Process and High-Temperature Oxidation Resistance of Pack-Aluminized Layers on Cast Iron

Pack aluminizing of spheroidal graphite cast iron with different aluminizing temperature and time was studied. Results showed that the thickness of aluminized layer increased with the increasing temperature and time. The optimized process parameters are as follow: the aluminizing packed temperature is 830 °C and the time is 3 h. The aluminized layer consisted of the inner FeAl and the outer Fe2Al5. Some graphite nodules were observed in the aluminide layer after aluminizing. The mass gain of the aluminized cast iron was 0.405 mg/cm2, being 1/12 of the untreated substrate after oxidation. The high temperature oxidation resistance can be improved effectively by pack aluminizing, even though there were graphite nodules in the aluminide layer.

Investigation of a Simultaneous Silicon-Modified Pack Aluminizing Method on Pure Nickel Using Quartz and RHA

This research aims to study the simultaneous silicon-modified pack aluminizing method using silica (SiO2) from Rice Husk Ash (RHA) which contains 99.45% SiO2 in comparison with commercial SiO2 in the form of quartz. Samples can thus be categorized into two groups: quartz-doped and RHA-doped. Simultaneous silicon-modified pack aluminizing of pure nickel was performed at 1000°C for 4 hours under an argon atmosphere. The pack used in this research was prepared from aluminum (Al), ammonium chloride (NH4Cl), alumina (Al2O3) and silica (SiO2, i.e. quartz and RHA) powder at ratios of 29:2:60:9 by weight, respectively. Post aluminized samples were characterized by glancing incident-angle X-ray diffractometer (GIXD). Quantitative analysis of the layer was performed using energy dispersive spectroscopy (EDS). A scanning electron microscope (SEM) was employed to observe the resulting microstructure. It was found that simultaneous silicon-modified pack aluminizing can be successfully performed by doping RHA and quartz into the pack. The aluminized layer consists of Ni2Al3 and NiAl3 with a small amount of silicon. RHA was found to be more effective than quartz as a silicon source providing a higher amount of silicon in the aluminized layer. Moreover, using RHA successfully forms a silicon-rich interdiffusion layer beneath the typical aluminized layer.