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1.
Martin C. Mataya Eric R. Nilsson Elliot L. Brown George Krauss 《Metallurgical and Materials Transactions A》2003,34(8):1683-1703
Stress-strain behavior and microstructure evolution during hot working of as-cast austenitic stainless steel alloy 316L were
investigated by uniaxial compression of cylindrical specimens at a strain rate of 1 s−1 over the temperature range 1000 °C to 1150 °C and up to a strain of one. The measured flow curves showed monotonic hardening,
indicating that dynamic recrystallization was not important in microstructural evolution. Static recrystallization was observed
to nucleate preferentially at the delta ferrite-austenite interphase boundaries. The recrystallization kinetics of the as-cast
material was compared to a relatively fine-grained wrought 316L material and found to be somewhat slower. However, the difference
between the two material conditions was not nearly as great as previously reported for as-cast and wrought 304L alloy. The
difference in behaviors between 316L and 304L is attributed to the relatively large amount and vermicular morphology of the
delta ferrite phase in the 316L, resulting in a relatively fine effective grain size, compared to the existing coarse columnar
structure, and concomitant enhancement of recrystallization. Compared to wrought 316L, the recrystallization rate of the as-cast
material was relatively sluggish, despite a relatively fine effective grain size. The difference is associated with the 100
orientations of the columnar grains with respect to the compression axis, producing a soft orientation and a reduced rate
of accumulation of dislocation density in the substructure. Also, compared to wrought 316L, the recrystallization rate of
the as-cast material tends to decrease with time, the drop occurring concurrently with spheroidization and dissolution of
the ferrite. It is suggested that (1) movement of the delta ferrite-austenite interphase boundary during spheroidization may
poison incipient recrystallization and (2) dissolution of delta ferrite can locally enrich the austenite matrix in Mo and
Cr, raising the local stacking fault energy and lowering grain boundary mobility to favor recovery over recrystallization
in the vicinity of the ferrite-austenite boundary. A kinetic model for recrystallization was developed and used to simulate
evolution of the first cycle of recrystallization during various thermal-mechanical treatment schedules typically employed
during the primary breakdown of as-cast material. 相似文献
2.
Effect of Initial Grain Size on the Evolution of {001}?100? Texture in Severely Deformed and Annealed High-Purity Nickel 总被引:1,自引:0,他引:1
P. P. Bhattacharjee N. Tsuji R. K. Ray 《Metallurgical and Materials Transactions A》2011,42(9):2769-2780
Development of cube texture ({100}〈001〉) was studied in high-purity Ni (99.97 pct) with widely different starting grain sizes
(~28 and 650 μm) following ultrahigh straining (ε
eq
= 6.4) by accumulative roll bonding (ARB) and annealing. The fine-grained starting material (FGSM) develops a much stronger
cube texture after different annealing treatments as compared to the coarse-grained starting material (CGSM), despite their
very similar bulk deformation texture. A lamellar type deformation structure is observed in both these materials, but the
CGSM shows a more fragmented structure and frequent presence of shear bands. The recrystallization texture of the two materials
differs right from the onset of recrystallization: cube-oriented grains nucleate and grow in the FGSM in sharp contrast to
the nucleation and growth of randomly oriented grains in lamellar as well as shear-banded regions of the CGSM. The observed
differences in the evolution of recrystallization texture in the two materials are discussed with regard to the microstructural
differences and pertinent theories on the formation of cube texture. 相似文献
3.
Hamed Mirzadeh Abbas Najafizadeh Mohammad Moazeny 《Metallurgical and Materials Transactions A》2009,40(12):2950-2958
The hot compression behavior of a 17-4 PH stainless steel (AISI 630) has been investigated at temperatures of 950 °C to 1150 °C
and strain rates of 10−3 to 10 s−1. Glass powder in the Rastegaev reservoirs of the specimen was used as a lubricant material. A step-by-step procedure for
data analysis in the hot compression test was given. The work hardening rate analysis was performed to reveal if dynamic recrystallization
(DRX) occurred. Many samples exhibited typical DRX stress-strain curves with a single peak stress followed by a gradual fall
toward the steady-state stress. At low Zener–Hollomon (Z) parameter, this material showed a new DRX flow behavior, which was called multiple transient steady state (MTSS). At high
Z, as a result of adiabatic deformation heating, a drop in flow stress was observed. The general constitutive equations were
used to determine the hot working constants of this material. Moreover, after a critical discussion, the deformation activation
energy of 17-4 PH stainless steel was determined as 337 kJ/mol. 相似文献
4.
