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1.
Effects of transient carbon deposition on the sodium sulfate-induced corrosion of nickel-base alloys
The role of solid carbon in accelerating the Na2SO4-induced corrosion of nickel-base alloys at high temperature has been investigated. Corrosion rates of salt-coated IN 738
alloy in an oxidizing atmosphere containing 0.1 pct SO2 were much increased when the alloy was initially exposed to a low concentration of methane for a short time at 1273 K (1000°C).
Crucible tests carried out with Ni-5 Al, Ni-30 Al, Ni-20Cr-15 Al and IN 738 specimens immersed in Na2SO4-carbon mixtures showed that corrosion of these alloys was dramatically enhanced if the carbon persisted long enough to form
a Na2S phase by reaction with the Na2SO4. In an oxidizing environment a graphitic carbon had a more pernicious effect on alloy corrosion resistance than a finely
dispersed carbon black which burnt away more readily. Corrosion rates in air were also accelerated in the presence of carbonized
crude oil residue such as might be formed as a result of incomplete fuel combustion in a gas turbine. 相似文献
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Mechanisms for the hot corrosion of nickel-base alloys 总被引:6,自引:0,他引:6
J. A. Goebel F. S. Pettit G. W. Goward 《Metallurgical and Materials Transactions B》1973,4(1):261-278
The Na2SO4-induced accelerated oxidation of nickel-base alloys containing elements such as Cr, Al, Mo, W, and V has been studied in
1.0 atm O2 in the temperature range of 650° to 1000°C. It has been found that the hot corrosion behavior of these alloys can usually
be characterized according to one of two types of attack: 1) Na2SO4-induced accelerated oxidation; 2) Na2SO4-induced catastrophic oxidation. In both types of hot corrosion, accelerated oxidation occurs as a result of the formation
of a liquid flux based on Na2SC>4 which dissolves the normally protective oxide scales. Catastrophic, or self-sustaining rapid
oxidation can occur in alloys which contain Mo, W, or V, because solutions of oxides of these elements with Na2SO4 decrease the oxide ion activity of the molten salts, producing melts which are acidic fluxes for oxide scales. The accelerated
oxidation type of attack which was observed with most alloys which did not contain Mo, W, or V, was more severe than for normal
oxidation, but much less severe than catastrophic oxidation. Na2SO4-induced accelerated oxidation occurs because the oxide ion activity of the Na2SO4 increases to the point where oxide scales can partially dissolve in the basic melt. Generally, this basic fluxing results
from the diffusion of sulfur from the Na2SO4 into the alloy. In some alloys, the formation of sulfides during basic fluxing is a sufficient condition to cause accelerated
oxidation. In other alloys, changes in the oxidation mechanism occur because of depletion of the alloy surface, concomitant
with basic fluxing, of those elements needed for protective oxide scales, such as aluminum and chromium. 相似文献
3.
The thermodynamic properties of dilute solutions of sulfur in pure liquid nickel were investigated at 1500, 1550, and 1575°C
for sulfur concentrations up to 0.7 wt pct. Based on the infinitely dilute, wt pct standard state, the equilibrium data obtained
for the reaction: H2(g) + S = H2S(g) were fitted by the equations: logK = − 1489/T − 1.772, and ΔG° = 6812 + 8.11T, cal/mole. For the solution ofS
2(g) in pure Ni according to the reaction: 1/2S
2(g) = S (in Ni), the standard free energy of solution is found to be: ΔG° = - 28,342 + 3.62T, cal/mole. For the very dilute
solutions of sulfur normally encountered in nickel-base melting, the activity coefficient of sulfur in pure Ni at 1575°C is
given by: log fS= -0.035 (pct S). The effects of alloying elements normally used in nickel-base alloys on the activity coefficient of sulfur
in molten nickel were investigated. The activity coefficient of sulfur is increased by all of the alloying elements studied,
as evidenced by the interaction parameters: eS
fe = +0.005, eS
Cr = +0.030, eS
Mo = +0.053, eS
Ti = +0.160, and eS
A1 = +0.133. Measured values of the activity coefficient of sulfur in the quaternary system Ni-S-Cr-Fe agreed reasonably well
with those predicted from binary and ternary data.
