Microstructures and thermal damage mechanisms of sintered polycrystalline diamond compact annealing under ambient air and vacuum conditions

The microstructures and thermal damage mechanisms of sintered polycrystalline diamond compact (PDC) were studied in ambient air and vacuum at the temperature up to 1000 °C. The microstructures and compositions of the annealed PDC were characterized by white light interferometer, X-ray diffractometry (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The results showed that no visible change in the morphologies of surface of PCD layers (PDC surfaces) was observed at 200 °C both in ambient air and vacuum. After annealing at 500 °C, numbers of spalling pits appeared on the PDC surface, and the stress-induced spall mechanism was the dominant thermal damage mechanism in ambient air and vacuum. With the temperature up to 800 °C, the annealed PDC surface in ambient air was seriously damaged with a mixed thermal damage mechanism such as graphitization, oxidation and stress-induced micro-cracks. Whereas, the thermal damage mechanism in vacuum was nearly the same as that at 500 °C. At 900 °C, only a dendritic phase of Co₃O₄ was contained on the annealed PDC surface due to extensive graphitization and oxidation in ambient air. When it comes to vacuum environment, many cracks were observed on the PDC surface and some fine diamond grains near the cracks spalled, which demonstrated that the thermal damage mechanisms consisted of stress-induced crack and spall mechanisms caused by the different thermal expansion coefficients between the diamond and Co phase. Compared with that at 900 °C, the degree of thermal damage reduced at 1000 °C in vacuum because of the diffusion of unevenly distributed Co.     

Unlubricated friction and wear behaviors of Al2O3/TiC ceramic cutting tool materials from high temperature tribological tests

The unlubricated friction and wear behaviors of Al₂O₃/TiC ceramic tool materials were evaluated in ambient air at temperature up to 800 °C by high temperature tribological tests. The friction coefficient and wear rates were measured. The microstructural changes and the wear surface features of the ceramics were examined by scanning electron microscopy. Results showed that the temperature had an important effect on the friction and wear behaviors of this Al₂O₃ based ceramic. The friction coefficient decreased with the increase of temperature, and the Al₂O₃/TiC ceramics exhibited the lowest friction coefficient in the case of 800 °C sliding operation. The wear rates increased with the increase of temperature. During sliding at temperature above 600 °C, oxidation of the TiC is to be expected, and the formation of lubricious oxide film on the wear track is beneficial to the reduction of friction coefficient. The wear mechanism of the composites at temperature less than 400 °C was primary abrasive wear, and the mechanisms of oxidative wear dominated in the case of 800 °C sliding operation.     

Preparation of Si3N4-TaC and Si3N4-ZrC composite ceramics and their mechanical properties

Si₃N₄-TaC and Si₃N₄-ZrC composite ceramics with sintering additives were consolidated in the sintering temperature range of 1500–1600 °C using a resistance-heated hot-pressing technique. The addition of 20–40 mol% carbide improved the sinterability of the ceramics. The ceramics were densely sintered under 0–40 mol% TaC or ZrC at 1500 °C, 0–80 mol% TaC at 1600 °C, and 0–60 mol% ZrC at 1600 °C. In ceramics sintered at 1500 °C, the proportion of α-Si₃N₄ was larger than that of β-SiAlON; α-Si₃N₄ transformed mostly to β-SiAlON at 1600 °C. Carbide addition was effective in inhibiting α-Si₃N₄-to-β-SiAlON phase transformation. Young's modulus for the dense Si₃N₄-TaC and Si₃N₄-ZrC ceramics increased with the carbide amount, and the hardness of dense Si₃N₄-ZrC and Si₃N₄-TaC ceramics increased from 14 GPa to 17 GPa with increasing α-Si₃N₄ content. Dense Si₃N₄-TaC and Si₃N₄-ZrC ceramics, with larger quantities of α-Si₃N₄ sintered at 1500 °C, exhibited high hardness; the fracture toughness of these ceramics decreased with increasing α-Si₃N₄ proportion. Both the hardness and fracture toughness of the dense Si₃N₄-TaC and Si₃N₄-ZrC ceramics were strongly related to the proportion of α-Si₃N₄ in the sintered body.     

