共查询到20条相似文献,搜索用时 15 毫秒
1.
M. F. Henry Y. S. Yoo D. Y. Yoon J. Choi 《Metallurgical and Materials Transactions A》1993,24(8):1733-1743
The growth pattern of γ precipitates in the grains and at the grain boundaries has been investigated in a Ni-24Co-4Al-4Ti-5Cr-5Mo
(weight percent) alloy of very small lattice misfit between the precipitate and the matrix phases under varying heat-treatment
conditions. When aged at temperatures lower than the solvus temperature (T
s = 1150 °C) by more than 30 °C after direct cooling from the solution-treatment temperature, the nucleation density is high.
In this condition, the supersaturation is quickly removed because of the overlapping diffusion fields and the precipitates
undergo Ostwald ripening from the early stage. The precipitates then have an equilibrium shape of spheres in the grains and
truncated spheres at nearly straight grain boundaries. The precipitates at the grain boundaries are coherent with one of the
grains, and their number density is not much larger than that in the grains, apparently because of a large contact angle (about
150 deg) with the grain boundary. Quenching the alloy after the solution treatment and aging at any temperature also produce
high precipitate number density and equilibrium shapes. When aged at temperatures just belowT
s (above 1140 °C), the nucleation density is low, the precipitates grow dendritically in the grains, and the grain boundaries
become serrated. The observed dendritic growth characteristics do not quantitatively agree with the predictions of Mullins
and Sekerka theory, but the discrepancy may be due to the uncertainties in both the observed and calculated quantities. By
deeply etching the matrix, it is shown that the grain boundary serration is produced by the precipitates growing preferentially
in the direction of the incoherent boundary because of the rapid solute diffusion along the grain boundary. The dendritic
growth and grain boundary serration can be obtained also by slowly cooling through the temperature range just belowT
s. 相似文献
2.
《Acta Metallurgica Materialia》1992,40(5):1051-1067
The morphology of NiFe2O4 precipitates in a NiO matrix has been studied using TEM. The spinel precipitates had a dendritic morphology when a polycrystalline sample of Fe-doped NiO was cooled at a constant rate from above the solvus temperature. They nucleate as octahedra bounded by {111} interfaces which then grow by a ledge mechanism until they reach a critical size and this shape becomes unstable. The precipitates then adopt a dendritic morphology characterized by branches in the 〈001〉 directions. The branches are bounded by {111} and {011} facets. HREM showed that during the initial stages of growth the interface is composed of a series of closely spaced ledges which are typically one spinel lattice-spacing high. Later, the ledge spacing decreases resulting in large flat {111} and {011} facets. Secondary branches were observed to form under large supersaturations of Fe when the precipitate spacing was large. The shape of the precipitates during the early stages of dendritic growth are very similar to those predicted by a Monte Carlo simulation which incorporates diffusional growth and anisotropic interface kinetics. The dendritic morphology is associated with the small lattice misfit, the large diffusion rate in Fe-doped NiO and the large undercooling necessary for nucleation. The diffusion rate is particularly large due to the concentration of cation vacancies being approximately half of the iron concentration. 相似文献
3.
D. M. Vanderwalker J. B. Vander Sande 《Metallurgical and Materials Transactions A》1981,12(10):1787-1793
Weak beam microscopy was used to examine the precipitation of the 17 phase (MgZn2) on low angle grain boundaries which had formed in an Al-2.84 wt pct Zn-1.95 wt pct Mg alloy. The low angle boundaries observed
in the partially recovered structure can be separated into two categories, planar and nonplanar. The planar boundaries form
either lozenge or hexagonal configurations. The nonplanar boundary dislocation intersections form a “chair”-shaped figure.
The geometry of the dislocation strain fields in the boundaries controls the precipitate growth and the size, shape, and position
of the precipitates on each boundary type. The lozenge boundary can have both equiaxed and lath shaped precipitates growing
upon it. The equiaxed precipitates form only at four dislocation junctions because at this position the strain field distribution
is symmetric. The lath precipitates are restricted to grow along dislocations in the boundary whose line direction is coincident
with the long axis of the precipitate since in these pinned dislocation segments there are high line tension forces present
to resist dislocation bowing. The “chair” boundary contains only lath precipitates, which begin to grow from alternate three
dislocation intersections and continue growth along the dislocation line. The contrast observed bordering the lath on each
side is produced by lattice dislocations. A proposed explanation for the above observations involves assuming that the dislocations
in the chair boundary dissociate into Lomer-Cottrell locks which have constricted-extended node pairs. A lath can begin growth
from the constricted node forcing the stair rod dislocation to dissociate. The reaction products of the stair rod can combine
with the partials in the Lomer-Cottrell lock to form the observed lattice dislocations. 相似文献
4.
