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Effect of TiO 2 Nanopowder on the Sintering Behavior of Nickel–Alumina Composites for Functionally Graded Materials
Author(s) -
Kruft Jonathan G.,
Bruck Hugh A.,
Shabana Yasser M.
Publication year - 2008
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2008.02571.x
Subject(s) - materials science , sintering , shrinkage , composite material , indentation hardness , porosity , nickel , vickers hardness test , composite number , relative density , microstructure , metallurgy
The use of TiO 2 nanopowder as a sintering aid in a pressureless sintering process has been investigated to improve the compatibility of the shrinkage rate in graded nickel–alumina composites. The results indicate that a 3 wt% TiO 2 nanopowder ball mixed into Al 2 O 3 powder substantially reduces sintered porosity in nickel–alumina composite specimens, improving the compatibility of shrinkage rates while increasing Vickers microhardness. Previously developed porosity reduction and sintering models were used to quantify improvement in shrinkage rates. However, the porosity reduction model had to be modified to account for sintering of agglomerated reinforcing particles in alumina‐rich composites. A power law sensitivity of Vickers microhardness to relative density was determined from homogeneous specimens. Vickers microhardness profiles of graded composites were then used to provide an insight into the effects of hydrostatic internal stresses that develop due to differential shrinkage, indicating that substantial hydrostatic stress retards shrinkage, which reduces microhardness at the interface of the nickel‐ and alumina‐rich regions and leads to crack formation without a nanopowder sintering aid.