Formation of High-Strength Zr-Nb-Cu-Ni-Al Alloys by Warm Extrusion of Gas Atomized Powders
- PDF / 10,645,978 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 1 Downloads / 211 Views
MM2.4.1
Formation of High-Strength Zr-Nb-Cu-Ni-Al Alloys by Warm Extrusion of Gas Atomized Powders E. A. Rozhkova, X. Y. Yang, P. B. Wheelock, J. Eckert a, U. Kühn b, and D. J. Sordelet Materials and Engineering Physics Program, Ames Laboratory (USDOE), Iowa State University, Ames, Iowa 50011 a Technische Universitat Darmstadt, D-64287 Darmstadt, Germany b IFW Dresden, PO Box 270016, D-01171 Dresden, Germany ABSTRACT Recently developed Zr-based metallic glass composites containing a ductile phase demonstrate improved mechanical properties such as high strength combined with good ductility compared to the glass monoliths. Zr-Nb-Cu-Ni-Al amorphous powders with bcc phase precipitates were obtained by high pressure gas atomization. Formation of the bcc phase in the amorphous matrix strongly depends on the material composition and cooling rates during solidification. Melt spinning using various wheel speeds selected to simulate the cooling rates during gas atomization was used to define a specific composition for gas atomization. Gas atomized powders were consolidated by warm extrusion. Various processing conditions including starting powder particle size, extrusion temperature and extrusion ratio were examined to obtain materials having various microstructural features. Structure and thermal stability of consolidated bulk metallic glass composites as well as selected mechanical properties will be discussed. INTRODUCTION Despite having unique mechanical properties such as high strength combined with high elastic strain, most bulk metallic glasses fail in a brittle manner and show limited plastic flow with no strain hardening at room temperatures. Catastrophic failure associated with formation of highly localized shear bands limits the potential utility of metallic glasses in many structural applications. Recently developed bulk metallic glass matrix composites with the a ductile second phase in form of crystalline solid solution particles [1], fiber and particle additives [2-4], or dispersed in-situ micrometer-sized precipitates [5,6] exhibit significantly improved ductility while retaining high fracture strength. This behavior is probably due to fact that particles of second phases prevent shear band propagation and initiate formation of multiple shear bands that lead to creation of additional fracture surface area [4]. Controlling the composite microstructure (size, volume fraction and morphology of second phase) may significantly enhance mechanical properties of the composite material. On one hand, it was observed that second phase particles with sizes comparable to the width of the shear bands have little effect in stopping their propagation [3]. On the other hand, larger sized dendrites effectively promote the initiation of propagating shear bands and at the same time act as attraction or pinning centers during shear band propagation, which may contribute to increased resistance to fracture [5,7]. However centimeter-scale bulk metallic glass matrix composites were prepared only using conventional casting techniques
Data Loading...
