The Experts below are selected from a list of 15519 Experts worldwide ranked by ideXlab platform

Mark A Gibson - One of the best experts on this subject based on the ideXlab platform.

  • the influence of minor mn additions on Creep Resistance of die cast mg al re alloys
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017
    Co-Authors: Suming Zhu, Jian Feng Nie, Mark A Gibson, Trevor B Abbott, Mark Alan Easton
    Abstract:

    Abstract Magnesium alloys normally contain minor amounts (~0.3%) of Mn to achieve improved corrosion Resistance by controlling the level of Fe during melting. It has been reported recently that minor Mn additions can significantly enhance the age hardenability of die-cast Mg–Al–RE alloys. This paper reports that minor Mn additions also have a remarkable influence in improving the Creep Resistance of die-cast Mg–Al–RE alloys. The secondary Creep rate of Mg–4Al–3La alloy at 175 °C/75 MPa is reduced by more than three orders of magnitude (from 5.9×10 -7  s -1 to 3.0×10 -10  s -1 ) by the addition of 0.32% Mn. The improvement in Creep Resistance is associated with the dynamic precipitation of nanoscale Al–Mn particles during Creep. The findings in this work shed new light on Creep Resistance of Mg–Al based alloys.

  • on the microstructural factors affecting Creep Resistance of die cast mg la rare earth nd y or gd alloys
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016
    Co-Authors: Serge Gavras, Jian Feng Nie, Suming Zhu, Mark A Gibson, Mark Alan Easton
    Abstract:

    Abstract Creep properties of high-pressure die-cast Mg–La-RE (Nd, Y or Gd) alloys, varying in ternary RE additions and in different heat treatment conditions, have been investigated. Through the use of short-term solution treatments (1 h at 520 °C) it was shown that the continuous intermetallic phase present in the eutectic at grain boundaries became discontinuous. This effect, in combination with the likely removal of the localised region of supersaturated solute in solid solution near grain boundaries, reduced the Creep Resistance. When relatively high concentrations of ternary alloying additions were used, solid solution strengthening and precipitation hardening appeared to compensate for the negative effect of reduced grain boundary reinforcement. Microstructural investigation revealed that Nd-containing alloys had fewer and larger dynamic precipitates present in the α-Mg matrix following Creep testing at 177 °C and 90 MPa. It was concluded that grain boundary reinforcement in combination with the thermal stability of the precipitates formed, which is ultimately related to the diffusivity of solute in solid solution, are also contributing factors to Creep Resistance.

  • the influence of individual rare earth elements la ce or nd on Creep Resistance of die cast magnesium alloy ae44
    Advanced Engineering Materials, 2016
    Co-Authors: Suming Zhu, Mark A Gibson, Mark Alan Easton, Trevor B Abbott, Jian Feng Nie
    Abstract:

    Three AE44 (Mg-4Al-4RE, wt%) alloys are prepared from individual RE elements, i.e., La, Ce, or Nd, by high-pressure die casting and the Creep Resistance of these alloys is evaluated. It is shown that the choice of RE elements has a significant influence on the Creep Resistance of AE44, with the La-containing alloy being the most Creep-resistant while the Nd-containing alloy the least Creep-resistant. Microstructural examinations suggest that the observed difference in Creep Resistance cannot be accounted for by the thermal stability of the Al11RE3 phase, as reported previously, but can be related to the volume fraction of intermetallic phases and the content of manganese.

  • evaluation of magnesium die casting alloys for elevated temperature applications microstructure tensile properties and Creep Resistance
    Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2015
    Co-Authors: Mark Alan Easton, Matthew S Dargusch, Mark A Gibson, Trevor B Abbott, Norbert Hort
    Abstract:

