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At least 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Interface-correlated bonding properties for a roll-bonded Ti/Al 2-ply sheet

Highlights: • The feasible post roll-bonding annealing condition of Ti/Al clad was deduced. • The optimum thickness of the TiAl{sub 3} IMC diffusive layer is about 200 nm. • A ‘zipper-like’ failure mode at the interface yields the maximum bonding strength. - Abstract: We investigated the influence of annealing conditions on the interface-correlated microstructural evolution and subsequent bonding properties of a warm roll-bonded Ti/Al clad sheet. A TiAl{sub 3} intermetallic compound layer with a thickness of 160 nm was initially generated at the joint interface between the Ti and Al alloys by warm rolling. When the annealing time and temperature were increased to a maximum of 6 h and 650 °C, respectively, the thickness of the TiAl{sub 3} layer increased to 320 nm. The feasible annealing conditions for the optimum bonding strength were within 550 °C-6 h and 600 °C-3 h. An improvement in the bonding strength between Ti and Al is strongly correlated with the generation of considerable metallurgical bonding. This is manifested in the zipper-like failure mode that occurs at the TiAl{sub 3} joint interface for a layer thickness of less than 300 nm.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Elimination of trench defects and V-pits from InGaN/GaN structures

The microstructural evolution of InGaN/GaN multiple quantum wells grown by metalorganic chemical vapor phase epitaxy was studied as a function of the growth temperature of the GaN quantum barriers (QBs). We observed the formation of basal stacking faults (BSFs) in GaN QBs grown at low temperature. The presence of BSFs terminated by stacking mismatch boundaries (SMBs) leads to the opening of the structure at the surface into a V-shaped trench loop. This trench may form above an SMB, thereby terminating the BSF, or above a junction between the SMB and a subsequent BSF. Fewer BSFs and thus fewer trench defects were observed in GaN QBs grown at temperatures higher than 830 °C. Further increase in the growth temperature of the GaN QBs led to the suppression of the threading dislocation opening into V-pits.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

{sup 1}H NMR relaxometry as an indicator of setting and water depletion during cement hydration

Proton nuclear magnetic resonance relaxometry has been used to detect setting and microstructure evolution during cement hydration. NMR measurements were performed since casting, during setting and until hardening (from 0 to 3 days). The mobility of water molecules was assessed by an analysis focused on the diagram of longitudinal relaxation time T{sub 1} generated by an Inversion Recovery sequence. The initial stiffening of the solid network was identified by an analysis of the relaxation rate 1/T{sub 1}. The kinetics of water depletion was investigated by using a simple one-pulse acquisition sequence. In parallel, conventional techniques (Vicat needle and temperature monitoring), as well as numerical simulations of hydration, were used to complement and validate these NMR results. Cement pastes and mortars with different water-to-cement ratios made of grey or white OPCs were tested. Furthermore, the effects of the addition of sand, super-plasticizer and silica fume on the hydration kinetics were investigated.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Decarburization and Carburization Behavior of Grade 91 Steel in Sodium Environments

