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1.
Electron-backscattered diffraction (EBSD) has been used to investigate the texture evolution during tensile deformation at
temperatures between 673 and 773 K of a coarse-grained commercial AZ31 magnesium alloy. A weak (0001) fiber texture was initially
present in the hot-rolled magnesium alloy plate. The [0001] directions of the grains spread 0 to 45 deg around the normal
direction (ND) of the magnesium alloy plate. This pre-existing weak texture evolved during tensile deformation into a strong
texture close to the {0001} 〈1
00〉. The [0001] directions of the grains rotated toward the orientations perpendicular to the tension axis of the samples,
indicating that the 〈11
0〉 slip system appeared to be the most active slip system, especially in the early stages of deformation. The EBSD Schmid-factor
analysis revealed that, however, with an increase in strain and the rotation of the (0001) slip plane, the {11
2} 〈11
〉 slip system appeared to be more favorable. The {1
00} 〈11
0〉 and {1
01} 〈11
0〉 slip systems remained favored throughout the strains investigated, indicating that {1
00} and {1
01} are two important slip planes for cross slip using the 〈11
0〉 slip vector. It is found that the misorientation across one coarse grain (as high as 38.2 deg) is accommodated by low-angle
grain boundaries (LAGBs). The formation of these LAGBs may be an intermediate stage of the coarse grain refinement that occurred
during deformation.
This article is based on a presentation made in the symposium entitled “Processing and Properties of Structural Materials,”
which occurred during the Fall TMS meeting in Chicago, Illinois, November 9–12, 2003, under the auspices of the Structural
Materials Committee. 相似文献
2.
Cyclic deformation behavior and dislocation substructure in the single crystals of Ti-Al alloy containing 2.0 pct Al (by atom)
with double prism slip at different cyclic strain amplitudes were examined. The testing results showed that Ti-2Al displayed
an initial slight cyclic hardening followed by a striking softening period, and a saturation stage was reached finally. Secondary
cyclic hardening was observed for most specimens before failure, specifically at the high cyclic strain amplitudes. The cyclic
resolved shear stress-strain curve (CSSC) was observed to contain a plateau in the testing strain range with a saturation
plateau stress of about 55 MPa. Trace analysis on the surface of specimens with an optical microscope shows that the (10
0) and (1
00) double prism slips can be distinguished from the traces on the (0001) surface of the fatigued specimens. The dislocation
substructure in the fatigued specimens was examined using a transmission electron microscope (TEM). The typical dislocation
configuration is the saturated dislocation bundles, which are tangled on the (10
0) and (1
00) slip planes and arranged parallel to the [0001] direction. 相似文献
3.
4.
The boundary structure of {10
1}, {10
2}, {11
1} and, {11
2} twins in hexagonal-close-packed (hcp) metals and the interaction of crystal dislocations with the first two twin types
have been studied previously using atomic-scale computer simulation. The interaction of crystal dislocations with {11
1} and {11
2} twin boundaries is described here and compared with the results for {10
1} and {10
2} twins. These four twins are found to create barriers to the motion of crystal dislocations gliding on the basal plane,
and the strength of the barrier depends in a relatively complex manner on crystallographic parameters and details of the atomic
structures of the interfaces. In some circumstances, crystal dislocations can be transmitted through the twin boundary, thereby
creating twinning dislocations.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
5.
Sungsoo Kim 《Metallurgical and Materials Transactions A》2006,37(1):59-68
Recently, it was proven that delayed hydride cracking (DHC) is accompanied by deformation twinning through the texture analysis
of a fractured surface. Thus, in order to understand the operation of deformation twinning, the texture variations by rolling
were investigated using Zr-2.5 pct Nb alloy with {11
0} 〈10
0〉 texture. It was observed that deformation twinning was operated predominantly in the range of a 5 to 15 pct strain. The
basal poles were rotated in the normal direction of a rolling plane with the strain, and the (0002) texture was fully reversed
after 15 pct strain. This finding was established to be due to the operation of the {10
2} and {11
1} twinning systems through the analysis of the inverse pole figure. It appeared that the degree and easiness of the twinning
operation was affected by changing the direction of compression during rolling with respect to the initial {11
0} 〈10
0〉 texture. The contribution of deformation twinning to strain was quantitatively calculated using the change in the basal
pole components.
This article is based on a presentation made in the symposium entitled “Processing and Properties of Structural Materials,”
which occurred during the Fall TMS meeting in Chicago, Illinois, November 9–12, 2003, under the auspices of the Structural
Materials Committee. 相似文献
6.
