Effects of processing parameters on the densification, microstructure and mechanical properties of pure tungsten fabricated by optimized selective laser melting: From single and multiple scan tracks to bulk parts

Selective Electron Beam Melting (SEBM) of Pure Tungsten: Metallurgical Defects, Microstructure, Texture and Mechanical Properties

“…No microcracks are seen; only pores (irregular shrinkage holes in the case of lack of fusion, and tiny spherical pores in cases of sufficient fusion and over-melting) exist in the SEBM-ed tungsten samples ( Figure 4 ). In SLM-ed tungsten samples, microcracks are usually inevitable [ 6 , 8 , 9 , 10 ], as shown in Figure 5 . A widely adopted aspect causing the microcrack formation in the SLM-ed samples is the high thermal stress generated by the high temperature gradient during the SLM process.…”

“…Each powder layer is also preheated. Therefore, the temperature gradient in SEBM is much lower than that in SLM for tungsten where the substrate can only be pre-heated up to 200 °C and there is no preheating for powder layers [ 8 ]. The lower temperature gradient in SEBM gives rise to a lower cooling rate, which in turn causes a much lower thermal stress [ 13 , 29 , 30 ] and low possibility of microcrack formation.…”

“…Rapid progress has been made in understanding the processing-microstructure-properties relationships of pure tungsten samples fabricated by SLM [ 3 , 4 , 5 , 6 , 7 ]. For example, the SLM-fabricated bulk pure tungsten samples of high relative densities of 95–98.51% can achieve an ultimate compressive strength up to 1.01 GPa after heat treatment [ 7 , 8 ]. Experimental observations also indicate that microcracks owing to high residual stresses induced by high temperature gradients in SLM-ed samples are inevitable [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ].…”

“…For example, the SLM-fabricated bulk pure tungsten samples of high relative densities of 95–98.51% can achieve an ultimate compressive strength up to 1.01 GPa after heat treatment [ 7 , 8 ]. Experimental observations also indicate that microcracks owing to high residual stresses induced by high temperature gradients in SLM-ed samples are inevitable [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ]. In SLM-ed samples, one can also find pores whose formation is most likely attributed to the entrapped protective inert gas (e.g., argon) by the Marangoni effect [ 7 , 12 ].…”

Selective laser melting of lanthanum oxide-reinforced tungsten composites: microstructure and mechanical properties

“…Selective laser melting (SLM), a metal additive manufacturing technique, enables to produce metal parts with complex structures directly [8][9][10][11][12][13][14][15]. At present, there have been some results in forming W and its alloys by SLM technique [16][17][18][19][20][21][22][23][24]. But it is still impossible to manufacture completely dense, crack-free, and high-performance W parts, which restricts the application of W parts.…”