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F H Samuel - One of the best experts on this subject based on the ideXlab platform.

  • role of modification and melt thermal treatment processes on the microstructure and tenSile properties of al Si alloys
    Materials & Design, 2015
    Co-Authors: A M Samuel, H W Doty, G H Garzaelizondo, F H Samuel
    Abstract:

    Abstract The present study was performed on an Al–7%Si–0.35%Mg alloy (A356 alloy) with the primary objective of improving the alloy performance through modification of the microstructure. Ultimate tenSile strength (UTS) can be improved by the addition of strontium (Sr), superheating or Sr modified melt thermal treatment. The melt thermal treatment process alone has no apparent influence on the UTS. Both Sr-modified and Sr-modified melt thermal treatment can help to improve the percentage elongation of A356 alloy castings. A higher percentage elongation can be reached at a higher cooling rate. The effect of solution heat treatment on the tenSile properties of various A356.2 alloy castings can be summed up as follows: (i) the yield strength of the A356.2 castings is Significantly improved after 8 h solution heat treatment due to the precipitation of Mg2Si, (ii) the yield strength remains more or less the same with further increase in solution treatment time to 80 h, and (iii) the UTS is greatly improved within the first 8 h of solution heat treatment and continues up to 80 h, where this improvement is attributed to Mg2Si precipitation, dissolution of Silicon within the Al-matrix and change in the Si Particle morphology (spheroidization). The ductility of the A356.2 alloys can also be conSiderably enhanced with solution heat treatment (e.g. from ∼6% in the non-modified casting in the as-cast condition to ∼10% after 80 h solution treatment).

  • optimizing the tenSile properties of al Si cu mg 319 type alloys role of solution heat treatment
    Materials & Design, 2014
    Co-Authors: Y M Han, A M Samuel, H W Doty, S Valtierra, F H Samuel
    Abstract:

    Abstract The work presented in this study was carried out on Al–Si–Cu–Mg 319-type alloys to investigate the role of solution heat treatment on the dissolution of copper-containing phases (CuAl2 and Al5Mg8Cu2Si6) in 319-type alloys containing different Mg levels, to determine the optimum solution heat treatment with respect to the occurrence of incipient melting, in relation to the alloy properties. Two series of alloys were investigated: a series of experimental Al–7 wt% Si–3.5 wt% Cu alloys containing 0, 0.3, and 0.6 wt% Mg levels. The second series was based on industrial B319 alloy. The present results show that optimum combination of Mg and Sr in this study is 0.3 wt% Mg with 150 ppm Sr, viz. for the Y4S alloy. The corresponding tenSile properties in the as-cast condition are 260 MPa (YS), 326 MPa (UTS), and 1.50% (%El), compared to 145 MPa (YS), 232 MPa (UTS), and 2.4% (%El) for the base alloy with no Mg. At 520 °C solution temperature, incipient melting of Al5Mg8Cu2Si6 phase and undissolved block-like Al2Cu takes place. At the same time, the Si Particles become rounder. Therefore, the tenSile properties of Mg-containing alloys are controlled by the combined effects of dissolution of Al2Cu, incipient melting of Al5Mg8Cu2Si6 phase and Al2Cu phase, as well as the Si Particle characteristics.

  • effect of grain refining and sr modification interactions on the impact toughness of al Si mg cast alloys
    Materials & Design, 2014
    Co-Authors: A M Samuel, H W Doty, S Valtierra, F H Samuel
    Abstract:

    Abstract The present work investigates the effects of various types of grain refiners on the impact properties of Sr-modified A356.2 alloys in both the as-cast and heated-treated conditions. The results showed that the addition of Ti and B greatly improves the alloy toughness, but only when the alloy was in a fully modified state; moreover, the right type of master alloy and addition levels must be used. The highest values of the total absorbed energy recorded for T6-tempered alloys were obtained uSing Al–5%Ti–1%B and Al–10%Ti master alloys in addition to 0.04%Ti. A Significant deterioration in the impact properties is observed due to the Sr–B interaction (in some cases). The improvements in toughness may be attributed to the change in Si Particle morphology as well as to the dissolution and fragmentation of a number of the intermetallics formed during the T6 temper.

