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Additive manufacturing may be a novel method for fabricating porous materials. These materials can achieve effective performance because of their internal geometries. Metal-additive manufacturing is expected to utilize thermal conduction materials and devices. We have developed a porous metal with effective isotropic thermal conductivity by using metal-selective laser melting additive manufacturing. The internal pore structure was designed by topology optimization, which is the most effective structural optimization technique to maximize effective thermal conductivity. The designed structure was converted to a three-dimensional STL model, which is a native digital format of additive manufacturing, and assembled as a test piece. Effective thermal conductivity was measured by a steady-state method in which the effective thermal conductivity was calculated from a one-dimensional temperature gradient and the heat flux of the test pieces. The test pieces showed an effective thermal conductivity close to the Hashin–Shtrikman or Maxwell–Eucken bound, which is the theoretical limit of effective performance with an error less than 10%. more...

In the present study, we have attempted to produce the porous Ti–Al intermetallic based alloys by pressure-sintering of the elemental powders of Ti and Al through a combustion reaction, with a NaCl space holder to achieve the development of a highly porous structure. The powders of Ti (particle size more...

In this study, the reactions in Ti–50 at.%Al powder mixture upon heating at constant heating rates were studied using DSC analysis. Heating up the mixture resulted in melting of aluminum at temperatures close to its melting temperature, which was manifested as an endothermic peak in DSC curves. The melting of aluminum was the onset of an intense exothermic reaction, so-called combustion synthesis reaction which results in the formation of titanium aluminide. The shift in exothermic peak temperature in various linear heating rates was used to calculate the apparent activation energy according to Kissinger-type model-free methods. Heating rates of 10, 20, 30, 40, and 50 K min−1 were used to estimate the activation energy based on DSC data. In order to study the effect of ball-milling on reaction behavior, the starting powder mixture was ball-milled for different times, and a comparison was made between non-ball-milled and ball-milled DSC curves. The results showed that ball-milling tends to diminish the endothermic peak of melting of aluminum and shift the exothermic reaction temperature to lower temperatures, apparently altering the mechanism from a solid–liquid to an almost solid–solid one. The activation energy of the process in the non-ball-milled state was found to be close to the activation energy of diffusion of aluminum in TiAl (220 kJ mol−1). However, the application of same model-free methods to the ball-milled samples showed unexpectedly increased values for activation energy. It would be appropriate to check other methods as well as for calculation of activation energy in the ball-milled systems. more...

Single-crystal micropillar compression tests were performed in this study to investigate the mechanical properties and deformation mechanisms of Cr-based Laves phases. The results showed that, the activated slip system in the C15–Cr2Nb was exclusively the basal slip {111}⟨110⟩, transiting from the pyramidal slip {11 2 ¯ 2}⟨ 1 ¯ 1 ¯ 23⟩ to the prismatic slips {10 1 ¯ 0}⟨0001⟩ and {11 2 ¯ 0}⟨1 1 ¯ 00⟩ in the C14–Cr2Ta with the increased inclination angle. The average compressive strength of the C15–Cr2Nb changed between 10.0 GPa and 11.7 GPa, and that of the C14–Cr2Ta ranged within 11.6–12.4 GPa. The compressive strength changed due to the evolutions of activated slip systems in both Laves phases. The critical resolved shear stress (CRSS) of the C15–Cr2Nb was estimated as 4.4–4.6 GPa, which was lower than 5.1–6.1 GPa in the C14–Cr2Ta, and the higher CRSS of the C14–Cr2Ta resulted from higher shear modulus. The mechanical properties and deformation mechanisms obtained were helpful for better understanding and designing the Cr-based Laves phase alloys. more...

Fe/epoxy resin hybrid structures were fabricated via three-dimensional open-cellular porous Fe/TiB2 composite layers by an in-situ reaction synthesis process. Pores in the porous layer were filled with an epoxy resin to form an interpenetrating phase layer (IPL) consisting of epoxy resin and Fe/TiB2 composite. The relationship between the tensile joint strength perpendicular to the joint interface and structures of the porous layer was investigated. The tensile joint strength increased with increasing the roughness of an end surface of the porous layer but decreased when the surface roughness was higher than approximately 30 μm. The decrement in the joint strength was caused by a transition of the fracture position from an epoxy resin/IPL interface to Fe/IPL interface due to poor adhesiveness of the porous layer/Fe interface. A high-resolution X-ray computed tomography (CT) was utilized for investigating change in area fraction of the epoxy resin with depth from the end surface of the IPL. Based on the X-ray CT and fractography, it was revealed that the joint strength could be understood in view of epoxy resin/IPL interfacial strength at the fracture position estimated from the mixture law when the adhesiveness of the porous layer/Fe interface was enough. Based on the results above, an in-situ reaction induced from a functionally graded powder condition was applied for enhancing joint strength. more...

