氮对K4169合金微观组织和力学性能的影响

EFFECT OF NITROGEN CONTENT ON THE MICROSTRUCTURE AND MECHANICAL PROPERTY OF K4169 ALLOY

摘要:

通过Thermo-Calc模拟计算,差热分析和等温凝固淬火试验(ISQ)相结合的方法,借助OM、SEM、EPMA及TEM等表征设备,系统研究了氮含量对K4169合金凝固组织演变行为、元素偏析行为以及力学性能的影响规律。结果表明,氮含量从17ppm增大到100ppm,合金中碳、氮化物的体积分数增大,氮化物析出温度升高。氮含量会影响碳化物的数量和形貌:在氮含量＜50ppm的合金中,MC型碳化物数量较多,尺寸较大且呈条状形貌；在氮含量为70ppm和100ppm的合金中大尺寸MC型碳化物数量显著减少,条型MC碳化物转变为块状。氮含量对K4169合金室温拉伸性能无明显影响,对高温持久性能影响很大。氮含量由17ppm增大到100ppm时,合金的高温持久寿命和延伸率分别从300小时和3%下降到2.26小时和2.34%。当氮含量超过30ppm时,合金的持久性能发生显著下降,因此,K4169合金的氮含量应控制在30ppm以内比较合理。

Abstract:

K4169 alloy is a widely used superalloy due to its excellent performance below 650℃. However, the residual impurities in the alloy will dramatically deteriorate the mechanical properties. In this research, the influence of nitrogen content on the microstructure and mechanical properties of superalloy K4169 has been systematically investigated through Thermo-Calc calculation, DSC analysis and quenching experiments with optical microscopy (OM), scanning electronic microscopy (SEM), electron-probe micro-analyzer (EPMA) and transmission electron microscope (TEM). The results indicate that when the content of nitrogen in the alloy increased from 17 ppm to 100 ppm, the precipitation temperature and the quantities of carbides and nitrides are also increased. Moreover it has been proved that the morphologies of carbides can be greatly affected by the content of the nitrogen. A number of large bar-like carbides can be identified when the N content is less than 17ppm and this number is decreased significantly when the content of N is increased to 70 and 100ppm. With the increasing content of N, the morphologies of MC carbides are changed from bar-like to block-like. The elevated temperature performance of this alloy can be greatly affected by the N content while the room temperature performance is rarely changed. When the content of N is increased from 17ppm to 100ppm, the creep-rupture life and elongation are both decreased obviously. Base on this research, as an overall consideration, it is rational to control the N content below 30ppm in K4169 alloy.