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1.
An electron microscopic investigation of Cu-9 wt pct Al alloy low thermal treated at 250°C for 30 min was performed in the deformed and non-deformed condition. For this composition and ordering treatment the alloy exhibits the higher increase in strength. It was found that the images formed in the non-deformed alloy, reveal the presence of ordered domains of an average size of 80Å, being the amount of order dependent of whether or not quenched-in vacancies are present. It is probable that the domains nucleate preferentially at stacking faults in the deformed condition. A periodic antiphase structure was determined from computations and comparison with electron diffraction data. The superlattice cell is based on the LI 2 type, tetragonal face centered with a period approximately three times the lattice parameter of the matrix, having three variants of orientation within an ordered region. 相似文献
2.
Transmission electron microscopy observations have been carried out for a Cu-14 pct Al-4 pct Ni (wt pct) alloy aged in the
thin foil state in an electron microscope. It was found that large cuboidal precipitates of the γ
2 phase and many small domains of a highly ordered phase form in the DO 3 matrix during aging. The small ordered domains form preferentially on matrix antiphase boundaries as well as within the antiphase
domains. The formation of γ
2 and the highly ordered phase, both of which are rich in alloy content, depletes the matrix of solute and thus raises the
transformation temperatures M
s and M
f. The small domains of the highly ordered phase prevent the propagation and reversion of martensite plates, leading to higher M
s-M f and A
fins-A f temperature intervals. 相似文献
3.
Transmission electron microscopy (TEM) methods have been used to examine the dislocation structures in thin foils of Ni 3Fe in four different states, corresponding to disordered and deformed; fully ordered and deformed; deformed when disordered and afterwards fully ordered; and deformed when disordered, afterwards fully ordered and additionally deformed. The study has been carried out on single crystals deformed at room temperature. In the disordered alloy slip is coarse and group motion of dislocations is prevailing, as is confirmed by the abundance of planar dislocation arrays. The dislocation structure of such a disordered deformed crystal remains unchanged after additional ordering by annealing 1000 h at 460°C. No rearrangement of the unit dislocations into superlattice dislocations is observed. The dislocations are preserved and since they are unit dislocations they are sessile. The additional deformation of this disordered deformed and afterwards fully ordered crystal proceeds by the glide of superlattice dislocations. They originate in the high internal stresses of the preserved unit dislocations. Cross slip from (111) onto (11̄1) planes is very frequent, whereas cross slip from (111) onto (010) planes is rather rare. The structure of the superlattice dislocations in fully ordered and deformed specimens consists of dipoles and bundles of dipoles of near edge orientation. Superlattice dislocations of near screw orientation are rarely observed, since they cross slip from (111) onto (11̄1) planes and annihilate in most cases. The experimental results on ordered Ni 3Fe samples differ characteristically from those reported in the literature on other alloys having the L1 2 long range ordered structure (e.g. Ni 3Al, Cu 3Au, Ni 3Ga). 相似文献
4.
It is now well established that a considerable improvement in the mechanical and chemical properties of the near surface regions of materials may be achieved by the use of high energy laser beams. By manipulating the laser power density and the time of interaction of the laser beam with an appropriately coated work piece, it is possible to achieve a surface chemistry that would have an improved resistance to wear, fatigue and corrosion failures. The change in chemistry at the surface is attained through the process of melting and mixing of the coating and a thin layer of the substrate. Solidification of this molten region at the surface results, due to an interplay of various forces, in the development of very complex microstructures. To analyse these in a piece of nickel that had been coated with a mixture of molybdenum and aluminium powders and then treated with a continuous wave CO 2 laser, extensive transmission electron microscopy was done on a thin foil obtained from near the bottom region of the recast pool. The foil was found to have a cellular microstructure comprising cells of the Ni 3Al (γ′) ordered phase. In the intercellular regions, two dispersed phases, namely, martensitic Ll 0 phase and Ni 2Al 3, and a contiguous phase, identified as a close derivative of the equilibrium δ-NiMo phase were found. A gradient in the degree of order could be observed within the γ′ cells. In the central portion of the cells, rapid solidification resulted, by the process of sequential ordering, in the development of a partially ordered alloy with very fine domains. In the peripheral regions of the cells, the alloy solidified by direct ordering into larger domains. This paper discusses some of these results. 相似文献
5.
