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Pamela A. Kobryn - One of the best experts on this subject based on the ideXlab platform.

  • Determination of interface heat-transfer coefficients for Permanent-Mold Casting of Ti-6Al-4V
    Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science, 2001
    Co-Authors: Pamela A. Kobryn, S. L. Semiatin
    Abstract:

    Interface heat-transfer coefficients (h 0) for Permanent-Mold Casting (PMC) of Ti-6Al-4V were established as a function of Casting surface temperature using a calibration-curve technique. Because Mold geometry has a strong effect on h 0, values were determined for both of the two limiting interface types, “shrink-off” and “shrink-on.” For this purpose, Casting experiments with instrumented Molds were performed for cylinder- and pipe-shaped Castings. The measured temperature transients were used in conjunction with two-dimensional (2-D) axisymmetric finite-element method (FEM) simulations to determine h 0(T). For the shrink-off interface type, h 0 was found to decrease linearly from 2000 to 1500 W/m2 K between the liquidus and the solidus, from 1500 to 325 W/m2 K between the solidus and the gap-formation temperature, and at a rate of 0.3 W/m2 K/K thereafter. For the shrink-on interface type, h 0 was found to increase linearly from 2000 to 2500 W/m2 K between the liquidus and the solidus temperatures, from 2500 to 5000 W/m2 K between the solidus and the gap-formation temperature, and to remain constant thereafter. The shrink-on values were up to 100 times the shrink-off values, indicating the importance of accounting for the interface geometry in FEM simulations of this process. The FEM-predicted Casting and Mold temperatures were found to be insensitive to certain changes in the h 0 values and sensitive to others. A comparison to published h 0 values for PMC of aluminum alloys showed some similarities and some differences.

  • Mold wear during Permanent-Mold Casting of Ti-6Al-4V
    Journal of Materials Engineering and Performance, 2001
    Co-Authors: Pamela A. Kobryn, S. L. Semiatin, R. Shivpuri
    Abstract:

    Mold wear during the Casting of Ti-6Al-4V in a Permanent (steel) Mold was investigated using a combination of macro- and micro-scale observations and measurements. For this purpose, a steel Mold with interchangeable inserts of three candidate Mold steels (H13, P20, and 1040) was used. Inserts were removed at regular intervals during Casting under prototype-production conditions and inspected to assess Mold wear. Two major Mold wear types were identified: soldering and “wrinkling.” Soldering was concluded to be a result of local over-heating of the Mold, and wrinkling a result of cyclic stresses caused by a combination of solid-state phase transformations and large temperature gradients. The 1040 inserts performed the best; soldering was less severe and wrinkling did not occur. The better performance of the 1040 inserts was attributed to lower Mold temperatures and thermal gradients due to the higher thermal conductivity of 1040 relative to H13 or P20.

  • Casting of Titanium Alloys.
    1996
    Co-Authors: Pamela A. Kobryn
    Abstract:

    Abstract : The purpose of this paper is to review important aspects of titanium alloy properties, Casting methods, and solidification modeling. The survey provides a background on the physical metallurgy of titanium alloys including alloying and microstructure, the investment Casting and Permanent Mold Casting processes, modeling of microstructure evolution during Casting using both empirical an analytical methods, and macroscopic modeling of Casting using both analytical and numerical methods. Special attention is given to modeling issues and future research issues and approaches.

R. Shivpuri - One of the best experts on this subject based on the ideXlab platform.

  • Mold wear during Permanent-Mold Casting of Ti-6Al-4V
    Journal of Materials Engineering and Performance, 2001
    Co-Authors: Pamela A. Kobryn, S. L. Semiatin, R. Shivpuri
    Abstract:

    Mold wear during the Casting of Ti-6Al-4V in a Permanent (steel) Mold was investigated using a combination of macro- and micro-scale observations and measurements. For this purpose, a steel Mold with interchangeable inserts of three candidate Mold steels (H13, P20, and 1040) was used. Inserts were removed at regular intervals during Casting under prototype-production conditions and inspected to assess Mold wear. Two major Mold wear types were identified: soldering and “wrinkling.” Soldering was concluded to be a result of local over-heating of the Mold, and wrinkling a result of cyclic stresses caused by a combination of solid-state phase transformations and large temperature gradients. The 1040 inserts performed the best; soldering was less severe and wrinkling did not occur. The better performance of the 1040 inserts was attributed to lower Mold temperatures and thermal gradients due to the higher thermal conductivity of 1040 relative to H13 or P20.

