SPONTANEOUS INFILTRATION OF Al MELTS INTO SiC PREFORM H. Nakae
Waseda University, Tokyo, Japan Y. Hiramoto
Hitachi Cable Ltd., Ibaragi, Japan (Prev. Graduate student, Waseda Univ.) Copyright © 2011 American Foundry Society Abstract
powder, causes a chemical reaction between the melt and the binder. The preform, dipped into the melt, was spontaneously infiltrated, and the infiltration process was confirmed by measurement of the preform weight change during the dipping. Nevertheless, the infiltration mechanism
O3 Introduction
Since the advent of metal matrix composites (MMC), SiC has been considered one of the most attractive candidates as a ceramic material for particulate reinforced metals and fiber-reinforced metals because of its low price and high hardness.1
The infiltration process is one of the most useful
fabrication methods for MMC. Nevertheless, the wettability between a molten metal and ceramics is usually so poor that the pressured infiltration processes have been widely used.2 To realize a pressureless infiltration process, i.e., sponta- neous infiltration, a good wettability between the molten metals and ceramics should be required. The contact angle was reported to be less than 50.7 degrees.3
One of the most
also reported that the spontaneous infiltra- tion process can be done at very high temperatures such as 1400 C (2552F) and 1500C (2732 F) using the SiC/Al-Si melt system.
nevertheless, it requires more than 10 hours at 900C (1652F) in a nitrogen atmosphere using Al-Si-5%Mg alloys. Xi et al.6
well-known spontaneous infiltration processes is the Lanx- ide Process;4,5
The infiltration process is one of the most useful fabrication methods for metal matrix composites (MMC). Nevertheless, the wettability between the molten metal and ceramics is usually so poor that pressured infiltration processes have been widely used. However, this process results in high production costs. Therefore, we have been developing a spontaneous infiltration process using an Al-Si-Mg melt and a SiC preform. The SiC preform, fabricated using a water glass binder mixed with Fe2
is still not clarified. To clarify the mechanism and further the development, additional experiments, using SiC particles with grain sizes of 30, 68, 220 and 420 µm, were carried out. In the preform, fabricated only with the fine particles, there is no infiltration. Nevertheless, if these fine particles were enclosed within the 420µm layers, spontaneous infiltration occurs. The onset of the infiltration occurred during the breaking of the melt oxide film along with a decrease in the gas pressure by the chemical reaction between the trapped gases in the preform and the Mg and Al in the melt.
Keywords: infiltration, spontaneous infiltration, wettability, reactive wetting
mixed with Fe3O4 between the melt and the binder7,8
powder that caused an exothermic reaction for improving their wetta-
tion was discussed, and the advantage of the Fe2 was confirmed due to its high partial pressure of oxygen.9,10
O3 powder and Fe3 O4
bility. The onset of the spontaneous infiltration occurs at a few hundred seconds after the preform dipping, and the infiltration is finished within a few seconds. The infiltration processes were confirmed by the measurement of the preform weight change during the dipping using a load sensor. The influence of iron oxide, Fe2
powder, on the infiltra- O3
powder
To clarify the mechanism and provide further development, experiments were carried out using SiC particles with grain sizes of 30, 68, 220 and 420 µm. The influence of the grain size on the infiltration and how to make a high volume frac- tion MMC using a mixture of these particles were studied.
Experimental Procedure Influence of SiC Particle Size on Infiltration
A spontaneous infiltration process has been developed, in which the infiltration occurs within a few hundred seconds using the Al-Si-Mg melt and SiC-preform system, made of
SiC particles with a grain size of 420 µm, at 900C (1652F) in air. The preform was fabricated using a water glass binder
International Journal of Metalcasting/Spring 11
The average diameters of the green carborundum particles (abbreviated SiCp) were 30 µm, 68 µm, 220 µm and 420 µm. Sixty grams of each SiCp were mulled and coated with 5 ml of the binder to form a 45 mm diameter x 25 mm thick preform. The binder was made of 240 ml pure water, 90 ml water glass binder and 50g Fe2
O3 powder and mixed using 23
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