Novel Pack Cementations: Alternating Current Field Enhanced Pack Cementations

Abstract Thermal chemical treatments can effectively improve the surface properties of steels to resist wear, erosion, fretting, and oxidation. Among the various types of thermo-chemical treatment, pack cementation is most often employed for diffusing boron, aluminum, chromium, or silicon into the surface of steel. Pack cementation is superior to other thermo-chemical treatments in process simplicity and flexibility. However, like many other thermo-chemical treatments, conventional pack cementation (CPC) has the disadvantages of a high processing temperature and a long processing duration for obtaining a thick case. A novel approach is presented to enhance pack cementations by applying an alternating current field (ACF) on specimens and pack media. An adjustable 50 Hz alternating current power source was connected to a pair of parallel electrodes set in pack media. Investigations were conducted into the influences of the ACF on pack boriding, aluminizing, chromizing, and silicon-aluminizing. Cases’ thicknesses, structures, phases, hardness distributions, and oxidation resistances were characterized with optical microscopy, X-ray diffraction, Vickers’ hardness testing, and oxidation testing. These treatments can be carried out effectively at temperatures much lower than temperatures for CPC. The ACF can optimize cases’ structures and phases as well as accelerate cases’ growth. Brittle phases, such as iron boride and Al5Fe2, formed on a steel surface by CPC can be easily and economically avoided. The new technology can endow steels with properties that are much better than those provided by CPC. It is suggested that the ACF can enhance chemical reactions among pack agents by heating pack media and intensifying vibrations of active species. The formation, activity, and diffusion of active species containing required elements are promoted. The electromagnetic effect and the heating effect of the ACF increase vacancy concentrations in specimens, which greatly enhance diffusion in treated specimens.