Phase composition and microhardness of the as-cast and long-time annealed Co_xNi_2−xCrFeTi multi-component alloys

The microstructure and microhardness of the arc-melted Co x Ni 2−x CrFeTi multi-component alloys, in both as-cast state and after annealing at 800 and 1000 °C for 30 days, were experimentally investigated by scanning electron microscopy (SEM) and x-ray diffraction (XRD). The volume fraction of the C14 phase increased with the Co content. The microstructure and microhardness of the alloys greatly changed after annealing at 800 or 1000 °C for 30 days. The eutectic structure appears in the as-cast alloys containing 5 ∼ 15 at% Co. The BCC phase exists in the as-cast and 800 °C annealed Co 0.25 Ni 1.75 CrFeTi alloy, while it transforms to the σ phase at 1000 °C. With the increase of the Co content, the D0 24 phase gradually transforms to the C14 phase and the alloy hardness increased. The microhardness of the alloy gradually decreases with the increase of annealing temperature. The maximum hardness of the as-cast alloys can achieve 1044 HV, while that for 800 and 1000 °C annealed alloys is 1027 and 956 HV, respectively.