Complex heat treatment operations and advanced manufacturing processes such as laser or electron-beam welding will see the metallic workpiece experience a considerable range of temperatures and heating/cooling rates. These intrinsic conditions will have a significant bearing upon the microstructure of the material, and in turn upon the thermo-mechanical properties. In this work, a diffusion-based approach to model the growth and shrinkage of precipitates in the alpha + beta field of the common titanium alloy Ti-6Al-4V is established. Further, the numerical model is extended using a JMA-type approach to explore the dependency of the beta-transus temperature on extremely high heating rates, whereby dissolution alone is too slow to accurately describe the alpha to beta-phase transformation. Experimental heat treatments at rates of 5, 50, and 500 °C/s were performed, and metallographic analysis of the samples was used to validate the numerical modeling framework predictions for lamellar shrinkage, while data from the literature has been used to evaluate the numerical modeling framework for the growth of equiaxed microstructures. The agreement between measurements and numerical predictions was found to be good.

中文翻译：

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Ti-6Al-4V 中 α + β 相的微观结构建模：一种基于扩散的方法

复杂的热处理操作和先进的制造工艺（如激光或电子束焊接）将使金属工件经历相当大的温度和加热/冷却速率范围。这些内在条件将对材料的微观结构产生重大影响，进而影响热机械性能。在这项工作中，建立了一种基于扩散的方法来模拟常见钛合金 Ti-6Al-4V 的 alpha + beta 场中析出物的生长和收缩。此外，使用 JMA 类型的方法扩展了数值模型，以探索 β-转变温度对极高加热速率的依赖性，由此单独溶解太慢而无法准确描述 α 到 β 相的转变。以 5、50、以 500 °C/s 的速度进行，样品的金相分析用于验证层状收缩的数值建模框架预测，而文献中的数据已用于评估等轴微结构生长的数值建模框架。发现测量值和数值预测之间的一致性很好。