Two heats of G91 steel have been investigated in sodium at 550-650°C to understand its corrosion behaviour, microstructural evolution, and tensile properties. Sodium exposure tests of subsized tensile and coupon specimens of G91 base metal and weldment were conducted in Argonne’s forced convection sodium materials testing loops. Maximum exposure times of ~39,000 h at 550°C, ~37,000 h at 600°C, and ~20,000 h at 650°C have been achieved, respectively. Thermal aging experiments of G91 steel were conducted in parallel, and the data of the sodium-exposed specimens were compared with the thermal aging data of the same heat to isolate the thermal aging effect from the effect of sodium exposure. It was found that the tensile strength of G91 steel can be reduced by more than 50% after sodium exposures at 650°C. The effect of a sodium environment on tensile properties is largely dependent on the carburization/decarburization behavior of G91 steel exposed to sodium. The carbon concentrations in sodium in Argonne’s SMT-1 and SMT-2 loops were determined by the equilibration method. The carbon activity in sodium was established by equilibrating high-purity nickel in sodium, analyzing the material for carbon, and using the reported data on the carbon solubility for this material. The carbon activity results were combined with the carbon solubility data in sodium to establish the carbon concentration in sodium. The carbon concentrations in the SMT-1 and SMT-2 loop were estimated to be 1.23 and 0.25 ppm, respectively. With this initial success, we will continue to monitor the carbon contents in the two loops to correlate the microstructural and mechanical property changes with the sodium purity. Future experiments will also consider sodium exposure tests in controlled carbon activities. Online monitoring and control of carbon contents in sodium in nuclear reactors would also be of interest. Thermodynamic analysis was conducted to understand the carburization-decarburization behavior of G91 steel exposed to sodium in the SMT-1 and SMT-2 loops. The equilibrium carbon activity in the alloy was evaluated by the thermodynamics of M 23 C 6 carbides. The calculated carburization-decarburization boundary showed that G91 would undergo decarburization at 650°C in the SMT-1 loop and carburization at 600°C in the SMT-2 loop, which is consistent with our findings from the sodium exposure tests. Future work will include thermodynamic analysis of the carbon concentration – activity relationship including the effect of carbide-forming elements, vanadium and niobium in G91 steel. Kinetics of carbon diffusion and the effect on microstructure and mechanical performance under various service conditions will also be investigated. The ultimate goal is to understand the mechanisms and the kinetics of carbon transfer in the sodium-steel system and to provide a basis for predicting the effect of long-term decarburization-carburization process on the integrity of reactor components.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2015

Coalescence-controlled and coalescence-free growth regimes during deposition of pulsed metal vapor fluxes on insulating surfaces

The morphology and physical properties of thin films deposited by vapor condensation on solid surfaces are predominantly set by the processes of island nucleation, growth, and coalescence. When deposition is performed using pulsed vapor fluxes, three distinct nucleation regimes are known to exist depending on the temporal profile of the flux. These regimes can be accessed by tuning deposition conditions; however, their effect on film microstructure becomes marginal when coalescence sets in and erases morphological features obtained during nucleation. By preventing coalescence from being completed, these nucleation regimes can be used to control microstructure evolution and thus access a larger palette of film morphological features. Recently, we derived the quantitative criterion to stop coalescence during continuous metal vapor flux deposition on insulating surfaces—which typically yields 3-dimensional growth—by describing analytically the competition between island growth by atomic incorporation and the coalescence rate of islands [Lü et al., Appl. Phys. Lett. 105, 163107 (2014)]. Here, we develop the analytical framework for entering a coalescence-free growth regime for metal vapor deposition on insulating substrates using pulsed vapor fluxes, showing that there exist three distinct criteria for suppressing coalescence that correspond to the three nucleation regimes of pulsed vapor flux deposition. The theoretical framework developed herein is substantiated by kinetic Monte Carlo growth simulations. Our findings highlight the possibility of using atomistic nucleation theory for pulsed vapor deposition to control morphology of thin films beyond the point of island density saturation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Quantitative Comparison of Ternary Eutectic Phase-Field Simulations with Analytical 3D Jackson–Hunt Approaches

For the analytical description of the relationship between undercoolings, lamellar spacings and growth velocities during the directional solidification of ternary eutectics in 2D and 3D, different extensions based on the theory of Jackson and Hunt are reported in the literature. Besides analytical approaches, the phase-field method has been established to study the spatially complex microstructure evolution during the solidification of eutectic alloys. The understanding of the fundamental mechanisms controlling the morphology development in multiphase, multicomponent systems is of high interest. For this purpose, a comparison is made between the analytical extensions and three-dimensional phase-field simulations of directional solidification in an ideal ternary eutectic system. Based on the observed accordance in two-dimensional validation cases, the experimentally reported, inherently three-dimensional chain-like pattern is investigated in extensive simulation studies. The results are quantitatively compared with the analytical results reported in the literature, and with a newly derived approach which uses equal undercoolings. A good accordance of the undercooling–spacing characteristics between simulations and the analytical Jackson–Hunt apporaches are found. The results show that the applied phase-field model, which is based on the Grand potential approach, is able to describe the analytically predicted relationship between the undercooling and the lamellar arrangements during the directional solidification of a ternary eutectic system in 3D.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Characterization of the microstructure of yttrium hydride under proton irradiation

