# Functionally Graded AISI 316L and AISI H13 Manufactured by L-DED for Die and Mould Applications
## 1 Introduction
### Metal Functionally Graded Materials and Applications to the Die and Mould Industry  
Although functionally graded materials (FGMs) were originally designed for heat-resistant applications [18; 19], nowadays FGMs are also employed for the control of deformation, pressure, wear, and corrosion, as well as for replacing sharp material transitions in which high stresses are generated [20]. Traditionally, FGMs have been mostly confined to developing ceramic coatings and composite materials [21], while little attention has been given to grading metallic materials. However, with the development of AM processes, such as the aforementioned L-DED [22], FGMs of complex metallic gradients of dissimilar alloys have become available. Obtaining good metallurgical bonds between dissimilar alloys is not trivial; in fact, complete solubility over all compositions and temperatures is not common in binary alloys, and it is much more complex in ternary or multicomponent alloys [23]. This issue might be addressed by introducing compositional gradients. Still, the manufacture of FGMs using L-DED is not without its challenges, mainly, lack of solubility, atomic structure mismatch, variation in the coefficient of thermal expansion (CTE), and formation of brittle intermetallic phases leading to cracking along the graded composition [24]. [PERSON] et al. [25] proposed laser synchronous preheating as a way of reducing residual stresses during the deposition process for avoiding the cracking phenomenon, as solidification cracking occurred when manufacturing graded Inconel 625 to AISI 316L samples. They effectively avoided cracks in the preheated samples, while cracking was found in the non-preheated samples from 90% 316L to 70% 316L. [PERSON] et al. [8], on the other hand, studied the microstructure, hardness, and tensile fracture of AISI 316L to Inconel 625 samples. Firstly, they observed gradient hardness along the graded region, which matched the microstructure. Also, the fracture in the tensile testing occurred in the AISI 316L section, while the interfaces survived the testing, owing to the graded transition. [PERSON] et al. [26] studied the microstructure of AISI 316L to Inconel 718 graded samples and found that austenitic formation was promoted in the graded region, leading to the loss of hardness in certain areas. [PERSON] et al. [24] analysed AISI 304L to Inconel 625 gradient samples, where they found cracks of several microns due to the formation of carbides in the graded section. In addition, [PERSON] et al. [27] compared deposition of AISI 316 onto mild steel substrate with the Fe/AISI 316 gradient deposition and found that while many pores and cracks were observed in the sharp transition, no cracking was detected in the graded sample. Finally, [PERSON] et al. [28] fabricated an Invar to AISI 316L graded part and found that while the composition distribution was linear, the hardness along the graded sample was distinctly nonlinear and justified it with the hardness not increasing linearly with the carbon content in the stainless steels.  
To sum up, although some research on FGMs of metallic alloys by L-DED has been carried out, little work on FGMs applied to the die and mould sector has been published, and no studies on FGMs with AISI H13 tool steel have been carried out. Therefore, with the aim of overcoming this gap, in the present work, an analysis of the microstructure and the mechanical properties of AISI 316L/ AISI H13 FGM was performed, as this combination of materials has a potential use in the repair and coating of tooling for hot-stamping processes. For that purpose, graded samples with 20% composition intervals from 100% AISI 316L to 100% AISI H13 have been manufactured using powder-based L-DED. Then, a metallographic analysis has been performed to assess the quality of the deposited material, the state of the interfaces, and the microstructures generated. Finally, microhardness measurements have been acquired along the coatings to evaluate the mechanical properties of the deposited material.