# Functionally Graded AISI 316L and AISI H13 Manufactured by L-DED for Die and Mould Applications
## 1 Introduction  
### Introduction to L-DED Processes  
Additive manufacturing (AM) technologies have emerged as an alternative to traditional manufacturing processes to produce complex, fully dense, and functional parts [1]. Additive processes were originally conceived as a tool to provide a quick representation of components, that is, rapid prototyping. However, owing to the significant advances in AM and materials development, the paradigm of AM has shifted to the manufacturing of end products [2]. Moreover, AM's ability to manufacture intricate parts, unachievable through conventional manufacturing methods, has led to these technologies being adopted in aerospace, medical, energy, and automotive industries for the production of high-performance components, therefore reaching a critical acceptance level in the industry [3]. Among the many technologies developed within the metal AM envelope, directed energy deposition (DED) excels. According to the International Standard ISO/ASTM 52900:2015, DED processes are those \"additive manufacturing processes in which focused thermal energy is used to fuse materials by melting as they are being deposited\" [4]. AmongDED technologies, powder-based laser-DED (L-DED) is commonly used in the industry [5]. In powder-based L-DED, a laser beam is focused onto the substrate surface, where a melt pool is created. Feedback in the powder form is simultaneously injected under a protective atmosphere, which avoids the oxidation phenomenon (Figure 1). The rapid solidification of the molten metal inherent to this process allows unique microstructures and phases to be formed, unachievable by equilibrium cooling [6]. As far as the application field of L-DED is concerned, and although it is capable of manufacturing fully functional end-parts, nowadays it is mostly employed for the remanufacture, repair, and coating of high-added-value parts in the aerospace or the die and mould industry [1]. In fact, the highly localised energy input of the laser provides a strong metallurgical bond between the added material and the substrate, while the base material retains its mechanical properties unimpaired due to the reduced heat-affected zone [7]. In the case of the die and mould industry, enhanced performance of the tooling and extended lifetime can be obtained by cladding wear and corrosion resistant coatings onto the dies/moulds [8]. On the other hand, refurbishment of the high-added-value tools to restore their functionality is also possible [9]. More specifically, L-DED enables the repair of tools for the hot-stamping process, extrusion, or casting process [10], where components are subjected to harsh corrosive, erosive, and wear conditions [11]. For this purpose, it is common practice to employ intermediate buffer layers to avoid cracking due to internal stresses and improve the weldability of materials [12], as demonstrated by [PERSON] et al. [13], who used AISI 316L stainless steel as an intermediate material when depositing AISI H13 hot-work tool steel over CR7V-L hot-work tool steel. In summary, repair of high-added-value components in the die and mould sector is of great interest for the industry; material compatibility issues in refurbishing need to be addressed by proposing new methodologies that incorporate advanced manufacturing techniques, such as multimaterial and functionally graded L-DED. Once it is established that L-DED has the capability of processing different metals such as tool steels, stainless steels, titanium alloys, nickel alloys, and copper alloys [1], it is worth highlighting that it also has the capability of working with several materials simultaneously (Figure 1), allowing for multimaterial components and graded structures to be manufactured. In the literature, authors agree that one of the main advantages of this technology is its capacity for in situ mixing of different materials [2; 14; 15]. This feature allows for locally tailored material properties, including transition joints when joining dissimilar metals, in situ manufacturing of composites, and alloying [14].