This study deals with early stages of sigma phase growth in a high end austenitic stainless steel – Alloy 28 (EN 1.4563/UNS N08028). Its precipitation kinetics was followed by a series of heat treatments at 800°C for holding times up to 30000 s. The samples were studied with high resolution scanning electron microscopy and atom probe tomography. Detailed image analysis of the micrographs made it possible to quantify the growth rate of the precipitates. It was shown that diffusion limited growth along grain boundaries was about 15 times faster than growth perpendicular to a grain face. By combining the image data with quantitative chemical analysis of the phase boundaries, it was possible to estimate diffusion coefficients in the lattice and in the grain boundaries; grain boundary diffusion coefficients were about 250 times those of the lattice.
展开▼
机译:该研究涉及高端奥氏体不锈钢合金28(EN 1.4563 / UNT N08028)中的Sigma相生长的早期阶段。其沉淀动力学之后是800℃的一系列热处理,可持续到30000秒。用高分辨率扫描电子显微镜和原子探测断层扫描研究了样品。微图的详细图像分析使得可以量化沉淀物的生长速率。结果表明,沿着晶界的扩散有限的生长比垂直于晶粒面的生长快约15倍。通过将图像数据与相位边界的定量化学分析相结合,可以估计晶格和晶界中的扩散系数;晶界扩散系数约为格子的约250倍。
展开▼