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1.
Microstructural study of the interface in laser-clad Ni-Al bronze on Al alloy AA333 and its relation to cracking 总被引:2,自引:0,他引:2
The interface toughness between a laser clad and the substrate determines whether the cladding is useful for engineering application.
The objective of this investigation is to correlate the interface properties of laser-clad Ni-AI bronze on Al alloy AA333
with the microstructure and crystal structure of the interface. Scanning electron microscopy (SEM) and transmission electron
microscopy (TEM) combined with energy-dispersive X-ray spectroscopy (EDX) are used to examine the interface. In a good clad
track, the interface is an irregular curved zone with a varying width (occasionally keyholing structure) from 30 to 150 μm.
A compositional transition from the Cu-rich clad (83 wt pct Cu) to the Al-rich substrate (3.2 wt pct Cu) occurs across this
interface. Three phases in the interface are identified in TEM: Al solid solution, θ phase, and γ1 phase, as described in the Cu-Al binary phase diagram. In a good clad track, the θ and γ1 phases are distributed in the Al solid solution. In a clad track with cracks, the interface structure spreads to a much larger
scale from 300 μm to the whole clad region. Large areas of θ and γ1 phases are observed. The mechanism of cracking at the interface is related to the formation of a twophase region of θ and
γ1 phases. To understand the microstructure, a nonequilibrium quasibinary Cu-Al phase diagram is proposed and compared with
the equilibrium binary Cu-Al phase diagram. It is found that the occurrence of many phases such as η1η2, ζ1, ζ2, ε1, ε2, γ0, β0, and β, as described in the equilibrium binary Cu-Al phase diagram, is suppressed by either the cladding process or by the
alloying elements. The three identified phases (Al solid solution, θ phase, and γ1, phase) showed significant extension of solubility.
Formerly Visiting Research Associate, Department of Mechanical and Industrial Engineering, Center for Laser Aided Material
Processing, University of Illinois at Urbana-Champaign, Urbana, IL 61801 相似文献
2.
Alloys and coatings for alloys for improved high temperature service life under aggressive atmo-spheres are of great contemporary
interest. There is a general consensus that the addition of rare earths such as Hf will provide many beneficial effects for
such alloys. The laser cladding technique was used to produce Ni-Cr-AI-Hf alloys with extended solid solution of Hf. A 10
kW CO2 laser with mixed powder feed was used for laser cladding. Optical, scanning electron (SEM) and scanning transmission electron
(STEM) microscopy were employed to characterize the microstructure of alloys produced during laser cladding processes. Microstructural
studies revealed grain refinement, considerable in-crease in solubility of Hf in the matrix, Hf-rich precipitates, and new
metastable phases. The size and morphology of γ′ (Ni3Al) phase were discussed in relation to its microchemistry and the laser processing conditions. This paper will report the
microstructural development in this laser clad Ni-Cr-AI-Hf alloy.
Formerly Visiting Assistant Professor, Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign. 相似文献
3.
Extended solid solution and nonequilibrium phase diagram for Ni-Al alloy formed during laser cladding 总被引:1,自引:0,他引:1
Due to rapid solidification in laser cladding, the composition of the solute in the cladding alloy often exceeds the solid
solubility limit far beyond that expected from the equilibrium phase diagram. Also, the effects of various process parameters
on the composition of the cladding alloy depend on the sign of the slope of the equilibrium phase diagram at the nominal composition
of the cladding powder. This paper uses a mathermatical model to determine the composition of metastable alloys and to study
the effects of various process parameters on the composition of extended solid solution in the cladding alloys of Ni-Al for
which the slope of the equilibrium phase diagram is positive at the nominal composition of the Ni-Al cladding powder. The
model considers concentration dependent freezing point and nonequilibrium partitioning of solute at the solid-liquid interface.
Because of this, nonequilibrium phase diagram can be obtained by following the methodology of this paper. 相似文献
4.
Coatings for superalloys for extended service in atmospheres at high temperature are of great interest at present. The addition
of reactive elements (RE’s) such as Hf to these coatings has a pronounced effect on their high-temperature oxidation resistance.
A laser-cladding technique was used to produce Ni-Al-Cr-Hf alloys with an extended solid solution of Hf in a nearstoichiometric
Ni3Al matrix. A 10 kW CO2 laser with mixed powder feed was used for the cladding process. Scanning electron microscope (SEM), transmission electron
microscope (TEM), and scanning transmission electron microscope (STEM) were employed for studies of microstructural evolution
of alloys produced during the laser-cladding process. Microstructural studies reveal the formation of dendrites with a solid
solubility of about 11 to 14 wt pct Hf and also a eutectic structure. Convergent-beam techniques and X-ray spectroscopy have
been applied to characterize the phases formed during the cladding process. 相似文献
5.