High moderation per unit volume solid moderator materials like yttrium hydride (YH x ) are necessary for compact nuclear microreactors. However, the phase stability and hydrogen transport processes of YH x under high-temperature irradiation are largely unknown. Proton irradiation was conducted on YH x at 300 °C and 580 °C to 0.2 dpa using 1 MeV or 2 MeV protons in a high-vacuum environment. The hydrogen concentration was determined before and after irradiation using elastic recoil detection analysis, and microstructural evolution was examined via post-irradiation scanning transmission electron microscopy and Raman spectroscopy. Dislocation loops and cavities were observed in all conditions; their distribution was correlated with the bombarding proton energy and ion irradiation temperature. This work revealed that hydrogen retention is proportional to the formation of traps for hydrogen gas atoms and identified pathways for hydrogen release. The relative contributions of bulk or fast diffusion paths, such as grain boundaries, delamination boundaries, and stacking faults are discussed; the primary mechanisms of hydrogen loss are likely based on diffusion, ruling out artefacts of the experimental design. In conclusion, the study suggests proton irradiation may be a strong surrogate to study hydrogen transport in hydride moderator materials under irradiation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

An Object-Oriented Finite Element Framework for Multiphysics Phase Field Simulations

The phase field approach is a powerful and popular method for modeling microstructure evolution. In this work, advanced numerical tools are used to create a phase field framework that facilitates rapid model development. This framework, called MARMOT, is based on Idaho National Laboratory's finite element Multiphysics Object-Oriented Simulation Environment. In MARMOT, the system of phase field partial differential equations (PDEs) are solved simultaneously with PDEs describing additional physics, such as solid mechanics and heat conduction, using the Jacobian-Free Newton Krylov Method. An object-oriented architecture is created by taking advantage of commonalities in phase fields models to facilitate development of new models with very little written code. In addition, MARMOT provides access to mesh and time step adaptivity, reducing the cost for performing simulations with large disparities in both spatial and temporal scales. In this work, phase separation simulations are used to show the numerical performance of MARMOT. Deformation-induced grain growth and void growth simulations are included to demonstrate the muliphysics capability.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Microstructure modeling of nuclear structural materials: Recent progress and future directions

Modeling and simulation of microstructures are essential to understand the complex responses and behaviors of nuclear materials in extreme environments. The needs to assess the extended life operation as well as the growing interest in accelerating nuclear materials development and qualification have stimulated the use of high-fidelity multiscale models aided by empirical and ab initio data. This paper reviews the role of various models across different length and time scales in investigating irradiation effects on microstructure evolution and degradation, in particular the embrittlement caused by radiation induced or enhanced formation of nanoscale chemical heterogeneities. The strength and limitations of these models, including classical rate theories, cluster dynamics, phase-field methods, and atomistic models informed by ab initio energies, are discussed with seminal examples. Challenges regarding the lack of thermo-kinetic data and theoretical treatments considering chemical complexities and magnetic excitations, as well as the stabilizing effect by excess point defects in nuclear structural materials are presented, along with potential solutions based on ab initio informed surrogate energy models and statistical sampling by Monte Carlo simulations. Further, the review then highlights the opportunities to leverage the advantages of different methods by establishing hybrid models by shared variables or coupled codes and applications. Finally, the review concludes with forward-looking remarks on how the use of physics-based models can aid the improvement of machine-learning models of property degradation and vice versa.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Thick sputtered tantalum coatings for high-temperature energy conversion applications

