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Effect of ultrasonic impact treatment on the surface integrity of nickel alloy 718 Zheng Zhou1,2 • Chang-Feng Yao1,2 • Yu Zhao1,2 • Yang Wang1,2 • Liang Tan1,2

Received: 22 June 2020 / Revised: 15 September 2020 / Accepted: 21 October 2020 Ó Shanghai University and Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract Ultrasonic impact treatment (UIT) is a type of surface strengthening technology that can improve the fatigue properties of materials by improving the surface quality, residual stress, and other aspects. In this study, the influence of ultrasonic impact parameters on the surface integrity of nickel alloy 718 was studied. The micro stress concentration caused by the surface morphology was also explored. The cosine and exponential decay functions were used to fit and characterize the distribution of residual stress and work hardening in the surface material. The results showed that the feed rate had the greatest influence on surface roughness, stress concentration, and surface residual stress. It was not appropriate to evaluate the surface hardening effect only by the number of impacts per unit area, the ultrasonic impact parameters such as feed speed and pre extrusion depth should also be considered. The grain refinement was obvious after UIT. The multiobjective optimization of machining parameters was performed with the objective of surface stress concentration and residual stress. A surface with a smaller surface stress concentration factor and larger compressive residual stress can be obtained simultaneously using medium linear

& Chang-Feng Yao [email protected] 1

Key Laboratory of High Performance Manufacturing for Aero Engine, Ministry of Industry and Information Technology, School of Mechanical Engineering, Northwestern Polytechnical University, Xi’an 710072, People’s Republic of China

2

Engineering Research Center of Advanced Manufacturing Technology for Aero Engine, Ministry of Education, School of Mechanical Engineering, Northwestern Polytechnical University, Xi’an 710072, People’s Republic of China

velocity, medium pre extrusion depth, and smaller feed rate. Keywords Nickel alloy 718  Ultrasonic impact  Surface stress concentration  Surface integrity  Grain refinement

1 Introduction Nickel-based superalloy 718 is widely used in the manufacture of aero-engine hot-end parts. In the production of aero-engine parts, the machined surface was often improved by subsequent strengthening technologies to improve the fatigue performance. In recent years, there has been an increasing amount of research on ultrasonic vibration-assisted processing technology. Compared with the traditional milling technology, the milling force of ultrasonic-assisted milling was slightly reduced [1]. Owing to the ultrasonic impact of the tool on the machined surface, the residual compressive stress level of the machined surface increased and the fatigue life improved [2]. Ultrasonic impact is a type of surface strengthening technology that introduces ultrasonic vibration on the basis of the traditio