S. L. Semiatin - One of the best experts on this subject based on the ideXlab platform.

  • Determination of interface heat-transfer coefficients for Permanent-Mold Casting of Ti-6Al-4V
    Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science, 2001
    Co-Authors: Pamela A. Kobryn, S. L. Semiatin
    Abstract:

    Interface heat-transfer coefficients (h 0) for Permanent-Mold Casting (PMC) of Ti-6Al-4V were established as a function of Casting surface temperature using a calibration-curve technique. Because Mold geometry has a strong effect on h 0, values were determined for both of the two limiting interface types, “shrink-off” and “shrink-on.” For this purpose, Casting experiments with instrumented Molds were performed for cylinder- and pipe-shaped Castings. The measured temperature transients were used in conjunction with two-dimensional (2-D) axisymmetric finite-element method (FEM) simulations to determine h 0(T). For the shrink-off interface type, h 0 was found to decrease linearly from 2000 to 1500 W/m2 K between the liquidus and the solidus, from 1500 to 325 W/m2 K between the solidus and the gap-formation temperature, and at a rate of 0.3 W/m2 K/K thereafter. For the shrink-on interface type, h 0 was found to increase linearly from 2000 to 2500 W/m2 K between the liquidus and the solidus temperatures, from 2500 to 5000 W/m2 K between the solidus and the gap-formation temperature, and to remain constant thereafter. The shrink-on values were up to 100 times the shrink-off values, indicating the importance of accounting for the interface geometry in FEM simulations of this process. The FEM-predicted Casting and Mold temperatures were found to be insensitive to certain changes in the h 0 values and sensitive to others. A comparison to published h 0 values for PMC of aluminum alloys showed some similarities and some differences.

  • Mold wear during Permanent-Mold Casting of Ti-6Al-4V
    Journal of Materials Engineering and Performance, 2001
    Co-Authors: Pamela A. Kobryn, S. L. Semiatin, R. Shivpuri
    Abstract:

    Mold wear during the Casting of Ti-6Al-4V in a Permanent (steel) Mold was investigated using a combination of macro- and micro-scale observations and measurements. For this purpose, a steel Mold with interchangeable inserts of three candidate Mold steels (H13, P20, and 1040) was used. Inserts were removed at regular intervals during Casting under prototype-production conditions and inspected to assess Mold wear. Two major Mold wear types were identified: soldering and “wrinkling.” Soldering was concluded to be a result of local over-heating of the Mold, and wrinkling a result of cyclic stresses caused by a combination of solid-state phase transformations and large temperature gradients. The 1040 inserts performed the best; soldering was less severe and wrinkling did not occur. The better performance of the 1040 inserts was attributed to lower Mold temperatures and thermal gradients due to the higher thermal conductivity of 1040 relative to H13 or P20.

  • Thermal Stress Development During Vacuum Arc Remelting and Permanent Mold Casting of Ingots
    Journal of Manufacturing Science and Engineering-transactions of The Asme, 1998
    Co-Authors: M. K. Alam, S. L. Semiatin, Z. Ali
    Abstract:

