【摘要】 通过粉末包埋渗法并经过真空均匀化热处理制备高比表面积的泡沫NiCrAl电热合金,考察了真空均匀化热处理温度对泡沫NiCrAl电热合金中金属元素蒸发的影响,采用SEM和XRD等分析手段,研究了泡沫NiCrAl的成分、结构及其与电阻率的关系.研究结果表明,以泡沫NiCr为基材通过调整渗Al温度及适当的真空均匀化热处理,能获得成分均匀、具有高表观电阻率的泡沫NiCr（20-30）Al（3-9）电热合金.泡沫NiCr渗Al后形成Ni固溶体,Cr,Ni₂Al₃,NiAl和Ni₃Al的多相结构,随着Al含量的增加电阻率降低.经过真空均匀化热处理后,当Al含量很低时,Al固溶在Ni固溶体中,电阻率比泡沫NiCr高且随Al含量增加而上升;当Al质量分数达到约5%时,表观电阻率达最大值;当Al含量更高时,除Ni固溶体外还有Ni₃Al相生成,电阻率又开始降低;Al和Cr含量均较高时,未溶解的Cr沉淀相会显著降低泡沫NiCrAl的电阻率,故泡沫NiCr30Al9不适宜用作电热合金.更多还原

【Abstract】 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.NiCr30A19 foam is not suitable as electro-thermal alloy.更多还原