Study of the Surface Integrity and High Cycle Fatigue Performance of AISI 4340 Steel after Composite Surface Modification

Hai Fu,Yilong Liang

doi:10.3390/met9080856

Abstract

In the field of materials science, the fabrication of a material with severe surface plastic deformation and a good surface state is an issue encountered in the development of counterbalanced gradient materials. For this paper, AISI 4340 steel was first processed with abrasive water jet peening (AWJP) and then with ultrasonic surface rolling (USRE) to obtain a good surface state while maintaining large plastic deformation. The AISI 4340 steel composite surface was therefore modified, and the surface integrity and cycle fatigue performance were analyzed. The results show that the plastic deformation layer of the modified composite surface of the 4340 steel was 310 µm from the surface of the sample, the grain size 40 µm from the surface layer was refined to 70 nm, and the maximum surface roughness Ra is 0.06. The fatigue limit of the modified composite surfaces obtained by the tensile fatigue test was 595.7 MPa, which was 85.7 MPa higher than the 510 MPa fatigue limit of the unmodified matrix, indicating that the method of composite surface modification can produce a deep deformation layer while maintaining good surface conditions. The results show that work hardening caused by a composite surface treatment is the most important factor for improving the fatigue performance of materials.

Highlights

Under normal service conditions, the damage of mechanical or structural parts is primarily caused by fatigue, and the fatigue failure of materials often starts at the surface, where cracks often start to form and propagate [1,2,3]
Specimen near the surface is shown, and it can be seen that the surface is severely plastically deformed
The subsurface layer forms a streamlined structure towards the rolling direction

Summary

Introduction

The damage of mechanical or structural parts is primarily caused by fatigue, and the fatigue failure of materials often starts at the surface, where cracks often start to form and propagate [1,2,3]. How to improve the surface quality of materials is an important consideration in material design and industrial application. Krahmer et al [5] takes the surface integrity and surface state as the consideration point, and abrasive water jet, wire electrodischarge machining, laser to replace the traditional milling processing of tensile samples, shortening the processing time and having great industrial value in industrial applications, In practical application literature [6,7,8,9], ball-burnishing means can be adopted to significantly improve the surface quality of materials, so as to improve the corrosion resistance and wear resistance of materials and reduce the wear ratio of materials. Torres et al [11] found that micro-cracks formed on the Metals 2019, 9, 856; doi:10.3390/met9080856 www.mdpi.com/journal/metals

Methods

Results

Discussion

Conclusion