Investigation of microstructure and properties of surface

nanocrystallization layer by rolling technology

Song Mingfu a, Liu Guimin b , Cai Zhihaic , Zhao Junjund

（Academy of Armored Force Engineering, National Key Laboratory for Remanufacturing,

Beijing，100072）

a songmf@163.com, b liuguimin2008@sina.com, c caizhihai2052@163.com, d zhaojj@163.com

Key words: pre-forcing rolling technology; Surface Nanocrystallization; deposited layer

Abstract. This article will introduce a new type of surface nano technology, that is the Surface

Nanocrystallization technology by pre-forcing rolling. A nanocrystalline surface layer was

fabricated on deposited layer by using pre-forceing rolling technology (PFRT) .The microstructure

of treated specimens was characterized by using scanning electron microscopy and transmission

electron microscopy. Experimental evidence showed, The technology can form a smooth surface on

the parts, so it can be used as the last process of the machining. The equipment has a simple

structure, similar to ordinary lathe tool, so can be used in the ordinary lathe or the machining center.

Experimental analysis indicated the coars crystal in the surface layer could be refined into

nanocrystalline by using the pre-forceing rolling technology, attaining optimizing surface structure

of metal parts.

Introduction

According to the theories of surface engineering, in the service environment, the failure of the

mechanical parts often begins in the surface. The fatigue and wear of the Materials is sensitive to

the surface structure and property, so the over performance and serving behavior can be enhanced

by the optimization of the surface organization and structure[1,2]. The Surface Nanocrystallization

is a new surface dispose technology, which can nanocrystallize the crystal of the surface, so that it

changes the structure and the physical and chemical properties greatly. Due to the nanocrystalline

structure and the strong compressive stress, the microhardness and contact fatigue resistance of the

element surface promote greatly. So it can enhance the wear resistant of the element surface, and

reduce the possibility of the fatigued crack[3,4].

This article will introduce a new type of surface nano technology, that is the Surface

Nanocrystallization technology by pre-forcing rolling. The rolling head with a pre-pressure rolls on

the surface of the parts, so that the surface material is plastically deformed, refinement the surface

grain by dislocation motion, so that the surface structure is detailed and homogeneous, to form a

thick compression stress layer. The technology can form a smooth surface on the parts, so it can be

used as the last process of the machining. The equipment has a simple structure, similar to ordinary

lathe tool, so can be used in the ordinary lathe or the machining center. By changing the grip end, it

can deal with the shaft parts and plane parts, without any additional power source, so can be used in

many scopes.

Applied Mechanics and Materials Vols. 395-396 (2013) pp 746-750Online available since 2013/Sep/03 at www.scientific.net© (2013) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMM.395-396.746

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 134.148.10.13, University of Newcastle, Callaghan, Australia-15/09/13,04:08:03)

Chuck Rolling head

Work piece

Saddle

Lo

ng

itu

din

al f

eed

axial feed

Chuck Rolling head Work piece

Longit

udin

al f

eed

axial feed

Saddle

The Surface Nanocrystallization technology by pre-forcing rolling

1.1 The type tools pre pressures rolling equipment features

Type tools pre-pressure rolling equipment suitable for the outer circle and the end face of the

shaft parts. The rolling equipment is the main body by the head and knife two parts. The tip portion

comprises: supporting the rollers and the roller. The cutter body including: built-in spring, pressure

regulator, shank (fixture). Wherein the cutter head of the roller and the direct contact with the

workpiece to complete the rolling of the workpiece. Support roller small roller for fixed head. The

knife spring of the body for pre-pressure is applied to the roller.

Pre-pressure rolling equipment is different from the traditional rolling equipment, the main

difference is that: different structures, the use of different purposes, and different processing effect.

Figure 2 is a schematic diagram type tools pre-pressure rolling equipment with traditional process

of rolling head comparison. The main structural difference is that the pre-pressure rolling device

with ordinary rolling equipment: the ordinary rolling device rolling head and the rear of the blade

body is usually rigid connection, which can be simplified as a rigid body, as shown in Figure 1. The

pre-pressure rolling device provided inside the spring, the preset pressure on the workpiece, it can

be simplified into the elastomer, as shown in Figure 2.

The main purpose of the conventional rolling apparatus is used to improve the part surface finish.

The pre-pressure rolling equipment is mainly used to improve and optimize the structure of the

surface microstructure to improve the surface properties. Works and processing effects due to the

different structure of the two devices, there are also differences. Ordinary rolling equipment to

reduce the surface roughness by the rigidity of the rolling head and the surface of the extrusion

purposes, and does not make the surface structure refinement. The force between the roller head and

the workpiece completely through the contact surface between the plastically deformed. Therefore

difficult to process for high hardness materials processing parts more surface dimensions change.

