Experimental Investigations Into the Carbide Cracking Phenomenon on Inconel 718 Superalloy Material

Inconel 718 (IN718) presents significant challenges in machining due to its high strength properties at high temperature, attributable to the hard niobium and titanium carbide phases. Machined surfaces (oblique turning) at conventional conditions of speeds and feeds, typically show a tendency of those carbides to crack, drag and smear under the machining stresses and deformation. Such behavior can severely debilitate the fatigue strength of the material, and cause accelerated damage. This paper describes the experimental investigations as well as the qualitative and quantitative studies undertaken to study and mitigate the impact of process variables and tool geometry parameters on the carbide surface cracking phenomenon. SEM observations showed the feed rate (or chip thickness), nose radius, and insert grade-edge geometry to have significant influences on the behavior of these surface carbides.