Large-area Electron Beam Irradiation Research Articles

Application of large-area electron beam irradiation to micro-edge filleting

Efficient micro-edge filleting with curvature radius from 10 to 100 μm for industrial products is required, since a demand for industrial components with precise and complex shape has been increasing recently. In large-area electron beam (EB) irradiation method, wide area of metal surface can be melted instantly and uniformly. Therefore, highly efficient surface finishing of metal can be performed. In addition, edge of convex part rounds since material removal and/or melting of the edge is preferentially done there due to difficulty of heat diffusion at the edge and concentration of EB. In this study, possibility of micro-edge filleting for workpiece with sharp edge by large-area EB irradiation was investigated. Experimental results show that micro-edge filleting without remarkable shape change of side surface near the edge can be performed under appropriate EB conditions. The curvature radius of edge can be controlled from sharp edge to rounded edge, and ideal curvature radius is obtained. Furthermore, thermo-fluid analysis with considering the concentration of EB to the edge was performed to clarify flow of molten metal and mechanism of edge shape change in the EB irradiation. Edge shape change can be simulated by the thermo-fluid analysis. It was made clear that surface tension is main driving force for edge shape change in large-area EB irradiation.

Surface smoothing of additively manufactured Ti-6Al-4V alloy by combination of grit blasting and large-area electron beam irradiation

AbstractAdditively manufactured (AMed) titanium products are typically produced by electron beam melting (EBM), since oxidation of titanium alloy surface can be suppressed in vacuum environment. The surface roughness of AMed titanium products becomes more than 200 µm Rz, and the very rough surface would lead to reduction in fatigue strength. Therefore, a post surface finishing process is required. Abrasive blasting is one of the common surface smoothing processes of AMed metal products. Large surface roughness can be decreased, and compressive residual stress can be introduced to the surface. However, there is a limitation to reduction of surface roughness to several µm Rz. On the other hand, it was recently found that AMed metal surface produced by powder bed fusion with laser beam could be smoothed by large-area electron beam (LEB) irradiation. However, it is difficult to smooth surface with large initial surface roughness, and a tensile residual stress may be generated on the surface. In this study, surface smoothing and change in residual stress of AMed titanium alloy (Ti-6Al-4 V) were proposed by combination of grit blasting and LEB irradiation. Surface roughness of AMed Ti-6Al-4 V alloy significantly decreases from 265 to about 2.0 µm Rz by combination of grit blasting and LEB irradiation. Reduction rate of surface roughness by LEB irradiation linearly increases with decreasing mean width of blasted surface. Influence of the mean width on smoothing effect by LEB irradiation can be explained by thermo-fluid analysis. Moreover, tensile residual stress caused by LEB irradiation can be reduced when LEB is irradiated to blasted surface.

Mo-rich layer formation on maraging steel and surface modification by large-area electron beam irradiation

Maraging steels have been typically applied to precise metal mold and products in aerospace industry, since they have excellent properties such as high strength and toughness. However, the maraging steels are inferior to other steels in some surface functions such as corrosion resistance. Hence, it is necessary to improve surface functions of maraging steel. On the other hand, large-area electron beam (EB) of 60 mm in diameter can instantly melt metal surface. Our previous study clarified that the surface roughness of alloy tool steels such as SKD11 in JIS specification could be reduced efficiently by the EB irradiation. Furthermore, the surface characteristics were also improved by formation of thin re-solidified layer with a fine microstructure. In this study, formation of Mo-rich layer in re-solidified layer on maraging steel surface by large-area EB irradiation was investigated. Mechanism for formation of Mo-rich layer was discussed by unsteady heat conduction analysis. In addition, surface finishing and improvement of surface characteristics of maraging steels by the EB irradiation were also examined. The experimental results show that surface roughness decreases to approximately 1.0µm R z in a few minutes under low energy densities conditions, and Mo-rich layer with thickness of a few micrometers is self-formed in re-solidified layer of EB irradiated surface. Moreover, water repellency, corrosion resistance and wear performance are improved by the formation of Mo-rich layer in re-solidified layer. Therefore, maraging steel surface can be finished and modified simultaneously by large-area EB irradiation method.

