The Effect of Ni Interlayers on Compaction of Mo/Mo Silicide Composites

Abstract

Reactions during compaction of Mo/Mo silicide wires with Ni interlayers are qualitatively assessed in this work. It appeared that due to extreme high temperature strength of MoSi2 hot pressing even at 1800°C/60 min/30 MPa in vacuum had not been sufficient to compact the Mo/Mo silicide wires in the absence of any additional interfacial layer. Therefore Ni had been chemically coated on the surface of Mo/Mo silicide wires that were subsequently compacted by hot pressing. Structural analysis revealed the reaction between Ni and MoSi2 resulting in the formation of ternary (MoNiSi) compounds. These established an interfacial bonding with minimal porosity.

Mo/Mo silicide composites prepared by pressure-assisted reactive infiltration

“…As already reported [3,4], when a Mo wire is dipped into excessively molten Si, rapid dissolution takes place. This reaction, exothermic in nature, is so rapid and intense that it cannot be effectively controlled.…”

“…This is not a trivial task as the newly formed silicides are very strong and difficult to deform. As reported even hot pressing at 1800 • C/60 min/30 MPa is not enough to perform the required compaction [3,4].…”

“…Various other approaches had been examined in order to perform the desired compaction. Nb in the form of wire or foil was attempted as a bonding agent in [3]. Secondary infiltration with Ni followed by HIP [6], as well as compaction via Ni interlayers [7] was experienced too.…”

Joining of Mo and MoSi2 and their interaction with nickel

“…One of the possibilities how to exploit the specific properties of both molybdenum silicide as a matrix and molybdenum as reinforcing component is to develop new class of high temperature composite material. This combination may provide a synergic effect yielding a material with excellent oxidation resistance and high strength, ductility and creep resistance [8].…”