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Vol. 61, No. 2, July, 2020

CHANGE IN CERAMIC OBJECT SURFACE LAYER STRUCTURE DURING OPERATION. PART 21 V. V. Kuzin,2,3 S. N. Grigor’ev,2 and M. A. Volosova2 Translated from Novye Ogneupory, No. 3, pp. 50 – 55, March, 2020.

Original article submitted March 2, 2020. An original procedure is used to study the kinetics of surface layer structural changes of a ceramic component surface layer outside the area of contact interaction during operation. The main features of this process are established and the effect the degree of defectiveness of the initial surface layer on changes that occur is revealed. Keywords: ceramic products (CP), ceramic surface layer (SL), ceramic failure, contact interaction region, ceramic structural elements, stress-strain state, wear area, contact area (CA).

10 mm, and the second was a VOK-71 CO without limitation of the number of defects with sizes up to 15 mm. Presence of pores was also permitted, opened during grinding in the VOK-71 CO SL from a second batch. VOK-71 CO with defects with sizes exceeding these limiting values were excluded from tests. Kinetics have been studied for the change in SL structure in the contact area (CA) with a width of 1 mm and located outside the area of contact reaction for VOK-71 CO with a workpiece. The CA had a common boundary with the wear area (WA). All changes in SL structure were recorded, including appearance of new structural elements (defects of a different nature) formed during VOK-71 CO operation.

INTRODUCTION The present article continues discussion of results for studying changes in the structure of a ceramic object surface layer (SL) during operation. In part 1 of the article the importance of research was substantiated, an original procedure was provided, and results were analyzed for studying a ceramic SL structure after diamond grinding and kinetics of the change in SL structure in the contact interaction area during operation [1]. In part 2 of the article results are analyzed for studying kinetics of the change in ceramic object SL structure outside the contact interaction area and the degree of the effect of defectiveness of an original SL on this process during cutting tests. Two batches of ceramic objects (CO) were used: the first batch included VOK-71 CO (ceramic of the Al2O3–TiC) system) with a nominally “defect-free” SL, and the second batch was VOK-71 CO with a “defective” SL. The classification index for the degree of SL defectiveness used was the average linear size of the following surface defects, i.e., a tear-out, transverse and longitudinal cracks (see Fig. 1 in part 1 of the article [1]) in an arbitrarily selected section with size of 0.1 ´ 0.1 mm. The first batch included a VOK-71 CO with a number of defects not more than five with sizes up to 1 2 3

RESULTS AND DISCUSSION Vibration and heat affected the condition of a VOK-71 CO SL in the CA spreading from a heat source in a WA by means of thermal conductivity; force loads do not operate in this area. Under action of these contactless loads (significantly lower than those th