Twins as barriers to basal slip in hexagonal-close-packed metals 总被引:2,自引:0,他引:2
The boundary structure of
,
,
, and
twins in hexagonal-close-packed (hcp) metals and the interaction of crystal dislocations with the first two twin types have
been studied previously using atomic-scale computer simulation. The interaction of crystal dislocations with
and
twin boundaries is described here and compared with the results for
and
twins. These four twins are found to create barriers to the motion of crystal dislocations gliding on the basal plane, and
the strength of the barrier depends in a relatively complex manner on crystallographic parameters and details of the atomic
structures of the interfaces. In some circumstances, crystal dislocations can be transmitted through the twin boundary, thereby
creating twinning dislocations.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
7.
Evolution of microstructure and texture in Mg-Al-Zn alloys during electron-beam and gas tungsten arc welding 总被引:3,自引:0,他引:3
The evolution of microstructure and texture in the AZ-series Mg alloys subjected to electron-beam welding and gas tungsten
arc welding are examined. Electron-beam welding is demonstrated to be a promising means of welding delicate Mg plates, bars,
or tubes with a thickness of up to 50 mm; gas tungsten arc welding is limited to lower-end thin Mg sheets. The grains in the
fusion zone (FZ) are nearly equiaxed in shape and ∼8 μm or less in size, due to the rapid cooling rate. The as-welded FZ microhardness and tensile strength are higher than the
base metals due to the smaller grain size. The weld efficiency, defined as the postweld microhardness or tensile strength
at the mid-FZ region divided by that of the unwelded base metal, is around 110 to 125 pct for electron-beam welding and 97
to 110 pct for gas tungsten arc welding. There are three main texture components present in the electron-beam-welded (EBW)
FZ, i.e.,
(with TD//
),
(with ND∧
∼15 deg), and
(with WD∧
∼30 deg), where TD, ND, and WD are the transverse, normal, and welding directions, respectively. The crystal growth tends
to align toward the most closed-packed direction,
. The texture in gas tungsten arc welded (GTAW) specimens is more diverse and complicated than the EBW counterparts, due to
the limited and shallow FZ and the lower cooling rate. The cooling rates calculated by the three-dimensional (3-D) and two-dimensional
(2-D) heat-transfer models are considered to be the lower and upper bounds. The cooling rate increases with decreasing Al
content, increasing weld speed, and increasing distance from the weld top surface. The influences of the FZ location, welding
speed, and alloy content on the resulting texture components are rationalized and discussed. 相似文献
8.
The development of characteristic dislocation structures in pure zirconium and zircaloy-4 fatigued under pull-push strain
control as the testing temperature and the cyclic strain range varied was examined using a thin-foil transmission electron
microscopy (TEM) technique. The slip planes and the twinning planes were determined by a standard stereographic trace analysis
technique. The first-order prismatic slip {10
0} is the primary deformation mode in zirconium and zircaloy-4 fatigued from room temperature (RT) to 873 K. The pyramidal
sli {
2
} is activated at 673 K and at high cyclic strain ranges, whereas the basal slip {0001} only appears in those specimens fatigued
at 873 K. The {10
2}, {11
1}, and {11
2} types of twins were detected in specimens fatigued at RT. Twinning becomes less frequent as the testing temperature increases.
The schematic map of the cyclic deformation modes as a function of the plastic strain range and the test temperature is described.
The dislocation configurations in fatigued pure zirconium specimens evolve from a planar arrangement to a cell structure as
the test temperature and the strain range increase. For zircaloy-4, the fatigued dislocation structure is parallel dislocation
lines at RT, cells at 673 K, and two sets of approximate mutually perpendicular dislocation bands at 873 K, respectively.
Finally, the fatigued dislocation-structure evolution map with the cyclic strain range and the test temperature are qualitatively
established for zirconium and zircaloy-4, respectively. The effect factors on the fatigue mechanism and the thermodynamic
and dynamic criteria of the dislocation-pattern evolution are discussed. 相似文献
9.
Creep crack growth rate (
) is usually characterized in terms of macroscopic load parameters, such as C*, C
t
and C(t), through the constant load test. However, load parameters are continuously changing during the test, and so is
. Here, by conducting constant C
t
and constant
tests, quasi-steady-state crack growth was obtained where
remained almost constant. Results indicate the
∼[C
t
]0.76 correlation, which differ from the
∼[C
t
]0.96 correlation of the constant load test. Discrepancies can be ascribed to the inclusion of the stage II data, which showed
no correlation between
and C
p
in the constant load analysis. Finally, the crack growth rate was well predicted using the Monkmam-Grant analysis in creep
crack growth. 相似文献
10.
