Surface modification of plasma nitriding on AlxCoCrFeNi high-entropy alloys

doi:10.1016/j.jmst.2020.01.057

Abstract

Abstract:

Plasma nitriding is successfully employed in treating Al_xCoCrFeNi high-entropy alloys (HEAs) with finely-divided Al content (i.e., x values in molar ratio, x = 0.1- 0.8) to develop wear-resistant structural materials. Nitridation greatly removes the Al from the matrix that completely deplete the Ni-Al enriched phase, forming nanoscaled nitrides (AlN and CrN) precipitations near the surface. Nitriding promotes the hardness of present alloys with values widely ranging from 276 HV to 722 HV. Interestingly, the higher content the Al, the smaller thickness the nitrides layer, but the higher hardness due to the increased amount of hard nitrides phases and volume fraction of BCC phase. Significantly, plasma nitriding considerably improves the wear resistance of Al_xCoCrFeNi HEAs by 4-18 times.

Key words: Plasma nitriding, High-entropy alloy, Microstructure, Hardness, Wear and tribology

Jinxiong Hou, Wenwen Song, Liwei Lan, Junwei Qiao. Surface modification of plasma nitriding on Al_xCoCrFeNi high-entropy alloys[J]. J. Mater. Sci. Technol., 2020, 48: 140-145.

Figures/Tables 7

Fig. 1. XRD patterns of (a) un-nitrided and (b) nitrided AlxCoCrFeNi HEAs.

Fig. 2. SEM images of the un-nitrided AlxCoCrFeNi HEAs: (a) x = 0.1; (b) x = 0.25; (c) x = 0.45; (d) x = 0.6; (e) x = 0.8. (f, g) Magnified microstructures of Al0.6CoCrFeNi and Al0.8CoCrFeNi HEAs with EDS elemental distribution maps, respectively.

Fig. 3. SEM images of nitrided AlxCoCrFeNi HEAs: (a) x = 0.1; (b) x = 0.25; (c) x = 0.45; (d) x = 0.6; (e) x = 0.8. (f, g) Magnified microstructures of Al0.6CoCrFeNi and Al0.8CoCrFeNi HEAs with EDS elemental distribution maps, respectively.

Fig. 4. SEM micrographs of the transverse cross-sections of nitrided AlxCoCrFeNi HEAs: (a) x = 0.1; (b) x = 0.25; (c) x = 0.45; (d) x = 0.6; (e) x = 0.8. (f) The relative chemical element intensity with the depth from the surface for Al0.1CoCrFeNi HEAs.

Fig. 5. Variations of substrate hardness and BCC-volume fraction as a function of Al content in AlxCoCrFeNi alloys.

Fig. 6. Friction coefficient as a function of the sliding time for un-nitrided (a) and nitride (b) AlxCoCrFeNi HEAs.

Table 1 Wear rates of unnitrided and nitrided AlxCoCrFeNi alloys.

Alloy designation	Wear rate (mm³/(N m))		Improved wear resistance (times)
	Unnitrided	Nitrided
Al_0.1CoCrFeNi	1.61 × 10^-4	3.95 × 10^-5	4
Al_0.25CoCrFeNi	1.47 × 10^-4	1.72 × 10^-5	9
Al_0.45CoCrFeNi	2.54 × 10^-4	1.65 × 10^-5	15
Al_0.6CoCrFeNi	2.53 × 10^-4	1.54 × 10^-5	16
Al_0.8CoCrFeNi	2.51 × 10^-4	1.33 × 10^-5	18

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