Experimental investigation on anti-wear of a bionic non ...€¦ · Experimental investigation on anti-wear of a bionic non-smooth surface made by laser texturing Z. W. Han, L. Q

Experimental investigation on anti-wear of a bionic non-smooth surface made by laser texturing

Z. W. Han, L. Q. Ren, Z. B. Liu & C. J. Yang Key Laboratory for Terrain-machine Bionics Engineering, Jilin University, Changchun, P. R. China

Abstract

The anti-wear ability of material surfaces is a hotspot of tribology research. Recently, it has been shown in bionics studies that the high anti-wear ability of some living creatures’ surface is related to their non-smoothness morphology. Such as pangolin; they live in soil and stone conditions, but they cannot be damaged by soil and stone at any time. This kind of bionic non-smoothness includes several morphology, such as squama, convex, concave and ripple shapes. In order to improve the anti-wear ability of roll, the bionic non-smoothness technology was employed. Four kinds of roll samples with different surface morphology, such as squama, convex, concave, ripple, were made by laser texturing technology. The metallurgical structures of the samples were analyzed, and their anti-wear abilities were tested. The experimental results show that the superfine metallurgical structure of a material surface can be obtained by laser texturing technology, and the anti-wear ability of material surfaces with bionic non-smoothness morphology increases. In the experimental conditions, the material surface with squama non-smoothness has the highest anti-wear ability. Keywords: bionics, laser texturing, non-smooth surface, anti-wear ability.

1 Introduction

Wear is one of the main modes in material and energy consumption [1]. When the surface of some parts wears, they cannot be used. There are many methods to improve anti-wear ability of material surfaces [2]-[4], but some of the methods have localizations in some extent. With the development of science and

Design and Nature II, M. W. Collins & C. A. Brebbia (Editors)© 2004 WIT Press, www.witpress.com, ISBN 1-85312-721-3

technology, the anti-wear ability of the surface of parts should be improved. Many countries in the world dedicate resources to explore new surface treatment methods to improve the anti-wear ability of materials, and study the effect of surface morphology of materials [5]. In the past twenty years, research in wear and anti-wear ability has evolved rapidly. It was found in bionics that although some soil-burrowing animals, such as dung beetles, ants, earthworms and pangolin spend most of their lives in the soil, their bodies do not stick to any soil and they can move freely. Some researchers have studied this for a long time and found that some parts of their body surfaces were a kind of geometrical non-smooth structure. The non-smooth structure was one of reasons why soil-burrowing animals do not stick to any soil. Fig.1 shows a kind of dung beetle. Fig.2 illustrates the non-smooth morphology of the head of the dung beetle. Based on the research of the principles of the non-smooth surfaces of soil-burrowing animals in anti-adhesion against soil, the concept of bionic non-smooth surfaces was presented and the bionic non-smooth methods were developed to reduce soil adhesion. In addition, it was shown that some soil-burrowing animals’ surfaces have high anti-wear ability, which is related to the geometrical non-smooth structures on the soil-burrowing animals’ body. It is a hint to study bionic anti-wear.

2 The optimum choice of non-smooth morphology surface

It is discovered in bionics study that a lot of living creatures have different geometrical non-smooth morphology on their surfaces, which living creatures adapt their survival environment to evolve and optimize by millions of years. These animals (such as pangolin, dung beetle and mole crickets, etc.) move back and forth in sand stone or soil for a long time, but their surfaces are not damaged. It was the reason that the non–smooth morphology of their surfaces has good ability of anti-wear. According to basic feature of geometric non-smooth structural unit, this kind of bionic non-smooth morphology mainly include squama, convex, concave, ripple and bristle shape, and so on. The non-smooth unit’s plane size of a dung beetle’s head is smaller than 80μm. Four kinds of non-smooth morphology, such as squama, convex, concave and ripple shape, were processed on roll samples for experiment. Considering the restriction of processing technology and distributed rule as well as the size of the bionic non-smooth unit, these non-smooth units’ sizes are 50µm-200µm, unit spans are 140µm-390µm, unit heights are 10µm -30µm, which are shown in Fig.3-Fig.6.