《Acta Metallurgica》1987,35(8):1995-2003
Alloys and coatings for alloys for improved high temperature service life under aggressive atmosphere are of great contemporary interest. There is a general consensus that addition of reactive elements such as Hf will provide many beneficial effects for such alloys. The laser cladding technique was used to produce Ni-Fe-Cr-Al-Hf alloys with extended solid solution of Hf. A 10 kW CO2 laser with mixed powder feed was used for laser cladding. Optical, scanning electron (SEM) and scanning transmission electron (STEM) microscopy were employed for microstructural evolution of alloys produced during laser cladding processes. The electron probe microanalysis and the auger electron spectroscopy were also used for micro-chemical analysis of different phases. Microstructural studies revealed a high degree of grain refinement, considerable increase in solubility of Hf in matrix and Hf rich precipitates and new metastable phases. This paper will report the microstructural development in this laser clad Ni-Fe-Cr-Al-Hf alloy. 相似文献
6.
By the method of calorimetry in isoperibolic conditions are determined integral and partial mixing enthalpies of liquid alloys of the Ni-Hf system at 1770 ± 5 K. Defined that liquid Ni-Hf alloys are formed with allocated large quantity of heat. The analysis of own and literary data has allowed to establish for mixing enthalpies of binary Ni-Hf liquid alloys dependence on temperature. With use of the Schröder equation are calculated the activities of studied alloys components from co-ordinates of liquidus line of the phase diagram of this system. Between calculated and experimentally established values of melts components activities of the Ni-Hf system is observed only qualitative consent. Are also calculated ΔG and ΔS of liquid Ni-Hf alloys. 相似文献
7.
The microstructure and hot corrosion behavior of Ni/Al–Cr composite claddings produced by gas tungsten arc welding (GTAW) on a 310 stainless steel substrate were studied. The phase analyses and the microstructure of the cladding layers were evaluated using optical microscopy, X-ray diffraction (XRD) and scanning electron microscopy. The influence of Cr addition (0, 5, 10 at% Cr) on the microstructure and hot corrosion behavior of the NiAl coatings was assessed. The cyclic hot corrosion behavior of the base metal and different claddings was investigated at 900°C and in static air, with a 2–3?mg/cm2 Na2SO4–10%NaCl (wt%). It was found that a dendritic microstructure was formed on the clad surfaces. The results of the XRD analyses indicated that a NiAl phase was synthesized in situ during GTAW cladding and the presence of Cr reduced the intensity of diffraction peaks of NiAl. Hot corrosion experiments also revealed that the addition of Cr had a crucial influence on the hot corrosion behavior of NiAl coatings. It was found that the larger the amount of Cr, the superior the resistance of the coatings to hot corrosion. This improvement was attributed to the formation of Al2O3 as a protective oxide layer, as evidenced by XRD patterns. However, the iron containing phases produced as a result of interactions with the substrate were found to be a detrimental factor influencing the corrosion properties of different cladded layers. 相似文献
8.
9.
Carl R. Ribaudo Jyoti Mazumder Dennis W. Hetzner 《Metallurgical and Materials Transactions B》1992,23(4):513-522
A new mechanism for the improved retention of alumina scales formed on laser-clad NiAICrHf alloys has been observed. Laser
cladding is the process where fine metal powders are rapidly melted and fused to a solid substrate using a CO2 laser. The
effects of laser cladding upon scale retention on NiAICrHf alloys after cyclic and isothermal exposure to air were investigated
using thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The calculated compressive
stress in the scale due to constrained cooling exceeded the probable compressive strength of alumina. Additions of up to ≈
2.5 wt pct Hf increasingly promote retention of scales grown at 1200 °C, with laser-clad samples of ≈ 2.5 wt pct Hf alloy
retaining almost completely intact scales. The improvement in scale retention is due to improved toughness in scales containing
hafnia polycrystallites, possiblyvia microcracking initiated by anisotropic thermal contraction of the hafnia. Laser cladding the 2.5 wt pct Hf alloy provides
a large concentration of ~ 1 μm Hf-rich particles that are precursors of the hafnia in the scale as well as a finer dendrite
spacing that reduces the mean free distance between particles.
Formerly Graduate Research Assistant, Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign 相似文献
10.
The laser surface cladding technique was used to formin situ Fe-Cr-Mn-C alloys on AISI 1016 steel substrate. In this process mixed powders containing Cr, Mn, and C with a ratio of 10∶1∶1
were delivered using a screw feed, gravity flow carrier gas aided system into the melt pool generated by a 10 kw CO2 laser. This technique produced ultrafine microstructure in the clad alloy. The microstructure of the laser surface clad region
was investigated by optical, scanning, and transmission electron microscopy and X-ray microanalysis techniques. Microstructural
study showed a high degree of grain refinement and an increase in solid solubility of alloying elements which, in turn, produced
a fine distribution of complex types of carbide precipitates in the ferrite matrix because of the high cooling rate. An alloy
of this composition does not show any martensitic or retained austenite phase. In preliminary wear studies the laser clad
Fe-Cr-Mn-C alloys exhibited far superior wear properties compared to Stellite 6 during block-on-cylinder tests. The improved
wear resistance is attributed to the fine distribution of metastable M6C carbides. 相似文献
11.