Biofunctionalization of Ti6Al4V alloy with metallic agents like Ag or Cu is a promising approach to add antibacterial properties and thus to reduce the risk of implant failure. This research investigates the in-situ alloying of Ti6Al4V(ELI) with 3 at.% Cu powders using Laser Powder Bed Fusion (L-PBF). The morphology and geometrical characteristics of the single tracks and layers were studied. Laser powers of 170 W and 340 W, and scanning speeds ranging from 0.4 to 1.4 m/s and 0.8–2.8 m/s were implemented. Single track results showed balling effect and humping at high scanning speeds, 1.4 m/s and 1.6 m/s, for each laser powder respectively. Conversely, keyhole formation occurred at lower scanning speeds of 0.4–0.6 m/s for 170 W laser power, and below and 0.8 m/s for 340 W laser power. For both laser powers, single layers resulted in smoother surfaces at lower scanning speeds. These results were used for the development of optimal process parameters for 3D cubes with 99.9 % density. Optimal process parameters were found for 170 W and 340 W laser powders at 0.7−0.9 and 1.0–1.2 m/s scanning speeds, respectively. In-situ alloying by L-PBF was challenging and a homogeneous distribution of Cu within the alloy was hard to achieve. The increase in laser power from 170 to 340 W resulted in small increase in homogenization. Microstructural analyses after stress-relieving treatment showed the presence of α’ and β phases, as well as CuTi2 intermetallic precipitates. The finer microstructure together with CuTi2 intermetallic precipitates resulted in an increase in hardness. This study demonstrates the potential for printing in-situ alloyed Ti6Al4V(ELI)- 3 at.% Cu for biomedical applications. However, further studies are required to determine the effectiveness of antibacterial properties. more...

An attempt was made to additively manufacture an Al–Fe binary alloy sample with a hypereutectic composition of 15 wt% Fe using a laser powder bed fusion (LPBF) process. The LPBF-built Al–15Fe alloy sample exhibited a microstructure consisting of a number of melt pools in which regions had locally melted and rapidly solidified due to scanning laser irradiation during the LPBF process. The α-Al (fcc) matrix consists of a number of elongated grains with a mean size of approximately 10 μm. These microstructural features correspond well to previous results of Al alloys additively manufactured by the LPBF process. It was found that relatively coarsened stable θ-Al13Fe4 phases with a length of a few micrometers were localized along the melt pool boundaries. Numerous spherical particles of a metastable Al–Fe intermetallic phase were finely distributed within the nanoscale eutectic microstructure consisting of α-Al and metastable Al6Fe phases inside the melt pools. The metastable phase formation corresponds well to the previous results on the rapidly solidified Al–Fe alloys. The refined multiple intermetallic phases produced by the LPBF process contribute to a high hardness of approximately 200 HV. The refined microstructure appeared stable at an elevated temperature of 300 °C. The high microstructural stability would sustain sufficient strength in a hostile environment for long-term periods of service at elevated temperatures above 200 °C. The present results were utilized to discuss the formation sequence of multiple Al–Fe intermetallic phases in rapid solidification by the LPBF process. more...

• This study focused on additive manufacturing (AM) of the Al–Fe binary alloy samples with a near-eutectic composition of 2.5 mass% Fe using the laser powder bed fusion (LPBF) process. The melt pool depth, relative density, and hardness of LPBF-fabricated Al–2.5Fe alloy samples under different laser power (P) and scan speed (v) conditions were systematically examined. The results provided optimum laser parameter sets (P = 204 W, v ≤ 800 mm s−1) for the fabrication of dense alloy samples with high relative densities >99%. Additionally, Pv-1/2, which is based on the deposited energy density model, was found to be a more appropriate parameter for additively manufacturing Al–2.5Fe alloy samples, and using it to simplify the relative densities of the samples made the determination of a threshold value for the laser parameters required to fabricate dense alloy samples. The microstructural and crystallographic characterization of the LPBF-built Al–2.5Fe alloy samples revealed a characteristic microstructure consisting of multi-scan melt pools that resulted from local melting and rapid solidification owing to laser irradiation during the LPBF process. Furthermore, a number of columnar grains with a mean width of ∼ 21 μm elongated along the building direction were also observed in the α-Al matrix. Numerous nano-sized particles of the metastable Al6Fe intermetallic phase with a mean size ∼ 90 HV, which is more than twofold higher than that of conventionally casted alloys that contain the coarsened plate-shaped Al13Fe4 intermetallic phase in equilibrium with the α-Al matrix. more...

