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991.
992.
Daniel G. Sanders Mamidala Ramulu 《Journal of Materials Engineering and Performance》2004,13(6):744-752
Superplastic forming (SPF) combined with diffusion bonding (DB) has been used successfully for the fabrication of titanium
aerospace hardware. Many of these applications have been for military aircraft, whereby a complex built-up structure has been
replaced with monolithic parts. Several methods for applying the two- and four-sheet titanium SPF/DB processes have been devised,
including the welding of sheets prior to forming and the use of silk-screened stop-off (yttria) to prevent bonding where it
is undesirable. Very little progress has been made in the past few years toward understanding and modeling the SPF/DB process
using constitutive equations and data by laboratory testing. Concerns that engineers face in designing for fatigue life, acceptable
design loads, and damage tolerance are currently being studied, but the database is very limited. This is a summary of past
work found in the literature and forms the foundation for additional research.
This paper was presented at the International Symposium on Superplasticity and Superplastic Forming sponsored by the Manufacturing
Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium
was organized by Daniel G. Sanders, The Boeing Company. 相似文献
993.
Yang Gao Lian-Tong An Cheng-Qi Sun Zhi-Jun Yan 《Journal of Thermal Spray Technology》2004,13(4):521-525
The effects of the composition of plasma gases (Ar-N2, Ar-H2), arc current, and voltage on the temperature and velocity of a low-power (5 kW) plasma torch in the arc field free region
has been investigated using an enthalpy probe. Coatings of Al2O3-13TiO2 were deposited under different conditions. The results show that in the Ar-N2 plasma, the enthalpy, temperature, and velocity change little with arc current and voltage when regulating the nitrogen proportion
in the plasma gas. The hardness of the resulting coatings is 800 to 900 kg/mm2 HV.300. For Ar-H2 plasma, however, increases in the H2 content in the mixture of the gases remarkably enhanced the velocity and heat transfer ability of the plasma jet, with the
result that the coatings showed high hardness up to 1200 HV. 相似文献
994.
Uma Batra S. Ray S. R. Prabhakar 《Journal of Materials Engineering and Performance》2003,12(5):597-601
A ductile iron containing 0.6% copper as the main alloying element was austempered at a fixed austempering temperature of
330 °C for a fixed austempering time of 60 min after austenitization at 850 °C for different austenitization periods of 60,
90, and 120 min. The austempering process was repeated after changing austenitization temperature to 900 °C. The effect of
austenitization temperature and time was studied on the carbon content and its distribution in the austenite after austenitization.
The effect of austenitization parameters was also studied on austempered microstructure, structural parameters like volume
fraction of austenite, X
γ
, carbon content C
γ
, and X
γ
C
γ
, and bainitic ferrite needle size, d
α
after austempering. The average carbon content of austenite increases linearly with austenitization time and reaches a saturation
level. Higher austenitization temperature results in higher carbon content of austenite. As regards the austempered structure,
the lowering austenitization temperature causes significant refinement and more uniform distribution of austempered structure,
and a decrease in the volume fraction of retained austenite. 相似文献
995.
Désirée Risch Alexander Brosius Matthias Kleiner 《Journal of Materials Engineering and Performance》2007,16(3):327-330
Electromagnetic sheet metal forming is a high speed forming process using pulsed magnetic fields to form metals with high
electrical conductivity such as aluminum. Thereby, workpiece velocities of more than 300 m/s are achievable, which can cause
difficulties when forming into a die. The kinetic energy, which is related to the workpiece velocity, must be dissipated in
a short time slot when the workpiece hits the die; otherwise undesired effects, for example rebound can occur. One possibility
to handle this shortcoming is to locally increase the stiffness of the workpiece. A modal analysis is carried out in order
to determine the stiffness of specific regions of the workpiece so that an estimation concerning the feasibility of the desired
geometry is possible in advance without doing cost and time consuming experiments. Thereby, the desired geometry of the workpiece
will be fractionized in significant sectors. This approach has to define the internal force variables acting on the cutting
edge, which are required to constrain the numerical model. Finally, a method will be developed with the objective of calculating
the stiffness of each sector. The numerical results will be verified by experiments.
This article was presented at Materials Science & Technology 2006, Innovations in Metal Forming symposium held in Cincinnati,
OH, October 15-19, 2006. 相似文献
996.
Zhongning Shi Junli Xu Zhuxian Qiu Zhaowen Wang Bingliang Gao 《JOM Journal of the Minerals, Metals and Materials Society》2003,55(11):63-65
The superalloys Cu-Ni-Al, Cu-Ni-Fe, and Cu-Ni-Cr were studied as anodes for aluminum electrolysis. The alloys were tested
for corrosion in acidic electrolyte molten salt and for oxidation in both air and oxygen. The results showed that the Cu-Ni-Al
anodes possess excellent resistance to oxidation and corrosion, and the oxidation rates of Cu-Ni-Fe and Cu-Ni-Al anodes were
slower than those of pure copper or nickel. During electrolysis, the cell voltage of the Cu-Ni-Al anode was affected most
by the concentration of alumina in cryolite molten salt. The Cu-Ni-Fe anode exhibited corrosion resistance in electrolyte
molten salt. Comparatively, the Cu-Ni-Cr anode showed poor resistance to oxidation and corrosion. The testing found that further
study is warranted on the use of Cu-Ni-Al and Cu-Ni-Fe as inert alloy anodes.
For more information, contact Zhongning Shi, Northeastern University, School of Materials and Metallurgy, WenhuiRoad No. 3,
Shenynag, Liaoning 110004 China; e-mail znshi@163.com 相似文献
997.