Growth morphology and number
per unit volume have been determined vs withdrawal velocity V over the range 0.1 to 4 mm/s for primary Mg2Si in a Bridgman-solidified hypereutectic Al-Mg-Si alloy. Primary Mg2Si shows a transition from irregular or regular polyhedral to dendritic with increasing V, and
increases with solidification cooling rate
according to the relationship
. These results are compared with corresponding ones for Al-Mg-Si alloy wedge castings and for primary silicon in hypereutectic
Al-Si alloys. 相似文献
11.
Two interstitial-free (IF) steels and a high-purity α-iron were deformed in torsion over the temperature range of 600 °C to
840 °C, and the textures produced were measured using conventional X-ray techniques. The conditions were chosen so that dynamic
recrystallization (DRX) would take place in the ferrite and static recrystallization would be avoided during cooling after
deformation. The DRX textures differ from those observed at room temperature and are dominated by the D1 (
)[111], D2(
)[111], and E2 (
)[111] components. The D2 becomes increasingly important as the strain is increased, which leads to weakening of the D1 and
disappearance of the E2 at large strains. Texture simulations were carried out using a DRX model based on sequential deformation,
nucleation, and growth steps. The types of oriented nucleation and selective growth required to reproduce the experimentally
observed textures are discussed. The simulations indicate that the low-energy nucleation mechanism plays a dominant role in
the formation of bcc DRX textures. The results are also interpreted in terms of the continuous (in situ) and discontinuous mechanisms of dynamic recrystallization. 相似文献
12.
Grain-growth inhibition in an Fe-10 mass pct Ni alloy, which was continuously cooled from a melt, was studied at 1673 K in
the presence of primary deoxidation products of ZrO2 or MgO particles. The mean grain size and grain-size distribution in a cross section were measured as a function of holding
time for up to 240 minutes. The grain growth was strongly inhibited by the inclusion particles and was influenced by the dissolved
Zr. In the Zr deoxidation, the number of particles per unit area (N
A) ranged from 80 to 650 mm−2, the ZrO2 particle size (
) varied from 1.1 to 1.6 μm, and the dissolved Zr level was below 1800 mass ppm. In the Mg deoxidation, the particle-number density was 90 to 270 mm−2, the MgO particle size was 1.1 to 1.7 μm, and the dissolved Mg level was below 20 mass ppm. In a logarithmic plot of the ratio of limiting mean grain diameter (
) to the mean particle diameter (
) against the volume fraction of particles (f
V), both the
value for a given f
V value, which ranged from 0.014 to 0.074 pct, and the slope were significantly lower than that predicted from the two-dimensional
relation
=(4/π) · f
V
/−1
, i.e., Zener’s limit. This discrepancy is discussed in light of the fraction of particles at the grain boundaries measured experimentally.
Normal grain growth was confirmed from the grain-size distribution observed as a function of holding time, which was best
described by the log-normal distribution. 相似文献
13.
The deformation behavior of a Burgers oriented α-β-Ti-13Mn bimetallic bicrystal was studied at two plastic strains, 0.52 and
2.08 pct. Two single crystals, α and β, each corresponding to the orientation of its respective bicrystal component were also
investigated. The stress axes were
and [1218]β. The interface planes were
and
and lay in the x’-z’ plane. The deformation behavior of the a component differed from that of the a single crystal because
of plastically induced stresses,T
y’z’
,T
x’z’
,T
x’y’
, and σ
x’x’
. Prismatic slip and
twinning were found in the single crystal α whereas the bicrystal revealed additionally pyramidal andc + a slip, the latter at the interface. Slip on the front and back surfaces was different and both thec + a and twinning systems acted to maintain compatibility. Slip in the β single crystal and the β bicrystal component were quite
similar. However, there were differences in the intensity and amount of primary slip, (231)
, on the front and back surfaces. The diminished amount of (231)
slip on the back surface was due to plastically induced stresses, and on the front surface the primary slip cross slipped
to
slip which triggeredc + a slip in α. On the back surface the dominant slip system was
which acted in response to the plastically induced stresses. An approximate calculation revealed that the interface deformation
zone had about twice the flow stress of the average bicrystal stress.
Formerly a Graduate Student in the Department of Physical and Engineering Metallurgy at Polytechnic Institute of New York,
Brooklyn, NY 相似文献
14.