Stanley Shapiro Derek E. Tyler Richard Lanam 《Metallurgical and Materials Transactions B》1974,5(11):2457-2469
The precipitation phenomena in the alloy copper-20 pct nickel-20 pct manganese have been investigated. Utilizing transmission
electron microscopy as the principal tool; the effects of aging temperature and time as well as prior cold work were studied.
For all aging temperatures the reaction products are the solute depleted fcc solid solution and an ordered structure with
fct symmetry. Three aging temperatures characterized by different precipitate morphologies were studied. At 350°C discontinuous
precipitation is the predominant mode of decomposition. Precipitate colonies nucleate at grain and twin boundaries and eventually
grow through the entire structure. Microtwinning of the colony matrix accompanies the precipitation reaction. At 450°C both
grain boundary nucleated discontinuous precipitates and fine periodic homogeneous arrays are observed in the absence of cold
work. The fine periodic arrays coarsen and eventually form nuclei for the ordered fct phase. The coarsening of the periodic
arrays prohibits the growth of the discontinuous precipitate early in the process, so only a small volume fraction of discontinuous
precipitate is formed at the grain boundaries. Aging subsequent to cold work results in ordered, fct precipitates heterogeneously
nucleated on dislocations. At 500°C no precipitate is observed in the absence of cold work. When aging is preceded by cold
work, the ordered fct phase appears as heterogeneously nucleated Widmanstatten laths. No grain boundary nucleated colonies
are observed at this temperature. 相似文献
5.
G. Chen J. K. Chen J. K. Lee W. T. Reynolds 《Metallurgical and Materials Transactions A》1994,25(10):2073-2082
The formation rate of growth ledges on a faceted precipitate strongly affects the growth kinetics and the shape of the precipitate.
An Eshelby-type model is used to compare the strain energy associated with the nucleation of a ledge on different facet planes
of a body-centered cubic (bcc) precipitate in face-centered cubic (fcc) matrix. Ledge nucleation is only likely at facet areas
where the interaction energy between the ledge and the precipitate is negative. The strain energy for ledge formation is not
symmetric on any of the facet planes, but it is symmetric about the center of the precipitate. For coherent precipitates comparable
to those observed in the Ni-Cr system, ledges form with the lowest strain energy on the broad facet of the precipitate implying
that precipitate thickening should occur faster than lengthening and widening. A procedure for modifying the Eshelby model
is suggested in order to allow strain-energy calculations of partially coherent precipitates. The strain energy for ledge
formation on at least one type of partially coherent lath is lowest for a ledge located on the facet perpendicular to the
crystallographic invariant line (IL). This situation favors precipitate lengthening in the invariant line direction. 相似文献
6.
《Acta Metallurgica》1985,33(4):649-658
High-resolution electron microscopy was used to study the interfacial structure of γ′ precipitates in an Al-15 wt% Ag alloy aged at 350°C. The results of these studies show that:
- 1.(1) all ledges are multiples of two {111} planes high, supporting the theory and conventional transmission electron microscopy observations that plate thickening occurs by passage of Shockley partial dislocations on alternate {111} planes
- 2.(2) most ledges are more than just two planes high, indicating a strong tendency toward diffusional and/or elastic interactions
- 3.(3) the terraces between ledges are atomically flat and ledges are uniformly stepped-down from the centers to the edges of isolated precipitates as predicted by the general theory of precipitate morphology
- 4.(4) the {111} planes are continuous across the edges of ledges, indicating that they are largely coherent and not disordered as treated in most kinetic analyses, and
- 5.(5) the edges of precipitate plates appear to be composed of similar two-plane ledges arranged vertically above one another and hence, may grow by the same mechanism of atomic attachment as ledges on the broad faces.
7.
