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1.
The authors systematically investigated the effects of tungsten fiber on failure mode as well as deformation and fracture
mechanisms in tungsten fiber-reinforced Zr 41.25Ti 13.75Ni 10Cu 12.5Be 22.5 bulk metallic glassy composite under uniaxial compression at room and high temperatures. At room temperature, the failure
mode of the composite changes from shear fracture to longitudinal splitting failure with increasing fiber volume fraction.
Similar to the observations in monolithic metallic glasses, the shear fracture angle of the composite is approximately equal
to 39∼40 deg, indicating that the Mohr-Coulomb criterion is suitable to give the critical shear fracture condition of the
composite. When the compression tests were performed below the glass transition temperature of Zr 41.25Ti 13.75Ni 10Cu 12.5Be 22.5 metallic glass T
g, the deformation behavior of the composite strongly depends on the strain rates and the test temperature, which is quite
similar to the deformation behavior of monolithic metallic glasses in the supercooled liquid region. The corresponding failure
mode of the composite changes from shear or splitting fracture to bending failure with decreasing strain rate or increasing
test temperature. The failure modes at the temperature near T
g are mainly controlled by the metallic glass matrix due to the decrease in its viscosity at high temperature. Based on these
multiple failure modes, the effects of test temperature and tungsten fiber volume fraction on deformation and fracture mechanisms
are summarized. 相似文献
2.
The evolution of micro-damage and deformation of each phase in the composite plays a pivotal role in the clarification of deformation mechanism of composite. However, limited model and mechanical experiments were conducted to reveal the evolution of the deformation of the two phases in the tungsten fiber reinforced Zr-based bulk metallic glass composite. In this study, quasi-static compressive tests were performed on this composite. For the first time, the evolution of micro-damage and deformation of the two phases in this composite, i.e., shear banding of the metallic glass matrix and buckling deformation of the tungsten fiber, were investigated systematically by controlling the loading process at different degrees of deformation. It is found that under uniaxial compression, buckling of the tungsten fiber occurs first, while the metallic glass matrix deforms homogeneously. Upon further loading, shear bands initiate from the fiber/matrix interface and propagate in the metallic glass matrix. Finally, the composite fractures in a mixed mode, with splitting in the tungsten fiber, along with shear fracture in the metallic glass matrix. Through the analysis on the stress state in the composite and resistance to shear banding of the two phases during compressive deformation, the possible deformation mechanism of the composite is unveiled. The deformation map of the composite, which covers from elastic deformation to final fracture, is obtained as well. 相似文献
3.
In this work, Zr 53Cu 18.7Ni 12Al 16.3 alloy has been cast into rod samples with different diameters. Glassy composites with various volume fractions of quenched-in crystalline are obtained. Their mechanical behaviors and fracture mechanisms have been investigated upon both quasistatic and dynamic loading. As the volume fraction of crystalline phase increases, the increase in the strain-rate sensitivity exponent could be attributed to the combination of the reduction of the shear band-related deformability and the enhancement of the dislocation-related deformability. These results may shed more insight on optimizing the microstructure and performance of bulk metallic glass composites in the future. 相似文献
4.
Tensile, compressive, cyclic tension-tension, and cyclic compression-compression tests at room temperature were systematically
applied to a Zr 52.5Cu 17.9Al 10Ni 14.6Ti 5 bulk metallic glass for comprehensive understanding of its damage and fracture mechanisms. Under tensile loading, the metallic
glass only displays elastic deformation followed by brittle shear fracture. Under compressive loading, after elastic deformation,
obvious plasticity (0.5 to 0.8 pct) can be observed before the final shear fracture. The fracture strength under compression
is slightly higher than that under tension. The shear fracture under compression and tension does not occur along the maximum
shear stress plane. This indicates that the fracture behavior of the metallic glass does not follow the Tresca criterion.
The fracture surfaces show remarkably different features, i.e., a uniform vein structure (compressive fracture) and round cores coexisting with the radiating veins (tensile fracture).
Under cyclic tension-tension loading, fatigue cracks are first initiated along localized shear bands on the specimen surface,
then propagated along a plane basically perpendicular to the stress axis. A surface damage layer exists under cyclic compression-compression
loading. However, the final failure also exhibits a pure shear fracture feature as under uniaxial compression. The cyclic
compression-compression fatigue life of the metallic glass is about a factor of 10 higher than the cyclic tension-tension
fatigue life at the same stress ratio. Based on these results, the damage and fracture mechanisms of the metallic glass induced
by uniaxial and cyclic loading are elucidated. 相似文献
5.
