SYNTHESIS AND ELECTRICAL PROPERTIES OF NiCrAl ELECTRO-THERMAL ALLOY FOAMS
Received date: 2012-07-25
Revised date: 2012-11-09
Online published: 2013-02-11
NiCrAl alloy is a kind of electro--thermal material with high temperature performance and metal foams have high specific surface area and high porosity. Therefore NiCrAl alloy foams can be used in many applications such as fluids heating, electro-thermal catalyst bed and so on. In this work the NiCrAl foams were made from NiCr foams by using pack-aluminizing and vacuum homogenizing heat treatment. Effects of the vacuum homogenizing heat treatment temperature on evaporation of metal elements were investigated. The composition and structure of the NiCrAl foams were analysed by SEM and XRD and their relationship with the apparent resistivity of NiCrAl foams was discussed. The results indicate that NiCrAl foams with uniform composition and structure can be prepared by the process of pack-aluminizing on NiCr foams. The composition of NiCrAl foams can be controlled by adjusting temperature of pack-aluminizing, and the uniform structure of NiCrAl foams is obtained after appropriate vacuum homogenizing heat treatment. After pack-aluminizing, the foams possessed multiphase structure consisting of Ni solid solution, Cr, Ni2Al3, NiAl, Ni3Al and their resistivity decreased with the Al content increasing. NiCrAl foams with low content of Al after vacuum homogenizing heat treatment had single Ni solid solution phase. The resistivity of NiCrAl foams is higher than NiCr foams's. NiCrAl foams exhibited the maximum apparent resistivity when the content of Al was about 5% (mass fraction). With the content of Al above 5% the resistivity of NiCrAl foams decreased due to the formation of Ni3Al phase. If the content of Cr and Al increased further Cr precipitation occurred in the alloy foams. Cr precipitation greatly lowered the resistivity of NiCrAl foams. NiCr30Al9 foam is not suitable as electro-thermal alloy.
ZHANG Yuelai , DUAN Deli , ZHAO Yuhang , HOU Sihan , LI Shu . SYNTHESIS AND ELECTRICAL PROPERTIES OF NiCrAl ELECTRO-THERMAL ALLOY FOAMS[J]. Acta Metall Sin, 2013 , 49(2) : 214 -220 . DOI: 10.3724/SP.J.1037.2012.00446
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