Faculty Profiles - OKAYASU Mitsuhiro

Papers - OKAYASU Mitsuhiro

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Mechanical properties and failure characteristics of a recycled CFRP under tensile and cyclic loading

Mitsuhiro Okayasu, Tomohiro Yamazaki, Kohei Ota, Keiji Ogi, Tetsuro Shiraishi

International Journal of Fatigue 55 ( Oct ) 257 - 267 2013.10

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

An examination has been made of the mechanical and failure properties of a recycled short carbon fiber reinforced plastic (rCFRP). The rCFRP samples were fabricated by the following process: the CFRP, consisting of epoxy resin with carbon fiber, is ground before mixing with acrylonitrile butadiene styrene resin with different weight fractions of CFRP. The tensile strength (sigma(UTS)) increased with increasing CFRP content, but dropped considerably for the sample with higher fiber content. From in situ measurement of localized failure in rCFRP, it appeared that material failure occurs even if a low tensile stress of 30% sigma(UTS) is applied. The localized damage was related to the pull-out (or debonding) of the fibers from the matrix. The fatigue strength increased with increasing the content of the recycled carbon fiber even for the samples with low tensile strength. This was attributed to the low crack driving force arising from severe crack closure. Details of the crack growth behavior were discussed using various crack growth models proposed in previous studies. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijfatigue.2013.07.005

Strain-induced martensite formation in austenitic stainless steel

Mitsuhiro Okayasu, Hironobu Fukui, Hiroaki Ohfuji, Tetsuro Shiraishi

Journal of Materials Science 48 ( 18 ) 6157 - 6166 2013.9

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

In situ measurements of the strain-induced martensitic transformation (SMTs) of SUS304 stainless steel that takes place during tensile loading at room temperature were performed around the notch of a dumbbell-shaped specimen where high stress concentration occurs. Even in the low plastic strain regime, with loading to 0.2 % proof stress (sigma (0.2)), some SMTs occurred. However, the area fraction of the Fe-alpha'-martensite phase did not increase significantly even when the sample was loaded to the ultimate tensile strength (sigma (UTS)). After the sigma (UTS) point, the total fraction of the Fe-alpha' phase increased dramatically to the fracture point (sigma (f)). The phase textures of Fe-alpha' and Fe-gamma were almost equal at (sigma (UTS) - sigma (f))/2, and the Fe-alpha' phase was observed over almost the entire measurement area around the notch at the sigma (f) point. However, the area fraction of the Fe-alpha' phase at the sigma (f) point decreased far away from the fracture surface, to an extent that the total fraction of the Fe-alpha' phase was almost the same as that of the Fe-gamma phase in an area about 1.7 mm from the fracture face. Different martensite characteristics were detected in the stainless steel, depending on the applied load level. This was attributed to the severity of deformation. In particular, deformation twinning, created around sigma (UTS), and severe plastic deformation before fracture make a strong Fe-alpha' phase. Details of this phenomenon are interpreted using various approaches, including electron backscatter diffraction analysis and finite element analysis.

DOI： 10.1007/s10853-013-7412-8

Mechanical properties of AC4CH alloys produced by heated mould continuous casting proces

M. Okayasu, S. Takeuchi, Y. Ohkura, T. Shiraishi

International Journal of Cast Metals Research 26 ( 3 ) 160 - 167 2013.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Maney Publishing

This paper reports an investigation of the mechanical properties of cast aluminium AC4CH alloys produced by a unique casting method known as the heated mould continuous casting (OCC) process. The tensile and fatigue strengths and material ductility of the OCC samples are much higher than that for the same alloy produced by conventional gravity casting. The high tensile and high fatigue strengths of the OCC samples are reflected by the presence of tiny round α-Al grains, and the high ductility of OCC is a result of the regularly organized crystal orientation. © 2013 W. S. Maney & Son Ltd.

