Accelerate pack boriding with reused boriding media by simultaneously employing Al and alternating current field

For making full use of reused boriding powder and accelerating pack boriding at a medium temperature, a novel approach was developed by adding Al powder in boriding agent and simultaneously applying a 50 Hz alternating current field (ACF) during treating. Boride coatings were investigated with optical microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy. By adding 2 wt-% Al and applying an ACF with a current of 2 A during the 4 h boriding at 750 °C, a boride coating with a thickness nearly 3 times the thickness of a coating by corresponding conventional pack boriding (CPB) is obtained. As the ACF current increases to 6 A, the coating thickness is about 10 times the thickness of coating by corresponding CPB. The Al's enhancing effect is attributed to the Al's reducing effect to the ferroboron in boriding agent to let the boron be released into atmosphere more efficiently.