    The development of thermal stresses in ingots during the vacuum arc remelting (VAR) as well as specialized Permanent Mold Casting (PMC) process was modeled via numerical solution of the two-dimensional, nonsteady-state heat conduction and stress equilibrium equations. The numerical analysis was carried out in conjunction with experimental studies of the mechanical properties and microstructure of a cracked VAR titanium aluminide ingot. Numerical solutions were obtained for different values of ingot diameter, crucible-ingot interface heat transfer coefficients, and lengths of the melted-and-resolidified ingot. For both VAR and PMC, model predictions revealed that the maximum tensile thermal stresses are developed at the bottom of the ingot; the magnitude of such stresses increases with ingot diameter and the magnitude of the interface heat transfer coefficients. The microstructural analysis of a cracked ingot indicated that the thermal cracking occurred in the temperature range where the alloy has very little ductility. The predicted development of large tensile stresses correlates well with observations of thermal cracking during VAR of near-gamma titanium aluminide alloy ingots. By contrast, the predicted thermal stresses developed during PMC are lower, thus suggesting an attractive alternative to VAR to obtain sound, crack-free ingots.

Daniel Eylon - One of the best experts on this subject based on the ideXlab platform.

  • Microstructure/property studies supporting development of low cost processes for TiAl automotive valves
    MRS Proceedings, 2011
    Co-Authors: P.e. Jones, W.j. Porter, M.m. Keller, Daniel Eylon
    Abstract:

    Lightweight gamma titanium aluminide automotive valves may significantly improve engine performance and fuel economy. However, low cost mass production processes must be developed to realize these gains. Permanent Mold Casting processes and low cost heat treatments are being developed to enable commercial introduction of TiAl automotive valves. Microstructural development, tensile, creep, and high cycle fatigue properties of Permanent Mold Ti-47Al-2Nb-1.75Cr (at%) Castings are compared with investment Castings of similar size. A recommendation is made to use as-HIP Castings for components not designed to damage tolerant criteria. This work was performed as pan of a vertically integrated team effort to transfer aerospace TiAl technology to the automotive market.

  • Development of Permanent-Mold cast TiAl automotive valves
    Intermetallics, 1999
    Co-Authors: Daniel Eylon, M.m. Keller, P.e. Jones
    Abstract:

    Abstract This paper presents the results of an EMTEC funded project to develop low-cost TiAl automotive valves. The alloy studied was Ti-47Al-2Nb-1.75Cr (at %). Over 800 valves were cast, using several variations of the Permanent-Mold process, in a multi-cavity steel Mold. Applying pressure during solidification improved the Casting fill. However, none of the Permanent-Mold Casting methods produced pore free as-cast valves. The as-cast microstructures of valves produced by Permanent-Mold Casting were much finer than investment Castings of similar section sizes. Of the Permanent-Mold Casting methods, the injection cast method exhibited the finest as-cast structure showing a potential for a new high output method for producing fine-grained TiAl components. Room temperature tensile properties of the Permanent-Mold material were superior to those of investment Castings with a similar microstructure. Two sets of valves were road tested for a total of 50000 km with average 2% fuel savings and no valve damage. There is a need to overcome few challenges before this technology can be implemented in the automotive industry.

  • The development of low-cost TiAl automotive valves
    JOM, 1997
    Co-Authors: M.m. Keller, P.e. Jones, W.j. Porter, Daniel Eylon
    Abstract:

    This paper presents the results of a project funded by the Edison Materials Technology Center to develop low-cost titanium aluminide automotive valves. In the course of the project, more than 800 valves were produced using several variations of the Permanent-Mold Casting process. Applying pressure during solidification improved the Casting fill; however, none of the Permanent Mold Casting methods produced pore-free as-cast valves. The as-cast microstructures of the valves were much finer than investmentcast microstructures of similar section sizes. The room-temperature tensile properties of the Permanent Mold Castings were superior to those of investment Castings of a comparable section size.

