Abstract
Nano-composite (NCD) and multi-layered (MLD) diamond coatings were deposited on cemented carbide tools using hot filament chemical vapour deposition (HFCVD) techniques. Appropriate annealings were conducted on the examined diamond coatings in order to be characterized by the same level of residual stresses. The crystalline structure of the employed diamond coatings was investigated by conducting Raman spectra. Inclined impact tests at ambient and elevated temperatures were carried out for assessing their temperature-dependent fatigue strength. Moreover, the wear behaviour of diamond coated inserts was investigating in milling aluminum foam. Raman spectra were also conducted on the treated diamond coatings for capturing potential crystalline changes developed due to the exercised thermal and dynamic mechanical loads during cutting. According to the attained results, the coexistence of sp2– and sp3-bonded phases in the cases of MLD diamond coatings results in an accelerated wear development, despite their structure capability to decelerate the crack propagation. As a result, nano-crystalline diamond coatings characterized only by sp3-bonded phase exhibit an improved wear behaviour. The cutting performance of the NCD coated inserts is further improved due to the enhanced tribological properties of the NCD coatings.
Highlights
Nano-composite (NCD) and multi-layered (MLD) diamond coatings can be effectively applied in machining of nonferrous materials such as of aluminium alloys, carbon fibre reinforced plastics etc. [1,2,3,4]
The high level of residual stresses in the diamond film structure is attributed to epitaxial crystal differences and thermal expansion coefficients mismatch of the diamond coating and its cemented-carbide substrate [4,7]
An effective way to reduce the structural residual stresses in the diamond film structure is attained by appropriate annealing
Summary
Nano-composite (NCD) and multi-layered (MLD) diamond coatings can be effectively applied in machining of nonferrous materials such as of aluminium alloys, carbon fibre reinforced plastics etc. [1,2,3,4]. Due to the superior adhesion characteristics of microcrystalline diamond layers and to improved tribological properties of nano-crystalline diamond ones, various micro- and nano-crystalline layer coating systems on cemented carbide substrates are manufactured and used effectively in machining procedures [5,6]. In the frame of this work, NCD and MLD coatings were produced and appropriately annealed in vacuum at a temperature of 400oC for possessing the same level of residual stresses [8]. By decoupling the effect of residual stresses in the diamond film structure on the films’ fatigue strength, the impact of a nano-crystalline structure or a combination of nano- and microcrystalline diamond layers on the wear behaviour of diamond coated tools was assessed
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