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1.
2.
The constitution of the ternary system Al-Cr-Ti is investigated over the entire composition range using X-ray diffraction
(XRD), energy-dispersive X-ray spectroscopy (EDS), differential thermal analysis (DTA) up to 1500 °C, and metallography. Solid-state
phase equilibria at 900 °C are determined for alloys containing ≤75 at. pct aluminum and at 600 °C for alloys containing >75 at. pct
Al. A reaction scheme linking these solid-state equilibria with the liquidus surface is presented. The liquidus surface for
≤50 at. pct aluminum is dominated by the primary crystallization field of bcc β(Ti,Cr,Al). In the region >50 at. pct Al, the ternary L12-type phase τ forms in a peritectic reaction p
max at 1393 °C from L + TiAl. Furthermore, with the addition of chromium, the binary peritectic L + α(Ti,Al) = TiAl changes into an eutectic L = α(Ti,Al) + TiAl. This eutectic trough descends monotonously through a series of transition reactions and ternary peritectics
to end in the binary eutectic L = Cr7Al45 + (Al). 相似文献
3.
A melting and solidification study of alloy 625 总被引:1,自引:0,他引:1
M. J. Cieslak T. J. Headley A. D. Romig T. Kollie 《Metallurgical and Materials Transactions A》1988,19(9):2319-2331
The melting and solidification behavior of Alloy 625 has been investigated with differential thermal analysis (DTA) and electron
microscopy. A two-level full-factorial set of chemistries involving the elements Nb, C, and Si was studied. DTA results revealed
that all alloying additions decreased the liquidus and solidus temperatures and also increased the melting temperature range.
Terminal solidification reactions were observed in the Nb-bearing alloys. Solidification microstructures in gastungsten-arc
welds were characterized with transmission electron microscopy (TEM) techniques. All alloys solidified to an austenitic (γ)
matrix. The Nb-bearing alloys terminated solidification by forming various combinations of γ/MC(NbC), γ/Laves, and γ/M6C eutectic-like constituents. Carbon additions (0.035 wt pct) promoted the formation of the γ/MC(NbC) constituent at the expense
of the γ/Laves constituent. Silicon (0.4 wt pct) increased the formation of the yJLaves constituent and promoted formation
of the γ/M6C carbide constituent at low levels (<0.01 wt pct) of carbon. When both Si (0.4 wt pct) and C (0.035 wt pct) were present,
the γ/MC(NbC) and γ/Laves constituents were observed. Regression analysis was used to develop equations for the liquidus and
solidus temperatures as functions of alloy composition. Partial derivatives of these equations taken with respect to the alloying
variables (Nb, C, Si) yielded the liquidus and solidus slopes t(m
L
, m
S
) for these elements in the multicomponent system. Ratios of these liquidus to solidus slopes gave estimates of the distribution
coefficients (k) for these same elements in Alloy 625. 相似文献
4.
Evolution of boride morphologies in TiAl-B alloys 总被引:2,自引:0,他引:2
M. E. Hyman C. McCullough C. G. Levi R. Mehrabian 《Metallurgical and Materials Transactions A》1991,22(7):1647-1662
The solidification of γ-TiAl alloys with relatively low (<2 at. pct) additions of boron is discussed. Binary Ti-Al alloys
containing 49 to 52 at. pct Al form primary α-(Ti) dendrites from the melt, which are subsequently surrounded by γ segregate
as the system goes through the peritectic reactionL + α →γ. Alloys between 45 and 49 at. pct Al go through a double peritectic cascade, forming primary β-(Ti) surrounded by α-(Ti) and
eventually by γ in the interdendritic spaces. Boron additions to these binary alloys do not change the basic solidifi-cation
sequence of the matrix but introduce the refractory compound TiB2 in a variety of mor-phologies. The boride develops as highly convoluted flakes in the leaner alloys, but needles, plates,
and equiaxed particles gradually appear as the B content increases above ∼1 at. pct. Increasing the solidification rate initially
promotes the formation of flakes over plates/needles and ultimately gives way to very fine equiaxed TiB2 particles in the interdendritic spaces of the metallic matrix. Furthermore, the primary phase selection in the 49 to 52 at.
pct Al range changes from α-(Ti) to β-(Ti) at supercoolings of the order of 200 K. The different boride morphologies are fully
characterized, and their evolution is rationalized in terms of differences in their nucleation and growth behavior and their
relationship to the solidification of the inter-metallic matrix.
