Jean-Eric Masse

Laser Surface Nitriding of Ti-6A1-4V Titanium Alloy

Abstract Titanium and its alloys are known for their high specific strength as well as fatigue and corrosion resistance. However, they suffer from poor wear and friction resistance, limiting their use in tribological applications. Nitriding of these materials may be carried out favourably to harden them and thus to improve both wear and friction resistance. The laser nitriding process involves using the intense energy of the laser to melt the surface in a nitrogen comprising atmosphere. This results in creation of a very hard layer consisting of dendritic structures of nitride. But the non-uniformity of the melt pool and cracks in the nitrided layers have been generally observed. Our study deals with the results of Ti-6Al-4V laser surface nitriding and with the effects of a sample preheating on the cracks generation.

The influence of position in overlap joints of Mg and Al alloys on microstructure and hardness of laser welds

Structure and properties of laser beam welding zone of dissimilar materials, AZ31 magnesium alloy and A5754 Aluminum alloy, are investigated. The microstructure and quality of the Mg/Al weld were studied by metallography, microhardness, and optical microscopy. Differences in physical and mechanical properties of both materials, magnesium and aluminum, affect weldability and resistance of this combination, and lead to the formation of intermetallic compounds in the welded metal.

Ceramic Coatings on Titanium Alloy by CO2 Laser Treatment

Abstract Titanium alloys are widely used in various industrial sectors, especially in aeronautics, due to these specific properties: low density, good corrosion resistance, and fairly good mechanical properties. However, they have low wear and gall resistance. This limits their use in tribological applications. To improve surface properties of titanium alloys, one solution is creating hard surface layers. One way of creating such layers is the application of surface treatment with continuous high-power CO2 laser allowing the dispersion of solid additives into the laser-melted zone. Our study deals with the effects of direct powder injection in the laser-melted zone of two different powders (TiC, WC) on increasing hardness and surface modifications of a titanium alloy. Characterizations of the treated areas are carried out using classical techniques (optical micrography, scanning electron microscopy and Vickers microhardness measurements).

Neutron Evaluation of Stress in Industrial Screws

Neutron diffraction measurements were used in this study in order to determine the axial stress state in loaded screw from a specific assembly. The knowing of stress gradient is need to qualify a standard gauge used to calibrate the response of in-situ measurements using ultrasonic nondestructive technique. US is well adapted to perform measurements of the evolution of stress state on industrial screws during service life of the bolded assemblies.

CO2 laser beam welding of AM60 magnesium-based alloy

Magnesium alloys have a 33% lower density than aluminum alloys, whereas they exhibit the same mechanical characteristics. Their application increases in many economic sectors, in particular, in aeronautic and automotive industries. Nevertheless, their assembly with welding techniques still remains to be developed. In this paper, we present a CO2 laser welding investigation of AM60 magnesium-based alloy. Welding parameters range is determinate for the joining of 3 mm thickness sheets. The effects of process parameters including beam power, welding speed, focusing position, and shielding gas flow are studied. Experimental results show that the main parameters that determine the weld quality are the laser beam power, the welding speed, and the shielding gas flow. The focal point position has a minor effect on weld quality, however, it has an influence on melting zone width. For optimized welding parameters, metallurgical observations show that after laser welding of AM60 alloy dendritic microstructure is observed on melting zone after high solidification rate. A small heat affected zone is also detected. Finally, hardness tests indicate that microhardness of the weld is higher than that of base metal.