High temperature strength and failure of the Ni-base superalloy PM 3030

The strength, fatigue life and fracture behavior of the oxide dispersion strengthened (ODS) nickel-base superalloy PM 3030 are investigated. The high Al content in PM 3030 leads to the formation of coherent gamma' particles and, thus, to additional precipitation strengthening. A coarse and elongated grain structure (R34) and two isotropic batches with mean grain sizes of 1 mu m (1190) and 17 mu m (R901315) are considered. Compressive constant strain rate tests and high cycle fatigue (HCF) tests are performed. Optical, scanning and transmission electron microscopy (OM, SEM and TEM) are carried out. The properties are compared with those of the solely oxide dispersion strengthened Ni-base alloy PM 1000 [Estrin, Y., Heilmaier, M., Drew, G., 1999. Creep properties of an oxide dispersion strengthened nickel-base alloy: the effect of grain orientation and grain aspect ratio. Mater. Sci. Eng. A 272(1), 163-173]. It is found that additional gamma hardening provides an increase in quasistatic strength by about a factor 2 and in HCF life by about a factor 10(2)-10(3) at temperatures up to 850 degrees C. When fatigue life is compared at a fixed ratio of stress amplitude-to-yield or ultimate compressive strength, R34 shows a fatigue life similar to that of PM 1000 at lower temperature (e.g. 600 degrees C) indicating that the quasistatic strength advantage is proportionally translated into improved fatigue performance; for higher temperatures (850 degrees C) however, R34 shows a shorter fatigue life as compared to PM 1000. Grain size reduction, as exemplified with the fine grain R90 batch, also provides an increase in strength up to the equicohesion temperature (T(E)) [Dieter, G.E., 1986. Mechanical Metallurgy. SI Metric Ed. McGraw-Hill Book Company, London]. Above T(E), faster diffusion and grain boundary sliding [Raj, R, Ashby, M.F., 1971. On the grain boundary sliding and diffusional creep. Metall. Trans. 2,1113-1127; Spingarn, J.R., Nix, W.D., 1978. Diffusional creep and diffusionally accommodated grain rearrangement. Acta Metall. 26, 1389-1398] lead to a drastic drop in strength for the R90 material. In contrast, the batch with intermediate grain size (R901315) shows strength comparable to that of R34 up to 850 degrees C. Furthermore, R901315 shows improved crack tolerance compared to its coarse grain counterpart R34. Due to premature crack initiating coarse oxide particles however, R901315 does not show any improvement in elongation to failure during tensile tests. Eliminating those coarse particles is expected to improve the ductility and toughness of this isotropic batch. (C) 2008 Elsevier Ltd. All rights reserved.

对氧化物弥散强化（ODS）镍基高温合金PM 3030的强度、疲劳寿命和断裂行为进行了研究。PM 3030中高含量的铝导致形成共格的γ′粒子，从而产生额外的沉淀强化。考虑了一种粗大且拉长的晶粒结构（R34）以及两种各向同性的批次，其平均晶粒尺寸分别为1μm（1190）和17μm（R901315）。进行了恒应变速率压缩试验和高周疲劳（HCF）试验。还进行了光学显微镜、扫描电子显微镜和透射电子显微镜（OM、SEM和TEM）观察。将其性能与单纯氧化物弥散强化的镍基合金PM 1000进行了比较[Estrin, Y., Heilmaier, M., Drew, G., 1999. 一种氧化物弥散强化镍基合金的蠕变性能：晶粒取向和晶粒长宽比的影响。材料科学与工程A 272(1), 163 - 173]。研究发现，在高达850°C的温度下，额外的γ硬化使准静态强度提高了约2倍，高周疲劳寿命提高了约10² - 10³倍。当在应力幅值与屈服强度或极限抗压强度的固定比值下比较疲劳寿命时，R34在较低温度（例如600°C）下显示出与PM 1000相似的疲劳寿命，这表明准静态强度优势按比例转化为疲劳性能的提高；然而，在较高温度（850°C）下，R34与PM 1000相比疲劳寿命较短。如细晶粒R90批次所示，晶粒尺寸减小也使强度在等内聚温度（T(E)）[Dieter, G.E., 1986. 机械冶金学。国际单位制版。麦格劳 - 希尔图书公司，伦敦]以下提高。在T(E)以上，更快的扩散和晶界滑动[Raj, R, Ashby, M.F., 1971. 关于晶界滑动和扩散蠕变。金属学报 2, 1113 - 1127；Spingarn, J.R., Nix, W.D., 1978. 扩散蠕变和扩散协调的晶粒重排。金属学报 26, 1389 - 1398]导致R90材料的强度急剧下降。相比之下，中等晶粒尺寸的批次（R901315）在高达850°C时显示出与R34相当的强度。此外，与粗晶粒的R34相比，R901315显示出更好的抗裂性。然而，由于粗大的氧化物颗粒过早引发裂纹，R901315在拉伸试验中在断裂伸长率方面没有任何改善。消除这些粗大颗粒有望提高这种各向同性批次的延展性和韧性。（C）2008爱思唯尔有限公司。保留所有权利。