CC BY
23
УДК 669.056.9
Radek Norbert, Jurji Shalapko
MANUFACTURE OF HETEROGENEOUS SURFACES BY ELECTRO SPARK DEPOSITION AND LASER BEAM
Cu-Mo coating on the carbon steel 45 deposited by electro-spark method with following laser beam processing are tested. The analysis involved measuring the macrogeometry and microhardness of selected areas after laser treatment. The coatings were deposited by means of the ELFA-541 and they were laser treated with the Nd:YAG, the laser parameters being variable
Introduction
Researchers concerned with tribological processes, especially boundary interaction of solid surfaces, are increasingly employing models of heterogeneous surfaces [1 ]. Surfaces described as heterogeneous consist of areas that differ from one another in geometrical, physicomechanical or physicochemical properties. The heterogeneity of surfaces is frequently due to the application of more than one technology, and can be constituted by:
- shaped surface features such as grooves, pits or channels resulting from milling, eroding, etching, laser-beam forming, etc.;
- areas with different physicochemical and physicomechanical properties, e.g. areas with diversified hardness and mechanical strength accomplished by local surfacing or selective surface hardening ( e.g. electron-beam machining, laser-beam forming or thermochemical treatment);
- areas with diversified surface microgeometry, e.g. areas eroded at the points of focus (laser treatment or electro-spark deposition), or areas with formed surface microgeometry, for instance, in terms of desired microroughness directivity or load capacity (laser and ESD technologies).
Heterogeneous surfaces can be obtained by different methods, laser treatment of electro-spark deposited coatings being one of them [2^6].
Materials and objectives
The testing process consisted of two stages: first, Cu-Mo coatings were electro-spark deposited on standard steel samples (45 steel); then, they were modified with a laser beam. The electro-spark deposition of Cu-Mo wires with a diameter of 1 mm was performed by means of an ELFA-541, a modernized device made by a Bulgarian manufacturer. The subsequent laser treatment was performed with the aid of a BLS 720 laser system employing the Nd:YAG type laser operating in the pulse mode.
The parameters of the electro-spark deposition established during the experiment include:
- current intensity I = 16A (for Cu I = 8A),
- table shift rate V = 0.5 mm/s,
- rotational speed of the head with electrode n = 4200 rev/min,
- number of coating passes L = 2 (for Cu L = 1),
- capacity of the condenser system C = 0.47 mF,
- pulse duration T = 8 ms,
- interpulse period Tp = 32 ms,
- frequency f = 25 kHz.
The investigations aimed at:
- observing the surface state by means of a stereoscopic microscope,
- analyzing the surface macrogeometry,
- measuring the microhardness with the Vickers method.
Discussion of results
The state of the heterogeneous Cu-Mo coatings electro-spark deposited on steel samples and then eroded with a laser beam were observed with the aid of an OLYMPUS SZ-STU2 stereoscopic microscope. The erosion was performed with the point pulsed-laser technique using the Nd: YAG type of laser under the following conditions:
- laser spot diameter, d = 0.7 mm,
- laser power, P = 10W; 20W; 30 W; 40 W; 50 W; 100 W; 150 W,
- beam shift rate, V = 1200 mm/min,
- nozzle-sample distance, h = 1 mm,
- pulse duration, t1 = 0.8 ms, 0.8 ms, 1.2 ms, 1.48 ms, 1.8 ms, 5.5 ms, 8 ms,
- frequency, f = 8 Hz.
As can be seen from Figs. 1 and 2, the effect of the laser erosion action is in the form of crates. The cavity depth depends mainly on the laser power density and the pulse duration.
Coatings with such geometry have various tribological applications. By rubbing the surface selectively, it is possible to produce cavities inside which hydrodynamic forces can be generated during fluid film lubrication. Moreover, the hard areas around the cavities are capable of bearing normal loads.
© Radek Norbert, Jurji Shalapko 2006 г. - 208 -
The investigations of the effects of the laser erosion involved measuring the diameters and depths of the cavities obtained at different laser powers. The results of the measurement performed with a PG-2/200 form surfer are presented in the form of graphs in Figs. 3 and 4. Studying the graphs, one notices that the higher the power of the laser beam, the greater the diameter and depth of the cavities. An exception is the cavity depth
produced at 150 W. The value is smaller than that obtained at 100 W (Fig.4). This might have been due to a considerable pulse duration (ti = 8 ms), the laser power being 150 W. However, if P = 100 W, the pulse duration t1 was 5.5 ms. In the case of lasers operating in the pulse mode, the power is averaged in time; thus, if the pulse durations are long, the laser beam is less effective.