Formerly Research Assistant, University of California-Santa Barbara (UCSB)
Formerly Professor of Materials and Dean of the College of Engineering at UCSB 相似文献
5.
The response of as-cast structures of 12 alloys in the Ti-Al-Mo system containing 44 to 50 at. pct Al and 2 to 6 at. pct Mo
to simple single step heat treatments in the temperature range 1373 to 1673 K is described. The microsegregation patterns
present in the cast structure persist to a large extent after heat treatment, especially below 1673 K. However, tentative
conclusions regarding phase equilibria in this temperature and composition range are drawn from the results. High-temperature
equilibria are dominated by the β, α+β, and α+γ phase fields, while the β+γ phase field dominates equilibrium below 1473 K. Three major types of transformation behavior are observed: a massive α to γ transformation, which occurs within the α phase on quenching from 1673 and 1573 K in alloys centered around the 48 pct Al composition; a eutectoid transformation from
α to B2+γ mixtures, which occurs at 1473 K and below in alloys centered around the 48Al-4Mo and 46Al-6Mo compositions; direct
γ precipitation in β, which occurs primarily in the 44Al-6Mo composition at 1273 K and below; and finally growth of γ lamellae in α+γ lamellar structures with B2 precipitation on lamellar interfaces, which occurs over a broad range of alloy compositions and
temperatures. 相似文献
6.
Fixed composition ratios of Fe and Zn corresponding to γ-(Fe3Zn110), Γ1-(Fe5Zn21), δ-(FeZn7), and ζ-(FeZn13) with the addition of 5 pct Al (wt) were ball milled in an argon gas atmosphere to form homogenous alloys. Nonisothermal
kinetic analyses of the mechanically alloyed materials, based on differential scanning calorimetry (DSC) measurements, revealed
two diffusion-controlled processes during the evolution of the δ+5 pct Al and ζ+5 pct Al compositions with activation energies of 227±2 and 159±1 kJ/mole, respectively. Other endothermic
and exothermic reactions detected for these compositions are consistent with the Fe-Zn-Al equilibrium phase systems with respect
to the formation of the Fe3Al, Fe2Al5, and δ-FeZn7 phases Based on the evidence of FeAl2 formation at 440 °C for the ζ+5 pct Al composition from X-ray diffraction (XRD) and DSC measurements, the revision/re-evaluation
of the Fe-Zn-Al equilibrium phase diagrams is proposed. The Γ+5 pct Al and Γ1+5 pct Al compositions evolved similarly through the same fields, except at 400 °C, where the former consisted of α-Fe + Γ + δ, while the later was without the Γ phase. 相似文献
7.
An investigation has been made into the solidification behavior and microstructural evolution of AM50, AM70, and AM90 alloys
during rheo-diecasting, their processibility, and the resulting mechanical properties. It was found that solidification of
AM series alloys under intensive melt shearing in the unique twin-screw slurry maker during rheo-diecasting gave rise to numerous
spheroidal primary magnesium (Mg) particles that were uniformly present in the microstructure. As a result, the network of
the β-Mg17Al12 phase was consistently interrupted by these spheroidal and ductile particles. Such a microstructure reduced the obstacle
of deformation and the harmfulness of the β-Mg17Al12 network on ductility, and therefore improved the ductility of rheo-diecast AM alloys. It was shown that, even with 9 wt pct
Al, the elongation of rheo-diecast AM90 still achieved (9 ± 1.2) pct. Rheodiecasting thus provides an attractive processing
route for upgrading the alloy specification of AM series alloys by increasing the aluminum (Al) content while ensuring ductility.
Assessment of the processibility of AM series alloys for semisolid processing showed that high Al content AM series alloys
are more suitable for rheo-diecasting than low Al content alloys, because of the lower sensitivity of solid fraction to temperature,
the lower liquidus temperature, and the smaller interval between the semisolid processing temperature and the complete solidification
temperature. 相似文献
8.
Solidification of M2 high speed steel 总被引:5,自引:0,他引:5
R. H. Barkalow R. W. Kraft J. I. Goldstein 《Metallurgical and Materials Transactions B》1972,3(4):919-926
The freezing process in AISI type M2 high speed tool steel (6 pct W, 5 pct Mo, 4 pct Cr, 2 pct V, 0.8 pct C) was studied by
metallographic and thermal analysis techniques. Unidirectional solidification of small laboratory melts in a modified crystal
growing apparatus was employed to provide metallographic sections of known macroscopic growth direction. Also cooling curves
were obtained on 40 g specimens solidified in thimble crucibles. X-ray microradiography, electron probe scanning techniques,
and quantitative microanalysis of dendrites and interdendritic carbides were extensively used to supplement conventional metallography.