Adaptive VN/Ag nanocomposite coatings with lubricious behavior from 25 to 1000 °C

A two-phase nanocomposite coating that consists of inclusions of silver in a vanadium nitride matrix (VN/Ag) was investigated as a potential adaptive coating with a reduced friction coefficient from 25 to 1000 °C. This nanocomposite structure was selected based on the premise that silver and silver vanadate phases would form on the surface of these coatings, reducing their friction coefficient in the (i) room to mid-range and (ii) mid-range to high temperatures, respectively. Silver and vanadium were expected to react with oxygen at high temperatures and create a lubricious silver vanadate film on the coating. The VN/Ag coatings were deposited using unbalanced magnetron sputtering and their elemental composition was evaluated using X-ray photoelectron spectroscopy. The tribological properties of the materials against Si₃N₄ balls were investigated at different temperatures. The lowest friction coefficients recorded for samples with identical compositions were 0.35, 0.30, 0.10 and 0.20 at 25, 350, 700 and 1000 °C, respectively. Post-wear testing Raman spectroscopy and X-ray diffraction (XRD) measurements revealed the formation of silver vanadate compounds on the surface of these coatings. In addition, real time Raman spectroscopy and high temperature XRD revealed that silver vanadate, vanadium oxide and elemental silver formed on the surface of these coatings upon heating to 1000 °C. Upon cooling, silver and vanadium oxide were found to combine at about 400 °C, leading predominantly to the formation of silver vanadate phases on the surface of these materials.     

Wear and friction of TiAlN/VN coatings against Al2O3 in air at room and elevated temperatures

TiAlN/VN multilayer coatings exhibit excellent dry sliding wear resistance and low friction coefficient, reported to be associated with the formation of self-lubricating V₂O₅. To investigate this hypothesis, dry sliding ball-on-disc wear tests of TiAlN/VN coatings on flat stainless steel substrates were undertaken against Al₂O₃ at 25 °C, 300 °C and 635 °C in air. The coating exhibited increased wear rate with temperature. The friction coefficient was 0.53 at 25 °C, which increased to 1.03 at 300 °C and decreased to 0.46 at 635 °C. Detailed investigation of the worn surfaces was undertaken using site-specific transmission electron microscopy (TEM) via focused ion beam (FIB) microscopy, along with Fourier transform infrared (FTIR) and Raman spectroscopy. Microstructure and tribo-induced chemical reactions at these temperatures were correlated with the coating’s wear and friction behaviour. The friction behaviour at room temperature is attributed to the presence of a thin hydrated tribofilm and the presence of V₂O₅ at high temperature.     

Self-lubricating mechanisms via the in situ formed tribo-film of sintered ceramics with hBN addition in a high humidity environment

Sliding wear tests against monolithic Si₃N₄ and austenitic stainless steel, respectively, were performed on Si₃N₄ ceramic with the addition of hBN solid lubricants. The friction coefficients and wear rates were measured. The wear surface features were examined by scanning electron microscopy (SEM) and laser scanning microscopy (LSM), and the chemical characterization of worn surface was made by Energy disperse spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Results showed that the friction coefficient and the wear rate decreased with the increase of hBN up to 20 vol% at high relative humidity (RH95%). When Si₃N₄-hBN ceramic composites sliding against stainless steel, with further increases in hBN content, the wear rate increased rapidly. The mechanism responsible were determined to be an in-situ formed tribo-chemical film composed of B-O and Si-O compounds between the pin-disc sliding couple. SEM observations showed that a black surface film is formed on the wear surface depending on the hBN content. The surface film associated with small friction coefficient of 0.03 and low wear rate with the magnitude of 10^− 6 mm³/Nm was formed by the releasing and smearing of the tribo-chemical reaction products of hBN and moisture on the wear surface when with 20 vol%hBN content. This tribo-chemical film acted as solid lubricant film between the sliding couple, and thus the couple entered to a state of boundary lubrication. Hence, the friction coefficient and the wear rate were significantly reduced. For Si₃N₄-hBN/stainless steel sliding pair, even at high relative humidity, no tribo-chemical film was observed on samples with 30 vol%hBN content, just because of a large degradation of mechanical properties of the composite with higher hBN content. At low relative humidity (RH25%), the wear mechanism for Si₃N₄-hBN sliding couple was mainly dominated by mechanical wear (abrasive or adhesive wear) due to the absence of tribo-chemical film on the wear surfaces, and higher friction coefficient and wear rate were obtained.     