The surface layer region and can not be formed due to the force between the rolling head and the

workpiece is fully achieved by the rigidity of the surface of the extrusion and, the a significantly

thicker microscopic strain region, therefore the ordinary rolling head can not be achieved grain

refinement, and improve organizational purposes.

Fig.1 Schematic illustration of

rolling device

Fig.2 Schematic illustration

of pre-forceing rolling device

Applied Mechanics and Materials Vols. 395-396 747

（a） （b）

Rolling spot （c）

Rolling trace

（d）

Rolling trace

1.2 Pre-pressure rolling surface of the nano-technology principle

Pre-pressure rolling surface of grain refinement principle similar to the principle of surface

mechanical grinding surface nanocrystallization. Applied load by rolling head acts at the surface of

the material, each role will be near the surface of the material produces a stress field, a small

volume element will be along a different direction of any stress Exchange plastically deformed

(Figure 3 a, b), when the follow-up loads in different positions of the surface of the material, a small

volume element of the newly generated stress Exchange will produce plastic deformation along the

other direction (see Figure 3b). Figures 3c and 3d is a schematic diagram of the stress field of the

surface layer when the shaft parts rolling, the rolling process, the surface formed by the adjacent

tracks stress field is formed superimposed. Thus, despite the macroscopic deformation amount of

the material is small, but the sum of any one small volume element along different directions

microscopic deformation amount is very large, through this special plastic deformation of the

material near the surface of grain refinement to the nano-volume level [5].

Fig 3 Stress field in the surface of working during pre-forceing rolling

Pre-forceing rolling technology in the application of the surface of the welding repair parts

2.1 Cross-sectional SEM micrographs

Figure 4 is a rough the surfacing layer cross-section morphology seen surfacing layer of coarse

dendrite. Figure 5 is a cross-sectional scanning electron micrograph of the surfacing the repair layer

by rolling treatment. Seen from Figure 5, a significant plastic deformation layer is formed in the

rolling surface, the severe plastic deformation layer thickness of approximately 15 μm. The

microscopic structure of the deformation zone was significantly different from the original

surfacing layer. Severe plastic deformation layer, layer of the original surfacing repair dendritic

structure no longer exists, the surface tissue was significantly refine [8-9]. The outermost surface

structure refinement is the most serious, decreased the extent of plastic deformation of the outside to

the inside, showing the stepped change trend.

748 Advanced Materials and Processes III

Figure 4. Cross-sectional SEM observation of Figure5. Cross-sectional SEM observation of

original samples the deposited layer

2.2 TEM observation of the nanocrystalline layer

Nanocrystal Deposited layer surface layer microstructure analysis using transmission electron

microscopy analysis techniques. Figure 6 is a sample surface nanocrystalline layer TEM bright and

dark field image and corresponding SAED spectrum. As can be seen from Fig. The sample surface

to form a uniform distribution of the grain size of equiaxed nanocrystals, grain size is concentrated

within a range of about a few nanometers to tens of nanometers, the average grain size of about

10nm. The Octavia and continuous diffraction rings show that there are a large number of crystal

grains, and having a large angle between each other and the random orientation difference in the

diffraction region.

Fig.6 TEM images of nanocrystalline surface layer in the deposited layer

(a) bright-field image; (b) dark-field image; (c) SAED pattern

Summary

This paper introduces a new type of surface nano-technology, pre-pressure rolling surface nano

technology. Introduces the technical characteristics of the equipment used and the basic principles.

The technical equipment of simple structure, no external energy, easy to operate, can be applied to

the widespread use of the repair unit can be cylindrical and the end face having a thickness uniform

nanocrystalline layer of the circular shaft of metal parts, to achieve optimization parts of the surface

quality, improve the purpose of the surface properties. Pre-pressure rolling technology surfacing

repair the surface prepared nanocrystalline layer the surfacing layer surface nanocrystalline layer

grain refinement and uniform, small grain size, around about 10nm. The study surface pre-the

pressure rolling technology equipment parts surface structure optimization, the purpose to improve

the surface quality.

Acknowledgements

The financial support for this work by Academy of Armored Force Engineering with the

creative fund under Grant (Project No.2012CJ070) is grateful acknowledged.

Applied Mechanics and Materials Vols. 395-396 749

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750 Advanced Materials and Processes III

Advanced Materials and Processes III 10.4028/www.scientific.net/AMM.395-396 Investigation of Microstructure and Properties of Surface Nanocrystallization Layer by Rolling

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