J. Koike 《Metallurgical and Materials Transactions A》2005,36(7):1689-1696
This article presents room-temperature deformation mechanisms in polycrystalline Mg alloys. Dislocation slip of basal 〈a〉
and prismatic 〈a〉 types are shown to occur nearly at the same ease when the basal planes are tilted in such a way that the
Schmid-factor ratio (equivalent to the critically resolved shear stress (CRSS) ratio) of prismatic 〈a〉 to basal 〈a〉 slip is
larger than a value ranging from 1.5 to 2.0, depending on the initial texture distribution and grain size. Grain-boundary
sliding (GBS) also occurs at room temperature up to 8 pct of total strain, enhanced by plastic anisotropy as well as by the
increasing number of grain-boundary dislocations. Twinning plays an important role in both flow and fracture behaviors. Twins
are induced mostly by stress concentrations caused by the anisotropic nature of dislocation slip. Twins can be classified
into two types based on their shape: a wide lenticular type and a narrow banded type. The wide twins are
twins appearing in the early stage of deformation and accompany little change of surface height. The narrow twins are
or
appearing in the late stage of deformation and accompany a substantial change in surface height. The formation of the narrow
twins seems to give rise to highly localized shear deformation within the twin, leading to strain incompatibility and to final
failure.
This article is based on a presentation made in the symposium entitled “Phase Transformations and Deformation in Magnesium
Alloys,” which occurred during the Spring TMS meeting, March 14–17, 2004, in Charlotte, NC, under the auspices of ASM-MSCTS
Phase Transformations Committee. 相似文献
15.
An analysis of retained austenite in austempered ductile iron 总被引:1,自引:0,他引:1
L. C. Chang 《Metallurgical and Materials Transactions A》2003,34(2):211-217
Data from the literature have been analyzed to understand aspects of the retained austenite in austempered ductile irons,
especially its relationship with the transformation mechanism of bainite. The final and initial carbon concentrations in austenite,
and C
γ
0
, respectively, are important in determining the maximum extent of reaction, and hence, the amount of austenite and and bainitic
ferrite
and C
γ
0
data have been expressed in terms of chemical compositions and reaction temperature, with reasonable agreement between experimental
and predicted results. It is demonstrated that, in connection with the lever rule, the calculated
and C
γ
0
values can be employed to predict the microstructural constituents of austempered ductile irons. 相似文献
16.
Shinji Ando Hideki Tonda Takushi Gotoh 《Metallurgical and Materials Transactions A》2002,33(3):823-829
The core structures of 〈c+a〉 dislocations in hexagonal-close-packed (hcp) metals have been investigated by molecular dynamics (MD) simulation using a
Lennard-Jones-type pair potential. The 〈c + a〉 edge dislocation has two types of core at 0 K; one is a perfect dislocation
(type A), and the other has two 1/2 〈c+a〉 partials (type B). Type A transforms to type B by abruptly increasing temperature from 0 K to 293 K, while type B is stable
in temperature range from 0 K to 293 K. In contrast, type A extends parallel to (0001) at 30 K, and this extended core is
still stable at 293 K. These results suggest that the 〈c+a〉 edge dislocation glides on the {11
2} as two 1/2 〈c+a〉 partial dislocations and becomes sessile due to changes of the core structure. The 〈c+a〉 screw dislocation spreads over two {10
1} planes at 0 K. The core transforms into a unsymmetrical structure at 293 K, which is spread over {11
2} and {10
1}, and core spreading occurs parallel to {11
2} at 1000 K. A critical strain to move screw dislocations depends on the sense of shear strain. The dependence of the yield
stress on the shear direction can be explained in terms of these core structures.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
17.
Crystallographic details of precipitates in Fe-22Cr-21Ni-6Mo-(N) superaustenitic stainless steels aged at 900 °C 总被引:1,自引:0,他引:1
Tae-Ho Lee Sung-Joon Kim Yun-Chul Jung 《Metallurgical and Materials Transactions A》2000,31(7):1713-1723
Crystallographic features of second phases and the effect of nitrogen addition on the microstructural evolution in superaustenitic
Fe-22Cr-21Ni-6Mo-(N) (all in wt pct) stainless steels during isothermal aging at 900 °C were investigated using scanning electron
microscopy (SEM) and transmission electron microscopy (TEM). Both alloys with and without nitrogen contained sigma phase and
M23C6 carbides in the solution treated condition. While four phases (sigma, M23C6, M6C, and chi) of intermetallics and carbides appeared sequentially as a function of aging time in the nitrogen-free alloy, two
nitrides (Cr2N and AlN) were additionally observed after long time aging of the nitrogen-containing alloy. The addition of nitrogen into
Fe-22Cr-21Ni-6Mo steel promoted a finer and more uniform distribution of precipitates during isothermal aging. The exact identification
and crystallography of various second phases were confirmed from the analyses of selected area diffraction patterns from various
orientations, stereographic projection, and energy dispersive spectroscopy. The orientation relationships between the precipitates
and austenite matrix can be summarized as follows: (1) two carbides (M23C6 and M6C): cube-on-cube orientation relationship; (2) chi phase: Kurdjumov-Sachs (K-S) orientation relationship; (3) two nitrides
(Cr2N and (AlN): (11
0)nitrides //(211)
γ
and [0001]nitrides //[
11]
γ
; and (4) sigma phase: (1) (
11)
γ
//(00
)
σ
and [
0]
γ
//[
0]
σ
or (2) (
10)
γ
//(
10)
σ
and [
2]
γ
//[113]
σ
. For the sigma phase, the former orientation relationship was predominant throughout aging, and the latter orientation relationship
was occasionally observed under limited aging conditions. 相似文献
18.
