Real Structure of Milled Inconel 738LC Turbine Blades

Abstract

Machining of nickel super-alloys is difficult since mechanical hardening and, consequently, extreme tool wear occur. In the case of turbine blades, castings can no longer meet stringent requirements for precision; hence, they are being ground or milled in order to comply with the demanded dimensions. In this contribution, castings made of Inconel 738LC were machined by four axis milling. The resulting surface of gas turbine blades are characterized by several surface integrity parameters with respect to the structural inhomogeneities caused by mutual effect of plastic deformations and thermal fields during the cutting process. Moreover, the impact of effective contact area of the cutter was considered as well. It will be shown that ideal machining parameters viewed from the standpoint of surface roughness and economy of the whole machining process can lead to appreciable tensile normal stresses.