共查询到20条相似文献,搜索用时 93 毫秒
1.
F. S. Lin E. A. Starke S. B. Chakrabortty A. Gysler 《Metallurgical and Materials Transactions A》1984,15(6):1229-1246
An alpha + beta Ti-6Al-2Nb-lTa-0.8Mo alloy with an initial Widmanstätten structure was thermally treated to produce a wide range of microstructures. The effects of individual microstructural parameters on deformation behavior and mechanical properties were investigated. The results show that the Widmanstätten colony boundaries are major barriers to slip. However, the slip distance can be decreased to a distance equal to the thickness of acicular alpha by transforming the beta phase in the Widmanstätten structure to martensite by quenching from 950°C. The decrease in slip distance is accompanied by a 25 pct increase in yield strength with no loss in ductility. A large decrease in ductility occurs after excursions above the beta-transus. The development of both equiaxed beta grains during heating in the beta phase field and continuous grain boundary alpha during cooling in the alpha + beta phase field leads to strain localization along prior beta grain boundaries. 相似文献
2.
I. Weiss F. H. Froes D. Eylon G. E. Welsch 《Metallurgical and Materials Transactions A》1986,17(11):1935-1947
The modification of lamellar alpha phase in Ti-6A1-4V by hot working was investigated with the aim of controlling morphology
(aspect ratio) and final grain size. The effect of strain was studied using forging at 955 °C (1750 °F), followed by annealing
at 925 °C (1700 °F) to allow the alpha morphology to adjust. Increasing the deformation from 6.5 pct to 80 pct reduction caused
the lamellar alpha morphology to become progressively more equiaxed upon annealing. TEM observations showed that annealing
of material deformed to 6.5 pct resulted in recovery of the alpha, without a noticeable change in the morphology, while higher
deformation resulted in plate shearing and beta cusp formation. It was found that material with an initial thin alpha plate
structure (thickness — 3.4 ώm) breaks up at a lower critical strain than a material with a thicker plate morphology (thickness
≃ 6 μm). The material with thin alpha plates more rapidly forms equiaxed alpha grains separated by beta phase, while the material
with a thicker plate structure exhibits more alpha/alpha boundaries after deformation and annealing. The morphology change
from alpha lamellae into lower aspect ratio grains was identified to be by a break-up of the alpha lamellae, essentially by
a two-step process: a formation of low and high angle alpha/alpha boundaries or shear bands across the alpha plates followed
by penetration of beta phase to complete the separation. This break-up takes place during hot deformation and subsequent annealing. 相似文献
3.
Z. Ahmad M. Farooque A. Ul Haq A. Q. Khan 《Metallurgical and Materials Transactions A》1997,28(12):2459-2465
Austenite and martensite textures were studied in 18 pct Ni 350-maraging steel as a function of various degrees of cold rolling.
The austenite phase in the samples was produced by repeated thermal cycling between ambient and 800 °C. The austenite phase
thus formed was mechanically unstable and transformed to the martensite phase after 30 pct cold rolling. The texture developed
as a result of cold rolling, and its effect upon microstructure and hardness has been studied. 相似文献
4.
J. E. Costa J. C. Williams A. W. Thompson 《Metallurgical and Materials Transactions A》1987,18(8):1421-1430
The effect of hydrogen on the mechanical properties of the metastable β alloy Ti-10V-2Fe-3Al was examined. The material was
beta annealed and water quenched (B/WQ) to yield a nominally all-β microstructure, with a small volume fraction of athermal
omega present. Tensile and notched bend bar tests were performed with differing levels of hydrogen concentration (~0 to >30
at. pct) obtained by Sieverts (gaseous) charging prior to beta annealing. The β phase was transformed to orthorhombic alpha
double prime martensite (β") upon deformation. The volume fraction and morphology of the alpha double prime depended on the hydrogen concentration. The
deformation-induced martensitic transformation changed from being stress-induced to being strain-induced with increased hydrogen
concentration. High hydrogen concentrations also resulted in changes in fracture mode. At high hydrogen concentrations, where
little or no martensite formed upon deformation, “intrinsic” (i.e., independent of microstructural modification) hydrogen effects were observed in the β phase. These intrinsic hydrogen effects,
deleterious in nature, were taken to be evidence of hydrogen embrittlement in the body-centered cubic β phase.