Fig. 1. Stereoscopic photograph of a Cu-Mo coating laser-eroded at 100 W (x 57 magnification)
Fig. 2. Stereoscopic photograph of a Cu-Mo coating laser-eroded at 20 W (x 57 magnification)
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ISSN 1727-0219 Вестникдвигателестроения № 2/2006
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Fig. 5. Distribution of microhardness on the surface of a laser-treated Cu-Mo coating
At the next stage, the Vickers microhardness test was conducted with a Chruszczow indenter at a load of 100 G. The measurements concerned Cu-Mo coatings laser-eroded at 20 W. The distribution of microhardness is shown in Fig. 5. It was established that there was an increase in microhardness at the points of laser machining, the increase being strictly related to the changes in the coating structure, and therefore, to the method of laser treatment. The surface hardening at the points of laser interaction and in the heat-affected zone (HAZ) follows the phase changes occurring in the material first heated and then immediately cooled.
The microhardness of the substrate (i.e. 45 steel) was, on average, 300 HVo 1. That of the ESD coatings amounted to about 430 hV0 1. The laser treatment of the ESD coatings caused an increase in microhardness to approximately 850-880 HV01. In the heat-affected zone, the microhardness fluctuated around 580-630 HV01. The laser beam surface forming resulted in changes in the microhardness of electro-spark deposited Cu-Mo coatings.
Conclusions
1. It is possible to diversify the surface of electro-spark deposited coatings, i.e. to obtain heterogeneous surfaces. The laser-affected areas are characterized by the occurrence of regular cavities, hardened areas and varied roughness.
2. The surface heterogeneity (i.e. the cavities) are desirable in sliding friction pairs. They may be used as reservoirs of lubricants as well as sources of hydrodynamic forces increasing the capacity of a sliding pair.
References
1. Antoszewski B.: Wiasno^ci laserowo i plazmowo modyfikowanych ^lizgowych wKziyw tarcia na przykiadzie uszczelniec czoiowych. Politechnika towiKtokrzyska - Rozprawy - nr 17, Kielce 1999, s.135.
2. Antoszewski B., Radek N.: Analiza niejednorodno^ci powierzchni ksztaitowanych metod№ elektroiskrow№. HUTNIK -Wiadomo^ci Hutnicze, Nr 7-8/2004, str. 310-312.
3. Antoszewski B., Radek N.: Ksztaitowanie powierzchni niejednorodnych poprzez obrybkK laserow№ powiok elektroiskrowych. Materiaiy Szkoiy Naukowej Obrybek Erozyjnych. Warszawa 2004, Zeszyt nr 10, str. 15-20.
4. Шалапко Ю.И., Каплун В.Г., Гончар В.В.Ла-зерная обработка электроискровых покрытий для обеспечения фреттингостойкости// Вестник двигателестроения. №1, 2002. - С.135-140.
5. Radek N., Antoszewski B.: Laser treatment of electro-spark deposited coatings. Materials Engineering, Vol. 12, No 4/2005, pp. 13-15.
6. Antoszewski B., Radek N., Tarelnik W., Wajs E.: Electro discharge and laser texturing of sliding face of mechanical seals. IX Intenationale Conference HERVIC0N-2005, Sumy, Ukraina, t.3; pp. 115-123.
Поступила в редакцию24.05.2006 г.
В статье исследуется покрытие Си-Мо, нанесенное электроискровым способом на сталь 45 с последующей обработкой лазерным облучением. Анализ покрытия состоял в определении макрогеометрии и микротвердости областей, которые испытывали действие лазера. Покрытие наносили на установке ЕЬБЛ-541 и облучали твердотельным лазером на основеШ.УЛО.
В стат1 досл1джуеться покриття Си-Мо, яке наносили в електро1скровий спос1б на сталь 45 з наступною обробкою лазерним опром1нюванням. Анал1з покриття включав визначення макрогеометрИ' та м1кротвердост1 областей, на як впливала д!я лазера. Покриття наносили на установи,\ Е1-ГЛ-541 / опром1нювали твердот1льным лазером на основ\ Ш. УЛв.