Thick sputtered tantalum (Ta) coatings on polished Inconel were investigated as a potential replacement for bulk refractory metal substrates used for high-temperature emitters and absorbers in thermophotovoltaic energy conversion applications. In these applications, high-temperature stability and high reflectance of the surface in the infrared wavelength range are critical in order to sustain operational temperatures and reduce losses due to waste heat. The reflectance of the coatings (8 and 30 μm) was characterized with a conformal protective hafnia layer as-deposited and after one hour anneals at 700, 900, and 1100 °C. To further understand the high-temperature performance of the coatings, the microstructural evolution was investigated as a function of annealing temperature. X-ray diffraction was used to analyze the texture and residual stress in the coatings at four reflections (220, 310, 222, and 321), as-deposited and after anneal. No significant changes in roughness, reflectance, or stress were observed. No delamination or cracking occurred, even after annealing the coatings at 1100 °C. Overall, the results of this study suggest that the thick Ta coatings are a promising alternative to bulk substrates and pave the way for a relatively low-cost and easily integrated platform for nanostructured devices in high-temperature energy conversion applications.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of Bi-Sb Addition and Solution Treatment on Microstructures and Mechanical Properties of Al-20 wt.% Mg{sub 2}Si Composites

In this study, the effects of compound modification with Bi and Sb and solution treatment on the microstructures evolution and the mechanical properties of Al-20 wt.% Mg{sub 2}Si composites were investigated. The specimens were observed by optical microscope, scanning electron microscope equipped with an energy-dispersive spectrometer and x-ray diffraction. The characterization results showed that 2.0 wt.% Sb and 0.2 wt.% Bi addition refined the primary Mg{sub 2}Si from 95 to 10 μm, accompanied by a change in morphology from coarse dendrites to dispersive fine polygons. After solution treatment at 540 °C for 15 h, the sharp polygonal primary Mg{sub 2}Si particles were blunted and the flake-like eutectic Mg{sub 2}Si phases were changed to small spherical particles, resulting in the increase in the Brinell hardness of the composites from HB 94.53 to 134.67. Mechanical tests revealed that both tensile strength and hardness of the composite were improved by compound modification with Bi and Sb, and the ultimate tensile strength (UTS) was increased from 216 MPa unmodified to 257 MPa with optimum modification of 2 wt.% Sb and 0.2 wt.% Bi. A propounded change in hardness from HB 94.53 to 130.67 was also investigated.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Influence of slag chemistry on the hydration of alkali-activated blast-furnace slag - Part II: Effect of Al{sub 2}O{sub 3}

The hydration and microstructural evolution of three alkali activated slags (AAS) with Al{sub 2}O{sub 3} contents between 7 and 17% wt.% have been investigated. The slags were hydrated in the presence of two different alkaline activators, NaOH and Na{sub 2}SiO{sub 3}{center_dot}5H{sub 2}O. The formation of C(-A)-S-H and hydrotalcite was observed in all samples by X-ray diffraction, thermal analysis and scanning electron microscopy. Higher Al{sub 2}O{sub 3} content of the slag decreased the Mg/Al ratio of hydrotalcite, increased the Al incorporation in the C(-A)-S-H and led to the formation of straetlingite. Increasing Al{sub 2}O{sub 3} content of the slag slowed down the early hydration and a lower compressive strength during the first days was observed. At 28 days and longer, no significant effects of slag Al{sub 2}O{sub 3} content on the degree of hydration, the volume of the hydrates, the coarse porosity or on the compressive strengths were observed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Bismuth borate zinc glass braze for bonding sapphire in air

Highlights: • Sapphire was brazed with a novel 50Bi{sub 2}O{sub 3}–40B{sub 2}O{sub 3}–10ZnO (mol.%) glass at temperatures of 600–700 °C for 20 min in air. • Bi{sub 4}B{sub 2}O{sub 9} and Bi{sub 24}B{sub 2}O{sub 39} were formed in the joints brazed at 600 and 625 °C, respectively. • ZnAl{sub 2}O{sub 4} particles were formed in the joints when the brazing temperature was 635 °C. • The maximum shear strength of 85 MPa was obtained for the joints brazed at 650 °C for 20 min. - Abstract: Reliable brazing of sapphire was successfully achieved by using a novel 50Bi{sub 2}O{sub 3}–40B{sub 2}O{sub 3}–10ZnO (mol%) glass braze and joining cycles that peak at temperatures of 600 − 700 °C for 20 min in air. The effect of the brazing temperature on microstructure evolution as well as mechanical properties of the sapphire/sapphire joints was investigated. The results showed that Bi{sub 4}B{sub 2}O{sub 9} and Bi{sub 24}B{sub 2}O{sub 39} were formed in the joints brazed at 600 and 625 °C, respectively. ZnAl{sub 2}O{sub 4} particles were formed in the joints when the brazing temperature was 635 °C due to a reaction between the glass and the sapphire substrate. With the brazing temperature increasing, ZnAl{sub 2}O{sub 4} particles exhibited steady growth, from ~ 160 nm at 635 °C to ~ 455 nm at 700 °C. Besides, ZnAl{sub 2}O{sub 4} particles began to aggregate when the temperature was 675 °C. The strength increased sharply when the brazing temperature increased to 635 °C, which was mainly attributed to the formation of ZnAl{sub 2}O{sub 4} particles in the joint domain. The maximum shear strength of 85 MPa was obtained for the joints brazed at 650 °C for 20 min. The joint shear strength decreased due to the aggregation of ZnAl{sub 2}O{sub 4} particles in the joint.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Vibro-acoustic Testing for Microstructure Characterization and Metrology: Technology Commercialization Fund—Fiscal Year 2017

