New technology can efficiently heal cracks in nickel based high-temperature alloys manufactured by laser additive manufacturing

Recently, Professor Zhu Qiang's team from the Department of Mechanical and Energy Engineering at Southern University of Science and Technology published their latest research findings in the Journal of Materials Science. The research team has proposed a new process for liquid induced healing (LIH) laser additive manufacturing of cracks. By controlling micro remelting at grain boundaries to introduce interstitial liquid film filling defects, cracks in components can be "welded" at the microscale. This research achievement is of great significance for breaking through the industry challenge of laser additive manufacturing of high crack sensitivity alloys.

Paper graphic abstract

Liquid induced hearing of cracks in nickel based superalloy fabricated by laser powder bed fusion - ScienceDirect
Laser additive manufacturing is a revolutionary technology that solves the problem of personalized and complex metal component integral forming, with huge application prospects. However, only over ten out of the hundreds of commonly used engineering alloys can stably achieve crack free printing, which is far from meeting the needs of replacing traditional processes.

Compared to processes such as casting and welding, laser additive manufacturing technology has inherent properties of micro zone ultra normal metallurgy and rapid solidification, making it more prone to cracking. There are two existing methods to deal with cracks in laser additive manufacturing. One is to suppress cracks during the printing process by adjusting the alloy solidification range, grain morphology, and component temperature gradient. However, there are significant differences in the effectiveness of different alloy systems, with narrow process windows and poor stability, making it difficult to completely eliminate cracks; The second is to use hot isostatic pressing (HIP) post-treatment to close cracks. However, HIP cannot repair surface defects and requires further processing to remove surface materials, which undoubtedly weakens the core advantage of additive manufacturing technology in forming complex structures.

In addition, the extremely high working conditions make HIP equipment complex and extremely expensive, making it only suitable for a small number of high value-added metal additive manufacturing components.

In this regard, the research team proposed the liquid induced healing (LIH) technology based on the technical idea of introducing intergranular continuous liquid film to "weld" cracks, and verified the feasibility and progressiveness of the LIH technology by taking the typical high crack sensitivity alloy IN738LC as the test alloy. The research results showed that the mechanical properties of the alloy were significantly improved after LIH technology treatment. In terms of tensile properties, the LIH state is higher than the cast state and hot isostatic pressing state, while in terms of high-temperature creep, the LIH state alloy exhibits properties comparable to precision casting and far higher than the hot isostatic pressing state.

It is reported that compared with the most reliable HIP technology currently available, LIH technology has significant advantages in defect elimination efficiency, universality, convenience, and cost. Firstly, it breaks through the technical limitations of its inability to heal surface defects, making it suitable for pore healing treatment of complex components without the need for additional machining to remove the surface; Secondly, the pressure required by LIH is less than 1/20 of that of HIP technology, eliminating safety hazards of high-pressure special equipment and simplifying equipment construction and cost; Thirdly, there is no need for insulation treatment, while HIP needs to be insulated at high temperatures for several hours, thereby improving process efficiency and reducing energy consumption costs.

Source: Sohu