共查询到20条相似文献,搜索用时 15 毫秒
1.
L. Farbaniec A. Abdul-Latif J. Gubicza G. Dirras 《Journal of Materials Science》2012,47(22):7932-7938
This article presents an application of the impact-induced deformation in effective grain refinement in polycrystalline nickel. Ultrafine-grained microstructure was processed by means of Dynamic Plastic Deformation at room temperature using a falling impactor with a maximum impact velocity of 10 m s−1. The commercially pure (98.4 wt%) starting material was characterised by a coarse-grained (~25 μm) microstructure. Electron backscattering diffraction and transmission electron microscopy studies showed that the initial equiaxed grains evolved into a laminar structure of submicron size narrow domains delineated by high-angle grain boundaries. The texture after deformation exhibits preferential orientations including a strong 〈220〉 fibre texture. The mechanical behaviour under quasi-static compression at room temperature and at a strain rate of 2 × 10−3 s−1 was investigated in directions parallel and perpendicular to the impact axis. Stress–strain responses showed an increased yield strength (440–520 MPa) compared with the initial state (90 MPa). The strain-hardening behaviour was found to strongly depend on the orientation of the compression axis. 相似文献
2.
D. E. Sefton M. A. Rist S. Gungor 《Journal of Materials Science: Materials in Electronics》2009,20(11):1083-1089
Compression experiments on bulk Sn-3.5Ag lead-free solder specimens have been carried out to help formulate the material constitutive
behaviour of this alloy using the concept of an evolving internal stress. Tests covered the temperature range 0–125 °C and
fixed strain rates between 3 × 10−7–3 × 10−3 s−1. Flow behaviour was found to be compatible with that for a deforming a tin-rich matrix (stress exponent n = 7, activation energy Q = 46.7 kJ/mol) in which the external applied stress is reduced by an internal back stress due to the presence of precipitate
phase particles. Stress–strain curves have been satisfactorily modelled using rate equations incorporating linear hardening
and diffusion-controlled recovery. Comparison with supplementary tension and creep experiments, and with data from other researchers,
indicates that inconsistencies in reported flow behaviour is most likely to be due to variations in initial microstructure
rather than the nature of the applied loading. 相似文献
3.
An Inconel 718 sheet alloy was tested in tension at a temperature of 965°C and an initial strain rate of 10−4 s−1 corresponding to the conditions for optimum superplastic deformation. Detailed observations and quantitative measurements
record the evolution of the δ-phase during tensile deformation. The experiments show that the total precipitation of the δ-phase
increases with strain but there is a decrease with strain in the number density of the needle/plate δ-phase particles and
a corresponding increase with strain in the number density of the blocky/globular δ-phase particles. 相似文献
4.
Cork is a natural cellular material with increasing industrial applications due to its remarkable combination of properties.
Its mechanical behaviour explains why it is often used for applications like sealing, packaging, insulation, vibration control,
weight reduction, flotation, sound damping, etc. However, the mechanical behaviour of cork when subjected to impact has not
been well investigated yet since the studies described in the literature generally focus strain rates below 10−1 s−1. Understanding the behaviour of cork at high rates of deformation becomes imperative when considering applications such as
crash protection. Hence, in the present work, the authors compare the quasi-static and dynamic response of four types of cork
when compressed axially at strain rates from 10−3 s−1 to 600 s−1. Data from the Split-Hopkinson Pressure Bars are used to generate stress–strain curves for natural and agglomerate cork samples,
and the results are discussed in terms of the cellular structure of cork. 相似文献
5.
Effect of joint stiffness on peel strength of diffusion bonded joints between Al–Li 8090 alloy sheet
《Materials Science & Technology》2013,29(12):1131-1140
AbstractThe peel behaviour of diffusion bonded joints between Al–Li 8090 alloy sheet depends upon joint geometry, sheet thickness, and the local stiffness of the bonded joint. The local stiffness was increased by bonding 8090 metal matrix composite onto the faces of the joint. At the superplastic forming temperature of 530°C the peel strengths of solid state or liquid phase diffusion bonded joints at peak load were increased from 5–7 N mm?1 to >8 N mm?1. This led to superplastic deformation of the sheet without peel fracture at the bonded joint. After air cooling and aging, the corresponding room temperature peel strengths were 174–252 N mm?1, compared with 30–54 N mm?1 for an unstiffened joint, an increase by a factor of 3·2–8·4. It was concluded that stiffened bonded joints would enable multiple thin sheet structures to be manufactured in Al–Li 8090 alloy via a diffusion bonding/superplastic forming (DB/SPF) technique. A DB/SPF technique for a three sheet structure is described.MST/1687 相似文献
6.