The early decomposition stages of Al-7.8at.%Li, Al-10.4at.%Li and Al-11.8at.%Li alloys were studied by high resolution electron microscopy. In all the above alloys, it was confirmed that in the as-quenched stage small ordered domains of Ll 2 structure were present surrounded by the disordered matrix. From this microstructure, it was concluded that the alloy was already decomposed as in the as-quenched stage. No clear evidence was found for congruent ordering which was proposed to occur prior to spinodal decomposition. Examination of the sublattices of the individual ordered domains also failed to give convincing evidence for congruent ordering. The present observations suggest that the kinetics of spinodal decomposition of this system is too fast to be detected by TEM. In order to slow down the decomposition kinetics, solution treated samples were quenched to just above the solvus line for δ′ and then to room temperature. By this heat treatment, a solution treated sample with muck weaker order spots could be obtained. However, this microstructure could not be interpreted as congruently ordered either based on the weak Ll 2 spots. As there is a limitation to the quenching speed, it is suggested that ordering and spinodal decomposition progress concomitantly during the observable range of time. 相似文献
6.
A Ni-52 at. pct Ti shape memory alloy, cold drawn to 30 pct, was annealed at 1173 K for 1 hour, water quenched, and then subjected
to differential scanning calorimetry (DSC). No evidence of the premartensitic R transformation was found during either the forward or the reverse transformation. Microstructurally, it was found that the
alloy possessed a relatively large volume fraction (∼0.05) of coarse second-phase brittle particles. These precipitates acted
as preferential sites for martensite plate nucleation and gave rise to a “starlike” morphology. The tensile and compressive
properties of the alloy in the as-received condition were also investigated. The alloy exhibited relatively good ductility
(fracture strain=0.28), which was attributed to its inherent ability to relieve or delay the development of plastic instabilities
through rapid strain hardening. In addition, X-ray diffraction (XRD) of deformed specimens indicated the presence of an extraintensity
peak corresponding to the B2 phase (110) B2 when the alloy was plastically deformed in compression. Accordingly, it is suggested that plastic deformation induces the
reverse transformation to the B2 phase in highly stressed local regions. Transmission electron microscopy (TEM) of deformed
martensite structures showed slip lines probably due to dislocation slip, as well as variant interpenetration. Besides, optical
and scanning microscopy of regions adjacent to the fractured surfaces indicated that fine martensite plates and/or “apparent”
new grains develop at regions of prior stress intensification (former crack-tip regions) during crack propagation. 相似文献
7.
Single crystals of a fully-ordered Cu 3Au alloy were deformed in compression at room temperature on a single glide system to a very high degree of plastic strain
in Stage II. Transmission electron microscopy observations showed a very high density of superlattice screw dislocations which
had cross-slipped onto {100} type planes. These cross-slipped superlattice dislocations were for the most part arranged as
plus-minus pairs, i.e. multipoles. It is this large density of cross-slipped superlattice dislocations which is believed responsible for the high
rate of work hardening observed in ordered Cu 3Au alloys.
J. CZERNICHOW, formerly Research Assistant, Engineering Materials Group and Department of Mechanical Engineering, University
of Maryland, College Park, Md. 相似文献
8.
A Ni-52 at. pct Ti shape memory alloy, cold drawn to 30 pct, was annealed at 1173 K for 1 hour, water quenched, and then subjected
to differential scanning calorimetry (DSC). No evidence of the premartensitic R transformation was found during either the forward or the reverse transformation. Microstructurally, it was found that the
alloy possessed a relatively large volume fraction (∼0.05) of coarse second-phase brittle particles. These precipitates acted
as preferential sites for martensite plate nucleation and gave rise to a “starlike” morphology. The tensile and compressive
properties of the alloy in the as-received condition were also investigated. The alloy exhibited relatively good ductility
(fracture strain = 0.28), which was attributed to its inherent ability to relieve or delay the development of plastic instabilities
through rapid strain hardening. In addition, X-ray diffraction (XRD) of deformed specimens indicated the presence of an extraintensity
peak corresponding to the B2 phase (110) B2 when the alloy was plastically deformed in compression. Accordingly, it is suggested that plastic deformation induces the
reverse transformation to the B2 phase in highly stressed local regions. Transmission electron microscopy (TEM) of deformed
martensite structures showed slip lines probably due to dislocation slip, as well as variant interpenetration. Besides, optical
and scanning microscopy of regions adjacent to the fractured surfaces indicated that fine martensite plates and/or “apparent”
new grains develop at regions of prior stress intensification (former crack-tip regions) during crack propagation. 相似文献
9.