We designed three Al-based cast alloys strengthened by T-Al6Mg11Zn11 intermetallic phases using a eutectic reaction (liquid → α(fcc) + T) in the Al–Mg–Zn ternary system and then fabricated them using solidification processes. Thermodynamic assessment provided target alloy compositions of Al–26.5Zn–21.5 Mg (at%), Al–23.5Zn–22.5 Mg (at%), and Al–13Zn–28Mg (at%) with the α -Al (fcc) phase in equilibrium with the T phase with high fractions (>60%). All of the alloys exhibited regularly arrayed fibers of the α phase embedded in a T-phase matrix in α/T two-phase eutectic microstructures. A slight effect of phase compositions on the fibrous eutectic morphology was observed, whereas the volume fraction of the T phase could be controlled according to the thermodynamic assessments. The fibrous α phases had faceted interfaces of {111} planes with a surrounding T-phase matrix, suggesting a low interfacial energy of the α/T interfaces. The fabricated eutectic alloys exhibited a high Vickers hardness (>230 HV) and high yield strength at elevated temperatures above 250 °C. The Mg-rich alloy with a composition of Al–13Zn–28Mg (at%) exhibited a relatively lower hardness, responsible for the low hardness of the T phase with a Mg-rich composition. The Mg-rich alloy exhibited the plasticity at a lower temperature of 200 °C but comparatively lower strength at elevated temperatures above 250 °C. These results indicated that chemical composition strongly affected the mechanical properties of the T phase in the eutectic alloys. The present results provide important insights into control of the mechanical properties of Al-based eutectic alloys reinforced by the T intermetallic phase. more...

To identify the dominant contributing factor in the anomalously high strength of Al–Si-based alloys fabricated by selective laser melting (SLM), microstructural characteristics of a SLM-built Al–10Si–0.3 Mg alloy (AlSi10Mg) and their changes upon annealing at elevated temperatures were investigated. The as-built AlSi10Mg alloy exhibits a peculiar microstructure comprising of a number of columnar α-Al (fcc) phase with concentrated Si in solution. Numerous nano-sized particles were observed within the α-Al matrix. At elevated temperatures, a number of Si phase (diamond structure) precipitates consumed the solute Si in the columnar α-Al phase, but the microstructure of the α-Al matrix changed slightly. After annealing at elevated temperatures, the tensile strength of the as-built AlSi10Mg alloy substantially decreased accompanied by a reduction in the strain hardening rate. The supersaturated solid solution of the α-Al phase containing numerous nano-sized particles enhanced the strain hardening, resulting in the anomalous strengthening of the SLM-built AlSi10Mg alloy. The microstructural features were formed due to rapid solidification at an extremely high cooling rate in the SLM process, which provides important insights into controlling the strength of Al–Si-based alloys fabricated by SLM., ファイル公開日: 2022/05/01 more...

This study characterizes the microstructure and its associated crystallographic features of bulk maraging steels fabricated by selective laser melting (SLM) combined with a powder bed technique. The fabricated sample exhibited characteristic melt pools in which the regions had locally melted and rapidly solidified. A major part of these melt pools corresponded with the ferrite (&alpha, ) matrix, which exhibited a lath martensite structure with a high density of dislocations. A number of fine retained austenite (&gamma, ) with a &lt, 001&gt, orientation along the build direction was often localized around the melt pool boundaries. The orientation relationship of these fine &gamma, grains with respect to the adjacent &alpha, grains in the martensite structure was (111)&gamma, //(011)&alpha, and [-101]&gamma, //[-1-11]&alpha, (Kurdjumov&ndash, Sachs orientation relationship). Using the obtained results, we inferred the microstructure development of maraging steels during the SLM process. The results depict that new and diverse high-strength materials can be used to develop industrial molds and dies. more...

