20-12-2012, 06:23 PM
Effect of CeO2 Addition on the Properties of FeAl based Alloy Produced by Mechanical Alloying Technique
Effect of CeO2 Addition on the Properties.docx (Size: 484.06 KB / Downloads: 136)
INTRODUCTION
From the mid-1900s, accelerating an effort has been directed towards increasing the temperature capability of existing materials systems and developing new material types. Understanding the material behaviour and control of component manufacture to ensure the desired behaviour have been key elements of these activities for all materials systems [1-5]. The requirement to operate at progressively higher temperatures will remain an on-going need for the foreseeable future. Many industries will benefit from increased operating temperatures. As for example, in electricity generation, the efficiency of ultra-supercritical pulverized coal power plant can be increased from the current 47% to 50% if the steam parameters can be increased from 290-bar/580C to 325-bar/625C [6]. This will give major saving in fuel and consequent environmental benefits. Materials with higher temperature capability are essential if these, and many other objectives, are to be met. High temperature materials research in the metals and alloys area are still an extremely important field, and new alloy and composite systems are continually being developed for new applications [7].
EXPERIMENTAL PROCEDURES
Mechanical alloying of a mixture of elemental powders which consist of 72 wt.% Fe (60 m, 99.9% purity), 28 wt.% Al (44 m, 99.9% purity) with two different additions of CeO2 at 0.5 and 1 wt.% were conducted using a high-energy planetary ball mill for 46 hours and the vials rotated at a speed of 200 rpm. Milling was undertaken at room temperature using hardened steel balls and the balls to powder ratio was set at 10 : 1 by weight. Milling was conducted in a dried argon atmosphere and 2 wt.% of stearic acid was added to the system to prevent excessive welding in the chamber. The milled powders were then hot pressed at 25 MPa into a cylindrical shape with 33 mm diameter and 3-4 mm height and sintered at 1150 oC for 1 hour. The hot pressed samples were cut into 6 pieces before being grinded to 240-1000 grit SiC papers and polished to 1 m diamond paste until the surface scratches were removed. After ultrasonically clean in ethanol for about 30 minutes, the samples were then oxidized at 1100 oC for 5 cycles, and each cycle consists of 8 hours heating in the tube furnace in laboratory atmosphere. The sample weights were recorded after each cycle as need to plot the weight change versus oxidation time graph to observe the oxidation kinetics. The accuracy of the weight measurement is 0.1 mg. The hardness test was determined based on the Rockwell method on the as consolidated material. Characterization was conducted on the as milled powders and on as consolidated material. Changes of sample surface were determined by scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX). The oxide layers were analysed by X-ray diffraction (XRD).
CONCLUSIONS
The present study demonstrates FeAl alloy with CeO2 addition can be synthesized by powder metallurgy followed by hot pressing technique. The CeO2 alloyed FeAl show improved microstructure, oxidation resistance and hardness. Increasing trend in the inherent properties of samples with an increase in wt.% of ceria shows that CeO2 particles as active element can impart superior properties to FeAl alloy.