The three-dimensional morphology of crystalline plates that form in as-cast Mg 65+x
(Cu 0.667Y 0.333) 30–x
Zn 5 ( x = 6, 12, 14, and 16) bulk metallic glass (BMG) composites was investigated by focused ion beam (FIB) tomography. The size,
shape, and distribution of the plates were found to be dependent both on alloy composition and cooling rate of the melt, whereby
rapid cooling and lower x values generated a lower volume fraction of plates due to a decreased propensity for crystallization. Using FIB tomography,
it was demonstrated that these plates may nucleate at micron-sized cuboidal, spherical, and irregularly shaped particles that
form first during the casting process. The plates subsequently grow in preferential directions during cooling of the alloy
to below the glass transition temperature to ultimately generate a multivariant, interwoven crystalline structure throughout
the amorphous matrix. This complex structure is argued to contribute to the improved toughness of the alloy by hindering the
propagation of gross shear bands and promoting the formation of multiple shear bands. 相似文献
6.
In the present study, (Zr55Cu30Al10Ni5)100−x
Nb(x=0,1,2,3) bulk metallic glass matrix/tungsten wire composites were fabricated by infiltration process. Structural studies were investigated by scanning electron microscopy and X-ray diffraction method. Also, mechanical behaviors of the materials were analyzed using quasi-static compressive tests. Results indicated that the best mechanical properties i.e., 2105 MPa compressive ultimate strength and 28 pct plastic strain before failure, were achieved in the composite sample with X = 2. It was also found that adding Nb to the matrix modified interface structure in W fiber/(Zr55Cu30Al10Ni5)98Nb2 since the stable diffusion band formation acts as a functionally graded layer. Finally, the observation of multiple shear bands formation in the matrix could confirm the excellent plastic deformation behavior of the composite. 相似文献
7.
We have investigated the mechanical behavior of a composite material consisting of a Zr 57Nb 5Al 10Cu 15.4Ni 12.6 metallic glass matrix with 60 vol pct tungsten particles under uniaxial compression over a range of strain rates from 10 −4 to 10 4 s −1. In contrast to the behavior of single-phase metallic glasses, the failure strength of the composite increases with increasing
strain rate. The composite shows substantially greater plastic deformation than the unreinforced glass under both quasi-static
and dynamic loading. Under quasi-static loading, the composite specimens do not fail even at nominal plastic strains in excess
of 30 pct. Under dynamic loading, fracture of the composite specimens is induced by shear bands at plastic strains of approximately
20 to 30 pct. We observed evidence of shear localization in the composite on two distinct length scales. Multiple shear bands
with thicknesses less than 1 μm form under both quasi-static and dynamic loading. The large plastic deformation developed in the composite specimens is
due to the ability of the tungsten particles both to initiate these shear bands and to restrict their propagation. In addition,
the dynamic specimens also show shear bands with thicknesses on the order of 50 μm; the tungsten particles inside these shear bands are extensively deformed. We propose that thermal softening of the tungsten
particles results in a lowered constraint for shear band development, leading to earlier failure under dynamic loading. 相似文献
8.
The rate-dependent deformation of Zr 38Ti 17Cu 10.5Co 12Be 22.5 bulk metallic-glass-reinforced porous tungsten matrix composites was investigated over a wide range of strain rates. The
composites were examined in two forms: the as-cast composite and the as-extruded composite by extrusion. In addition to showing
greater strain hardening, the as-cast composite also shows much more obvious strain rate dependence of flow stress than the
as-extruded composite. Microhardness tests were performed on the tungsten and the metallic glass phase in both composites,
respectively. The results from the microhardness measurements indicate that the strain rate sensitivity of the as-extruded
composite is primarily a result of strain rate sensitivity of the tungsten phase. 相似文献
9.
研究体积分数为60%的连续钨丝/Zr41.2Ti13.8Cu12.5Ni10Be22.5块体金属玻璃复合材料准静态压缩变形过程中剪切带的演化过程。发现在弹性变形段不形成剪切带,剪切带是在塑性变形过程中产生并发展的,且剪切带的数量随着变形量的增加而增大,间距随着变形量的增加而减小;当间距减小到一定值时产生剪切裂纹并不断扩展,最终导致断裂破坏。 相似文献
10.
