Трибологічна поведінка електродугових покриттів із порошкових дротів системи Fe-Cr-B-Al за робочих умов штоків запірних вентилів ТЕС

Abstract

Досліджено трибологічну поведінку електродугових покриттів із ПД системи Fe-Cr-B-Al за робочих умов штоків запірних вентилів ТЕС. Встановлено, що коефіцієнт тертя досліджуваних покриттів за умов сухого тертя та прикладеному навантаженні більше 4 МПа є таким же, як і для сталі ШХ 15. Виявлено, що дані покриття добре працюють у контакті з графітовим ущільненням. Також виявлено позитивний вплив просочування електродугових покриттів синтетичними оливами для умов роботи сухого тертя, що зумовлено їхньою структурою, і не залежить від системи легування.

The tribological behavior of arc sprayed coatings made of Fe-Cr-B-Al cored wires has been investigated under the service conditions of the heat power plant valve spindle. The arc sprayed coatings have a characteristic lamella structure, lamellas being the solidified droplets separated by oxide films of different nature and thickness, the grinded surface of which is the composite –in the matrix from steel lamellas the particles of oxide phases are available, therefore the structure of such coatings causes their special tribological behavior. It was investigated, that in the dry friction condition under loading of 2 MPa, the friction coefficient of the ШХ 15 steel is lower than for the coating obtained from Fe-Cr-B-Al cored wire, and is equal to 0.32, and under loading more than 4 MPa it equals 0.42. It testifies that under loading less than 2 MPa the tribological properties of ШХ 15 steel are better, however with the increase of loading this phenomenon is not available. It was suggested to investigate the influence of solid lubricant CaF2 on the friction coefficient behavior of arc sprayed coatings made of Fe-Cr-B-Al cored wires. The adding of the CaF2 powder to the mixture of cored wires provides the change of the coating friction coefficient and its behavior is similar to the behavior of the ШХ 15 steel friction coefficient, but, nevertheless, the nominal values are too high and under loading – 5 MPa it equals 0.4. It was found that under the dry friction condition when the loading was 5-6 MPa the temperature on the surface of the coating equals 250-300ºС and the oxide films are formed there. The oxide film is formed on the surface on steel – less-alloyed Cr, on coatings – much-alloyed Cr. In the friction tests these oxide films break and form abrasive particles which cause the significant abrasive wear of both, coating and counterbody – 3X13 steel. It was found that such coatings have very low values of friction coefficients – 0.12-0.15 under conditions of the dry friction in contact with counterbody with built-in graphite. Moreover, with the increase of loading from 2 to 10 MPa the friction coefficient decreases. It was explained by the fact that arc sprayed coatings have on its surface pores and the graphite is accumulated in them during friction and then it forms the boundary friction film on the friction surface. It was found that during wear resistance tests the ШХ15 steel wears the least but its counterdody made of 3X13 steel is subject to significant wear under the dry friction condition, therefore the total wear of this friction pair is higher than for the arc sprayed coating. The positive influence of sealing arc sprayed coatings with synthetic oil was revealed too for the dry friction condition. It was determined that sealing of arc sprayed coatings made of Fe-Cr-B-Al cored wires with synthetic oil Synth 5W40 provides the increasing of their wear resistance in 12 times as compared with those made of ШХ 15 steel and in 9 times as compared with unsealed coatings. The sealed arc sprayed coatings made of Fe-Cr-C-Al cored wires provide the increase of their wear resistance in 9 times in comparison with ШХ 15 steel and in 5 times as compared with unsealed coatings. Such influence of sealing coatings with oil on their wear resistance is likely to be caused by their structure which depends on spraying parameters and doesn’t depend on their alloying system.