Development of a method for carbide additivation on tool steel powders via a functional polymer binder to enhance the processability, microstructural isotropy, and strength of hard ferrous alloys

碳含量较高的钢，例如冷作钢和高速钢，已被证明难以通过LPBF加工。高碳钢在LPBF过程中有形成冷裂纹的倾向。工艺参数以及合金含量对LPBF处理高合金工具钢裂纹形成机制的影响尚未完全了解。而预合金粉末似乎是有限的合金含量由于开裂，合金含量可以通过使用不同的制备原料提高。为了扩大可加工合金的范围，增强合金已经获得关注。各种碳化物已被添加到基础钢中，主要是通过球磨，并通过LPBF处理。球磨是耗时的，并且可能导致粉末的球形度降低。人造卫星是另一种通过粘结剂用精细添加剂装饰大母粉颗粒的方法。卫星颗粒防止由于粉末的尺寸和密度效应而导致的局部分层，并且已经报道可以降低各向异性和晶粒尺寸。虽然Ti、Al、Co合金已被卫星化，但腐蚀敏感钢尚未被卫星化。最近，已经发表了许多具有不同程度取代基的多糖（作为生物基聚合物网络）的成功磷酸化。多糖结构中磷酸基团取代度的增加可以增强抗氧化活性（这与腐蚀抑制有关），这是由于多糖的异头碳上存在的氢原子的活化。该项目的主要目标是通过功能性聚合物粘合剂（多糖磷酸盐）为硬质铁合金（如工具钢）提供一种新的可靠的碳化物添加方法，以提高微观结构的各向同性和加工性能。工具钢的改性旨在通过降低冷裂纹和热裂纹的倾向来改善可加工性，并获得均匀的各向同性和细晶粒显微组织。未熔化的碳化物在LPBF过程中作为合金各向同性凝固的形核位点。粒度和纹理成为项目成功的关键性能指标。通过热力学平衡和Scheil-Gulliver凝固计算开发合金。研究内容包括粉体的卫星化对粉体流变学和热物理性质的影响。通过尺度桥接微观结构表征分析了LPBF的可加工性和微观结构的形成，并通过静态和动态力学测试表征了各向同性微观结构对力学性能的优势。

Steels with higher carbon contents, e.g. cold-work and high-speed steels, have proven to be difficult to process by LPBF. High carbon steels show a tendency for cold crack formation during LPBF processing. The influence of the processing parameters as well as the alloying content on the cracking formation mechanisms of high alloyed tool steels processed by LPBF is not yet fully understood. Whereas pre-alloyed powders seem to be limited in the alloying content due to cracking, the alloying content can be enhanced by using differently prepared feedstocks. In order to enhance the range of processable alloys, reinforced alloys have gained focus. Various carbides have been added to base steels, mainly by ball milling, and were processed by LPBF. Ball milling is time consuming and can result in reduced sphericity of the powder. Satelliting is another method for decorating large parent powder particles with fine additives by a bonding agent. Satellited particles prevent a local demixing due to size and density effects of the powder and have been reported to reduce anisotropy and grain size. Whereas Ti, Al, Co alloys have been satellited, corrosion susceptible steels have not been satellited yet. Recently, a number of successful phosphorylation of polysaccharides (as bio-based polymer network) with a different degree of substituents have been published. An increase of the degree of phosphate groups substituents in the polysaccharides structure could enhance anti-oxidant activities (which are related to corrosion inhibition) due to activation of hydrogen atoms present on anomeric carbon of polysaccharides. The main objective of this project is to provide a new and reliable method of carbide additivation to hard ferrous alloys such as tool steels via a functional polymer binder (polysaccharide phosphate) in order to enhance the microstructural isotropy as well as the processability. The modification of the tool steel aims at improving the processability by reducing the tendency to cold and hot cracking, and at a homogeneous isotropic and fine-grained microstructure. Unmolten carbides function as nucleations sites for the isotropic solidification of the alloy during LPBF. Grain size and texture become key performance indicators for the success of the project. The alloys are developed by thermodynamic equilibrium and Scheil-Gulliver solidification calculations. The investigation includes the influence of powder satelliting on rheological and thermophysical powder properties. The processability in LPBF and the microstructure formation is analysed by scale-bridging microstructural characterizations and the advantages of an isotropic microstructure on mechanical properties is characterized by static and dynamic mechanical tests.