Banoth Santhosh, Palleda Thaviti Naidu, Shimazu Sota, Kakehi Koji
Department of Mechanical Systems Engineering, Tokyo Metropolitan University, 1-1, Minami-Osawa, Hachioji-City, Tokyo 192-0397, Japan.
Materials (Basel). 2021 Feb 28;14(5):1143. doi: 10.3390/ma14051143.
We studied the effects of the rare earth element yttrium (Y) on the hot cracking and creep properties of Hastelloy-X processed by selective laser melting. We used two different alloys to study hot cracking in Hastelloy-X: one with 0.12 mass% yttrium added and one with no yttrium. Y-free Hastelloy-X exhibited less cracks, mainly due to the segregation of Si, W, and C resulting in SiC- and WC-type carbides at the grain boundary and interdendritic regions. On the other hand, more cracks formed in the Y-added Hastelloy-X specimen because of segregation of Y, resulting in the formation of yttrium-rich carbide (YC). Post-heat treatment was conducted at 1177 °C for 2 h, followed by air cooling, to obtain good creep properties. We carried out a creep test along the vertical and horizontal directions. Despite having more cracks, the Y-added as-built Hastelloy-X specimen showed longer creep life and ductility than the Hastelloy-X specimen. This was mainly because of the formation of YO and SiO inside the grains. After solution treatment, the Y-added specimen's creep life was eight times longer than that of the Y-free solution-treated specimen. This was mainly because of the maintenance of the columnar grain morphology even after solution treatment. In addition, the formation of MC carbides, YO, and SiO improved creep life. To summarize the effect of Y, Y addition promoted the formation of cracks, which brought about creep anisotropy; however, it improved creep properties through the stabilization of oxygen and the promotion of discrete carbide precipitation, which prohibited the migration and sliding of grain boundary.
我们研究了稀土元素钇（Y）对选择性激光熔化加工的哈氏合金X的热裂纹和蠕变性能的影响。我们使用了两种不同的合金来研究哈氏合金X中的热裂纹：一种添加了0.12质量%的钇，另一种未添加钇。不含钇的哈氏合金X裂纹较少，主要是由于硅、钨和碳的偏析，导致在晶界和枝晶间区域形成了SiC和WC型碳化物。另一方面，添加钇的哈氏合金X试样中形成了更多裂纹，这是由于钇的偏析，导致形成了富钇碳化物（YC）。进行了1177℃下2小时的后热处理，随后空冷，以获得良好的蠕变性能。我们沿垂直和水平方向进行了蠕变试验。尽管添加钇的铸态哈氏合金X试样裂纹更多，但与哈氏合金X试样相比，其蠕变寿命更长，延展性更好。这主要是因为在晶粒内部形成了YO和SiO。固溶处理后，添加钇的试样的蠕变寿命比未添加钇的固溶处理试样长八倍。这主要是因为即使在固溶处理后，柱状晶形态仍得以保持。此外，MC碳化物、YO和SiO的形成提高了蠕变寿命。总结钇的作用，添加钇促进了裂纹的形成，这导致了蠕变各向异性；然而，它通过稳定氧和促进离散碳化物析出改善了蠕变性能，这抑制了晶界的迁移和滑动。