Formerly at Carnegie Mellon University. 相似文献
5.
The structures of the martensite of four CuZnAI alloys with Al contents ranging from 9 to 20.8 at. pct were investigated using
transmission electron microscopy. It was found that the structure of the martensite changed from 9R (having formed from a
parent phase with B2 order) to 18R (DO3 parent) as the Al content was increased from 9 to 13.6 at. pct. The 0.2 pct proof stress of polycrystalline specimens initially
decreased with increasing Al, corresponding to the change of order, and then increased. It is argued that the mechanism of
yielding is the formation of mechanical twins which reorient the martensite, and an explanation of the change of yield stress
with composition is given in terms of changes in the nature and extent of ordering affecting the twin boundary energy. 相似文献
6.
Peng-Heng Chang 《Metallurgical and Materials Transactions A》1984,15(4):671-678
The effects of two processing variables, prior cold reduction and temper rolling, on the mechanical properties of a continuously
annealed 0.05 pct C low alloy dual phase steel were studied. It was found that cold rolling affected the strength of the dual
phase steel through its influence on the recrystallized ferrite grain size. The correlation between yield strength and mean
free path in ferrite was shown to follow a Hall-Petch type relationship. Similarly, temper rolling also had a pronounced effect
on the yield strength of the steel. The effect was strongly dependent upon the previous overaging treatment; the lower the
overaging temperature, the stronger the effect. Basically, the effect of temper rolling on dual phase steel was not much different
from that on mild steel and HSLA in terms of the change in yield strength and yield point elongation. Another interesting
observation was the influence of quenching rate on the strength of the dual phase steel. A slower quenching rate in the heavier
gauge dual phase steel caused pearlite rims to form around martensite colonies and thus decreased the strength of the steel. 相似文献
7.
P. H. Chang P. G. Winchell G. L. Liedl 《Metallurgical and Materials Transactions A》1983,14(1):163-173
Quantitative stereology was applied to study the transformation behavior and the microgeometry of athermally transformed martensite for two austenite grain sizes in Fe-1.4 wt pct C-0.02 wt pct P alloy and commercial 01 tool steel. The effects of prior austenite grain boundaries and the existing martensite plates on the nucleation of martensite were studied and each was found to play different roles during the transformation. Autocatalytic nucleation was found to be less than that for a burst transformation. Prior austenite grain boundaries were found to have a strong influence on the initial nucleation of martensite. Plate thickness was constant during the transformation except for coarsegrained 01 tool steel after ~60 pct transformation. The plate radius decreased slowly with fraction transformed and was found to be independent of the mean free path in austenite initially, but decreases with the decreasing mean free path in the later stages. 相似文献
8.
A study has been made of the effect of grain refinement on the mechanical and the strain-memory properties of β-CuAlNi alloys.
Addition of 0.5 pct Ti to CuAINi decreased the grain growth rate of the beta phase significantly. This appeared to be due
mainly to the small fraction of the titanium in solid solution in the β-CuAlNi. By controlled annealing, a grain size as small
as 15 μrn could be obtained, though some second phase γ2 was present due to incomplete precipitate dissolution. Stress-strain curves for most specimens in both the strain-memory
and pseudoelastic states showed a three-stage characteristic with a region of lower slope between two regions of higher modulus.
