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Wear properties of aluminum alloys fabricated by laser powder bed fusion 査読有り国際共著国際誌

Gong S., Takata N., Kobashi M., Shin S.E.

Tribology International 187 巻 2023年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Tribology International

The production of an aluminum alloy using the laser powder bed fusion (LPBF) process results in a unique microstructure that differs from that of the same alloy when cast; this microstructure is advantageous for wear resistance. This study compared the wear resistance of Al-12Si and Al-2.5Fe (mass%) binary alloys produced by LPBF process with their cast equivalents, to analyze their suitability for lightweight wear-resistant parts. The wear resistance of the LPBF-produced alloys was significantly improved owing to the increase in hardness induced by the rapid cooling rate of the LPBF process and the dense dispersion of the fine secondary phase. Thus, Al alloys fabricated using LPBF can provide excellent wear resistance and possess the potential for application as industrial materials.

DOI： 10.1016/j.triboint.2023.108769

B2-structured Fe<inf>3</inf>Al alloy manufactured by laser powder bed fusion: Processing, microstructure and mechanical performance 査読有り国際共著国際誌

Vilardell A.M., Pelcastre L., Nikas D., Krakhmalev P., Kato M., Takata N., Kobashi M.

Intermetallics 156 巻 2023年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Intermetallics

Prealloyed Fe3Al was successfully manufactured by laser powder bed fusion. The best set of process parameters led to parts with a relative density of 99.5 %, a surface roughness, Sa, of 31.5 ± 5.6 μm and a hardness of 319 ± 14 HV0.1. Its microstructure as well as its mechanical properties at room and high temperatures were analyzed. The results of the chemical composition showed minor variations in aluminum content oscillating between 21 and 28 at.% along the melt pool. Additionally, elongated grains were observed to grow parallel to the building direction, as well as the development of a weak {001} texture along the building direction. The mechanical properties were influenced by the temperature. Compression tests showed a loss in strength with the increase in temperature, from a yield strength of 621 ± 40 MPa at room temperature to 89 ± 20 MPa at 650 °C. Reciprocating sliding wear tests showed that fragmentation of the intermetallic at room temperature occurs, whereas plastic deformation dominated at higher temperatures. For all temperatures, tribochemical wear was also present due to the oxidation of wear debris.

DOI： 10.1016/j.intermet.2023.107849

Effect of low-temperature annealing on electrical resistivity and mechanical properties of laser-powder bed fused AlSi10Mg alloy 査読有り国際誌

Miyajima Y., Nakamura Y., Konishi Y., Ishikawa K., Wang W., Takata N.

Materials Science and Engineering: A 871 巻 2023年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials Science and Engineering: A

The AlSi10Mg sample was additive-manufactured using laser powder bed fusion (L-PBF), and subsequent low-temperature annealing (LTA) at 413K or 473 K was applied. Vickers hardness tests show the peak at around 160 HV by 473 K annealing and around 145 HV by 413 K annealing. The flow stress of tensile and compression deformations are also affected by LTA, and peak aging condition gives the highest 0.2% proof stress. 0.2% proof stress obtained by tensile tests is around 270 MPa, whereas that obtained by compression tests is between 326 MPa and 386 MPa. Electrical resistivity at 293 K changes from approximately 80 nΩm down to around 60 nΩm, whereas that at 77 K changes from around 40 nΩm down to around 20 nΩm. The estimated concentration of solute Si in the as-built specimen is between 2.5 mass% and 2.9 mass%, corresponding to the previous results using energy-dispersive X-ray spectroscopy. The lattice constant obtained from XRD increased from 0.4043 nm up to 0.4048 nm by LTA. Both electrical resistivity and XRD measurement indicate a decrease in the concentration of solute atoms. Microstructure observations revealed numerous nano-sized precipitates of Si phase with a plate-like or granular morphologies in α-Al grains due to LTA.

DOI： 10.1016/j.msea.2023.144876

Design of Al–Fe–Mn alloy for both high-temperature strength and sufficient processability of laser powder bed fusion 査読有り国際誌

Wang W., Takata N., Suzuki A., Kobashi M., Kato M.

