Martensitic transformation in Cu-2be alloys induced by explosive cladding
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I.
INTRODUCTION
THEmartensitic transformation is known to occur in some Cu alloys such as Cu-AI, Cu-Sn, and Cu-Zn. It takes place during fast cooling, extensive plastic deformation, or thin film preparation. ~,2 In Cu-Be alloys martensitic transformation was not observed, although the formation of certain "unknown" phases was reported, t Fillnow et al. 3 postulated the" possible occurrence of a martensitic transformation in Cu-Be alloys, while Bowles et al. 4 applied a phenomenological theory of martensitic transformation to describe the aging phenomena. Nordstrom et a l . " investigated Cu-Be alloys which were subjected to shock loading at various shock pressures. Although they did not detect any phase transformation, one has to be aware of the basic differences between shock loading and explosive welding. While during shock loading the interacting metal plates are subjected to a plane wave and the residual deformation is of an order of a few percent, 6 explosive welding is characterized by jet collision and the residual strains may reach a few hundred percent. 7 Recent investigations of microstructure changes induced by explosive cladding in the bond region s demonstrated the formation of a new phase. The present paper summarizes the crystallographic details of this phase and demonstrates that it results from a martensitic transformation.
II. MATERIALS AND EXPERIMENTAL PROCEDURE The material used in this study was as-cast Cu-2Be alloy with the following composition (in weight percent): Be (1.96), Co (0.01), Ni ( M martensitic transformation: (a) the orthorhombic lattice incorporated in the cubic lattice, (b) shearing along Ill2] on (111) plane.
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b0 = a/2[112], as a base plane for new unit cell (see Figure 5(a)). Assuming that the Cu-Be alloy is in the state of solid solution the lattice parameter of the fcc Cu-2Be was taken to be 0.357 nm ~swhich leads to the scalar length of the vectors a and b 0.252 nm and 0.437 nm, respectively. Now, to complete the unit cell, a third vector perpendicular to the base plane is drawn, and its value is c0 = a [ l l l ] (0.618 nm). This new ORTH cell (a, b, c) is built on three subsequent (111)planes. If, however, a stacking fault is formed, the ABCABC sequence transforms to ABAB, one with two subsequent (111)planes only (see Figure 5(b)). In that case c* = 2/3 co = 0.412 nm. Consequently, the ORTH cell has the following parameters: a* = 0.252, b* = 0.437, and c* --- 0.412 nm along the indices [100], [010], and [001], respectively (see shadowed cell Figure 5(a)). As a result of the shear the atom located in the 1, 1,0 position of the cubic lattice is shuffled to the facecentered position of the orthorhombic cell (see Figure 5(a)). METALLURGICAL TRANSACTIONS A
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Fig. 6--Superimposed stereographic projections of orthorhombic and cubic crystals. P represents the pole of the orthorhombic plane misoriented 4 deg fro
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