Effect of structure and residual stresses of diamond coated cemented carbide tools on the film adhesion and developed wear mechanisms in milling

A Critical Review of Measures for an Effective Application of Nano-Structured Coatings in Milling

“…During this test, depending on the applied repetitive impact load, a fatigue failure in the NCD coating-substrate interface develops after a certain number of impacts causing the film detachment. After this damage, the highly compressive stresses in the NCD coating structure are released elevating the coating in the detached circular region up to a certain maximum height (bulge formation) [11]. Characteristic diamond film bulges developed at certain impact loads, after approximately the shown number of impacts are shown in Fig.…”

“…The bars at the right figure part demonstrate the determined thermal and structural equivalent stresses in the investigated coating cases. These stresses were determined by means of the mentioned analytical methods [11], taking into account the mechanical properties and the dimensions (diameter and height) of the formed bulges. In the case of NCD insert group, the structural residual stresses are negligible at ambient temperature compared to the thermal ones.…”

“…For determining the maximum residual stress in the investigated diamond coatings, the experimental-analytical procedure described in [11,12] was employed. The experimental procedure comprises the conduct of inclined impact tests on the coated specimens.…”

“…Multilayered diamond coating systems, with successive nano-and micro-structured layers, can absorb a part of the residual stresses because of the more deformable microstructured layers compared to nanocomposite ones. The latter coatings possess increased brittleness due to their large compressive stresses which deteriorates the cutting performance [11]. It is worth mentioning that a prevailing mechanical property affecting significantly the cutting performance of diamond coated cemented carbide inserts is the fatigue strength of the diamond coating-substrate interface.…”

“…Moreover, nano multi-layer PVD structures has to be applied for restricting the film brittleness [7,8]. Furthermore, diamond coatings deposited on cemented carbide tools are characterized by high residual stresses in their structure mainly due to epitaxial crystal differences and thermal expansion coefficients mismatch of the diamond coating and its cemented-carbide substrate [9][10][11]. Multilayered diamond coating systems, with successive nano-and micro-structured layers, can absorb a part of the residual stresses because of the more deformable microstructured layers compared to nanocomposite ones.…”