Additive Manufacturing 68 巻 2023年4月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Additive Manufacturing

This paper presents a novel design concept for Al alloys with both sufficient laser powder bed fusion (L-PBF) processability and high-temperature mechanical performance using an Al–Fe–Mn ternary alloy with a refined α-Al/Al6M (M = Fe, Mn) two-phase microstructure. The near-eutectic (liquid → α-Al(fcc) + Al6M) composition of Al–2.5Fe–2Mn (mass%) was designed to avoid the formation of coarse primary intermetallics (having a detrimental effect on the PBF processability for densification) based on non-equilibrium liquidus projection thermodynamic calculations. The designed Al–2.5Fe–2Mn alloy powder exhibited sufficient L-PBF processability, and fully dense centimeter-sized samples (relative densities of above 99%) were successfully prepared. The L-PBF Al–2.5Fe–2Mn alloy samples exhibited a significantly refined solidification microstructure consisting of Al6M and α-Al phases in the melt-pool regions. Fe and Mn alloying elements contributed to the formation of nanoscale Al6M-phase particles and a high solid solution concentration in the α-Al matrix. The strength of the L-PBF Al–2.5Fe–2Mn alloy was slightly reduced at higher temperatures, but remained above 240 MPa at an elevated temperature of 300 °C. This superior high-temperature mechanical performance was attributed to the high thermal stability of the refined α-Al/Al6M two-phase microstructure and the formation of nanosized Al6M-phase precipitates.

DOI： 10.1016/j.addma.2023.103524

Microstructural origin of anisotropic tensile ductility of Al-Si alloy manufactured by laser powder bed fusion 査読有り国際誌

Otani Y., Takata N., Suzuki A., Kobashi M., Kato M.

Scripta Materialia 226 巻 2023年3月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Scripta Materialia

Aluminum alloys fabricated by laser powder bed fusion (L-PBF) exhibit anisotropic tensile ductility. To identify microstructural origins in melt-pool (MP) structures (formed by the L-PBF process) contributing to the anisotropic ductility, the local strain distribution inside the MP structure in deformation was quantified by a combination of digital image correlation (DIC) strain analysis and in-situ SEM observations of tensile tests. It was found that higher strain was localized in locally coarsened microstructures (softer regions) along melt-pool boundaries (MPBs). The strain localization played a significant role in crack initiation (and propagation) around MPBs, contributing to fracture. The strain localization at MPBs changed depending on the geometrical relation of the MPBs with the loading direction (LD), which was controlled by the LD with respect to the building direction of L-PBF samples. The three-dimensional MPB distribution related to the LD would be responsible for the anisotropic ductility.

DOI： 10.1016/j.scriptamat.2022.115259

Austenite Reversion Behavior of Maraging Steel Additive-manufactured by Laser Powder Bed Fusion 査読有り

Takata N., Ito Y., Nishida R., Suzuki A., Kobashi M., Kato M.

Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan 109 巻 ( 3 ) 頁： 201 - 214 2023年

担当区分：筆頭著者,　責任著者記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan

This study was set to fundamentally investigate the characteristics of austenite reversion occurring in maraging steels additive-manufactured by laser powder bed fusion (L-PBF). The maraging steel samples manufactured under different L-PBF process conditions (laser power P and scan speed v) were subjected to heat treatments at 550°C for various durations, compared with the results of the austenitized and water-quenched sample with fully martensite structure. The L-PBF manufactured samples exhibited the martensite structure (including localized austenite (γ) phases) containing submicron-sized cellular structures. Enriched alloy elements were detected along the cell boundaries, whereas such cellar structure was not found in the water-quenched sample. The localized alloy elements can be rationalized by the continuous variations in the γ-phase composition in solidification during the L-PBF process. The precipitation of nanoscale intermetallic phases and the following austenitic reversion occurred in all of the experimental samples. The L-PBF manufactured samples exhibited faster kinetics of the precipitation and austenite reversion than the water-quenched sample at elevated temperatures. The kinetics changed depending on the L-PBF process condition. The enriched Ni element (for stabilizing γ phase) localized at cell boundaries would play a role in the nucleation site for the formation of γ phase at 550°C, resulting in the enhanced austenite reversion in the L-PBF manufactured samples. The variation in the reaction kinetics depending on the L-PBF condition would be due to the varied thermal profiles of the manufactured samples by consecutive scanning laser irradiation operated under different P and v values.

