SMALL ENERGY MULTI-IMPACT AND STATIC FATIGUE PROPERTIES OF CEMENTED CARBIDES

Abstract

The small energy multi-impact (SEMI) and static fatigue properties of cemented carbides with different Co content (11, 15, and 18%) are studied. It is established that the cemented carbide with higher cobalt content ensures longer SEMI and static fatigue life, when the impact energy is lower than the impact fracture energy at one time and the static stress is lower than the bending strength (σbb). However, with the same value of λ (the ratio of the impact energy to the impact fracture energy at one time) and θ (the ratio of the static stress to the bending strength), the SEMI and static fatigue life of three alloys decrease with increasing the Co content. It is determined that the cemented carbide with a Co content of 18% has a higher dynamic fatigue and static fatigue sensitivity and corresponding weak fatigue crack propagation resistance, which means that high cobalt alloys need a higher safety factor under operating conditions. The static fatigue life of notched samples is lower than that of smooth samples. When θ equals to 0.8, the fatigue life ratio of three smooth samples and three notched samples (with Co content of 18, 15, and 11%) is approximately1 : 2 : 7 and 1 : 1 : 2, respectively, indicating that pre-notched samples cover the defects of cemented carbides. The fracture of the hardmetals bearing low energy (SEMI and static fatigue) results from the growth and connection of holes (or coarse WC) and micro-cracks.