DOI： 10.1179/1743133612Y.0000000046

Crystallisation characteristics of primary silicon particles in cast hypereutectic Al-Si alloy

M. Okayasu, S. Takeuchi, T. Shiraishi

International Journal of Cast Metals Research 26 ( 2 ) 105 - 113 2013.4

Language：English Publishing type：Research paper (scientific journal) Publisher：MANEY PUBLISHING

The crystallisation characteristics of primary silicon particles in a cast hypereutectic Al-Si alloy were examined using various casting processes. The size of the primary silicon particles depends on the cooling rate. However, the primary silicon particles cannot be crystallised completely when the cooling rate is>20 K s , since uncrystallised Si atoms migrate to the regions at low cooling rates, producing large primary Si particles. Moreover, turbulent metal flow under conditions of high cooling rate leads to the macrosegregation of the primary Si particles, resulting in poor mechanical properties. From the crystallisation characteristics obtained, a suitable solidification criterion can be proposed. © 2013 W. S. Maney & Son Ltd. -1

DOI： 10.1179/1743133612Y.0000000040

Fatigue properties (S-N and da/dN-dδ) of cast aluminium alloys

M. Okayasu, S. Takasu, A. Niikura, S. Okano, T. Shiraishi

International Journal of Cast Metals Research 26 ( 2 ) 82 - 91 2013.4

Language：English Publishing type：Research paper (scientific journal)

In this paper, the fatigue strengths of cast aluminium alloys have been examined using the S-N and da/dN-dδ approaches on various cast samples having different microstructural characteristics. These were made by several different casting techniques, namely gravity casting, die casting and twin rolled continuous casting. Owing to the different microstructures, the fatigue properties varied. The S-N relations, e.g. the endurance limit, of the twin-rolled casting were apparently high compared to the other cast samples. The high fatigue strength was related to the high tensile strength and high ductility caused by the tiny spherical α-Al phase and fine eutectic structure. On the other hand, the low fatigue strength for the gravity and die cast samples was caused by the high stress concentration caused by the α-Al phase and needle-like eutectic silicon. Unlike the fatigue strength in the S-N approach, the da/dN-dδ relationships for the twin rolled casting sample, i.e. the resistance to fatigue crack propagation, were low compared to the gravity casting and the die cast samples. Such a difference in the crack growth resistance was influenced by the crack growth characteristics. For example, for the gravity cast and the die cast samples, the crack growth occurs in the grain boundaries of the coarse α-Al phase and along the long eutectic silicon grains (zigzag crack path), which promotes a strong crack closure tendency, leading to high crack growth resistance. The difference in the fatigue strength determined from the S-N relation and da/dN-dδ relation was interpreted by experimental and numerical examination of the stress-strain distribution. © 2013 W. S. Maney & Son Ltd.

DOI： 10.1179/1743133612Y.0000000030

Material properties of bismuth layered ferroelectrics and lead zirconate titanate piezoelectric ceramics

Mitsuhiro Okayasu, Yuki Sato, Satoshi Takasu, Mamoru Mizuno, Tetsuro Shiraishi

Ceramics International 39 ( 3 ) 3301 - 3306 2013.4

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

The material properties of bismuth layer-structured ferroelectrics (BLSFs) and lead zirconate titanate (PZT) piezoelectric ceramics have been investigated. The fatigue strength of the PZT sample was higher than that of the BLSF. The electrical properties were altered as a result of cyclic loading. The piezoelectric constant (d(33)) and electromechanical coupling coefficient (k(33)) decreased with increasing applied load for both piezoelectric ceramics. However, the rate of reduction for the BLSF sample is smaller than that for the PZT ceramic. This different rate is attributed to the different material characteristics. During cyclic loading, the strain value increased with increasing cycle number for the PZT sample. Like the PZT ceramic, the strain value increases for the BLSF but the back strain occurred after the cyclic loading was conducted for certain period of times. This different strain behavior is influenced by the different domain switching characteristics and this was clarified from the respective strain-electric field relationships. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

DOI： 10.1016/j.ceramint.2012.10.018

Mechanical properties of SPCC low carbon steel joints prepared by metal inert gas welding

Mitsuhiro Okayasu, Yuki Ohkura, Tatsuaki Sakamoto, Shuhei Takeuchi, Hiroaki Ohfuji, Tetsuro Shiraishi

Materials Science and Engineering A 560 ( 10 ) 643 - 652 2013.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

