Hardness and friction of N 2+ and Al + implanted B 4C

Abstract

Surfaces of boron carbide (B 4C) were implanted with 200 keV N 2 + or 100 keV Al + ions to a dose of 8 × 10 17 cm −2. Ultralow load indentation via the Nanoindenter was used to determine the changes in surface hardness and elastic modulus following implantation. A pin-on-disk testing device in ultrahigh vacuum was used for measuring changes in friction and wear of the implanted disks. Results of hardness measurements show that the hardness of the nitrogen-implanted sample drops to about 58% of the unimplanted hardness, and that for the aluminum-implanted sample drops to about 52% of the unimplanted value. The elastic modulus also falls to approximately 62% of its unimplanted value for both implantations. Friction and wear studies conducted in UHV show an increase in friction of both implantations from 0.5–0.6 after one cycle to 0.8–1.1 after ten cycles. This is larger than the 0.17–0.25 values measured for pure B 4C. The wear is significantly reduced in the early cycles of the implanted samples relative to the unimplanted ones. The dramatic softening and improved wear behavior are probably due to the formation of an amorphous surface layer.