Effects of silicon and chromium additions on glass forming ability and microhardness of Co-based bulk metallic glasses

Abstract

<span style="font-size:9.0pt;mso-bidi-font-size:10.0pt;mso-ansi-language:EN-AU" lang="EN-AU">Effects<span style="font-size:9.0pt;mso-bidi-font-size:10.0pt" lang="EN-US"> of<span style="font-size:9.0pt;mso-bidi-font-size:10.0pt;mso-ansi-language: EN-GB" lang="EN-GB"> silicon and chromium<span style="font-size:9.0pt; mso-bidi-font-size:10.0pt" lang="EN-US"> additions on glass forming ability (GFA) and microhardness of a Co-Fe-Ta-B bulk metallic glass are investigated by using differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). It is found that partial substitution of boron by silicon promotes the GFA of the alloy. Fully amorphous rod of 4 mm is fabricated by suction casting Co₄₃Fe₂₀Ta_5.5B_26.5Si₅ alloy. However, partial replacement of cobalt by chromium decreased the GFA significantly. In fact, critical casting thickness of Co₃₉Cr₄Fe₂₀Ta_5.5B_26.5Si₅ alloy is determined as 2 mm. It is also determined that microhardness values of the amorphous alloys are about 1200HV₃₀₀. This value is lower than the hardness of the base alloy,1455HV₃₀₀, and it is believed that decrease in hardness results from the reduction in boron contents of the alloys.

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