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The intermetallic compounds NiTi, NiTi2, CuZr, CuTi2, and Zr3Al were irradiated by 2 MeV protons at various temperatures between -175 °C and - 4 4 °C to a fluence of 1.9 X 1022 H + /m 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., NiTi2) or contain branching features resembling river patterns. In some cases (especially in CuZr) these are similar to the markings seen on the surfaces 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 considerable evidence for irradiation-induced ductility. In such cases, exemplified by the results on NiTi and Zr3Al, the fracture surfaces contain dimples, characteristic of ductile fracture, suggesting that disordering promotes ductility.

I. INTRODUCTION In recent years considerable research has been directed to the subject of the crystalline-to-amorphous (C-A) transition in metallic alloys, particularly intermetallic compounds. Amorphous alloys have been produced by a variety of methods, the most common of which is rapid quenching from the liquid state. Other methods involve solid state reactions, wherein the amorphous phase forms from initially crystalline phases via low temperature diffusion, mechanical alloying, or irradiation. Irradiation with energetic particles has long been known to induce the C-A transition in certain intermetallic compounds. The first observation of such a transition was reported by Bloch1 in the intermetallic compound U6Fe under neutron bombardment. Thereafter numerous experiments2"21 have shown that the irradiation-induced C-A transition occurs in a number of intermetallic compounds under neutron, heavy-ion, and electron irradiation. Neutron and/or heavy-ion irradiation produce a series of collision cascades, inducing local disorder in an initially ordered alloy. If the irradiation temperature is low enough, the disordered regions will freeze-in rapidly and transform to the amorphous phase, as in the case of rapid quenching from a)

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