    Several families of magnesium die-casting alloys have been developed to operate at the elevated temperatures experienced in automotive powertrain applications. Most alloys are based on the Mg-Al system with alloying additions such as silicon, strontium, calcium, and rare earth elements (RE), although alloys with RE as the primary alloying constituent are also considered. This work presents an evaluation of the tensile properties and Creep Resistance of the most common magnesium die-casting alloys, in conjunction with the analysis of microstructure. The alloys investigated include AS31 (Mg-3Al-1Si), AJ52 (Mg-5Al-2Sr), MRI153A (Mg-9Al-1Ca-0.1Sr), MRI153M (Mg-8Al-1Ca-0.3Sr), MRI230D (Mg-6.5Al-2Ca-1Sn-0.3Sr), AXJ530 (Mg-5Al-3Ca-0.2Sr), AE42 (Mg-4Al-2RE), AE44 (Mg-4Al-4RE), and AM-HP2+ (Mg-3.5RE-0.4Zn). It is shown that, among the various alloys evaluated, MRI230D, AXJ530, and AM-HP2+ have higher yield strength than the Al alloy A380, but the ductility is relatively low at room temperature for these alloys. In contrast, AS31 and the AE series alloys have very good room temperature ductility, but their yield strength is lower than that of A380. In terms of Creep Resistance, MRI230D, AXJ530, AE44, and AM-HP2+ are all comparable to the Al alloy counterpart at 423 K and 448 K (150 °C and 175 °C). Microstructural factors that are most important to the strength and Creep Resistance of the Mg die-casting alloys are discussed.

  • the relationship between microstructure and Creep Resistance in die cast magnesium rare earth alloys
    Scripta Materialia, 2010
    Co-Authors: Suming Zhu, Mark A Gibson, Mark Alan Easton, Jian Nie
    Abstract:

    Abstract Die-cast Mg–La, Mg–Ce and Mg–Nd binary alloys varying in composition have been used to investigate Creep Resistance and its relation to microstructure. The remarkable differences in Creep Resistance observed in these alloys are shown to be related to different levels of rare earth (RE) solute supersaturated in the α-Mg matrix. The results seem to suggest that strengthening of the α-Mg matrix by solid solution and/or precipitation is more important than grain boundary reinforcement by intermetallic phases for the Creep Resistance of Mg–RE alloys.

Suming Zhu - One of the best experts on this subject based on the ideXlab platform.

  • the influence of minor mn additions on Creep Resistance of die cast mg al re alloys
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017
    Co-Authors: Suming Zhu, Jian Feng Nie, Mark A Gibson, Trevor B Abbott, Mark Alan Easton
    Abstract:

    Abstract Magnesium alloys normally contain minor amounts (~0.3%) of Mn to achieve improved corrosion Resistance by controlling the level of Fe during melting. It has been reported recently that minor Mn additions can significantly enhance the age hardenability of die-cast Mg–Al–RE alloys. This paper reports that minor Mn additions also have a remarkable influence in improving the Creep Resistance of die-cast Mg–Al–RE alloys. The secondary Creep rate of Mg–4Al–3La alloy at 175 °C/75 MPa is reduced by more than three orders of magnitude (from 5.9×10 -7  s -1 to 3.0×10 -10  s -1 ) by the addition of 0.32% Mn. The improvement in Creep Resistance is associated with the dynamic precipitation of nanoscale Al–Mn particles during Creep. The findings in this work shed new light on Creep Resistance of Mg–Al based alloys.

  • on the microstructural factors affecting Creep Resistance of die cast mg la rare earth nd y or gd alloys
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016
    Co-Authors: Serge Gavras, Jian Feng Nie, Suming Zhu, Mark A Gibson, Mark Alan Easton
    Abstract:

    Abstract Creep properties of high-pressure die-cast Mg–La-RE (Nd, Y or Gd) alloys, varying in ternary RE additions and in different heat treatment conditions, have been investigated. Through the use of short-term solution treatments (1 h at 520 °C) it was shown that the continuous intermetallic phase present in the eutectic at grain boundaries became discontinuous. This effect, in combination with the likely removal of the localised region of supersaturated solute in solid solution near grain boundaries, reduced the Creep Resistance. When relatively high concentrations of ternary alloying additions were used, solid solution strengthening and precipitation hardening appeared to compensate for the negative effect of reduced grain boundary reinforcement. Microstructural investigation revealed that Nd-containing alloys had fewer and larger dynamic precipitates present in the α-Mg matrix following Creep testing at 177 °C and 90 MPa. It was concluded that grain boundary reinforcement in combination with the thermal stability of the precipitates formed, which is ultimately related to the diffusivity of solute in solid solution, are also contributing factors to Creep Resistance.