To better understand the fatigue and tensile properties of SPCC steels welded by metal inert gas welding, the mechanical properties of the welded component in several localized regions, e.g., weld metal, heat affected zone (HAZ) and base metal, were investigated. The tensile and fatigue properties of the weld metals were high compared to the other areas (base metal and HAZ) due to the precipitated Ti containing oxide inclusions in acicular ferrite (bainite). Two typical microstructures were mainly observed in the heat affected zones (HAZ): (i) bainite in a ferrite matrix (HAZ-B) and (ii) a ferrite phase with low internal stress (HAZ-A). The hardness of HAZ-B was higher than HAZ-A because of the partially formed bainite structure and precipitated Ti containing oxide inclusions. The mechanical properties of the weld sample were further investigated using test specimens that included all regions, i.e., weld metal, HAZ and base metal (BHW). The tensile and fatigue properties of the BHW sample were found to be lower than those in all other regions, which was influenced by the high internal stress. The mechanical properties were analyzed using microstructural and crystal characteristics, as examined by TEM and EBSD analysis. In addition, the fatigue strength can be precisely evaluated using a modified Goodman diagram. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2012.10.008

Development of New White Canes to Assist the Mobility of Visually Impaired People

M. Okayasu

Journal of The Japan Society for Welfare Engineering 15 ( 2 ) 23 - 29 2013

Mechanical and wear properties of Cu-Al-Ni-Fe-Sn-based alloy

M. Okayasu, D. Izuka, Y. Ninomiya, Y. Manabe, T. Shiraishi

Advances in Materials Research 2 ( 4 ) 221 - 235 2013

Material Properties of Cast Aluminium Alloys Produced by Various Casting Processes

Mitsuhiro Okayasu, Kohei Ota, Shuhei Takeuchi, Tetsuro Shiraishi

Light Metals Technology 765 241 - + 2013

Language：English Publishing type：Research paper (international conference proceedings) Publisher：TRANS TECH PUBLICATIONS LTD

The material and mechanical properties of cast aluminium alloys, produced using various casting technologies, have been investigated experimentally. In this study, several casting processes were selected, including gravity casting (GC), cold-chamber diecasting (CD), hot-chamber diecasting (HD), squeeze diecasting (SQ), twin rolled continuous casting (TRC) and heated mould continuous casting (HMC). Although all cast samples were made of the same aluminium alloy of Al-Si-Cu (ADC12), different material properties were obtained, in particular microstructural characteristics, crystal orientation and residual stress. In this instance, the microstructures of the GC and CD samples were formed mainly of coarse alpha-Al phase and needle-shaped eutectic structures; and a microstructure of fine round grain and tiny eutectic structures were observed for the HC, TRC and HMC samples. On the other hand, spherical shaped a-Al phase with a relatively large size was detected in SQ. The different microstructural characteristics led to different mechanical properties. A uniformly orientated lattice structure was detected in the HMC and SQ samples, which gave high material ductility. High internal compressive stress high dislocation density, arising from the rolling process, led to the high tensile properties for the TRC procedure. Various cast defects, such as blow holes and shrinkage porosity, were detected in GC and CD, which gave a reduction in their tensile properties.

DOI： 10.4028/www.scientific.net/MSF.765.241

New Experimental Techniques for In-situ Measurement of the Damage Characteristics of Piezoelectric Ceramics under High Cycle Fatigue Testing

M. Okayasu, Y. Sato

Experimental Mechanics 52 ( 8 ) 1009 - 1020 2012.10

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

To better understand the failure characteristics of lead titanate zirconate (PZT) piezoelectric ceramics, in-situ measurements of displacement and crack growth rates were conducted during high cycle fatigue testing, e. g., 5 kHz. A commercial PZT ceramic (used in a buzzer) was employed as the specimen. To examine the failure characteristics, two newly proposed systems were used: (i) a high speed camera system and (ii) a condenser microphone system. The former system consisted of two high speed cameras with an analytical system, which could measure the displacement of the PZT ceramic during the cyclic loading. The maximum displacement value of the ceramic was found to be approximately 20 μm at 0.5 kHz. The three-dimensional shape of the PZT ceramic during cyclic loading could be clearly observed. With the latter system, the displacement intensity arising from the ceramic vibration was detected continuously. It was found that the crack growth rate was not correlated with the fatigue frequency due to the resonance caused by the ceramic oscillation. There is a linear relationship between the crack growth rate and sonar intensity. On the basis of the crack growth behavior, the failure characteristics of the PZT ceramic could be clearly determined. © 2011 Society for Experimental Mechanics.