The effect of ordering on susceptibility to hydrogen embrittlement of a Ni-base superalloy (alloy C-276) has been investigated
by means of tensile tests in air and with hydrogen-charging in 1N-H 2SO 4 solution. The annealed specimen has exhibited intergranular fracture by hydrogen-charging, resulting in a marked reduction
in tensile elongation and ultimate tensile strength. The mode of fracture was changed by aging at 773 K, and the transgranular
fracture has been found to be dominant in the aged specimens. The susceptibility to hydrogen embrittlement, as identified
by the test method used in this study, seems to be reduced by short-term aging, though it turns out to be increased again
by further aging. The fractured boundaries have been characterized using electron channeling pattern (ECP) analysis of adjacent
grains. It is found that the misorientation of grain boundaries plays an important role in fracture, and ∑3 boundaries, twin
boundaries in a face-centered cubic (fcc) lattice, are most likely to fracture in the aged specimens. Transmission electron
microscopy (TEM) observation has shown that a short-range ordering reaction from a disordered fcc lattice into an ordered
Ni 2(Cr, Mo) (Pt 2Mo type) super-lattice takes place by aging, and hence, superdislocation triplets with APB (antiphase boundary) become predominant
when deformed. It is also seen that in the aged specimens, deformation twinning is another mode of deformation, and this leads
to the transgranular fracture at twin boundaries by hydrogen-charging. These results suggest that a change in the mode of
deformation after aging plays a major role in fracture due to hydrogen embrittlement as a consequence of the heterogeneous
interaction between slip dislocations and twin boundaries. 相似文献
10.
The room temperature tensile properties of age-hardened Cu-3.6 wt pct Ti were investigated. The resulting structures of both
single- and double-aged samples were examined by transmission electron microscopy. Emphasis was placed on the correlation
of structure with mechanical properties. Isothermal aging at 400°C resulted in an increase in yield strength from that of
40 ksi in the solution-treated alloy to a maximum of 98 ksi after aging for 10,000 min (167 hr). The structure associated
with maximum strength was that of an aligned disordered cubic coherent precipitate. Examination of deformed specimens showed
that slip was heterogeneous both within a grain and along a given shear band. Aging at 550°C resulted in the same aligned
cubic coherent precipitate as at 10 min, but continued-isothermal holding caused the growth of a weaker recrystallized structure
and thus a decrease in strength. It was concluded that overaging in this system was due entirely to the consumption of the
continuous precipitate by the discontinuous. This recrystallized constituent was found to be composed of a copper-rich solid
solution and Cu3Ti arranged in alternate parallel lamellae. The hcp Cu 3Ti precipitate had its close-packed plane parallel to the {Ill} plane of the matrix, and edge dislocations were found to take
up the misfit between these two structures. A series of single- and multiple-aging treatments gave three completely recrystallized
structures with approximately the same yield strength. However, the total elongation of these structures decreased as the
final aging temperature was reduced. This was attributed to an ordering reaction in the Cu 3Ti plates at lower temperatures. Direct evidence of a change in deformation characteristics was obtained by examining specimens
deformed to the same extent, but having different degrees of order induced by varying the final aging temperature. The disordered
plates were shown to plastically deform along with the matrix, but the ordered plates fractured.
Formerly Graduate Student, Department of Metallurgy and Materials Sciences, New York University, Bronx, N. Y.
This paper is based upon a thesis submitted by H. T. MICHELS in partial fulfillment of the requirements of the degree of Doctor
of Philosophy at New York University. 相似文献
11.
The effects of plastic deformation on the magnetic properties of austenite structure in an Fe-40% Ni-2 % Mn alloy is investigated by using Mossbauer spectroscopy and Differential Scanning Calorimetry (DSC) techniques The morphology of the alloy has been obtained by using Scanning Electron Microscopy (SEM). The magnetic behaviour of austenite state is ferromagnetic. After plastic deformation, a mixed magnetic structure including both paramagnet- ic and ferromagnetic states has been obtained at the room temperature. The volume fraction changes, the effective hyperfine fields of the ferromagnetic austenite phase and isomery shift values have also been determined by Mossbauer spectroscopy. The Curie point (Tc) and the Neel temperature (TN) have been investigated by means of DSC system for non-deformed and deformed Fe-Ni-Mn alloy. The plastic deformation of the alloy reduces the TN and enhances the paramagnetic character of austenitic Fe-Ni-Mn alloy. 相似文献
12.
