Effects of process combinations of milling, grinding, and polishing on the surface integrity and fatigue life of GH4169 components

Abstract

The nickel-based superalloy GH4169 is widely applied in the aviation industry due to its outstanding mechanical properties. However, many blades of GH4169 are still produced by milling and manual polishing, which is costly and unreliable. In this article, GH4169 superalloy components manufactured with combination processes of milling, grinding, and polishing were comparatively studied involving surface integrity and fatigue performance. Test results indicate that the final polishing is the most dominant process that influences the high-cycle fatigue life of GH4169 components. Samples produced via cubic boron nitride grinding and numerical control polishing with a diamond-rubber wheel exhibit fatigue limits of 150 MPa higher than the milled and manually polished samples. Cubic boron nitride grinding induces a considerable compressive residual stress profile with a magnitude of -930 MPa and a depth of 200 μm. Milling induces a typical “hook” residual stress profile with 318 MPa at the surface. Polishing affects the machined surface by two ways, the removal effect and the squeezing effect. The squeezing effect induces a shallow compressive residual stress with approximately −1000 MPa, therefore improves the surface condition. However, inevitable omissions, scratches, texture disorders, and knock marks in hand-polishing are the main causes of the unstable high-cycle fatigue life of hand-polished components.

Impact of grinding wheel specification on surface integrity and residual stress when grinding Inconel 718

“…16 The mechanical impact can be observed at low radial engagements, through the burnishing effect, but also where lower grinding forces are found, increasing the magnitude of compressive stresses. 15,17 Work carried out by Quan et al 18 when machining GH4169 (a material similar to Inconel 718) identified compressive residual stress conditions when grinding with electroplated cBN grinding wheels to a magnitude and depth to bulk of -765 MPa and 200 mm respectively.…”

“…The interaction between surface integrity metrics and resultant component fatigue performance has been reported by several authors. 18,22 Novovic et al 22 reported that a complex relationship exists between fatigue life and workpiece microstructure, surface topography and surface integrity. However, it is generally concluded that fatigue life is benefited from compressive residual stress regimes, but that surface roughness can temper the effect.…”

A multi-particle abrasive model for investigation of residual stress in belt grinding of titanium alloys

“…It is commonly used in the manufacture of blades for aeroengines, and can significantly improve the aero-engine service life and performance. [1][2][3] However, titanium alloy has low rigidity and easily deforms. During machining, the springback of the surface is large, which can produce severe friction and lead to processing defects such as burns.…”

Experimental evaluation of electrophoretic deposition-assisted polishing

“…Mostly, the constant-voltage EDP is utilized due to the easier configuration, as shown in Figure 1. 21,22 Only some limited research is available in the literature concerning the EPDAP method to date. Tsui and Yan 7 studied surface polishing of stainless steel by EPDAP using silicon carbide abrasives.…”