Bulk amorphous Al-alloys by ball milling and spark-plasma-sintering
Final Report Abstract
In this project, novel bulk Al-based alloys with high content of Al have been produced by powder metallurgy methods from amorphous and partially amorphous materials. Different processing routes, i.e. mechanical alloying of elemental powder mixtures, controlled pulverization of melt-spun glassy ribbons and gas atomization, have been employed for the production of the Al-based powders. Among the different processing routes, gas atomization is the best choice for the production of Al-based amorphous and partially amorphous powders as precursors for the subsequent consolidation step because it allows the production of large quantities of powders with homogeneous properties (e.g. structure and thermal stability) along with a uniform size distribution of particles. Amorphous and nanocrystalline powders have to be consolidated to achieve dense bulk specimens. However, consolidation of these phases is not an easy task and special care has to be taken with respect to accurate control of the consolidation parameters in order to achieve dense bulk specimens without inducing undesirable microstructural transformations (e.g. crystallization and grain coarsening) or insufficient particle bonding. Consequently, the thermal stability as well as the effect of temperature on viscosity and phase formation have been studied in detail in order to select the proper consolidation parameters. Following their characterization, the Al-based powders have been consolidated into bulk specimens by hot pressing (HP), hot extrusion and spark plasma sintering (SPS) and their microstructure and mechanical properties have been extensively investigated. Consolidation into highly-dense bulk samples cannot be achieved without extended crystallization of the glassy precursors. Nevertheless, partial or full crystallization during consolidation leads to remarkable mechanical properties. For example, HP Al84Gd6Ni7Co3 samples display a remarkably high strength of about 1500 MPa, which is three times larger than the conventional high-strength Al-based alloys, along with a limited but distinct plastic deformability (3.5 – 4%). Lower strength (930 MPa) but remarkably larger plastic strain exceeding 25 % has been achieved for the Al87Ni8La5 gas-atomized powders consolidated by SPS above their crystallization temperature. Similarly, HP Al90.4Y4.4Ni4.3Co0.9 bulk samples display high compression strength ranging between 820 and 925 MPa combined with plastic strain in the range 14 – 30%. The results indicate that the mechanical behavior of the consolidated specimens is strictly linked with their microstructure. High strength and reduced plasticity are observed when a residual amorphous phase is present. On the other hand, reduced strength but enhanced plastic deformation is a result of the complete crystallization of the glass and of the formation of a partially or fully interconnected network of deformable fcc Al. The results obtained in the course of this project clearly indicate that the combined devitrification and consolidation of amorphous precursors is a particularly attractive method for the production of lightweight Al-based materials characterized by high strength combined with considerable plastic deformation. Through this method, the mechanical properties of the consolidated samples can be varied within a wide range of strength and ductility depending on the microstructure and the consolidation techniques used. This might open a new route for the development of novel and innovative high-performance Al-based materials for ecofriendly transport applications.
Publications
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“Crystallization kinetics and consolidation of mechanically alloyed Al70Y16Ni10Co4 glassy powders”. Journal of Alloys and Compounds 477 (2009) 171
K.G. Prashanth, S. Scudino, B.S. Murty, J. Eckert
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“Crystallization kinetics of Zr65Ag5Cu12.5Ni10Al7.5 glassy powders produced by ball milling of pre-alloyed ingots”. Materials Science and Engineering A 513-514 (2009) 279
K. G. Prashanth, S. Scudino, K.B. Surreddi, M. Sakaliyska, B. S. Murty, J. Eckert
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“Formation of nanocrystalline matrix composite during spray forming of Al83La5Y5Ni5Co2”. Metallurgical and Materials Transactions A, 40A (2009) 450
V. C. Srivastava, K. B. Surreddi, V. Uhlenwinkel, A. Schulz, J. Eckert, H. W. Zoch
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“High-strength Al87Ni8La5 bulk alloy produced by spark plasma sintering of gas atomized powders”. Journal of Materials Research 24 (2009) 2909
S. Scudino, K. B. Surreddi, H. V. Nguyen, G. Liu, T. Gemming, M. Sakaliyska, J. S. Kim, J. Vierke, M. Wollgarten, J. Eckert
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“Mechanical properties of Al-based metal matrix composites reinforced with Zr-based glassy particles produced by powder metallurgy”. Acta Materialia 57 (2009) 2029
S. Scudino, G. Liu, K. G. Prashanth, B. Bartusch, K. B. Surreddi, B. S. Murty, J. Eckert
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“Powder metallurgy of Al-based metal matrix composites reinforced with -Al3Mg2 intermetallic particles: Analysis and modeling of mechanical properties”. Acta Materialia 57 (2009) 4529
S. Scudino, G. Liu, M. Sakaliyska, K. B. Surreddi, J. Eckert
