Alloy Design for Paticle Strengthened Materials for High Temperature Use

颗粒强化是提高蠕变强度最有效的方法。本研究旨在为颗粒增强（PS）材料的合金设计提供基础知识。许多PS材料是通过热不稳定的沉淀物来增强的。析出相的粗化严重影响PS材料的蠕变性能。基于非稳态蠕变概念，对PS材料的蠕变数据进行分析，得到如下蠕变方程：epsilon=A {1-exp(-alpha)} +beta {exp(alpha)-1} epsilon：应变，t：时间(1)该方程有A、B和alpha三个参数表征蠕变变形。这些参数为微观组织退化、蠕变机理和合金设计提供了有用的信息。PS材料通常具有通过热挤压制成的拉长的晶粒形状。晶粒形状对蠕变强度有显著影响。由于相容性要求，蠕变变形在晶界处受到限制。晶界滑动解除了约束，从而增强了蠕变变形。这就是晶粒形状依赖蠕变强度的原因。以复合材料为例，研究了α _2- ti_3al / γ - tial层状金属间化合物的蠕变。菌落大小变粗，体积分数增大，抗蠕变能力增强。片层间距对蠕变强度没有影响。在合金设计中，我们必须了解材料在使用条件下的蠕变性能。长期特性是通过短期数据的外推来评估的，而外推会引入误差。讨论了外推误差产生的原因，并提出了消除外推误差的方法。

Particle strengthening is the most effective way for improving creep strength. This study aims at providing basic knowledge of alloy design for particle strengthened (PS) materials.1. Many of PS materials are strengthened by thermally unstable precipitates. The coarsening of the precipitates strongly affects creep properties of PS materials. Creep data of PS materials have been analyzed by the following creep equation based on non-steady-state creep concept :epsilon=A {1-exp(-alphat)} +beta {exp(alphat)-1} epsilon : strain, t : time (1)This equation has three parameters, A,B and alpha, that characterize creep deformation. These parameters provide useful information about microstructural degradation, creep mechanism and alloy design.2. PS materials often have an elongated grain shape made by hot extrusion. The grain shape has a significant effect on creep strength. Creep deformation is constrained at grain boundaries due to the compatibility requirement. Grain boundary sliding releases the constraint, and consequently enhances creep deformation. This is the cause of the grain shape dependent creep strength.3. Creep of alpha_2-Ti_3Al/gamma-TiAl lamellar intermetallics has been studied as an example of composite materials. Coarsening of colony size and increase in gamma volume fraction result in higher creep resistance. Lamellar spacing, however, has no effect on creep strength.4. In the alloy design, we must know creep properties under a service condition of the material. The long term properties are evaluated by extrapolation from short term data, and the extrapolation introduces an error. The cause of the extrapolation error has been discussed, and it has been proposed how to eliminate the extrapolation error.