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1.
The equilibrium grain boundary segregation of antimony was investigated in iron base alloys (Fe-Sb, Fe-C-Sb, Fe-Ni-Sb) after annealing at temperatures between 550 and 750°C. Utilizing Auger electron spectroscopy (AES) the concentration of antimony at intergranular fracture faces was determined as a function of bulk concentration and equilibration temperature. The segregation of antimony in Fe-Sb alloys with mass contents of between 0.012 and 0.094 % Sb was described by the Langmuir-McLean equation. The evaluation leads to the free enthalpy of segregation Δ Gsegr = ?19 kJ/mol - T 28 J/mol K. The relatively low value for the segregation enthalpy Δ H = ?19 kJ/mol indicates a rather small tendency for grain boundary segregation of Sb. However, its embrittling effect is strong, scanning electron micrographs (SEM) of fractured samples show that the percentage of intergranular fracture strongly increases with an increasing coverage of antimony at the grain boundaries. The data for Fe-0.93% Sb and Fe.1.91% Sb (mass contents) do not fit in the thermodynamic evaluation obviously due to formation of antimonide precipitates in the grain boundaries. The addition of carbon to Fe-Sb alloys results in a higher grain boundary cohesion which is caused by two effects of carbon, displacement of antimony from the grain boundaries by carbon and enhanced grain boundary cohesion. In the Fe-Ni-Sb alloys additional segregation of nickel was found at the grain boundaries but no enhanced antimony segregation, as expected from previous models of other authors, assuming Ni-Sb cosegregation. 相似文献
2.
Steel produced in an electric arc furnace contains a high amount of copper (Cu) that causes a surface-cracking phenomenon
called surface hot shortness. It is known that tin (Sn) can exacerbate the hot shortness problem. A series of iron (Fe)-0.3 wt pct
Cu- x wt pct Sn alloys with an Sn content ranging from 0.03 to 0.15 wt pct was oxidized in air at 1423 K (1150 °C) for 60 seconds,
300 seconds, and 600 seconds using thermogravimetry. A numerical model developed in a previous article was applied to predict
the liquid– γFe interface concentrations and interface morphology in the Fe-Cu-Sn ternary system. Scanning electron microscopy investigations
show that (1) The interface between the oxide and the metal is planar as predicted by the numerical model, (2) Sn leads to
severe Cu-rich liquid penetration and cracking along the grain boundaries, and (3) open cracks with Fe oxides were found beneath
the oxide–metal interface. The focused ion beam serial-sectioning technique was used to reveal a three-dimensional structure
of cracks in the grain boundary containing Cu-rich liquid and Fe oxides. 相似文献
3.
The effects of Sb, Sn, and Zr additions on the creep properties of Ni and Ni + 20 pct Cr are reported. Antimony and tin additions
(~1 wt pct) induce extensive grain boundary cavitation in nickel, while smaller antimony additions had little effect on Ni
+ 20 pct Cr. Addition of 0.11 pct Zr to Ni + 20 pct Cr greatly inhibited grain boundary cavitation and reduced its Coble creep
rate. Auger electron spectroscopy of cavitated specimens provided direct evidence of impurity segregation to cavity surfaces.
Residual sulfur segregated most strongly, and was observed on cavity surfaces in all cavitated specimens. Tin segregated somewhat
less intensely than sulfur, and antimony segregated only slightly. Segregation of antimony and sulfur to uncavitated portions
of Ni + 1 pct Sb grain boundaries was also observed. These results are discussed in terms of segregation effects on energetic
and transport properties of the grain boundaries and cavity surfaces.
This paper is based on a presentation made at the symposium “The Role of Trace Elements and Interfaces in Creep Failure” held
at the annual meeting of The Metallurgical Society of AIME, Dallas, Texas, February 14-18, 1982, under the sponsorship of
The Mechanical Metallurgy Committee of TMS-AIME. 相似文献
4.