R. Polini S. Kumashiro M. J. Jackson M. Amar W. Ahmed H. Sein 《Journal of Materials Engineering and Performance》2006,15(2):218-222
Deposition of diamond films onto various substrates can result in significant technological advantages in terms of functionality
and improved life and performance of components. Diamond is hard, wear resistant, chemically inert, and biocompatible. It
is considered to be the ideal material for surfaces of cutting tools and biomedical components. However, it is well known
that diamond deposition onto technologically important substrates, such as co-cemented carbides and steels, is problematic
due to carbon interaction with the substrate, low nucleation densities, and poor adhesion. Several papers previously published
in the relevant literature have reported the application of interlayer materials such as metal nitrides and carbides to provide
bonding between diamond and hostile substrates. In this study, the chemical vapor deposition (CVD) of polycrystalline diamond
on TiN/SiN
x
nc (nc) interlayers deposited at relatively low temperatures has been investigated for the first time. The nc layers were
deposited at 70 or 400 °C on Si substrates using a dual ion beam deposition system. The results showed that a preliminary
seeding pretreatment with diamond suspension was necessary to achieve large diamond nucleation densities and that diamond
nucleation was larger on nc films than on bare sc-Si subjected to the same pretreatment and CVD process parameters. TiN/SiN
x
layers synthesized at 70 or 400 °C underwent different nanostructure modifications during diamond CVD. The data also showed
that TiN/SiN
x
films obtained at 400 °C are preferable in so far as their use as interlayers between hostile substrates and CVD diamond
is concerned.
This paper was presented at the fourth International Surface Engineering Congress and Exposition held August 1–3, 2005 in
St. Paul, MN. 相似文献
998.
Dong-il Shin François Gitzhofer Christian Moreau 《Journal of Thermal Spray Technology》2007,16(1):118-127
Metal-based thermal barrier coatings (MBTBCs) have been produced using high frequency induction plasma spraying (IPS) of iron-based
nanostructured alloy powders. The study of MBTBCs has been initiated to challenge issues associated with current TBC materials
such as difficult prediction of their “in-service” lifetime. Reliability of TBCs is an important aspect besides the economical
consideration. Therefore, the study of MBTBCs, which should posses higher toughness than the current TBC materials, has been
initiated to challenge the mechanical problems of ceramic-based TBCs (CBTBCs) to create a new generation of TBCs. The thermal
diffusivity (TD) (α) properties of the MBTBCs were measured using a laser flash method, and density (ρ) and specific heat
(C
p) of the MBTBCs were also measured for their thermal conductivity (k) calculation (k = αρ
C
p). 相似文献
999.
Advances in fabricating superplastically formed and diffusion bonded components for aerospace structures 总被引:1,自引:0,他引:1
Larry D. Hefti 《Journal of Materials Engineering and Performance》2004,13(6):678-682
Superplastic forming and diffusion bonding (SPF/DB) production hardware is being fabricated today for aerospace applications.
Metal tooling is being used to bring the titanium sheets into contact so diffusion bonding can occur. However, due to material
sheet and tooling tolerances, good bond quality is difficult to achieve over large areas. A better method for achieving DB
is to use “stop-off” inside sealed sheets of titanium, which constitutes a pack, and then the pack is bonded using external
gas pressure. A good method for heating the pack for this process is to use induction heating. Components using “stop-off”
that were diffusion bonded first and then superplastically formed have shown much better bond quality than components that
were produced using matched metal tooling. This type of tooling has been successful at bonding small areas as long as the
exerted pressure is concentrated on the area where bonding is required. Finite element modeling is providing weight effect
solutions for titanium SPF/DB aerospace structures.
This paper was presented at the International Symposium on Superplasticity and Superplastic Forming, sponsored by the Manufacturing
Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium
was organized by Daniel G. Sanders, The Boeing Company. 相似文献
1000.
V. M. El’kin E. A. Kozlov E. V. Kakshina Yu. S. Moreva 《The Physics of Metals and Metallography》2006,101(3):208-217
A thermodynamically complete equation of two-phase (γ, α) state of cerium was derived in terms of a pseudobinary solid-solution model developed by Aptekar’ and Ponyatovskii. According to the model, unalloyed cerium is considered to be a substitutional solid solution whose components are represented by atoms with different electron configurations. The free energy of the individual phases (solid-solution components) is represented as a sum of three terms that describe the atomic interaction at T = 0 K, quasi-harmonic lattice vibrations, and the combined contribution of the anharmonicity and thermally excited electrons. The equation of state is shown to adequately describe the unusual behavior of cerium under the effect of static actions. In this work, calculations of the dynamic compression of cerium are performed. The calculations indicate that, up to the completion of the γ-α transition, the formation of the shockwave front in cerium is impossible and compression of cerium occurs in an isentropic wave of simple compression. As the pressure increases, a multiwave configuration with the participation of isentropic and shock waves is realized in cerium. The initial state in which the shock wave is propagated changes depending on the wave intensity; i.e., the initial state “slides” along the leading isentropic wave. The shock adiabat was shown to not pass through the very complex range of metastable existence of α-, α′-, and α″ phases. This provides prerequisites for experimental finding the α-ε transformation which can occur in the shock wave and is not masked with the preceding α-α′ and α′-α″ transformations. When assuming the absence of the α-ε transformation, the calculated coordinates of the point corresponding to the start of melting in the shock wave are p melt = 11.3 GPa and T melt = 1130 K. 相似文献