  • the effects of mischmetal cooling rate and heat treatment on the eutectic Si Particle characteristics of a319 1 a356 2 and a413 1 al Si casting alloys
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008
    Co-Authors: El O Sebaie, A M Samuel, F H Samuel, H W Doty
    Abstract:

    Abstract The effects of mischmetal, cooling rate and heat treatment on the eutectic Si Particle characteristics of A319.1, A356.2 and A413.1 Al–Si casting alloys were investigated and recorded for this study. Mischmetal was added to the alloys in the form of Al–20% mischmetal master alloy to produce four levels of mischmetal addition (0, 2, 4 and 6 wt%). The alloys were also modified with strontium (∼250 ppm) to study the combined modification effect of Sr and mischmetal at both high and low cooling rates corresponding to dendrite arm spacings of ∼40 and 120 μm, respectively. The alloys were subjected to solution heat treatment (495 °C/8 h for A319.1 and A413.1 alloys, and 540 °C/8 h for A356.2 alloy) to investigate its effect on the eutectic Si Particle morphology. An optical microscope-image analyzer system was used to measure the characteristics of eutectic Si Particles such as area, length, roundness ratio and aspect ratio, in order to monitor the modifying effect of mischmetal, as well as the combined modification effect of mischmetal and Sr. For each alloy sample examined, the Si Particle characteristics were measured over an area of 50 fields and the average Particle characteristics were thus determined. The eutectic Si Particle measurements revealed that partial modification was obtained with the addition of mischmetal while full modification was achieved with the addition of Sr in the as-cast condition, at both high and low cooling rates. The interaction between Sr and mischmetal was observed to weaken the effectiveness of Sr as a Si Particle-modifying agent. This effect was particularly evident at the low cooling rate. During solution heat treatment, the eutectic Si Particles in the non-modified alloys underwent rapid coarsening, otherwise known as Ostwald ripening, whereas those in the Sr-modified alloys exhibited a high spheroidization rate. The coarsening was evidenced by an increase in the thickness of the Si Particles, clearly observed in the A356.2 alloy at both cooling rates. In the alloys containing mischmetal, the presence of this mixture of rare earth elements reduced the coarsening of the Si Particles slightly.

  • effect of metallurgical parameters on the hardness and microstructural characterization of as cast and heat treated 356 and 319 aluminum alloys
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007
    Co-Authors: F H Samuel, Mahmoud M Tash, F Mucciardi, H W Doty
    Abstract:

    Abstract The present study was undertaken to investigate the effect of metallurgical parameters on the hardness and microstructural characterization of as-cast and heat-treated 356 and 319 alloys, with the aim of adjusting these parameters to produce castings of suitable hardness and Fe-intermetallic volume fractions for subsequent use in studies relating to the machinability of these alloys. By measuring the amount of Fe- and Cu-intermetallics formed and the changes in the eutectic Si Particle characteristics resulting from alloying additions (Fe, Mn, Mg), Sr-modification, and heat treatment of the 356 and 319 alloys, and the corresponding hardness values, it was posSible to determine which conditions or metallurgical parameters yielded the required Fe-intermetallic volume fractions of 2 and 5% and hardness levels of 85 and 115 BHN. These levels conform to the most common levels observed in the commercial application of these alloys. The 356 and 319 alloys were examined in the as-cast and heat-treated conditions, uSing different combinations of grain refining, Sr-modification, and alloying additions. Aging treatments were carried out at 155, 180, 200, and 220 °C for 4 h, followed by air cooling, as well as at 180 and 220 °C for 2, 4, 6, and 8 h to determine conditions under which the specified hardness levels of 85 and 115 HBN could be obtained. Hardness measurements were carried out uSing a Brinell hardness tester. Peak hardness was observed in the 356 and 319 alloys at different aging conditions, depending upon the Fe-intermetallic type present in the alloy and whether the alloy was modified or not. Aging at 220 °C revealed a hardness peak at 2 h aging time in both 356 and 319 alloys. Addition of Mg to 319 alloys produced a remarkable increase in hardness at all aging temperatures. This may be explained on the baSis of the combined effect of Cu- and Mg-intermetallics in the 319 alloys, where hardening during aging occurs by the cooperative precipitation of Al 2 Cu and Mg 2 Si phase Particles [P. Ouellet, F.H. Samuel, J. Mater. Sci. 34 (1999) 4671–4697; P.N. Crepeau, S.D. Antolovich, J.A. Worden, AFS Trans. 98 (1990) 813–822]. Iron-intermetallic volume fraction measurements were carried out on polished specimens of the 356 and 319 alloys uSing electron probe microanalySis, for both as-cast and heat-treated conditions. Copper-intermetallic volume fractions were also measured for the 319 alloys to determine the amount of undissolved CuAl 2 phase. It was observed that the unmodified alloys displayed higher Fe-intermetallic surface fractions than the modified alloys. The copper-intermetallic surface fractions, on the other hand, were higher in the Sr-modified alloys than the unmodified alloys. These observations may be attributed to the effect of Sr on (a) the dissolution and fragmentation of the β-Fe-intermetallics in the matrix, the solution heat treatment also contributing to this effect; (b) severe segregation of Al 2 Cu and Al 2 MgCu phases in areas away from the eutectic Si regions, slowing down the dissolution of the Al 2 Cu phase during solution treatment; (c) altering the precipitation sequence of α-Al 15 (Fe, Mn) 3 Si 2 from post-dendritic to pre-dendritic, the latter being expected to improve the alloy strength due to its precipitation within the α-Al dendrites.