H. S. Ryoo S. K. Hwang B. K. Kim H. S. Chung 《Metallurgical and Materials Transactions A》2000,31(8):1925-1935
The process of triangular prism formation and abnormal grain growth of WC was modeled using pseudo-Monte-Carlo simulation
based on atomic adsorption and the coalescence mechanism. Grains of WC evolved into a triangular prism shape due to {10
0} and {1
10} planes of fast growth rate. Coalescence of {10
0} and {1
00} planes subsequent to the anisotropic evolution was the main reason for the abnormal grain growth. The probability of coalescence
computed by the Monte-Carlo method agreed well with a theoretical prediction. Experimental evaluation of the computational
model was made in sintered WC-25 wt pct Co alloy. The experimental alloy was made with WC powder of different particle size,
0.8 μm and −325 mesh, respectively, and with two different sintering conditions: solid-phase sintering and liquid-phase sintering.
The sample made from the coarse powder (−325 mesh) showed the same morphological characteristics as those of the original
milled state, whereas the sample made from the fine powder (0.8 μm) assumed a triangular prism shape quickly during solid-phase sintering. The anisotropic growth process of the latter sample
could be explained by using the adsorption and coalescence model. 相似文献
19.
Diffusion studies were carried out in the Fe-Ni-Al system at 1000 °C with solid-solid diffusion couples assembled with β (B2), β′ (bcc), and γ (fcc) single-phase alloys for the development of diffusion structures, diffusion paths, and for the determination of interdiffusion
and intrinsic diffusion coefficients. The diffusion structures were examined by optical and scanning electron microscopy,
and the concentration profiles were determined by electron microprobe analysis. Diffusion couples included several series
of β vs γ and β′ vs γ diffusion couples characterized by a common terminal alloy bonded to several terminal alloys with varying compositions. The
development of planar and nonplanar interfaces, as well as two-phase layers, as observed in various couples, were related
to the diffusion paths. The interdiffusion fluxes of individual components were calculated directly from the experimental
concentration profiles, and the diffusional interactions among components were examined in the light of zero-flux planes (ZFPs)
and flux reversals, which were identified in several couples. Ternary interdiffusion coefficients (
(i, j = Al, Ni)), with Fe considered as the dependent concentration variable, were evaluated at composition points of the intersection
of diffusion paths of single-phase couples and of multiphase couples that developed planar interfaces. The interdiffusion
coefficients were the largest in magnitude for the β′ alloys, especially near the β/β′ miscibility gap, and decreased for the β and γ alloys. In the β and γ phases, the main interdiffusion coefficient for Al was larger than those for Ni and Fe. Also, Fe interdiffused faster than
Ni in the Fe-rich β and β′ phases. The cross-interdiffusion coefficients (
and
) were negative in all three phases. In general, the
coefficients were larger in magnitude than the
coefficients; however, the magnitude of
was greater than that of
near the β/(β + γ) phase boundary on the ternary isotherm. In the β phase, the magnitude of
(i, j=Al, Ni) coefficients increased over 1 to 2 orders of magnitude with a decrease in the Al concentration and increase in the
Fe/Ni concentration ratio. Interdiffusion coefficients, extrapolated from the ternary coefficients for binary alloys, were
consistent with those in literature. Intrinsic diffusion coefficients were also determined at selected compositions. In addition,
tracer diffusion coefficients were estimated for the binary Fe-Al and Ni-Al alloys at selected compositions, from an extrapolation
of ternary interdiffusion coefficients. 相似文献
20.
The crystallographic direction of growth in directionally solidified magnesium alloy AZ91 has been studied by TEM and EBSP
techniques in SEM. The main direction of growth is found to be
. The dendrites have sixfold symmetry around the main direction, with secondary arms lying along the traces of the (0001),
, and
-planes, respectively. The secondary arms lying in the basal plane are crystallographically of the same type as the main direction:
and
. 相似文献