Interphase boundary structure of bcc precipitates formed at fcc-matrix grain boundaries in a Ni-43 mass pct Cr alloy has been
studied experimentally using transmission electron microscopy (TEM) and theoretically analyzed using a geometrical model (near-coincidence
site (NCS) lattice model). On both sides of the grain boundary, regardless of the presence of near-rational orientation relationship
Kurdjumov-Sachs(K-S) or Nishiyama-Wassermann(N-W), precipitate(bcc)/matrix(fcc) interphase boundaries exhibit planar facets
that often contain ledges and regularly aligned, line defects. The analysis indicates that the facet planes correspond to
the planes of higher NCS densities for either of the near-rational orientation relationships or the irrational orientation
relationships. Similar results are obtained for the precipitate/matrix interface, which lost its original orientation relationship
through matrix recrystallization. It is suggested that some partial coherency is expected even for interfaces with an irrational
orientation relationship formed during grain boundary precipitation.
This article is based on a presentation made at the symposium entitled “The Mechanisms of the Massive Transformation,” a part
of the Fall 2000 TMS Meeting held October 16–19, 2000, in St. Louis, Missouri, under the auspices of the ASM Phase Transformations
Committee. 相似文献
8.
A study has been made of the crystallography of proeutectoid ferrite precipitated at high angle austenite grain boundaries in an Fe-0.47 pct C alloy, isothermally transformed above the eutectoid temperature. Using the Kossel X-ray microdiffraction technique, ferrite orientations have been determined in relation to the orientations of both matrix grains at the grain boundary; the austenite orientations were derived indirectly. It has been observed that the ferrite, irrespective of morphology, possessed an orientation relationship with respect to at least one matrix grain which approximated to the Kurdjumov-Sachs and, to a lesser extent, the Nishiyama relationships. At several of the boundaries the ferrite was allowed to possess an orientation relationship with both matrix grains and it has been shown that the ferrite orientation at these boundaries was often influenced by the orientation of both matrix grains. Several instances have been observed in which preferential growth occurred into the austenite grain with which the precipitate did not have a specific orientation relationship. The results have been compared with the work of Ryder, Pitsch and Mehl,5 and factors governing the observation of Widmanstatten sideplates have been discussed. 相似文献
9.
A study has been made of the crystallography of proeutectoid ferrite precipitated at high angle austenite grain boundaries
in an Fe-0.47 pct C alloy, isothermally transformed above the eutectoid temperature. Using the Kossel X-ray microdiffraction
technique, ferrite orientations have been determined in relation to the orientations of both matrix grains at the grain boundary;
the austenite orientations were derived indirectly. It has been observed that the ferrite, irrespective of morphology, possessed
an orientation relationship with respect to at least one matrix grain which approximated to the Kurdjumov-Sachs and, to a
lesser extent, the Nishiyama relationships. At several of the boundaries the ferrite was allowed to possess an orientation
relationship with both matrix grains and it has been shown that the ferrite orientation at these boundaries was often influenced
by the orientation of both matrix grains. Several instances have been observed in which preferential growth occurred into
the austenite grain with which the precipitate did not have a specific orientation relationship. The results have been compared
with the work of Ryder, Pitsch and Mehl,5 and factors governing the observation of Widmanstatten sideplates have been discussed. 相似文献
10.
Crystallographic and mechanistic aspects of growth by shear and by diffusional processes 总被引:1,自引:0,他引:1
H. I. Aaronson T. Furuhara J. M. Rigsbee W. T. Reynolds J. M. Howe 《Metallurgical and Materials Transactions A》1990,21(9):2369-2409
Growth by shear and by diffusional processes, both taking place predominantly by means of ledge mechanisms, are reviewed for
the purpose of distinguishing critically between them at the atomic, microscopic, and macroscopic levels. At the atomic level,
diffusional growth is described as individual, poorly coordinated, thermally activated jumps occurring in the manner of biased
random walk, whereas growth by shear is taken to be tightly coordinated “glide” of atoms to sites in the product phase which
are “predestined” to within the radius of a shuffle. Obedience to the invariant plane strain (IPS) surface relief effect and
the transformation crystallography prescribed by the phenomenological theory of martensite is shown to be an unsatisfactory
means of distinguishing between these two fundamentally different atomic growth mechanisms. In substitutional alloys, continuous
differences in compositionand in long-range order (LRO) from the earliest stages of growth onward are concluded to be the most useful phenomenological
approach to achieving differentiation. At a more fundamental level, however, the details of interphase boundary structure
are the primary determinant of the operative mechanism (when the driving force for growth is sufficient to permit either to
occur). In the presence of a stacking sequence change across the boundary, terraces of ledges are immobile irrespective of
their structural details during diffusional growth. Kinks on the risers of superledges are probably the primary sites for
diffusional transfer of atoms across interphase boundaries. In martensitic transformations, on the other hand, terraces containing
edge dislocations in glide orientation or pure screw dislocations are mobile and accomplish the lattice invariant deformation
(LID), though probably only after being overrun by a transformation dislocation. Risers associated with transformation dislocations
are also mobile and cause the crystal structure change during growth by shear. The successes achieved by the invariant line
(IL) component of the phenomenological theory of martensite in predicting precipitate needle growth directions and precipitate
plate habit planes (Dahmen and co-workers) are here ascribed to the rate of ledge formation usually being a minimum at an
interface containing an IL, primarily because nuclei formed sympathetically at this boundary orientation are likely to have
the highest edge energies. Since martensite plate broad faces also contain the IL, the ability of the phenomenological theory
to predict the habit plane and the orientation relationships of both precipitate and martensite plates is no longer surprising.
