L’influence de l’électroérosion et du micro-grenaillage sur les propriétés de surface de l’Inconel 718

Abstract

Inconel 718 is a nickel-based superalloy used for the manufacturing of parts subjected to fatigue at high temperature. The machining process of Inconel 718 can be a challenge with the high mechanical strength of the material and tool wear. The use of the wire EDM process allow to extract a sample without contact between the tool and the material. To enhance fatigue properties, shot peening is widely used to induce a layer of compressive residual stress even though most of the time it is at the expense of the surface finish. Fine particle shot peening is a modification of standard shot peening where the shot diameter is smaller. The goal of this modification is to keep the compressive stress layer while keeping or improving the roughness of the surface. The goal of this research is to document the effect of fine particle shot peening and wire EDM on the surface properties of Inconel 718. The first test was done with fine particle shot peening to evaluate different shot peening media. Shot peening was done on wire EDM samples using shot diameter of 150 μm, 200 μm and 300 μm. The shot peening process reduced surface roughness and induced compressive residual stress of approximately -950 MPa depending on the shot diameter and the shot material. The second test was done to evaluate the effect of the shot peening pressure and the nozzle height on surface properties. The pressure varied from 0,05 MPa to 0,30 MPa and the nozzle height varied from 25 mm to 125 mm. With higher shot peening pressure, there is an increase in roughness and residual stress on the surface and in depth. With a higher nozzle height, there is a decrease in roughness, without affecting residual stress on the surface or in depth. In addition, three surface finishes obtained by wire EDM were studied, one rough and two of finition. The samples with lower roughness have a higher fatigue performance. Grain size was also studied and divided in three categories: fine grain of 10-15 μm, intermediate grain of 15- 25 μm and coarse grain of 25-30 μm. The effect of grain size on the fatigue properties was also studied. It is difficult to evaluate the effect of grain size on the fatigue properties since the surface finish has the biggest influence.

Date	20 Aug 2021
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Philippe Bocher (Supervisor)