The laser surface cladding technique was used to formin situ Fe-Cr-Mn-C alloys on AISI 1016 steel substrate. In this process mixed powders containing Cr, Mn, and C with a ratio of 10:1:1
were delivered using a screw feed, gravity flow carrier gas aided system into the melt pool generated by a 10 kw CO2 laser. This technique produced ultrafine microstructure in the clad alloy. The microstructure of the laser surface clad region
was investigated by optical, scanning, and transmission electron microscopy and X-ray microanalysis techniques. Microstructural
study showed a high degree of grain refinement and an increase in solid solubility of alloying elements which, in turn, produced
a fine distribution of complex types of carbide precipitates in the ferrite matrix because of the high cooling rate. An alloy
of this composition does not show any martensitic or retained austenite phase. In preliminary wear studies the laser clad
Fe-Cr-Mn-C alloys exhibited far superior wear properties compared to Stellite 6 during block-on-cylinder tests. The improved
wear resistance is attributed to the fine distribution of metastable M6C carbides. 相似文献
12.
Ni-Al-Cr-Hf coatings with an extended solid solution of Hf were fabricated by laser cladding a premixed powder with a Ni-Al-Cr-Hf
ratio of 70∶20∶7∶3 onto a substrate of RENé 80. Isothermal oxidation tests in slowly flowing air reveal that the claddings
have a lower weight-gain rate than the substrate itselt. Microchemistry and microstructures of the oxidized samples were examined
using scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). The improvement in oxidation resistance is
believed to be at least partially due to the formation of large numbers of hafnium-rich oxide spikes penetrating the unoxidized
sample. 相似文献
13.
Phase equilibria in the bcc Fe-Ge system have been investigated by means of electron probe microanalysis and transmission electron microscopy. Two kinds of ordered phases, B2 and DO3 types, have been detected, the B2 phase being formed from the disordered A2 phase by a 2nd order transition. The DO3 phase is also formed from the B2 phase by a 2nd or higher order transition at higher temperatures. Below about 820 °C, however, the transition becomes a 1st order, and a miscibility gap between these ordered phases occurs in the composition range from 13 to 16 at. pct Ge. It has been also confirmed that the solubility of Ge in the bec phase shows a retrogression due to the formation of DO3 phase. On the basis of these experimental results, the phase diagram for the Fe-Ge system has been partly revised. 相似文献
14.
Mechanical alloying of nb-al powders 总被引:1,自引:0,他引:1
Zhixue Peng C. Suryanarayana F. H. Froes 《Metallurgical and Materials Transactions A》1996,27(1):41-48
The effect of mechanical alloying (MA) on solid solubility extension, nanostructure formation, amorphization, intermetallic
compound formation, and the occurrence of a face-centered cubic (fcc) phase in the Nb-Al system has been studied. Solid solubility
extension was observed in both the terminal compositions and intermetallic compounds: 15 pct Nb in Al and 60 pct Al in Nb,
well beyond the equilibrium and even rapid solidification levels (2.4 pct Nb and 25 pct Al, respectively) and increased homogeneity
range for the NbAl3 phase. Nanostructured grains formed in all compositions. In the central part of the phase diagram, amorphization occurred
predominantly. Only NbAl3, the most stable intermetallic, formed during MA; in most cases, a subsequent anneal was required. On long milling time,
an fcc phase, probably a nitride, formed as a result of contamination from the ambient atmosphere. 相似文献
15.
The Fe-Cr-C claddings formed by arc surface welding with different La2O3 additions were investigated. The microstructures were observed by optical microscopy (OM), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The phase structures were measured by X-ray diffraction (XRD). The wear resistances of the claddings were tested by friction and wear experiment. On this basis, the carbide refinement mechanism by inclusion enriched with La was discussed theoretically. The results showed that, the microstructure of the Fe-Cr-C cladding consisted of primary (Cr,Fe)7C3 carbides and eutectic (γ-Fe+(Cr,Fe)7C3 ) structure. With La2O3 addition increasing, the primary carbides were refined, and the mass loss of the cladding decreased gradually. The Fe-Cr-C cladding with 4wt.% La2O3 addition had a best wear resistance behaviour. The RE inclusion LaAlO3 as heterogeneous nuclei of the primary M7C3 was medium effective, and could refine the M7C3 carbides. Besides, the wear resistance could be improved by adding La2O3 in the claddings. 相似文献
16.