DOI： 10.1007/s11340-011-9550-8

The effects of artificial asperities on crack closing behavior in quenched and tempered medium carbon steel

Mitsuhiro Okayasu, Zhirui Wang

Journal of Mechanical Science and Technology 26 ( 10 ) 3081 - 3090 2012.10

Language：English Publishing type：Research paper (scientific journal) Publisher：KOREAN SOC MECHANICAL ENGINEERS

To better understand the effect of an asperity on crack closure behavior, K-CMOD relations were examined using artificial asperity/wedge, inserted into the fatigue crack in a three point bending specimen made of a hardened medium carbon steel. Experimental results revealed that the unloading phase of the K vs. CMOD curve exhibited a concave shape if soft artificial asperity (Al alloy) was inserted, signifying acceleration in the CMOD decrease at zero applied load. This was mainly related to elastic and plastic deformation in the wedge material during the unloading process. On the contrary, the linear unloading portion of K vs. CMOD was obtained as hard asperity (high carbon steel) was employed, which specified deceleration in the CMOD decrease at zero applied load, where the only elastic deformation in the asperity was affected. From their unloading curves, the severity of crack closure or Delta K-eff value was found to be related to the strength of the asperity material. The values of Delta K-eff were examined in two different ways, e.g., (i) the remote displacement method and (ii) the adjusted compliance ratio method (ACR). The Delta K-eff value, measured using both approaches, decreases with increasing wedge strength, such as hardness and yield strength. The rate of reduction in Delta K-eff was, however, changed depending on the manner of Delta K-eff examination, in which the Delta K-eff decreased at a higher rate for the compliance ratio method and at a lower rate for the remote displacement method. The reason for this is discussed in the present work.

DOI： 10.1007/s12206-012-0836-2

Effects of anisotropic microstructure of continuous cast Al-Cu eutectic alloys on their fatigue and tensile properties

Mitsuhiro Okayasu, Ryo Sato, Satoshi Takasu

International Journal of Fatigue 42 ( Sept ) 45 - 56 2012.9

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

The objective of this work is to explore the effects of anisotropic microstructure on the material properties of a continuous cast Al-33%Cu eutectic alloy, produced by the Ohno continuous casting technique (OCC). A clear anisotropic microstructure was obtained in the OCC samples, namely a fine lamellar eutectic structure with unidirectional growth along the axial direction. The eutectic structure was formed by a primary alpha-Al phase and secondary CuAl2 phase. The hardness of CuAl2 is about 2.8 times higher than that of the alpha-Al phase. Due to the anisotropic microstructure, the mechanical properties of the OCC samples depended on the loading direction. The tensile and fatigue properties of the OCC samples in the longitudinal direction were more than 30% higher than those in the perpendicular direction. In addition, the mechanical properties were influenced directly by the fine eutectic structure in the longitudinal direction. The ultimate tensile strength of the OCC sample in the longitudinal direction could be estimated theoretically using three different parameters: solid-solution strengthening, interlamellar eutectic structure and work hardening strengthening. (C) 2011 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijfatigue.2011.05.015

A study of the effects of vibration on the electric power generation properties of lead zirconate titanate piezoelectric ceramic

Mitsuhiro Okayasu, Daisuke Sato, Yuki Sato, Masashi Konno, Tetsuro Shiraishi

Ceramics International 38 ( 6 ) 4445 - 4451 2012.8

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

To better understand how the electric power generated from PZT piezoelectric ceramics is affected by mechanical loading conditions the power generation was examined during cyclic loading under various loading conditions. The electric power generation was continuously examined using a monitoring system that we have recently developed. This system revealed that the electric power increased with increase of the applied load but then decreased when the applied load exceeded a certain level. In addition, greater electric power was generated with a simple beam configuration compared with a cantilevered beam. The change of electric power generation was directly related to the stress direction; high stress in the tetragonal structure parallel to the c-axis gave rise to high electric power generation. On the other hand, material failure, including domain switching and crack generation, caused a reduction of the electric power generated. Based upon our experimental data, suitable loading conditions to give high piezoelectric energy generation have been clarified. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

