Microscopic phase-field simulation of L1_2 and D0_(22) phases during the early precipitation process of Ni-Cr-Al alloys

The influence of temperature on the precipitation mechanism and sequence of L 12 and D022 phases during the early precipitation process of a Ni-15.Sat%Cr-14at%Al alloy was simulated based on the microscopic phase-field model. In the range from 873 to 1373 K, the precipitation mechanism transformed from spinodal decomposition to non-classic nucleation and growth; the incubation period prolonged gradually with increasing temperature. The volume fraction of L12 phases increased and that of D022 phases decreased. D022 phases disappeared at 1373 K, and finally single-phase L12 phases were formed.

超重力场对Al-Ni-Cr合金凝固组织及显微硬度的影响

采用光学显微镜(OM)、扫描电镜(SEM)、能谱分析(EDS)、X射线衍射分析(XRD)和显微硬度计,研究了超重力场对Al97.2Ni2.5Cr0.3合金凝固组织及显微硬度的影响。结果表明,超重力场凝固试样的显微组织可以分为两部分,一是心部区域占80%以上,为Al-Al3Ni共晶组织;二是表层组织占20%以下,由初生α-Al和Al-Al3Ni共晶组织组成。超重力场可以细化合金组织,当超重力系数G为3 000时,初生α-Al细化最明显,平均晶粒尺寸为10.13μm;当G为2 000时,Al3Ni细化最明显,棒状共晶直径和棒状共晶间距分别为72nm和92nm;超重力凝固试样中,合金的心部硬度高于表层硬度。心部区域和表层组织不同的主要原因是两者的Ni含量不同,而这是由于超重力场下对流加剧导致溶质原子易于扩散。