利用ThermecMaster-Z热模拟实验机测定了一种Nb-V-Ti微合金化高强度钢08MnCr(S2)在910~1 200℃不变形(静态)和变形(动态)奥氏体0.05~30℃/s冷速下连续冷却转变(CCT)曲线,并分析和观察了对应的相变及组织。实验结果表明,提高轧后的冷却速度使Ar 3降低,导致钢的晶粒进一步细化;冷却速度大于10℃/s开始出现贝氏体转变。提高加热温度时相变温度降低,变形奥氏体相变温度较不变形奥氏体相变温度高。冷速较低时,铁素体晶粒呈多边形;冷速高时,铁素体晶粒多呈尖角形。 相似文献
13.
We have studied the ordering processes of a Ni-20.1at.%Mo alloy using the many-beam imaging technique with the aid of an image processing method. No microdomain is detected in high resolution electron micrographs of the alloy quenched from 1000°C, but lattice modulations which probably be attributed to concentration waves appear parallel to the {210} planes at the initial ordering stage. It is revealed that the observed contrasts of D1 a-type and D0 22-type microdomains are apparently formed with superpositions of different pairs of the {210} lattice modulations. When the alloy is annealed at 650°C for 192 h, Ni 2Mo domains appear in between the Ni 4Mo domains, and their composition is determined to be the stoichiometry (32at.%Mo) by the energy dispersive X-ray (EDX) analysis. The superstructure images of Ni 4Mo and Ni 2Mo are discussed in comparison with computer simulations by the multislice method. 相似文献
14.
A phenomenological calculation of phase equilibria by combining the cluster variation method (CVM) with the Lennard-Jones-type
(L-J-type) pairwise atomic interaction energies has been attempted for the Fe-Pd-Ni ternary system in order to examine the
possibility of Ni as the substituting element for Pd. The calculated Ni content in an Fe-Pd-based L1 0 ordered phase at 863 K shows fairly good agreement with the experimental analysis performed for Fe-5Pd-5Ni alloy by energy-dispersive
X-ray spectroscopy of a transmission electron microscope. The detailed calculation indicates that Ni is preferentially substituted
in a Pd site in the L1 0-ordered phase, which can be interpreted by the Lennard-Jones-type pairwise potentials employed for the present study. It
is concluded from the thermodynamic point of view that Ni is a promising candidate as the substituting element for Pd in an
Fe-Pd-based L1 0 ordered phase. 相似文献
15.
A newly designed composition of non-equiatomic Fe40Cr25Ni15Al15Co5 medium-entropy alloy (MEA) was produced by induction melting (IM). The as-cast alloy was found to consist of a two-phase microstructure of BCC (2.87 ± 0.01 Å) and ordered B2 (2.88 ± 0.02 Å) type phases. The structures of these phases were confirmed through X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. It was observed that the Ni-Al-enriched ordered B2 phase of cuboidal shapes (~ 100 to 200 nm) is homogeneously distributed in Fe-Cr-rich BCC matrix with a cube-on-cube orientation relationship. The formation of the columnar dendrites (width 50 to 100 μm) was identified through optical microscopy (OM). The structural and microstructural stability of the alloy was investigated by heat-treating the alloy through different schedules. Heat-treated samples at different temperatures (< 1273 K) exhibit a similar type of two-phase microstructure with columnar dendrites. However, compositional rearrangement takes place during long time exposure to develop polymorphically related phases. The alloy was observed to possess a high compressive yield strength and hardness, i.e., ~ 1047 MPa and 391 ± 9 HV, respectively, at room temperature. Heat-treated samples at 600 °C and 900 °C (873 K and 1173 K) showed an increase in yield strength and ultimate strength with a significant increase in plasticity due to the increase in volume fraction of B2 phase and softening of the BCC matrix phase. The thermal stability and high strength of this alloy may open new avenues for high-temperature applications. 相似文献
16.
The influence of microstructure on the strength and fracture toughness of 18 Ni (350) maraging steel was examined. Changes
in microstructure were followed by X-ray and neutron diffraction and by optical and electron microscopy. These observations
have been correlated with the fracture morphology established by scanning electron microscopy. Air cooling this alloy from
the austenitizing temperature results in a dislocated martensite. During the initial stage of age hardening, molybdenum atoms
tend to cluster (forming preprecipitates) and the cobalt assumes short range ordered positions. Subsequent aging results in
Ni 3Mo and σ-FeTi with overaging being associated with the formation of equilibrium reverted austenite and Fe 2Mo. The fracture behavior is examined in terms of elementary dislocation precipitate interactions. It is suggested that the
development of coplanar slip in the underaged conditions leads to its increased stress corrosion susceptibility and decreased
fracture toughness. The optimum aged condition is then associated with cross-slip deformation. The fracture behavior of the
overaged condition is a dynamic balance between a brittle matrix and the ductile (crack blunting) reverted austenite. 相似文献
17.
