Damages of hot-pressed boron carbide during solid target boronization in Uragan-3M torsatron

The investigation of hot-pressed boron carbide erosion caused by the are-re gime of a solid target boronization (STB) procedure was carried out. The sa mple had a high density (2.44 g/cm(3), B 78.2 a.m.%, C 21.5 a.m.%) of and w as used as a head plate of the movable limiter during the pulsed discharge cleaning campaign in the Uragan-3M (U-3M) torsatron. The total number of pu lses during STB was about 2 x 10(4) (n(e) = 2 x 10(12) cm(-3), T-e = 10-15 eV, B = 0.035 T, the plasma pulse duration t = 50 ms, the negative pulsed b iasing of B4C-plate with an amplitude of up to 200 V had a time duration of 10-50 ms). As was shown by an optical examination of the surface morpholog y of the exposed sample, the character and intensity of damages of the limi ter surface strongly varied depending on the distance from. the plasma colu mn axis. The most damaged sites were covered with many craters of 0.1-1.2 m m in diameter and spallings with a size up to 5 mm. The possible physical m echanisms of these damages and erosion behavior of hot-pressed in vacuum bo ron carbide caused by the are-regime of STB are discussed. (C) 1998 Elsevie r Science B.V. All rights reserved.