ISSN:
1662-9752
Quelle:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Thema:
Maschinenbau
Notizen:
The degradation in ambient atmosphere of Al/SiCp composites prepared by the reactiveinfiltration of SiCp preforms containing fly ash has been investigated. SiCp/fly-ash preforms in theform of plates (3 cm x 4 cm x 0.5 cm) with 50 % porosity are infiltrated by an Al- 8 Si-15 Mg (wt.%) alloy under argon atmosphere at 1050, 1100 and 1150 ºC, for 50, 60 and 70 min.Characterization by XRD, SEM and EDX of composite specimens shortly after processing do notreveal the presence of the unwanted Al4C3 phase. However, in addition to Al, Si and SiC, MgAl2O4and Mg2Si phases are detected. One month after the infiltration trials, white and gray powders arepresent on the composite specimens, accompanied by pitting corrosion and cracks which propagatewith time. Although analysis by XRD of the degradation products reveals only Al4C3 in addition tothe above mentioned phases, results from SEM, IR absorption and ICP also suggest the presence ofAl(OH)3 and Mg(OH)2, probably from the interaction of Al4C3 and Mg2Si with water. It isconsidered that Mg2Si in the powders acts as an anode in a galvanic couple with atmosphericmoisture as the electrolyte. The crack pathway through SiC, intermetallic AlFeMnSi and Si richzones implies that one or more of these phases worked as the cathode. In summary, degradation ofthe composites is explained by the combined effect of galvanic corrosion caused by second phasesand the interaction of Al4C3 with atmospheric moisture
Materialart:
Digitale Medien
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/02/17/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.560.139.pdf
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