The thermal fission-induced crystalline-to-amorphous transformation in U 6 Fe
- PDF / 856,218 Bytes
- 8 Pages / 593 x 841.68 pts Page_size
- 62 Downloads / 141 Views
ReedO. Elliott Materials Science and Technology Division, University of California, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (Received 22 October 1987; accepted 15 February 1988) The crystalline-to-amorphous transformation in U 6 Fe produced by thermal fission fragment damage was studied using resistivity and differential scanning calorimetry. The results are described in terms of a model of radiation-produced defect buildup in the crystalline matrix followed by transformation of small regions to an amorphous phase when a critical local defect concentration is reached. This can occur directly in a single cascade or from cascade overlap. The total resistivity is modeled assuming an inhomogeneous media consisting of a crystalline matrix containing a dose-dependent concentration of defects and amorphous zones. The crystallization behavior is initially, starting at Tc = 388 K, a kinetically limited process of shrinkage of amorphous zones that gradually transforms to nucleation and growth in fully amorphous material at Tc = 555 K.
I. INTRODUCTION The crystalline-to-amorphous transformation in intermetallic alloys induced by particle irradiation has been extensively studied over the last few years.1"3 Much of this work has focused on determining the alloy systems in which it takes place and under what irradiation conditions it is observed using x-ray and electron diffraction techniques. From these investigations the simple picture that has been developed is that the point defects initially produced by the irradiation induce a heterogeneous transformation from the crystalline phase to an amorphous phase by increasing the free energy of the material. The free-energy increase is due to some form of defect that evolves from the irradiationproduced point defects or is a subset of the initial defects and builds up to a sufficient concentration to make the transformation energetically favorable. Various models proposing the interstitial,4 vacancy, 56 interstitial and vacancy,7 interstitial/vacancy complex,8 and chemical disorder9 as the defect have been published. Strong supporting evidence for the defect being one or more of the above defects, or at most a very small cluster or complex, is that they are not observable in the transmission electron microscopy (TEM) prior to amorphization.3 Essentially no damage is observed until amorphous zones appear. The irradiated material at some intermediate dose prior to complete amorphization, according to the above discussion, will consist of amorphous regions in a crystalline matrix containing defects. This heterologous phase should have properties that are characteristic of J. Mater. Res. 3 (3), May/Jun 1988
http://journals.cambridge.org
both the crystalline and amorphous phases. For example, the amorphous zones, if they are truly amorphous in the sense of rapidly quenched material and not just highly disordered, should undergo crystallization at some temperature Tx as in the rapidly quenched material. Other properties such as the resistivity in the amorphous zon
Data Loading...