H W Doty - One of the best experts on this subject based on the ideXlab platform.

  • role of modification and melt thermal treatment processes on the microstructure and tenSile properties of al Si alloys
    Materials & Design, 2015
    Co-Authors: A M Samuel, H W Doty, G H Garzaelizondo, F H Samuel
    Abstract:

    Abstract The present study was performed on an Al–7%Si–0.35%Mg alloy (A356 alloy) with the primary objective of improving the alloy performance through modification of the microstructure. Ultimate tenSile strength (UTS) can be improved by the addition of strontium (Sr), superheating or Sr modified melt thermal treatment. The melt thermal treatment process alone has no apparent influence on the UTS. Both Sr-modified and Sr-modified melt thermal treatment can help to improve the percentage elongation of A356 alloy castings. A higher percentage elongation can be reached at a higher cooling rate. The effect of solution heat treatment on the tenSile properties of various A356.2 alloy castings can be summed up as follows: (i) the yield strength of the A356.2 castings is Significantly improved after 8 h solution heat treatment due to the precipitation of Mg2Si, (ii) the yield strength remains more or less the same with further increase in solution treatment time to 80 h, and (iii) the UTS is greatly improved within the first 8 h of solution heat treatment and continues up to 80 h, where this improvement is attributed to Mg2Si precipitation, dissolution of Silicon within the Al-matrix and change in the Si Particle morphology (spheroidization). The ductility of the A356.2 alloys can also be conSiderably enhanced with solution heat treatment (e.g. from ∼6% in the non-modified casting in the as-cast condition to ∼10% after 80 h solution treatment).

  • optimizing the tenSile properties of al Si cu mg 319 type alloys role of solution heat treatment
    Materials & Design, 2014
    Co-Authors: Y M Han, A M Samuel, H W Doty, S Valtierra, F H Samuel
    Abstract:

    Abstract The work presented in this study was carried out on Al–Si–Cu–Mg 319-type alloys to investigate the role of solution heat treatment on the dissolution of copper-containing phases (CuAl2 and Al5Mg8Cu2Si6) in 319-type alloys containing different Mg levels, to determine the optimum solution heat treatment with respect to the occurrence of incipient melting, in relation to the alloy properties. Two series of alloys were investigated: a series of experimental Al–7 wt% Si–3.5 wt% Cu alloys containing 0, 0.3, and 0.6 wt% Mg levels. The second series was based on industrial B319 alloy. The present results show that optimum combination of Mg and Sr in this study is 0.3 wt% Mg with 150 ppm Sr, viz. for the Y4S alloy. The corresponding tenSile properties in the as-cast condition are 260 MPa (YS), 326 MPa (UTS), and 1.50% (%El), compared to 145 MPa (YS), 232 MPa (UTS), and 2.4% (%El) for the base alloy with no Mg. At 520 °C solution temperature, incipient melting of Al5Mg8Cu2Si6 phase and undissolved block-like Al2Cu takes place. At the same time, the Si Particles become rounder. Therefore, the tenSile properties of Mg-containing alloys are controlled by the combined effects of dissolution of Al2Cu, incipient melting of Al5Mg8Cu2Si6 phase and Al2Cu phase, as well as the Si Particle characteristics.

  • effect of grain refining and sr modification interactions on the impact toughness of al Si mg cast alloys
    Materials & Design, 2014
    Co-Authors: A M Samuel, H W Doty, S Valtierra, F H Samuel
    Abstract:

    Abstract The present work investigates the effects of various types of grain refiners on the impact properties of Sr-modified A356.2 alloys in both the as-cast and heated-treated conditions. The results showed that the addition of Ti and B greatly improves the alloy toughness, but only when the alloy was in a fully modified state; moreover, the right type of master alloy and addition levels must be used. The highest values of the total absorbed energy recorded for T6-tempered alloys were obtained uSing Al–5%Ti–1%B and Al–10%Ti master alloys in addition to 0.04%Ti. A Significant deterioration in the impact properties is observed due to the Sr–B interaction (in some cases). The improvements in toughness may be attributed to the change in Si Particle morphology as well as to the dissolution and fragmentation of a number of the intermetallics formed during the T6 temper.