  • the influence of individual rare earth elements la ce or nd on Creep Resistance of die cast magnesium alloy ae44
    Advanced Engineering Materials, 2016
    Co-Authors: Suming Zhu, Mark A Gibson, Mark Alan Easton, Trevor B Abbott, Jian Feng Nie
    Abstract:

    Three AE44 (Mg-4Al-4RE, wt%) alloys are prepared from individual RE elements, i.e., La, Ce, or Nd, by high-pressure die casting and the Creep Resistance of these alloys is evaluated. It is shown that the choice of RE elements has a significant influence on the Creep Resistance of AE44, with the La-containing alloy being the most Creep-resistant while the Nd-containing alloy the least Creep-resistant. Microstructural examinations suggest that the observed difference in Creep Resistance cannot be accounted for by the thermal stability of the Al11RE3 phase, as reported previously, but can be related to the volume fraction of intermetallic phases and the content of manganese.

  • the relationship between microstructure and Creep Resistance in die cast magnesium rare earth alloys
    Scripta Materialia, 2010
    Co-Authors: Suming Zhu, Mark A Gibson, Mark Alan Easton, Jian Nie
    Abstract:

    Abstract Die-cast Mg–La, Mg–Ce and Mg–Nd binary alloys varying in composition have been used to investigate Creep Resistance and its relation to microstructure. The remarkable differences in Creep Resistance observed in these alloys are shown to be related to different levels of rare earth (RE) solute supersaturated in the α-Mg matrix. The results seem to suggest that strengthening of the α-Mg matrix by solid solution and/or precipitation is more important than grain boundary reinforcement by intermetallic phases for the Creep Resistance of Mg–RE alloys.

  • microstructural analysis of the Creep Resistance of die cast mg 4al 2re alloy
    Scripta Materialia, 2008
    Co-Authors: Suming Zhu, Jian Feng Nie, Mark A Gibson, Mark Alan Easton, Trevor B Abbott
    Abstract:

    The microstructure and microstructural stability of die-cast AE42 (Mg–4Al–2RE) alloy were investigated by transmission electron microscopy. It is shown that the formation of Mg17Al12 after ageing at 200 °C is not due to the decomposition of A111RE3 as reported in the literature, but, rather, is associated with the supersaturation of Al solute in the α-Mg matrix. The level of Al solute retained in the α-Mg matrix after die-casting is suggested to be an important factor in influencing Creep Resistance.

Mark Alan Easton - One of the best experts on this subject based on the ideXlab platform.

  • the influence of minor mn additions on Creep Resistance of die cast mg al re alloys
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017
    Co-Authors: Suming Zhu, Jian Feng Nie, Mark A Gibson, Trevor B Abbott, Mark Alan Easton
    Abstract:

    Abstract Magnesium alloys normally contain minor amounts (~0.3%) of Mn to achieve improved corrosion Resistance by controlling the level of Fe during melting. It has been reported recently that minor Mn additions can significantly enhance the age hardenability of die-cast Mg–Al–RE alloys. This paper reports that minor Mn additions also have a remarkable influence in improving the Creep Resistance of die-cast Mg–Al–RE alloys. The secondary Creep rate of Mg–4Al–3La alloy at 175 °C/75 MPa is reduced by more than three orders of magnitude (from 5.9×10 -7  s -1 to 3.0×10 -10  s -1 ) by the addition of 0.32% Mn. The improvement in Creep Resistance is associated with the dynamic precipitation of nanoscale Al–Mn particles during Creep. The findings in this work shed new light on Creep Resistance of Mg–Al based alloys.

  • on the microstructural factors affecting Creep Resistance of die cast mg la rare earth nd y or gd alloys
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016
    Co-Authors: Serge Gavras, Jian Feng Nie, Suming Zhu, Mark A Gibson, Mark Alan Easton
    Abstract:

    Abstract Creep properties of high-pressure die-cast Mg–La-RE (Nd, Y or Gd) alloys, varying in ternary RE additions and in different heat treatment conditions, have been investigated. Through the use of short-term solution treatments (1 h at 520 °C) it was shown that the continuous intermetallic phase present in the eutectic at grain boundaries became discontinuous. This effect, in combination with the likely removal of the localised region of supersaturated solute in solid solution near grain boundaries, reduced the Creep Resistance. When relatively high concentrations of ternary alloying additions were used, solid solution strengthening and precipitation hardening appeared to compensate for the negative effect of reduced grain boundary reinforcement. Microstructural investigation revealed that Nd-containing alloys had fewer and larger dynamic precipitates present in the α-Mg matrix following Creep testing at 177 °C and 90 MPa. It was concluded that grain boundary reinforcement in combination with the thermal stability of the precipitates formed, which is ultimately related to the diffusivity of solute in solid solution, are also contributing factors to Creep Resistance.