It was found that σ1, (the transition stress between stages 1 and 2) and (dσ/dε@#@) (the slope of stage 2) increased with grain size according to a (g.s.)-1/2 relationship. The ultimate tensile strength and strain to fracture also followed a similar Hall-Petch relationship. The alloys
showed higher strength in the martensitic state than in the pseudoelastic one. The presence of second-phase particles had
no significant effect on the mechanical properties and martensite deformation behavior. Fracture strains as high as 7 pct
were obtained at the finest grain sizes. It was found that the strain-memory and pseudoelastic recovery properties were not
affected significantly by decreasing grain size and the presence of second phase particles. Maximum recovery strains of 6.5
pct were obtained in fine grain samples.
Formerly Graduate Student, Department of Metallurgical Engineering, University of British Columbia 相似文献
9.
Influence of texture on fatigue properties of Ti-6Al-4V 总被引:1,自引:0,他引:1
Tensile properties, high cycle fatigue strength, and fatigue crack propagation behavior were evaluated on highly textured
Ti-6Al-4V material to investigate the influence of a preferred crystallographic orientation on mechanical properties. Thermomechanical
treatments were used to develop three different textures: a basal, basal/transverse, and transverse type, all of which exhibited
the same homogeneously equiaxed microstructure. The Young’s modulus was found to vary between 107 and 126 GNm-2, and yield strength changed from 1055 to 1170 MNm-2. Ductility was only slightly affected by texture. High cycle fatigue and fatigue crack growth measurements were performed
in vacuum, laboratory air, and a 3.5 pct NaCl solution. It is shown that laboratory air can be regarded as a quite corrosive
environment. In vacuum the highest fatigue strength values were measured whenever loads were perpendicular to basal planes.
However, these conditions had the highest susceptibilities to air and 3.5 pct NaCl solution environments. Nearly no influence
of texture on fatigue crack propagation was found in vacuum, but in a corrosive environment crack growth parallel to (0002)-planes
was much faster than perpendicular to these planes. To explain the corrosive effect on the fatigue properties of the textured
material hydrogen is thought to play a key role. 相似文献
10.
The effect of penultimate grain size on the texture of Cu-Sn alloys has been investigated using the modulus method. It was observed that in alloys which exhibited the brass-type texture, the large grained specimens yielded a smaller proportion of textured material than those which were fine grained. In alloys which exhibited transition textures, however, the larger grain size specimens exhibited a greater amount of material residing in the brass-type components. As might be expected, increasing the rolling reduction diminished the effect of penultimate grain size upon rolling. The 50:50 texture transition for 971/2 pct reduction occurred at 0.55 at. pct Sn. Unlike Cu-Zn and Cu-Al alloys, the percentage of brass-type texture reached a maximum at 1.8 at. pct Sn and then decreased for tin contents up to 5.06 at. pct. A self-consistent explanation, based on the “dislocation interaction” hypothesis, has been offered to account for the experimental observations. The present results indicate that the twinning processper se, can actually be detrimental to, rather than promote the formation of the brass-type texture in Cu-Sn alloys. 相似文献
11.
The effects of crystallographic texture and precipitate distribution on macroscopic anisotropy in aluminum alloys were investigated.
In order to simultaneously consider the effects of crystallographic texture and precipitate distribution on macroscopic anisotropy,
predictions of plastic properties were carried out using an anisotropic yield function based on the material texture and a
combined isotropic-kinematic hardening rule. The input to the model was a single stress-strain curve, the crystallographic
texture, and the precipitate volume fraction, shape, and habit planes. It was shown that the kinematic hardening rule, which
expresses a translation of the yield surface in stress space, was a function of all the parameters describing the precipitate
distribution. The model was applied to the case of an extruded and recrystallized binary Al-3 wt pct Cu alloy deformed in
uniaxial compression in different directions. Excellent agreement was observed between the experimental and predicted yield
stress anisotropy and the specimen cross section shape anisotropy. Gaussian distributions of grain orientations around ideal
texture components typical of aluminum alloys were generated using computer simulations. These textures were combined with
the isotropic-kinematic hardening rule determined for the Al-3 wt pct Cu binary alloy to theoretically assess the influence
of precipitates on the r-value (the width-to-thickness plastic strain ratio in uniaxial tension) and yield stress anisotropy for aluminum sheets.