利用等离子熔覆设备堆焊制备了三种不同成分的镍基合金层(Ni46、Ni67、Ni60/35WC),制样后在旋转圆盘空蚀试验机上对制备的合金层进行了空蚀磨损实验.采用SEM、XRD、显微硬度、失重分析法对空蚀前后的合金层进行了对比分析.结果表明:所有堆焊层的失重均大于对比的304不锈钢;SEM形貌观察堆焊层组织中存在缺陷或孔隙,空蚀后组织中的缺陷呈裂纹状发展,因此空蚀伴随着强烈的疲劳损失过程;XRD分析表明空蚀过程诱发了Ni60/35WC表面的相变;另外,空蚀还引起了材料Ni67和Ni60/35WC加工硬化,而Ni46出现了加工软化. 相似文献
17.
C. Sudha T. N. Prasanthi V. Thomas Paul S. Saroja M. Vijayalakshmi 《Metallurgical and Materials Transactions A》2012,43(10):3596-3607
Ti-5Ta-2Nb alloy was clad on 304L austenitic stainless steel (SS) using the explosive cladding process. Both Ti-5Ta-2Nb and 304L austenitic steel were severely deformed due to high pressure (in the gigapascal range) and strain rate (105/s), which are characteristics of explosive loading conditions. Consequent changes produced in the microstructure and crystal structure of both the alloys are studied using electron microscopy techniques. The microstructure of both Ti-Ta-Nb alloy and 304L steel showed evidence for the passage of the shock waves in the form of a high number density of lattice defects such as dislocations and deformation twins. In addition, both the alloys showed signatures of phase transformation under nonequilibrium conditions resulting in metastable transformation products. 304L SS showed martensitic transformation to both ????(bcc) and ??(hcp) phases. Microscopic shear bands, shear band intersections, and twin boundaries were identified as nucleation sites for the formation of strain-induced phases. Ti-Ta-Nb alloy underwent metastable phase transformation to an fcc phase, which could be associated with regions having a specific morphology. 相似文献
18.
Phase equilibria in the bcc Fe-Ge system have been investigated by means of electron probe microanalysis and transmission
electron microscopy. Two kinds of ordered phases, B2 and DO3 types, have been detected, the B2 phase being formed from the disordered A2 phase by a 2nd order transition. The DO3 phase is also formed from the B2 phase by a 2nd or higher order transition at higher temperatures. Below about 820 °C, however,
the transition becomes a 1st order, and a miscibility gap between these ordered phases occurs in the composition range from
13 to 16 at. pct Ge. It has been also confirmed that the solubility of Ge in the bec phase shows a retrogression due to the
formation of DO3 phase. On the basis of these experimental results, the phase diagram for the Fe-Ge system has been partly revised. 相似文献
19.
The vaporization of alloys of the Ni-Hf system was investigated in the temperature range between 1200 and 1650 K by Knudsen
effusion mass spectrometry. The different compositions of the 16 alloy samples investigated covered the complete homogeneity
range of the Ni-Hf system. The partial pressure of Ni was determined over all samples. The thermodynamic activities of Ni
and Hf in the alloys were evaluated from these pressures and by Gibbs-Duhem integration. In addition, Gibbs energies of formation,
enthalpies of formation, and entropies of formation resulted for the nine intermetallic phases of the Ni-Hf system. Beside
similar thermodynamic data for the evaporation reactions were studied. The data obtained are discussed and a method for distinguishing
the congruent melting compounds from the peritectic ones by defining stability factors calculated from the Gibbs energies
of formation is suggested. 相似文献
20.
《Acta Metallurgica Materialia》1992,40(8):1873-1881
During the past several years, a great deal of progress has been made in the use of both pulsed and continuous wave (CW) lasers in materials processing. Usually pulsed laser is used for annealing semiconductors and CW laser for alloying and cladding substrate materials. Inherent rapid cooling in such processes invariably produces novel materials due to nonequilibrium segregation of solute atoms during solidification. Such nonequilibrium phenomena have drawn a lot of interest in both theoretical and applied areas of solid-state physics and materials science. Dilute solution theory is adequate to study nonequilibrium solute (dopant) segregation during laser annealing of semiconductors because the concentration of solute atoms is very small compared to that of the solvent (host) atoms. Using kinetic model of nonequilibrium solidification, several studies have been already carried out under dilute solution approximation to derive an expression for nonequilibrium partition coefficient. However, concentrated solutions are frequently encountered in laser cladding and alloying processes. The nonequilibrium partitioning of solute in binary concentrated solutions is modeled in this study, and an expression for nonequilibrium partition coefficient with only one unknown parameter is obtained. 相似文献