Strength Variations during Mechanical Alloying Through the Nanostructural Range
- PDF / 838,978 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 67 Downloads / 283 Views
Q11.3.1
Strength Variations during Mechanical Alloying Through the Nanostructural Range Christopher A. Schuh, David T. Schoen, and Alan C. Lund Department of Materials Science and Engineering, Massachusetts Institute of Technology 77 Massachusetts Avenue, Cambridge, Massachusetts, USA 02139 ABSTRACT During processes of mechanical alloying the characteristic structural length scales of an alloy, including the phase domain size and the crystallite grain size, decrease gradually to a nanocrystalline or even amorphous final state. This method therefore allows a unique avenue to explore the structure-property relationship over several orders of magnitude in length scale. In this work we have considered an ideal equiatomic Ti-Zr system deformed through multiple coldrolling passes to refine the structural length scales into the nanometer range. The variation of the hardness of the system with decreasing length scale is discussed in terms of traditional HallPetch scaling, chemical mixing and the phase evolution of the system, as well as other possible contributions to the hardness variations during processing. INTRODUCTION Techniques of severe plastic deformation have been of continual interest in the production of novel metallic microstructures. For example, mechanical milling or mechanical alloying techniques have been extensively used to produce nanocrystalline [1-4] and amorphous metals [5-7], as well as two-phase nanocomposites [8, 9]. An interesting aspect of these techniques is that they traverse many orders of magnitude of the material’s characteristic structural length scale, and thereby offer a means of exploring scaling laws from micro- to nanoscale regimes. For example, using pure powders in a high-energy ball mill, Koch and co-workers [10, 11] have explored variations in hardness and tensile ductility of Zn as a function of the ball milling time. They reported interesting scaling behavior in the nanoscale regime, in which both hardness and ductility first increase with decreasing grain size, then peak and subsequently decrease when the grain size reduces into the nanometer-range. In a separate work on cryogenic milling of the same material [12], this group has reported oscillatory variations in hardness with milling time, which they attributed to periodic recrystallization in the nanoscale regime. The interesting studies described above are among many in which various authors have used mechanical milling or accumulative roll-bonding approaches to produce single-component nanocrystalline metals. There are also many studies that have examined the mixing and phase evolution of multicomponent systems during similar processes (see Ref. [13] for a recent comprehensive review). In the simple case of a two-component system, the structure evolved during these processes is initially a multilayered structure of the two pure components, which refines progressively with milling time. Concurrently, the average grain sizes of the two components are known to refine with roughly the same kinetics as the layered structure [14].
Data Loading...