Improvement in Corrosion Resistance of Al-Cu Alloy by Large-area Electron Beam Irradiation

Improvement in Corrosion Resistance of Al-Cu Alloy by Large-area Electron Beam Irradiation

Study on Smoothing of Hole Wall Surface by Electron Beam Polishing under Control of Magnetic Field

A surface finishing method by large-area electron beam (EB) irradiation called EB polishing has been developed recently. Highly efficient surface smoothing of mold steels with planar shape can be performed by the EB polishing. However, it is difficult to smooth wall and bottom surfaces in hole shape by the EB polishing, since the EB tends to concentrate on entrance edge or upper inside wall of hole, and the energy density of EB on the wall and bottom surface of hole may decrease. Our previous study showed that the bottom surface could be smoothed by EB polishing under control of magnetic field around the workpiece. It is highly expected that EB can be also guided to the whole area of hole wall surface under appropriate control of magnetic field there.In this study, smoothing of hole wall surface by EB polishing under control of magnetic field around the workpiece was proposed. As a basic study for smoothing of hole wall surface, L-shaped workpiece was prepared by combining two stainless steel plates, and magnet was set under the workpiece. The electromagnetic field analysis results suggested that EB could be guided to the whole area of side surface by setting magnet under appropriate setting position, since magnetic force lines are uniformly distributed on whole area of side surface. In addition, magnetic flux destiny on the side surface more increases by setting a yoke made of steel on the magnet. The experimental results show that smoothed area with the surface roughness of less than 1.5μmRz can be obtained on the whole area of side surface. Therefore, the whole area of side surface can be uniformly smoothed by guiding the EB to the side surface under appropriate control of magnetic field.

Synergy Effect of Abrasive Blasting and Large-area EB Irradiation on Surface Finishing of AMed Titanium Alloy

Among a broad spectrum of AM technologies, electron beam melting (EBM) is widely applied in AM process for producing titanium alloy parts. In general, AMed metal products have very rough surface of more than 200µmRz, since relatively large beads are arranged on their surface by scanning electron beam. Moreover, surface irregularities such as spatter and cavity are also generated on the surface. Rough surface and surface irregularities would lead to reduction in surface strength and poor appearance. Therefore, post surface finishing processes are required to smooth the surface of AMed metal products. One of the common surface smoothing processes is abrasive blasting. Large surface roughness can be decreased by abrasive blasting, and compressive residual stress can be introduced to the surface. However, there is a limitation to reduction of surface roughness. On the other hand, in large-area electron beam (large-area EB, LEB) irradiation method developed recently, mold steel surface can be finished by melting it in a few minutes. However, it is not easy to smooth surface with large initial surface roughness, and a tensile residual stress may be generated on the surface.In this paper, surface smoothing of AMed titanium alloy by combination of abrasive blasting and large-area EB irradiation was proposed. At first, the AMed titanium alloy surface was blasted to reduce the initial large surface roughness to some extent and change the surface topography. Then, large-area EB was irradiated to the blasted surface. It is made clear that surface roughness significantly decreases when large-area EB is irradiated to the blasted surface with small mean width. Moreover, tensile residual stress generated in large-area EB irradiation can be reduced by abrasive blasting. Therefore, combination of abrasive blasting and large-area EB irradiation is effective for efficient reduction of large surface roughness of AMed titanium alloy.

Surface smoothing and repairing of additively manufactured metal products by large-area electron beam irradiation

In general, surface of additively manufactured (AMed) metal products has large roughness due to arrangement of bead shapes, and surface irregularities such as spatter and cavity. Furthermore, surface elemental composition of AMed products may be changed from that of metal powder. In this study, efficient surface smoothing and repairing of AMed metal products by large-area electron beam irradiation were experimentally investigated. Experimental results show that spatter and cavity can be completely removed and surface roughness significantly reduces. Elemental composition of AMed surface can be also changed to that of original metal powder due to the removal of oxidized surface.

