An effort to fabricate and characterize in-situ formed graded structure in a ceramic-metal system

Monolithic alumina and alumina–silver composite containing 15.0 vol.% of silver have been fabricated via pressureless sintering approach. By virtue of the inherent high vapour pressure of silver at elevated temperature during sintering, a decreasing silver gradient was observed between the bulk and the surface of the composite material. As a consequence of this phenomenon, a functionally graded structure of alumina–silver could be observed having the core rich in silver (in alumina matrix) and the surface rich in mostly alumina. Hardness and fracture toughness data evaluation reveals the fact that the surface of the composite specimen has higher hardness and lower fracture toughness due to lesser silver content, whereas, the core (bulk) of the sample has higher fracture toughness and lower hardness due to higher silver content. This kind of graded structure could be ideal as a cutting tool or wear-resistant material, which demands a harder surface (for machining) followed by a tougher core (for flaw-tolerance). Both the flexural strength and fracture toughness values of alumina are observed to improve with incorporation of silver and the associated potential strengthening and toughening mechanisms are identified in relation with the observed microstructural features.