DOI： 10.2355/tetsutohagane.TETSU-2022-066

Effects of Mn and Cu Additions on Solidification Microstructure and High-Temperature Strength of Cast AlFe Binary Alloy 査読有り国際誌

Okano N., Takata N., Suzuki A., Kobashi M.

Materials Transactions 64 巻 ( 2 ) 頁： 492 - 499 2023年

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials Transactions

In order to investigate the effects of Mn and Cu additions on solidification microstructure and high-temperature strength of cast AlFe alloys, we have fabricated various AlFe-based alloys with compositions of Al1%Fe, Al1%Fe1%Mn, Al1%Fe1%Cu, and Al1%Fe1%Cu1%Mn (mol%) solidified at different cooling rates (0.3 K·s11 and 145 K·s11). In the Al1%Fe binary alloy, the coarsened ª-Al13Fe4 phase with a needle-shaped morphology was often observed in the furnace-cooled sample (0.3 K·s11), whereas the cast sample (145 K·s11) exhibited several elongated ¡ phases surrounded by fine ¡/Al6Fe eutectic microstructure. Such a solidification microstructure was observed in the cast Al1%Fe1%Cu alloy, whereas the Al23CuFe4 phase was locally formed in the finally solidified zone in the furnace-cooled sample. In the Al1%Fe1%Mn alloy, the Al6(Fe, Mn) phase was formed regardless of the cooling rate. Finer ¡/Al6(Fe, Mn) two-phase eutectic microstructure was almost entirely occupied in the cast sample. The fine eutectic microstructure was observed in the cast Al1%Fe1%Cu1%Mn alloy as well. Compression tests for cast alloy specimens revealed that the Al1%Fe1%Cu1%Mn alloy exhibited the highest strength level among the studied alloy specimens, indicating the combined addition of Mn and Cu elements could be effective in improving the high-temperature strength of the cast AlFe alloys.

DOI： 10.2320/matertrans.MT-LA2022010

Introducing Hatch Spacing into Deposited Energy Density toward Efficient Optimization of Laser Powder Bed Fusion Process Parameters 査読有り

Kunieda M., Suzuki A., Takata N., Kato M., Kobashi M.

Materials Transactions 64 巻 ( 6 ) 頁： 1099 - 1106 2023年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials Transactions

The optimization of processing parameters is indispensable for the laser powder bed fusion (L-PBF) process. The deposited energy density (DED) is one of the process indexes for the L-PBF process and has a simplified formula of P v 0.5, where P is the laser power, and v is the scan speed. This parameter describes the change in the relative density and the melt pool morphology with laser power and scan speed well, whereas it does not include the effect of other processing parameters, e.g., hatch spacing (S). In the present study, an attempt was made to incorporate the effect of S into DED. Al12Si (mass%) alloy cube samples were fabricated by L-PBF under various P, v, and S, for evaluating the relative density and the melt pool morphology. The melt pool depth and width of L-PBF-manufactured Al12Si alloy increased linearly with P v 0.5 and did not exhibit a clear correlation with S. Based on the experimental observation, the effect of hatch spacing on DED was estimated to be S 0.5, and a new index of P v 0.5 S 0.5 was proposed. This index described the change in the relative density of the L-PBF-manufactured Al12Si alloy with laser conditions (P, v, and S) well when the thermal conduction mode melting was dominant. This study also indicated the limitation of the applicability of P v 0.5 S 0.5 under the keyhole or transition mode melting.

DOI： 10.2320/matertrans.MT-ME2022002

Improved high-temperature creep properties of heat-resistant Al-Mg-Zn-Cu-Ni quinary alloy by adding a trace amount of Ti 査読有り Open Access

Kondo M., Suzuki T., Li R., Takata N.

Keikinzoku/Journal of Japan Institute of Light Metals 73 巻 ( 6 ) 頁： 260 - 265 2023年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Keikinzoku/Journal of Japan Institute of Light Metals

The present study investigated the effect of trace titanium (Ti) addition on high-temperature creep properties of a heat-resistant quinary aluminum (Al) alloy, with a composition of Al-5Mg-3.5Zn-2Cu-2Ni (mol%). Both the quinary alloy and Ti-added alloy were solution-treated at 480°C and then aged at 200°C for 10 hours. The creep tests were conducted at 200°C under 105 MPa. The addition of trace Ti element reduced the minimum creep rate and delayed the onset of the tertiary creep stage (creep acceleration), resulting in the extended creep rupture life of the Al-5Mg-3.5Zn-2Cu-2Ni quinary alloy. The creep rupture life of the Ti-added alloy was higher than that of the A7075 alloy but lower than that of the A2618 alloy, whereas the initial creep rate (up to 0.2% in strain) of the Ti-added quinary alloy was lower than that of the A2618 alloy. The superior creep properties were presumably due to the enhanced stability of the fine precipitation morphologies of the T-Al6Mg11Zn11 phase by solute Ti inside the α-Al matrix.

