Elsevier

Materials Letters

Volume 65, Issue 9, 15 May 2011, Pages 1268-1271
Materials Letters

Effect of surface nanocrystallization on the tribological properties of 1Cr18Ni9Ti stainless steel

https://doi.org/10.1016/j.matlet.2011.01.041Get rights and content

Abstract

Surface nanocrystallization of 1Cr18Ni9Ti austenite stainless steel was conducted by the supersonic fine particles bombarding (SFPB) technique. The friction coefficients and wear losses in air and vacuum were tested to analyse the effect of surface nanocrystallization on the tribological properties of 1Cr18Ni9Ti steel. The results show that the microstructure of the surface layer was refined into nano-grains successfully by SFPB treatment; furthermore, strain-induced martensitic transformation occurred during the treatment. The tribological properties of SFPB treated samples enhanced greatly, The dominant wear mechanism of the original 1Cr18Ni9Ti stainless steel is abrasive wear and adhesive wear, while it transfers to the combined action of fatigue wear, abrasive wear and adhesive wear after surface nanocrystallization by SFPB.

Research Highlights

► A nanocrystalline surface layer was fabricated on the 1Cr18Ni9Ti stainless steel by the supersonic fine particles bombarding (SFPB) technology. ► The SFPB treatment induced grain refinement and martensitic phase transformation in the top surface layer. ► The increase of hardness and surface activity of stainless steel after SFPB treatment can enhance its tribological properties notably. ► The dominant wear mechanism of the original 1Cr18Ni9Ti steel are abrasive wear and adhesive wear, while it transfers to the combined action of fatigue wear, abrasive wear and adhesive wear after surface nanocrystallization by SFPB.

Introduction

Nanomaterials with unique structure and excellent properties have attracted great scientific attention since last century [1]. Recently, surface nanocrystallization is considered the most likely breakthrough in the engineering applications of nanotechnology [2]. The surface nanocrystallization of metal materials can improve their physical and chemical properties notably, especially the tribological properties [3]. Applying impact energy of certain frequency and intensity to a component surface to induce severe plastic deformation is the main method of surface nanocrystallization [4]. Researchers have developed mechanical attrition treatment (SMAT), ultrasonic shot peening (USSP), supersonic fine particles bombardment (SFPB) and other surface nanocrystallization process, and fabricated nanocrystalline surface layer on pure iron, carbon steel, stainless steel and other materials successfully [5]. Among them, the SFPB technology is very suitable for the surface nanocrystallization of components with complex shape or large dimension, making it have large engineering application potentiality.

In this study, the 1Cr18Ni9Ti steel was treated by SFPB. The microstructure and mechanical properties of the SFPBed (SFPB treated) 1Cr18Ni9Ti steel were studied to reveal the effect of surface nanocrystallization on the tribological properties.

Section snippets

Experimental details

The material used in this study was a commercial 1Cr18Ni9Ti austenite stainless steel. Before the surface nanocrystallization treatment, the 1Cr18Ni9Ti samples were polished to an average roughness of 0.08 μm. And the SFPB process was described in detail in our previous reports [6].

The surface microstructure of the SFPBed samples was characterized by the H-800 transmission electron microscopy (TEM, operated at 120 KV). The thin foil specimens for TEM observation were prepared by polishing and

Microstructure and mechanical properties

Fig. 1 shows the bright-field TEM images of the top surface layer and of the layer about 20 μm deep from the treated surface. It can be seen from Fig. 1(a) that the microstructure of the top surface layer consists of roughly equiaxed nanograins, and the inserted selected area electron diffraction (SAED) pattern indicates that the nanograins with random crystallographic orientations can be exactly indexed as bcc α phase. It can be concluded that the SFPB treatment induced transformation from γ

Discussion

Experimental results indicated that, in both vacuum and air conditions, the friction coefficients and wear losses of the surface nanocrystallized 1Cr18Ni9Ti decreased obviously. And the tribological properties didn't change with the atmospheric pressure notably, which is significantly different from the original 1Cr18Ni9Ti. The nanocrystalline layer was formed and the martensitic phase transformation was also induced on the SFPBed surface, resulting in a dramatic increase in surface hardness

Conclusions

The 1Cr18Ni9Ti stainless steel was surface nanocrystallized successfully by SFPB technology, and the surface hardness increased notably resulting from grain refinement and martensite phase transformation after the SFPB treatment. The nanocrystalline surface layer with high hardness can reduce the adhesive wear and abrasive wear effectively. The higher surface activity of the nanocrystallized layer is helpful for forming oxide film during wearing, which can enhance its tribological properties in

Acknowledgements

This research was financially supported by the 973 Project (2007CB607601), the NSFC (50975285), and the Advanced Maintenance Research Project (9140A270304090C8501).

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