The IPS relief effect at a free surface can be generated by precipitate plates when growth ledges are generated predominantly
on only one broad face and only one of several crystallographically equivalent Burgers vectors of growth ledges is operative.
Both pReferences probably result from larger reductions in transformation strain energy for the particular geometry with which
a given plate intercepts the free surface. Precipitate morphology often differs significantly from that of martensite even
if precipitates are plate-shaped and can readily differ very greatly. Whereas martensite morphology is determined by the need
to minimize shear strain energy, that of precipitates derives from the more flexible base of the interphase boundary orientation-dependence
of the reciprocal of the average intergrowth ledge spacing, as modified by both the orientation-dependence of interkink spacing
on growth ledge risers and the spacing/ height ratio dependence of diffusion field overlap upon growth kinetics.
This paper is based on a presentation made in the symposium “Interface Science and Engineering” presented during the 1988
World Materials Congress and the TMS Fall Meeting, Chicago, IL, September 26–29, 1988, under the auspices of the ASM-MSD Surfaces
and Interfaces Committee and the TMS Electronic Device Materials Committee. 相似文献
11.
G. Spanos W. T. Reynolds R. A. Vandermeer 《Metallurgical and Materials Transactions A》1991,22(6):1367-1380
The influence of interphase boundary ledges on the growth and morphology of proeutectoid ferrite and proeutectoid cementite
precipitates in steel is examined. After reviewing current theoretical treatments of growth by the ledge mechanism, investigations
that clearly document the presence and motion of ledges with thermionic emission electron microscopy (THEEM) and transmission
electron microscopy (TEM) are reviewed. A fundamental distinction is made between two types of ledges: (1) mobile growth ledges
whose lateral migration displaces the inter-phase boundary and (2) misfit-compensating structural ledges. Both types of ledges
strongly affect the apparent habit plane and aspect ratio of precipitate plates. Agreement between measured growth rates of
proeutectoid ferrite and cementite (plates and allotriomorphs) and predicted growth kinetics assuming volume diffusion-controlled
migration of ledge-free disordered boundaries is shown to be consistently poor. Physically realistic growth models should
incorporate the ledge mechanism. More accurate comparisons of the growth models with experimental data will need to account
for observed ledge heights, interledge spacings, and ledge velocities. In this vein, the sluggish growth kinetics of cementite
allotriomorphs observed in an Fe-C alloy are shown to be quantitatively consistent with a strong increase in interledge spacing
with time.
This paper is based on a presentation made in the symposium “The Role of Ledges in Phase Transformations” presented as part
of the 1989 Fall Meeting of TMS-MSD, October 1–5, 1989, in Indianapolis, IN, under the auspices of the Phase Transformations
Committee of the Materials Science Division, ASM INTERNATIONAL. 相似文献
12.
R. W. Fonda M. A. Mangan G. J. Shiflet 《Metallurgical and Materials Transactions A》1998,29(8):2101-2110
The effect of undercooling on the morphology of the cellular precipitation reaction in Cu-3 Pct Ti is examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and serial sectioning experiments. The reaction front formed at small undercooling, which exhibits strong faceting of the precipitate growth interfaces, gradually changes with increasing undercooling to a smoothly curved reaction front with concave precipitate growth interfaces and convex grain boundary segments. This concealment of the faceted reaction front appears to be due to the rapid accumulation of growth ledges with increasing undercooling. This study also indicates that the cellular precipitation reaction, at small undercooling, is initiated by Widmanstätten precipitation. At larger undercoolings, a second mechanism is responsible for cellular genesis. Finally, contrary to accepted models of colony development, serial sectioning experiments show that nucleation of additional lamellae may occur at the faces of existing lamellae, from where they extend laterally to achieve the characteristic interlamellar spacing for that temperature. 相似文献
13.