Amir Momeni Kamran Dehghani Golam Reza Ebrahimi Hamid Keshmiri 《Metallurgical and Materials Transactions A》2010,41(11):2898-2904
The hot deformation behavior of AISI 410 martensitic stainless steel was investigated by conducting hot compression tests
between 1173 K (900 °C) and 1423 K (1150 °C) and between strain rates of 0.001 s−1 to 1 s−1. The hyperbolic sine function described the relation well between flow stress at a given strain and the Zener–Hollomon parameter
(Z). The variation of flow stress with deformation temperature gave the average value of apparent activation energy as 448 kJ/mol.
The strain and stress corresponding to two important points associated with flow curve (i.e., peak strain and the onset of steady-state flow) were related to the Z parameter using power-law equations. A model also was proposed based on the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation
to estimate the fractional softening of dynamic recrystallization at any given strain. This model can be used readily for
the prediction of flow stress. The values of n and k, material constants in the JMAK equation, were determined for the studied
material. The strains regarding the peak and the onset of steady-state flow were formulated in term of applied strain rate
and the constants of the JMAK equation. A good agreement was found between the predicted strains and those obtained by the
experimental work. 相似文献
5.
Effect of initial microstructure on plastic flow and dynamic globularization during hot working of Ti-6Al-4V 总被引:1,自引:0,他引:1
Plastic flow behavior and globularization kinetics during subtransus hot working were determined for Ti-6Al-4V with three
different transformed beta microstructures. These conditions consisted of fine lamellar colonies, a mixture of coarse colonies
and acicular alpha, and acicular alpha. Isothermal hot compression tests were performed on cylindrical samples at subtransus
temperatures and strain rates typical of ingot breakdown (i.e., T∼815 °C to 955 °C,
∼0.1 s−1). For all three material conditions, true stress-true strain curves exhibited a peak stress followed by noticeable flow softening;
the values of peak stress and flow softening rate showed little dependence on starting microstructure. On the other hand,
the kinetics of dynamic globularization varied noticeably with microstructure. By and large, the globularization rate under
a given set of deformation conditions was most rapid for the fine acicular microstructure and least rapid for the mixed coarse-colony/acicular
structure. At temperatures close to the beta transus, however, the difference in globularization rates for the three microstructures
was less, an effect attributed to the rapid (continuous) coarsening of the laths in the acicular microstructure during preheating
prior to hot working. The absence of a correlation between the globularization kinetics and the observed flow softening at
low strains suggested platelet/lath bending and kinking as the primary deformation mechanism that controls the shape of the
flow curves. 相似文献
6.
Influence of microstructure on the flow behavior of duplex stainless steels at high temperatures 总被引:1,自引:0,他引:1
O. Balancin W. A. M. Hoffmann J. J. Jonas 《Metallurgical and Materials Transactions A》2000,31(5):1353-1364
Three kinds of duplex stainless steel, with different ferrite-to-austenite ratios, were deformed in torsion over the temperature
range 900 °C to 1200 °C; the corresponding microstructural evolution was observed and correlated with the deformation conditions.
The shapes of the high-temperature flow curves depend strongly on the volume fractions of the phases, the characteristics
of the ferrite-austenite interface, and the active softening mechanism. At low volume fractions of austenite, the mechanical
behavior is determined by the ferrite matrix and the flow curves are typical of materials that soften by continuous dynamic
recrystallization. When the volume fraction of austenite is increased, coherent γ particles distributed within the grains and at the grain boundaries hinder the deformation of the softer α matrix, increasing both the yield and the peak stress. These peaked flow curves are characterized by rapid work hardening
followed by extensive flow softening; under these conditions, the hard austenite particles become aligned with the deformation
direction after large strains. At high volume fractions of austenite (∼50 pct), the material tends to form a duplex structure,
with the flow curves displaying extended work-hardening and work-softening regions; however, a drastic decrease is observed
in ductility because of the dissimilar plastic behaviors of the two phases. 相似文献
7.
