A comparative study of borided pure niobium, tungsten and chromium

Pure niobium (Nb), tungsten (W) and chromium (Cr) were boronized at 940 degrees C for 2, 4 and 8h. The borided samples were characterized by X-ray diffraction, Scanning electron microscope and microhardness tests. Tribological investigation was conducted. X-ray study showed the presence of NbB2, WB, and CrB. The hardnesses of boride layers formed on the pure Nb, W and Cr were 2500, 2500 and 1700 HV, respectively, whereas the hardnesses of the pure Nb, pure W and pure Cr were 110, 445 and 115 HV, respectively. Nb boride layers ranged in thickness from 8 to 22 pin, whereas W boride layers ranged in thickness from 10 to 42 pm, and the thickness of Cr boride layer varied from 4 to 12 mu m with boronizing time. The boriding of W resulted in thicker boride layer compared to the boriding of Nb and Cr at given time. The frictional behaviour and wear mechanicms differ in modes and scales. (c) 2006 Elsevier Ltd. All rights reserved.