DOI： 10.2464/jilm.73.260

Influence of Dislocation Substructure on Size-Dependent Strength of High-Purity Aluminum Single-Crystal Micropillars 査読有り

Takata N., Uesugi S., Zhu T., Takeyasu S., Suzuki A., Kobashi M.

Materials Transactions 64 巻 ( 8 ) 頁： 1952 - 1958 2023年

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials Transactions

In order to understand the influence of dislocation substructures on the size-dependent strength (smaller is stronger) of micron-sized metals, we have fabricated single-crystal cylindrical micropillars with various diameters approximately ranging from 1 to 10µm, which were prepared on the surface of the fully annealed sample and the subsequently cold-rolled samples of high-purity aluminum (Al). The annealed micropillars exhibited a size dependence of the resolved shear stress required for slip. The shear stress (¸i) normalized by shear modulus (G) and the specimen diameter (d) normalized by Burgers vector (b) followed the correlation of ¸i/G = 0.33(d/b)10.63. The size-dependent strength was reduced by cold-rolling, resulting in lower power-law exponents (0.2630.31) for the correlation in the cold-rolled specimens. The fine dislocation substructures introduced by the cold-rolling could be associated with the reduced size-dependent strength, which can be rationalized using the stochastic model of the dislocation source length in an assumption of homogenously distributed dislocations existing in the experimental micropillars. The inhomogeneous dislocation substructure with various dislocation cell sizes would contribute to a variation in the measured strength depending on the location, likely due to the probability of exiting the dislocation cell walls (local variation in dislocation density) in the micropillars fabricated on the cold-rolled Al samples. [doi:10.2320/matertrans.MT-L2023004]

DOI： 10.2320/matertrans.MT-L2023004

Investigation of dominant contributors to high strength of additively manufactured Al-Fe alloy by using single-crystal micropillar compression tests 査読有り

Choshi A., Zhu T., Takata N., Suzuki A., Kobash M.

Keikinzoku/Journal of Japan Institute of Light Metals 73 巻 ( 11 ) 頁： 523 - 529 2023年

担当区分：責任著者記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Keikinzoku/Journal of Japan Institute of Light Metals

In this study, we aim to address the dominant microstructural parameter of the high strength of Al-Fe alloy components additive-manufactured by the laser powder bed fusion (L-PBF) process. This study systematically investigated the compression response of single-crystal micropillars with a fixed diameter of approximately 3 μm prepared on the surfaces of the L-PBF built Al-2.5%Fe binary alloy sample, and the subsequently heat-treated samples (300°C and 500°C), together with the slowly solidified Al-2.5%Fe alloy sample for comparison. The single-crystal micropillars of the L-PBF built sample exhibited a high yield strength of approximately 250 MPa and pronounced strain hardening. The compressed single-crystal specimens exhibited a uniform deformation indicating the activated multi-slip systems. Such a trend was observed in the 300°C heat-treated sample. However, the relatively low yield strength and strain hardening rate were found in single-crystal micropillars of the 500°C heat-treated sample as well as the slowly solidified sample. In the compressed micropillars, a single-slip system was dominantly activated. These results indicated that numerous nano-sized Al 6Fe-phase particles (contained in the specimens of the L-PBF built sample and the 300°C heat-treated sample) could contribute to high yield strength and the enhanced activation of multi-slip systems resulting in the pronounced strain hardening.

DOI： 10.2464/jilm.73.523

Design of heat-resistant Al–Mg –Zn–Cu–Ni quinary alloy: Controlling intermetallic phases and mechanical performance at elevated temperature 査読有り国際誌

Li R., Takata N., Suzuki A., Kobashi M.