3 Materials and methods

In the experiments, Laser Texturing Technique (LTT) was used to melt the specimen surface of roll mould at the same intervals, which made the laser pulse with high energy density and high repeated frequency organized by single pulse or many pulses. At the same time, the melting was blew to move in the definite incidence by using the auxiliary air with the definite ingredient, pressure and flux, and were piled up at the edge of melted pool in terms of specific request to


514 Design and Nature II

Figure 1: A dung beetle.

Figure 2: The non-smooth morphology of the head of a dung beetle.

Figure 3: Surface morphology of convex sample (×90).


Design and Nature II 515

Figure 4: Surface morphology of concave sample (×90).

Figure 5: Surface morphology of squama sample (×90).

Figure 6: Surface morphology of ripple sample (×90).



form different non-smooth surface morphology with definite distributed rule on the specimen surface of roll model. The sample was manufactured on special Laser Texturing machine equipped with 2000T-L numerical control system. The sample of roll model is hollow cylinder, the internal diameter is 16mm, and the external diameter is 40mm. The height is 10mm, and the material is QT50-5 of nodular cast iron. The four kinds of treated non–smooth surface morphology were observed by using XTJ-30 television camera microscope, and the micro-morphology was shown in Fig.3-Fig.6. Abrasion experiment was done on MM-200 abrasion wear machine, and the surface layer was not disappeared completely under the experimental condition. The abrasion sample is rectangle, and its dimensions is 10mm*20mm*30mm. The material is 45 steel. The loads are 40N and 80N. The rotational speeds are 200r/m and 400r/m, and the wear time is 45min. The experiments were done at room temperature with fixed abrasion specimen. The circular model roll revolved, and each experiment repeated three times under each test condition. The abrasion was weighted with electronic balance, and data was taken average value.

4 Results and discussions

4.1 The anti-wear of strengthening layer on the non-smooth surface

Compared experiments of anti-wear were done between the raw smooth surface, and four kinds of non-smooth surfaces with laser processing. Under two conditions of high speed with low load (rev 400r/m, load 40N) and low speed with high load (rev 200r/m, load 80N), the test of anti-wear was done. The experimental results are shown in Fig.7 and Fig.8. From Fig.7(a) and Fig.8(a), the anti-wear of the sample with bionic non-smooth surface processed by laser texturing is much better than that of the raw smooth sample, and the wear rate of raw smooth sample exceeds ten times than that of the non-smooth sample processed by laser texturing, even a hundred times. If the anti-wear was improved only because of the structural phase transform hardness in the course of the laser processing, the anti-wear times cannot reach so high. The non-smooth morphology plays a crucial role in improving anti-wear. Since the anti-wear of smooth and non-smooth specimen is not in the same level, it is difficult to know which kind of non-smooth surface is more anti-wear in Fig.7 and Fig.8. The wear data of the specimens with non-smooth surface were shown in Fig.7(b) and Fig.8(b). It was found in Fig.7(b) and Fig.8(b) that the anti-wear of the sample with squama non-smooth surface morphology was better than others in two experimental conditions. The specimen with squama non–smooth surface has the highest anti-wear ability in the experimental conditions.



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Figure 7: Anti-wear graph of the sample under high velocity and low load.

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Figure 8: Anti-wear graph of the sample under low velocity and high load.