Alumina film sputter deposition on mold steel by large-area electron beam irradiation

During the large-area EB irradiation, plasma generation is confirmed by collision of electrons with vaporized workpiece materials above the substrate surface due to its high energy density. This phenomenon would cause the sputtering of target material when it is set near the substrate surface. Thus, there is a possibility for coating a target material on the substrate surface by the large-area EB irradiation. The simultaneous sputter deposition of target material with melting and resolidification of workpiece surface by the large-area EB would improve the adhesion strength between the coated film and the workpiece surface. In this study, a new ceramics coating method with sputtering of target tube by large-area EB irradiation is proposed. Ceramic target tube made of alumina is put on the substrate surface of mold steel, and the large-area EB is irradiated to the substrate surface. The alumina film with thickness of several micro meter can be formed on the substrate surface. Moreover, the film formation mechanism is discussed by changing material property of a jig supporting the alumina target tube. The spectrum of plasma generated on the substrate surface during the EB irradiation is also analyzed. It is made clear that the magnetic property of jig greatly influences on the film formation. Furthermore, main components of plasma generated on workpiece surface during the process are components of steel in the case of low number of EB irradiation, while much more alumina component as a film is detected in the case of high number of EB irradiation.

Highly Efficient Surface Repairing of AMed Metal Parts by Large-area EB Irradiation

In additive manufacturing (AM) processes, three dimensional (3D) objects can be produced by using 3D modelling data. Nowadays, a laser powder bed fusion (LPBF) is becoming popular in AM processes for producing metal parts in the industry field. In general, surface irregularities such as spatter and cavity are generated on the surface. These surface irregularities would lead to increase in surface roughness and reduction in surface fatigue strength. Therefore, surface finishing method is required to repair these surface irregularities. Shot blasting, milling and grinding are typically used for the surface finishing of AMed metal parts. However, these methods have some problems such as remaining of shot grain, tool wear and long processing time.On the other hand, in a large-area electron beam (EB) irradiation method developed recently, high energy density of EB can be obtained without focusing the beam. Therefore, the large-area EB with a diameter of about 60 mm can be used for melting and evaporating material surface instantly, and highly efficient surface finishing of metals such as mold steels and biomaterials was possible. It is expected that the spatter and cavity on the AMed metal parts can be removed in short time by the large-area EB irradiation.In this study, the possibility of surface repairing and surface smoothing for AMed metal parts by large-area EB irradiation is investigated. Then, the mechanism of surface repairing and surface smoothing is also discussed by observation of surface and cross-sectional microstructure. Experimental results show that surface irregularities such as spatter and cavity can be completely repaired in a few minutes by the EB irradiation. Furthermore, bead shape on AMed metal surface is removed with high number of EB irradiation, and surface roughness is significantly decreases. Therefore, surface repairing and surface smoothing for AMed metal parts can be efficiently done by large-area EB irradiation.

Clarification of Temperature Distribution for Metals with Different Thermal Conductivity in Large-area Electron Beam Irradiation

High energy density of electron beam (EB) with diameter of about 60 mm is obtained in a large-area EB irradiation method. This method can be used for melting and evaporating material surface instantly, and highly efficient surface finishing of metals such as mold steels and biomaterials is possible. Furthermore, surface functions such as corrosion resistance, water repellency and wear resistance can be improved since a thin modified layer with fine microstructure is formed on the EB irradiated surface. It is expected that thick modified layer is effective to maintain their surface functions for long-term. However, the material surface is slightly removed in formation of modified layer. Therefore, control and prediction of removal and modified layer thickness are important in order to obtain appropriate modified layer thickness and to keep the shape accuracy for metals with different thermal properties. In order to predict the removal and modified layer thickness, it is necessary to clarify the temperature distribution in depth direction and its time variation in large-area EB irradiation. In this study, changes of removal and modified layer thickness on metal workpiece with different thermal conductivity are investigated by calculation of temperature distribution in large-area EB irradiation. It is made clear that the modified layer thickness of workpiece with low thermal conductivity is larger than that with high one, while the removal layer thickness is almost the same regardless of thermal conductivity. Furthermore, analytical removal and modified layer thickness obtained by our unsteady heat conduction analysis agree well with the experimental ones. Therefore, our unsteady heat conduction analysis model has high accuracy, and it is possible to predict variations of removal and modified layer thickness on workpiece with different thermal conductivity.

Large-Area Electron Beam Melting: Frequency Analysis and Critical Frequency Prediction

During large-area electron beam irradiation, high energy flux pulses of electrons melt a thin layer of material. The objective of this work is to analyze the spatial frequencies of a turned, S7 tool steel surface before and after electron beam melting. It was observed that high frequency features are significantly reduced following melting, but lower frequency features were created and increased the unfiltered areal average roughness. Previous work on laser remelting-based polishing derived a critical frequency that defines the frequency above which higher frequency features are dampened. As the critical frequency depends on the melt duration that the surface experiences, a one-dimensional, transient temperature prediction model was created for this work to estimate the melt time for a single electron beam pulse. This model allowed for the calculation of a critical frequency that showed good ability to predict the frequencies that are dampened.

