Selective Laser Melting Additive Manufacturing of Hard-to-Process Tungsten-Based Alloy Parts With Novel Crystalline Growth Morphology and Enhanced Performance

Abstract

Selective laser melting (SLM) additive manufacturing (AM) of hard-to-process W-based parts with the addition of 2.5 wt.% TiC was performed using a new metallurgical processing mechanism with the complete melting of the high-melting-point powder. The influence of SLM processing parameters, especially laser scan speed and attendant laser fluence (LF), on densification behavior, microstructural development, and hardness/wear performance of SLM-processed W-based alloy parts was disclosed. The densification response of SLM-processed W-based parts decreased both at a low LF of 10.7 J/mm2, caused by the limited SLM working temperature and wetting characteristics of the melt, and at an excessively high LF of 64 J/mm2, caused by the significant melt instability and resultant balling effect and microcracks formation. The laser-induced complete melting/solidification mechanism contributed to the solid solution alloying of Ti and C in W matrix and the development of unique microstructures of SLM-processed W-based alloy parts. As the applied LF increased by lowering laser scan speed, the morphologies of W-based crystals in SLM-processed alloy parts experienced a successive change from the cellular crystal to the cellular dendritic crystal and, finally, to the equiaxed dendritic crystal, due to an elevated constitutional undercooling and a decreased thermal undercooling. The optimally prepared W-based alloy parts by SLM had a nearly full densification rate of 97.8% theoretical density (TD), a considerably high microhardness of 809.9 HV0.3, and a superior wear/tribological performance with a decreased coefficient of friction (COF) of 0.41 and a low wear rate of 5.73 × 10−7 m3/(N m), due to the combined effects of the sufficiently high densification and novel crystal microstructures of SLM-processed W-based alloy parts.