It was shown that, for these textures, the precipitate distribution had the effect of reducing plastic anisotropy, in agreement
with the trends generally observed in practice. 相似文献
12.
Manpreet Singh Anindya Das T. Venugopalan Krishnendu Mukherjee Mahesh Walunj Tarun Nanda B. Ravi Kumar 《Metallurgical and Materials Transactions A》2018,49(2):463-475
The effects of microstructure parameters of dual-phase steels on tensile high strain dynamic deformation characteristic were examined in this study. Cold-rolled steel sheets were annealed using three different annealing process parameters to obtain three different dual-phase microstructures of varied ferrite and martensite phase fraction. The volume fraction of martensite obtained in two of the steels was near identical (~ 19 pct) with a subtle difference in its spatial distribution. In the first microstructure variant, martensite was mostly found to be situated at ferrite grain boundaries and in the second variant, in addition to at grain boundaries, in-grain martensite was also observed. The third microstructure was very different from the above two with respect to martensite volume fraction (~ 67 pct) and its morphology. In this case, martensite packets were surrounded by a three-dimensional ferrite network giving an appearance of core and shell type microstructure. All the three steels were tensile deformed at strain rates ranging from 2.7 × 10?4 (quasi-static) to 650 s?1 (dynamic range). Field-emission scanning electron microscope was used to characterize the starting as well as post-tensile deformed microstructures. Dual-phase steel consisting of small martensite volume fraction (~ 19 pct), irrespective of its spatial distribution, demonstrated high strain rate sensitivity and on the other hand, steel with large martensite volume fraction (~ 67 pct) displayed a very little strain rate sensitivity. Interestingly, total elongation was found to increase with increasing strain rate in the dynamic regime for steel with core–shell type of microstructure containing large martensite volume fraction. The observed enhancement in plasticity in dynamic regime was attributed to adiabatic heating of specimen. To understand the evolving damage mechanism, the fracture surface and the vicinity of fracture ends were studied in all the three dual-phase steels. 相似文献
13.
A 0.4 pct C-2 pct Si-1 pct Cr-1 pct Mo steel was quenched and tempered at 773 K (500 °C) and deformed by multi-pass caliber rolling (i.e., warm tempforming). The microstructures and the mechanical properties of the warm tempformed steels were investigated as a function of the rolling reduction. At rolling reductions of more than 28 pct, not only extension of the martensite blocks and/or the packets in the rolling direction (RD) but also a grain subdivision became more significant, and an ultrafine elongated grain (UFEG) structure with a strong ??110??//RD fiber deformation texture was formed after 78 pct rolling. The tensile deformation behavior became significantly anisotropic in response to the evolution of UFEG structure. The longitudinal yield strength (??y) of the quenched and tempered sample increased from 1480 to 1860 MPa through the 78 pct rolling, while the transverse ??y leveled off at around 1600 MPa up to 28 pct rolling. The transverse true fracture stress was also markedly degraded in contrast to the longitudinal one. Charpy impact properties were enhanced at a rolling reduction of 52 pct or more. The 52 pct-rolled sample underwent a ductile-to-brittle transition in the temperature range from 333 K to 213 K (60 °C to ?60 °C), while the 78 pct-rolled sample showed an inverse temperature dependence of the impact toughness because of brittle delamination. The tensile and Charpy impact properties are discussed in association with the microstructural evolution. 相似文献
14.
M. Papa Rao V. Subramanya Sarma S. Sankaran 《Metallurgical and Materials Transactions A》2014,45(12):5313-5317
Ultrafine-grained dual phase microalloyed V-Nb steel with ultimate tensile strength of 1371 MPa and uniform elongation of 16 pct characterized by bimodal ferrite grain structure was obtained through warm rolling and subsequent intercritical annealing. The bimodal ferrite grain structure with uniform dispersion of Nb/V carbides and strong γ-fiber texture promoted high strain hardening rate and high uniform elongation and high strength is attributed to ultrafine-grained ferrite and martensite. 相似文献
15.
