The Effect of Nitrogen Flow Rate on the Loadbearing Capacity from Nano- to Macro-Hardness of Austenitic Stainless Steels Magnetron Sputtering-Coated with Stainless Steel Films

Garzón, Carlos M.; Vergara, Giovanny A.; Recco, Abel A. C.

doi:10.1590/1980-5373-MR-2019-0453

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Original Article • Mat. Res. 23 (3) • 2020 • https://doi.org/10.1590/1980-5373-MR-2019-0453 copy

The Effect of Nitrogen Flow Rate on the Loadbearing Capacity from Nano- to Macro-Hardness of Austenitic Stainless Steels Magnetron Sputtering-Coated with Stainless Steel Films

Authorship SCIMAGO INSTITUTIONS RANKINGS

UNS S31603 stainless steel (SS) substrates were covered by reactive magnetron-sputtering with protective SS coatings of the same steel specification. A mechanical characterization study (through nano-, micro- and macro-hardness tests) of samples obtained under two different sputtering conditions and varying the N₂ gas flow rate was carried out. This contribution aimed at appraising the effects of varying the nitrogen flow rate on hardness, elastic modulus, and susceptibility to indentation-induced crack formation of the coated SSs. Nitrogen-free samples displayed body-centered cubic (BCC) films with 9.0-9.4 GPa hardness and 203-206 GPa elastic modulus, while their susceptibility to indentation-induced cracking varied between superior and moderated among the two sets of sputtering conditions studied. Samples alloyed with 4-6 N at-% displayed a predominantly face-centered cubic (FCC) structure, 9.4 GPa hardness, 196-218 GPa elastic modulus, and superior resistance to crack formation. Samples with 11.5-22.0 N at-% were fully composed of the FCC structure, displayed 12.4-15.2 GPa hardness, 188-193 GPa elastic modulus, and moderated resistance to indentation-induced crack formation. Samples with 47.0 N at-% displayed FCC compound nitride structure, for which hardness and elastic modulus were 8.1 GPa and 139 GPa, respectively. These samples displayed low resistance to crack formation.

Keywords:
stainless steels; S-phase; loadbearing capacity; steel films; composite hardness; fragile failure

Sputtering conditions	N₂ flow rate, sccm	Phase fraction dimensionless			Average N-content, at-%	Hardness GPa	Elastic modulus GPa
Sputtering conditions	N₂ flow rate, sccm	Ferrite	S-phase^* * S-phase is a FCC crystal structure with expanded lattice constant, with regard to nitrogen-lean austenite, due to nitrogen dissolution.	MN nitride^§ § MN nitride is a compound phase with FCC crystal structure. Distinction between S-phase and MN nitride was made in accordance with Kappaganthu and Sun33. XRD scans are presented in Figure 2.	Average N-content, at-%	Hardness GPa	Elastic modulus GPa
Non-substrate heating, non-bias, 7 Wcm^-2	0	1.0	0.0	0.0	0	9.4^±0.5	206^±16
	0.53^±0.03	0.05^±0.02	0.95^±0.02	0.0	6.0^±2.0	9.4^±0.5	196^±17
	1.82^±0.04	0.0	1.0	0.0	22.0^±4.0	15.2^±0.7	193^±8
	11.3^±0.05	0.0	0.0	1.0	47.0^±6.0	8.1^±0.6	139^±10

573 K substrate heating, -250 V bias, 10.3 Wcm^-2
	0	1.0	0.0	0.0	0	9.0^±0.5	203^±17
	0.53^±0.03	0.07^±0.02	0.93^±0.02	0.0	4.0^±2.0	9.4^±0.6	218^±20
	1.82^±0.04	0.0	1.0	0.0	11.5^±3.0	12.4^±0.9	188^±13

Sputtering conditions	N2 flow rate, sccm	Critical load Knoop tests kgf	Critical load Vickers tests kgf	HF performance index Rockwell tests dimensionless
Non-substrate heating, non-bias, 7 Wcm^-2	0	No cracking^* * No formation of cracks was observed for indentation loads up to 2.0 kgf.	3.0	2
	0.53^±0.03	No cracking*	No cracking&	1
	1.82^±0.04	1.0	0.05	4
	11.3^±0.05	0.025	0.025	6
573 K substrate heating, -250 V bias, 10.3 Wcm^-2	0	No cracking*	No cracking^&	1
	0.53^±0.03	No cracking*	No cracking^&	1
	1.82^±0.04	No cracking*	10.0	3

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