在 Gleeble- 3500型热模拟试验机上,利用应力松弛试验研究了含磷高强IF钢第二相粒子的析出行为。结果表明,微合金元素析出钉扎住了位错与晶界,导致应力松弛曲线呈现出3个阶段的特征。试验用钢的PTT曲线呈现典型的“C”曲线形状,最快析出的鼻子点温度约为850 ℃,在此温度下,第二相粒子析出开始时间与结束时间分别为14和246 s,随着弛豫时间的增加,第二相粒子的析出数量逐渐增多,形貌逐渐粗化,析出粒子为Ti4C2S2 和TiC,主要呈圆形颗粒形貌。由于试验钢种采用磷强化,在析出的第二相粒子中存在棒形和长条形FeTiP,同时由于磷的晶界偏聚,所以FeTiP同样存在晶界析出的规律。 相似文献
14.
《Acta Metallurgica》1986,34(12):2399-2409
Grain boundary precipitation in a commercial alloy 7075 Al has been studied using transmission electron microscopy. The crystallography of the precipitates and the matrix is characterized in terms of the misorientation between the grains and the orientation of the grain boundary. The only particles observed at both low and high angle boundaries were precipitates of the equilibrium η phase. Precipitation tends to occur by the establishment of a crystallographic orientation relationship with respect to one grain. A single variant is normally found at a boundary at which copious precipitation occurs; this is frequently the case at low angle boundaries. The grain boundary orientation plays the decisive role on the nucleation of the precipitates. Whenever the boundary plane is close to the habit plane of particular variant, copious nucleation of that variant occurs. The grain boundary orientation also plays an important role in precipitate growth through its influence on the mobility of the nucleus-matrix interface, which strongly depends on the orientation of the interface. 相似文献
15.
Creep induced instability of strengthening precipitates at grain boundaries is of general concern in the applications of many high temperature alloys. Having shown that the general validity of the existing mechanism for such an instability in nickel-base superalloys may be considered suspect, this paper reports and discusses the effects of both tensile and compressive creep on γ′ grain boundary precipitate morphology in an alloy consisting of γ′ (Ni3Al) precipitates in a γ (nickel solid solution) matrix. We find that the uniform distribution of γ′ precipitates is altered by the application of uniaxial creep stress, with the stress-induced precipitate morphology depending strongly on stress sense. Tensile creep results in the dissolution of γ′ precipitates at grain boundaries aligned more or less transverse to the stress axis, with an accompanying increase in volume fraction of γ′ precipitates at grain boundaries oriented parallel to, or almost parallel to the stress axis. In contrast, the reverse change in morphology occurs during compressive creep. The observed morphology changes and their dependence on stress sense are shown to be consistent with the flow of chromium atoms from grain boundaries that are under normal compression towards grain boundaries that are under normal tension. The results conclusively demonstrate that Herring-Nabarro type diffusion in multiphase, polycrystalline alloys can cause chemical changes in grain boundary regions which, in the extreme, result in phase changes at grain boundaries. The results and proposed mechanism are discussed in terms of the findings of other investigations. 相似文献
16.
T. Furuhara H. J. Lee E. S. K. Menon H. I. Aaronson 《Metallurgical and Materials Transactions A》1990,21(6):1627-1643
Interphase boundary structures generated during diffusional transformations in Ti-base alloys, especially the proeutectoid
α and eutectoid reactions in a β-phase matrix, are reviewed. Partially coherent boundaries are shown to be present whether
the orientation relationship between precipitate and matrix phases is rational or irrational. Usually, these structures include
both misfit dislocations and growth ledges. However, grain boundary α allotriomorphs (GBA’s) do not appear to develop misfit
dislocations at partially coherent boundaries. Evidently, these dislocations can be replaced by ledges which provide a strain
vector in the plane of the interphase boundary. The bainite reaction in Ti-X alloys produces a mixture of eutectoid α and
eutectoid intermetallic compound. Both eutectoid phases are partially coherent with theβ matrix, and both grow by means of the ledge mechanism, though unlike pearlite the ledge systems of the two phases are structurally
independent. Even after deformation and recrystallization, the boundaries between the eutectoid phases and theβ matrix, as well as between these phases, are partially coherent. Titanium and zirconium hydrides have partially coherent
interphase boundaries with respect to theirβ matrix. The recent observation of ledgewise growth of γ TiH within situ high-resolution transmission electron microscopy (HRTEM) suggests that, repeated suggestions to the contrary, these hydrides
do not grow by means of shear transport of Ti atoms at rates paced by hydrogen diffusion.
