Papers by Author: P. Chevrier

Abstract: This paper reviews some recent results concerning surface integrity of materials processed with two important developing techniques: high speed machining (HSM) – here applied to the difficult case of Ti alloys – and low energy high current pulsed electron beam (LEHCPEB) surface treatment of steels. The effect of the processing parameters on the development of microstructure, texture and residual stresses is detailed for modifications occurring both at the surfaces and sub-surfaces.

Abstract: A titanium alloy Ti-6 Al(wt%)-4V(wt%) was treated in air by Nd:YAG laser radiation (wavelength of 1.064 %m) in continuous mode. Targets were irradiated globally with different levels of energy (accumulated fluence) at constant power. Different focal lengths and beam displacement velocities were used. Cross section microstructural observations were carried out by scanning electron microscopy. Backscattered electron imaging reveals microstructural modifications in samples. A structural phase transformation of beta (bcc) to alpha prime (hcp) phase was observed. The depth of the transformed zone observed by phase transformation is dependent on the treatment parameters. Conformity between microstructural observations and the treatment parameters is discussed with reference to thermal simulations.

Abstract: Machining of modern materials requires high performance tools. More than 60% of metal cutting tools used are coated to limit abrasive wear. As the harder material known to man, diamond and consequently Chemical Vapour Deposited (CVD) diamond coatings allow to increase performances of tungsten carbide tools, i.e. tool life, machined surface quality, and to decrease costs. However, CVD diamond coated tools quality is very dependent on the surface preparation as much as the fabrication process parameters. This paper aims to discuss the influence of pretreatments before deposition, and thermal stresses induced by the cooling operation. Diamond deposition process is described emphasizing the role of every step and its function. Some numerical simulations of the residual stresses at the interface are presented, enlightening that tool geometry is an important factor while using a coating, and that tools must be designed for the diamond coating.