Contents lists available at ScienceDirect International Journal of Refractory Metals & Hard Materials journal homepage: www.elsevier.com/locate/IJRMHM Perspectives of metal-diamond composites additive manufacturing using SLM-SPS and other techniques for increased wear-impact resistance Ramin Rahmani a,b, ⁎ , Miha Brojan b , Maksim Antonov a , Konda Gokuldoss Prashanth a,c,d a Department of Mechanical and Industrial Engineering, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia b Laboratory for Nonlinear Mechanics, Faculty of Mechanical Engineering, University of Ljubljana, Askerceva 6, SI-1000 Ljubljana, Slovenia c Erich Schmid Institute of Materials Science, Austrian Academy of Science, Jahnstraße 12, A-8700 Leoben, Austria d CBCMT, School of Mechanical Engineering, Vellore Institute of Technology, 632014, Tamil Nadu, India ARTICLEINFO Keywords: Selective laser melting Spark plasma sintering Hard material 3D printing Metal-diamond powders Wear-impact resistance Finite element simulation ABSTRACT In this paper, a new route is introduced to fabricate parts with increased wear and impact resistance for use in tunneling and mining applications. A combination of selective laser melting (SLM) and spark plasma sintering (SPS) to 3D print functionally graded lattices (FGL) that are later flled with metal-diamond composites was used. It was demonstrated that a cellular lattice plays an important role in the consolidation of diamond par- ticles. Impact-abrasive laboratory experiments with tribological device, developed in-house, were carried out to characterize the fabricated samples. The results show that the balance of nickel, molybdenum, and chromium signifcantly afects the performance of the fabricated specimens. The addition of a higher content of MoeCr, Ni and coated diamond particles guarantees higher impact-abrasive resistance of the composite. Our experimental results show that the FGL structure allows a more accurate distribution of diamond particles (variable metal/ refractory material content) across the structure and our fnite element simulations showed increased ductility and impact absorption ability due to a more uniform distribution of stresses throughout the volume. 1. Introduction Additive manufacturing has an immense potential to assist in the development of new classes of materials with precisely engineered microstructures that can work in extremely harsh conditions. For ex- ample, a combination of selective laser melting (SLM) of metals and spark plasma sintering (SPS) of metallic, ceramic or composite mate- rials enables the production of composites using functionally graded lattice (FGL) structures with continuous metal lattices for optimized strength and sintered/embedded hard reinforcements for optimized hardness [1,2]. A cost-efcient drag bit for deep geothermal drilling or tunnel boring machines [3] in which harsh impact-abrasive conditions apply is an excellent example of application to test the limits of additive manufacturing (AM) methods, such as 3D printing of metallic and composite materials with diamond inclusions [4,5]. SLM is a rapid prototyping technology based on the powder bed fusion process with the high heating and cooling rate (10 4 –10 6 K/s [6]) that enables the creation of complicated parts and assemblies directly from computer-aided design (CAD) models. The feeding mechanism is used to deposit agglomerated powders in front of a rubber wiper that sweeps the powder on the building area to form a thin uniform layer. The minimal possible thickness of the spread layer depends on fow- ability, sphericity and wiper height adjustment. The laser then pulses and heats the powder on the building area to form a solid object. With this system, the objects are built layer by layer on e.g. Ti6Al4V platform with the help of a servomotor driven elevator that moves downwards by a distance equal to the layer thickness and after every wiping and sintering sequence. The process is carried out in an argon protective environment with a pressure of 6 mbar and an oxygen level < 0.5% [7]. Powders are deposited, melted and consolidated layer by layer with the prescribed thickness (e.g. 0.25–0.5 μm for SLM50) to manufacture dense layers and CAD designed dimensions. The basis of the SLM classifcation is usually platform sizes e.g. SLM50, SLM280 or SLM500 (that corresponds to 50, 280 and 500 mm and is prescribing the max- imum size of the object that is possible to print) [8]. Unmelted/non- consolidated powders outside the platform, wiped out during the job or after fnishing the job can be recycled which is an advantage of AM technology regarding powder consumption [9]. Another beneft of SLM is the ability to use a wide scope of metal, ranging from Ti-, Fe-, Al-, Ni-, Co- to Cu-based powders [10]. Parts fabricated by this technology show better fatigue resistance, fracture toughness and tribological properties compared to their cast counterparts [11]. https://doi.org/10.1016/j.ijrmhm.2020.105192 Received 18 December 2019; Accepted 9 January 2020 ⁎ Corresponding author at: Department of Mechanical and Industrial Engineering, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia E-mail addresses: ramin.rahmaniahranjani@taltech.ee, ramin.rahmaniahranjani@gmail.com (R. Rahmani). International Journal of Refractory Metals & Hard Materials 88 (2020) 105192 Available online 10 January 2020 0263-4368/ © 2020 Elsevier Ltd. All rights reserved. T