The strain-hardening of cell wall in porous metals decreases the energy absorption properties. In order to suppress the strain hardening, porous hybrid materials consisting of ductile Al and Ti phases and brittle Al3Ti phase were synthesized by reaction sintering between Al and Ti powders with NaCl space holder. Changes in the porous structure and microstructure with sintering were investigated. Area fraction of Al3Ti phase formed at Al/Ti interface increased following the Johnson-Mehl-Avrami-Koromogrov (JMAK) equation of three-dimensional diffusion-controlled growth with zero nucleation rate. The growth of Al3Ti phase led to the formation of pores and cracks in cell wall by Kirkendall effect and volume shrinkage. Effect of microstructure on compressive properties of the porous Al/Al3Ti/Ti hybrids were also investigated. Porous hybrids consisting of α-Al matrix exhibited the plateau region with positive slopes due to the strain hardening of α-Al phase. Porous hybrids consisting of Al3Ti matrix exhibited the plateau region with the slope of almost zero, resulting in high energy absorption capacity and efficiency. Fractography revealed that crack propagated in brittle Al3Ti phase but arrested at α-Al phase. These results were used to discuss the microstructure for improving energy absorption properties., ファイル公開：2022-03-03 more...

The influence of the joining temperature history on the mechanical behavior of an Al alloy (A5052)/Polyamide-6 (PA6) lap joint was investigated. PA6 is a semi-crystalline thermoplastic and its mechanical behavior depends on its crystalline properties, which are affected by thermal processing. The A5052/PA6 joining process was carried out at 215 °C using a hydraulic hot-press. The temperature was decreased from 215 °C to various pre-set temperatures at a cooling rate of about 2 °C/s followed by air cooling under the application of pressure. The crystallinity of PA6 and strength of the lap joint increased with a decrease in the joining temperature from 215 to 190 °C and remained constant at temperatures below 190 °C. The thermoanalytical examination revealed that the crystallinity increase was caused by slow cooling. The results demonstrated that slow cooling is an effectual approach to improve the bonding strength. The fractography analysis results showed that the fracture mode of PA6 changed from ductile to brittle with an increase in its crystallinity., ファイル公開：2022-02-01 more...

An anomalously reduced size-dependent strength of commercial-purity aluminum (Al) single-crystal micropillars with diameters ranging approximately from 1 to 10 μm is reported. High-purity Al (99.99%) single-crystal micropillars exhibited an obvious size dependence of the resolved shear stress for slip. The measured shear stress resolved onto a primary slip system (τi) scaled by the shear modulus (G) and the pillar diameter (d) scaled by the Burgers vector (b) showed the following correlation: τi/G = 0.33(d/b)−0.63, which agreed well with previous works. However, the commercial-purity Al samples exhibited a lower power-law exponent (0.19) for their size-dependent strength, resulting in (τi/G) = 0.006(d/b)−0.19. TEM characterization revealed the local presence of Al–Fe intermetallic precipitates surrounded by relatively high-density dislocations in annealed commercial-purity Al samples. These results indicate the relatively high-density dislocations could be responsible for the reduced size-dependent strength, which was confirmed by the remarkably reduced size dependence of their resolved shear stress by prior cold rolling. The reduced size-dependent strength can be rationalized using the stochastic model of the dislocation source length. Thus, this study provides a new insight to allow the application of the micropillar compression test to commercially produced Al alloys. more...

In this paper, a novel processing method (reactive precursor method) to manufacture high-melting point porous Al-Ti intermetallics is investigated. Especially, morphological control of porous structure is focused. In the reactive precursor process, precursors are made by blending aluminum and titanium powders. The precursor is heated to ignite an exothermic reaction (so called “combustion reaction”) between the elemental powders. Pore formation is a well-known intrinsic feature of the combustion reaction, and we tried to control the pore morphology. Fundamentally, the closed-cell structure can be obtained when the maximum temperature during the reaction exceeds the melting point of the reaction product. By blending the exothermic agent powder in the precursor, the maximum temperature is increased and the reaction products are melted. The porosity is controlled by the maximum temperature. In contrast, an open-cell porous structure can be obtained when the maximum temperature is below the melting point of the reaction product. Microwave heating turned out to be an effective method to create an open cell structure. A powdery substance that does not react with other elemental powders (heat-absorbing agent powder) decreases the temperature during the reaction. Closed, open and bimodal-sized open pores have been achieved by the reactive precursor process so far. more...