  • the influence of individual rare earth elements la ce or nd on Creep Resistance of die cast magnesium alloy ae44
    Advanced Engineering Materials, 2016
    Co-Authors: Suming Zhu, Mark A Gibson, Mark Alan Easton, Trevor B Abbott, Jian Feng Nie
    Abstract:

    Three AE44 (Mg-4Al-4RE, wt%) alloys are prepared from individual RE elements, i.e., La, Ce, or Nd, by high-pressure die casting and the Creep Resistance of these alloys is evaluated. It is shown that the choice of RE elements has a significant influence on the Creep Resistance of AE44, with the La-containing alloy being the most Creep-resistant while the Nd-containing alloy the least Creep-resistant. Microstructural examinations suggest that the observed difference in Creep Resistance cannot be accounted for by the thermal stability of the Al11RE3 phase, as reported previously, but can be related to the volume fraction of intermetallic phases and the content of manganese.

  • evaluation of magnesium die casting alloys for elevated temperature applications microstructure tensile properties and Creep Resistance
    Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2015
    Co-Authors: Mark Alan Easton, Matthew S Dargusch, Mark A Gibson, Trevor B Abbott, Norbert Hort
    Abstract:

    Several families of magnesium die-casting alloys have been developed to operate at the elevated temperatures experienced in automotive powertrain applications. Most alloys are based on the Mg-Al system with alloying additions such as silicon, strontium, calcium, and rare earth elements (RE), although alloys with RE as the primary alloying constituent are also considered. This work presents an evaluation of the tensile properties and Creep Resistance of the most common magnesium die-casting alloys, in conjunction with the analysis of microstructure. The alloys investigated include AS31 (Mg-3Al-1Si), AJ52 (Mg-5Al-2Sr), MRI153A (Mg-9Al-1Ca-0.1Sr), MRI153M (Mg-8Al-1Ca-0.3Sr), MRI230D (Mg-6.5Al-2Ca-1Sn-0.3Sr), AXJ530 (Mg-5Al-3Ca-0.2Sr), AE42 (Mg-4Al-2RE), AE44 (Mg-4Al-4RE), and AM-HP2+ (Mg-3.5RE-0.4Zn). It is shown that, among the various alloys evaluated, MRI230D, AXJ530, and AM-HP2+ have higher yield strength than the Al alloy A380, but the ductility is relatively low at room temperature for these alloys. In contrast, AS31 and the AE series alloys have very good room temperature ductility, but their yield strength is lower than that of A380. In terms of Creep Resistance, MRI230D, AXJ530, AE44, and AM-HP2+ are all comparable to the Al alloy counterpart at 423 K and 448 K (150 °C and 175 °C). Microstructural factors that are most important to the strength and Creep Resistance of the Mg die-casting alloys are discussed.

  • the relationship between microstructure and Creep Resistance in die cast magnesium rare earth alloys
    Scripta Materialia, 2010
    Co-Authors: Suming Zhu, Mark A Gibson, Mark Alan Easton, Jian Nie
    Abstract:

    Abstract Die-cast Mg–La, Mg–Ce and Mg–Nd binary alloys varying in composition have been used to investigate Creep Resistance and its relation to microstructure. The remarkable differences in Creep Resistance observed in these alloys are shown to be related to different levels of rare earth (RE) solute supersaturated in the α-Mg matrix. The results seem to suggest that strengthening of the α-Mg matrix by solid solution and/or precipitation is more important than grain boundary reinforcement by intermetallic phases for the Creep Resistance of Mg–RE alloys.

Jian Feng Nie - One of the best experts on this subject based on the ideXlab platform.

  • the influence of minor mn additions on Creep Resistance of die cast mg al re alloys
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017
    Co-Authors: Suming Zhu, Jian Feng Nie, Mark A Gibson, Trevor B Abbott, Mark Alan Easton
    Abstract:

    Abstract Magnesium alloys normally contain minor amounts (~0.3%) of Mn to achieve improved corrosion Resistance by controlling the level of Fe during melting. It has been reported recently that minor Mn additions can significantly enhance the age hardenability of die-cast Mg–Al–RE alloys. This paper reports that minor Mn additions also have a remarkable influence in improving the Creep Resistance of die-cast Mg–Al–RE alloys. The secondary Creep rate of Mg–4Al–3La alloy at 175 °C/75 MPa is reduced by more than three orders of magnitude (from 5.9×10 -7  s -1 to 3.0×10 -10  s -1 ) by the addition of 0.32% Mn. The improvement in Creep Resistance is associated with the dynamic precipitation of nanoscale Al–Mn particles during Creep. The findings in this work shed new light on Creep Resistance of Mg–Al based alloys.