There is a need in nuclear reactors to inspect irradiated materials and structures. A portable scanning infrastructure for a material characterization technique called vibro acoustography (VA) is being developed by the Idaho National laboratory for nuclear applications to characterize fuel, cladding materials, and structures. The proposed VA technology is based on ultrasound and acoustic waves; however, it provides information beyond what is available from the traditional ultrasound techniques and can expand the knowledge on nuclear material characterization and microstructure evolution. VA technique has several advantages over traditional characterization techniques. VA is a non-contact submersion technique that is inherently wireless transmission and reception (from the ultrasonic transmitter to the acoustic receiver). The transmission medium can be most liquids used for reactor cooling such as water and sodium. For nuclear in-pile applications, the Ultrasonic Transducer (UT) will need to have a line of sight location that is within lower radiation flux zones. Multiple UT sources can be frequency multiplexed to allow a single hydrophone receiver to monitor several locations. The reactor structure can also be an integral part of the transmission system acting as waveguides to deliver the acoustic signal to an acoustic receiver. Because of the long wavelength of the acoustic signal, the acoustic receiver does not have to be line of sight with respect to the component under test. The focusing and generation of the acoustic beat frequency from two ultrasonic waves allows for the potential to ultrasonically image complex shapes. These features will significantly reduce experiment complexity, installation times and cost while being safe and easy to use.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Near-isothermal furnace for in situ and real time X-ray radiography solidification experiments

In this paper, we present a newly developed near-isothermal X-ray transparent furnace for in situ imaging of solidification processes in thin metallic samples. We show that the furnace is ideally suited to study equiaxed microstructure evolution and grain interaction. To observe the growth dynamics of equiaxed dendritic structures, a minimal temperature gradient across the sample is required. A uniform thermal profile inside a circular sample is achieved by positioning the sample in the center of a cylindrical furnace body surrounded by a circular heater arrangement. Performance tests with the hypo-eutectic Al-15wt.%Cu and the near-eutectic Al-33wt.%Cu alloys validate the near-isothermal character of the sample environment. Controlled cooling rates of less than 0.5 K min{sup −1} up to 10 K min{sup −1} can be achieved in a temperature range of 720 K–1220 K. Integrated in our rotatable laboratory X-ray facility, X-RISE, the furnace provides a large field of view of 10.5 mm in diameter and a high spatial resolution of ∼4 μm. With the here presented furnace, equiaxed dendrite growth models can be rigorously tested against experiments on metal alloys by, e.g., enabling dendrite growth velocities to be determined as a function of undercooling or solutal fields in front of the growing dendrite to be measured.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Assessment of semi-empirical potentials for the U-Si system