A Fe-15 wt pct Cr-15 wt pct Ni alloy monocrystal was deformed dynamically (strain rate ∼10 4 s −1) by the collapse of an explosively driven thick-walled cylinder under prescribed initial temperature and strain conditions.
The experiments were carried out under the following conditions: (a) alloy in austenitic state, temperature above transformation
temperature; (b) alloy in transformed state; and (c) alloy at temperature slightly above M
s
, propitiating concurrent shear-band propagation and martensitic transformation. The alloy exhibited profuse shear-band formation,
which was a sensitive function of the deformation condition. Stress-assisted and strain-induced martensitic transformation
competes with shear localization. The alloy deformed at a temperature slightly above M
s
shows a significantly reduced number of shear bands. The anisotropy of plastic deformation determines the evolution of strains
and distribution of shear bands. The different conditions showed significant differences that are interpreted in terms of
the microstructural anisotropy. Calculated shear-band spacings based on the Grady-Kipp (GK) and Wright-Ockendon (WO) theories
are compared with the observed values. The microstructure within the shear bands was characterized by transmission electron
microscopy. Regions of sub-micron grain sizes exhibiting evidence of recrystallization were observed, as well as amorphous
regions possibly resulting from melting and rapid resolidification.
This article is based on a presentation given in the symposium “Dynamic Deformation: Constitutive Modeling, Grain Size, and
Other Effects: In Honor of Prof. Ronald W. Armstrong,” March 2–6, 2003, at the 2003 TMS/ASM Annual Meeting, San Diego, California,
under the auspices of the TMS/ASM Joint Mechanical Behavior of Materials Committee. 相似文献
18.
Isothermal annealing at 500 °C for various lengths of time after rapid quenching from 900 °C results in different degrees
of ordering in Ni 2Cr. Tensile specimens of disordered and ordered Ni 2Cr were subjected to hydrogen embrittling and nonembrittling environments before and during tensile testing. The hydrogen
embrittlement susceptibility was determined by reduction-in-area losses (RA loss) after failure. The results of the tensile
tests indicated that the disordered alloy and highly ordered alloy were the most susceptible to hydrogen embrittlement. The
RA loss in each case was approximately 70 pct. The tests revealed a minimum susceptibility to hydrogen embrittlement between
40 and 50 pct order. The fracture surfaces of the specimens, as examined by scanning electron microscopy, showed that the
extent of embrittlement is correlated with the amount of intergranular failure. The mechanisms for failure in Ni 2Cr appear to depend upon the extent of aging in the alloy. 相似文献
19.
The crystallization path of an amorphous Cu 60Ti 40, alloy was studied using differential scanning calorimetry (DSQ), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The samples were Cu-Ti films≈ 10 μm in thickness prepared by magnetron sputter deposition onto rotating glass substrates. Two exothermic peaks were observed at 418° and 433°C, respectively, with no evidence of a glass transition. Observations from TEM and XRD at various stages of isochronal crystallization indicate that the initial amorphous structure transforms first to a metastable microcrystalline b.c.c. structure prior to formation of the ordered equilibrium Cu 3Ti 2 crystalline phase. The intermediate metastable structure is initially favored since it requires only topological ordering of the atoms into a simple unit cell, without significant diffusion, whereas the final ordered structure requires atom rearrangement over longer distances. The contrast of this sequence of events to that of a similar Cu-Zr alloy is discussed. Analysis of the fully crystallized alloy by convergent beam diffraction is consistent with a P4/nmm space group for the equilibrium phase. 相似文献
20.
The phase transition in an Fe-23.2 at. pct Al-4.1 at. pct Ni alloy has been investigated by means of transmission electron
microscopy. In the as-quenched condition, the microstructure of the alloy is a mixture of (A2 + B2) phases. When the as-quenched
alloy is aged at temperatures ranging from 500 °C to 1050 °C, the phase transition sequence is found to be (A2 + B2∗) → (B2
+ B2∗) → B2 → A2, where B2∗ is also a B2-type phase. It is worthwhile to note that the coexistence of two kinds of ordered
B2 phase has not previously been observed by other workers in the Fe-Al-Ni ternary alloy system. 相似文献
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