The oxidation behaviour of 8090 Al−Li alloy sheet was studied after exposure for short times (<5 min) in laboratory air, moist
air, moist argon and hydrogen at 530°C. Oxidation was greater at grain boundaries in hydrogen but not in air. Sites of rapid
local oxidation (number density 9 to 8 × 103 cm−2) were associated with insoluble particles. Four types of growth morphology were identified with these sites. Some growths
believed to be spinel, were 10 to 25 μm diameter and grew to ≈1 mm in height at 2μm sec−1. Pits beneath these growths were ≈25 μm diameter and 10 to 20 μm deep. A qualitative model is proposed for rapid oxidation
in Al−Li alloys and the effect of these sites on weight gain measurements, surface contamination and mechanical properties
is discussed. 相似文献
7.
The high temperature deformation characteristics of a commercial β -titanium alloy Ti-3Al-8V-6Cr-4Mo-4Zr have been studied
in the temperature range 830–925∘C. The alloy exhibited superplasticity in a narrow temperature and strain rate range i.e.
850–865∘C and 5× 10− 5–3× 10− 3 s− 1 respectively, with a maximum elongation of 634% at 855∘C. The superplastic behaviour in the alloy is considered to arise
as a result of subgrain formation at the higher strain rates (region III) which enhances diffusional creep at lower strain
rates (region II). The activation energy values for regions II and III were found to be close to the lower of the two activation
energy values (129.2 KJ/mole) proposed to describe self diffusion in β -phase suggesting that the rate controlling mechanism
during high temperature deformation of the alloy was that for lattice diffusion. 相似文献
8.
Deformation and microstructural behaviours of a 20% (volume percent) particle reinforced 6061 Al matrix composite have been
studied by torsion from 25 to 540°C with strain rates of 0.1, 1 and 5 s−1. The logarithmic stress versus reciprocal temperature relationship exhibits two slopes indicating different deformation mechanisms.
The 20% Al2O3/6061 Al composite shows a greater hardening behaviour than those of the 10% Al2O3/6061 Al composite and of the monolithic alloy. Above 250°C, TEM investigations reveal much smaller subgrain size and higher
volume of non-cellular substructures, as well as dynamic recrystallization nuclei in the 20% Al2O3/6061 Al composite in comparison to those of the 10% Al2O3/6061 Al composite and matrix alloy the same test condition. The torsion fracture surface was studied and compared to the
three point bending failure specimens. 相似文献
9.
A Ray P Barat P Mukherjee A Sarkar S K Bandyopadhyay 《Bulletin of Materials Science》2007,30(1):69-71
Plastic flow behaviour of low carbon steel has been studied at room temperature during tensile deformation by varying the
initial strain rate of 3·3 × 10−4s−1 to a final strain rate ranging from 1·33 × 10−3s−1 to 2 × 10−3s−1 at a fixed engineering strain of 12%. Haasen plot revealed that the mobile dislocation density remained almost invariant
at the juncture where there was a sudden increase in stress with a change in strain rate and the plastic flow was solely dependent
on the velocity of mobile dislocations. In that critical regime, the variation of stress with time was fitted with a Boltzmann
type Sigmoid function. The increase in stress was found to increase with final strain rate and the time elapsed in attaining
these stress values showed a decreasing trend. Both of these parameters saturated asymptotically at a higher final strain
rate. 相似文献
10.
