Important Factors Affecting the Stability of Substructure in Heat-resistant Materials

在项目期间，我们证实了蠕变过程中亚晶的生长（即，在耐热钢、Al-Cu合金和商业镁合金中观察到的Ostwald熟化和亚结构退化都是应变依赖性的，尽管迄今为止还没有注意应变对结构退化的影响。此外，亚晶界所需的临界应力逃脱钉扎的沉淀物进行了检查。结果表明，亚雨尺寸在低于临界应力的应力范围内保持不变，而在高于临界应力的应力范围内开始增大。理论上，临界应力与试验温度无关，但实测的临界应力与温度有关。为了明确这种温度依赖性的原因，作为测试温度的函数测量沉淀物的平均尺寸和颗粒间间距。实验 ...更多信息 结果表明，颗粒间距随着测试温度的增加而增加，这是因为在施加应力之前加热到测试温度期间发生颗粒粗化。分析表明，临界应力的温度依赖性仅是明显的。临界应力的大小与Mater.Trans.44（2003），239 - 246中提出的模型计算的理论值几乎相等。由于T91钢的结构退化与亚晶界的迁移有关，因此可以认为位错运动（塑性应变）促进了结构退化。实际上，这类结构退化的起源与应变增强Ostwald熟化的起源似乎不同，但我们可以认为，这两种现象的起源是相同的，因为阻碍亚晶界迁移的沉淀物的生长也可以通过亚晶界的运动来辅助。这是因为这种类型的溶质是有效的，以加强他们的矩阵，但是，这些溶质是易于引入溶质传输辅助位错运动，并最终导致应变增强的沉淀物的生长。到目前为止，具有相对大尺寸错配的溶质优选地被添加到耐热材料中以强化其基体，然而，这些元素对应变增强的沉淀物粗化敏感。应变增强的结构退化是目前在合金设计中没有考虑到的，然而，重要的是要重新考虑合金元素，考虑到清除效应，导致应变增强的沉淀物粗化。少

In the project term, we confirmed that the growth of subgrain during creep (i.e., degradation of substructure) and the Ostwald ripening observed in a heat resistant steel, Al-Cu alloys and a commercial magnesium alloy were all strain dependent notwithstanding that attention was not paid to the effect of strain on the structural degradation so far. Furthermore, the critical stress necessary for subgrain boundary to escape from pinning of precipitates was examined. The results showed that the subrain size remained unchanged in a stress range below the critical stress while it begins to increase in a stress range above the critical stress. On the theoretical basis, the critical stress is expected to be independent of testing temperature, however, the measured critical stress was temperature-dependent. In order to clear the reason for this temperature dependence, the average size and inter-particle spacing of precipitates were measured as a function of testing temperature. The experimental … More results showed that the inter-particle spacing increased with increase in testing temperature because particle coarsening occurred during heating to testing temperature before stress application. The analysis showed that the temperature dependence of critical stress was only apparent. The magnitude of critical stress was almost equal to the theoretical one calculated from the model proposed in Mater.Trans.44(2003),239-246.Since the structural degradation of T91 steel is associated with migration of subboundary, we can view that the structural degradation was promoted by dislocation motion (plastic strain). Actually, the origin of structural degradation of this type is seemingly different from the strain enhanced Ostwald ripening, however, we can view that the origin of both phenomena is the same because the growth of precipitates which hinder the sub-boundary migration can also be assisted by the motion of subboundary.Generally, many heat-resistant materials contain solute atoms with a relatively large size misfit. This is because solutes of this type are effective to strengthen their matrix, however, these solutes are liable to introduce the solute transport assisted by dislocation motion, and eventually lead to strain-enhanced growth of precipitates. So far, solutes with a relatively large size misfit were preferably added to heat-resistant materials to strengthen their matrix, however, these elements are susceptible to strain enhanced coarsening of precipitates. Strain enhanced structural degradation was not taken into account so far in alloy designing, however, it is important to re-consider the alloying elements taking into account the scavenging effect which causes the strain enhanced coarsening of precipitates. Less