TRIBOLOGICAL CHARACTERISTICS OF THE SURFACE LAYER WITH BORON UNDER SLIDING FRICTION ONDITIONS

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TRIBOLOGICAL CHARACTERISTICS OF THE SURFACE LAYER WITH BORON UNDER SLIDING FRICTION ONDITIONS

Journal Title: Tribologia - Year 2009, Vol 223, Issue 1

Abstract

The properties of the frictional slide couplings depend on the constructional material used and technology applied during the production process. The tribological properties of the frictional coupling are the resultant of the coupling construction and properties of the cooperating surfaces. The surface layer may be shaped by technological processes through the correct material selection used for these elements and technology applied for the surface treatment. Currently, numerous methods are used in producing the surface layers, which protect against tribological wear; however, particularly advantageous properties feature those coatings with boron. These coatings feature a high degree of the hardness of the structures, resistance to wear and corrosion, and good fatigue properties, depending on the technological preparation of the base. The purpose of the study to determine the influence of the boron modification of the technological surface layer on the characterisation of the operation of frictional pairs under the conditions of mixed friction, and in practical application, increasing of the durability and reliability of frictional pairs and, in consequence, whole technical objects, such as automobiles. In order to create surface layers modified with boron, technological processes were selected that allowed for the creation of these layers on the elements of a combustion engine. These processes were used for the treatment of the surface layer of annular samples for stand test on the T-05 block-on-ring wear tester. Three types of steel were used in the creation of annular samples, 38CrAlMo5-10, 46Cr2, and 30MnB4. Samples from 38CrAlMo5-10 steel were nitrided in the atmosphere H2 + N2, at the temperature of 500°C for 6 hours. Samples from 46Cr2 steel were borided in powder, at the temperature of 950°C for 8 hours. In the boronizing process, powder of the following composition was used: B4C-30%, Al2O3 -68%, NH4Cl and NaF. Samples from 46Cr2 steel were also laser-borided, with the use of CO2 laser (power of beam P = 2 kW, spot diameter d = 4 mm, energy density 160 W/mm2, tracking speed v = 16 mm/s, gas carrier argon). The boronizing process consisted in covering the annular sample with the layer of amorphous boron and liquid glass and melting with a laser beam. Also, the samples from steel 46Cr2 were covered with a TiB2 coating, using the PVD method (temperature 400°C, time 40 min, pressure in ionization chamber p = 2,5 x 10-2 bara). The sample of 30MnB4 steel was hardened and tempered, and hardening was at the temperature of 800°C, and drawing temper was at the temperature of 450°C. Modified surface layers of annular samples were matched under test conditions with counter samples made from AlSn20 bearing alloys. Tested slide pairs were lubricated during the stand test with 15W/40 Lotos mineral engine oil. On the basis of the tests and the analysis of the results, it was concluded that the boron-modified surface layers can be applicable in the slide couplings operating under mixed friction conditions, and their tribological properties are the effect of the interaction between the surface layers of the slide coupling elements and the lubricating oil. The modified surface layer in the process of boronizing in powder coupled with the AlSn20 bearing alloy is characterised by low friction resistance and temperature, which ensures that the slide coupling has conducive conditions for start-up and fast stabilisation of the friction conditions. In turn, the laser borided surface layer and layer TiB2 causes intensive friction processes in the slide coupling, which generates high friction resistance and temperature and intensifies the processes of bearing alloy wear. It was stated that the use of 30MnB4 steel in the slide coupling after the hardening and tempering ensures similar work parameters and a comparable level of wear of the bearing alloy, as in the application of 38CrAlMo5-10 steel with a nitrided surface. The research proved that the lubrication of the friction area with the mineral oil has an influence on the decrease of wear of the bearing alloy and the decrease of the matching parameters of the moment of friction and temperature, mainly in the couplings with the AlSn20 alloy counter samples. Using the boron-modification processes of surface layers in slide couplings operating under the conditions of mixed friction, it is possible to decrease the costs of material using mild-alloy steel or carbon steel and to decrease the costs of exploitation by increasing the durability of elements. However, each time surface layers with boron are used on a large scale, it should be preceded by economic calculation.<br/><br/>

Authors and Affiliations

Janusz Lubas

Keywords

EP ID EP516620
DOI -
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