Corrosion Behavior of Detonation Gun Sprayed Fe-Al Type Intermetallic Coating
The detonation gun sprayed Fe-Al type coatings as an alternative for austenitic valve steel, were investigated using two different methods of testing corrosion resistance. High temperature, 10-hour isothermal oxidation experiments at 550, 750, 950 and 1100 °C show differences in the oxidation behavior of Fe-Al type coatings under air atmosphere. The oxide layer ensures satisfying oxidation resistance, even at 950 and 1100 °C. Hematite, α-Al2O3 and metastable alumina phases were noticed on the coatings top surface, which preserves its initial thickness providing protection to the underlying substrate. In general, only negligible changes of the phase composition of the coatings were noticed with simultaneous strengthening controlled in the micro-hardness measurements, even after 10-hours of heating at 1100 °C. On the other hand, the electrochemical corrosion tests, which were carried out in 200 ppm Cl− (NaCl) and pH ~4 (H2SO4) solution to simulate the acid-rain environment, reveal higher values of the breakdown potential for D-gun sprayed Fe-Al type coatings than the ones for the bulk Fe-Al type alloy and Cr21Mn9Ni4 austenitic valve steel. This enables these materials to be used in structural and multifunctional applications in aggressive environments, including acidic ones.
Crystalline oxalic acid aided FeAl intermetallic alloy sintering. Fabrication of intermetallic foam with porosity above 45
Abstract Intermetallic Fe–Al foam was formed via organic compound assisted sintering. To the starting mixture of iron and aluminum elemental powders various amount of crystalline oxalic acid (COA), (COOH)2•2H2O was added as the foaming agent. Due to the decomposition reaction, gaseous products were formed and behaved as the foaming agents. With this approach Fe–Al intermetallic foam was formed and major role of the COA was confirmed by elemental maps. In the pores, remaining traces of carbon were found. It was also found that at 3 wt% of COA additive the greatest porosity equal 48,5%±4,3% was obtained. Above 3 wt% the formed foam was defragmenting. Additionally, to investigate functional application of the formed Fe–Al intermetallic foam, the pressure drop of air during penetration the porous material was examined. It was found that increased porosity of the sintered material allowed to increase the flow of the air through the metallic foam.
Surface roughness monitoring by singular spectrum analysis of vibration signals
Abstract This study assessed two methods for enhanced surface roughness (Ra) monitoring based on the application of singular spectrum analysis (SSA) to vibrations signals generated in workpiece-cutting tool interaction in CNC finish turning operations i.e., the individual analysis of principal components (I-SSA), and the grouping analysis of correlated principal components (G-SSA). Singular spectrum analysis is a non-parametric technique of time series analysis that decomposes a signal into a set of independent additive time series referred to as principal components. A number of experiments with different cutting conditions were performed to assess surface roughness monitoring using both of these methods. The results show that singular spectrum analysis of vibration signal processing discriminated the frequency ranges effective for predicting surface roughness. Grouping analysis of correlated principal components (G-SSA) proved to be the most efficient method for monitoring surface roughness, with optimum prediction and reliability results at a lower analytical-computational cost. Finally, the results show that singular spectrum analysis is an ideal method for analyzing vibration signals applied to the on-line monitoring of surface roughness.