  • the effects of mischmetal cooling rate and heat treatment on the eutectic Si Particle characteristics of a319 1 a356 2 and a413 1 al Si casting alloys
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008
    Co-Authors: El O Sebaie, A M Samuel, F H Samuel, H W Doty
    Abstract:

    Abstract The effects of mischmetal, cooling rate and heat treatment on the eutectic Si Particle characteristics of A319.1, A356.2 and A413.1 Al–Si casting alloys were investigated and recorded for this study. Mischmetal was added to the alloys in the form of Al–20% mischmetal master alloy to produce four levels of mischmetal addition (0, 2, 4 and 6 wt%). The alloys were also modified with strontium (∼250 ppm) to study the combined modification effect of Sr and mischmetal at both high and low cooling rates corresponding to dendrite arm spacings of ∼40 and 120 μm, respectively. The alloys were subjected to solution heat treatment (495 °C/8 h for A319.1 and A413.1 alloys, and 540 °C/8 h for A356.2 alloy) to investigate its effect on the eutectic Si Particle morphology. An optical microscope-image analyzer system was used to measure the characteristics of eutectic Si Particles such as area, length, roundness ratio and aspect ratio, in order to monitor the modifying effect of mischmetal, as well as the combined modification effect of mischmetal and Sr. For each alloy sample examined, the Si Particle characteristics were measured over an area of 50 fields and the average Particle characteristics were thus determined. The eutectic Si Particle measurements revealed that partial modification was obtained with the addition of mischmetal while full modification was achieved with the addition of Sr in the as-cast condition, at both high and low cooling rates. The interaction between Sr and mischmetal was observed to weaken the effectiveness of Sr as a Si Particle-modifying agent. This effect was particularly evident at the low cooling rate. During solution heat treatment, the eutectic Si Particles in the non-modified alloys underwent rapid coarsening, otherwise known as Ostwald ripening, whereas those in the Sr-modified alloys exhibited a high spheroidization rate. The coarsening was evidenced by an increase in the thickness of the Si Particles, clearly observed in the A356.2 alloy at both cooling rates. In the alloys containing mischmetal, the presence of this mixture of rare earth elements reduced the coarsening of the Si Particles slightly.

  • effect of metallurgical parameters on the hardness and microstructural characterization of as cast and heat treated 356 and 319 aluminum alloys
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007
    Co-Authors: F H Samuel, Mahmoud M Tash, F Mucciardi, H W Doty
    Abstract:

    Abstract The present study was undertaken to investigate the effect of metallurgical parameters on the hardness and microstructural characterization of as-cast and heat-treated 356 and 319 alloys, with the aim of adjusting these parameters to produce castings of suitable hardness and Fe-intermetallic volume fractions for subsequent use in studies relating to the machinability of these alloys. By measuring the amount of Fe- and Cu-intermetallics formed and the changes in the eutectic Si Particle characteristics resulting from alloying additions (Fe, Mn, Mg), Sr-modification, and heat treatment of the 356 and 319 alloys, and the corresponding hardness values, it was posSible to determine which conditions or metallurgical parameters yielded the required Fe-intermetallic volume fractions of 2 and 5% and hardness levels of 85 and 115 BHN. These levels conform to the most common levels observed in the commercial application of these alloys. The 356 and 319 alloys were examined in the as-cast and heat-treated conditions, uSing different combinations of grain refining, Sr-modification, and alloying additions. Aging treatments were carried out at 155, 180, 200, and 220 °C for 4 h, followed by air cooling, as well as at 180 and 220 °C for 2, 4, 6, and 8 h to determine conditions under which the specified hardness levels of 85 and 115 HBN could be obtained. Hardness measurements were carried out uSing a Brinell hardness tester. Peak hardness was observed in the 356 and 319 alloys at different aging conditions, depending upon the Fe-intermetallic type present in the alloy and whether the alloy was modified or not. Aging at 220 °C revealed a hardness peak at 2 h aging time in both 356 and 319 alloys. Addition of Mg to 319 alloys produced a remarkable increase in hardness at all aging temperatures. This may be explained on the baSis of the combined effect of Cu- and Mg-intermetallics in the 319 alloys, where hardening during aging occurs by the cooperative precipitation of Al 2 Cu and Mg 2 Si phase Particles [P. Ouellet, F.H. Samuel, J. Mater. Sci. 34 (1999) 4671–4697; P.N. Crepeau, S.D. Antolovich, J.A. Worden, AFS Trans. 98 (1990) 813–822]. Iron-intermetallic volume fraction measurements were carried out on polished specimens of the 356 and 319 alloys uSing electron probe microanalySis, for both as-cast and heat-treated conditions. Copper-intermetallic volume fractions were also measured for the 319 alloys to determine the amount of undissolved CuAl 2 phase. It was observed that the unmodified alloys displayed higher Fe-intermetallic surface fractions than the modified alloys. The copper-intermetallic surface fractions, on the other hand, were higher in the Sr-modified alloys than the unmodified alloys. These observations may be attributed to the effect of Sr on (a) the dissolution and fragmentation of the β-Fe-intermetallics in the matrix, the solution heat treatment also contributing to this effect; (b) severe segregation of Al 2 Cu and Al 2 MgCu phases in areas away from the eutectic Si regions, slowing down the dissolution of the Al 2 Cu phase during solution treatment; (c) altering the precipitation sequence of α-Al 15 (Fe, Mn) 3 Si 2 from post-dendritic to pre-dendritic, the latter being expected to improve the alloy strength due to its precipitation within the α-Al dendrites.

