材料期刊网

含Hf的镍基高温合金存在Ni_5Hf相,它是影响合金初熔的主要因素之一。当该相的量大于1.0v-％时,在加热示差热分析(DTA)曲线上的1135-1160℃处出现Ni_5Hf相的熔化峰。P.D法定向铸锭上、下端存在明显的Ni_5Hf偏析,因而对初熔的敏感性明显不同。 Ni_5Hf相的初熔促进了共晶γ′和M_3B_2的熔化。低碳与无碳含Hf合金的初熔倾向更大,缓冷组织和固溶处理的升温速度对初熔是敏感的。 高于3V-％的初熔量将会降低合金的持久强度,其断裂主要沿Ni_5Hf初熔区和共晶γ′之间的界面扩展。采用1150℃8h预处理能消除全部的Ni_5Hf相,有效地控制含Hf合金的初熔。

One of the chief factors influencing the incipient melting in Hf-bearing DS Ni-base superalloys was found out to be Ni_5Hf-phase. The melting peak at 1135—1160℃ showing Ni_5Hf-phase more than 1.0 v.-% has been determined by DTA on heating. A distinguishable segregation of Ni_5Hf in both ends of the directionally solidified ingots by PD technique was shown, and their sensitivities to incipient melting are quite different consequently, The incipient melting of Ni_5Hf-phase may induce the solution of γ+γ′ eutectic and M_3B_2. It was also obtained that the low-carbon or carbon-free Hf-bearing alloys have stronger tendency to incipient melting, as well as the slow cooling microstructure and the increasing rate of solid solution temperature are sensitive to it. The reduction of rupture strength of the alloys may be caused by the presence of incipient melting of Ni_5Hf more than 3 v.-%. Their rupture is propagated mainly along the interface between the melting zone of Ni_5Hf and the eutectic γ′. By means of pretreatment at 1150℃ for 8h, the Ni_5Hf-phase may be completely eliminated, thus the incipient melting of the Hf-bearing alloys may be effectively brought under control.