An In Situ Synchrotron Investigation of Synthesis of Surface Alloys Formed by a Pulsed Electron Beam Irradiation

The results are presented for an in situ synchrotron investigation of phase composition evolution during surface alloy synthesis. Surface alloys 3–5 µm thick are synthesized using pulsed melting with a microsecond low-energy, high-current electron beam. Three bilayer systems are studied: Ti(1000)/Zr, Y(1000)/Zr, and Mo(1000)/Zr, representing (1) alloys forming continuous solid solutions, (2) alloys with limited solubility and (3) alloys forming intermetallic compounds, respectively. In the first case, a surface alloy forms through the continuous solution of Ti in α-Zr as a homogeneous equilibrium substitutional solid solution with an average Ti concentration of 40 at.%. In the second case, gradual dissolution of Y in α-Zr forms an inhomogeneous metastable oversaturated solution with average and surface Y concentrations of 18 and 32 at.%, respectively. In the third case, an inhomogeneous metastable surface alloy forms, consisting of α- and β-Zr phases, with the latter predominating. The average and surface Mo concentrations are 30 and 42 at.%, respectively. Prior to the formation of β-Zr with a high Mo content, a nonequilibrium unidentified phase appears that could be referred to as a high-concentration solid solution of crystalline Mo with Zr embedded in it from the melt.