Carbon and vanadium contents of M2 were varied in order to observe the effect of an austenite and ferrite stabilizer on the
thermal analysis curves and microstructure. The nonequilibrium freezing process in M2 includes three major liquid-solid reactions:
1) Liquid → Ferrite, 1435°C; 2) Liquid + Ferrite → Austenite, 1330°C; 3) Liquid → Austenite + M6C + MC, 1240°C. These reactions account for the as-cast structure of the commercial alloy. The addition of carbon depresses
the liquidus (1) and solidus temperatures (3) and narrows the gap between the liquidus (1) and peritectic transformation (2).
This gap is eliminated at > 1.39 wt pct C, where the initial freezing reaction is the crystallization of austenite. The accompanying
microstructural change is the elimination of σ eutectoid dendrite cores. The addition of vanadium promotes ferrite formation
by strongly depressing the peritectic reaction and thus widening the gap between the liquidus and the peritectic. 相似文献
9.
Mengtao Xie Randolph Helmink Sammy Tin 《Metallurgical and Materials Transactions A》2012,43(4):1259-1267
In the current investigation, the effect of Cr on the solidification characteristics and as-cast microstructure of pseudobinary
γ-δ eutectic alloys based on a near-eutectic composition (Ni-5.5Al-13.5Nb at. pct) was investigated. It was found that Cr additions
promote the formation of a higher volume fraction of γ-δ eutectic microstructure in the interdendritic region. Increasing levels of Cr also triggered morphological changes in the
γ-δ eutectic and the formation of γ-γ′-δ ternary eutectic during the last stage of solidification. A detailed characterization of the as-cast alloys also revealed
that Cr additions suppressed the liquidus, solidus, and γ′ precipitation temperature of these γ/γ′-δ eutectic alloys. A comparison of the experimental results with thermodynamic calculations using the CompuTherm Pandat database
(CompuTherm LLC, Madison, WI) showed qualitative agreement. 相似文献
10.
The graded material of Ti6Al4V-Rene88DT superalloy, which has shown the potential to be applied in aeroengines, was fabricated
from prealloyed metal powders using the technique of laser rapid forming (LRF). A compositional gradient, from 100 pct Ti6Al4V
to Ti6Al4V-38 pct Rene88DT, was achieved within a thickness of laser deposit of 54 mm. The solidification behavior and the
phase evolution of the compositionally graded material were studied. The results of the X-ray diffraction (XRD) analysis together
with the metallographic study showed that a series of phase evolutions, α + β → α + β + Ti2Ni → β + Ti2Ni, along the compositional gradient have occurred. The hardness value of the graded material was measured along the compositional
gradient, and the results were explained in terms of the various phases present. The condition for columnar-to-equiaxed transition
observed in the graded material was explained, based on Hunt’s criterion. Finally, the morphology of β + Ti2Ni anomalous eutectic is discussed.
相似文献
T.M. Yue (Professor)Email: |
11.
Ductile shape memory (SM) alloys of the Cu-AI-Mn system have been developed by controlling the degree of order in the β phase.
Additions of Mn to the binary Cu-Al alloy stabilize the β phase and widen the single-phase region to lower temperature and
lower Al contents. It is shown that Cu-Al-Mn alloys with low Al contents have either the disordered A2 structure or the ordered
L21 structure with a lower degree of order and that they exhibit excellent ductility. The disordered A2 phase martensitically
transforms to the disordered Al phase with a high density of twins. The martensite phase formed from the ordered L21 phase has the 18R structure. The SM effect accompanies both the A2 → Al and L21 → 18R martensitic transformations. These alloys exhibit 15 pct strain to failure, 60 to 90 pct rolling reduction without
cracking, and 80 to 90 pct recovery from bend test in the martensitic condition. Experimental results on the microstructure,
crystal structure, mechanical properties, and shape memory behavior in the ductile Cu-AI-Mn alloys are presented and discussed. 相似文献
12.
