Microstructure and Mechanical Properties of Nickel-Microalloyed Cr-19Si Alloys

Abstract

The effects of trace Ni addition on the microstructure and mechanical properties of Cr-19Si hypereutectic alloy were studied. The existence of the Ni element added to the as-cast alloy and the refinement mechanism of primary Cr₃Si dendrites were analyzed and studied. The results show that after the addition of Ni element, a small amount of Ni is dissolved into the two-phase structure, and the intermetallic compound Cr₃NiSi is formed at the grain boundary, and a new Ni-rich phase Cr₈NiSi is formed in the crystal. It can also effectively refine the Cr₃Si dendrites and expand the proportion of Cr_ss in the solidified structure. The room temperature properties of the alloy also change significantly with the addition of Ni. When 1 wt.% Ni is added, the room temperature performance of the alloy is improved the most; the room temperature compression performance is improved by about three times, the microhardness is increased by 3.8%, and the room temperature fracture toughness is increased by 23.8%. It is mainly caused by the strengthening of fine grain, solid solution, and dispersion, which are caused by the addition of Ni. Based on the BCT dendrite growth model and the M-T fast eutectic solidification model, the competitive growth of the Cr₃Si dendrite and eutectic microstructure during the solidification of the Cr-19Si alloy was calculated. Combined with the effect of Ni addition on the solidification morphology, the effects of Ni addition on dendrite growth and melt undercooling were analyzed. The results show that when the undercooling is lower than 31.4356 K, the growth rate of eutectic structures is higher than that of Cr₃Si dendrites. When the undercooling is higher than 31.4356 K, the growth rate of Cr₃Si dendrite begins to increase rapidly and exceeds the growth rate of eutectic structures. The addition of Ni can decrease the tip radius of the Cr₃Si dendrites and increase the undercooling of the Cr₃Si dendrites during solidification.