Structure and tribological properties of AlCrTiN coatings at elevated temperature

In this study, we analyzed the high temperature tribological behavior of AlCrTiN coatings deposited on WC substrates by low cathodic arc technique. The coatings chemical composition, Al 31 at.%, Cr 16 at.%, Ti 7 at.% and N 46 at.%, and the bonding state were evaluated by X-ray photoelectron spectroscopy. The mechanical properties of the coatings were studied by scratch-test and nanohardness depth sensing indentation. The morphology of the coatings surface, ball scars, wear tracks and wear debris as well as the oxidized samples was examined by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The structure was analyzed using X-ray diffraction (XRD). Wear testing was carried out using a high temperature tribometer (pin-on-disc) with alumina balls as counterparts. The evaluation of the friction coefficient with the number of cycles (sliding distance) was assessed at different temperatures and the wear rates of the coatings and balls were determined; the maximum testing temperature was 800 °C. The coating showed an excellent thermal stability and wear resistance. The friction reached a maximum at 500 °C and then decreased, whereas the wear rate was negligible up to 600 °C and increased significantly at higher temperatures.     

Influence of wire-EDM on high temperature sliding wear behavior of WC10Co(Cr/V) cemented carbide

This paper reports the friction and wear response of WC–10%Co(Cr/V) cemented carbide with different surface finishes, attained by grinding (G) and wire-EDM, respectively, during sliding experiments at 400 °C. For comparison, tests under the same conditions were carried out at 25 °C. The wear experiments were performed under a normal force of 14 N, which produced a Hertzian maximum pressure of 3.10 GPa, and a sliding speed of 0.3 m/s against WC–6%Co(Cr/V) balls of 6 mm diameter. At 25 °C the average values of the friction coefficients were 0.36 ± 0.04 and 0.39 ± 0.06 for the ground and wire-EDM surface finishes, respectively. The mechanical behavior of both systems at 25 °C was assessed by carrying out analytical calculations of the stress field created by a circular sliding contact under a spherical indenter, where the residual stresses were considered. The theoretical results are in agreement with the experimental data, indicating that the wire-EDM sample has a specific wear rate, which is approximately 3.1 times greater than that corresponding to the G sample at 25 °C. At 400 °C, an increase in the friction coefficients takes place up to values of 0.75 ± 0.1 and 0.71 ± 0.8, for the ground and wire-EDM surface finishes, respectively. The increase was associated to an adhesive mechanism, which is more pronounced for the G sample. However, for the wire-EDM sample this increase was more linked to a marked abrasive mechanism. The wear rates for both samples at 400 °C are similar to those obtained at 25 °C, which indicates that apparently the test temperature does not have an important effect on the wear rate. However, it is known that temperature influences considerably the residual stress nature. Therefore, these results were explained by taking into account the wear mechanisms between the tribopairs in view of the mechanical characteristics and the morphological features obtained from SEM coupled with EDS analysis.     

Role of nitrogen on the oxidative stability of Ti5Si3 based alloys at elevated temperature

Ti₅Si₃ has been extensively studied as a candidate material for high temperature application due to its high melting point (2130 °C), low density (∼4.3 g/cm³) and excellent oxidation resistance in oxygen above 1000 °C. However, stoichiometric Ti₅Si₃ alloy experiences accelerated oxidation during exposure in air above 1000 °C. It was proposed that nitrogen was responsible for the increased oxidation in air. In the present study, the isothermal reaction kinetics of Ti₅Si₃ in nitrogen at 1000 °C was investigated. Compared to a slow parabolic oxidation rate in oxygen, a faster linear reaction rate was observed when Ti₅Si₃ is exposed to nitrogen. Further studies on the oxidation behavior for changing nitrogen/oxygen atmospheres showed that Ti₅Si₃ is stable for exposure up to 400 h at 1000 °C when the gas contained 50% N₂. Breakaway oxidation occurs after short exposures when the gas contained at least 75% N₂, and the reaction rate increased as the concentration of N₂ increased. Furthermore, time to breakaway oxidation decreases with the increasing nitrogen partial pressure. Extensive analysis of the oxidation products with SEM and XRD revealed that the formation and fast growth of a nitride-containing subscale interferes with the establishment of the continuous protective silica scale and contributes to the breakaway oxidation.     