Cast AlFe alloys containing several percent iron have low ductility because of their brittle precipitates. Therefore, precipitate refinement is very important for improving their mechanical properties. In recent decades, severe plastic deformation processes have been developed to achieve this grain refinement. For example, our previously proposed severe plastic deformation process, called compressive torsion, is quite effective for not only grain refinement but also precipitate refinement even in brittle materials. In the present work, precipitate refinement of cast Al—Fe alloys by compressive torsion and the resulting improvements in their tensile properties were investigated. Compressive torsion with various numbers of revolutions was applied to Al—Fe alloys at 373 K. Then, the alloys were subjected to tensile testing at room temperature, 473 K, and 573 K. The obtained experimental results indicated that the initial eutectic microstructure of the alloys disappeared after the compressive torsion processing. All large precipitates with sizes of more than 200 μm were refined, and their sizes were reduced to several tens of micrometers. Furthermore, these refined precipitates were dispersed homogenously in the alloy microstructure. In result, the tensile properties of the alloys, namely, their strength and elongation, were improved remarkably. In particular, the elongation reached more than 30% at room temperature. more...

Topology optimization approach was used for the design of Ti6Al4V ELI lattice structures with stiffness and density close to the human bone for implant applications. Three lattice designs with volume densities of 35 %, 40 % and 45 % and corresponding elastic modulus of 18.6 GPa, 23.1 GPa 27.4 GPa close to the human bone were generated. Laser powder bed fusion (LPBF) technique was used for the manufacturing of the specimens. Physical measurements and mechanical characterization of specimens were assessed by microCT analyses and compression test, perpendicular and parallel to the building direction of the specimens. LPBF Ti6Al4V ELI manufactured lattice structures showed deviations in wall thickness in comparison with the generated designs, leading to an increase in relative porosity but also a decrease in elastic modulus in comparison with the original designs. Horizontal walls of the lattice structures showed higher wall thickness in comparison with the vertical walls, leading to anisotropic behaviour of the lattice structures. Higher elastic modulus and compression strength were obtained when thicker walls were oriented along the loading direction of the compression test, showing a complete failure by dividing the specimens into two neighbouring halves. All specimens showed 45° diagonal shear fracture along the structure. On the other hand, higher energy absorption at first maximum compression strength peak was observed when samples were tested parallel to the building direction (when thinner walls were oriented along the loading compression direction). Results showed that designed lattice structures can possess the levels of human bones’ stiffness and therefore can reduce/avoid stress shielding on implant applications. more...

To elucidate the adhesion properties of anticorrosion hydroxide films formed on aluminum (Al)-alloy sheets prepared by the steam coating process, cracks that propagated inside the hydroxide film formed on Al–Mg–Si alloy (6061 grade) sheets were characterized. Continuous hydroxide films with different thicknesses of 0.7 μm and 1.4 μm formed at different temperatures of 180 °C and 200 °C, respectively. Microstructural characterizations revealed that these hydroxide films exhibited a dual-layer structure consisting of a polycrystalline γ-AlO(OH) layer (on the surface side) and a continuous amorphous layer (on the Al-alloy side). Bending tests caused numerous cracks inside the hydroxide films under tension and compression. On the tensile-strained surface, numerous vertical cracks penetrated through the hydroxide films, although their delamination was not observed. On the compressive-strained surface, local delamination of the upper γ-AlO(OH) layer occurred. However, cracks were not observed in the lower amorphous layer on the Al-alloy substrate deformed under compression. These results indicate that the dual-layer-structured hydroxide film prepared by steam coating exhibits remarkable adhesion to the Al-alloy substrate. more...

Combustion foaming of Al-Ti intermetallics was observed in-situ by X-ray radioscopy at the Technical University Berlin, Germany, and at the experimental station ID-19 of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. The acquisition rates were 6.7 fps and up to 500 fps, respectively. This allowed for observing in detail the internal structure development during combustion foaming of extruded Al-Ti powder compacts made with Al/Ti molar ratios of 3, 4 and 7 and containing 10 and 20 vol.% exothermic agent (Ti + B4C). At the beginning of the foaming process, μm-sized pores were observed. Foam shrinkage and pore coarsening started immediately after the combustion process. Specimens made with an Al/Ti ratio = 7 showed pore coarsening and a longer solidification time. Specimens with 10 vol.% exothermic agent experienced less volume expansion and pore coarsening than specimens with 20 vol.% exothermic agent. The specimens with an Al/Ti ratio = 4 contained fewer micropores than the one with an Al/Ti ratio = 3. more...

The aluminum foam sandwich (AFS) was examined its formability in die forging. The AFS specimens with different lengths were prepared by roll and bonding precursor process and the AFS specimens were compressed with single or double projected dies. The foam core in the AFS is successfully compressed only in a part under a die projection even at room temperature. However some parts of AFS specimens near the foot of a projection and between the double projections were deformed without touching with the die faces. In the case of single projection die, the length of AFS specimens affected greatly the compressive strain near the foot edges of projections. However, in the case of double projection die, the strain of AFS between the projections was not affected by the specimens’ length. more...

