Interfacial characterization in ductile refractory metals reinforced MoSi2 based laminated composites

Efforts to develop MoSi2 for high temperature structural applications have been hampered by its extreme brittleness at temperatures below 1000 °C. In the present work, toughening of MoSi2 at lower temperatures has been explored using the ductile refractory metals as reinforcements. Model tri-layer laminated composites were made using Mo, Ta and Nb sheets sandwiched in between two layers of MoSi2 based matrix. As these refractory metals are thermodynamically unstable with MoSi2, interfacial reaction layers were observed between MoSi2 and the refractory metal sheets. The main reaction product was identified to be as M5Si3 (M = Mo, Ta or Nb) consuming a part of the thickness of the ductile metal sheets. The Ta sheet reinforced laminated composite exhibited the minimum thickness of the reaction zone (~ 10 μm) suggesting that the Ta has better chemical compatibility with MoSi2 as compared to Mo and Nb. Micro-hardness measurements made in the reaction zone revealed that the reaction products in all the three laminated composites were hard and brittle in nature. A quantitative idea of the thickness and micro-hardness values of the interfacial reaction layers is very useful to give some important guidelines to obtain the enhanced mechanical properties in MoSi2 based laminated composites.