Effects of Sequential Operation with Heat Treatment and Mechanical Milling on Work Hardening for Superalloy GH4169

Pingzhong Zhu,Xiaoping Ren,Qinghua Song,Zhanqiang Liu,Bing Wang

doi:10.3390/met11091367

Abstract

Engineering components are usually manufactured with sequential production processes. Work hardening due to previous production processes affects the machinability of the workpiece in subsequent operations. In this research, the surface work hardening of a workpiece manufactured by two sequential processes with heat treatment/milling (HT + M) and milling/heat treatment (M + HT) of superalloy GH4169 was investigated. First, the surface microstructure characteristics, including plastic deformation and grain size of the machined workpiece surface processed by the two sequential processes, were quantitatively presented. Then, the microhardness on the machined workpiece surface and its cross-section was measured and analyzed. Finally, a surface microhardness calculation model considering twin boundary deformation was proposed. Here, we also present the microstructure evolution principle of the machined workpiece surface by the two sequential processes. It was found that the degree of work hardening of HT + M machining was 179%, whereas that of M + HT was only 101%. The research results can be applied to the optimized selection of process sequence for manufacturing superalloy GH4169.

Highlights

Nickel-based superalloy GH4169 (Inconel 718) can maintain good comprehensive performance at a high temperature and is widely used in hot-end components, such as turbine discs and the turbine blades of an aero-engine [1]
The objective of this study was to examine the microhardness distribution on the workpiece surface of GH4169 processed by sequential operations of solution heat treatment and a milling operation, and to reveal the work hardening mechanism required to optimize the selection of the process sequence for GH4169 production operations
When the as-received GH4169 was processed by the HT + M process, different changes appeared on the workpiece surface in the microstructure compared with the M + HT workpiece

Summary

Introduction

Nickel-based superalloy GH4169 (Inconel 718) can maintain good comprehensive performance at a high temperature and is widely used in hot-end components, such as turbine discs and the turbine blades of an aero-engine [1]. The excellent high temperature strength leads to poor machinability of GH4169 alloy, which is mainly manifested in a significant tendency toward work hardening [2]. A large degree of work hardening can improve the microhardness and strength of the workpiece surface, but increases the difficulty of subsequent cutting operations and affects the surface quality of the finished machined parts [3]. The mechanical and thermal loads exerted by the machining process cause severe plastic deformation on the workpiece surface, which leads to changes in the microstructure of the material, including grain refinement and phase transformation, and, changes in the microhardness of the machined surface [4]. Consideration should not be limited to only the influence of a single cutting process on the workpiece surface quality

Objectives

Methods

Results

Conclusion