Resubmission: High-strength, low-stress cemented carbide-steel brazed joints due to dispersed gamma-Fe-Co-Cu precipitates in the copper-rich fillet

本研究项目的总体目标是通过持续使用所有被钎焊材料连接系统的冶金允许的强度增加措施，最大限度地提高硬质合金-马氏体-钢钎焊连接的连接质量。从加工技术领域的可能应用角度来看，这是在增加使用寿命以及增加工具的进给力的背景下完成的，例如钎焊锤钻，硬质合金刀片锯片或具有大面积连接表面的刀架。除了应用适当的温度-时间制度和选择合适的钎焊材料外，本研究项目的重点越来越多地放在将促进润湿的Ni层引入现有的接头材料系统以及在钎焊缝内产生的材料机制上，从而提高钎焊接头的质量。通过电弧PVD将Ni层应用于难以湿化的马氏体时效钢，在钎焊过程中溶解在钎焊熔体中，并在钎焊区形成合金，这样，在凝固后，钎焊材料结构中存在精细分散的γ - fe - co沉淀，并且存在细缝，脆性相减少的界面转变，与基材无缺陷结合。对本研究项目具有重要科学意义的两个基本材料工艺因素是Cu-Ni- fe合金典型的析出淬透性和Cu和Ni元素在彼此中的完全溶解度。因此，所描述的γ - fe - co相的形态不仅受到温度-时间分布的影响，还受到Ni层功变化对钎焊区化学成分的影响，而且富cu基体相的延展性也得到了有针对性的调整，从而对复合材料的整体性能产生了积极的影响。该研究项目还具有很高的技术相关性，因为选择了钎焊硬质合金钢常用的高熔点钎料Cu，使钎焊过程的时间-温度曲线与马氏体时效钢的时间-温度转变行为一致，因此下游回火过程导致钢和钎焊材料同时析出硬化。在这个过程中，热辐射的整体传热模式和必要时在真空炉中普遍存在的制造被利用，因此，与局部热输入的钎焊工艺（例如感应钎焊）相比，对机械钢性能有一个整体的积极影响。

The overall objective of this research project is to maximize the joint quality of the cemented carbide-maraging-steel brazed joint by consistently using all strength-increasing measures permitted by the metallurgy of the material joint system to be brazed. From the point of view of possible applications in the field of machining technology, this is done against the background of increasing the service life as well as increasing the feed forces of tools such as brazed hammer drills, cemented carbide-tipped saw blades or tool holders with large-area joining surfaces. In addition to the application of an adequate temperature-time regime and the selection of a suitable brazing material, the focus of this research project is increasingly on the introduction of a wetting-promoting Ni layer into the existing joint material system as well as on the resulting material mechanisms within the brazed seam which increase the brazed joint quality. A Ni layer applied by arc PVD to the otherwise difficult-to-wet maraging steel dissolves in the brazing melt during the brazing process and alloys the brazing zone in such a way that, after solidification, both finely dispersed gamma-Fe-Co precipitates are present in the brazing material structure and fine-seamed, brittle-phase-reduced interfacial transitions with a defect-free bond to the base materials. Two elementary material-technological factors, which are of scientific importance for this research project, are the precipitation hardenability typical for Cu-Ni-Fe alloys and the complete solubility of the elements Cu and Ni in each other. Thus, not only the morphology of the described gamma-Fe-Co phases is influenced by an adapted temperature-time profile as well as the change of the chemical composition of the brazing zone by the variation of the Ni layer work, but also the ductility of the Cu-rich matrix phase is adjusted in a targeted manner, so that a positive influence on the global composite properties is brought about. The research project is also of high technical relevance, since the choice of the high-melting solder Cu, which is commonly used for brazing carbide-steel, brings the time-temperature profile of the brazing process into line with the time-temperature transformation behavior of the maraging steel, so that the downstream tempering process results in simultaneous precipitation hardening in both the steel and the brazing material. In this process, the holistic heat transfer modes of thermal radiation and, if necessary, fabrication prevailing in the vacuum furnace are utilized, so that, in contrast to brazing processes with a local heat input (e.g. induction brazing), there is a holistic positive influence on the mechanical steel properties.