  • on the microstructural factors affecting Creep Resistance of die cast mg la rare earth nd y or gd alloys
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016
    Co-Authors: Serge Gavras, Jian Feng Nie, Suming Zhu, Mark A Gibson, Mark Alan Easton
    Abstract:

    Abstract Creep properties of high-pressure die-cast Mg–La-RE (Nd, Y or Gd) alloys, varying in ternary RE additions and in different heat treatment conditions, have been investigated. Through the use of short-term solution treatments (1 h at 520 °C) it was shown that the continuous intermetallic phase present in the eutectic at grain boundaries became discontinuous. This effect, in combination with the likely removal of the localised region of supersaturated solute in solid solution near grain boundaries, reduced the Creep Resistance. When relatively high concentrations of ternary alloying additions were used, solid solution strengthening and precipitation hardening appeared to compensate for the negative effect of reduced grain boundary reinforcement. Microstructural investigation revealed that Nd-containing alloys had fewer and larger dynamic precipitates present in the α-Mg matrix following Creep testing at 177 °C and 90 MPa. It was concluded that grain boundary reinforcement in combination with the thermal stability of the precipitates formed, which is ultimately related to the diffusivity of solute in solid solution, are also contributing factors to Creep Resistance.

  • the influence of individual rare earth elements la ce or nd on Creep Resistance of die cast magnesium alloy ae44
    Advanced Engineering Materials, 2016
    Co-Authors: Suming Zhu, Mark A Gibson, Mark Alan Easton, Trevor B Abbott, Jian Feng Nie
    Abstract:

    Three AE44 (Mg-4Al-4RE, wt%) alloys are prepared from individual RE elements, i.e., La, Ce, or Nd, by high-pressure die casting and the Creep Resistance of these alloys is evaluated. It is shown that the choice of RE elements has a significant influence on the Creep Resistance of AE44, with the La-containing alloy being the most Creep-resistant while the Nd-containing alloy the least Creep-resistant. Microstructural examinations suggest that the observed difference in Creep Resistance cannot be accounted for by the thermal stability of the Al11RE3 phase, as reported previously, but can be related to the volume fraction of intermetallic phases and the content of manganese.

  • microstructural analysis of the Creep Resistance of die cast mg 4al 2re alloy
    Scripta Materialia, 2008
    Co-Authors: Suming Zhu, Jian Feng Nie, Mark A Gibson, Mark Alan Easton, Trevor B Abbott
    Abstract:

    The microstructure and microstructural stability of die-cast AE42 (Mg–4Al–2RE) alloy were investigated by transmission electron microscopy. It is shown that the formation of Mg17Al12 after ageing at 200 °C is not due to the decomposition of A111RE3 as reported in the literature, but, rather, is associated with the supersaturation of Al solute in the α-Mg matrix. The level of Al solute retained in the α-Mg matrix after die-casting is suggested to be an important factor in influencing Creep Resistance.

  • precipitation hardened mg ca zn alloys with superior Creep Resistance
    Scripta Materialia, 2005
    Co-Authors: Xiang Gao, Suming Zhu, Barrington Charles Muddle, Jian Feng Nie
    Abstract:

    Abstract The present paper reports the development of Creep resistant Mg–Ca–Zn based alloys that can be strengthened via age hardening. The Mg–1Ca–1Zn–0.6Zr (wt.%) alloy shows tensile and Creep properties superior to magnesium alloy AZ91. The addition of 1 wt.% Nd to this alloy leads to further improvements in yield strength and Creep Resistance.

David C Dunand - One of the best experts on this subject based on the ideXlab platform.

