An Investigation of the Effect of Sintering Conditions on the Mechanical Behavior of Electroplated Nickel Foams
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TRODUCTION
METALLIC foams are widely used in various industries due to their unique properties such as high stiffness-to-weight ratio and superior energy absorption ability under compression.[1,2] Nickel-base alloy foams possess a special position among metallic foams. Their excellent oxidation resistance with high activity catalyst capability makes them the best candidates for high-temperature catalyst substrates, filters, supercapacitors, and heat exchangers.[3–7] Many researchers expend a lot of effort to improve the corrosion resistance, mechanical, and microstructural properties of nickel foams by different modification methods such as chromizing, aluminization, and combustion synthesis.[8–13] Scholars continually look for an economical and facile method of preparing this product. There are two commercially common methods to fabricate nickel foams: (1) chemical vapor deposition (CVD) and (2) electrodeposition on a
FAEZE BARZEGAR, AKRAM SALEHI, and AHMAD MOLOODI are with the Materials Research Group, Iranian Academic Center for Education, Culture and Research (ACECR), Mashhad Branch, P.O. Box 91779-49367, Mashhad, Iran. Contact e-mails: [email protected], [email protected] Manuscript submitted October 28, 2018. Article published online June 12, 2019. 1988—VOLUME 50B, AUGUST 2019
porous organic foam substrate followed by removal of the polymeric substrate.[14,15] The preparing condition, the product morphology, and the removal treatment of substrate are the effective factors on the mechanical and microstructural properties of nickel foams. There are many works studying a method of removing polymeric substrate in the manufacturing process of nickel foams; most of them present a two-step thermal treatment. The goal of the first step is to remove polyurethane substrate, which is generally removed by burning in air. In this stage, there is a possibility of contaminates in the nickel foam microstructure caused by residual carbon. The second step is to anneal the nickel foam in a reductive atmosphere to reach the desired ductility level for workability and to reduce any nickel oxide formed in the previous step.[16,17] This two-step method has some disadvantages. (1) When the polymer burns in the air, it tends to embrittle. This may complicate obtainment of the optimal structure in the second step. (2) This type of heat treatment causes shrinkage due to nickel oxidation followed by reduction, which may create internal stresses and new cracks. This method is not economical owing to the excessive time involved and the use of two furnaces.
METALLURGICAL AND MATERIALS TRANSACTIONS B
Cushnie and Campbell[18] invented a two-step method for removing polymeric substrate in a two-zone-controlled-atmosphere furnace. Compared to other methods, their method is time effective and minimizes the shrinkage of nickel structures during the thermal decomposition process. Their method includes exposing a nickel-coated polymer substrate to a temperature of at least 873 K (600 C) for a time duration less than 5 seconds. After the pol
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