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1.
Plasma nitrocarburising was carried out with various CO gas compositions with 3 mbar at 570°C for 3 hours. After treatment,
different cooling rates (fast cooling, slow cooling and gas cooling) were used to investigate their effect on the structure
of the compound layer, the ε phase being the outer part of the compound layer and the γ′ phase being the inner part The CO
gas composition influenced the constitution of the compound layer produced, i.e. high CO contents were essential for the production
of an ε phased compound layer, as did a variation of the cooling rate, with a large amount of γ′ phase transformed from the
ε phase during slow cooling. The transformation was reduced with an increasing cooling rate and prevented by a fast cooling
rate of approximately 18.5°C/sec at 500°C, at which temperature this transformation began. 相似文献
2.
Insup Lee 《Metals and Materials International》2008,14(1):77-81
Plasma nitrocarburizing and post-oxidation treatments were performed to improve the wear and corrosion resistance of S45C
steel. Plasma nitrocarburizing was conducted for 3 h at 570°C in a nitrogen, hydrogen and methane atmosphere to produce the
ε-Fe2−3(N,C) phase. It was found that the compound layer produced by plasma nitrocarburising was predominantly composed of the ∈-phase
with traces of the γ′-Fe4(N,C) phase. The thickness of the compound layer was approximately 12 μm and the diffusion layer was approximately 300 μm
in thickness. Plasma post oxidation was performed on nitrocarburized samples with various oxygen/hydrogen ratios at a constant
temperature of 500°C for 1 h. The very thin magnetite (Fe3O4) layer 1 μm to 2 μm in thickness on top of the compound layer was obtained by plasma post oxidation. It was also confirmed
that further improvement of the corrosion characteristics of the nitrocarburized compound layer was possible with an application
of the superficial magnetite layer. Finally, throttle valve shafts of S45C steel were treated under optimum plasma processing
conditions. Accelerated life time test results using a throttle body assembled with a shaft treated by plasma nitrocarburising
and post oxidation showed that plasma nitrocarburizing and plasma post-oxidation processes could be a viable technology in
the very near future in place of Cr6 plating. 相似文献
3.
G. Hinojosa P. S. Schabes-Retchkiman J. Oseguera 《Journal of Materials Engineering and Performance》1998,7(3):312-316
A study of nitride-phase formation in alloys nitrided by glow discharge plasma nitriding was performed by high-resolution
electron microscopy. The iron and steel samples were nitrided above and below the eutectoid transformation point (590 ‡C).
After nitriding, the samples were annealed for several treatment times at 400 ‡C. The microstructure and identification of
the iron nitrided phases formed by nitriding and annealing were investigated by x-ray diffraction (XRD), optical microscopy
(OM) and mainly high resolution electron microscopy (HREM) in a JEOL-4000EX high resolution microscope at 400 kV. The results
of the characterization show a surface ε compact nitride layer, which is transformed into ε + γ during cooling. The tempering
process affects the surface hardness of the samples. After an initial increase relative to the untreated sample, the microhardness
diminishes after long treatment times. This behavior is correlated with the αt’’ phase appearance, growth, and transformation. 相似文献
4.
Dayong Cai Pulin Nie Jiaping Shan Wenchang Liu Mei Yao Yukui Gao 《Journal of Materials Engineering and Performance》2006,15(5):614-617
Mechanical surface treatment by shot peening followed by aging at 700 and 740 °C was performed on Inconel 718. A previously
proposed XRD method (Ref 10) for the quantitative phase analysis of Inconel 718 allowed for the determination of the precipitation
kinetics of the γ″ phase in the shot-peened layer and the matrix, respectively. The residual compressive stress field induced
by shot peening and its relaxation behavior during aging were also determined. The relaxation process can be described by
the Zener-Wert-Avrami function. The precipitation rate in the γ″ phase in the shot-peened layer is greatly accelerated, which
causes differences in the γ″ phase amounts between the skin and the core during aging, especially during the initial stage.
The high precipitation rate of the γ″ phase in the shot-peened layer can be interpreted by the nonequilibrium segregation
of niobium. 相似文献
5.
6.
Chang-Yong Jo Doo-Hyun Kim Seong-Moon Seo In-Soo Kim Seung-Joo Choe David Knowles 《Metals and Materials International》2000,6(2):117-123
Thermal exposure tests were carried out at the same temperature and duration as those of creep tests. Growth of γ′ either
in the matrix or in the interdendritic regions was observed during high temperature thermal exposure. The growth of γ′ caused
an isolated γ island in the γ/γ′ eutectics within which fine HfC particles precipitated. Some directional coarsening of γ′
was found in the specimens exposed at 1050°C. MC carbide reaction with the y matrix was observed in crept and thermally exposed
specimens. Needle-like precipitate, a kind of TCP, was found in the specimen crept at 1050°C for 400 hours. 相似文献
7.