  • influence of γ raft orientation on Creep Resistance of monocrystalline co based superalloys
    Materialia, 2020
    Co-Authors: Dingwen Chung, David C Dunand
    Abstract:

    Abstract The Creep behavior of a monocrystalline Co-based γ − γ ′ superalloy (Co–28.8Ni–6.2Al–1.8Ti–2.0W–2.7Mo–1.8Nb–0.9Ta, at%) is investigated for two types of rafted γ′-phase: (i) rods parallel (p-type) and (ii) plates perpendicular (n-type) to [001]. The tensile Creep behavior of these two rafted microstructures (and a control unrafted microstructure) is measured at 900 ∘C for various Creep stresses up to a Creep strain of 3%. At the highest stress of 305 MPa (2–4 h Creep to 3% strain), microstructures with n-type rafts provide better Creep Resistance than p-type rafts and unrafted cuboids, consistent with n-type plates oriented perpendicular to stress being more effective at hindering dislocation motion. At an intermediate stress of 250 MPa (10–20 h to 3% Creep strain), n-type rafts still provide the highest overall Creep Resistance, but this effect is less pronounced due to the rafts disintegrating under tensile load. At the lowest stress of 205 MPa (100–220 h to 3% Creep strain), n-type rafts provide the least Creep Resistance, as they first disintegrate then transform into p-type rafts. Specimens starting with p-type rods and unrafted cuboids microstructures show better Creep Resistance, but start to exhibit onset of tertiary Creep from their extensively rafted microstructure. The evolution of Creep strain rate (and thus the time to reach 3% strain) for the three stresses and three microstructures studied is affected by the rafting evolution, as well as γ − γ ′ topological inversion and development of inhomogeneous γ′ spatial distribution.

  • mn and mo additions to a dilute al zr sc er si based alloy to improve Creep Resistance through solid solution and precipitation strengthening
    Acta Materialia, 2020
    Co-Authors: David N Seidman, Anthony De Luca, David C Dunand
    Abstract:

    Abstract Compressive Creep experiments were utilized to investigate the influence of small additions of 0.25 at.% Mn and 0.10 at.% Mo on the Creep Resistance of a cast Al-0.08Zr-0.02Sc-0.01Er-0.10Si at.% alloy. The Mn- and Mo-modified alloy displays significantly enhanced Creep Resistance at 300 and 400 °C, due to solid-solution strengthening and the formation of two types of precipitates: Al3(Zr,Sc,Er)(L12)-nanoprecipitates and α-Al(Mn,Mo)Si submicron platelets or cuboidal-shaped precipitates. The Creep threshold stresses at 300 and 400 °C are 37 and 24 MPa, respectively, versus 19 and 15 MPa for the unmodified alloy. At 300 °C, the Creep exponent n is found to change from 4.4 in the base alloy, to 3 in the modified alloy, consistent with a change from climb- to glide-controlled dislocation Creep. The Mn- and Mo-modified alloy exhibits an as-cast grain-structure, which is finer (~0.35 mm versus 0.6 mm) and more equiaxed grains than the unmodified alloy, which is anticipated to enhance deformation by diffusional-Creep. Nevertheless, diffusional-Creep Resistance at 400 °C remains high for the modified alloy, due to precipitation of submicron α-Al(Mn,Mo)Si-precipitates at grain boundaries (GBs). At 400 °C, the diffusional Creep threshold-stress is ~14 MPa, three times that of the unmodified alloy, which also display fewer and coarser Al3(Zr,Sc,Er)(D023) precipitates at GBs. Creep Resistance in the modified alloy does not deteriorate after 16 days of stress testing at 400 °C, highlighting the excellent coarsening Resistance of the L12- and α-precipitates. This new castable, heat-treatable aluminum alloy therefore represents an important technological advance for utilization at higher temperatures under stress.

  • aging and Creep Resistance of a cast hypoeutectic al 6 9ce 9 3mg wt alloy
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2020
    Co-Authors: David C Dunand
    Abstract:

    Abstract A ternary Al-6.9Ce-9.3Mg (wt.%) hypoeutectic alloy, consisting of equal amounts of α-Al(Mg) solid-solution regions and Al(Mg)-Al11Ce3 eutectic colonies, is investigated in terms of its aging and Creep Resistance. The eutectic regions exhibit a microhardness of 1230 MPa, which is thrice the value of Al-Al11Ce3 eutectic regions in a binary Al-12.5Ce (wt.%) near-eutectic alloy, demonstrating that Mg in solid-solution enhances the strengthening provided by the micron-scale highly-branched Al11Ce3 phase. X-ray diffraction measurements during ambient-temperature tensile testing reveal that load is being transferred from the Al(Mg) matrix to the Al11Ce3 phase, confirming that the fine eutectic microstructure displays composite strengthening in addition to the expected precipitation- and solid-solution strengthening. The hardness remains effectively unchanged after aging at 450 °C for up to 8 weeks, indicating excellent coarsening Resistance of the Al11Ce3 phase. The ternary alloy exhibits Creep Resistance at 300 °C slightly inferior to the near-fully eutectic binary Al-12.5Ce (wt.%) alloy, consistent with the presence of large regions of fast-Creeping primary Al(Mg) solid-solution matrix between the strong Al(Mg)-Al11Ce3 eutectic colonies in the hypoeutectic ternary alloy.