DOI： 10.1016/j.ceramint.2012.02.018

Mechanically controlled domain structure in PZT piezoelectric ceramics

Mitsuhiro Okayasu, Yuki Sato, Mamoru Mizuno, Tetsuro Shiraishi

Ceramics International 38 ( 6 ) 4579 - 4585 2012.8

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

The influence of the mechanically applied load on the piezoelectric properties and domain switching characteristics has been investigated experimentally using a soft lead zirconate titanate (PZT) piezoceramic, which de-poled to make randomly orientated domain structures. Mechanical loads were applied to rectangular PZT ceramics under compressive and tensile stresses. With the applied stress, 90 degrees domain switching occurred in many locations in the PZT ceramics, where the higher stress caused more severe domain switching. The domain switching occurred with different directions, depending on the stress direction. For instance, the (2 0 0) peak increased and the (0 0 2) peak decreased when more severe compressive stress was applied. The opposite trend was detected as more severe tensile stress was applied; the (2 0 0) peak decreased and the (0 0 2) peak increased. With the applied loading process, the domains (long tetragonal c-axis) were orientated regularly in the PZT ceramics. Furthermore, like the electrically poled PZT ceramics, the domain orientations were more aligned when the sample surfaces were constrained during the loading process. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

DOI： 10.1016/j.ceramint.2012.02.036

A study of the mechanical properties of an Al-Si-Cu alloy (ADC12) produced by various casting processes

M. Okayasu, Y. Ohkura, S. Takeuchi, S. Takasu, H. Ohfuji, T. Shiraishi

Materials Science and Engineering A 543 ( 1 ) 185 - 192 2012.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

The mechanical properties of an Al-Si-Cu alloy (ADC12), produced using various casting technologies, have been examined experimentally. Four different casting processes were employed, including gravity casting (GC), cold-chamber die-casting (CD), twin rolled continuous casting (TRC) and the Ohno continuous casting process (OCC). Although these produced the same Al-Si-Cu aluminum alloy, different mechanical properties were obtained, in particular microstructural characteristics and dislocation density. The microstructure of GC and CD samples was formed mainly with coarse α-Al phase and needle-shaped Si and Fe based eutectic structures. In contrast, a fine round α-Al phase and tiny eutectic structures were observed for the TRC and OCC samples. Such a change of microstructure was caused by the different casting process parameters, namely injection speed, casting pressure and cooling rate. High internal stress as well as high dislocation density was detected for GC and TRC, caused by the high shrinkage force and high applied rolling force, respectively. Because of the different material properties, the tensile and fatigue strength were altered. A clear Hall-Petch relation with σ =k d +B was obtained, and the fatigue properties were evaluated with the power law dependence σ =σ N . The mechanical properties obtained were also analyzed in relation to the crystal orientation and lattice mis-orientation angle. © 2012 Elsevier B.V.. 0.2 y a f f -0.5 -b

DOI： 10.1016/j.msea.2012.02.073

Study of resonance fatigue properties of piezoelectric ceramics using new fatigue testing system

M. Okayasu, Y. Sato, M. Mizuno, T. Shiraishi

Advances in Applied Ceramics 111 ( 4 ) 181 - 186 2012.5

Language：English Publishing type：Research paper (scientific journal) Publisher：MANEY PUBLISHING

To better understand the material damage of lead zirconate titanate (PZT) ceramics, fatigue tests have been carried out using a newly proposed testing system. The material damage was evaluated with the change in sonar intensity from the ceramics, where a sensing control was operated using a condenser microphone system. This testing system produces cyclic loading with a wide range of fatigue frequencies: 1 Hz-72 kHz. The influence of fatigue frequency on the fatigue properties of a PZT ceramic has been investigated, and it appeared that the fatigue strength is not linearly correlated with the fatigue frequency. The reason for this is due to the resonance caused by the oscillation. Thus, the fatigue frequency can change the severity of sample vibration. The extent of sample vibration is associated with the sonar intensity from the ceramic, which is linearly related to the crack growth rate. Details of the resonance fatigue properties have been systematically examined. © 2012 Institute of Materials, Minerals and Mining.

