Thermal stability of nanostructured iron–chromium alloys for interconnect application of solid oxide fuel cells

Abstract

The thermal expansion mismatch between a metallic substrate and its external oxide scale generates a strain on cooling that is the primary cause of spallation of protective oxide scales. This study investigates the thermal stability, by means of thermal expansion and oxidation behaviour, of the nanostructured FeCr alloy prepared by different consolidation techniques by means of the spark plasma sintering (SPS) method and to compare with conventional sintering technique by means of hot pressing (HP). This has potential application as interconnect in solid oxide fuel cell. Commercially available ferritic steel is chosen as a comparison of another high Cr ferritic model alloy. The beneficial effect of the reactive element by means of lanthanum onto the alloy surface that is introduced using ion implantation is also explored. The specific aspects studied were the effects of nanocrystalline structure, influenced by sintering method and surface treatment through La ion implantation of chromia forming alloys, which may improve their high thermal stability. Oxidation testing was conducted at 900-1100uC for 100 h in laboratory air. Characterisations using X-ray diffraction, scanning electron microscopy and energy dispersive Xray spectroscopy were carried out before and after each route or process to investigate the microstructure, phase change and formation of the oxide layer. The results revealed that the FeCr alloy prepared by SPS were more effective to retain nanocrystalline and better properties than those prepared by HP and the commercially available ferritic alloy. For all types of specimens, the presence of La had no detectable effect on thermal expansion but a major effect on scale adherence. The coefficients of thermal expansion for the alloy prepared by SPS were lower than those prepared by HP, and the scale adherence to the La implanted alloy was generally superior. The results consistently showed that a better reduction in oxidation resistance corresponds to excellent nanostructured alloy and La implantation.

The Effect of Ultrasonic Treatment on the Oxidation Resistance and Microstructure of Fe₈₀Cr₂₀Alloy Powder at High Temperature Oxidation Process

“…The lower parabolic rate constant indicated the longer lifetime of Fe 80 Cr 20 alloys. The similar influence of the mass gain and parabolic rate constant pattern on the metallic interconnect was investigated by [1,3,4,16] since the parabolic rate constant value is obtained from mass gain value. Smaller mass gain will produce smaller parabolic rate constant.…”

“…In recent years, metallic material is started to developing metallic interconnect since more advantages which are compared with ceramic material. Metallic has availability in terms of manufacture interconnect for SOFC since can improve the properties easily, low cost and high thermal conductivity [1][2][3][4][5]. Primary problems in metallic interconnect are the growth rate still occur at the high temperature SOFC [1,2].…”

“…Metallic has availability in terms of manufacture interconnect for SOFC since can improve the properties easily, low cost and high thermal conductivity [1][2][3][4][5]. Primary problems in metallic interconnect are the growth rate still occur at the high temperature SOFC [1,2]. In previous research, the increasing interconnect lifetime, corrosion resistance and electrical conductivity of the samples were treated by ultrasonic technique [3].…”

“…In previous research, the increasing interconnect lifetime, corrosion resistance and electrical conductivity of the samples were treated by ultrasonic technique [3]. Oxidation kinetics of the FeCr alloy has been studied by researches [1][2][3][4] due to the chromium forming alloys are most favorable candidates which is formed chromia (Cr 2 O 3 ) scale with low growth rate and high electrical conductivity [2,[5][6][7]. Minimum content of FeCr alloys is about 18 wt% Cr, it can reduce oxides scale at high temperatures [6].…”

Evaluation of Thermal Properties of the Fe₈₀Cr₂₀ Nanostructure for Interconnect Application in High Temperature

“…The chromium content of protective single phase layer at least 17-20% which is depend on temperature, surface treatment and minor alloying addition [7,8]. Developing Fe 80 Cr 20 nanocrystalline is required since its properties in long term oxidation [9,10]. It conducted using high energy ball milling which is able to synthesis the single phase FeT(T=Cr, Cu and Ni) binary alloy.…”