Astafurov, Sergey V.

Astafurova, Elena G.

Esipov, R. S.

Maier, G. G.

Melnikov, E. V.

Moskvina, V. A.

Nikolaev, A. A.

Panchenko, M. Yu.

Ramazanov, K. N.

Reunova, K. A.

Russian

Tomsk State University Repository

     ТЕЗИСЫ ДОКЛАДОВ     МЕЖДУНАРОДНАЯ КОНФЕРЕНЦИЯ  «Физическая мезомеханика. Материалы с многоуровневой иерархически организованной структурой и интеллектуальные производственные технологии»,  посвященная 90-летию со дня рождения основателя и первого директора ИФПМ СО РАН академика Виктора Евгеньевича Панина   в рамках  Международного междисциплинарного симпозиума  «Иерархические материалы: разработка и приложения  для новых технологий и надежных конструкций»    5–9 октября 2020 года  Томск, Россия      Томск         Издательство ТГУ 2020   Секция 4. Научные основы разработки материалов с многофазной иерархически организованной структурой, в том числе для экстремальных условий эксплуатации 309 DOI: 10.17223/9785946219242/199 THE EFFECT OF A COMPOSITION OF A SATURATING GAS IN ION-PLASMA TREATMENT ON SURFACE LAYER PROPERTIES IN AUSTENITIC STAINLESS STEEL  1Moskvina V.A., 1Maier G.G., 2Ramazanov K.N., 2Esipov R.S., 2Nikolaev A.A.,  1Astafurov S.V., 1Melnikov E.V., 1Panchenko M.Yu., 1Reunova K.A., 1Astafurova E.G. 1Institute of Strength Physics and Materials Science SB RAS, Tomsk 2Ufa State Aviation Technical University, Ufa  A morphology of a microstructure, a microhardness and a phase composition of the surface layers produced by ion-plasma treatment (IPT) in specimens of AISI 316L-type stainless steel (SS) were studied in dependence on a composition of saturating gases. The original homogenized billets of austenitic AISI 316L-type were cold rolled at room temperature to a 40 % total strain and annealed at a temperature of 1050°C for 5 h followed by water-quenching. Further, two portions of steel specimens were subjected to IPT at a temperature of 540°C for 12 h, gas pressure of 300 Pa in different gas mixtures: 25 % N2 + 5 % C2H2 + 70 % Ar (IPT-NCH) for the first portion and 30 % N2 + 8 % H2 + 62 % Ar (IPT-NH) for the second portion of the specimens. Initial specimens (pre-IPT) possess fully austenitic coarse-grained structure (d=55 μm) as it has been revealed by light microscopy (LM) and transmission electron microscopy. According to data of electron back scattered diffraction, the vast majority of boundaries possess high-angle misorientations and grains are randomly misoriented in the specimens. The fraction of high-angle boundaries in the austenite structure is 0.90. X-ray diffraction (XRD) patterns for pre-IPT specimens contain reflections corresponded to the γ-austenite with a lattice parameter aγ =3.597 Å. IPTs with gases of two different compositions promote a formation of the surface hardened layers in specimens of AISI 316L-type SS. The addition of hydrogen to the saturating gas contributes to facilitation of the diffusivity of nitrogen and an increase of the hardened layer thickness (tl): tl≈10-13 μm in IPT-NCH specimens and tl≈22-28 μm in IPT-NH specimens. According to LM, a double-layered microstructure is observed on the etched cross-section surfaces of both IPT-NCH and IPT-NH specimens. The outer (surface) layer possesses a high etchability but the underlying diffusion layer (subsurface one) has poor etchability. The interface between these layers is clearly distinguishable. The morphology observations by LM are in good agreement with distribution of microhardness values to depth of IPT-assisted surface layers. The microhardness distribution profiles over the depth of the hardened surface layer and the diffusion subsurface layer vary nonlinearly and ―flatten‖ after the matrix is reached (50-55 μm depth in cross-sectional direction) for IPT-NCH and IPT-NH specimens. The microhardness distribution profile in IPT- NCH specimens is smoother than that in IPT-NH, with a gradual decrease in microhardness values to the depth, while IPT-NH ones are characterized by a sharp transition to a diffusion layer with a high scatter of microhardness values. The diffusion subsurface layers extend up to 50-55 μm in depth from the surface for both types of specimens. The surface microhardness of the specimens was greatly improved by IPT-processing: 16.4 ± 0.5 GPa for IPT-NCH case and slightly less for IPT-NH specimens (14.9 ± 0.8 GPa). These values are four times higher than that for the initial 316L-type SS (3.7 ± 0.5 GPa, load of 50 g).  XRD patterns of both IPT regimes indicate a formation of expanded austenite (Fe-γN,C) which has an increased lattice parameter due to the incorporation of solute atoms (N or/and C) into the crystal lattice of austenite. In XRD pattern corresponding to IPT-NH specimens peaks of expanded austenite phase are more strongly shifted and peaks of Fe4N phase has a higher intensity compared to IPT-CNH specimens. This suggests that IPT-NH specimens possess a higher concentration of interstitials (nitrogen) in solid-solution of austenite in comparison with hardened layer in IPT-CNH specimens. Also, the reflections for Cr(N,C), α-Fe and Fe4(N,C) phases are observed which imply that the similar phase decomposition mechanism is inherent for both IPT-NCH and IPT-NH processing regimes. The study was funded by Russian Foundation for Basic Research, project No. 20-38-70031. 

The effect of a composition of a saturating gas in ion-plasma treatment on surface layer properties in austenitic stainless steel

http://vital.lib.tsu.ru/vital/access/services/Download/vtls:000786846/SOURCE1

The effect of a composition of a saturating gas in ion-plasma treatment on surface layer properties in austenitic stainless steel

Abstract

Similar works

Full text

Available Versions

Tomsk State University Repository