Influence of crystallography and bonding on the structure and migration of irrational interphase boundaries
- PDF / 842,314 Bytes
- 21 Pages / 576 x 792 pts Page_size
- 17 Downloads / 220 Views
NTRODUCTION
WHEN Professor James C.M. Li (University of Rochester) invited me during the fall of 2001 to consider the possibility of receiving the 2004 Hume-Rothery Award, I expressed surprise because my main connection with phase stability has been the derivative one of determining the driving force for phase transformations. However, since this consideration did not dissuade the TMS-ASM Alloy Phases Committee, which sponsors this award annually, the offer was accepted because it provided the opportunity to develop a symposium oriented toward tackling a problem that had been puzzling me for more than 30 years. As a consequence of recent developments in modeling irrational interphase boundaries, a solution to this problem then appeared to be near at hand.[1–4] The original problem was how planar facets generated at interphase boundaries during the massive transformation can halt growth under a high (and often continH.I. AARONSON, deceased, was R.F. Mehl University Professor Emeritus in the Department of Materials Science and Engineering at Carnegie Mellon University, Pittsburgh, PA 15213-3890, U.S.A. He was also Visiting Professor in the School of Physics and Materials Engineering at Monash University, Victoria 3800, Australia, and Adjunct Professor in the Department of Materials Science and Engineering at the University of Virginia, Charlottesville, VA 22904-4745, U.S.A. This article is based on a presentation made in the “Hume-Rothery Symposium on Structure and Diffusional Growth Mechanisms of Irrational Interphase Boundaries,” which occured during the TMS Winter meeting, March 15–17, 2004, in Charlotte, NC, under the auspices of the TMS Alloy Phases Committee and the co-sponsorship of the TMS-ASM Phase Transformations Committee. METALLURGICAL AND MATERIALS TRANSACTIONS A
uously increasing) driving force despite the irrational lattice orientation relationship and irrational conjugate habit planes characterizing these boundaries.[4–9] Figure 1 illustrates such boundaries formed during the : m transformation in a Ti-Al alloy.[8] In some alloy systems, linear misfit compensating defects are absent at most if not all faceted and other interphase boundaries formed during massive transformations,[1–9] though these defects are present at all interphase boundaries, at least during the : m transformation in Ag-26 at. pct Al.[10] Further, it was now being recognized that such boundaries are not a unique characteristic of the massive transformation. Irrational planar boundaries appear to be present at grain boundary allotriomorphs formed during precipitation from solid solution, though more recent work has shown these boundaries to be partly coherent in two metallic alloy systems at both their near-rational and irrational orientation relationships interfaces.[11,12] Irrational boundaries supposedly also comprise the edges of the alternating ferrite and cementite plates in pearlite[13,14,15] and of the precipitate plates or laths that lead the cellular (discontinuous precipitation) reaction.[13,16] Shiflet et al., howe
Data Loading...
