Undulation of W/matrix interface by resintering of cyclically heat-treated W-Ni-Fe heavy alloys

Abstract

When liquid-phase-sintered W-Ni-Fe alloys were cyclically heat treated at 1100 °C and resintered at 1485 °C, undulation of W/matrix interface resulted. The irregularity of the interface increased with the number of heat-treatment cycles. The residual thermal stress of W grains measured by X-ray diffraction increased with the number of heat-treatment cycles and exceeded the yield stress of W single crystal in certain crystallographic directions. A calculation by the finite element method (FEM) also showed nonuniform distribution of thermal stress on W grains. Local yielding of W grains is believed to occur during the cyclic heat treatment. The observed undulation of W/matrix interface appears therefore to result from preferential dissolution of material from regions with higher strain energy and precipitation of material at regions with lower strain energy at the resintering temperature. The undulation disappeared with the grain growth during prolonged resintering.