4.2 The microstructure of the strengthening layer and the strengthening principle

The metallographic material of the samples matrix is ox-eye ferrite, pearlite and sphericity graphite as shown in Fig.9. The balling effect is not very good, and it

s quam a

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is around level three. There are many mass graphite, air hole or inclusion. The content of pearlite is few, which is about 20%-30%. Therefore, the anti-wear is very low. Fig.10 shows the microstructure photo of the laser processing re-melt strengthening zone. It was found in Fig.10 that the surface structure had great changes after the sample surface being processed by laser, and the structure was made of ledeburite, first cementite and undissolved sphericity graphite. There are few martensite in the transitional layer. It is the reason that the laser shines on local surface of metal and makes it heat quickly to the state of melting to form a melted pool. It’s the second reason that the mobile laser, the short time of treatment, the input limited heat, the small melted pool, form the ledeburite with high hardness and anti-wear, when laser is put aside and the cast chill by itself. In this course, graphite also dissolves, and a partial carbon and ferrite form reticulate first cementite. Graphite does not transform completely since heat is limited. The microstructure of the transition zone is shown in Fig.10(b), which occurs phase change by function of heat from melted layer in the transition zone. Pearlite is changed to austenite, and graphite becomes thin. The speed of self-cold way can meets the thermodynamic condition that martensite forms, and hardness improves. In the structure of surface, ledeburite has high hardness and anti-wear. The hardness of cementite is very high (about 800HB), but the ductility and toughness are very low, especially the network distribution is very obvious. So, the surface is particular hard, its anti-wear is much better than that of matrix material, but it is more crisp and thin. Therefore, big load cannot be endured, otherwise surface is easily crushed so that the anti-wear becomes low.

Figure 9: Micro-structure of sample base materials (×100).

Besides the factor that the anti-wear of samples enhanced by laser processing, the load and the wear of mould roll were changed after bionic non-smooth morphology was processed on the surface of mould roll. The non-smooth morphology makes the abrasion of the surface of mould roll transfer from customary adhesion and plough state to roll state, reduce the force of adhesion



apparently; and change the state of huge distributed force. The non-smooth unit of mould roll surface becomes hard phase after laser processing, and forms hard points one by one, which forms the local vibrated state of roll surface during the abrasion. The non-smooth unit of mould roll surface alleviates and counteracts the complex alternating stress that roll endured during the abrasion, alleviates the failure degree of roll fatigue, and improves the anti-wear of roll finally.

(a) remelting zone (×400)

×100)

Figure 10: Micro-structure of sample hardened by laser.

(b) transition zone (



5 Conclusions

a) The local re-melted strengthening on the samples surface was treated by using the Laser Texturing Technique, which formed very tiny ledeburite structures in re-melted zone increasing the anti-wear of the surface. b) The anti-wear rate of the sample with different non-smooth surface morphology is different, but the anti-wear of surface is great improved for parts or components. c) Under the experimental conditions, the anti-wear of the sample with squama surface is the best in the four kinds of selected samples with bionic non-smooth surface morphology.

Acknowledgements

The authors are grateful for the financial support provided by the National High Technology Research and Development Program of China (863 Program) (No.2002AA331180), Trans-Century Training Program Foundation for the Talents by Chinese Ministry of Education (2003), and the Natural Science Foundation of Jilin Province (No. 2002628-2).

References

[1] Meng, H.C., & Ludema, K.C., Wear models and predictive equations: their form and content. Wear, 181-183(2), pp. 443-457, 1995.

[2] Xia, Y.Q., Liu, W.M. & Xue, Q.J., Friction and wear behavior of nodular cast iron modified by a laser micro-precision treatment sliding against steel under the lubrication of liquid paraffin containing various additives. Wear, 253(7-8), pp. 752-758, 2002.

[3] Schmidt, G. & Steinhauser, S. Characterization of wear protective coatings. Tribology International, 29, pp. 207-214, 1996.

[4] Woydt, M. Skopp, A., Dorfel, I. & Witke, K., Wear engineering oxides/anti-wear oxides. Wear, 218(1), pp. 84-95, 1998.

[5] Ren, N. & Lee, Si.C., The effects of surface roughness and topography on the contact behavior of elastic bodies. ASME J. Tribol., 116, pp. 804-811, 1994.



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Experimental investigation on anti-wear of a bionic non ...€¦ · Experimental investigation on anti-wear of a bionic non-smooth surface made by laser texturing Z. W. Han, L. Q