R. M. Imayev V. M. Imayev M. Oehring F. Appel 《Metallurgical and Materials Transactions A》2005,36(3):859-867
The hot-working behavior of γ(TiAl)-based alloys was investigated in order to understand fundamental aspects of the evolution of the microstructure and
to establish guidelines for advanced alloy design and processing. The investigations involved a wide range of Al compositions
and are based on metallographic investigations of the deformed samples. Particular emphasis was placed on the effects of phase
composition and casting texture. It was found that the behavior of dynamic recrystallization was significantly influenced
by the Al content of the alloys. Under the same deformation conditions, dynamic recrystallization was fastest for alloys with
nearly stoichiometric composition, whereas the recrystallization kinetics decreased for lower or higher Al contents. This
result can be attributed to the effect of the Al concentration on the micromechanisms of deformation and diffusion as well
as on the initial cast microstructure, which changed from fully lamellar to equiaxed near-γ microstructures by raising the Al content from 45 to 50 at. pct. Further, it was observed that the casting texture, i.e., the orientation of lamellae with respect to the deformation axis, significantly influenced the recrystallization behavior.
In this respect, the development of shear bands due to kinking and bending of lamellae is concluded to play an important role
in the recrystallization behavior and seems, in general, to be a particular feature of the microstructural evolution of lamellar
alloys on hot working. 相似文献
8.
H. J. McQueen 《Metallurgical and Materials Transactions A》2002,33(2):345-362
In the hot working at constant strain rate (
) of Al and α Fe alloys at 0.5 to 0.9 T
M (absolute melting temperature), steady-state deformation is achieved in similarity to creep, which is usually at constant
stress. After an initial strain-hardening transient, the flow stress becomes constant in association with a substructure which
remainsequiaxed and constant in the spacing of sub-boundaries and of dislocations in both walls and subgrains. All these spacings
become larger at higher temperature (T) and lower
values as well as with lower stress, being fully consistent with the relationships established in creep. Because hot working
can proceed to a much higher true strain in torsion (∼100) and compression (∼2) as well as in extrusion (∼20) and rolling
(∼5), it is possible to confirm that grains continue to elongate while the subgrains within them remain equiaxed and constant
in size. When the thickness of grains reaches about 2 subgrain diameters (d
s), the grain boundaries with serrations (∼d
s) begin to impinge and the grains pinch off, becoming somewhat indistinguishable from the subgrains; this has been called
geometric dynamic recrystallization (DRX). In polycrystals as at 20 °C, deformation bands form and rotate during hot working
according to the Taylor theory, developing textures very similar to those in cold working. In metals of lower dynamic recoverability
such as Cu, Ni, and γ Fe, new grains nucleate and grow (discontinuous DRX), leading to a steady state related to frequently renewed equiaxed grains,
containing an equiaxed substructure that develops to a constant character and defines the flow stress.
This article is based on a presentation made in the workshop entitled “Mechanisms of Elevated Temperature Plasticity and Fracture,”
which was held June 27–29, 2001, in San Diego, CA, concurrent with the 2001 Joint Applied Mechanics and Materials Summer Conference.
The workshop was sponsored by Basic Energy Sciences of the United States Department of Energy. 相似文献
9.
The origin of the γ fiber recrystallization texture in interstitial-free (IF) steel developed during continuous annealing
has been investigated by scanning electron microscopy (SEM) and orientation imaging microscopy (OIM). Nucleation of {111∼<uvw> oriented crystals occurs in deformation banded γ grains and therefore a comprehensive study of microstructure of cold-rolled
IF steel in the sections perpendicular to the rolling and transverse directions (TDs) and the rolling plane (RP) has been
carried out to understand the formation, geometry, and microstructural features of recrystallization. The RP section gave
abundant evidence of orientation gradients formed in γ oriented grains that had been subject to orientation splitting to give
deformation bands. These orientation gradients across a single grain are around 5 to 30 deg and this orientation difference
is sufficient to form nuclei with mobile interfaces during annealing and hence to create chains of γ oriented new grains in
the original hot band γ grain envelopes. A grain impingement model requiring orientation pinning is then proposed to explain
how these grains, contained in deformed γ grain envelopes, grow out into their neighbors to dominate the final recrystallization
texture of IF steel. The α deformed grains contain only small lattice curvatures, and therefore in-grain nucleation is rare.