DOI： 10.1179/1743676111Y.0000000055

Effect of domain wall characteristics on material properties of lead zirconate titanate piezoelectric ceramics

M. Okayasu, Y. Sato, M. Mizuno, T. Shiraishi

Advances in Applied Ceramics 111 ( 4 ) 187 - 195 2012.5

Language：English Publishing type：Research paper (scientific journal) Publisher：MANEY PUBLISHING

To better understand the material properties of lead zirconate titanate (PZT) ceramics, the influence of domain wall characteristics on the electrical and mechanical properties of PZT ceramics has been investigated. To obtain various domain wall characteristics, the poling process was carried out with different patterns with respect to the PZT ceramic. The domain walls were aligned in the PZT ceramic in the direction perpendicular to the poling direction. Such domain wall characteristic produced different crack growth behaviours. The crack growth occurred mainly along the domain walls of {110} for a (crack growth direction perpendicular to the poling direction) because of the high stress concentration between the domain walls. In contrast, the crack propagated along both domain walls and grain boundaries for a (crack growth direction parallel to the poling direction), leading to high crack growth resistance and good mechanical properties. The fracture toughness K values for the PZT ceramics in the a and a directions were about 0.5 and 2.6 MPa m respectively. It also appeared that the domain walls collapsed when a number of poling processes are conducted along different directions. These PZT ceramics had high mechanical properties due to the low stress concentrations. © 2012 Institute of Materials, Minerals and Mining. 31 33 IC 31 33 1/2

DOI： 10.1179/1743676111Y.0000000057

Mechanical properties of Al-Si-Cu alloys produced by the twin rolled continuous casting process

Mitsuhiro Okayasu, Ryo Sato, Satoshi Takasu, Akio Niikura, Tetsuro Shiraishi

Materials Science and Engineering A 534 ( 1 ) 614 - 623 2012.2

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

The mechanical properties of cast aluminum alloys (ADC12: Al-Si-Cu alloy), created by the twin rolled continuous casting (TRC) process are explored. The TRC-ADC12 exhibits an anisotropic microstructure formed by a fine dendritic microstructure of the columnar and equiaxial grains in the longitudinal direction. Deformation twinning occurs in the TRC sample for several reasons including a high strain rate, high rolling force and fine grains; lattice rotation occurs along {1 1 1} and {1 1 (2) over bar}. The tensile and fatigue strengths of the TRC samples are about twice those of the same aluminum alloy produced by conventional gravity casting. This increase is attributed to the fine grains and fewer casting defects for the TRC samples. The 0.2% proof stress of the TRC samples can be estimated by two different parameters, solid-solution strengthening k root c and secondary dendrite arm spacing k(y)/root d. An anisotropic microstructure of the TRC samples makes a slight difference in the mechanical properties between the longitudinal and perpendicular directions, and the tensile and fatigue strengths of the samples in the longitudinal direction are slightly higher than those in the perpendicular direction. Based upon the microstructural characteristics, further details of the mechanical and fatigue properties are discussed based on experimental and numerical data. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2011.12.018

Relevance of instrumented nano-indentation for the assessment of the mechanical properties of eutectic crystals and alpha-Al grain in cast aluminum alloys

Mitsuhiro Okayasu, Satoshi Takasu, Mamoru Mizuno

Journal of Materials Science 47 ( 1 ) 241 - 250 2012.1

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

To better understand the material properties of cast aluminum alloys, the mechanical properties of microscopic structures (the eutectic structure and the alpha-Al phase) have been systematically examined using a special nano-indentation hardness test machine. In this approach, a triangular indentation is applied directly to the eutectic structure or alpha-Al phase, and the mechanical properties evaluated through hardness and load-strain relationships. The hardness of the eutectic phase varied, depending on the structural characteristics of the different intermetallic compounds. High values of hardness were obtained structures of the DO(3) type, e.g., Al(5)FeSi, but low hardness for CuAl(2) and Mg(2)Si. The hardness of CuAl(2) and Mg(2)Si had almost the same values as that of the alpha-Al matrix. In addition, from the nano-indentation hardness test, the effects of alpha-Al grain characteristics on the mechanical properties were clarified. The hardness of the alpha-Al grain was linearly related to the grain size and the distance from the grain boundary, where the higher the hardness, the smaller the grain size and the closer to the grain boundary. The hardness level was attributed to the different severity of slip resistance of the atoms during the indentation loading.

DOI： 10.1007/s10853-011-5791-2

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