Nb-1 wt pct Zr/218W long-fiber composite monotapes, nominally containing 0 to 70 vol pct of 218 tungsten fibers, were fabricated
by arc spraying the Nb-1 pct Zr matrix onto the tungsten fibers. The monotapes were consolidated by hot pressing and hot isostatic
pressing techniques. Tensile tests conducted between 1400 and 1600 K, under engineering strain rates varying between 1.5×10 −5 and 1.5×10 −3 s −1, demonstrated that composites containing 70 vol pct of fibers had the highest strength-to-density ratio. Microstructural
observations of specimens tested at 1400 K revealed that composites containing less than 50 vol pct of fibers showed extensive
matrix cavitation, fiber-matrix debonding, and necking of the fibers. Above 50 vol pct, the composite matrix was less prone
to cavitation, with an increasing tendency toward shear deformation of the fibers as the fiber volume fraction increased.
No fiber damage was observed at 1400 K away from the fractured end, but significant fiber damage was observed at higher temperatures.
A phenomenological model is presented to rationalize these observations.
This article is based on a presentation made in the Symposium “Mechanisms and Mechanics of Composites Fracture” held October
11–15, 1998, at the TMS Fall Meeting in Rosemont, Illinois, under the auspices of the TMS-SMD/ASM-MSCTS Composite Materials
Committee. 相似文献
11.
The room temperature brittleness has been a long standing problem in bulk metallic glasses realm.This has seriously limited the application potential of metallic glasses and their composites.The elastic deform-ation behaviors of metallic glass matrix composites are closely related to their plastic deformation states. The elastic deformation behaviors of Cu48-xZr48Al4Nbx(x=0, 3 at.%) metallic glass matrix composites (MGMCs) with different crystallization degrees were investigated using an in-situ digital image correlation (DIC) technique during tensile process.With decreasing crystallization degree, MGMC exhibits obvious elastic deformation ability and an increased tensile fracture strength.The notable tensile elasticity is attrib-uted to the larger shear strain heterogeneity emerging on the surface of the sample.This finding has impli-cations for the development of MGMCs with excellent tensile properties. 相似文献
12.
Copper mold cast cylinders of (Ti 0.5Cu 0.25Ni 0.15Sn 0.05Zr 0.05) 100−x
Mo
x
composites are prepared. Addition of Mo in the bulk glass-forming alloy induces the formation of a dendrite/matrix composite.
For 3-mm-diameter cylinders, the matrix exhibits a homogenous ultrafine microstructure for Mo content of 2.5 at. pct, and
a fine eutectic microstructure for 5 at. pct Mo. For 5-mm-diameter cylinders, the matrix exhibits a dendritic microstructure
for 2.5 at. pct Mo, and exhibits a coarser eutectic microstructure for 5 at. pct Mo. Despite the formation of a dendrite/nanostructured
matrix composite in the cylinders, the quenched surface layer with a nanoscale grain size dominates the deformation and fracture
of the 3-mm-diameter cylinders. More than 56 vol pct quenched layer leads to a distensile fracture mode and the samples exhibit
high fracture strength and high Young’s modulus but low ductility. For 5-mm-diameter cylinders, the composite microstructure
becomes dominant due to its more than 64 vol pct volume fraction leading to a cone-shaped fracture surface. The samples exhibit
lower yield strength and lower Young’s modulus but better ductility compared to the 3-mm-diameter cylinders. The mechanical
behavior of the Mo-bearing composites strongly depends on the microstructural homogeneity and casting defects formed upon
solidification. 相似文献
13.
Ti-based bulk metallic glasses (BMGs) with large compressive plasticity were developed in the Ti-rich part of Vitreloy series
BMGs (Ti 65–x
Zr
x
Cu 9Ni 8Be 18 alloys with x = 0, 5, 10, 15, and 20). The current materials exhibit high fracture strength reaching ~2.3 GPa and plastic strains up to
~8.3 pct after partial substitution of Zr by Ti. The plasticity of the investigated alloys strongly depends on the Zr content,
which affects the elastic constants, such as Poisson’s ratio and shear modulus. This, in turn, has an impact on the shear
transformation zone (STZ) volume and, hence, on the shear banding of the glasses. 相似文献
14.
Fracture and deformation characteristics of the Ti-based metallic glass matrix composite have been studied by the tensile test and the in situ TEM tension test. Typically, the composite exhibits the high strength and considerable plasticity. Microscopically, it was found that shear deformation zone formed at the crack tip in glass phase, which can bring about quick propagation of shear bands. However, the plastic deformation zone nearby the crack tip in dendrites will postpone or retard the crack extension by dislocations. The attributions of micro-deformations to mechanical properties of composites were discussed. 相似文献
15.