The Cu-Cr composite material is widely used as an electrode material in a vacuum circuit breakers used in electric power systems. It is generally produced by sintering processes, and then Cr particles were refined in the surface part. Using the Compressive Torsion Process (CTP) which is one of the severe plastic deformation processes, the Cu-Cr composite powder can be fully dense consolidated without sinter, and the Cr particles are refined in surface layer portion at the same time. In this study, the CTP was applied to the laminated material of Cu-Cr composite and Cu powders and the possibility of consolidation and Cr particle refinement of the laminated material was investigated. The consolidation of Cr-Cu/Cu laminated powder was possible by the CTP, and Cr particles near a drive end were extremely refined. Hardness and tensile strength of the laminated material were medium between both single Cu-Cr and Cu specimens. It means they were largest and the same level as Cu-Cr single composite near the end of a cylindrical specimen, and decreased gradually toward the middle part of Cu layer until the same level as Cu single material. more...

Long-scale Al–Ti intermetallic foam was fabricated by self-propagating high-temperature synthesis (SHS) mode combustion reaction with the help of exothermic agent and preheating treatment. The effect of exothermic agent and preheating condition on the SHS mode combustion reaction foaming of the long-scale Al–Ti intermetallic foam was investigated. Maximum temperature of combustion reaction, reaction propagation speed and porosity of specimen were increased by increasing the amount of exothermic agent. A correspondence relation between the distribution of porosity and the distribution of the maximum temperature throughout the self propagation direction was indicated. Long-scale Al–Ti foam which had 60–70% porosity and uniformed porosity distribution was earned with 623 and 673 K homogenous preheating. It was due to the appearance of Al 3 Ti liquid phase throughout the observation point of the specimen during the combustion reaction by the preheating treatment. more...

The present work reports experimental studies on self-propagating high-temperature synthesis of titanium aluminides. Powder mixture of different Ti:Al atomic ratios were adopted and pressed to make compacts. The compacts were heated up to the ignition temperature from one end using induction heating, giving rise to self-sustaining reaction along the compacts. The propagation of reaction front was monitored using a color CCD camera. X-ray Diffraction analyses showed that the main products constituents were TiAl, Ti3Al and TiAl3 in the case of Ti:Al atomic ratios of 1:1, 3:1, and 1:3, respectively; rapid preheating to temperatures close to ignition temperature resulted in minimization of the occurrence of undesired phases. The effects of various parameters such as the green compact density and titanium particle size on the ignition time, combustion wave velocity, and combustion temperature were more...

Open-cell structured porous titanium/ceramics composite was synthesized by a reactive precursor method using titanium and boron carbide (B 4 C) as reactant powders. Pore morphology was controlled by adding heat absorbing powder (titanium diboride: TiB 2 ) in the Ti+B 4 C blended powder. The effects of molar blending ratio of titanium and B 4 C and the amount of heat absorbing powder addition on the cell morphology (either open or closed) were investigated. Fine and homogeneous open-cell structure was achieved by adding appropriate amount of heat absorbing agent powder (>15 vol%), and the relative density of the specimen after the reaction became closer to that of the precursor by increasing TiB 2 volume fraction. When the volume fraction of TiB 2 addition was 20%, the open-cell fraction was maintained as 1.0 regardless of the relative density of the precursor. more...

Nickel titanium (NiTi) foams were made by combustion synthesis of powders with the help of ZrH2 as foaming agent and TiB2 as endothermic agent. In this paper, we investigated the effect of elemental powder size on the foaming. The powder size of Ni and Ti affected the ignition temperature of the combustion reaction, cell morphology and microstructure of the foams. The cell morphology of the foams was also modified by the powder size of TiB2. more...

Closed cell nickel titanium (NiTi) alloy foams were made by combustion synthesis with the help of both foaming agent and endothermic agent powders. Nickel, titanium, the foaming agent (ZrH2) and the endothermic agent (TiB2) powders were mixed and pressed at room temperature into cylindrical compacts. By heating these powder compacts up to an ignition temperature of the combustion reaction, NiTi alloy specimens are made. In this method, pores in the specimens are made by the gas generation from the foaming agent during melting of NiTi alloy due to the high heat of combustion reaction. Cell wall rupture of these foams caused by the gas generation is successfully prevented by the endothermic agent addition which increases the viscosity of molten NiTi alloy. An optimum amount of endothermic agent addition turned out to be in between 30 and 35 vol%. This volume fraction range is close to the one that makes adiabatic temperature of the combustion reaction below melting point of NiTi alloy. Specimens made by the addition of 40 vol% endothermic agent did not foam sufficiently. Porosity of the NiTi alloy foams increased by increasing the additive amount of the foaming agent by 1 mass%. Cell wall rupture and large pore formation became remarkable by increasing the foaming agent addition. more...