Murat Tiryakioglu - One of the best experts on this subject based on the ideXlab platform.

  • Si Particle Size and aspect ratio distributions in an al 7 Si 0 6 mg alloy during solution treatment
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008
    Co-Authors: Murat Tiryakioglu
    Abstract:

    Abstract D357 castings were solution treated at 540 °C for 1, 4, 16 and 64 h. The Size and aspect ratio data were collected uSing digital image analySis. The data indicate that the Particles follow the LSW coarsening after a solution treatment time of 4 h. The Particle Size distributions are Significantly wider than that suggested by the LSW distribution and the one suggested by Llorca. Among the distributions tested, two- and three-parameter lognormal distribution provided the best fits for Size and aspect ratio, respectively.

  • the effect of solution treatment and artificial aging on the work hardening characteristics of a cast al 7 Si 0 6 mg alloy
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2006
    Co-Authors: Murat Tiryakioglu
    Abstract:

    Abstract Al–7%Si–0.6%Mg (D357) alloy castings were heat treated for four different solution treatment times at 540 °C (1, 4, 16 and 64 h) and Six different artificial aging times at 160 °C (0, 2.5, 5, 10, 20 and 40 h). TenSile work hardening characteristics were investigated by Kocks–Mecking plots for each specimen. The effects of Si Particle morphology (solution treatment) and matrix strength (aging) on Kocks–Mecking (Stage III) work hardening model parameters were studied. It was found that (i) the shearing–bypasSing tranSition in β″ precipitates takes place at or slightly after peak strength, and (ii) solution treatment, i.e., the Size and aspect ratio of Si Particles, has a profound effect on the Stage III work hardening characteristics of D357.

Mihee Park - One of the best experts on this subject based on the ideXlab platform.

  • flexible dimenSional control of high capacity li ion battery anodes from 0d hollow to 3d porous germanium nanoParticle assemblies
    Advanced Materials, 2010
    Co-Authors: Mihee Park
    Abstract:

    Adv. Mater. 2010, 22, 415–418 2010 WILEY-VCH Verlag Gm Porous nanostructured metals have been investigated for their various applications, such as catalysts, gas and thermal sensors, and electronics. Approaches for preparing such porous materials include coating templates and removing these templates by etching or thermal annealing. Recently, the depoSition of metals on porous biomineral templates (diatoms with porous Silica frustules with a 3D structure) to acquire 3D porous metals has been reported. Another approach to 3D porous metal or metal oxides has been widely used in photonic devices, and this method involves the infiltration of a Silica template within the void spaces of a face-centered cubic colloidal crystal mode of microspheres (opals). USing this method, Ge has been syntheSized through a two-step process conSisting of hydrolySis of an alkoxide and subsequent reduction to metallic Ge. On the other hand, CVD or electrodepoSition uSing Ge2H6 [15] or GeCl4 [16] above 300 8C has also been used, but GeO2 formation from the reaction between Ge and SiO2 was inevitable. Oxides resulted in the formation of a lithium inactive Li2O phase during the first charge (lithium insertion), leading to a decrease in coulombic efficiency. Furthermore, the preparation of the Silica opal template was very complex and laborious. Recently, Cho and co-workers reported a Simple synthetic method for preparing 3D porous Si Particles, whereby the phySical blending of a SiO2 template and a Si precursor leads to a 3D porous bulk Si Particle with a pore wall thickness and a Particle Size of >40 nm and >10mm, respectively. Currently, many projects focus on alternative high-capacity anode materials for the replacement of currently used graphite electrodes in Li secondary batteries. Such candidates are Si, Sn, and Ge. The latter metal has also been in the spotlight because of its high theoretical capacity (ca. 1600mAhg ) and faster Li diffuSivity than Si (400 times faster). However, mechanical stresses, related to the volume changes during lithium alloying and leaching (Mþ xLiþþ xe $ LixM (0 x 4.4)), induce a rapid decay in mechanical stability. As a consequence, the electrode suffers from cracking and crumbling (pulverization) as well as from a consequent loss of electronic interParticle contact and exfoliation from the current collector. In this regard, porous nanoParticles with ordered pore arrays are the best candidates to minimize and accommodate the volume changes of the metals during lithium alloying and leaching. To date, there have been no reports on the syntheSis of 0D and 3D porous Ge nanoParticle assemblies fabricated by controlling the amount of template and Ge precursors used. Herein, we report the syntheSis and electrochemical properties of 0D hollow and 3D porous Ge nanoParticle assemblies prepared by etching a thermally annealed phySical mixture of SiO2 and ethyl-capped Ge gels at 800 8C. By tuning the weight fraction of ethyl-Ge gels relative to the amount of SiO2, either 0D hollow nanoParticles or 3D porous Ge nanoParticle assemblies (Scheme 1) can be obtained. The 3D porous Ge retains almost 99% of its capacity after 100 cycles at 1C rate (1⁄4 1.6Ag ). Figure 1a shows the SEM image of the SiO2 templates, which conSists of relatively monodispersed nanospheres with a diameter of about 200 nm. USing a weight fraction of SiO2 and the ethyl-capped Ge gel solution of 7:3 (SiO2/Ge), hollow Ge Particles with a Size of around 220 nm were obtained and no ordering between the nanoParticles was observed (Fig. 1b). Upon increaSing the ratio to 5:5, a Similar Particle morphology to the 7:3 ratio (SiO2/Ge) was observed, but the regularity between the Particles appeared to increase (see Supporting Information, Fig. S1). When the weight ratio was increased to 3:7 (SiO2/Ge), relatively well-ordered 3D porous nanoParticle assemblies with a pore Size of around 200 nm and a wall thickness of 20 nm were observed (Fig. 1c and d). The difference between the 0D hollow and 3D porous Ge assemblies is their regularity as shown in Figure 1. 0D hollow Ge nanoParticles could be dispersed into a solvent, whereas 3D porous Ge nanoParticles maintained their form when immersed into a solvent. In contrast to previously reported 3D porous Si bulk Particles with a Similar weight fraction, the pore wall thickness of our assemblies is half the Size and the presence of ordered porous nanoParticles can be observed. This difference can be associated to the treatment in vacuum for 10min to introduce a homogenous distribution of the gel solution between the Particles. The X-ray diffraction (XRD) pattern of both the 0D and 3D Ge nanoParticle assemblies confirmed the presence of the cubic diamond phase (Supporting Information, Fig. S2).

