Micro-scale impact testing on cemented carbides

Probe geometry and surface roughness effects in microscale impact testing of WC-Co

“…In a Hertzian (elastic) stress field the maximum tensile stress is at the circle of contact and falls off dramatically below the top surface. [22] Figures 2 and 5 show that the region with greatest cracking extends significantly beyond the Hertzian contact radius, as has been observed in cyclic impact loading with a 5 mm radius Si3N4 indenter [5] and in micro-impact tests on other cemented carbides [16]. This is considered to be due plasticity resulting in pile-up moving the peak radial tensile stresses outward.…”

“…The impact resistance of the cutting tool grade tested in this study after polishing can be directly compared to highly polished samples of grades used in oil and gas drilling applications that were studied previously with a 20 µm probe under the same test conditions. [16] Since cemented carbides show a smaller-is-stronger size effect in hardness [11,28] the indentation peak load was the same in ref. [16] and the current study.…”

“…[16] Since cemented carbides show a smaller-is-stronger size effect in hardness [11,28] the indentation peak load was the same in ref. [16] and the current study. In that study two cemented carbide grades with 5-7 wt.% of mixed Co-Ni binder with H ~22-23 GPa and H 3 /E 2 = 0.25-0.33 GPa showed better resistance.…”

“…It has been used recently to evaluate the behaviour of three cemented carbide grades commonly used for oil and gas applications under micro-scale impact fatigue, two of them having similar hardness and toughness values, one with the presence of cubic phases. [16] The highest resistance to impact fatigue was not achieved by the hardest and stiffest grade, nor the toughest grade, but for one with highest ratio of hardness (H) to elastic modulus (E) and H 3 /E 2 . It is generally accepted for cemented carbides that high toughness is important in highly loaded mechanical contact, but the micro-and macro-tests above suggest that for optimum durability a suitable combination of high hardness and toughness is required.…”

“…[17,18] Some impact tests with a 20 m end radius probe were performed under the same experimental conditions as in ref. [16] , allowing the results to be compared to those obtained on the grades tested in that study. The influence of mechanical properties such as H 3 /E 2 on impact resistance is investigated.…”