These grains are mostly consumed by invading γ grains toward the end of the recrystallization process. 相似文献
10.
Plastic-flow behavior and microstructural development in a cast alpha-two titanium aluminide 总被引:3,自引:0,他引:3
S. L. Semiatin K. A. Lark D. R. Barker V. Seetharaman B. Marquardt 《Metallurgical and Materials Transactions A》1992,23(1):295-305
Plastic-flow behavior and microstructural development were investigated for a cast α2 titanium aluminide, Ti-24Al-11Nb (atomic percent), using the isothermal hot-compression test. Regimes of warm- and hot-working
behavior were inferred from flow curves adjusted for deformation heating effects. Plots of flow stress as a function of inverse
temperature and estimates of the strain-rate-sensitivity index confirmed the transition from warm to hot-working conditions
over a rather narrow temperature range. Hot working in theα
2 +β phase field was also marked by a rather high activation energy (viz., ∼1080 kJ/mole) for the controlling deformation process, which appeared to consist of dynamic globularization of the ordered-α
2 phase. A sharp decrease in the activation energy was noticed when the deformation temperature was increased above the β-transus.
Microstructural observations also indicated development of an unrecrystallized structure during warm working, with cavities
and wedge cracks being found near the bulged free surfaces of the upset specimens. The plastic-flow phenomenology exhibited
a number of similarities to that found in the wrought version of the Ti-24Al-11Nb alloy.
Formerly Senior Research Scientist, Metalworking Group, Battelle Memorial Institute, Columbus, OH 43201 相似文献
11.
H. -G. Brokmeier M. Oehring U. Lorenz F. Appel H. Clemens 《Metallurgical and Materials Transactions A》2004,35(11):3563-3579
The evolution of preferred orientations during processing appears to be of significant importance for the use of γ-titanium aluminide alloys, since the desired lamellar microstructures exhibit a strong anisotropy of mechanical properties.
In this work, texture development has been investigated after hot extrusion and sheet rolling, which are considered to be
technologically relevant wrought processes. As texture evolution certainly is dependent on several factors, involving deformation
properties, recrystallization kinetics, and, particularly, the phase constitution at hot-working temperature, different processing
conditions and alloy compositions were investigated. By comparing the results, it is indicated that the determined textures
can be understood by the deformation modes of the dominating phase at hot-working temperature and the subsequent phase transformations.
However, the current understanding of texture evolution is far from being complete, as no model can be presented which quantitatively
accounts for the contribution of the different processes mentioned. 相似文献
12.
J. B. Clark R. K. Garrett T. L. Jungling R. I. Asfahani 《Metallurgical and Materials Transactions A》1992,23(8):2183-2191
The influence of transverse rolling passes on the recrystallization texture was investigated in an effort to strengthen the
{111} 〈uvw〉 type components and reduce the intensity of the {100} 〈0vw〉 components, improve the uniformity of the microstructure, and refine the grain size in high-purity tantalum plate. Tantalum,
from three different ingot breakdown processes, received an additional 80 pct reduction in the transverse direction (perpendicular
to the ingot centerline) in the processing schedule prior to final annealing. This work investigated the influence of the
additional transverse rolling passes on the development of texture in the as-rolled tantalum and also in rolled plus annealed
tantalum. After annealing, the tantalum plates had significantly strengthened {111} 〈uvw〉 crystallographic orientations, not only for the side forged process, but also for the upset and side forged tantalum. For
tantalum processed by extrusion, the transverse rolling did not improve the final recrystallized texture. 相似文献
13.
