Laser‐Based Additive Manufacturing of WC–Co with High‐Temperature Powder Bed Preheating^†

Abstract

The field of additive manufacturing (AM), and especially laser powder‐bed fusion (LPBF), is constantly growing. Process windows for a large variety of materials are already developed. Nevertheless, some materials are still difficult to manufacture with LPBF. One of these materials is the tungsten carbide/cobalt‐based hard metal (WC–Co), which is conventionally produced by powder metallurgy including liquid‐phase sintering. Most approaches to manufacture WC–Co with LPBF show a high porosity, undesirable phases in the microstructure, and inhomogeneous carbide distribution. However, the production of WC–Co cutting tools by LPBF will offer some benefits such as production of geometrically optimized inner cooling channels or optimized geometry of the cutting edges. Herein, WC with 17 wt% Co is processed by LPBF with a powder‐bed heating of 900 °C. Afterwards microstructure, density, and hardness are determined. In addition, X‐ray diffraction (XRD) analysis is performed to determine the phase composition. To investigate the edge‐holding properties of LPBF‐manufactured WC–Co cutting tools, stock removal tests are conducted on three different workpiece materials.

Ti(C,N) and WC-Based Cermets: A Review of Synthesis, Properties and Applications in Additive Manufacturing

“…The research has extensively covered additive manufacturing of WC-Co hard metals that are produced by powder metallurgy, including conventional liquid-phase sintering [113]. Fries et al processed WC with 17 wt.% Co by laser powderbed fusion (LPBF) with a powder-bed heating of 900 °C [114].…”

The structure and the properties of WC-Co samples produced by SLM technology and carbon-doped prior to HIP processing

“…The occurrence of CC structural defects can be limited in various ways. For example, the formation of cracks can be prevented in the CC structure by increasing the binder content (Khmyrov et al , 2016), by multiple remelting of the powder layer (Fortunato et al , 2019) or by preheating the build platform to high temperatures (Fries et al , 2020). The occurrence of pores can be influenced by the type and quality of the powder used (Chen et al , 2019) and its processing parameters (Uhlmann et al , 2015).…”

Evaluation of a High-Temperature Pre-Heating System Design for a Large-Scale Additive Manufacturing System

“…The stainless steel 304 heater holders rest on the stainless steel 304 inner and outer faces connected to stainless steel 304 pillars and the baseplate is bolted to the pillars through the inner face component using M20 mild (low carbon) steel bolts. Studies have shown that using a preheating system minimizes tensile residual stresses [6][7][8][9][10][11][12], therefore improving the quality of the part and reducing part premature failure during building. A 510 Watt Nd-YAG laser was used by Liu et al [6] to preheat yttria-stabilized zirconia ceramics to a maximum temperature of 2500 °C and observe a reduction in vertical cracks and porosity.…”

“…Studies reviewed had lower build volumes compared to that of the Aeroswift platform, but they had higher heating power compared to the Aeroswift platform since it utilizes 6 kW to heat its current build volume. Calprio et al [10] used 960 W to heat a 38 mm diameter Studies have shown that using a preheating system minimizes tensile residual stresses [6][7][8][9][10][11][12], therefore improving the quality of the part and reducing part premature failure during building. A 510 Watt Nd-YAG laser was used by Liu et al [6] to preheat yttria-stabilized zirconia ceramics to a maximum temperature of 2500 • C and observe a reduction in vertical cracks and porosity.…”

“…They reduced residual stresses by 88.3% when preheating at 470 • C; furthermore, no substantial stresses were formed when preheating at 570 • C, 670 • C, and 770 • C. Roehling et al [8] used an in situ annealing approach to reduce residual stresses in 316L steel bridges fabricated by LPBF using four laser diodes as preheating devices with 1.25 kW power each and observed that preheating at 625 • C substantially lowered residual stresses. Fries et al [9] built crackfree tool inserts of WC-17Co at 900 • C baseplate preheating using an inductive heating device. They obtained microstructural and mechanical properties comparable to tools produced through conventional methods.…”