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Title: Fractographic finger printing of proton-irradiation-induced disordering and amorphization of intermetallic compounds

Abstract

The intermetallic compounds NiTi, NiTi/sub 2/, CuZr, CuTi/sub 2/, and Zr/sub 3/Al were irradiated by 2 MeV protons at various temperatures between --175 /degree/C and --44 /degree/C to a fluence of 1.9/times/10/sup 22/ H/sup +//m/sup 2/. Transmission electron microscopy, electron diffraction, and x-ray diffraction were used to evaluate the extents of disordering and amorphization induced by irradiation in the samples. Both phenomena progressed to varying extents in the five compounds, depending on the irradiation temperature and dose. It was observed that the C-A transition began before the degree of long-range order was reduced significantly, and that the amorphous phase nucleated homogeneously throughout the crystalline matrix. A major finding of the current investigation is that the technique of scanning electron fractography provides a useful correlation between the features of the fractured surfaces and the microstructural alterations induced by the proton irradiations. When amorphization is complete the fracture surfaces are either featureless (e.g., NiTi/sub 2/) or contain branching features resembling river patterns. In some cases (especially in CuZr) these are similar to the markings seen on the surface of fractured amorphous ribbons produced by melt-spinning. In general, however, there is not a particularly good correlation between the features on the fracture surfacesmore » of the irradiated and melt-spun ribbons. When the microstructure consists of amorphous regions embedded in a partially disordered crystalline matrix, there is consierable evidence for irradiation-induced ductility. In such cases, exemplified by the results on NiTi and Zr/sub 3/Al, the fracture surfaces contain dimples, characteristic of ductile fracture, suggesting that disordering promotes ductility.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Department of Materials Science and Engineering, University of California, Los Angeles, California 90024 (US)
OSTI Identifier:
5948340
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Mat. Res.; (United States); Journal Volume: 4:3
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALUMINIUM COMPOUNDS; PHYSICAL RADIATION EFFECTS; COPPER COMPOUNDS; NICKEL COMPOUNDS; TITANIUM COMPOUNDS; ZIRCONIUM COMPOUNDS; DOSE RATES; ELECTRON DIFFRACTION; INTERMETALLIC COMPOUNDS; LOW TEMPERATURE; MEV RANGE 01-10; ORDER-DISORDER TRANSFORMATIONS; PROTONS; TEMPERATURE DEPENDENCE; TRANSMISSION ELECTRON MICROSCOPY; X-RAY DIFFRACTION; ALLOYS; BARYONS; COHERENT SCATTERING; DIFFRACTION; ELECTRON MICROSCOPY; ELEMENTARY PARTICLES; ENERGY RANGE; FERMIONS; HADRONS; MEV RANGE; MICROSCOPY; NUCLEONS; PHASE TRANSFORMATIONS; RADIATION EFFECTS; SCATTERING; TRANSITION ELEMENT COMPOUNDS 360106* -- Metals & Alloys-- Radiation Effects; 360102 -- Metals & Alloys-- Structure & Phase Studies