Jingqi Zhang Hongshuang Di Hongtao Wang Kun Mao Tianjun Ma Yu Cao 《Journal of Materials Science》2012,47(9):4000-4011
The hot deformation behavior of Ti-15-3 titanium alloy was investigated by hot compression tests conducted in the temperature
range 850–1150 °C and strain rate range 0.001–10 s−1. Using the flow stress data corrected for deformation heating, the activation energy map, processing maps and Zener–Hollomon
parameter map were developed to determine the optimum hot-working parameters and to investigate the effects of strain rate
and temperature on microstructural evolution of this material. The results show that the safe region for hot deformation occurs
in the strain rate range 0.001–0.1 s−1 over the entire temperature range investigated. In this region, the activation energy is ~240 ± 5 kJ/mol and the ln Z values vary in range of 13.9–21 s−1. Stable flow is associated with dynamic recovery and dynamic recrystallization. Also, flow instabilities are observed in
the form of localized slip bands and flow localization at strain rates higher than 0.1 s−1 over a wide temperature range. The corresponding ln Z values are larger than 21 s−1. The hot deformation characteristic of Ti-15-3 alloy predicted from the processing maps, activation energy map, and Zener–Hollomon
parameter map agrees well with the results of microstructural observations. 相似文献
11.
Specimens were prestretched in the range 0 to 7% plastic deformation prior to artificial ageing, or were duplex aged, to investigate
the effect of dislocation substructure and of S(Al2CuMg) particles on plastic flow during room and elevated temperature tensile tests. The yield stresses increased in Al-Li-Cu-Mg-Zr
alloys 8090 and 8091 after stretching, due to the dislocation cells introduced by the stretch and also to the nucleation and
growth of the S-phase particles on these dislocations. Up to 400 K the modulus-normalized proof stresses for the variously
treated materials were constant, but they fell at higher temperatures, as dislocation climb mechanisms operated. The proof
stresses of alloy 8090 fell at a temperature 50 K lower than alloy 8091, and this difference is considered to arise from the
differing volume fraction of S-phase in the two alloys. The work hardening rate (ϑ) at a strain of 0.2% was measured between
300 and 500 K. In alloy 8090, the temperature at which dynamic recovery occurs was influenced by the degree of stretch, but
this was not so in alloy 8091. In alloy 8090, the substructure introduced by stretching was able to act as a dislocation sink
during dynamic recovery, whereas in alloy 8091 the higher copper content brought about more S-phase precipitation which was
sufficient to inhibit this effect. The athermal hardening rate (ϑo) was obtained by extrapolation of the ϑ-σt curves, giving ϑo=10000 GPa, for alloy 8090 and ϑo=8500 G Pa, for alloy 8091. This difference may reflect a higher mobile dislocation density in alloy 8090 due to the lower
volume fraction of S-phase particles in that material. 相似文献
12.
Woei-Shyan Lee Chi-Feng Lin Tao-Hsing Chen Hsin-Hwa Hwang 《Journal of Materials Science》2008,43(5):1568-1575
A compressive split-Hopkinson pressure bar apparatus and transmission electron microscopy (TEM) are used to investigate the
deformation behaviour and microstructural evolution of Ti–15Mo–5Zr–3Al alloy deformed at strain rates ranging from 8 × 102 s−1 to 8 × 103 s−1 and temperatures between 25 °C and 900 °C. In general, it is observed that the flow stress increases with increasing strain
rate, but decreases with increasing temperature. The microstructural observations reveal that the strengthening effect evident
in the deformed alloy is a result, primarily, of dislocations and the formation of α phase. The dislocation density increases
with increasing strain rate, but decreases with increasing temperature. Additionally, the square root of the dislocation density
varies linearly with the flow stress. The amount of α phase increases with increasing temperature below the β transus temperature.
The maximum amount of α phase is formed at a temperature of 700 °C and results in the minimum fracture strain under the current
loading conditions. 相似文献
13.
R. U. Vaidya Z. R. Xu X. Li K. K. Chawla A. K. Zurek 《Journal of Materials Science》1994,29(11):2944-2950
The ageing kinetics of a silicon carbide particle-reinforced Al-Li (8090) matrix composite and unreinforced alloy, both made by spray forming, were investigated. Ageing treatments, without any straining after solutionizing, and with a 2% plastic strain after solutionizing, were employed. The peak ageing times of the matrix in the composite was shorter than that of the unreinforced alloy. The enhanced hardening rate of the matrix in the composite was attributed to the higher dislocation density induced as a result of the plastic deformation occurring at the particle/matrix interface. This plastic deformation is a result of the large difference in the coefficient of thermal expansion between the particles and matrix. Subjecting the samples to a 2% plastic strain reduced the peak ageing times even further. The tensile strength of the composite samples was marginally higher than that of the unreinforced alloy. Samples subjected to 2% plastic straining prior to ageing also exhibited higher strength values. The strain to failure of all the samples did not recover in the over-aged state. 相似文献
14.
