Plasma-sprayed ceramic coatings on the base of powders diffusion alloyed. Part II. Properties of coatings
Eugene Feldshtein, Oleg Devojno, Olga Yatskevich
Quarterly No. 1, 2010 pages 86-90
DOI:
keywords: ceramic coating, microhardness, microstructure, phase composition, wear resistance
abstract Plasma-sprayed coatings on the base of ceramic powders Al2O3, Al2O3-Мо and Al2O3-В were investigated. Before plasma spraying surfaces of specimens were machined by cast iron shot. Plasma spraying of coats was realized with plasma current strength 420 A and voltage 80 V. The distance between plasma nozzle and surface sprayed was equal 90 mm, process gas - nitrogen with consumption 3 m3/h. Depth of coatings after processing was equal 0.5-0.7 mm, base material - steel C45. Coatings investigated have high microhardness, in particular ceramic Al2O3 - 15 GPa on average, ceramic alloyed Al2O3-Мо-12.9 GPa on average and ceramic alloyed Al2O3-В – 10.65 GPa on average. The analyze of microstructures of coatigs using scanning microscope „Mira” allowed to find, that ceramic coatings consist of quasi molten and then harden particles. The molten intensity of coat particles is grown in direction Al2O3 - Al2O3 - Мо - Al2O3 - В. The X-ray structure analysis fulfilled on universal diffractometer ДРОН-3.0 using program package ARSANAL allowed to find the presence of alpha-Fe at the interfaces between coat and base material. It signifies the process of iron diffusion from steel base material into contact layers of ceramic coat has a place. Useful increase intensity of alpha-Fe diffraction lines for coatings alloyed is evidence that boron and molybdenum act on process of iron diffusion from steel base material into contact layers of ceramic coat as accelerants. The presence of iron boride Fe3B into the interface surfaces is evidence of chemical interactions between Al2O3-В coat and base material. When plasma spraying high-temperature modification alpha-Al2O3 is forming predominantly into upper layers of coat and low-temperature modification gamma-Al2O3 is forming predominantly into layers adjoining to base material. The percentage of alpha-Al2O3 modification in coatings from alumina alloyed is higher greatly in comparison with coat from alumina not alloyed. When dry friction with constant loading the surface of Al2O3 coating abrades more quickly in comparison with coatings from alumina diffusion alloyed, wear intensity of ceramic alloyed by boron is smaller greatly. When dry friction with increase loading the coat from alumina alloyed by molybdenum is completely destroyed during very shot time of friction, ceramic coatings alloyed by boron work successfully although their wear intensity increases in comparison with alumina Al2O3.