Materials Science and Engineering: A 857 巻 2022年11月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials Science and Engineering: A

Owing to good formability, wrought Al alloys are used in a wide range of industries, including turbochargers in automobile engines. The development of Al alloys with increased high-temperature strength is necessary to improve the fuel efficiency of engines. In this study, a modified heat-resistant Al–Mg–Zn–Cu–Ni quinary alloy with superior high-temperature strength and creep rupture life at 200 °C (potential temperature in service for compressor radial impellers) was designed. The thermodynamic assessments provided a modified alloy composition of Al–5Mg–3.5Zn–2Cu–2Ni (at %) exhibiting α-Al phase in equilibrium with T-Al6Mg11Zn11 and Al3(Ni, Cu)2 phases at elevated temperatures. The experimental alloy showed granular T and Al3(Ni, Cu)2 phases often located on grain boundaries in the α-Al matrix, although the undissolved Al3Ni phase (formed in solidification) locally remained. Apart from the T phase, the η-Zn2Mg phase containing Cu element preferentially precipitated on grain boundaries. A large number of fine precipitates were dispersed homogeneously in the grain interior after the aging at 200 °C or 300 °C. Compared to the base alloy with a ternary composition of Al–5Mg–3.5Zn (at %) and conventional Al alloys, the designed quinary alloy (pre-aged at 200 °C for 10 h) showed a high strength at elevated temperatures above 200 °C. The creep-rupture life at 200 °C/105 MPa was remarkably extended to 665 h by the addition of Cu and Ni elements into the base ternary alloy. The rupture life was more than ten times longer than one (57 h) of the ternary alloys. The alloy modification based on the thermodynamic calculations provides an effective approach for designing lightweight Al alloys with superior high-temperature strength and creep rupture life.

DOI： 10.1016/j.msea.2022.144055

Effect of solute Ni on thermal activation process of plastic deformation in Fe–18Cr single-crystal micropillars 査読有り国際誌

Zhu T., Li H., Takata N., Kobashi M., Yoshino M.

Materials Science and Engineering: A 857 巻 2022年11月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials Science and Engineering: A

The aim of the present study was to identify the effect of solute Ni element on the plastic deformation and its thermal activation process of 18Cr ferritic stainless steels. Single-crystal micropillars with different diameters of approximately 2 and 5 μm were fabricated on the surface of Fe–18%Cr–Ni alloy sheets containing different contents of Ni (0–2 mass%). Compression tests were performed on the micropillars at different initial strain rates to investigate the strain rate sensitivity (m) of stress for the slip initiation and the specimen-size dependence of the m value. In micropillars with a small diameter of 2 μm, the Fe–18%Cr binary alloy specimen exhibited a relatively higher strain-rate sensitivity of initial slip stress (m = 0.12), whereas m was reduced to 0.01 by adding 2% Ni. The same trend was observed in micropillars with a larger size of approximately 5 μm. The experimental results were utilized to evaluate the activation volume of plastic deformation. The activation volumes of the Fe–18%Cr alloy and alloy containing 1% Ni followed the specimen-size dependence trend of activation volume in bcc metals; however, the alloy containing 2% Ni exhibited larger activation volumes, suggesting a different thermal activation process presumably due to the significant interaction that occurred between dislocations and solute Ni atoms in bcc solid-solutions.

DOI： 10.1016/j.msea.2022.144076

Machine-learning assisted optimization of process parameters for controlling the microstructure in a laser powder bed fused WC/Co cemented carbide 査読有り国際誌

Suzuki A., Shiba Y., Ibe H., Takata N., Kobashi M.

Additive Manufacturing 59 巻 2022年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Additive Manufacturing

A Single laser scan was performed on a sintered WC/Co composite and the process conditions were optimized to realize a WC/Co two-phase microstructure in a WC/Co composite fabricated by laser powder bed fusion (L-PBF). Laser irradiation on the sintered WC/Co composites generated two different microstructural regions. One is composed of WC and Co phases (WC/Co two-phase region), and the other includes W2C and W3Co3C phases (WC decomposition region). In the L-PBF-fabricated WC/Co composites, these two microstructural regions are distributed in a complex manner and their fractions varies depending on the laser parameters. Using a convolutional neural network model that is trained with the micrographs of single-laser-scanned WC/Co composites, the fractions of the two microstructural regions in the WC/Co composites fabricated by the L-PBF under various laser conditions were quantified. Multiple linear regression analyses revealed that the laser power and spot size contribute more than the scan speed, which has been verified by numerical analysis based on the moving heat source model. A support vector machine (SVM) suggested that low laser power and low scan speed are required for suppressing the WC decomposition in the consolidated samples. The WC decomposition has been successfully suppressed in the samples fabricated under SVM-recommended conditions.