The effects of grain boundary serration on boron segregation and liquation cracking behavior in a simulated weld heat-affected
zone (HAZ) of a wrought nickel-based superalloy 263 have been investigated. The serrated grain boundaries formed by the developed
heat treatment were highly resistant to boron segregation; the serrated sample contained 41.6 pct grain boundaries resistant
to boron enrichment as compared with 14.6 pct in the unserrated sample. During weld thermal cycle simulation, liquated grain
boundaries enriched with boron were observed at the peak temperature higher than 1333 K (1060 °C) in both unserrated and serrated
samples; however, serrated grain boundaries exhibited a higher resistance to liquation. The primary cause of liquation in
this alloy was associated with the segregation of the melting point depressing element boron at grain boundaries. The hot
ductility testing result indicated that the serrated grain boundaries showed a lower susceptibility to liquation cracking;
the grain boundary serration led to an approximate 15 K decrease in the brittle temperature range. These results reflect closely
a significant decrease in interfacial energy as well as a grain boundary configuration change by the serration. 相似文献
5.
The role of chromium, carbon, chromium carbides, and phosphorus on the intergranular stress corrosion cracking (IGSCC) resistance
of Ni-Cr-Fe alloys in 50 pct NaOH at 140 °C is studied using controlled-purity alloys. The effect of carbon is studied using
heats in which the carbon level is varied between 0.002 and 0.063 wt pct while the Cr level is fixed at 16.8 wt pct. The effect
of Cr is studied using alloys with Cr concentrations between 5 and 30 wt pct. The effect of grain boundary Cr and C together
is studied by heat-treating the nominal alloy composition of Ni-16Cr-9Fe-0.035C, and the effect of P is studied using a high-purity,
P-doped alloy and a carbon-containing, P-doped alloy. Constant extension rate tensile (CERT) results show that the crack depth
increases with decreasing alloy Cr content and increasing alloy C content. Crack- ing severity also correlates inversely with
thermal treatment time at 700 °C, during which the grain boundary Cr content rises and the grain boundary C content falls.
Phosphorus is found to have a slightly beneficial effect on IG cracking susceptibility. Potentiodynamic polarization and potentiostatic
current decay experiments confirm that Cr depletion or grain boundary C enhances the dissolution at the grain boundary. Results
support a film rupture-anodic dissolution model in which Cr depletion or grain boundary C (independently or additively) enhances
dissolution of nickel from the grain boundary region and leads to increased IG cracking. 相似文献
6.
Increased interest has been paid to grain boundary segregation in alloy K-500 due to severe intergranular cracking recently
observed in forged bars. However, little systematic study of this segregation has been performed so far. A detailed auger
electron spectroscopy (AES) study of grain boundary segregation in alloy K-500 has been carried out as a function of alloy
chemistry. To determine C segregation, the C and O contamination rates in a vacuum chamber were measured and the necessary
condition for C grain boundary segregation determination was established. It has been found that severe C, Al, and Cu segregation
to grain boundaries occurred and depended on alloy chemistry. High bulk Ni and low bulk Al promoted C and Al grain boundary
segregation, and low bulk Ni and high bulk Al significantly enhanced Cu segregation to grain boundaries. The depth profiles
of intergranularly segregated elements also showed different features for high and low Ni content alloys. In high Ni alloys,
C and Al levels dropped continuously as a function of distance from the grain boundaries but the Cu level dropped only slightly.
In low Ni alloys, the Al and C levels rose from relatively low grain boundary levels to a peak at a certain distance from
the grain boundary where the high grain boundary Cu level dramatically dropped. Transmission electron microscope (TEM) observation
revealed a grain boundary γ′-depleted zone followed by a region with coarser and denser γ′ particles in low Ni and high Al alloys but quite uniformly distributed γ′ particles with no depleted zone in high Ni and low Al alloys. These can be explained by the observed segregation behavior.
The occurrence of Cu segregation is explained according to available theories about surface segregation in binary Ni-Cu alloys,
and the segregation of C and Al to grain boundaries is suggested to be probably due to their interaction with Ni and Cu. 相似文献
7.