This paper is based on a presentation made in the symposium “Interfaces and Surfaces of Titanium Materials” presented at the
1988 TMS/AIME fall meeting in Chicago, IL, September 25–29, 1988, under the auspices of the TMS Titanium Committee. 相似文献
17.
《Acta Metallurgica Materialia》1992,40(2):275-283
An energetically unfavourable situation can develop when coherent particles are bypassed by migrating grain boundaries. This is due to the precipitates being exposed to incoherent interfaces in the new matrix. In this work, the rotation of precipitate particles to low energy, coherent orientations in the new matrix is shown to be one of several possible responses to this situation. A physical and kinetic model for the rotation is put forward and the results of calculations of rotation rate presented. It is shown that particle rotation is controlled by interfacial diffusion and depends upon alloy composition, time, temperature and particle size and shape. The possibility of particle rotation occurring during particle/boundary contact is also discussed. This is shown to depend upon the nature of the boundary type. Generally, boundaries moving under large driving pressures with high velocities (e.g. phase transformation interfaces), are less likely to allow rotation during particle/boundary contact than less mobile boundaries such as those in grain growth and recrystallization. Experimental results from SAD and TEM of a Ti stabilized austenitic stainless steel containing a dispersion of coherent TiC precipitates is also presented and supports the particle rotation model. 相似文献
18.
Noémie Ott Shravan K. Kairy Yuanming Yan Nick Birbilis 《Metallurgical and Materials Transactions A》2017,48(1):51-56
The grain boundary microstructure of Al-Cu-Li alloy AA2050 was investigated for different isothermal aging times to rationalize intergranular corrosion (IGC) characteristics. In the underaged condition, the dominant grain boundary precipitates are fine T1 (Al2CuLi). Extended aging revealed that grain boundaries were decorated by large T1 precipitates and S′ phase (Al2CuMg), with S′ growth not dimensionally constrained. Such a transition in the precipitate type at grain boundaries is a unique feature of the Al-Cu-Li system. 相似文献
19.
通过一系列实验研究了Monel K-500合金的冲击韧性。结果表明,合金经550~650℃时效后其冲击断口呈沿晶形貌;在750~850℃时效时,其冲击韧性与强度呈正相关关系。根据对合金在不同热处理状态的析出相形态及分布的研究,揭示了形成这些现象的原因。合金在550~650℃时效时,在晶内析出的γ’相呈球状均匀分布,而在部分晶界附近的γ’相呈条棒状或排成帘状垂直于晶界分布,由此导致时效态合金在断裂时,裂纹沿晶界扩展。在750~850℃时效会导致合金形成大量沿晶界网状分布的二次MC相,从而降低合金的冲击韧性。 相似文献
20.
Ömer N. DOĞAN G. M. Michal H. -W. Kwon 《Metallurgical and Materials Transactions A》1992,23(8):2121-2129
The growth behavior of austenite grains in the presence of A1N precipitates varies with the temperature and time of anneal.
To study this behavior, two iron alloys, (in weight percent) a 0.1 carbon base chemistry with 0.03A1/0.01N and 0.09A1/0.04N,
respectively, were annealed between 1000 °C and 1200 °C for times of up to 180 minutes. Using optical microscopy, as many
as 1000 austenite grains per heat-treatment condition were measured. Conditions of sup- pressed, abnormal, and uniform grain
growth were observed. Using an extraction replica tech- nique, the size, shape, and distribution of the A1N particles were
determined using transmission electron microscopy (TEM). The largest grain boundary curvatures calculated, using the Hellman-
Hillert pinning model, were in close agreement with independent calculations of curvatures using the grain size data. The
largest grains in the lognormal size distribution of austenite grains were found to be the ones with the potential to grow
to abnormally large sizes. 相似文献