Koo Hyun Lee Ki Suk Nam Youl Min Park Pyung Woo Shin Deuk Yong Lee Yo-Seung Song 《Metals and Materials International》2002,8(4):381-385
Plasma nitrocarburized AISI 1020 steels were oxidized for 15, 30 and 60 min to evaluate their corrosion and microstructural properties. After plasma nitrocarburizing for 3 h at 570°C in a gas mixture comprising 85 vol.% N2, 12vol.% H2 and 3 vol.% CH4, the compound layer composed of ɛ-Fe2–3(N,C) and γ’-Fe4(N,C) phases and the diffusion layer above the matrix were observed. The top oxide layer, consisting mainly of magnetite (Fe2O4) and hematite (Fe2O3) phases, forms after post-oxidation treatment at 500°C. However, the oxide layer was severely degraded by spallation as a result of increases in post-oxidizing time. The difference in corrosion resistance should be attributed to the thickness of the top oxide layer, which was governed by post-oxidizing time. 相似文献
8.
Composition and heat-treatment effects on the adhesion strength of Sn-Zn-Al solders on Cu substrate 总被引:2,自引:0,他引:2
Shan-Pu Yu Min-Hsiung Hon Hsin-Chien Wang Moo-Chin Wang 《JOM Journal of the Minerals, Metals and Materials Society》2000,52(6):36-39
Intermetallic layer growth at the solder/substrate interface during soldering and subsequent aging in service can affect bond
strength and dimensional stability. In this work, interfacial structure and bonding strength studies were performed on lead-free,
Sn-Zn-Al solders as a function of composition and aging time. With the x value of Sn-x(5Al-Zn) solder increasing from 5 wt.%
to 40 wt.%, the adhesion strength of bonding decreased from 11.2±0.5 MPa to 3.3±0.9 MPa while the thickness of the γ-Cu5Zn8 intermetallic compound layer increased from less than 1 μm to about 2 μm. Simultaneously, the adhesion strength of Sn-x(5Al-Zn)
solders with x=5, 9, 20, 30, and 40 decreased as the aging time at 150°C increased from 0 to 1,000 hours.
For more information, contact M.-C. Wang, National Kaohsiung Institute of Technology, Department of Mechanical Engineering,
415 Chien-Kung Road, Kaohsiung 80782, Taiwan; telephone 886-6-258-5663; fax 886-6-250-2734. 相似文献
9.
This paper addresses the influence of cyclic stress-induced martensitic transformation on fatigue crack growth rates in metastable
austenitic stainless steels. At low applied stress and mean stress values in AISI type 301 stainless steel, fatigue crack
growth rate is substantially retarded due to a cyclic stress-induced γ-α′ and γ-ε martensitic transformation occurring at
the crack-tip plastic zone. It is suggested that the transformation products produce a compressive residual stress at the
tip of the fatigue crack, which essentially lowers the effective stress intensity and hence retards the fatigue crack growth
rate. At high applied stress or mean stress values, fatigue crack growth rates in AISI type 301 steels become almost equal
to those of stable AISI type 302 alloy. As the amount of transformed products increases (with an increase in applied or mean
stress), the strain-hardening effect brought about by the transformed martensite phase appears to accelerate fatigue crack
growth, offsetting the contribution from the compressive residual stress produced by the positive volume change of γ → α′
or ε transformation. 相似文献
10.
Yee-Wen Yen Joachim Gröbner Rainer Schmid-Fetzer Yee-Wen Yen Steve C. Hansen 《Journal of Phase Equilibria》2003,24(2):151-167
A thermodynamic assessment of the Hg-Sn system has been carried out using the CALPHAD method. The comprehensive assessment
covers the extensive phase diagram data as well as the enthalpy, activity, and vapor pressure data. Two cases of intermetallic
compounds in the Hg-Sn system are considered. Case 1 considers the intermetallic compounds β, γ, and HgSn4 as having no solubility and can thus be treated as the stoichiometric phases β-HgSn38, γ-HgSn12, and HgSn4. Case 2 uses a sublattice model to more accurately describe a solubility of the γ phase; it also considers the stoichiometric
δ-HgSn7 phase. The ε phase was considered to be metastable and neglected in the thermodynamic assessment. Thermodynamic parameters
have been optimized using all the assessed experimental thermodynamic and phase equilibrium data. Both calculated phase diagrams
of the Hg-Sn system (Cases 1 and 2) and the thermodynamic data are reasonable and satisfactory when compared with literature
data. Future crucial experiments are suggested. 相似文献
11.
