| Popis: |
The working capacity of indenters made from hard alloy VK8 under conditions of reinforcing finishing treatment with ultrasonic tools was investigated. The morphology of the surface of the wear pad and its state after cobalt (Co) etching-out was studied using electron microscopic methods. It was determined that at low processing speeds the boundaries of the WC appear clearly, which is associated with intense interfacial slip and destruction along these boundaries. When the treatment speed reaches 50 m/min and above, the WC boundary is lubricated, which is caused by intensive plastic deformation of cobalt and destruction on this phase. It was shown that the wear of the carbide tool VK8 mainly occurs as a result of fatigue failure and the curve of wear versus the processing speed has a nonlinear character. It was found that along with plastic deformation of cobalt at small and medium processing speeds, plastic deformation by sliding takes place in some tungsten carbides WC. Slip bands are thin and extended within single carbide only. The expansion of the slip bands is impeded by the high fragility of tungsten carbide. The slip bands lie at a depth not exceeding 0.6 um, The destruction of tungsten carbide along the slip bands with a slight expansion of them is extremely rare. At processing speeds of 80, 120 m/min, no slip bands are observed, apparently, the temperature in the friction zone reached at these speeds is sufficient for processes such as polygonization. |
