Comprehensive analysis of pulsed plasma nitriding preconditions on the fatigue behavior of AISI 304 austenitic stainless steel

This study aims to draw an exact boundary for microstructural and mechanical behaviors in terms of pulsed plasma nitriding conditions.The pulsed plasma nitriding treatment was applied to AISI 304 austenitic stainless steel at different temperatures and durations.Results reveal that nitriding depth increased as process temperature and duration increase.The nitriding depth remarkably increased at 475℃for 8 h and at 550℃for 4 h.An austenite structure was transformed into a metastable nitrogen-oversaturated body-centered tetragonal expanded austenite(S-phase)during low-temperature plasma nitriding.The S-phase was converted to CrN precipitation at 475℃for 8 h and at 550℃for 4 h.Surface hardness and fatigue limit increased through plasma nitriding regardless of process conditions.The best surface hardness and fatigue limit were obtained at 550℃for 4 h because of the occurrence of CrN precipitation.

Characterization and Tribological Performance of Titanium Nitrides in Situ Grown on Ti6Al4V Alloy by Glow Discharge Plasma Nitriding

Titanium(Ti)nitrides were in situ grown on Ti6Al4V alloy(TA)using a glow discharge plasma nitriding(GDPN).The morphology,chemical composition,phase and mechanical property of the obtained nitrided TA were analyzed using a scanning electron microscope(SEM),energy dispersive spectroscope(EDS),X-ray diffraction(XRD),and nanoindentation tester,respectively.The tribological performances of un-nitrided and nitrided TAs were evaluated using a ball-on-plate wear tester,and the wear mechanism was also discussed in detail.The results show that the nitrided layer with the compound and diffusion layers is formed on the nitrided TA,which is composed of δ-TiN and a-Ti phases.The nanohardness and elastic modulus of nitrided TA are 6.05 and 143.13 GPa,respectively,higher than those of un-nitrided TA.The friction reduction and anti-wear performances of nitrided TA are better than those of un-nitrided TA,and the wear mechanism is primary abrasive wear,accompanying with adhesive wear,which is attributed to the formation of Ti nitrides with the high nanohardness and elastic modulus.

Sheath Characteristic in ECR Plasma Nitriding

The sheath plasma characteristics changing with the negative bias applied to the substrate during electron cyclotron resonance plasma nitriding are studied. The sheath characteristics obtained by a Langmuir single probe and an ion energy analyzer show that when the negative bias applied to the substrate is increasing, the most probable energy of ions in the sheath and the full width of half maximum of ions energy distribution increase, the thickness of the sheath also increases, whereas the saturation current of ion decreases. It has been found from the optical emission spectrum that there are strong lines of N2 and N+2. Based on our experiment results the mechanism of plasma nitriding is discussed.

Surface modification of plasma nitriding on AlxCoCrFeNi high-entropy alloys

Plasma nitriding is successfully employed in treating AlxCoCrFeNi high-entropy alloys(HEAs)with finelydivided 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(AIN 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 re sistance of AlxCoCrFeNi HEAs by 4-18 times.

Optimization Study of Pulsed DC Nitrogen-Hydrogen Plasma in the Presence of an Active Screen Cage

A glow discharge plasma nitriding reactor in the presence of an active screen cage is optimized in terms of current density,filling pressure and hydrogen concentrations using optical emission spectroscopy(OES).The samples of AISI 304 are nitrided for different treatment times under optimum conditions.The treated samples were analyzed by X-ray diffraction(XRD) to explore the changes induced in the crystallographic structure.The XRD pattern confirmed the formation of iron and chromium nitrides arising from incorporation of nitrogen as an interstitial solid solution in the iron lattice.A Vickers microhardness tester was used to evaluate the surface hardness as a function of treatment time(h).The results showed clear evidence of improved surface hardness and a substantial amount of decrease in the treatment time compared with the previous work.

Effect of Treatment Temperature on Iron Nitride Foils Irradiated with Nitrogen Plasma

We investigated the effect of treatment temperature on the magnetic property of iron nitride foils irradiated with nitrogen plasma. The iron nitride foils irradiated with nitrogen plasma were composed of ε-Fe2-3N, γ’-Fe4 N and γ nitrogen austenite in α-Fe of the matrix. The saturation magnetization of the iron nitride foils decreased with increasing the surface temperature. The coercive force of the iron nitride foils increased with increasing the surface temperature.

Enhancing the mechanical and anticorrosion properties of 316L stainless steel via a cathodic plasma electrolytic nitriding treatment with added PEG

A cathodic plasma electrolytic nitriding(CPEN)treatment with a urea aqueous solution was performed on 316L stainless steel to rapidly improve its surface properties in this work.Test results show that the PEG2000 macromolecules increased the nitriding energy via enhancing the ability to bond the produced gas film to the metal/electrolyte interface.The cross-sectional morphologies indicate that a thick nitrided layer was obtained when the urea concentration was 543 g I^-1,corresponding to a Vickers hardness 450 HV(0.1),which was 3.5 times larger than that of the substrate.The nitrided layer mainly contained expanded austenite(γN),oxides and iron nitrides(e.g.,Fe3O4 and FeN(0.076)).In terms of its performance,coefficient of friction(COF)of the nitride layer decreased to nearly two-thirds that of the untreated layer,and the passivation current densities of the nitrided sample in a 3.5%NaCl solution decreased by an order of magnitude compared to that of the substrate.Therefore,the approach presented herein provides an attractive way to modify the effect of CPEN in a urea aqueous solution.

Effect of Fast Multiple Rotation Rolling on Microstructure and Properties of Ti6Al4V Alloy

Using fast multiple rotation rolling(FMRR),a nanostructure layer was fabricated on the surface of Ti6Al4V alloy.The microstructure of the surface layer was investigated using optical microscopy,transmission electron microscopy,scanning electron microscopy,and X-ray diffraction.The results indicated that a nanostructured layer,with an average grain size of 72—83 nm,was obtained in the top surface layer,when the FMRR duration was 15 min.And the average grain size further reduced to 24—37 nm when the treatment duration increased to 45 min.High density dislocations,twins,and stacking faults were observed in the top surface layer.The microhardness of FMRR specimen,compared with original specimen,was significantly increased.A uniform,continuous and thicker compound layer was obtained in the top surface of FMRR sample,and the diffusion speed of N atom in the top surface layer was accelerated.FMRR treatment provides corrosion improvement.

Wear Behavior and Mechanism of a Sliding Pair of 0.1C-3Cr-2W-V Nitrided Steel Rubbing against an Aluminum Bronze Alloy

Wear behavior and mechanism of plasma nitrided steel oscillating against a heat-treated and an untreated aluminum bronze alloy were investigated using an Optimol SRV tribometer.The influence of heat treatment on the mechanical properties of the alloy was evaluated.Furthermore,the wear debris was also examined to understand the wear mechanisms.The results show that a 220-230μm nitrided layer,which was harder than the substrate,was obtained on the steel surface.The tensile strength and hardness of the alloy are found to be significantly improved by the heat treatment associated with low impact toughness.The heat treatment of the alloy did not obviously decrease the friction coefficient of the nitrided steel-bronze couple.However,the wear loss of the nitrided steel increased when it mated with the treated bronze by a severe three-body abrasion.The nitrided steel was mainly damaged by fatigue spalling.Under plane contact conditions,the wear debris was mainly generated from the bronze part and can escape from the interface before being oxidized,leading to the phase structure of all the debris being copper rather than copper oxides.