  • flexible dimenSional control of high capacity li ion battery anodes from 0d hollow to 3d porous germanium nanoParticle assemblies
    Advanced Materials, 2010
    Co-Authors: Mihee Park
    Abstract:

    Adv. Mater. 2010, 22, 415–418 2010 WILEY-VCH Verlag Gm Porous nanostructured metals have been investigated for their various applications, such as catalysts, gas and thermal sensors, and electronics. Approaches for preparing such porous materials include coating templates and removing these templates by etching or thermal annealing. Recently, the depoSition of metals on porous biomineral templates (diatoms with porous Silica frustules with a 3D structure) to acquire 3D porous metals has been reported. Another approach to 3D porous metal or metal oxides has been widely used in photonic devices, and this method involves the infiltration of a Silica template within the void spaces of a face-centered cubic colloidal crystal mode of microspheres (opals). USing this method, Ge has been syntheSized through a two-step process conSisting of hydrolySis of an alkoxide and subsequent reduction to metallic Ge. On the other hand, CVD or electrodepoSition uSing Ge2H6 [15] or GeCl4 [16] above 300 8C has also been used, but GeO2 formation from the reaction between Ge and SiO2 was inevitable. Oxides resulted in the formation of a lithium inactive Li2O phase during the first charge (lithium insertion), leading to a decrease in coulombic efficiency. Furthermore, the preparation of the Silica opal template was very complex and laborious. Recently, Cho and co-workers reported a Simple synthetic method for preparing 3D porous Si Particles, whereby the phySical blending of a SiO2 template and a Si precursor leads to a 3D porous bulk Si Particle with a pore wall thickness and a Particle Size of >40 nm and >10mm, respectively. Currently, many projects focus on alternative high-capacity anode materials for the replacement of currently used graphite electrodes in Li secondary batteries. Such candidates are Si, Sn, and Ge. The latter metal has also been in the spotlight because of its high theoretical capacity (ca. 1600mAhg ) and faster Li diffuSivity than Si (400 times faster). However, mechanical stresses, related to the volume changes during lithium alloying and leaching (Mþ xLiþþ xe $ LixM (0 x 4.4)), induce a rapid decay in mechanical stability. As a consequence, the electrode suffers from cracking and crumbling (pulverization) as well as from a consequent loss of electronic interParticle contact and exfoliation from the current collector. In this regard, porous nanoParticles with ordered pore arrays are the best candidates to minimize and accommodate the volume changes of the metals during lithium alloying and leaching. To date, there have been no reports on the syntheSis of 0D and 3D porous Ge nanoParticle assemblies fabricated by controlling the amount of template and Ge precursors used. Herein, we report the syntheSis and electrochemical properties of 0D hollow and 3D porous Ge nanoParticle assemblies prepared by etching a thermally annealed phySical mixture of SiO2 and ethyl-capped Ge gels at 800 8C. By tuning the weight fraction of ethyl-Ge gels relative to the amount of SiO2, either 0D hollow nanoParticles or 3D porous Ge nanoParticle assemblies (Scheme 1) can be obtained. The 3D porous Ge retains almost 99% of its capacity after 100 cycles at 1C rate (1⁄4 1.6Ag ). Figure 1a shows the SEM image of the SiO2 templates, which conSists of relatively monodispersed nanospheres with a diameter of about 200 nm. USing a weight fraction of SiO2 and the ethyl-capped Ge gel solution of 7:3 (SiO2/Ge), hollow Ge Particles with a Size of around 220 nm were obtained and no ordering between the nanoParticles was observed (Fig. 1b). Upon increaSing the ratio to 5:5, a Similar Particle morphology to the 7:3 ratio (SiO2/Ge) was observed, but the regularity between the Particles appeared to increase (see Supporting Information, Fig. S1). When the weight ratio was increased to 3:7 (SiO2/Ge), relatively well-ordered 3D porous nanoParticle assemblies with a pore Size of around 200 nm and a wall thickness of 20 nm were observed (Fig. 1c and d). The difference between the 0D hollow and 3D porous Ge assemblies is their regularity as shown in Figure 1. 0D hollow Ge nanoParticles could be dispersed into a solvent, whereas 3D porous Ge nanoParticles maintained their form when immersed into a solvent. In contrast to previously reported 3D porous Si bulk Particles with a Similar weight fraction, the pore wall thickness of our assemblies is half the Size and the presence of ordered porous nanoParticles can be observed. This difference can be associated to the treatment in vacuum for 10min to introduce a homogenous distribution of the gel solution between the Particles. The X-ray diffraction (XRD) pattern of both the 0D and 3D Ge nanoParticle assemblies confirmed the presence of the cubic diamond phase (Supporting Information, Fig. S2).