A correlation between sulfur and antimony grain boundary segregation has been observed on inter-granular surfaces of iron
by Auger electron spectroscopy (AES). The slope of a plot of S/Sb indicated a ratio of two antimony atoms per sulfur atom
arriving at the grain boundary, while the ratio for the total S/Sb at the grain boundary was about 1.2. These results were
obtained with Fe, Fe + 0.07Mn, Fe + 0.03Sb, Fe + 0.1Mn + 0.02Sb, and Fe + 0.1Mn + 0.05Sb (at. pct) alloys. Possible expla-nations
for this correlated segregation, such as cosegregation of sulfur and antimony, precipitation of a thin layer of antimony sulfide,
and compctitive segregation with carbon and nitrogen, were evalu-ated using AES, X-ray photoelectron spectroscopy (XPS), and
scanning transmission electron mi-croscopy with energy-dispersive X-ray (STEM-EDS). The results of these analyses indicated
that there was no resolvable antimony sulfide phase in the grain boundary and that S and Sb were not chemically bound at the
grain boundary in a two-dimensional phase. The S was shown to be strongly bound to the iron in a chemical state close to that
of an iron sulfide, but the Sb was in the elemental state. Nor could this correlated segregation be satisfactorily explained
by a cosegregation process nor by compctitive segregation with other elements. The most plausible explanation appears to involve
the effect of sulfur on the activity/solubility of antimony or antimony on the activity/solubility of sul-fur, as explained
by an increase in the ratio X
c
/ X
Co
in the Brunauer-Emmett-Teller (BET) adsorption isotherm adapted for equilibrium segregation in solids. 相似文献
8.
A systematic study has been conducted of the sintering, sintered microstructure and tensile properties of a range of lower cost Ti-Fe-Si alloys, including Ti-3Fe-(0-4)Si, Ti-(3-6)Fe-0.5Si, and Ti-(3-6)Fe-1Si (in wt pct throughout). Small additions of Si (??1?pct) noticeably improve the as-sintered tensile properties of Ti-3Fe alloy, including the ductility, with fine titanium silicides (Ti 5Si 3) being dispersed in both the ?? and ?? phases. Conversely, additions of ?>1?pct Si produce coarse and/or networked Ti 5Si 3 silicides along the grain boundaries leading to predominantly intergranular fracture and, hence, poor ductility, although the tensile strength continues to increase because of the reinforcement by Ti 5Si 3. Increasing the Fe content in the Ti- xFe-0.5/1.0Si alloys above 3?pct markedly increases the average grain size and changes the morphology of the ??-phase phase to much thinner and more acicular laths. Consequently, the ductility drops to <1?pct. Si reacts exothermically with Fe to form Fe-Si compounds prior to the complete diffusion of the Fe into the Ti matrix during heating. The heat thus released in conjunction with the continuous external heat input melts the silicides leading to transient liquid formation, which improves the densification during heating. No Ti-TiFe eutectoid was observed in the as-sintered Ti-Fe-Si alloys. The optimum PM Ti-Fe-Si compositions are determined to be Ti-3Fe-(0.5-1.0)Si. 相似文献
9.
The impact of micro-alloying on tensile behavior at strain rates in various ranges is examined using five types of extruded Mg-0.3 at. pct Mn–0.1 at. pct X ternary alloys, where X is selected as a common element, Al, Li, Sn, Y or Zn. Microstructural observations reveal that the average grain size of these extruded alloys is between 1 and 3 μm, and these micro-alloying elements segregate at grain boundaries. In room temperature tensile and compression tests, these results show that the mechanical properties and deformation behavior are influenced by the micro-alloying element, even as a small addition of 0.1 at. pct. Mg–Mn–Y and Mg–Mn-Zn alloys show higher strength and smaller strain rate sensitivity (m-value) among the present alloys, owing to the rate-controlling mechanism as dislocation slip. On the other hand, the Mg–Mn–Li alloy exhibits the largest elongation to failure in tension and the highest strain rate sensitivity, associated with high contribution of grain boundary sliding to deformation. These differences are due to the grain boundary segregation of the micro-alloying elements. Compared to the common Mg alloys, the present ternary alloys also show a trade-off relationship between strength and ductility, which is similar to that of the well-known Mg alloys; however, these properties of the Mg–Mn system ternary alloys could be controlled via the type of micro-alloying elements with a chemical content of 0.1 at. pct. 相似文献
10.
The grain boundary fracture surfaces of several Ir + 0.3 pct W alloys have been examined using Auger electron spectroscopy.
Dopant additions (between 10 and 80 wt ppm) of Al, Fe, Th, Ni and Rh are shown to result in thorium enriched grain boundaries.
Inert ion sputtering experiments suggest that the thorium enriched region at the grain boundaries is probably only a few atom
layers thick. The other dopants (Al, Fe, Ni and Rh) do not appear to influence the segregation of thorium, and their function
(if any) in improving the high temperature impact properties of this alloy is unclear at this time. 相似文献
11.