Influences of the compositions and mechanical properties of HVOF sprayed bimodal WC-Co coating on its high temperature wear performance

In this work, the bimodal WC-Co coatings were sprayed by high-velocity oxygen-fuel (HVOF), and the conventional WC-Co coatings were also fabricated for comparison. The microstructure, mechanical properties and high temperature wear performance were investigated. The bimodal WC-Co coating presented denser structure (porosity lower than 1.0%), higher average hardness (1164 HV0.1) and fracture toughness (11.5 ± 1.4 MPa·m^1/2) than that of conventional coating. The Weibull analysis of microhardness data of the bimodal coating presents a mono-modal distribution. The friction coefficient and wear rate of the bimodal coating were 0.61 and 2.96 × 10^− 6 mm³·N^− 1·m^− 1, respectively, which is lower than that of conventional coating at the test temperature of 450 °C. The tribofilm could be formed on the worn surface of bimodal WC-Co coating, which is composed of WO₃ and CoWO₄. The formation of tribofilm could reduce friction and wear.     

Sliding behavior and wear mechanism of iron and cobalt-based high-temperature alloys against WC and SiC balls

The sliding behaviors of two typical high-temperature alloys of GH2132 and GH605 against WC and SiC balls were investigated at environments from room temperature to 800 °C with a sliding speed of 50 to 125 m/min under a load of 10 to 20 N. The wear performances of high-temperature alloys, WC and SiC balls were rated and their mechanisms were discussed. The four sliding pairs exhibited the markedly different sliding behaviours, in which the GH2132/WC sliding pair had the maximum friction coefficient with 125 m/min under 10 N at room temperature. The variation trends of ball wear rates with the ambient temperature were at odds with those of friction coefficient. The higher friction coefficient did not always lead balls to suffer from the higher wear rate. The maximum worn depth approximated to 250 μm for the GH2132/WC sliding pair with higher friction coefficient. The GH605/WC sliding pair exhibited the lower friction coefficient and lower worn depth of plate. Whether at room temperature or high temperature, the GH605/SiC sliding pair significantly exhibited good wear resistance with a minor damage of ball and plate despite of its higher friction coefficient.     

Wear mechanism of CrN/NbN superlattice coating sliding against various counterbodies

Wear properties of CrN/NbN superlattice coating deposited on the WC-12Co substrate was investigated while using 100Cr6 steel, SiC and Al₂O₃ ball as counterbodies for friction pairs. The value of friction coefficient and wear rate was lowest at ~ 0.01 and 2.6 × 10^− 7 mm³/Nm, respectively, when coating slides against Al₂O₃ ball. In contrast, friction coefficient and wear rate were increased while sliding with steel and SiC ball. The deviation in friction coefficient was described by mechanical and chemical properties of these balls. Hardness of Al₂O₃ and SiC ball was comparable but significant deviation in friction coefficient was observed. That is related to oxidation resistance of these balls which is high for Al₂O₃ compared to SiC ball as evident by Raman analysis of the wear track. However, hardness and oxidation resistance were low for steel ball which shows oxidational wear mechanism.     

Kinetic effect of boron on the thermal stability of Si–(B–)C–N polymer-derived ceramics

The isothermal mass loss of two polymer-derived ceramics with compositions SiC_1.4N_0.9 and SiC_1.5N_1.0B_0.05 were measured as a function of time using thermal gravimetric analysis at various temperatures ranging between 1580 and 1720 °C. The process of mass loss, attributed to the reaction Si₃N₄ + 3C → 3SiC + 2N₂^↑, takes substantially more time for the boron-containing ceramic compared with the boron-free one. The continuous formation of SiC crystallites as the product of the reaction between Si₃N₄ and C was revealed through X-ray diffraction (XRD) measurements during the course of the reaction. The kinetics of this reaction was studied using a generalized model for the analysis of chemical reaction kinetics. Consequently, the effective activation energies for the Si₃N₄ degradation were estimated to be 11.6 ± 0.5 eV and 17.1 ± 0.7 eV for the Si–C–N and Si–B–C–N ceramics, respectively. Moreover, the results obtained indicate that the dominant mechanisms of the Si₃N₄ degradation are strongly influenced by the presence of boron. For the Si–C–N ceramic, the chemical reaction at interfaces of the reactants and the crystallization of SiC as the reaction product are proposed to be the main probable stages controlling the progress of the investigated reaction. However, the local diffusion of C out of BNC_x turbostratic layers surrounding the Si₃N₄ nanocrystals and the gas (N₂) release from the reaction zone are suggested to be the most plausible processes limiting the progress of Si₃N₄ degradation for the Si–B–C–N ceramic.     