This work constitutes a portion of the work performed by W. F. VENAL for the Ph.D. degree from the University of Illinois
at Chicago Circle.
Formerly Professor of Metallurgical Engineering at UICC. 相似文献
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B. A. Borok R. P. Shchegoleva L. S. Golubeva É. N. Ostrovskaya M. I. Chikunov M. I. Kunis 《Powder Metallurgy and Metal Ceramics》1972,11(5):405-409
Conclusions A process has been developed for the manufacture of a Ni-Cr-Si-Fe-B brazing alloy in powder form, designated as PKh12N75S8R, and also brazing alloy powder No. 6MA, which is a mechanical mixture of 85% of PKh12N75S8R powder and 15% of molybdenum. Using alloy powder No. 6MA (instead of PKh12N75S8R) for brazing high-alloy steels raises the secondary melting (unbrazing) temperature of the brazed joint.Translated from Poroshkovaya Metallurgiya, No. 5 (113), pp. 82–88, May, 1972. 相似文献
7.
采用真空液相烧结法制备了4种掺加不同B含量的Ni-Cr-Mo合金,研究了B对其组织与性能的影响。研究结果表明,B与Mo、Cr、Ni等合金元素在烧结时可以形成共晶液相,通过原位化学反应,生成Mo2NiB2、(Mo,Cr)2NiB2陶瓷相。热腐蚀性试验表明,形成的硼化物相具有较好的耐腐蚀性,能够有效提高Ni-Cr-Mo合金的耐热腐蚀性能。 相似文献
8.
H. Chaung J. B. Lumsden R. W. Staehle 《Metallurgical and Materials Transactions A》1979,10(12):1853-1857
Auger electron spectroscopy has been used to investigate surface segregation on nickel single crystals and grain boundary
segregation in Ni 200. Sulfur was found to be the main segregating species in the temperature range 550 to 850°C. Segregated
sulfur was shown to catalyze the anodic dissolution kinetics when nickel is exposed to sulfuric acid. Its presence in the
grain boundaries of Ni 200 causes susceptiblity to IGSCC.
H. CHAUNG, formerly with the Department of Metallurgical Engineering, The Ohio State University
R. W. STAEHLE, formerly with the Department of Metallurgical Engineering, The Ohio State University 相似文献
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The oxidation of presulfidized chromium, Ni?Cr, and Ni?Al alloys, and complex nickel base alloys was studied at 1000°C in 1.0 atm of oxygen. Sulfur-rich surface layers were produced in the pretreatment by using H2S?H2 mixtures. Presulfidized chromium oxidized at a rate similar to that of sulfur-free chromium. The oxidation rate of presulfidized Ni?Cr alloys was affected by sulfur only when liquid nickel sulfide was present which accelerated the oxidation rate by creating rapid diffusion paths through the Cr2O3 scale. The oxidation behavior of presulfidized Ni?Al alloys, with aluminum contents sufficient for the formation of a protective Al2O3 layer in the sulfur-free condition, was influenced by sulfur only when aluminum sulfide was formed in the presulfidation treatment which caused the Al2O3 scale to be porous. The oxidation behavior of nickel-base alloys containing both chromium and aluminum was insensitive to the presence of sulfides when the concentration of aluminum in the alloy was such that a protective Al2O3 scale was formed during oxidation of the sulfur-free alloy and aluminum sulfide was not formed in the presulfidizing treatment. 相似文献
14.
The low cycle fatigue of three wrought nickel-base alloys 总被引:1,自引:0,他引:1
H. F. Merrick 《Metallurgical and Materials Transactions B》1974,5(4):891-897
The low cycle fatigue behavior of three wrought nickel-base alloys, alloy 901, Waspaloy and alloy 718, has been examined at
both room temperature and 811 K (1000°F). The fatigue properties can be rationalized in terms of the Manson-Coffin equation
relating total strain range with the number of cycles to failure. For a given total strain range the fatigue life of the alloys
at 811 K (1000°F) is substantially less than at room temperature. Microstructural examination revealed that crack nucleation
and initial propagation was of classical stage I type. The cracks develop at the surface of test specimens and propagate along
slip planes. Evidence is presented to relate the observed fatigue softening with shear and dissolution of γ precipitates. 相似文献
15.
