Upper Limit of Strengthening and Its Improvement in Nano-lamellar Materials

纳米层状材料的强化上限及其改进

基本信息

批准号：
15360361
负责人：
MARUYAMA Kouichi
金额：
$ 9.79万
依托单位：
TOHOKU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

项目摘要

TiAl alloys are the most promising light material for high temperature structural applications. The alloys take a lamellar structure consisting of α_2Ti_3Al and γ TiAl phases, and their strength increases with decreasing lamellar thickness. However there is an upper limit in the strengthening. In this study the causes of the upper limit were examined and it was proposed how to improve the upper limit.1.Misfit dislocations on α_2/γ lamellar boundaries disappear when lamellar thickness λ is reduced below 50nm, resulting in loss of boundary resistance to dislocation motion. Therefore, the yield stress vs. 1/√<λ> curve deviates from the Hall-Petch relation and yield stress has an upper limit at fine λ.2.The upper limit of yield stress can be improved if we can introduce the misfit dislocations to α_2/γ lamellae less than 50nm thickness. Lattice misfit determines the lower limit of lamellar thickness for the introduction of misfit dislocations, and a lattice misfit larger than 1.5% is required to improve the upper limit.3.Coarsening and sphoroidization of lamellae are the major microstructural degradation that cause loss of deformation resistance. The degradation is driven by the interfacial energy and is faster in finer lamellar structure. The degradation proceeds by the migration of lamellar boundaries, and can be retarded by reducing the mobility of lamellar boundaries.4.TiAl alloys contain four types of lamellar boundaries, and the α_2/γ boundaries have the lowest mobility. It was confirmed that a material having a high density of α_2/γ boundaries shows better creep deformation resistance due to its improved microstructure stability.

TIAL合金是高温结构应用的最有希望的轻质材料。合金采用由α_2TI_3AL和γTIAL相组成的层状结构，其强度随着层状厚度的降低而增加。但是，加强有上限。在这项研究中，检查了上限的原因，并提出了如何改善上限。1。当层状厚度λ降低到50nm以下时，对α_2/γ层状边界的脱位消失了，从而导致对位错运动的边界抵抗力丧失。因此，屈服应力与1/√<λ>曲线偏离了霍尔西蚀刻关系，而屈服应力在细λ2上具有上限。22。如果我们可以将MISDFIT位错引入α_2/γ层状层状小于50nm的厚度，则可以提高屈服应力的上限。晶格刻度贴层确定层状厚度的下限以引入畸形位错，并且需要大于1.5％的晶格Missfit来改善上限。3。层状和固定层的固定化和sphoroidation是导致抗变形损失的主要显微结构降解。降解是由界面能量驱动的，并且在较细的层状结构中更快。降解是通过层状边界的迁移来进行的，并且可以通过降低层状边界的迁移率来阻碍。4。tial合金包含四种类型的层状边界，并且α_2/γ边界具有最低的迁移率。已经证实，由于其改善的微观结构稳定性，具有高密度α_2/γ边界的材料显示出更好的蠕变发育耐药性。