Improvement in Mechanical Properties of Cryogenically Treated WC-5 wt% NbC Hard Materials Sintered by Pulsed Current Activated Sintering

Abstract

Recently, the necessity of designing and applying tool materials that perform machining of difficult-to-cut materials in a cryogenic treatment where demand is increasing. The objective of this study is to evaluate the performance of cryogenically treated WC-5 wt% NbC hard materials fabricated by a pulsed current activated sintering process. The densely consolidated specimens are cryogenically exposed to liquid nitrogen for 6, 12, and 24 h. All cryogenically treated samples exhibit compressive stress in the sintered body compared with the untreated sample. Furthermore, a change in the lattice constant leads to compressive stress in the specimens, which improves their mechanical performance. The cryogenically treated samples exhibit significant improvement in mechanical properties, with a 10.5 % increase in Vickers hardness and a 60 % decrease in the rupture strength compared with the untreated samples. However, deep cryogenic treatment of over 24 h deteriorates the mechanical properties indicating that excessive treatment causes tensile stress in the specimens. Therefore, the cryogenic treatment time should be controlled precisely to obtain mechanically enhanced hard materials.