Ti-Fe binary alloys were rapidly solidified by the melt-spinning technique, and four compositions were examined: Ti-5 wt pct
Fe, which is the critical composition for theβ to ω athermal transformation; Ti-10 wt pct Fe, which represents a hypoeutectoid composition; the eutectoid composition Ti-15
wt pct Fe; and Ti-20 wt pct Fe, as an example of a hypereutectoid alloy. The Ti-5 wt pct Fe rapidly solidified ribbons are
composed of two different structures. The first consists of α′-martensite plates inβ matrix and the second, athermal ω particles inβ matrix. The Ti-10, 15, and 20 wt pct Fe alloys are also composed of two structures. These areβ grains and isothermal-like ω particles inβ matrix. A solidification model is suggested which explains the existence of two different microstructures at the same composition
and the for-mation of two kinds of ω particles. 相似文献
13.
A regular solution model is fit to experimental equilibrium temperatures(T
0) and pressures(P
0) for diffusionlessδ→α transformations in Pu-Ga and Pu-Al alloys, in order to define the chemical free energy change ΔG forδ→ α transformation. Analysis of reported isothermalδ→ αtransformation rate data in terms of nucleation-controlled martensitic kinetics gives a nucleation activation energyQ which is a nonlinear function of ΔG. The activation volumeV
* defined byδQ/δΔG is of the order of 10 to 40 atomic volumes, suggestive of rate control by an interfacial Peierls barrier. The grain size
dependence of the transformation-start temperature at a fixed cooling rate of 2.08 × 10-2 Ks-1 is measured in a Pu-1.7 at. pct Ga alloy, revealing an inhibition of transformation at fine grain sizes. The overall kinetic
behavior is characteristic of a martensitic mechanism. 相似文献
14.
J. N. DuPont M. R. Notis A. R. Marder C. V. Robino J. R. Michael 《Metallurgical and Materials Transactions A》1998,29(11):2785-2796
The solidification reaction sequences of experimental superalloys containing systematic variations in Fe, Nb, Si, and C were
studied using differential thermal analysis (DTA) and microstructural characterization techniques. The reaction sequences
responsible for microstructural development were found to be similar to those expected in the Ni-Nb-C ternary system and commercial
superalloys of comparable composition. The solute-rich interdendritic liquid generally exhibited two eutectic-type reactions
at the terminal stages of solidification: L → (γ+NbC) and L → (γ+Laves). The Ni-base alloys with a high C/Nb ratio represented the only exception to this general solidification sequence.
This group of alloys terminated solidification with the L → (γ + NbC) reaction and did not exhibit the γ/Laves constituent. At similar levels of solute elements (Nb, Si, and C), the Fe-base alloys always formed more of the γ/Laves eutectic-type constituent than the corresponding Ni-base alloys. Silicon additions also increased the amount of the
γ/Laves constituent that formed in the assolidified microstructure, while C additions promoted formation of γ/NbC. The influence of Nb was dependent on the C content of the alloy. When the C content was low, Nb additions generally
promoted formation of γ/Laves, while Nb additions to alloys with high C led to formation of the γ/NbC constituent. The results of this work are combined with quantitative analyses for developing γ-Nb-C pseudoternary solidification diagrams in a companion article. 相似文献
15.
Bikas C. Maji Madangopal Krishnan Gouthama R. K. Ray 《Metallurgical and Materials Transactions A》2011,42(8):2153-2165
The effect of Si addition on the microstructure and shape recovery of FeMnSiCrNi shape memory alloys has been studied. The
microstructural observations revealed that in these alloys the microstructure remains single-phase austenite (γ) up to 6 pct Si and, beyond that, becomes two-phase γ + δ ferrite. The Fe5Ni3Si2 type intermetallic phase starts appearing in the microstructure after 7 pct Si and makes these alloys brittle. Silicon addition
does not affect the transformation temperature and mechanical properties of the γ phase until 6 pct, though the amount of shape recovery is observed to increase monotonically. Alloys having more than 6 pct
Si show poor recovery due to the formation of δ-ferrite. The shape memory effect (SME) in these alloys is essentially due to the γ to stress-induced ε martensite transformation, and the extent of recovery is proportional to the amount of stress-induced ε martensite. Alloys containing less than 4 pct and more than 6 pct Si exhibit poor recovery due to the formation of stress-induced
α′ martensite through γ-ε-α′ transformation and the large volume fraction of δ-ferrite, respectively. Silicon addition decreases the stacking fault energy (SFE) and the shear modulus of these alloys and
results in easy nucleation of stress-induced ε martensite; consequently, the amount of shape recovery is enhanced. The amount of athermal ε martensite formed during cooling is also observed to decrease with the increase in Si. 相似文献
16.