DOI： 10.1016/j.addma.2022.103089

Controllable tensile performance of additively manufactured Al–Fe alloy 査読有り国際誌

Qi X., Takata N., Suzuki A., Kobashi M., Kato M.

Materials Science and Engineering: A 855 巻 2022年10月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials Science and Engineering: A

Achieving both high strength and ductility is challenging in additive manufacturing of Al alloys using the laser powder bed fusion (L-PBF) process by altering the laser conditions to control the microstructural characteristics. The current work focuses on the influence of varying laser energy density (ED), which is adjusted by different sets of laser power (P) and scan speed (v), on the microstructure-tensile property relationships of the L-PBF-fabricated Al–2.5%Fe alloy under varying laser conditions (P = 204–230 W, v = 450–600 mm/s) with a fixed powder layer thickness (t = 30 μm) and hatch distance (h = 30 μm). With increasing ED (= P/v·t·h), a slight increase in the average size of the columnar α-Al grains was found in the experimental samples concurrently with a higher fraction of <001>-oriented grains. Nanosized particles of the Al6Fe phase with an increased tendency to interconnect were observed in the matrix inside the melt pool, and the θ phase formed within the submicron-sized cellular structure along the melt pool boundaries (MPBs). A low tensile ductility, induced by the local microstructural inhomogeneities across MPBs, was found in all specimens tensile-deformed along the building direction, which was characterized by a preference fracture along the MPBs. At higher applied ED, the tensile ductility of the experimental Al–2.5Fe alloy was significantly improved with only a slight decrease in tensile strength. The difference in concentration of Fe across the MPBs in the matrix was also moderately diminished, which is consistent with the reduced local difference in microhardness across the MPBs under higher ED conditions. Therefore, the present results demonstrate that local microstructural inhomogeneities across MPBs can be controlled by the laser conditions, thereby producing both high strength and good ductility in the L-PBF processed Al–Fe alloys.

DOI： 10.1016/j.msea.2022.143893

Enhancing the solid-state joinability of A5052 and CFRTP via an additively manufactured micro-structure 査読有り国際誌

Iwata K., Suzuki A., Kim S.G., Takata N., Kobashi M.

Journal of Materials Processing Technology 306 巻 2022年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Materials Processing Technology

An Al alloy (A5052) sheet was joined with a carbon fiber-reinforced thermoplastic (CFRTP) sheet by hot pressing without melting the CFRTP sheet (that is, solid-state joining). A micro-structure was manufactured via laser irradiation of Al-Ti-C powders bedded on the A5052 sheet. The laser irradiation to Al-Ti-C powders generates numerous particle-shaped protrusions additively on the A5052 sheet, which facilitate the infiltration of CFRTP and mechanically interlock with the CFRTP sheet. To determine the optimal conditions for joining A5052 and CFRTP consisting of a polyamide 6 (PA6) matrix, the effects of joining temperature during hot pressing on the interfacial structure and joint strength were investigated. The maximum joint strength was attained at the joining temperature of 210 °C. At lower temperatures, PA6 was not sufficiently softened to infiltrate the micro-structure, resulting in lower joint strengths. At higher temperatures, carbon fibers (CFs) were exposed on the CFRTP surface and inhibited the penetration of PA6 and CFs into the micro-structure, thereby lowering the joint strength. To infiltrate PA6 and CFs into the micro-structure, hot pressing was performed in a gradient temperature field. The proposed process enabled appropriate infiltration of CFs and PA6 into the micro-structure and led to high and stable joint strength. It is expected that using the additively manufactured micro-structure approach proposed herein, the operating windows of various cutting-edge joining processes can be expanded to more moderate and lower energy conditions.