Study of the mechanical properties,toughening and strengthening mechanisms of Si3N4/Si3N4w/TiN nanocomposite ceramic tool materials

Si₃N₄/Si₃N_4w/TiN nanocomposites were fabricated by a hot-pressing technology with different sintering processes. The effect of nanoscale TiN and Si₃N_4w on the mechanical properties was investigated. The microstructure and indention cracks were observed by scanning electron microscopy, transmission electron microscopy and energy-dispersive spectrometry investigations. The research results showed that Si₃N₄/Si₃N_4w20/TiN5 nanocomposites containing 5 vol.% of nanoscale TiN and 20 vol.% of nanoscale Si₃N_4w, which were sintered under a pressure of 30 MPa at a temperature of 1650 °C for 40 min, had optimum mechanical properties. The addition of both nanoscale TiN and nanoscale Si₃N_4w contributed to the microstructural evolution and an improvement of the mechanical properties. The toughening and strengthening mechanisms are discussed for Si₃N₄/Si₃N_4w20/TiN5 nanocomposites.     

Effect of sintering temperature on the structure and properties of polycrystalline cubic boron nitride prepared by SPS

The polycrystalline cubic boron nitride (PcBN) with Si₃N₄–AlN–Al₂O₃–Y₂O₃ ceramic system as binding agents was prepared by spark plasma sintering (SPS). The starting materials Si₃N₄, AlN, Al₂O₃, Y₂O₃, and cBN in the ratio of 22:14:10:4:50 were heated to a sintering temperature between 1250 °C and 1450 °C at a heating rate of 300 °C/min, with a holding time of 5 min in nitrogen atmosphere. The microstructure, phase constitution, microhardness and fracture toughness of the prepared PcBN were then studied. It was shown that the Si₃N₄–AlN–Al₂O₃–Y₂O₃–cBN polycrystalline materials were densified in a very short sintering time resulting in materials with relative densities of more than 95%. When the sintering temperature increased, the microhardness and fracture toughness of prepared PcBN were also increased. The microhardness of PcBN prepared at 1250–1450 °C was between 28.0 ± 0.5 GPa and 48.0 ± 0.9 GPa, and its fracture toughness K_IC was from 7.5 ± 0.2 MPa m^1/2 to 11.5 ± 0.3 MPa m^1/2. Microstructure study showed that the ceramic-binding agents bonded with cubic boron nitride particles firmly. Our work demonstrated that spark plasma sintering technology could become a novel method for the preparation of PcBN cutting materials.     

Synthesis and characterization of MoSi2-Mo5Si3 nanocomposite by mechanical alloying and heat treatment

The nanocomposite of MoSi₂-Mo₅Si₃ powder was synthesized by mechanical alloying from Mo and Si powder mixture at room temperature. The phase evaluation of powder after various milling durations and heat treatments were assessed via X-ray diffraction (XRD) and a differential thermal analysis (DTA). Morphology and microstructure of powder particles were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results revealed that nanocomposite of MoSi₂-Mo₅Si₃ powder was synthesized by combustion reaction of Mo and Si powder using ball milling. In the early stages of ball milling β-MoSi₂ was produced. However with continued milling for 48 h α-MoSi₂ and Mo₅Si₃ phases were formed. DTA results of 24 h and 48 h as milled mechanical alloyed specimens showed a well-defined peak at 852 °C and 920 °C relating to the formation of α-MoSi₂. The activation energy for 24 h and 48 h milled specimens were –128.6 KJ/mol and –121.4 KJ/mol respectively. Annealing the milled specimens at 1000 °C for 2 h revealed the phase transformation of β-MoSi₂ to α-MoSi₂ and the formation of Mo₅Si₃. The crystallite size of α-MoSi₂ and Mo₅Si₃ were about 9 nm and 12 nm after 48 h mechanical alloying. These values increased slightly to 18 nm and 14 nm after annealing at 1000 °C.     

Al2O3/Mo composite and its tribological behavior against AISI201 stainless steel at elevated temperatures

Al₂O₃-reinforced molybdenum (Mo) composites were successfully prepared by powder metallurgy to improve the wear resistance of Mo components at high temperature. The reinforced Al₂O₃ particles are uniformly distributed in the Mo matrix; thus, the Al₂O₃/Mo composite is harder than monolithic Mo. The friction coefficients of both monolithic Mo and the Al₂O₃/Mo composite decrease by 37% and 42%, respectively, at 700 °C compared with those at room temperature (self-lubricating phenomenon). This phenomenon is attributed to the formation of very soft MoO₃ and FeMoO₄ metal oxides on the friction surface at high temperature. The Al₂O₃/Mo composite has better wear resistance than monolithic Mo at both room temperature and at 700 °C. The notable resistance of the composite particularly at 700 °C can be attributed to its increased hardness and the soft tribofilm forming on the worn surface.     