The hot deformation behavior of Al 2024 was studied by isothermal hot compression tests in the temperature range of 250–500 °C
and strain rate range of 10−3 to 102 s−1 in a computer-controlled 50 kN servo-hydraulic universal testing machine (UTM). The results show that the flow stress of
Al 2024 alloy increases with strain rate and decreases after a peak value, indicating dynamic recovery and recrystallization.
The processing map exhibits two domains of optimum efficiency for hot deformation at different strains, including the low
strain rate domain at 500 °C and between 10−2 and 10−1 s−1 and the high strain rate domain in 250 and 300 °C in the strain rate range of 101 to 102 s−1. An attempt has been made in this article to generate a new hybrid 4D process map which illustrates contours of power dissipation
and instability in the 3D space of strain rate, temperature, and strain. 相似文献
15.
《Materials Science & Technology》2013,29(3):303-312
AbstractThe effect of sillimanite reinforcement on the dry sliding wear behaviour of aluminium silicon alloy (BS LM6) composite was investigated using a pin-on-disc sliding wear test machine. The composite specimens were prepared using the liquid metallurgy technique and 10 wt-% of sillimanite particles were incorporated in the matrix alloy. Sliding wear tests were conducted at applied pressures between 0.2 and 1.6 MPa and speeds of 1.89, 3.96 and 5.55 m s-1. The matrix alloy was also prepared and tested under identical conditions in order to enable comparison. It was observed that the sillimanite reinforced composite exhibited a lower wear rate than the matrix alloy. Increase in applied load increased the wear rate while increase in speed exhibited the reverse effect. The seizure pressure of the composite was significantly higher than that of the matrix alloy. The temperature rise near the contacting surface and the coefficient of friction were less in the composite than in the matrix alloy. SEM micrographs of the worn surface and subsurface were used to predict the nature of the wear mechanism. 相似文献
16.
Polymeric foams are commonly used in many impact-absorbing applications and thermal-acoustic insulated devices. To improve
their mechanical performances, these structures have to be modeled. Constitutive equations (for their macroscopic behavior)
have to be identified and then determined by appropriate tests.Tests were carried out on polypropylene foams under high strain
rate compression. In this work, the material behaviour has been determined as a function of two parameters, density and strain
rate. Foams (at several densities) were tested on a uniaxial compression for initial strain rates equal to 0.34 s−1 and on a new device installed on a flywheel for higher strain rates. This apparatus was designed in order to do stopped dynamic
compression tests on foam. With this testing equipment, the dynamic compressive behaviour of the polymeric foam has been identified
in the strain rate range [6.7.10−4s−1, 100s−1].Furthermore, the sample compression was filmed with a high speed camera monitored by the fly wheel software. To complete
this work, picture-analysis techniques were used to obtain displacement and strain fields of the sample during its compression.
Comparisons between these results and stress-strain responses of polypropylene foam allow a better understanding of its behaviour.
The multiscale damage mechanism, by buckling of the foam structure, was emphasised from the image analysis. 相似文献
17.
Serrated flow in a Ni–Co–Cr-base superalloy was studied in three microstructural conditions (SUB, SUBA, and SUPER) from 25
to 750 °C by tensile test at initial strain rates ranging from 8 × 10−5 to 3 × 10−3 s−1. The results showed that the SUB and SUBA samples had fine grain size of about 9 μm, whereas the SUPER samples had coarse
grain size of about 600 μm. The tertiary γ′ fraction was about 0 in the SUB, 5% in the SUBA, and 15% in the SUPER samples,
respectively. The types and temperature ranges of serration were different in the alloy with SUB, SUBA, and SUPER microstructures.
It is proposed that the tertiary γ′ fraction and size had great effects on the serrated flow of the alloy with different microstructures. 相似文献
18.
