Final technical report. [Heterogeneous nucleation and growth in metal alloys]

We have refined a heat treatment to obtain coherent, heterogeneous nucleation of precipitates on dislocations in a high purity binary alloy. This allowed, for the first time, a quantitative comparison to be made for coherent heterogeneous nucleation. This part of the research resulted from our concern about the role of dislocations in sub-boundaries in aluminum alloys and directed us to first examine isolated dislocations in the binary Al-Li systems. We were able to design the experiment so the heterogeneous nucleation of AL{sub 3}Li occurred. Previously, only homogeneous nucleation of Al{sub 3}Li had been examined

Microstructural effects on the fatigue behavior of Fe-C-X alloys. [Dual-phase steels]

Objective was to study dual phase steels. Macroscopic effects of reversing the continuous phase from ferrite to martensite was examined. The next section looks at the role of carbide distribution and morphology precipitated within ferrite during thermal cycling. Finally, finite element modeling is used to assist in understanding the experimental results

THE EFFECT OF PLASTIC DEFORMATION ON T1 PRECIPITATION

The enhancement of T1 precipitation in Al-Li-Cu alloys by stretching prior to aging (i.e., cold work) and the subsequent increase in alloy strength has been documented [1]. The role of matrix dislocations in the nucleation and growth of T1 plates, however, has not been studied in detail. In this paper the effect of different levels of plastic strain on the T1 particle distributions as a function of aging time at 190 C will be quantified. Additionally, the precipitation mechanism will be explored in order to better understand the role of matrix dislocations as nucleation sites and their effect on T1 plate growth