The effects of α and β phase interactions on the room-temperature tensile and creep deformation behavior of α + β titanium
alloys with Widmanst?tten microstructures were studied using Ti-6.0 wt pct Mn and Ti-8.1 wt pct V as the model two-phase alloy
systems. This article, Part I, deals with tensile deformation. It was found that when the α phase is present as thin (<10-μm)
plates in the α + β alloys, significant twinning occurs. No significant twinning was observed in single-phase alloys with
the same chemistry and similar grain size. Additionally, the β phase of Ti-8.1 V deforms by stress-induced hexagonal martensite
(α′), while only twinning occurs in the single-phase β alloy with the same chemistry. Twinning in the α phase in association
with stress-induced martensite (SIM) in the β phase was observed for the first time in a two-phase titanium alloy. This behavior
is explained in terms of a number of factors including elastic interaction stresses between the α and β phases, coherency
between the α phase and hexagonal martensite, and β phase stability. 相似文献
16.
用连续退火模拟试验机,在实验室试制了冷轧高硅DP590,并通过扫描电镜、EBSD、透射电镜和力学性能测试研究了不同退火温度(735~835℃)对其组织和力学性能的影响。结果表明:退火温度对高硅双相钢强度和塑性有重要的影响,当退火温度为785℃时,材料获得良好的综合力学性能。不同温度退火后得到的组织均为铁素体和均匀分布在其晶界上的岛状马氏体;利用EBSD技术清晰地观察到离散分布于铁素体和马氏体晶界处的残余奥氏体。运用透射电镜观察到马氏体周围的位错线及位错团,这是双相钢连续屈服特性的重要保障。 相似文献
17.
The load partitioning between two phases in a cold-rolled duplex stainless steel has been experimentally studied in situ by X-ray diffraction, for different loading directions. It was found that the load partitioning between the two phases is
dependent on the loading direction. For loading in the rolling direction, both phases deform plastically to the same degree,
while more plastic deformation occurs in the austenitic phase during loading in the transverse direction. For loading in the
45-deg direction, more plastic deformation occurs in the ferritic phase. The strong crystallographic texture in the ferritic
phase makes the material anisotropic, with a higher stiffness and yield strength in the transverse direction compared to the
rolling direction. The measured texture was used as input to theoretical predictions of both elastic and plastic anisotropy.
The plastic anisotropy was predicted by assuming intragranular slip as the main deformation mechanism. The predicted anisotropic
material properties were then used in finite-element simulations to study the flow behavior of the material in different directions.
The predicted flow behavior was found to be in good agreement with the experimentally observed load partitioning between the
phases for loading in the rolling and transverse directions. However, the yield strength of the ferritic phase during loading
in the 45-deg direction was found to be lower than what was predicted. The reason for this is the difference in slip characteristics
in different sample directions, because of the morphological texture. 相似文献
18.
