Annealing effects on the structure and mechanical properties of r.f.-sputtered Cr-B hard thin films

Cr-B thin films were synthesized by an r.f. plasma-assisted magnetron sputt ering method using pure CrB2 target on quartz glass, glass ceramic, NaCl si ngle crystal and silicon wafer substrates. After the sputtering process, th e as-deposited Cr-B thin films were annealed at 773, 973 and 1173 K for 5 h . The influence of annealing temperature on the structure and properties of Cr-B thin films was investigated, Although the films were deposited at low temperature (T-S/T-M < 0.1) in this study, X-ray diffraction and transmiss ion electron microscopy observation results indicate that fine crystalline grains are still formed in these films. With increasing annealing temperatu re, the grain size increased gradually from 10 to 30 nm. The compressive st ress in the Cr-B films is rather small due to the long target-substrate dis tance of this apparatus which reduces the atomic peening effect. The hardne ss decreased scarcely with increasing annealing temperature from about 21 G Pa for as deposited to about 19 GPa for 1173 K owing to the grain growth an d relaxation of residual stress. The present study shows that Cr-B thin fil ms can be used below 1200 K with stable structure and high hardness. (C) 20 00 Elsevier Science S.A. All rights reserved.