One of the practical applications of porous aluminum is the core material for panel/foam sandwich structures. To manufacture the foam/ panel sandwich structure by a powder processing route, a sheet type precursor is essential. Therefore, a foaming behavior of aluminum sheet precursor (pure Al, 6061Al and Al-7Si) was examined. The foaming behavior was examined by the projected area of a precursor recorded by two video cameras from horizontal (lateral-side observation) and vertical (top-surface observation) directions. Average diameters and vertical/ horizontal Feret diameter ratios were used to evaluate pore morphology. Free foaming behavior of the sheet type precursors was extremely unidirectional along the compression direction of the rolled precursor. With regard to pure aluminum and 6061Al precursors, the pore morphology at the early stage of foaming was extremely anisotropic (flat shape), while the pore morphology became spherical when the specimen reached to the maximum expansion. As for the Al-7Si precursors, such flat anisotropic pores were not observed even at the early stage of foaming. [doi:10.2320/matertrans.L-MZ201113] more...

The reactive infiltration of molten aluminum into a powder preform was investigated as a processing route for aluminum nitride (AlN) matrix composites. As the powder preform, titanium and boron nitride (BN) powders were blended and compacted, the infiltration occurred spontaneously at temperatures ranging from 1073 K to 1673 K. The conversion ratio of BN to TiB2 and AlN turned out to be insufficient ( more...

Magnesium matrix composites were fabricated with the help of a reaction between magnesium and silicon oxide (SiO2) powders. The specimens were prepared by two processing routes (a powder processing route and an infiltration route). The basic reaction behavior was investigated by heating compacted SiO2 and magnesium powder blends. The effects of aluminum oxide (Al2O3) powder addition on the microstructures were investigated by the infiltration route. Magnesium oxide (MgO) and magnesium silicide (Mg2Si) were synthesized by the reaction between magnesium and SiO2. By the powder processing route, an explosive reaction took place when the volume blending ratios of SiO2/Mg were in between 20/80 and 30/70, and the specimens were highly porous. This explosive reaction became remarkable by decreasing the SiO2 powder size. The thermodynamic calculation revealed that the adiabatic temperature (Tad) of the specimen exceeded the boiling point of magnesium when SiO2/Mg were in between 20/80 and 30/70. Molten magnesium infiltrated into the SiO2 powder phase spontaneously under the heating condition of 800°C for 3.6 ks. The microstructure after the infiltration consisted of MgO, Mg2Si and magnesium. The course MgO agglomerates, which might be formed by the high temperature at aninfiltration front, were observed in the microstructure after the infiltration. By blending an Al2O3 powder (30 vol%, 50 vol%) in the SiO2 powder, the MgO phase became finer to several microns. The pores were hardly visible in the microstructure of the specimens fabricated by the infiltration route. The micro-Vickers hardness data showed that the hardness of the specimen was improved by blending the Al2O3 powder. more...

Porous titanium carbide (TiC) and TiC/Ti composites were synthesized by self-propagating high-temperature synthesis (SHS). Titanium and carbon powders were blended by various Ti/C blending ratios. The heat of reaction between titanium and carbon was high enough to induce the self-sustaining reaction of TiC formation on condition that some processing parameters (Ti/C ratio and porosity of the precursor) were appropriately selected. When the Ti/C blending ratio was high, the excess amount of titanium absorbed the heat of reaction. Consequently, the heated zone was not heated up to the ignition temperature. On the other hand, when the Ti/C ratio was low, high thermal conductivity of the precursor prevented an ignition of the heated side of precursors. The pore morphology was controlled by changing the Ti/C ratio and the preheat temperature. more...

Compressive torsion process (CTP) which was developed by authors is effective process for grain and precipitates refinement of metallic materials with a severe plastic deformation. In the CTP, a cylindrical specimen is subjected to simultaneous compressive and torsional loading without change in its shape. However, metal flow and strain distribution in the processed specimen are not cleared, because the deformation is very large and complicated. In the present work, visualization of internal deformation of specimen processed by CTP was investigated using dual alloy etching technique. Two kinds of aluminum alloy were prepared by cutting on fan-like shape and alternately placed to a cylindrical shape. After CTPing, contrasts in the specimen were observed by polishing and etching. The internal distribution of shear strain was quantified by measuring the displacement of interface between the alloys. As a result, the visualization and quantification of internal deformation was successfully carried out using the technique. The internal strain distribution was varied not only in radial direction but also in longitudinal direction because of frictional constraint on the lateral face. A laminate contrast of the alloys observed on the vertical cross section was well related with the strain distribution in the specimen. more...

