Micro-Casting of Titanium Alloys Using 3D-Printed Self-Boiling Molds

由于其高的比强度和耐腐蚀性，钛合金被广泛用于各种应用，例如高价值的医疗产品，人工关节和骨骼、植入物和外科手术工具等。然而，通常用于其制造的常规机加工和锻造工艺在机械性能和生产率方面受到限制。该奖项支持使用新型功能模具（即通过三维（3D）打印生产的自沸腾模具）进行钛合金零件和从微米到数十毫米的铸造特征的新型铸造方法的基础研究。制造创新是通过沸腾传热机制来实现的，沸腾传热机制有助于在模具壁的所有点处进行传热控制以调节冷却速率，从而操纵铸造微观结构。这项研究对美国工业的影响将是一项具有竞争力的技术，用于控制铸造钛部件的关键性能，主要用于医疗应用，并结合3D打印功能模具。正如预期的那样，这一创新的溢出效应将对整个铸造行业产生影响。同样重要的是，该项目将为研究生和本科生提供一个材料、铸造和3D打印的多学科培训平台，以培养下一代劳动力。该项目的总体目标是对自沸腾模具方法的基本理解，以主动控制铸造零件各个位置的熔融合金的温度历史，从而控制其微观结构和机械性能。预测熔融金属的冷却速率之间的关系的分析基础的陶瓷模具和沸腾介质的特性的影响将被追求和建立沿着的方法设计所需的冷却速率，确保所需的微观结构分布的模具。首先，不同的自沸腾模具拓扑结构的表征将在一个专门设计的试验台上进行研究，以建立沸腾模式和模具壁性能和结构之间的关系，这是确定模具壁冷却性能的关键因素。其次，将通过基于元胞自动机方法的数值模型的制定来解决给定的微观结构分布的冷却速率的确定。专门设计的蓝宝石模具将用于模型验证，通过可视化的成核过程，熔融金属流动和温度测量。接下来，将致力于基于模型的确定的自沸腾模具的设计的冷却速率分布的属性，使用试验台的实验验证。最后，将使用3D打印（基于直接墨水书写）、烧结和浸渍方法进行自沸腾模具制造，然后进行微型铸造性能评估，并在微型腹腔镜镊子上进行演示。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Because of their high specific strength and corrosion-resistance, titanium alloys are widely used in various applications such as high-value medical products, e.g., artificial joints and bones, implants, and surgical tools, etc. However, conventional machining and forging processes typically used in their manufacture are limited in mechanical properties and productivity. This award supports fundamental research of a novel casting method for titanium-alloyed parts and cast features ranging from microns to tens of millimeter by using a new type of functional molds, namely, self-boiling molds, produced by three-dimensional (3D) printing. The manufacturing innovation is accomplished through the mechanisms of boiling heat transfer that facilitate heat transfer control at all points of a mold wall to adjust the cooling rate, thus, manipulating the cast microstructures. The impact of this research on US industry will be a competitive technology for controlling key properties of cast titanium components, principally for medical applications, in conjunction with 3D printing functional molds. The spillover effects of this innovation will, as anticipated, have an impact on the casting industry as a whole. Equally important, the project will provide a multidisciplinary training platform in materials, casting and 3D printing for graduate and undergraduate students for next-generation workforce development.The overarching goal of this project is a fundamental understanding of the self-boiling mold methodology to actively control the temperature history of molten alloys at various locations of a cast part and, thereby, its microstructure and mechanical properties. The analytical foundation for predicting the relationship between the cooling rate of the molten metal influenced by the characteristics of a ceramic mold and boiling medium will be pursued and established along with methods for designing molds of the required cooling rates that assure the desired microstructure distribution. First, the characterization of different self-boiling mold topologies will be studied on a specially designed testbed to establish the relation between boiling modes and mold wall properties and construction, a key factor for determining the cooling performance of the mold wall. Second, the determination of the cooling rates for a given microstructure distribution will be addressed through the formulation of a numerical model based on the Cellular Automaton method. Specially designed sapphire molds will be used for model verification through the visualization of the nucleation process, molten metal flow and temperature measurements. Next, a model-based determination of the self-boiling mold’s properties for a designed cooling rate distribution will be devoted, verified by experiments using the testbed. At the end, self-boiling mold fabrications using 3D printing (based on direct ink writing), sintering and impregnation methods will be conducted followed by micro-casting performance evaluations, demonstrated on micro-laparoscopic forceps.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.