The elastic constants, fracture toughness, fracture morphology, and crack-tip plastic zone of a bulk amorphous alloy (bulk
metallic glass), with the composition Zr-10Al-5Ti-17.9Cu-14.6Ni (at. pct), were investigated. The room-temperature fracture
toughness reached values as high as 69 MPa&mrm. However, it showed considerable scatter, which is, at least in part, due to
microcrystalline regions in the castings. Controlled crack propagation could not be obtained in chevron-notched specimens.
The fracture-surface morphologies of chevron-notched specimens varied as the crack advanced, and this effect is probably related
to differences in the crack propagation rate. Controlled fracture resulting in featureless fracture surfaces was observed
during in-situ transmission electron microscope (TEM) fracture experiments. The plastic zone of a fatigue-precracked bulk flexure specimen
was examined in situ in an atomic-force microscope (AFM). Shear displacements up to 2 &gm m were found. The AFM observations did not reveal any cracks associated with the shear steps. Sectioning of shear steps using
a focused ion beam (FIB) with a diameter of 5 nm also did not reveal any cracks. 相似文献
16.
Nb-1 wt pct Zr/218W long-fiber composite monotapes, nominally containing 0 to 70 vol pct of 218 tungsten fibers, were fabricated
by arc spraying the Nb-1 pct Zr matrix onto the tungsten fibers. The monotapes were consolidated by hot pressing and hot isostatic
pressing techniques. Tensile tests conducted between 1400 and 1600 K, under engineering strain rates varying between 1.5×10 −5 and 1.5×10 −3 s −1, demonstrated that composites containing 70 vol pct of fibers had the highest strength-to-density ratio. Microstructural
observations of specimens tested at 1400 K revealed that composites containing less than 50 vol pct of fibers showed extensive
matrix cavitation, fiber-matrix debonding, and necking of the fibers. Above 50 vol pct, the composite matrix was less prone
to cavitation, with an increasing tendency toward shear deformation of the fibers as the fiber volume fraction increased.
No fiber damage was observed at 1400 K away from the fractured end, but significant fiber damage was observed at higher temperatures.
A phenomenological model is presented to rationalize these observations.
L.J. GHOSN, formerly Researcher with Case Western Reserve University, Cleveland, OH 44115
This article is based on a presentation made in the Symposium “Mechanisms and Mechanics of Composites Fracture” held October
11–15, 1998, at the TMS Fall Meeting in Rosemont, Illinois, under the auspices of the TMS-SMD/ASM-MSCTS Composite Materials
Committee. 相似文献
17.
The room temperature mechanical properties of the metallic glass Cu 46Zr 54 have been investigated as a function of aging time at 375°C (15°C below T
g). The results indicate that the tensile fracture stress and hardness of this material can be changed by such thermal processing.
Fracture stress and hardness are increased with short times at temperature by structural relaxation. Also, the presence of
a very small volume fraction of crystalline phase causes the shear stiffness of the material to increase markedly providing
an additional increase in fracture stress and hardness. Continued devitrification causes embrittlement and the decrease of
fracture stress, as predicted by the model of two-phase materials; however, hardness continues to increase, reflecting the
increasing volume fraction of the harder crystalline phases. Embrittlement and decreasing fracture stress are enhanced by
the stress concentration effect at the crystallites which causes void formation and growth.
ROBERT L. FREED formerly with the Department of Materials Science and Engineering, MIT 相似文献
19.
Gd-based bulk metallic glass has drawn strong attention because of its large magnetic entropy changes. Thermal stability of metallic glass is a very important issue for its application. In the paper, crystallization behavior of Gd53Al24Co20Zr3 bulk metallic glass was investigated using non-isothermal differential scanning calorimetric (DSC) technique. Attention was given to the analytic details. The crystallized volume fractions as a function of temperature were derived from the DSC signals, where heat capacity change between amorphous phase and crystalline phase was considered. The local activation energies at different crystallized volume fraction were estimated using Doyle-Ozawa and Agrawal methods. The results suggested that the Doyle-Ozawa equation was appropriate to get local activation energy due to its simplicity and accuracy. The local activation energy depended on the crystallized volume fraction. Function reflecting crystallization mechanism was also deduced. The crystallization mechanism of the Gd-based bulk metallic glass was discussed. 相似文献
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