The effectiveness of a grain boundary etching method for the non-destructive analysis of intergranular segregation of P in
iron-based alloys was examined by using a saturated aqueous solution of picric acid containing sodium tridecylbenzene sulfonate.
Among all the alloys examined only those doped with P suffered selective etching attack against grain boundaries. The degree
of the etching attack in a P-doped NiCr steel was found to have a linear relation with the concentration of grain boundary
P as measured by Auger electron spectroscopy. From these evidences, the grain boundary etching method was concluded to be
useful as a technique analyzing the grain boundary concentration of P in NiCr steels. The application of the method was successfully
made to CrMo and C-free NiCr steels which are hard to exhibit perfect intergranular fracture. The application was not successful
to Fe-40 pct Ni and Fe-3 pct Si alloys whose surfaces were unstable electrochemically compared with those of NiCr and CrMo
steels. 相似文献
12.
The solid solubilities of Sn and Sb in α-Fe have been determined by means of lattice parameter measurements. The Sb solubility
ranges from a maximum of 11 wt pct (5.4 at. pct) at 1000°C down to 5.3 wt pct (2.5 at. pet) at 600°C; the Sn solubility ranges
from a maximum of 17.7 wt pct (9.2 at. pet) at 900°C to 6.5 wt pct (3.2 at. pet) at 600°C. These solubilities are remarkably
large in view of the large sizes of the Sb and Sn atoms in relation to the Fe atom. It was not possible to rationalize the
variation of the α-phase lattice parameter with Sb or Sn content from the point of view of atomic diameter or atomic volume.
The addition of 1 wt pct Ni lowers the Sb solubility at 600°C from 5.3 to 3.5 wt pct (2.5 to 1.6 at. pet); the effect of Cr
on the Sb solubility appears to be small. The addition of 1 wt pct Ni or 1 wt pct Cr lowers the Sn solubility from 6.5 to
5.2 wt pct (3.2 to 2.5 at. pet). It was found that a substantial amount of Ni substitutes for Fe in both the FeSb phase and
the Fe 5Sn 3 phase.
Formerly Research Fellow, Department of Metallurgy and Materials Science and LRSM, University of Pennsylvania 相似文献
13.
A series of electrochemical, immersion, and constant extension rate tests was conducted on samples of Ni-16Cr-9Fe in sodium
tetrathionate at room temperature. Samples were heat treated to produce severe chromium depletion at the grain boundaries.
Titrimetric analysis of the tetrathionate solution, before and after exposure to a sensitized alloy, under an applied cathodic
current shows that the tetrathionate ion is reduced. The species primarily responsible for the observed IGA in immersion tests
and IG cracking in constant extension rate tests is the tetrathionate ion, S 4O 6
-, although elemental S also causes shallow IGA. The mechanism responsible for the observed IGA and IG cracking in sensitized
Ni-Cr-Fe alloys is stress assisted intergranular attack with the effect of stress being purely mechanical in nature. The degree
of IGA and IG cracking is directly related to the grain boundary chromium content. Samples with less than 5 wt pct Cr at the
grain boundary are rapidly attacked while those with 8 wt pct Cr are less susceptible and 12 wt pct Cr renders the grain boundary
immune to attack. Lower extension rates and higher Na 2S 4O 6 concentrations represent more aggressive conditions for attack. 相似文献
14.
The effect of copper on proeutectoid cementite precipitation was investigated by examining the isothermal transformation characteristics
of Fe-C and Fe-C-Cu alloys that had comparable carbon contents. The TTT diagrams generated for the Fe-1.43 wt pct C and the
Fe-1.49 wt pct C-4.90 wt pct Cu alloys showed that the kinetics of proeutectoid cementite precipitation were not significantly
affected by copper. The morphology of the proeutectoid cementite, as seen in the optical microscope, was also substantially
the same in both alloys. However, transmission electron microscopy revealed the presence of small epsilon-copper precipitates
within the proeutectoid cementite of the copper containing steel. It was concluded that this precipitation of ε-Cu took place
at the cementite : austenite interphase boundaries, and that the transport of copper to the precipitates was accomplished
by interphase boundary diffusion. The small influence of copper on the kinetics of proeutectoid cementite precipitation is
discussed in terms of diffusional growth theories and the structure of the cementite : austenite interphase boundary. 相似文献
15.
