Densification, Microstructure and Properties of 90W-7Ni-3Fe Fabricated by Selective Laser Melting

Abstract

The preparation of refractory tungsten and tungsten alloys has always been challenging due to their inherent properties. Selective laser melting (SLM) offers a choice for preparing tungsten and tungsten alloys. In this work, 90W-7Ni-3Fe samples were prepared by selective laser melting and investigated. Different process parameter combinations were designed according to the Taguchi method, and volumetric energy density (VED) was defined. Subsequently, the effects of process parameters on densification, phase composition, microstructure, tensile properties, and microhardness were investigated. Nearly a full densification sample (≥99%) was obtained under optimized process parameters, and the value of VED was no less than 300 J/mm3. Laser power had a dominant influence on densification behavior compared with other parameters. The main phases of 90W-7Ni-3Fe are W and γ-(Ni-Fe), dissolved with partial W. In addition, 90W-7Ni-3Fe showed a high tensile strength (UTS = 1121 MPa) with poor elongation (<1%). A high average microhardness (>400 HV0.3) was obtained, but the microhardness presented a fluctuation along building direction due to the inhomogeneous microstructure.

Microstructure and strengthening mechanisms of 90W–7Ni–3Fe alloys prepared using laser melting deposition

“…This is mainly because LMD provides larger melt pools than SLM, which helps to homogenize the microstructure and reduce the porosity. The strength of one of the data points for a SLM sample is higher than that of the present LMD sample, which is believed to be related primarily to the small reported powders/W grains of 4-11 µm in this sample [23], rather than a result of the processing route. It has been shown, for example, that if small powders are used even higher strength can be obtained with LMD, while still retaining a uniform elongation of ~5% for a 75W-17.5Ni-7.5Fe alloy [27].…”

“…quasi-static tensile tests at strain rates in the order of 10 -4 ~10 -3 s -1 ). Compared to SLM-processed WHAs [16,23], LMD-produced WHAs can result in a better ductility. This is mainly because LMD provides larger melt pools than SLM, which helps to homogenize the microstructure and reduce the porosity.…”

“…reducing the processing time [2,[10][11][12][13][14][15][16]. Among these methods, additive manufacturing (AM), using methods such as laser melting deposition (LMD) or selective laser melting (SLM), has attracted much interest due to its potential to allow near net-shape manufacturing of complex components directly from digital models [15][16][17][18][19][20][21][22][23][24][25][26][27]. The high energy density of the laser beam can heat up the powders quickly (typically in the order of 10 -3 ~10 -1 s), while a small molten volume results in a fast cooling rate as the beam moves to the next local volume.…”

“…The ultrafast heating and cooling rates of LMD and SLM (>10 3 ~10 4 K/s) can significantly reduce the time during which structural coarsening can occur. However, for SLM-processed WHAs, the combination of a relatively small melt pool (on the order of 100 µm) and very fast cooling rates (10 5 ~10 6 K/s) [28] can lead to lack of fusion, thereby resulting in a limited rearrangement of the W particles [16,18,[20][21][22][23]. As such, even with the use of powder-preheating, the microstructure of SLM-processed WHAs often contains a non-uniform distribution of W particles and a large number of pores, which makes SLM-processed WHAs very brittle [16].…”

W–Ni–Fe Refractory Alloy Sintered by Hot Oscillating Pressure Under Different Amplitudes

“…Tungsten heavy alloys (WHAs) have many excellent physical and chemical properties, [1][2][3][4][5][6][7][8] such as high strength, high melting point, good wear resistance, low expansion coefficient, and good radiation shielding ability. The 90W-7Ni-3Fe alloy is one typical refractory tungsten alloy, [9,10] which possesses high density, high strength, and a low coefficient of thermal expansion. Because of the ultrahigh melting temperature of tungsten, powder metallurgy was the most useful and promising technology.…”