Microtexture and grain boundary evolution during microstructural refinement processes in SUPRAL 2004
Terry R. McNelley Michael E. McMahon CDR U.S. Navy 《Metallurgical and Materials Transactions A》1997,28(9):1879-1887
Electron backscatter pattern (EBSP) analysis of as-processed, processed and annealed, and superplastically deformed specimens
of commercially processed SUPRAL 2004 material has been employed to reveal the boundary misorientation distribution and evolution.
Earlier studies using X-ray diffraction (XRD) and transmission electron microscopy on this alloy have attributed the transition
to microstructures capable of supporting extensive superplastic flow to continuous recrystallization occurring early in the
deformation process. The micro- and mesotextural data of the present study show that the deformation texture evident in the
as-processed material persists without the formation of recrystallization texture components and remains up to the apparent
onset of the grain boundary sliding (GBS) regime. Comparison of the correlated and uncorrelated boundary misorientation data
illustrates that the development of boundaries misoriented by ∼5 to 15 deg is not random in nature. There is no evidence of
recrystallization involving the formation and migration of high-angle boundaries during the refinement process. Microtextural
and boundary data from this study provide evidence that the microstructural transition enabling superplastic mechanical behavior
of SUPRAL 2004 may be described by a recovery-dominated, continuous process involving the development of moderately misoriented
boundaries and leading to a refined microstructure with a boundary distribution of low interfacial energy character. 相似文献
14.
R. M. Imayev V. M. Imayev M. Oehring F. Appel 《Metallurgical and Materials Transactions A》2005,36(13):859-867
The hot-working behavior of γ(TiAl)-based alloys was investigated in order to understand fundamental aspects of the evolution
of the microstructure and to establish guidelines for advanced alloy design and processing. The investigations involved a
wide range of Al compositions and are based on metallographic investigations of the deformed samples. Particular emphasis
was placed on the effects of phase composition and casting texture. It was found that the behavior of dynamic recrystallization
was significantly influenced by the Al content of the alloys. Under the same deformation conditions. dynamic recrystallization
was fastest for alloys with nearly stoichiometric composition, whereas the recrystallization kinetics decreased for lower
or higher Al contents. This result can be attributed to the effect of the Al concentration on the micromechanisms of deformation
and diffusion as well as on the initial cast microstructure, which changed from fully lamellar to equiaxed near-γ microstructures
by raising the Al content from 45 to 50 at. pct. Further, it was observed that the casting texture, i.e., the orientation of lamellae with respect to the deformation axis, significantly influenced the recrystallization behavior.
In this respect, the development of shear bands due to kinking and bending of lamellae is concluded to play an important role
in the recrystallization behavior and seems in general, to be a particular feature of the microstructural evolution of lamellar
alloys on hot working.
R.M. IMAYEV and V.M. IMAYEV, Senior Scientists, formerly with the GKSS Research Centre, Institute for Materials Research 相似文献
15.
M. R. Barnett 《Metallurgical and Materials Transactions A》2003,34(9):1799-1806
A series of hot-compression tests and Taylor-model simulations were carried out with the intention of developing a simple
expression for the proof stress of magnesium alloy AZ31 during hot working. A crude approximation of wrought textures as a
mixture of a single ideal texture component and a random background was employed. The shears carried by each deformation system
were calculated using a full-constraint Taylor model for a selection of ideal orientations as well as for random textures.
These shears, in combination with the measured proof stresses, were employed to estimate the critical resolved shear stresses
for basal slip, prismatic slip, 〈c+a〉 second-order pyramidal slip, and {
} twinning. The model thus established provides a semianalytical estimation of the proof stress (a one-off Taylor simulation
is required) and also indicates whether or not twinning is expected. The approach is valid for temperatures between ∼150 °C
and ∼450 °C, depending on the texture, strain rate, and strain path. 相似文献
16.