A M Samuel - One of the best experts on this subject based on the ideXlab platform.

  • role of modification and melt thermal treatment processes on the microstructure and tenSile properties of al Si alloys
    Materials & Design, 2015
    Co-Authors: A M Samuel, H W Doty, G H Garzaelizondo, F H Samuel
    Abstract:

    Abstract The present study was performed on an Al–7%Si–0.35%Mg alloy (A356 alloy) with the primary objective of improving the alloy performance through modification of the microstructure. Ultimate tenSile strength (UTS) can be improved by the addition of strontium (Sr), superheating or Sr modified melt thermal treatment. The melt thermal treatment process alone has no apparent influence on the UTS. Both Sr-modified and Sr-modified melt thermal treatment can help to improve the percentage elongation of A356 alloy castings. A higher percentage elongation can be reached at a higher cooling rate. The effect of solution heat treatment on the tenSile properties of various A356.2 alloy castings can be summed up as follows: (i) the yield strength of the A356.2 castings is Significantly improved after 8 h solution heat treatment due to the precipitation of Mg2Si, (ii) the yield strength remains more or less the same with further increase in solution treatment time to 80 h, and (iii) the UTS is greatly improved within the first 8 h of solution heat treatment and continues up to 80 h, where this improvement is attributed to Mg2Si precipitation, dissolution of Silicon within the Al-matrix and change in the Si Particle morphology (spheroidization). The ductility of the A356.2 alloys can also be conSiderably enhanced with solution heat treatment (e.g. from ∼6% in the non-modified casting in the as-cast condition to ∼10% after 80 h solution treatment).

  • optimizing the tenSile properties of al Si cu mg 319 type alloys role of solution heat treatment
    Materials & Design, 2014
    Co-Authors: Y M Han, A M Samuel, H W Doty, S Valtierra, F H Samuel
    Abstract:

    Abstract The work presented in this study was carried out on Al–Si–Cu–Mg 319-type alloys to investigate the role of solution heat treatment on the dissolution of copper-containing phases (CuAl2 and Al5Mg8Cu2Si6) in 319-type alloys containing different Mg levels, to determine the optimum solution heat treatment with respect to the occurrence of incipient melting, in relation to the alloy properties. Two series of alloys were investigated: a series of experimental Al–7 wt% Si–3.5 wt% Cu alloys containing 0, 0.3, and 0.6 wt% Mg levels. The second series was based on industrial B319 alloy. The present results show that optimum combination of Mg and Sr in this study is 0.3 wt% Mg with 150 ppm Sr, viz. for the Y4S alloy. The corresponding tenSile properties in the as-cast condition are 260 MPa (YS), 326 MPa (UTS), and 1.50% (%El), compared to 145 MPa (YS), 232 MPa (UTS), and 2.4% (%El) for the base alloy with no Mg. At 520 °C solution temperature, incipient melting of Al5Mg8Cu2Si6 phase and undissolved block-like Al2Cu takes place. At the same time, the Si Particles become rounder. Therefore, the tenSile properties of Mg-containing alloys are controlled by the combined effects of dissolution of Al2Cu, incipient melting of Al5Mg8Cu2Si6 phase and Al2Cu phase, as well as the Si Particle characteristics.