Recently, industrial technology for both improving thermal conductivity and controlling the coefficient of thermal expansion of heat sink materials has became an important issuebecause of the downsizing of electronic devices. We have been investigating the innovative processing method for TiB2 dispersed Cu matrix composite by reactive infiltration process in which the combustion reaction of elemental powders (Ti+2B+Cu → TiB2+Cu) and pressureless infiltration of molten Cu into porous reaction product (TiB2/Cu composite) are combined. By this process, fine TiB2particles (2~3µm) can be dispersed in Cu matrix homogeneously. However, for better thermal conductivity and reduced thermal expansion, 3-dimentionally continuous inter-penetrating structure of TiB2 and Cu phases is suitable. In this study, we researched the effects of Cu powder size and volume fraction in Ti,B,Cu green powder compact on the microstructure of the combustion synthesized TiB2/Cu composite. When Cu powders were smaller than 45µm, TiB2 particles were uniformly dispersed in Cu matrix. However, when Cu powders were larger than 150µｍ, monolithic Cu area without TiB2 dispersion was formed. The monolithic Cu area tended to be connected each other by increasing the amount of Cu powders. This resulted in the formation of 3-dimensionally continuous inter-penetrating TiB2/Cu microstructure. more...

The combustion synthesis of titanium aluminide (TiAl) starting from elemental powders in the self-propagating mode was investigated. A novel technique involving inductive preheating and ignition was utilized to initiate the reaction in a powder mixture compact. The effects of compact green density, titanium particle size, and mechanical activation of powder mixture on the propagation rate and combustion temperature were evaluated. It was found that mechanical activation of green powder mixture up to 2 h, and using finer titanium particles resulted in higher reaction front propagation rates. The optimum value of relative density with respect to front propagation velocity was determined to be within the range of 65–70%. The maximum combustion temperature was similarly obtained in the above range of relative density, but it was not significantly affected by the titanium particle size. The time-to-ignition was found to be highly influenced by titanium particle size and milling time. The products were characterized by X-ray diffraction and it was found out that the products were solely consisted of the TiAl phase without any other detectable phases. more...

Porous Al–Ti intermetallics and Al3Ti/Al composites were fabricated by combustion foaming process. Fundamentally, aluminum and titanium powders were blended (Al/Ti mole blending ratios ranging from 0.33 to 10.0). Additionally, boron carbide (B4C) powder was blended as exothermic agent since the heat of TiC and TiB2 formation is much higher than those of Al–Ti intermetallics. The blended powder compact was heated to induce the combustion reaction. Isotropic closed pores were produced by this process. By adding 10 vol.% exothermic agent, the porosity exceeded 60% in a wide range of Al/Ti ratios (3.0–10.0). It was confirmed that high heat of reaction of exothermic agent assisted the complete conversion of aluminum and titanium powders to Al3Ti. more...

Porous Al3Ti/Al composites were fabricated by the combustion foaming process and the effect of elemental powder size on porosity and cell morphology was investigated. High porosity was obtained by using the small titanium powders. Pores also became larger and more spherical by using the small titanium powders. Pore size became smaller and porosity became higher by decreasing the aluminum powder size. This tendency was remarkably observed on the specimens with high Al/Ti ratio (7.0). more...

Porous magnesium was fabricated from a precursor made of AZ91 magnesium machined chips. The effect of thermal conditions (heating rate, heating temperature and cooling rate) of the precursor on foaming behavior and pore morphology was investigated. The precursor started to expand at around the solidus temperature of AZ91 magnesium alloy, and accelerated its expansion rate after the temperature exceeded the liquids line. The maximum expansion was sustained only for a few seconds, and the specimen shrunk rapidly by heating the specimen continuously. The degree of maximum expansion became higher and the pore size became smaller by increasing the heating rate from 1 K/s to 3 K/s. The porosity of porous magnesium increased by increasing the processing temperature up to 660°C, whereas the pore size became larger and inhomogeneous. The cooling rate also turned out to be an important factor to maintain high porosity. With the low cooling rate, pores tended to collapse and porosity became lower during the cooling period. more...