Citation Formats

Cheng, J., Yuan, M., Wagner, C. N. J., and Ardell, A. J.. Fractographic finger printing of proton-irradiation-induced disordering and amorphization of intermetallic compounds. United States: N. p., 1989. Web.
Cheng, J., Yuan, M., Wagner, C. N. J., & Ardell, A. J.. Fractographic finger printing of proton-irradiation-induced disordering and amorphization of intermetallic compounds. United States.
Cheng, J., Yuan, M., Wagner, C. N. J., and Ardell, A. J.. 1989. "Fractographic finger printing of proton-irradiation-induced disordering and amorphization of intermetallic compounds". United States. doi:.
@article{osti_5948340,
title = {Fractographic finger printing of proton-irradiation-induced disordering and amorphization of intermetallic compounds},
author = {Cheng, J. and Yuan, M. and Wagner, C. N. J. and Ardell, A. J.},
abstractNote = {The intermetallic compounds NiTi, NiTi/sub 2/, CuZr, CuTi/sub 2/, and Zr/sub 3/Al were irradiated by 2 MeV protons at various temperatures between --175 /degree/C and --44 /degree/C to a fluence of 1.9/times/10/sup 22/ H/sup +//m/sup 2/. Transmission electron microscopy, electron diffraction, and x-ray diffraction were used to evaluate the extents of disordering and amorphization induced by irradiation in the samples. Both phenomena progressed to varying extents in the five compounds, depending on the irradiation temperature and dose. It was observed that the C-A transition began before the degree of long-range order was reduced significantly, and that the amorphous phase nucleated homogeneously throughout the crystalline matrix. A major finding of the current investigation is that the technique of scanning electron fractography provides a useful correlation between the features of the fractured surfaces and the microstructural alterations induced by the proton irradiations. When amorphization is complete the fracture surfaces are either featureless (e.g., NiTi/sub 2/) or contain branching features resembling river patterns. In some cases (especially in CuZr) these are similar to the markings seen on the surface of fractured amorphous ribbons produced by melt-spinning. In general, however, there is not a particularly good correlation between the features on the fracture surfaces of the irradiated and melt-spun ribbons. When the microstructure consists of amorphous regions embedded in a partially disordered crystalline matrix, there is consierable evidence for irradiation-induced ductility. In such cases, exemplified by the results on NiTi and Zr/sub 3/Al, the fracture surfaces contain dimples, characteristic of ductile fracture, suggesting that disordering promotes ductility.},
doi = {},
journal = {J. Mat. Res.; (United States)},
number = ,
volume = 4:3,
place = {United States},
year = 1989,
month = 5
}
  • The authors present the results of a systematic molecular dynamics simulation of the crystalline-to-amorphous transformation in the ordered intermetallic compounds of the Ni-Zr system, NiZr, NiZr{sub 2} and Ni{sub 3}Zr. Using embedded-atom potentials fitted to the equilibrium properties of these compounds, the simulation examines the relative importance of chemical disordering and point defect generation in inducing amorphization. Fundamental aspects of the amorphization process have been investigated in detail by monitoring the changes in the potential energy, volume, radial distribution function, structure factor and elastic constants as a function of irradiation dose. The results obtained are compared with recent experimental observations.
  • The crystalline-to-amorphous (c-a) phase transformation in the intermetallic compound, Zr/sub 3/Al, during room temperature bombardment with 1.0-MeV Kr/sup +/ has been investigated. Transmission electron microscopy and Brillouin scattering techniques were used to determine the lattice parameter and shear elastic constant as a function of the degree of long-range order. Results show that a large (approx.50%) elastic softening and dilatation strain (approx.3%) due to disordering precede the onset of amorphization. These results indicate that chemical disordering is an important driving force for the c-a transformation, and that the mechanism is an elastic shear instability. It is also shown that the volumemore » dependence of the shear elastic constant associated with radiation-induced disordering and eventual amorphization is virtually identical to that associated with the heating to melting of many solids. The origin and implications of this parallelism between solid-state amorphization and melting are discussed. 21 refs., 6 figs.« less
  • Solid-state amorphization resulting from the introduction of chemical disorder and point defects in the ordered intermetallic compounds CuTi, CuTi{sub 2}, and Cu{sub 4}Ti{sub 3} was investigated, with use of the isobaric-isothermal molecular-dynamics method in conjunction with embedded-atom potentials. Antisite defects were produced by randomly exchanging Cu and Ti atoms, and vacancies and interstitials were created by removing atoms at random from their normal sites and inserting atoms at random positions in the lattice, respectively. The potential energy, volume expansion, and pair-correlation function were calculated as functions of the numbers of atom exchanges and point defects. The results indicated that, althoughmore » both chemical disordering and point-defect introduction increased the system energy and volume, the presence of point defects was essential to trigger the crystalline-to-amorphous transition. By comparing the pair-correlation function calculated after the introduction of point defects with that of the quenched liquid alloy, the critical damage dose (in dpa, displacements per atom) for amorphization was estimated for each compound: {similar to}0.7 dpa for CuTi, {similar to}0.5 dpa for CuTi{sub 2}, and {similar to}0.6 dpa for Cu{sub 4}Ti{sub 3}. At the onset of amorphization, the volume expansions were found to be {similar to}1.9%, {similar to}3.7%, and {similar to}1.7% for these respective compounds. In general, the results obtained in the present work are in good agreement with experimental observations.« less
  • Ion-irradiation induces amorphization in many intermetallics and ceramics, but spinel (MgAl{sub 2}O{sub 4}) is considered a ``radiation resistant`` ceramic. Spinel was irradiated with 1.5 MeV Kr{sup +} at 20 K and observed {ital in} {ital situ} by transmission electron microscopy (TEM). The spinel remained crystalline to a high dose of 1{times}10{sup 16} ions/cm{sup 2}, without any evidence of amorphization. Another spinel was preimplanted with Ne (400 keV and 50 keV). The microstructure revealed a still crystalline material with 8 nm interstitial loops. After irradiation with 1.5 MeV Kr{sup +} (20 K), amorphization, a result of cation disordering, initiated at amore » dose of 1.7{times}10{sup 15} ions/cm{sup 2}. At a dose of 1{times}10{sup 16} ions/cm{sup 2}, the spinel was partially amorphous and the remaining crystalline domains disordered. These results show that spinel can be disordered and that amorphization can be triggered by the introduction of stable defects, followed by ion irradiation at low temperature.« less
  • Irradiation-induced amorphization was studied in situ in the high voltage electron microscope interfaced to a tandem accelerator. Variation of elastic properties during irradiation was studied with Brillouin scattering spectroscopy, and its relation to amorphization were explored. Four important topics were investigated. (1) The temperature dependence of the critical dose for amorphization and its correlation with chemical disordering were studied in CuTi and Zr{sub 3}Al with 1-MeV electron irradiation from 10 to 295 K. Similar temperature dependence was observed in CuTi between the critical dose for amorphization and the chemical disordering rate. Chemical disordering is a major driving force for amorphization.more » The critical dose for amorphization of Zr{sub 3}Al was twenty times larger than that of CuTi and attributed to the differences in point defect mobility and ordering energy. (2) Projectile mass dependence of amorphization behavior was studied in CuTi irradiated with Ne{sup +},Kr{sup +},Xe{sup +}ions. The dose dependence of the amorphous volume fraction indicated that with increasing mass from Ne{sup +} to Kr{sup +} amorphization kinetics changes from the cascade overlap to the direct-impact amorphization. In relation to the kinetics variation, the critical temperature increased with increasing projectile mass and explained in terms of the thermal stability of the primary damage. (3) Effects of simultaneous and sequential irradiation with Kr+ and electrons were studied in CuTi and Zr{sub 3}Al. Both additive and retardation effects were observed depending on temperature and the electron-to-Kri dose rate ratio and explained as the interaction between point defects and cascade damages. (4) Study of elastic properties during Kr{sup +} irradiation revealed that in FeTi, a large dilation and shear modulus softening accompanied with chemical disordering preceded amorphization, but not observed in NiAl.« less