  • effect of grain refining and sr modification interactions on the impact toughness of al Si mg cast alloys
    Materials & Design, 2014
    Co-Authors: A M Samuel, H W Doty, S Valtierra, F H Samuel
    Abstract:

    Abstract The present work investigates the effects of various types of grain refiners on the impact properties of Sr-modified A356.2 alloys in both the as-cast and heated-treated conditions. The results showed that the addition of Ti and B greatly improves the alloy toughness, but only when the alloy was in a fully modified state; moreover, the right type of master alloy and addition levels must be used. The highest values of the total absorbed energy recorded for T6-tempered alloys were obtained uSing Al–5%Ti–1%B and Al–10%Ti master alloys in addition to 0.04%Ti. A Significant deterioration in the impact properties is observed due to the Sr–B interaction (in some cases). The improvements in toughness may be attributed to the change in Si Particle morphology as well as to the dissolution and fragmentation of a number of the intermetallics formed during the T6 temper.

  • the effects of mischmetal cooling rate and heat treatment on the eutectic Si Particle characteristics of a319 1 a356 2 and a413 1 al Si casting alloys
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008
    Co-Authors: El O Sebaie, A M Samuel, F H Samuel, H W Doty
    Abstract:

    Abstract The effects of mischmetal, cooling rate and heat treatment on the eutectic Si Particle characteristics of A319.1, A356.2 and A413.1 Al–Si casting alloys were investigated and recorded for this study. Mischmetal was added to the alloys in the form of Al–20% mischmetal master alloy to produce four levels of mischmetal addition (0, 2, 4 and 6 wt%). The alloys were also modified with strontium (∼250 ppm) to study the combined modification effect of Sr and mischmetal at both high and low cooling rates corresponding to dendrite arm spacings of ∼40 and 120 μm, respectively. The alloys were subjected to solution heat treatment (495 °C/8 h for A319.1 and A413.1 alloys, and 540 °C/8 h for A356.2 alloy) to investigate its effect on the eutectic Si Particle morphology. An optical microscope-image analyzer system was used to measure the characteristics of eutectic Si Particles such as area, length, roundness ratio and aspect ratio, in order to monitor the modifying effect of mischmetal, as well as the combined modification effect of mischmetal and Sr. For each alloy sample examined, the Si Particle characteristics were measured over an area of 50 fields and the average Particle characteristics were thus determined. The eutectic Si Particle measurements revealed that partial modification was obtained with the addition of mischmetal while full modification was achieved with the addition of Sr in the as-cast condition, at both high and low cooling rates. The interaction between Sr and mischmetal was observed to weaken the effectiveness of Sr as a Si Particle-modifying agent. This effect was particularly evident at the low cooling rate. During solution heat treatment, the eutectic Si Particles in the non-modified alloys underwent rapid coarsening, otherwise known as Ostwald ripening, whereas those in the Sr-modified alloys exhibited a high spheroidization rate. The coarsening was evidenced by an increase in the thickness of the Si Particles, clearly observed in the A356.2 alloy at both cooling rates. In the alloys containing mischmetal, the presence of this mixture of rare earth elements reduced the coarsening of the Si Particles slightly.

  • parameters controlling the performance of aa319 type alloys part ii impact properties and fractography
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2004
    Co-Authors: A M Samuel, F H Samuel, H W Doty, C Ravindran, S Valtierra
    Abstract:

    Abstract The Charpy impact energy of Al–Si–Cu AA319-type alloys was measured in terms of the total absorbed energy. The Charpy specimens were machined from end-chilled castings to incorporate the effect of cooling rate on the impact properties. Unnotched specimens were used to increase the accuracy of the measurements, and to emphaSize the effect of microstructure. The influence of the microconstituents on the impact strength was investigated by adding various alloying elements (i.e. Sr, Fe, and P) to the AA319 base alloy, and applying two different heat treatments (T5, and T6). The results show that strontium-modification enhances the impact properties, so that the Sr-modified AA319 alloy exhibits the highest impact properties compared to the base, and other alloys at any given dendrite arm spacing (DAS). The impact energy increases with increase in cooling rate, while iron, and phosphorus additions have a detrimental influence due, respectively, to the formation of β-Al5FeSi, and phosphorus oxide Particles during solidification. T6 treatment asSists in the even distribution, and dissolution of the microconstituents (including the block-like CuAl2 Particles) into the aluminum matrix. With more Cu available for strengthening during aging, the impact toughness is greatly enhanced. In the unmodified AA319 base alloy, crack initiation, and propagation occur mainly through Si-Particle fracture, and the mechanism of void coalescence. In the Sr-modified, 1.2% Fe-containing 319 alloys, however, crack initiation takes place through fragmentation of β-Al5FeSi, Si, and CuAl2 or Cu2FeAl7 Particles. Crack propagation occurs through cleavage of the β-Fe platelets, and fracture of the Cu-intermetallics, and brittle Si Particles. Such samples exhibit very low impact energies.