《Acta Metallurgica》1982,30(6):1121-1131
The transient creep behaviour of two anisotropic nickel-base alloys (viz directionally solidified IN738LC and the in situ composite γ-γ-Cr3C2) has been examined following a wide range of stress changes. The response following an unloading loading sequence depends critically on the magnitude of the stress change and on the time spent on the reduced load. When a proportion of the stress is removed and immediately replaced delay periods of zero creep. Δt′, before creep recommences are obtained in both alloys although the magnitudes of Δt′ are 3–100 times greater for the composite than for the superalloy. When the reduced stress is maintained for long periods (⪆ 10 h) conventional primary creep, rather than delay periods are observed. A model is proposed that accounts for the transient strains in terms of the stress redistributions between fibre and matrix in the composite and across the dendritic structure in the superalloy. The implications of the results to the cyclic creep behaviour of these materials are discussed. 相似文献
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The effects of microstructure on the fatigue and creep crack growth of Waspaloy and P/M Astroloy were evaluated at 650°C.
In Waspaloy, changes in γ′ size and distribution did not markedly affect fatigue crack growth. An increase in fatigue crack
growth rate occurred at low test frequencies and was associated with a transition to intergranular crack propagation. In P/M
Astroloy, a coarser grain size lowered the fatigue crack growth rate. Serrated grain boundaries, though beneficial under creep
loading, have no effect in fatigue. 相似文献
19.
Hugh Morrow D. L. Sponseller M. Semchyshen 《Metallurgical and Materials Transactions A》1975,6(2):477-485
The effects of molybdenum and aluminum on the mean linear thermal expansion coefficients from room temperature to 1050°C were
determined for two types of nickel-base alloys. The Solid Solution Alloys were cast and homogenized Ni-Co-Cr-Mo alloys with
0, 312, and 612 nominal wt pct molybdenum concentrations. The Gamma Prime Alloys were wrought and heat-treated Ni-Cr-Mo-Al(Ti)
alloys with 0, 2, 5, and 8 nominal wt pct molybdenum in each of four aluminum plus titanium levels (3 pct Al, 412 pct Al,
6 pct Al, or 1 pct Al + 312 pct Ti nominal wt pct). Thermal expansion coefficients were determined on at least two specimens
from each alloy.
It was found that molybdenum lowers the thermal expansion coefficients of both the cast Ni-Co-Cr solid solutions and the wrought
Ni-Cr-Al(Ti) two-phase alloys. Both aluminum and titanium were also observed to decrease expansion coefficients in the two-phase,
γ + γ, alloys. Results are discussed in terms of relative melting point effects between solute and solvent elements, and in
terms of the volume fraction of the γ phase present. 相似文献
20.
The breakdown of single-crystal solidification in high refractory nickel-base alloys 总被引:1,自引:0,他引:1
The breakdown of single-crystal solidification has been studied over a wide range of solidification conditions in ten superalloys
with large variations in Re, Ta, and W content. Over the range of experimental conditions investigated, grain defect formation
was sensitive to local thermaland solutal conditions. For a fixed alloy composition and withdrawal rate, the transition from single-crystal to equiaxed solidification
did not occur abruptly. Instead, as thermal gradients were decreased in a series of experiments, isolated, highly misoriented
columnar grains with the same composition as that of the base alloy developed in the presence of positive (stabilizing) thermal
gradients with increasing frequency until the advance of the single-crystal front was completely blocked. The onset of columnar
grain formation occurred when the primary dendrite arm spacing exceeded a critical value, corresponding to a morphological
transition in the dendritic array. The onset of “freckling” was observed at the same primary dendrite arm spacing where misoriented
columnar grains began to appear. In experiments with varying levels of refractory alloy content, there was also a strong correlation
between the onset of grain formation and freckle formation. These observations strongly suggest that in high refractory content
superalloys, the breakdown of single-crystal solidification and the formation of misoriented grains as well as freckle-type
defects are sensitively dependent on thermosolutal convection processes. 相似文献