Aurélien Besnard

Metal-to-Dielectric transition induced by annealing of oriented titanium thin films

Titanium thin films were deposited by DC magnetron sputtering. The glancing angle deposition (GLAD) method was implemented to prepare two series of titanium films: perpendicular and oriented columnar structures. The first series was obtained with a conventional incident angle α of the sputtered particles (α = 0°), whereas the second one used a grazing incident angle α = 85°. Afterwards, the films were annealed in air using six cycles of temperature ranging from 293 K to 773 K. DC electrical conductivity was measured during the annealing treatment. Films deposited by conventional sputtering (α = 0°) kept a typical metallic-like behavior versus temperature (σ300 K = 2.0 × 106 S m-1 and TCR293 K = 1.52 × 10-3 K-1), whereas those sputtered with α = 85° showed a gradual transition from metal to dielectric. Such a transition was mainly attributed to the high porous structure, which favors the oxidation of titanium films to tend to the TiO2 compound.

Effect of RGPP process on properties of Cr-Si-N coatings

Abstract CrSiN films were deposited by reactive radio frequency magnetron sputtering in an Ar+N2 gas mixture. The nitrogen gas was injected in the deposition chamber using two methods: the classical constant injection and pulsed injection, the latter known as the reactive gas pulsing process (RGPP). Argon gas was continuously injected, whereas nitrogen gas was pulsed during the deposition. The RGPP was used to adjust the chemical composition and, consequently, allowed the improvement of the coating characteristics. The effect of process parameters such as silicon content and gas pulsing conditions (especially duty cycle α) on the crystallographic structure, chemical composition and morphology of the CrSiN layers is reported. It was found that the surface morphology evolves from a pyramid-like feature for 100% duty cycle to a typical cauliflower-like aspect, when duty cycle decreases to 84%. For shorter duty cycles, the growth produced a denser coating, with round and finer clusters.

Investigation of the Effect of Residual Stress Gradient on the Wear Behavior of PVD Thin Films

The control of residual stresses has been seldom investigated in multilayer coatings dedicated to improvement of wear behavior. Here, we report the preparation and characterization of superposed structures composed of Cr, CrN and CrAlN layers. Nano-multilayers CrN/CrAlN and Cr/CrN/CrAlN were deposited by Physical Vapor Deposition (PVD) onto Si (100) and AISI4140 steel substrates. The Cr, CrN and CrAlN monolayers were developed with an innovative approach in PVD coatings technologies corresponding to deposition with different residual stresses levels. Composition and wear tracks morphologies of the coatings were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, atomic force microscopy, x-ray photoelectron spectroscopy, energy-dispersive x-ray spectroscopy, x-ray diffraction and 3D-surface analyzer. The mechanical properties (hardness, residual stresses and wear) were investigated by nanoindentation, interferometry and micro-tribometry (fretting-wear tests). Observations suggest that multilayer coatings are composed mostly of nanocrystalline. The residual stresses level in the films has practically affected all the physicochemical and mechanical properties as well as the wear behavior. Consequently, it is demonstrated that the coating containing moderate stresses has a better wear behavior compared to the coating developed with higher residual stresses. The friction contact between coated samples and alumina balls shows also a large variety of wear mechanisms. In particular, the abrasive wear of the coatings was a combination of plastic deformation, fine microcracking and microspallation. The application of these multilayers will be wood machining of green wood.

Flank wear prediction in milling AISI 4140 based on cutting forces PCA for different cutting edge preparations

One of the criteria mastering the choice of a cutting tool is its wear resistance. For coated inserts, prior to the coating process, edge preparation method choice will impact their performance. So, a classification based on its impact on wear resistance is needed. Indeed, the flank wear of three coated cemented carbide inserts presenting differently prepared edges (untreated, dragging and magneto-abrasive machining) is explored experimentally. Those inserts are used to face mill the hardened AISI 4140 low alloy steel. Further, by means of the principal component analysis (PCA), correlations between the online measured cutting forces and flank wear behaviour are investigated. In view of this analysis, for each studied case, the statistical law predicting flank wear relying on cutting forces components is established with fair approximation. However, the experimental results have quantitatively shown that edge preparation could be in some cases not beneficial for tool wear resistance of the milling inserts considering either maximal or average flank wear.