurred. The γ grains nucleated in unrecrystallized α grains were most probably incorporated into the grain interior of recrystallized α grains. They did not have any specific orientation relation (OR) with recrystallized α grains and grew in an isotropic manner. On the other hand, the intragranular γ grains nucleated in recrystallized α grains had a Kurdjumov–Sachs (K-S) OR with the α grains and grew in a considerably anisotropic manner. They preferentially grew along the common direction of surface traces
of {110}
α
/{111}
γ
. Approximately half of grain boundary (GB) allotriomorphs had either the K-S OR or the Nishiyama–Wasserman (N-W) OR with
the parent α grains. The γ allotriomorphs predominantly grew into the α grain having the special OR with themselves. The GB character distribution of γ phase at high temperatures was measured. The fraction of CSL boundaries was as high as 63 pct, particularly that of Σ3 grain
boundaries (GBs) was 54 pct. 相似文献
15.
Sang H. Kim Nack J. Kim H. H. Chung Sung G. Pyo S. J. Hwang 《Metallurgical and Materials Transactions A》1998,29(9):2273-2283
The present study is concerned with γ-(Ti52Al48)100−x
B
x
(x=0, 0.5, 2, 5) alloys produced by mechanical milling/vacuum hot pressing (VHPing) using melt-extracted powders. Microstructure
of the as-vacuum hot pressed (VHPed) alloys exhibits a duplex equiaxed microstructure of α2 and γ with a mean grain size of 200 nm. Besides α2 and γ phases, binary and 0.5 pct B alloys contain Ti2AlN and Al2O3 phases located along the grain boundaries and show appreciable coarsening in grain and dispersoid sizes during annealing
treatment at 1300 °C for 5 hours. On the other hand, 2 pct B and 5 pct B alloys contain fine boride particles within the γ
grains and show minimal coarsening during annealing. Room-temperature compressing tests of the as-VHPed alloys show low ductility,
but very high yield strength >2100 MPa. After annealing treatment, mechanically milled alloys show much higher yield strength
than conventional powder metallurgy and ingot metallurgy processed alloys, with equivalent ductility to ingot metallurgy processed
alloys. The 5 pct B alloy with the smallest grain size shows higher yield strength than binary alloy up to the test temperature
of 700 °C. At 850 °C, 5 pct B alloy shows much lower strength than the binary alloy, indicating that the deformation of fine
5 pct B alloy is dominated by the grain boundary sliding mechanism.
This article is based on a presentation made in the symposium “Mechanical Behavior of Bulk Nanocrystalline Solids,” presented
at the 1997 Fall TMS Meeting and Materials Week, September 14–18, 1997, in Indianapolis, Indiana, under the auspices of the
Mechanical Metallurgy (SMD), Powder Materials (MDMD), and Chemistry and Physics of Materials (EMPMD/SMD) Committees. 相似文献
16.
M. Valsan D. H. Sastry K. Bhanu sankara Rao S. L. Mannan 《Metallurgical and Materials Transactions A》1994,25(1):159-171
Strain-rate effects on the low-cycle fatigue (LCF) behavior of a NIMONIC PE-16 superalloy have been evaluated in the temperature
range of 523 to 923 K. Total-strain-controlled fatigue tests were performed at a strain amplitude of ±0.6 pct on samples possessing
two different prior microstructures: microstructure A, in the solution-annealed condition (free of γ′ and carbides); and microstructure
B, in a double-aged condition with γ′ of 18-nm diameter and M23C6 carbides. The cyclic stress response behavior of the alloy was found to depend on the prior microstructure, testing temperature,
and strain rate. A softening regime was found to be associated with shearing of ordered γ′ that were either formed during
testing or present in the prior microstructure. Various manifestations of dynamic strain aging (DSA) included negative strain
rate-stress response, serrations on the stress-strain hysteresis loops, and increased work-hardening rate. The calculated
activation energy matched well with that for self-diffusion of Al and Ti in the matrix. Fatigue life increased with an increase
in strain rate from 3 × 10-5 to 3 × 10-3 s-1, but decreased with further increases in strain rate. At 723 and 823 K and low strain rates, DSA influenced the deformation
and fracture behavior of the alloy. Dynamic strain aging increased the strain localization in planar slip bands, and impingement
of these bands caused internal grain-boundary cracks and reduced fatigue life. However, at 923 K and low strain rates, fatigue
crack initiation and propagation were accelerated by high-temperature oxidation, and the reduced fatigue life was attributed
to oxidation-fatigue interaction. Fatigue life was maximum at the intermediate strain rates, where strain localization was
lower. Strain localization as a function of strain rate and temperature was quantified by optical and scanning electron microscopy
and correlated with fatigue life. 相似文献
17.
Alfirano Shingo Mineta Shigenobu Namba Takashi Yoneda Kyosuke Ueda Takayuki Narushima 《Metallurgical and Materials Transactions A》2011,42(7):1941-1949
The effect of the addition of Si or Mn to ASTM F75 Co-28Cr-6Mo-0.25C alloys on precipitate formation as well as dissolution
during solution treatment was investigated. Three alloys—Co-28Cr-6Mo-0.25C-1Si (1Si), Co-28Cr-6Mo-0.25C-1Mn (1Mn), and Co-28Cr-6Mo-0.25C-1Si-1Mn
(1Si1Mn)—were heat treated from 1448 K to 1548 K (1175 °C to 1275 °C) for a holding time of up to 43.2 ks. In the case of
the as-cast 1Si and 1Si1Mn alloys, the precipitates were M23C6-type carbide, η phase (M6C-M12C–type carbide), and π phase (M2T3X-type carbide with a β-Mn structure), while in the case of the as-cast 1Mn alloy, M23C6-type carbide and η phase were detected. The 1Si and 1Si1Mn alloys required longer heat-treatment times for complete precipitate
dissolution than did the 1Mn alloys. During the solution treatment, blocky dense M23C6-type carbide was observed in all the alloys over the temperature range of 1448 K to 1498 K (1175 °C to 1225 °C). At the heat-treatment
temperature of 1523 K (1250 °C), starlike precipitates with stripe patterns—comprising M23C6-type carbide and metallic face-centered-cubic (fcc) γ phase—were detected in the 1Si and 1Si1Mn alloys. A π phase was observed
in the 1Si and 1Si1Mn alloys heat treated at 1523 K and 1548 K (1250 °C and 1275 °C) and in the 1Mn alloy heat treated at
1548 K (1275 °C); its morphology was starlike-dense. The addition of Si appeared to promote the formation of the π phase
in Co-28Cr-6Mo-0.25C alloys at 1523 K and 1548 K (1250 °C and 1275 °C). Thus, the addition of Si and Mn affects the phase
and morphology of the carbide precipitates in biomedical Co-Cr-Mo alloys. 相似文献
18.
19.