DOI： 10.1016/j.jmatprotec.2022.117629

Microstructural Variations in Laser Powder Bed Fused Al-15%Fe Alloy at Intermediate Temperatures 査読有り国際誌

Wang, WY; Takata, N; Suzuki, A; Kobashi, M; Kato, M

MATERIALS 15 巻 ( 13 ) 2022年7月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials

The samples of the Al–15Fe (mass%) binary alloy that were additively manufactured by laser powder bed fusion (L-PBF) were exposed to intermediate temperatures (300 and 500◦C), and the thermally induced variations in their microstructural characteristics were investigated. The L-PBF-manufactured sample was found to have a microstructure comprising a stable θ-Al13Fe4 phase localized around melt-pool boundaries and several spherical metastable Al6Fe-phase particles surrounded by a nanoscale α-Al/Al6Fe cellular structure in the melt pools. The morphology of the θ phase remained almost unchanged even after 1000 h of exposure at 300◦C. Moreover, the nanoscale α-Al/Al6Fe cellular structure dissolved in the α-Al matrix; this was followed by the growth (and nucleation) of the spherical Al6Fe-phase particles and the precipitation of the θ phase. Numerous equiaxed grains were formed in the α-Al matrix during the thermal exposure, which led to the formation of a relatively homogenous microstructure. The variations in these microstructural characteristics were more pronounced at the higher investigated temperature of 500◦C.

DOI： 10.3390/ma15134497

その他リンク： https://www.mdpi.com/1996-1944/15/13/4497

Fast scanning calorimetry study of Al alloy powder for understanding microstructural development in laser powder bed fusion 査読有り国際誌

Naoki Takata, Mulin Liu, Hongmei Li, Asuka Suzuki, Makoto Kobashi

Materials and Design 219 巻 2022年7月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials and Design

We examined the variation in the solidification microstructure of AlSi10Mg alloy powder over a wide range of cooling rates controlled by using the fast scanning calorimetry (FSC) technique. Two exothermic peaks derived from the primary solidification of the α-Al phases and the α-Al/Si eutectic reaction were detected. These exothermic peaks became broader and shifted to lower temperatures at higher cooling rates. Focus ion beam (FIB) milling enables microstructural characterization of AlSi10Mg powder solidified at controlled cooling rates above 102 °C·s−1 in the FSC equipment. The sample solidified at 4 × 104 °C·s−1 exhibited a fine microstructure consisting of a primary α-Al phase surrounded by lamellar-shaped Si phases. The fraction of the Si phase continuously decreased with increasing cooling rate, indicating higher content of solute Si element in the α-Al phase solidified at a higher cooling rate. The secondary dendrite arm spacing (λ) of the primary α-Al phase decreased in the sample solidified at a higher cooling rate (dT/dt). The relation follows a general equation of λ = A (dT/dt)-n (A: 38.4, n: 0.33) in wide range of cooling rate (10-1 ∼ 104 °C·s−1). The results were utilized to discuss the cooling rate of Al alloys during the laser powder bed fusion (L-PBF) process.

DOI： 10.1016/j.matdes.2022.110830

その他リンク： https://www.sciencedirect.com/science/article/pii/S026412752200452X

Negative strain rate sensitivity of yield strength of Al-Si alloy additive-manufactured using laser powder bed fusion 査読有り国際誌

Takata N., Liu M., Suzuki A., Kobashi M., Kato M.

Scripta Materialia 213 巻 2022年5月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Scripta Materialia

This article reports an unexpected finding of the mechanical behavior of Al-12%Si alloy manufactured using the laser powder bed fusion (L-PBF) process. The as-manufactured specimen has a negative strain rate sensitivity of flow stress at an early stage of tensile deformation (below 3% in strain). The post heat-treated specimens exhibited a positive strain-rate sensitivity and none of these specimens exhibited a serrated stress-strain curve, indicating a mechanism different from the Portevin–LeChatelier effect. Transmission electron microscopy revealed the dynamic precipitation of the nano-sized Si-phase inside the supersaturated solid solution of the α-Al matrix in the as-manufactured specimen deformed at ambient temperatures. The dynamically precipitated Si phase interacted with the introduced dislocations, enhancing the flow stress during the early stages of plastic deformation. The dynamic precipitation could contribute to the negative strain-rate sensitivity of the flow stress at an early stage of tensile deformation (including the yield strength).

DOI： 10.1016/j.scriptamat.2022.114635

計算状態図を基にした耐熱アルミニウム鍛造合金の設計と組織制御招待有り査読有り

高田尚記, 鈴木飛鳥, 小橋眞

まてりあ 61 巻 ( 4 ) 頁： 195 - 201 2022年4月

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