Boron doped bcc-W (WBx, x = B/W) films were deposited on Si(100) substrates by magnetron cosputtering pure W and B targets. Our results reveal that when the absolute value of substrate bias voltage (V-b) increases from floating to 240 V, the value of x monotonously decreases from 0.18 to 0.04, accompanied by a phase transition from a mixture of tetragonal gamma-W2B and body-centered cubic gamma-W(B) phase (-V-b <= 60 V) to alpha-W(B) single phase (-Vb > 60 V). Hardness, depending on Vb, increases first and then drops, where the maximum hardness of 30.8 GPa was obtained at -Vb > 60 V and far higher than pure W and W2B theoretical value. In the mixed phase structure, the grain boundaries strengthening, HallPetch effect and solid-solution strengthening induced by B dominate the strengthening mechanism. Astonishingly, the film grown at -Vb = 120 V still possesses twice higher hardness than pure W, wherein unexpectedly low (6.7 at.%) B concentration and only the single alpha-W(B) phase can be identified. In this case, both Hall-Petch effect and solid-solution strengthening work. Besides, low friction coefficient of similar to 0.18 can be obtained for the films with alpha-W(B) phase, which is competitive to that of reported B-rich transition-metal borides, such as TiB2, CrB and CrB2. (C) 2017 Elsevier B.V. All rights reserved.