  • cast near eutectic al 12 5 wt ce alloy with high coarsening and Creep Resistance
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2019
    Co-Authors: Yang Liu, Richard A Michi, David C Dunand
    Abstract:

    Abstract This study investigates the Creep behavior of a cast, coarse-grained Al-12.5 wt.% Ce (Al-2.7 at.% Ce) alloy, consisting of an eutectic microstructure (α-Al with ~11 vol.% submicron Al11Ce3 “Chinese script” platelets) with ~3 vol.% primary, micron-scale Al11Ce3 plates. Upon aging at 322 °C for 8 weeks or at 400 °C for 12 weeks, the microhardness of the alloy remains unchanged, demonstrating excellent coarsening Resistance of the strengthening Al11Ce3 phase. In addition, no coarsening of Al11Ce3 is observed metallographically after 3 weeks under compressive loads of 13–70 MPa at 260–350 °C. When tested to failure under a constant tensile stress of 23 MPa at 300 °C, the alloy shows primary, secondary and tertiary Creep regimes, and fails after 19 days at 17% tensile strain, demonstrating both high Creep ductility and high Creep Resistance. Under compressive and tensile Creep conditions, the alloy exhibits high apparent stress exponents (n = 9–11), which translate into threshold stresses for dislocation Creep of 34, 22, and 14 MPa at 260, 300 and 350 °C, respectively. The Creep Resistance of Al-12.5 wt.% Ce is higher than that of Al-Sc-Zr-based alloys (with ~0.3 vol.% of coherent nanoprecipitates) and similar to cast, eutectic Al-6 wt.% Ni (with ~11 vol.% of incoherent Al3Ni micro-fibers). For as-cast grain sizes of 2–3 mm, Al-12.5 wt.% Ce exhibits a transition from dislocation Creep to diffusional Creep at strain rates of ~10−7 s−1, with a threshold stress of 19 MPa in compression at 260 °C and 5 MPa in tension at 300 °C.

  • increasing the Creep Resistance of fe ni al cr superalloys via ti additions by optimizing the b2 l21 ratio in composite nano precipitates
    Acta Materialia, 2018
    Co-Authors: Sung Il Baik, Peter K Liaw, Shao Yu Wang, David C Dunand
    Abstract:

    Abstract The Fe-10Cr-10Ni-6.5Al-3.4Mo-0.25Zr-0.005B (wt.%) ferritic FBB8 superalloy shows good Creep Resistance due to the presence of B2-NiAl precipitates, created upon aging. When titanium is added to the alloy, L21-Ni2TiAl sub-precipitates are developed within the B2-NiAl main precipitates. The microstructural evolutions of these B2/L21 composite precipitates - radius, number density, volume fraction, edge-edge distance, and B2/L21 phase fraction - are studied here for Ti additions spanning up to 4 wt%. As Ti increases from 0 to 3.5 wt%, the alloy strength at ambient temperature rises due to an increase of the L21 sub-precipitate volume fraction within the B2 precipitates, which enhances their lattice misfit with the matrix up to ∼1.26%, and increases coherency strengthening. The alloy strength drops sharply for 4 wt% Ti, consistent with the precipitates losing (i) their composite structure (by becoming a fully L21 phase), (ii) their coherency with the matrix (and showing high dislocation density at their interfaces), and (iii) their coarsening Resistance (increasing abruptly in size). Creep Resistance at 700 oC follows a similar trend (raising from 0 to 3.5 wt% Ti and dropping sharply at 4 wt% Ti); this trend is consistent with the lattice misfit between the coherent B2/L21 precipitates and the matrix increasing with the L21 fraction, thus producing a stronger elastic stress field, which makes the climb bypass of the precipitates by the matrix dislocations more difficult.