Accident tolerant fuels (ATF) are being developed in response to the Fukushima Daiichi accident in Japan. One of the options being pursued is U-Si fuels, such as the U 3 Si 2 and U 3 Si 5 compounds, which benefit from high thermal conductivity (metallic) compared to the UO2 fuel (semi-conductor) used in current Light Water Reactors (LWRs). The U-Si fuels also have higher fissile density. In order to perform meaningful engineering scale nuclear fuel performance simulations, the material properties of the fuel, including the response to irradiation environments, must be known. Unfortunately, the data available for U-Si fuels are rather limited, in particular for the temperature range where LWRs would operate. The ATF HIP is using multi-scale modeling and simulations to address this knowledge gap. Even though Density Functional Theory (DFT) calculations can provide useful answers to a subset of problems, they are computationally too costly for many others, including properties governing microstructure evolution and irradiation effects. For the latter, semi-empirical potentials are typically used. Unfortunately, there is currently no potential for the U-Si system. In this brief report we present initial results from the development of a U-Si semi-empirical potential based on the Modified Embedded Atom Method (MEAM). The potential should reproduce relevant parts of the U-Si phase diagram as well as defect properties important in irradiation environments. This work also serves as an assessment of the general challenges associated with the U-Si system, which will be valuable for the efforts to develop a U-Si Tersoff potential undertaken by Idaho National Laboratory (also part of the ATF HIP). Going forward the main potential development activity will reside at INL and the work presented here is meant to provide input data and guidelines for that activity. The main focus of our work is on the U 3 Si 2 and U3Si 5 compounds, because they are the main nuclear fuel candidates. U 3 Si 5 is derived from USi 2 in the AlB 2 structure by creating 1/6 vacant sites on Si sublattice. The ordering of these vacancies will not be studied in any detail here.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2011

Influence of cooling rate on the development of multiple generations of {gamma}' precipitates in a commercial nickel base superalloy

The compositional and microstructural evolution of different generations of {gamma}' precipitates during the continuous cooling of a commercial nickel base superalloy, Rene88DT, has been characterized by three dimensional atom probe tomography coupled with energy-filtered transmission electron microscopy studies. After solutionizing in the single {gamma} phase field, continuous cooling at a very high rate results in a monomodal size distribution of {gamma}' precipitates with a high nucleation density and non-equilibrium compositions. In contrast, a relatively slower cooling rate ({approx} 24 deg. C/min) results in a multi-modal size distribution of {gamma}' precipitates with the larger first generation primary precipitates exhibiting close to equilibrium composition, along with the smaller scale secondary {gamma}' precipitates, exhibiting non-equilibrium composition (excess of Co and Cr, depleted in Al and Ti). The composition of the {gamma} matrix near these precipitates also exhibits similar trends with the composition being closer to equilibrium near the primary precipitates as compared to the secondary precipitates. - Highlights: {yields} Effect of cooling rate on the precipitation of {gamma}' particles in commercial nickel base superalloy. {yields} Couples EFTEM and 3DAP studies to determine the composition and morphology of {gamma}' precipitates. {yields} Determination of near and far field compositional variations within the gamma matrix leading to subsequent precipitation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Research on Resistance Heating Behavior of High-Strength Steel and its Hot-Stamping Forming

A hot-stamping process of high-strength steel sheet using resistance heating (RH) was developed to improve springback and formability. The RH curves of S355J2W steel and the microstructure and mechanical properties after RH were explored to control and guide the RH time and the selected current density for the subsequent RH hot-stamping forming. Moreover, scanning electron microscopy observations revealed the microstructure evolution in RH and the improvement of mechanical properties at a current density of 0-6.67 A mm{sup −2}, showing the advantage of the application of RH to these materials. The results showed that steel strength can be increased by up to 3.2% and the elongation can be improved by up to 33% after RH. In addition, the forming height increased and the forming angle is closer to the desired angle with the increased current density in cap-shaped RH hot-stamping forming experiment, which means that the forming accuracy is improved. A comparison of the forming accuracy of cap-shaped parts formed by RH under different current densities with those heated to the same temperature by furnace heating (FH) shows that there is no obvious difference between them. The heating time of RH is much shorter than that of the FH, and the surface quality of the parts formed by RH hot-stamping is better than that of the parts formed by FH hot-stamping. These results demonstrate that the RH method has the advantages of efficiency, safety, energy saving and the improvement of surface quality as well as a clear understanding of the benefits of RH hot-stamping forming for materials properties and forming accuracy; this work also develops and applies fundamental theory to practical engineering of bogie cover plate manufacturing.

36 MATERIALS SCIENCE↗