Interfacial behavior in the brazing of silicon nitride joint using a Nb-foil interlayer

Silicon nitride (Si₃N₄) samples prepared the spark plasma sintering (SPS) technique, which had different amounts of oxide additives, were used as disc-preforms. The surfaces of the materials to be bonded during the brazing process (ceramic, metal and filler alloys) were previously coated with thin layer of silver and then stacked together with these preforms. Sandwich-like specimens of Si₃N₄/Cu–Zn/Nb/Cu–Zn/AISI-304 combinations were joined at 1000 °C using 5, 20, and 40 min holding times under an inert atmosphere. Analysis by scanning electron microscopy revealed un-joined zones between the ceramic and metallic parts after 5 min of treatment. For holding times >20 min, homogenous and non-porous Si₃N₄/Cu–Zn/Nb interfaces were obtained. The thicknesses of the resulting ceramic–metal interfaces increased from ～10 to >25 μm as the holding time was increased. The amount of additives used during the preparation of the Si₃N₄ ceramics had a direct effect on the decomposition rate of Si₃N₄ during the joining process. The largest decomposition of Si₃N₄ was observed at 1000 °C/40 min from the less dense ceramic preforms (4 wt% of additives in this case), which in turn induced the migration of Si atoms through the interface to promote the formation of Si-based components. In contrast, when using larger amounts of additives (8 wt%) during sintering of the ceramic performs, it becomes more difficult for N and Si to dissociate upon brazing. When the diffusion rate of Si is low, it migrates toward the metal part, which limits the formation of Si-based components.     

Effects of environmental atmospheres on tribological behaviors of sintered polycrystalline diamond sliding against silicon nitride

To explore the effect of various atmosphere the tribological behaviors of the sintered polycrystalline diamond compacts (PDCs), the friction and wear behaviors of PDCs sliding against Si₃N₄ balls were evaluated by a ball-on-disk tribometer under nitrogen, argon, oxygen and air (10% relative humidity) environments, respectively. The energy dispersive X-ray spectrum (EDS), Raman spectroscopy, scanning electron microscopy (SEM) and atomic force microscope (AFM) were conducted to investigate the microstructure evolution of worn surface. The results demonstrated that the low friction appeared in argon and nitrogen environment. The formations of consecutive carbonaceous transfer films on wear scars contributed to decrease the friction during sliding process. The wear of PDCs and Si₃N₄ balls were serious in argon and nitrogen environment, but slight in oxygen and air conditions. There is a direct relationship between material removal and running-in period. The passivation effect of dangling bond under oxygen and air conditions can shorten the running in period thus weaken the wear.     

Impact of selective oxidation during inline annealing prior to hot-dip galvanizing on Zn wetting and hydrogen-induced delayed cracking of austenitic FeMnC steel

The present study discusses the impact of selective oxidation during in-line annealing of Fe–23%Mn–0.6%C–0.3%Si steel on surface and sub-surface properties and is focused on hot-dip galvanizability and susceptibility to hydrogen-induced delayed cracking. Annealing temperature (700–1100 °C) and dewpoint DP (? 15/?30/?50 °C) of the 5%H₂–N₂ annealing atmosphere were varied in order to investigate Zn wetting in dependence on selective oxidation of Mn and Si. Sub-surface microplasticity (hardness, pop-in frequency, pop-in activation load) was examined by electrochemical nanoindentation in-situ to hydrogen charging (ECNI) to assess hydrogen/material interactions. Zn wetting fails if external Mn and Si oxidation is not avoided by performing high reductive bright annealing (1100 °C/DP ? 50 °C). Zn wetting will however turn to increase if a roughly globular MnO layer appears and Si is internally oxidized (700–900 °C/DP ? 15 °C). Selective oxidation further affects hydrogen/material interactions by influencing the local distribution of solid-soluted Mn: ECNI results indicate hydrogen-induced dislocation demobilization (HEDE mechanism) or dislocation mobilization (HELP mechanism) in dependence on the local amount of solid-soluted Mn within the sub-surface. Macroscopic delayed cracking seems to occur earlier if HELP is predominating. The gained results benefit understanding the impact of selective oxidation on galvanizability and susceptibility to hydrogen-induced failure of austenitic FeMnC steel and advance further developments in processing high Mn alloyed steels.