半个世纪以来, 以γ´´和γ´相强化的Ni-Fe基高温合金Inconel 718(GH4169)由于其优异的力学和工艺性能, 在650 ℃以下的高温环境中得到了广泛的应用. 本文采用热力学计算以及合金设计理论与大量的力学性能相结合, 不仅在常规热处理并且在高温长期时效状态下来研究主要强化元素Nb, Ti, Al和杂质元素P, S以及微合金化元素Mg的作用. 采用金相, SEM, TEM, EDS, SAED以及电解萃取和相化学分析等综合分析方法, 对各类析出相γ´´, γ´, δ, δ´´, σ和α-Cr进行定性的分析, 同时亦采用Auger能谱仪分析晶界元素的偏聚行为. 研究结果表明, 为提高GH4169原型合金的性能, 主要强化元素 Nb应控制在高限(5.4%-5.5%), 降低S到10×10-6以下, 提高P至150×10-6以下, 并添加适量的Mg. 为提高GH4169合金的使用温度到680 ℃甚至更高, 必须通过合金化的途径来提高主要强化相 γ´´/γ´的最高稳定温度和控制晶界析出相. 为此, 680 ℃或更高一点温度使用的改进型 GH4169合金中Nb仍应控制在高限(5.4%-5.5%), S控制到10×10-6以下, P提高到150×10-6, 配合适量的Mg微合金化, 同时要提高Al含量至1.0%-1.5%, Ti含量不变仍控制在1%左右, 改进型GH4169合金不仅在650 ℃以上显示出优良的高温组织稳定性, 并且亦提高了高温力学性能.
γ´´ and γ´ strengthened Ni-Fe base superalloy Inconel 718 (GH4169) is world-widely used under 650 ℃ because of its excellent mechanical properties and metallurgical workability. The effects of main strengthening elements Nb, Ti, Al, minor elements P, S and micro-alloying element Mg on mechanical properties and structure stability have been studied for this alloy at standard heat treatment and long time aging conditions both by means of mechanical tests (tensile, stress rupture and creep, cyclic stress rupture and crack propagation etc.) and detail structure analyses (SEM, TEM, EDS, SAED, phase separation and micro-chemical analyses etc.) and also Auger analyses on grain boundary segregation behavior. For quality improvement of conventional GH4169, Nb content should be controlled at high level (5.4%-5.5%) with low content of S (<10×10-6) and high level of P (but less than 150×10-6) and with micro-alloying element Mg also. For 680 ℃ even higher temperature used modified GH4169 the γ´´/γ´ highest stable temperature must be raised and the grain boundary precipitates should be controlled. Nb content should be still controlled at high level (5.4%-5.5%), Al content should be raised to 1.0%-1.5% and Ti content still be kept at 1%; S must be controlled to less than 10×10-6 and P should be raised to a high level but less than 150×10-6 and also with micro-alloying element Mg. The modified GH4169 to be used at 680 ℃ or even higher temperature has good thermal structure stability and high mechanical properties above 650 ℃.
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