Grain boundary segregation in iron-sulfur-carbon alloys containing up to 100 wt ppm sulfur and up to 90 wt ppm carbon has
been investigated with Auger electron spectroscopy (AES). The results show the site compctition on grain boundaries between
the segregation of sulfur and carbon. The segregation energy of sulfur is estimated to be 75 kJ/mol. Impact tests of these
alloys were carried out. Iron-sulfur alloys with less than 20 wt ppm carbon fractured by the intergranular mode with high
ductile-brittle transition temperatures (DBTT’s). Addition of up to 90 wt ppm carbon to the binary alloys prevented the intergranular
fracture caused by the grain boundary segregation of sulfur, and decreased the DBTT. Carbon, when segregated to grain boundaries,
drives sulfur away from the boundaries and also increases the grain boundary cohesion. The DBTT values of the iron-sulfur-carbon
alloys are analyzed in terms of the degree of grain boundary segregation of sulfur and carbon. It is shown that sulfur decreases
the grain boundary cohesion of iron more severely than phosphorus if compared at the same degree of grain boundary segregation.
Formerly Graduate Student 相似文献
17.
High cycle fatigue tests in vacuum have been performed on ordered (Fe, Co, Ni) 3V alloys between 25 °C and 850 °C. Heat-to-heat variations in fatigue properties of a Co-16.5 wtpct Fe-25 pct alloy, LRO-1, appeared to be due to differing quantities of grain boundary precipitates. Modification of this alloy with 0.4 pct Ti, to produce an alloy designated LRO-23, reduced the density of grain boundary precipitates and increased ductility, resulting in superior fatigue strength at high temperatures. The fatigue lives of LRO-1 and LRO-23 decreased rapidly above 650 °C, and increased intergranular failure was noted. The fatigue resistance of a cobalt-free alloy, Fe-29 pct Ni-22 pct V-0.4 pct Ti (LRO-37), was examined at 25 °C, 400 °C, and 600 °C; there was little evidence for intergranular fracture at any of these temperatures. Fatigue behavior of the LRO alloys is compared to that of conventional high temperature alloys. 相似文献
18.
Recent experimental and simulation results have indicated that high-temperature grain growth in nanocrystalline (NC) materials
can be suppressed by introducing dopant atoms at the grain boundaries. However, the influence of grain boundary dopants on
the mechanical behavior of stabilized NC materials is less clear. In this work, molecular dynamics (MD) simulations are used
to study the impact of very low dopant concentrations (<1.0 at. pct Sb) on plastic deformation in single-crystal and NC Cu.
A new interatomic potential for low Sb concentration Cu-Sb solid-solution alloys is used to model dopant/host and dopant/dopant
interatomic interactions within the MD framework. In single-crystal models, the strained regions around the Sb atoms act as
heterogeneous sources for partial dislocation nucleation; the stress associated with this process decreases with increasing
Sb concentration. In NC models, MD simulations indicate that Sb dopants randomly dispersed at the grain boundaries cause an
increase in the flow stress in NC Cu, implying that Sb atoms at the grain boundaries retard both grain boundary sliding and
dislocation nucleation from grain boundary regions. 相似文献
19.
The aim of this work is to partially substitute Fe and Mn for Ni in the 3HA piston alloy and to study the consequences through
microstructural evaluation and the thermal analysis technique. Three types of near-eutectic alloys containing (2.6 wt pct
Ni-0.2 wt pct Fe-0.1 wt pct Mn), (1.8 wt pct Ni-0.75 wt pct Fe-0.3 wt pct Mn), and (1 wt pct Ni-1.15 wt pct Fe-0.6 wt pct
Mn) were produced, and their solidification was studied at the cooling rate of 0.9 K/s (°C/s) using the computer-aided thermal
analysis technique. Optical microscopy and scanning electron microscopy were used to study the microstructure of the samples,
and energy dispersive X-ray (EDX) analysis was used to identify the composition of the phases. Also, the quantity of the phases
was measured using the image analysis technique. The results show that Ni mainly participates as Al 3Ni, Al 9FeNi, and Al 3CuNi phases in the high Ni-containing alloy (2.6 wt pct Ni). In addition, substitution of Ni by Fe and Mn makes Al 9FeNi the only Ni-rich phase, and Al 12(Fe,Mn) 3Si 2 appears as an important Fe-rich intermetallic compound in the alloys with the higher Fe and Mn contents. 相似文献
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