Vladimir Gantchenko Patrice Jouinot Alain Köster 《Journal of Materials Science》2008,43(15):5342-5349
A mechanical modelling is proposed in order to describe viscoplastic behaviour without hardening of a nickel-base super alloy
loaded at high temperature (900 °C) with strain rates varying within a wide range (from 10−1 to 10−4 s−1). A mathematical law is associated to the viscoplastic model; the parameters of the law are identified from monotonic biaxial
tests of membranes loaded by pressure of inert gas (disk pressure testing under helium). The viscoplastic law provides calculated
stresses with accuracy better than 1% at the highest strain rates and 4% at the lowest strain rates; the identified yield
stress is a logarithmical function of strain rate as for other metallic alloys studied in the bibliography. The parameters
identified from biaxial tensile tests of disks have been successfully used to calculate the stresses during stabilized tension–compression
loops of cylindrical specimens. The proposed experimental method and behaviour model are interesting because the disk biaxial
testing is much more easily performed at high temperature than the tension–compression testing of cylindrical specimens. 相似文献
19.
O. N. Senkov J. M. Scott S. V. Senkova F. Meisenkothen D. B. Miracle C. F. Woodward 《Journal of Materials Science》2012,47(9):4062-4074
Compression properties of a refractory multi-component alloy, Ta20Nb20Hf20Zr20Ti20, were determined in the temperature range of 296–1473 K and strain rate range of 10−1–10−5 s−1. The properties were correlated with the microstructure developed during compression testing. The alloy was produced by vacuum
arc melting, and it was hot isostatically pressed (HIPd) and homogenized at 1473 K for 24 h prior to testing. It had a single-phase
body-centered cubic structure with the lattice parameter a = 340.4 pm. The grain size was in the range of 100–200 μm. During compression at a strain rate of έ = 10−3 s−1, the alloy had the yield strength of 929 MPa at 296 K, 790 MPa at 673 K, 675 MPa at 873 K, 535 MPa at 1073 K, 295 MPa at
1273 K and 92 MPa at 1473 K. Continuous strain hardening and good ductility (ε ≥ 50%) were observed in the temperature range
from 296 to 873 K. Deformation at T = 1073 K and έ ≥ 10−3 s−1 was accompanied by intergranular cracking and cavitation, which was explained by insufficient dislocation and diffusion mobility
to accommodate grain boundary sliding activated at this temperature. The intergranular cracking and cavitation disappeared
with an increase in the deformation temperature to 1273 and 1473 K or a decrease in the strain rate to ~10−5 s−1. At these high temperatures and/or low-strain rates the alloy deformed homogeneously and showed steady-state flow at a nearly
constant flow stress. Partial dynamic recrystallization, leading to formation of fine equiaxed grains near grain boundaries,
was observed in the specimens deformed at 1073 and 1273 K and completed dynamic recrystallization was observed at 1473 K. 相似文献
20.
Hydrogen diffusivity and solubility were determined by electrochemical hydrogen permeation tests in samples of Pd0.97 Al0.03 and Pd0.97 Ce0.03 in the as received and internally oxidized conditions. Internal oxidization caused the appearance of nanosized oxide precipitates
in the Pd matrix. The shape and size of precipitates and also the coherence between the precipitates and the matrix were observed
by transmission electron microscopy (TEM). Electrochemical hydrogen permeation tests revealed that the presence of oxides
increases the apparent hydrogen solubility, S
app, but decreases the hydrogen diffusivity, D
app. The values of D
app were 2.0 × 10−11 m2 s−1 for vacuum heat treated Pd0.97 Al0.03 alloy and 4.0 × 10−12 m2 s−1 for internally oxidized Pd0.97 Al0.03 alloy. However, the concentration of trapped hydrogen was 49 mol H.m−3 for the Pd0.97 Al0.03 alloy in the vacuum heat treated condition and 403 mol H.m−3 for the Pd0.97 Al0.03 alloy in the internally oxidized condition. Both heat treatments were performed at 1073 K for 24 h. The influence of the
nature, size and distribution of the precipitates on the hydrogen permeation parameters are discussed in this paper. 相似文献