Multiscale structure and properties of cast and deformation processed polycrystalline NiTi shape-memory alloys 总被引:1,自引:0,他引:1
Carl P. Frick Alicia M. Ortega Jeffrey Tyber Ken Gall Hans J. Maier 《Metallurgical and Materials Transactions A》2004,35(7):2013-2025
The objective of this study is to examine fundamental processing-structure-property relationships in polycrystalline NiTi
bars. Three different polycrystalline Ti-50.9 at. pct Ni (Ti-55.7 wt pct Ni) materials were examined: (1) cast, (2) cast then
hot rolled, and (3) cast, hot rolled, then cold drawn. The structure of the materials was investigated at various scales ranging
from nanometers to micrometers. The cast materials contained random crystallographic textures along the loading axis of the
extracted samples. The hot-rolled and cold-drawn materials contained a strong 〈111〉 texture parallel to the deformation-processing
direction. The high-temperature hot-rolling process facilitated recrystallization and recovery, and curtailed precipitate
formation, leaving the hot-rolled and cold-drawn materials in near solutionized states. The cold-drawn material contained
a high density of dislocations and martensite. After a mild aging treatment, all three materials contained distributed coherent
Ti3Ni4 precipitates on the order of 10 nm in size. The cast material was capable of full shape-memory transformation strain recovery
up to approximately 5 pct strain at room temperature under both tension and compression. The hot-rolled and cold-drawn materials
demonstrated significant tension-compression stress-strain asymmetry owing to their strong crystallographic texture. Under
compression, the deformation-processed materials were only capable of 3 pct transformation strain recovery while under tension
they were capable of nearly 7 pct transformation strain recovery. Based on the present results, the presence of small coherent
Ti3Ni4 precipitates is determined to be the driving force for the favorable strain transformation strain recovery properties in
all three materials, despite drastically different grain sizes and crystallographic textures. The unique dependence of elastic
modulus on stress-state, temperature, and structure is also presented and discussed for the deformation-processed materials.
In addition, we demonstrate that the appearance of a Lüders band transformation under tensile loading can be controlled by
material structure. Specifically, the presence of significant martensite and dislocations in the cold-drawn materials was
shown to mitigate the Lüders band propagation and result in a more gradual transformation. 相似文献
19.
The effect of various grain structures, produced by thermomechanical treatments, on the monotonie tensile properties of the
Al-Cu-Li-Mn-Cd alloy 2020 was investigated. Materials having a completely or partially recrystallized structure exhibit elongations
between 4 and 8 pct when aged to peak strength. For both cases the low ductility is associated with (a) planar deformation,
(b) random texture, (c) the presence of large intermetallic compounds along the recrystallized grain boundaries, and (d)
precipitate free zones. The first three enhance crack nucleation at high angle grain boundaries, and subsequent crack propagation
occurs along the precipitate free zones. The completely unrecrystallized materials have elongations between 10 and 13 pct
in both longitudinal and transverse directions. The high ductility is associated with a sharp texture and a transgranular
fracture mode. The maximum ductility is obtained by reducing the unrecrystallized grain size. The results of this study suggest
that improved properties of a 2020-type alloy may be obtained by lowering the Fe and Si contents to remove coarse constituent
phases, eliminating Cd, and replacing Mn with Zr in order to obtain a highly textured, unrecrystallized structure. 相似文献
20.
A detailed characterization of two dissimilar high-strength steels, SCMV and Aermet 100, joined by inertia friction welding
(IFW)—a solid-state welding technique—was undertaken using high energy synchrotron X-ray diffraction and advanced electron
microscopy in order to understand the dramatic hardness variation across such a weld. It was found that the severe high-temperature
deformation in the thermomechanically affected zones (TMAZs) of the weld, stabilized ordered, and nanosized FeCo zones in
Aermet 100 and about 12 to 14 vol pct austenite in SCMV (Ni equivalent 9 wt pct). The ordered FeCo zones in Aermet 100 resulted
in exceptionally high hardness values of 700 to 725 HV. Very close to the weld line, the TMAZ of Aermet 100 also displayed
a region with about 15 vol pct austenite, while in the parent material, 8 to 9 vol pct was typically observed. No indication
of martensite was found in the weld region of Aermet 100. Ferrite texture analysis at different locations within the TMAZs
on either side of the weld showed that SCMV develops a very strong α-fiber texture near the weld line and, in addition, a γ-fiber texture toward the heat-affected zone (HAZ), suggesting the presence of ferrite during welding near the weld line and
recrystallization further away. The ferrite texture development in the TMAZ of Aermet 100 was relatively weak, suggesting
that austenite is a dominant phase in the TMAZ during IFW. 相似文献