Study on Improvement of Wear Resistance for Zirconia by Large-area Electron Beam Irradiation

Zirconia has been widely applied for cutting tools and biomaterials, since it has superior mechanical properties such as high fracture toughness, bending strength and biocompatibility in ceramics. In order to maintain its surface functions for long-term, further improvement of wear resistance for zirconia has been required. In this study, improvement of wear resistance for zirconia is proposed by large-area electron beam (EB) irradiation. Experimental results show that mean width in roughness curve of zirconia surface increases with increasing the energy density of EB, although the maximum height in surface roughness is almost same as the ground surface. In friction and wear test, coefficient of friction reduces with increasing the energy deinsity of EB since ball material smoothly slides on the EB irradiated zirconia surface. Furthermore, it is made clear that wear resistance of zirconia significantly improves by the EB irradiation under appropriate energy density.

Fundamental Study on Filleting by Using Large-area Electron Beam Irradiation Method

Fundamental Study on Filleting by Using Large-area Electron Beam Irradiation Method

Human Skeletal Stem Cell Response to Multiscale Topography Induced by Large Area Electron Beam Irradiation Surface Treatment.

The healthcare socio-economic environment is irreversibly changing as a consequence of an increasing aging population, consequent functional impairment, and patient quality of life expectations. The increasing complexity of ensuing clinical scenarios compels a critical search for novel musculoskeletal regenerative and replacement strategies. While joint arthroplasty is a highly effective treatment for arthritis and osteoporosis, further innovation and refinement of uncemented implants are essential in order to improve implant integration and reduce implant revision rate. This is critical given financial restraints and the drive to improve cost-effectiveness and quality of life outcomes. Multi-scale modulation of implant surfaces, offers an innovative approach to enhancement in implant performance. In the current study, we have examined the potential of large area electron beam melting to alter the surface nanotopography in titanium alloy (Ti6Al4V). We evaluated the in vitro osteogenic response of human skeletal stem cells to the resultant nanotopography, providing evidence of the relationship between the biological response, particularly Collagen type I and Osteocalcin gene activation, and surface nanoroughness. The current studies demonstrate osteogenic gene induction and morphological cell changes to be significantly enhanced on a topography Ra of ~40 nm with clinical implications therein for implant surface treatment and generation.

Influence of Material Property on Thickness of Modified Layer Generated by Large-area Electron Beam

In large-area electron beam (EB) irradiation method developed recently, high energy density of EB can be obtained without focusing the beam. Therefore, the wide area of material surface can be melted instantly, and high efficient surface finishing is possible. Moreover, surface functions such as corrosion resistance and water repellency of the metal molds were improved by the large-area EB irradiation, since thin resolidified layer was formed on the metal surface. It is expected that thick modified layer is effective to maintain their surface functions for long-term. Therefore, control and prediction of the modified layer thickness are important in order to obtain appropriate modified layer thickness on metals with different material properties. In this study, variations of modified layer thickness on metals with different material property are experimentally investigated. Furthermore, electron behavior during large-area EB irradiation is simulated by using an electron track analysis, and prediction of the modified layer thickness is tried with temperature distributions by using an unsteady heat conduction analysis. Experimental results show that the modified layer thickness increases with increasing energy density. The thickness with high relative permeability is larger than that with low one. Analytical results of the modified layer thickness in unsteady heat conduction analysis show quantitative agreement with experimental ones. Furthermore, the modified layer thickness on the metals with different thermal property and density is also discussed. Then, the modified layer thickness of metals with different material property can be predicted by using our unsteady heat conduction analysis model.