The flow and fracture of MP35N (35 Co, 35 Ni, 20 Cr, 10 Mo) has been studied by uniaxial com-pression and plane strain bending
in the temperature range 1000 to 1200 °C and strain rate range 0.01 to 10 s•1. This covers the normal bar rolling production conditions (∼1100 °C and 1 to 5 s“•1). The strain to fracture in plane strain bending was found to increase with increasing strain rate, roughly coinciding with
the increase of the strain to the peak stress in the flow curves. Within most of the temperature and strain rate ranges investigated
and under plane strain bending deformation conditions, microvoid nucleation was found to be concurrent with or greatly enhanced
by the onset of dynamic recrystallization. Under these deformation conditions, flow concentration or localization along the
soft layers of newly recrystallized grains oriented along the maximum shear stress directions near the surface generated microvoid
nucleation and damage, in effect overriding the stress relieving and crack isolation effects normally associated with the
occurrence of dynamic recrystallization. As the tem-perature was decreased toward 1000 °C and the strain rate was increased
toward 10 s•1, an apparent transition to a microvoid nucleation mode by wedge cracking was observed, even at the maximum rate of 10 s•1. A further decrease in deformation temperature to 900 °C at a strain rate of 10 s•1, however, removed all evidence of microvoid nucleation (of the wedge type or otherwise) as well as any trace of dynamic recrystallization
within the maximum strain imposed in the plane strain bending tests. 相似文献
17.
18.
D. W. Brown S. P. Abeln W. R. Blumenthal M. A. M. Bourke M. C. Mataya C. N. Tomé 《Metallurgical and Materials Transactions A》2005,36(4):929-939
Weakly textured hot-pressed (HP) beryllium and strongly textured hot-rolled beryllium were compressed using a split-Hopkinson
pressure bar (SHPB) (strain rate ∼4500 s−1) to a maximum of 20 pct plastic strain as a function of temperature. The evolution of the crystallographic texture was monitored
with neutron diffraction and compared to polycrystal plasticity models for the purpose of interpretation. The macroscopic
response of the material and the active deformation mechanisms were found to be highly dependent on the orientation of the
load with respect to the initial texture. Specifically, twinning is inactive when loaded parallel to the strong basal fiber
but accounts for 27 pct of the plastic strain when loaded transverse to the basal fiber. In randomly textured samples, 15
pct of the plastic strain is accomplished by twinning. The role of deformation mechanisms with components out of the basal
plane (i.e., twinning and pyramidal slip) is discussed. 相似文献
19.
The present article describes the microstructural changes during recrystallization annealing of a 73 pct cold-rolled Ni3Al(B,Zr) alloy along with a study of the recrystallization kinetics. The deformed γ regions, mostly within and near the shear bands, appear to recrystallize first. The recrystallization front leaves behind
a lamellar discontinuous precipitation within the newly formed strain-free γ grains, when annealing is done at lower temperatures. At higher annealing temperatures, the precipitates within γ assume a globular morphology. This precipitate is presumably made up of γ′ particles. When γ recrystallization is nearly complete, the γ′ regions start to recrystallize. The two-stage recrystallization process is also corroborated from the kinetics results,
which show that the activation energy up to 50 pct recrystallization of the material is only 117 kJ/mole, whereas beyond 50
pct until the completion of recrystallization, an activation energy of ∼274 kJ/mole is obtained. 相似文献
20.
Sandip Ghosh Chowdhury Samar Das B. Ravikumar P. K. De 《Metallurgical and Materials Transactions A》2006,37(8):2349-2359
This paper deals with the evolution of texture in AISI 316L austenitic stainless steel during annealing after 95 pct cold
rolling. After 95 pct cold rolling, the texture is mainly of the brass type {110}〈112〉, along with a scatter toward the S
orientation {123}〈634〉 and Goss orientation {011}〈100〉. Weak evidence of Cu component is observed at this high deformation
level. During annealing, recovery is observed before any detectable recrystallization. Recrystallization proceeds through
nucleation of subgrain by twinning within the deformed matrix and, later, preferential growth of those to consume the deformed
matrix. After recrystallization, the overall texture intensity was weak; however, there are some discernible texture components.
There was no existence of the brass component at this stage. Major components are centered on Goss orientation and Cu component
{112}〈111〉 as well as the BR component {236}〈385〉. Also, a few orientations come up after recrystallization (i.e., {142}〈2−11〉 and {012}〈221〉). With increase in annealing temperature, the textural evolution shows emergence of weak texture
with another new component, {197}〈211〉. The evolution of texture was correlated with the deformation texture through twin
chain reaction. 相似文献