Failure analysis of tungsten carbide bearing on screw drill

The tungsten carbide bearing (TC bearing) is the main factor affecting the safety and durability of a screw-drilling tool. The TC bearing transmits torque and is subjected to severe radial shock, contact fatigue and corrosion. The failure of TC bearings are analyzed in detail and characterized by optical microscope (OM) and high resolution scanning electron microscopy (HRSEM) with energy spectrometer (EDS), electronic probe microanalyzer (EPMA), X-ray diffractometer (XRD), Rockwell hardness tester, and differential thermal and thermo gravimetric analyzer (DTA-TGA). The results showed that hot cracking of cemented carbide block of YG8 (WC-92%, Co-8%) mainly results from the diffusion of Co elements entering into the solder and W2C and Co3W3C brittle phases formation during heating and holding time. The W2C and Co3W3C phases promote initiation and propagation of brittle crack in the cooling stage and during working, resulting in fracture and detachment of YG8. Based on these results and failure analysis of TC bearings, some effective measures proposed to optimize the production process.