Magnetic fixtures for enhancement of smoothing effect by electron beam melting

In large-area electron beam (EB) irradiation method developed recently, high energy density EB can be obtained without focusing the beam. Therefore, large-area EB of 60mm in diameter can be used for instant melting and evaporation of the wide area material surface, and high efficient surface finishing is possible. However, if the workpiece has a hole shape, the EB concentrates in the entrance edge or inside wall of the hole. Thus, it is difficult to smooth the hole bottom surface. Previous study showed that the surface smoothing and micro-deburring effects for non-magnetic workpiece could be improved by setting a magnetic block under the workpiece, since the electrons tend to concentrate the magnetic block along magnetic lines. In this study, smoothing of hole bottom surface was experimentally investigated by setting a magnetic block under a workpiece in large-area EB irradiation. Expansion of smoothing area of the bottom surface was also tried by setting a through hole at the center of the magnetic block. It was clarified that wide area of hole bottom surface could be smoothed by large- area EB irradiation by setting the magnetic block under workpiece. The surface roughness decreased to less than 3.0μmRz at the area of hole bottom surface. When the hole diameter was 20mm and hole depth was less than 40mm, smoothing area of 10mm in diameter was obtained by using the magnetic block. Moreover, the smoothing area was sufficiently expanded by setting a through hole with an appropriate diameter in magnetic block.

Study on Clarification of Large-Area EB Irradiation Phenomenon by Electron Track Analysis

In large-area electron beam (EB) irradiation method, uniformly high energy density can be obtained without focusing the beam. Large-area EB can be used for melting and evaporating metal surface instantly. It was clarified that high efficient surface finishing of metal mold steels, ceramics and cemented carbides was possible by the large-area EB irradiation. Furthermore, the tip of convex shape was often rounded after large-area EB irradiation with remarkable material removal at the tip. This phenomenon is probably caused due to the heat accumulation and electrons concentration at the tip. However, electrons behavior near the workpiece surface during large-area EB irradiation has not yet been clarified. In this study, electron track analysis was conducted in order to clarify electrons behavior during large-area EB irradiation. At first, analytical model of the large-area EB irradiation apparatus was built. Then, the EB diameter on the workpiece surface was experimentally measured with different energy density in order to evaluate the accuracy of our analytical model. The calculated results of EB diameter were in good agreement with the experimental ones. In addition, the electrons concentration phenomenon at the tip of convex shape was clarified by calculating energy density distribution on the surface obtained with electron track analysis. The analytical results indicated that the energy density increased from edge to tip of convex shape, while the energy density was constant in the case of planar shape. Experimented results also showed that removal thickness increases with high relative permeability. These results were similar tendency to the energy density distribution. Therefore, electrons concentration on the tip could be simulated by the electron track analysis.

Expansion of Smoothed Area on Hole Bottom Surface by Setting Magnetic Block in Large-area Electron Beam Irradiation

Expansion of Smoothed Area on Hole Bottom Surface by Setting Magnetic Block in Large-area Electron Beam Irradiation

Prediction of rounding phenomenon at corner tips in large-area electron beam irradiation

In large-area electron beam (EB) irradiation method, corner tip of workpiece is generally rounded since removal of material at the tip is done preferentially. Investigation of the shape change is necessary to clarify rounding phenomenon with irradiation of EB. In this study, the shape changes of corner tips were experimentally investigated by Scanning Electron Microscope (SEM) observation of the cross sections. Then, electron track analysis in the EB irradiation was conducted to clarify an electron concentration at the tip. Unsteady heat conduction analysis at the tip was also done with considering the EB concentration at the tip and an electron penetration effect into the surface. The shape changes were estimated by simulation of temperature distribution at the tips. Experimental results show that the curvature radius increases with shot number of EB. The estimated shape changes show quantitatively good agreement with the experimental ones. These results indicate that the rounding phenomenon at the tips by large-area EB irradiation can be predicted by our electron track and unsteady heat conduction analysis model.

電子軌道解析による大面積電子ビーム照射現象の基礎的研究

In large-area electron beam (EB) irradiation method, uniformly high energy EB can be obtained without focusing the beam. Large-area EB can be used for melting and evaporating metal surface instantly. Furthermore, the tip of convex shape is often rounded after large-area EB irradiation with remarkable material removal at the tip. This phenomenon is probably caused due to the electrons concentration at the tip. However, electrons behavior near the workpiece surface during large-area EB irradiation has not yet been clarified. In this study, electron track analysis was conducted in order to clarify electrons behavior during large-area EB irradiation. At first, analytical model of the large-area EB irradiation apparatus was built. Then, the EB diameter on the workpiece surface was experimentally measured with different energy density in order to evaluate the accuracy of our analytical model.