Wislei R. Osorio Pedro R. Goulart Amauri Garcia Givanildo A. Santos Carlos Moura Neto 《Metallurgical and Materials Transactions A》2006,37(8):2525-2538
It has been reported that the mechanical properties and the corrosion resistance (CR) of metallic alloys depend strongly on
the solidification microstructural arrangement. The correlation of corrosion behavior and mechanical properties with microstructure
parameters can be very useful for planning solidification conditions in order to achieve a desired level of final properties.
The aim of the present work is to investigate the influence of heat-transfer solidification variables on the microstructural
array of both Al 9 wt pct Si and Zn 27 wt pct Al alloy castings and to develop correlations between the as-cast dendritic
microstructure, CR, and tensile mechanical properties. Experimental results include transient metal/mold heat-transfer coefficient
(h
i), secondary dendrite arm spacing (λ2), corrosion potential (E
Corr), corrosion rate (i
Corr), polarization resistance (R
1), capacitances values (Z
CPE), ultimate tensile strength (UTS, σ
u
), yield strength (YS, σ
y
), and elongation. It is shown that σ
U
decreases with increasing λ2 while the CR increases with increasing λ2, for both alloys experimentally examined. A combined plot of CR and σ
U
as a function of λ2 is proposed as a way to determine an optimum range of secondary dendrite arm spacing that provides good balance between both
properties. 相似文献
17.
T. Hamajima G. Luetjering S. Weissmann 《Metallurgical and Materials Transactions B》1972,3(11):2805-2810
The influence of aluminum additions to a Ti-7 at. pet Mo alloy on the phase equilibria was investigated. The microstructures
of the alloys, Ti-7 pct Mo-7 pct Al and Ti-7 pct Mo-16 pct Al, were determined by light and electron microscopy. It was found
that with increasing aluminum concentration the formation of the metastable w phase was suppressed. In the Ti-7 pct Mo-16
pct Al alloy the β phase decomposed upon quenching by precipitating coherent, ordered particles having a B2 type of crystal
structure (β2). At low temperatures the equilibrium phases for this alloy were β + α+ β
2, whereas at high temperature (850° to 950°C) the Ti3Al phase was in two-phase equilibrium with the β phase. The four-phase equilibrium which exists at a temperature of about
550°C involves the reaction β + Ti3Al ⇌ α + β2.
G. LUETJERING, formerly Staff Member Materials Research Center, Allied Chemical Corp., Morristown, N. J., 相似文献
18.
Nickel-rich β-NiAl alloys, which are potential materials for high-temperature shape-memory alloys, show a thermoelastic martensitic transformation,
which produces their shape memory effect. However, the transformation to Ni5Al3 phase during heating of NiAl martensite can interrupt the reversible martensitic transformation; consequently, the shape
memory effect in NiAl martensite might not appear after heating. The phase transformation process in binary Ni-(34 to 37)Al
martensite was investigated by differential thermal analysis (DTA) method, and we found that the condition of reversible martensitic
transformation was not the β → Ni5Al3 transformation, but rather the M → Ni5Al3 transformation occurring at 250 °C to 300 °C. Therefore, the transformation temperature of M → Ni5Al3 determined the highest operating temperature for the shape memory effect. For verifying the critical temperature, the phase
transformation process was investigated for eight ternary Ni-33Al-X alloys (X=Cu, Co, Fe, Mn, Cr, Ti, Si, and Nb). Only Ti,
Si, and Nb additions were found to be effective in dropping the M
s temperature, and they facilitated the shape memory effect in Ni-33Al-X alloys. In particular, the addition of Si and Nb raised
the transformation temperature of M → Ni5Al3, a potentially beneficial effect for shape memory at higher temperatures.
This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented
at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint
Committee on Mechanical Behavior of Materials. 相似文献
19.
20.
J. A. Taylor G. B. Schaffer D. H. StJohn 《Metallurgical and Materials Transactions A》1999,30(6):1651-1655
The mechanism by which iron causes casting defects in the AA309 (Al-5 pct Si-1.2 pct Cu-0.5 pct Mg) may be related to the
solidification sequence of the alloy. Superimposing calculated segregation lines on the liquidus projection of the ternary
Al-Si-Fe phase diagram suggests that porosity is minimized at a critical iron content when solidification proceeds directly
from the primary field to the ternary Al-Si-βAl5FeSi eutectic point. Solidification via the binary Al-βAl5FeSi eutectic is detrimental to casting integrity. This hypothesis was tested by comparing the critical iron content observed
in the standard AA309 alloy to that of a high-silicon (10 pct Si) variant of this alloy. 相似文献