Yee-Wen Yen Joachim Gr?bner Rainer Schmid-Fetzer Yee-Wen Yen Steve C. Hansen 《Journal of Phase Equilibria and Diffusion》2003,24(2):151-167
A thermodynamic assessment of the Hg-Sn system has been carried out using the CALPHAD method. The comprehensive assessment
covers the extensive phase diagram data as well as the enthalpy, activity, and vapor pressure data. Two cases of intermetallic
compounds in the Hg-Sn system are considered. Case 1 considers the intermetallic compounds β, γ, and HgSn4 as having no solubility and can thus be treated as the stoichiometric phases β-HgSn38, γ-HgSn12, and HgSn4. Case 2 uses a sublattice model to more accurately describe a solubility of the γ phase; it also considers the stoichiometric
δ-HgSn7 phase. The ε phase was considered to be metastable and neglected in the thermodynamic assessment. Thermodynamic parameters
have been optimized using all the assessed experimental thermodynamic and phase equilibrium data. Both calculated phase diagrams
of the Hg-Sn system (Cases 1 and 2) and the thermodynamic data are reasonable and satisfactory when compared with literature
data. Future crucial experiments are suggested. 相似文献
12.
This study discusses the development of a phase transformation in 24Cr-14Ni-0.7Si stainless steel after aging under various
aging temperatures, times, and N2/Air ratios. The observation of OM indicated that the initial state of δ-ferrite in the test material appeared as complete
dendrite structures at short aging times and then exhibited lacy and dispersed structures when the aging time increased. This
led to a gradual austenitization transformation as the nitrogen/air ratio increased, accelerating the δ/σ phase transformation
and retarding the δ/γ phase transformation at the same time. The δ/σ phase transformation was dominant when the aging temperature
was 800 °C. A line scanning analysis of the EPMA showed that the X-ray spectrum of Cr at the δ/γ interphase boundary was raised.
In addition, Si showed lower X-ray spectrum energy after the δ/γ phase transformation. Clearly, Si had a stabilizing effect
on the δ-ferrite and σ-phase. Furthermore, it had the fastest precipitation ratio for the δ/σ phase transformation at 800°C
among all aging temperatures. 相似文献
13.
C. -W. Yang D. B. Williams J. I. Goldstein 《Journal of Phase Equilibria and Diffusion》1996,17(6):522-531
The low-temperature Fe-Ni phase diagram was assessed experimentally by investigating Fe-Ni regions of meteorites using high
resolution analytical electron microscopy techniques. The present phase diagram differs from the available experimental phase
diagram based on observations of meteorite structure, but it is consistent with the available theoretical diagram in that
α/Ni3Fe equilibrium was found at low temperatures. The a phase containing 3.6 wt.% Ni is in local equilibrium with the γ′ (Ni3Fe) phase containing 65.5 wt.% Ni, while the γ′' (FeNi) phase is present as a metastable phase. The new phase diagram incorporates
a monotectoid reaction (γ1 → α + γ2, where (γ1 is a paramagnetic fcc austenite, a is a bcc ferrite, and γ2 is a ferromagnetic fcc austenite) at about 400 °C, a eutectoid reaction (γ2 → α + γ′) at about 345 °C, and a miscibility gap associated with a spinodal region at low temperatures. The miscibility gap
is located between 9.0 and 51.5 wt. % Ni at ∼200 °C. The new low-temperature Fe-Ni phase diagram is consistent with all the
phases observed in the metallic regions of meteorites. 相似文献
14.
Diffusion and phase transformation on interface between substrate and NiCrAlY in Y-PSZ thermal barrier coatings 总被引:1,自引:0,他引:1
NiCrAlY/Y2O3-Y-PSZ (yttria-partially stabilized zirconia) thermal barrier coatings were developed on a superalloy (Ni-10Co-9Cr-7W-5Al,
wt.%) surface. The superalloys were first coated with a bond coat of Ni-19Cr-8Al-0.5Y (wt.%) alloy that was deposited by low-pressure
plasma spraying and then covered with a top coat of ZrO2-8wt.%Y2O3 by air plasma spraying. The microstructure near the interface was analyzed using an optical microscope, a scanning electron
microscope, microhardness measurements, and x-ray diffraction, and the phases of composition were measured using an electron
probe microanalyzer after exposure at 1100°C for different times in air or a vacuum. The reaction processes also were simulated
using diffusion-controlled transformation (DICTRA) software in which diffusion was considered as being only the γ phase, and the γ′ phase was treated as spheroidal particles in γ. From the authors’ results, it can be concluded that a γ′-phase layer is observed at the interface between substrate and bond coat, and its thickness increases with increasing exposure
times in air at 1100 °C. This layer showed good cohesion with the substrate and bond coat. It can also be concluded that the
formation of the γ′-phase layer can be predicted from DICTRA simulation. The simulation also shows the same trend of the composition profiles
as experimental data. 相似文献
15.