  • Development of a low cost Permanent Mold Casting process for TiAl automotive valves
    1995
    Co-Authors: P.e. Jones, W.j. Porter, Daniel Eylon, G. Colvin
    Abstract:

    This paper reviews progress made in the development of a low cost Permanent Mold Casting process for TiAl automotive valves. The issues studied include Mold life, Mold/metal reaction, shrinkage void control, dimensional control, and post Casting processes. More than 800 Ti-47Al-2Nb-1.75 Cr (at%) valves were produced by gravity, centrifugal, and pressure assisted Casting methods on a laboratory scale. Microstructures, tensile, creep, and fatigue properties of as-HIP and as-heat treated valves are described. Process scale up challenges identified in this work are also discussed.

P.e. Jones - One of the best experts on this subject based on the ideXlab platform.

  • Microstructure/property studies supporting development of low cost processes for TiAl automotive valves
    MRS Proceedings, 2011
    Co-Authors: P.e. Jones, W.j. Porter, M.m. Keller, Daniel Eylon
    Abstract:

    Lightweight gamma titanium aluminide automotive valves may significantly improve engine performance and fuel economy. However, low cost mass production processes must be developed to realize these gains. Permanent Mold Casting processes and low cost heat treatments are being developed to enable commercial introduction of TiAl automotive valves. Microstructural development, tensile, creep, and high cycle fatigue properties of Permanent Mold Ti-47Al-2Nb-1.75Cr (at%) Castings are compared with investment Castings of similar size. A recommendation is made to use as-HIP Castings for components not designed to damage tolerant criteria. This work was performed as pan of a vertically integrated team effort to transfer aerospace TiAl technology to the automotive market.

  • Development of Permanent-Mold cast TiAl automotive valves
    Intermetallics, 1999
    Co-Authors: Daniel Eylon, M.m. Keller, P.e. Jones
    Abstract:

    Abstract This paper presents the results of an EMTEC funded project to develop low-cost TiAl automotive valves. The alloy studied was Ti-47Al-2Nb-1.75Cr (at %). Over 800 valves were cast, using several variations of the Permanent-Mold process, in a multi-cavity steel Mold. Applying pressure during solidification improved the Casting fill. However, none of the Permanent-Mold Casting methods produced pore free as-cast valves. The as-cast microstructures of valves produced by Permanent-Mold Casting were much finer than investment Castings of similar section sizes. Of the Permanent-Mold Casting methods, the injection cast method exhibited the finest as-cast structure showing a potential for a new high output method for producing fine-grained TiAl components. Room temperature tensile properties of the Permanent-Mold material were superior to those of investment Castings with a similar microstructure. Two sets of valves were road tested for a total of 50000 km with average 2% fuel savings and no valve damage. There is a need to overcome few challenges before this technology can be implemented in the automotive industry.

  • The development of low-cost TiAl automotive valves
    JOM, 1997
    Co-Authors: M.m. Keller, P.e. Jones, W.j. Porter, Daniel Eylon
    Abstract:

    This paper presents the results of a project funded by the Edison Materials Technology Center to develop low-cost titanium aluminide automotive valves. In the course of the project, more than 800 valves were produced using several variations of the Permanent-Mold Casting process. Applying pressure during solidification improved the Casting fill; however, none of the Permanent Mold Casting methods produced pore-free as-cast valves. The as-cast microstructures of the valves were much finer than investmentcast microstructures of similar section sizes. The room-temperature tensile properties of the Permanent Mold Castings were superior to those of investment Castings of a comparable section size.

  • Development of a low cost Permanent Mold Casting process for TiAl automotive valves
    1995
    Co-Authors: P.e. Jones, W.j. Porter, Daniel Eylon, G. Colvin
    Abstract:

    This paper reviews progress made in the development of a low cost Permanent Mold Casting process for TiAl automotive valves. The issues studied include Mold life, Mold/metal reaction, shrinkage void control, dimensional control, and post Casting processes. More than 800 Ti-47Al-2Nb-1.75 Cr (at%) valves were produced by gravity, centrifugal, and pressure assisted Casting methods on a laboratory scale. Microstructures, tensile, creep, and fatigue properties of as-HIP and as-heat treated valves are described. Process scale up challenges identified in this work are also discussed.