| Abstract: | Adhesion and Interfacial Reactions in the αAl 2 O 3/ Ni Composite System. Composite models consisting of a zylindrical sapphire rod surrounded by a sintered nickel ring are used to determine the influence of small amounts of titanium or zirconium (as alloying additions in the nickel) on the adhesion and compatibility between the composite components. Poor nickel gives temporally and thermally stable-shear strength values between 50 and 70 N/mm2. With nickel containing 0,05 at.-% Ti or Zr the shear strength increases to 250–280 N/mm2 by using favourable sintering conditions (i. e. 1300°C, 1 h). This increase is caused by an improvement of adhesion which can be explained by the formation of strong chemical bonds. These bonds are produced by chemical reactions between the sapphire surface and the alloyed active metals Ti or Zr in the nickel. With longer sintering times, higher sintering temperatures, and/or higher active metal concentrations, these reactions cause roughening of the sapphire surface and precipitation of active metal oxide phases at the interface or in the adjacent nickel zone. Those reactions-caused alterations of the interface region are changing the shear behaviour and can lead to a decrease of shear strength. The shear strength values of such specimens dont allow conclusions of the real adhesion between the components. |