Yong-Kwon Jeong Chang-Yong Jo Yeong-Hwan Kim In-Bae Kim 《Metals and Materials International》1997,3(4):224-229
The 8 phase precipitation behavior of cold drawn alloy 718 has been investigated at 1116 K as a function of cold drawn ratio
and aging time. The planar markings formed by cold drawing were identified as deformation twins and developed more clearly
as cold drawing ratio increases. The grain boundaries and twins were played as nucleation site of δ precipitation, therefore,
cold drawing enhanced the precipitation of δ particles. As the cold drawing ratio and aging time increased the amount of round-shaped
δ also increased. In a specimen which was 50% cold drawn and aged for 4 hrs. the finely dispersed δ phase precipitated throughout
the material. As aging time increased. The round-shaped δ phase changed to plate-like morphology, and the morphology transformation
time was increased with cold drawing ratio. With a 50% cold drawn specimen, the transformation time was 7 hrs. On the other
hand, for the 50% cold drawn specimen aged for one hour at 1116 K, nucleation of the strain free grain was observed. 相似文献
16.
The thermodynamic properties of the Fe-Mn-Si system are analyzed by means of thermodynamic models for the individual phases.
Special attention is paid to the γ → ε martensitic transition. A complete set of parameters, from which arbitrary sections
of the phase diagram as well as the Ms and As temperatures may be calculated, is given. 相似文献
17.
The thermodynamic properties of the Fe-Mn-Si system are analyzed by means of thermodynamic models for the individual phases.
Special attention is paid to the γ → ε martensitic transition. A complete set of parameters, from which arbitrary sections
of the phase diagram as well as the Ms and As temperatures may be calculated, is given. 相似文献
18.
Three solid phases are involved in the phase equilibria of the important intermetallic compound N13Al near its melting point, β, γ′(Ni3AI) and γ. The generally-accepted phase diagram involves a eutectic reaction between γ′ and γ, but some recent studies agree
with an older diagram due to Schramm, 5 which has a eutectic reaction between the β and γ′ phases. This work uses diffusion
couple experiments to evaluate the equilibria at temperatures just below the liquidus, and it examines the liquidus region
using quenched, directional solidification experiments that preserve the microstructures formed at the solidification front.
At the growth rate studied, 61 μm/s, the eutectic forms between the γ and γ′ phases, as in the Schramm diagram. 相似文献
19.
J. D. Verhoeven J. H. Lee F.C Laabs L. L. Jones 《Journal of Phase Equilibria and Diffusion》1991,12(1):15-23
Three solid phases are involved in the phase equilibria of the important intermetallic compound N13Al near its melting point, β, γ′(Ni3AI) and γ. The generally-accepted phase diagram involves a eutectic reaction between γ′ and γ, but some recent studies agree
with an older diagram due to Schramm, 5 which has a eutectic reaction between the β and γ′ phases. This work uses diffusion
couple experiments to evaluate the equilibria at temperatures just below the liquidus, and it examines the liquidus region
using quenched, directional solidification experiments that preserve the microstructures formed at the solidification front.
At the growth rate studied, 61 μm/s, the eutectic forms between the γ and γ′ phases, as in the Schramm diagram. 相似文献
20.
The Effect of Heat Treatment on the Oxidation Behavior of HVOF and VPS CoNiCrAlY Coatings 总被引:1,自引:0,他引:1
Free-standing VPS and HVOF CoNiCrAlY coatings were produced. The as-sprayed HVOF coating retained the γ/β microstructure of
the feedstock powder, and the VPS coating consisted of a single (γ) phase. A 3-h, 1100 °C heat treatment in vacuum converted
the single-phase VPS coating to a two-phase γ/β microstructure and coarsened the γ/β microstructure of the HVOF coating. Oxidation
of free-standing as-sprayed and heat-treated coatings of each type was carried out in air at 1100 °C for a duration of 100 h.
Parabolic rate constant(s), K
p, were determined for free-standing, as-sprayed VPS and HVOF coatings as well as for free-standing coatings that were heat
treated prior to oxidation. The observed increase in K
p following heat treatment is attributed to a sintering effect eliminating porosity from the coating during heat treatment.
The lower K
p values determined for both HVOF coatings compared to the VPS coatings is attributed to the presence of oxides in the HVOF
coatings, which act as the barrier to diffusion. Oxidation of the as-sprayed coatings produced a dual-layer oxide consisting
of an inner α-Al2O3 layer and outer spinel layer. Oxidation of the heat-treated samples resulted in a single-layer oxide, α-Al2O3. The formation of a thin α-Al2O3 layer during heat treatment appeared to prevent nucleation and growth of spinel oxides during subsequent oxidation. 相似文献