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Clean-integrity processing of nuclear-grade AISI 316L austenitic stainless steel components finished by the wire brush and sequent flap discs is performed for high-performance manufacturing of the nuclear power plant equipment. Two steel wire brushes of AISI 304 austenitic stainless steel and 65Mn carbon spring steel are used for the grinding under a spindle speed of 550–2000 rpm. Sequent polishing is carried out by the flap discs using silicon carbide cloth under 2000 rpm. An equivalent pitting corrosion resistance to that of the original stainless steel in 3.5% NaCl solution is obtained for finished samples by the combined processes. The contaminants composition of ground stainless steel samples is determined by the redness degree of chromaticity inspection. The contaminants microstructure and finishing-induced microstructure are dependent on the impedance phase angle change in eddy current impedance diagrams. The surface clean-integrity of nuclear-grade stainless steel is characterized by the series of nondestructive evaluation methods. [ABSTRACT FROM AUTHOR]

[Display omitted] • High-performance manufacturing theory and methodology enables integrated design and processing. • Material–product–process linking is established on the pivot role of surface integrity. • Metal cutting is demonstrated from a trial-and-error approach to a knowledge-based approach. • Material-oriented regularization solves the integrated design and processing inverse problem. • Process signature concept is consolidated to incorporate the coupling effect of processing. Greater integration of materials, product and processes is demanded ultimately toward a knowledge-based control of advanced manufacturing. We propose a framework of high-performance manufacturing theory and methodology to enable the integrated design and processing of a product, with a material–product–process linking developed on the pivot role of surface integrity determining the final performance. Metal cutting, as a representative process of conventional manufacturing, is demonstrated for the new development of manufacturing from a trial-and-error approach to a knowledge-based approach under the framework. A physical model of integrated design and processing is established on thermodynamics for cutting of a metastable AISI 304 austenitic stainless steel component during processing under the multi-source constraints of component geometry, material and structure, where surface integrity changes in surface residual stress and martensitic phase fraction are predicted by FEM modeling. The profound processing effect is described by process signature that derives a quantitative correlation of processing loads in effective force/power input and material loading in transferred/dissipated thermal and mechanical energies to the surface integrity changes. A material-oriented regularization (MOR) method is thus contrived as incorporating the process signature by utilizing identified characteristic correlations of high sensitivity to solve the involved inverse problems. The processing parameters of cutting speed/depth of cut and the design parameters of geometry are synergistically determined through the required surface integrity toward a desired final fatigue performance. The high-performance manufacturing overcomes the intrinsic trial-and-error limitations of conventional manufacturing, knowledgeably considering the coupling effect of processing in the design otherwise merely employed as an empirical design criterion in the past. [ABSTRACT FROM AUTHOR]

• TiAlN thin films were deposited by deep oscillation magnetron sputtering. • Low deposition temperature was adjusted in oscillation voltage on-time and off-time. • Microstructure of TiAlN thin films changed from Zone I to Zone T with peak power. • Fracture toughness of TiAlN thin films in Zone T was optimized at a peak power. • Bombarding energy E bi and mobility D of species were discussed in deposition process. TiAlN thin films were deposited on Si(100) and AISI 304 austenitic stainless steel substrates at the low deposition temperature below 250℃ by the deep oscillation magnetron sputtering (DOMS), respectively. The peak sputtering power changed from 58.7 kW to 129.9 kW by adjusting the oscillation voltage on-time (τ on) / off-time (τ off) ratio with 6–12 μs to 30 μs. All TiAlN thin films have a face centered cubic structure with a composition of Ti 0.22 Al 0.28 N 0.50. With increasing the peak powers, a transit of the columnar morphology in Zone I with the preferred orientation of c-TiAlN(111) to a compact morphology in Zone T with c-TiAlN(200) was characterized. The hardness, residual stress, and H/E and H3/E2 ratios of TiAlN thin films increased with the maximal values obtained at the peak power of 90.2 kW, and then slightly decreased. Correspondently, the fracture toughness (K IC) of TiAlN thin films on Si(100) and AISI 304 stainless steel increased firstly from 0.56 MPa∙m1/2 to 1.10 MPa∙m1/2 and from 0.58 MPa∙m1/2 to 1.08 MPa∙m1/2 as the structure from Zone I with c-TiAlN(111) to Zone T with c-TiAlN(200), and then decreased to 0.94 MPa∙m1/2 and 0.71 MPa∙m1/2 at the structure of Zone T with c-TiAlN(200), respectively. The higher K IC values of Ti 0.22 Al 0.28 N 0.50 thin films in Zone T were achieved on Si(100) and AISI 304 stainless steel at 90.2 kW. The excellent mechanical properties of TiAlN thin films on Si(100) and AISI 304 stainless steel substrates were carried out by using DOMS at the low deposition temperature. [ABSTRACT FROM AUTHOR]

Abstract: A high nitrogen face-centered-cubic phase (γN) was obtained on the nitrided surface of 1Cr18Ni9Ti austenitic stainless steel by plasma-based low-energy nitrogen ion implantation. No pitting corrosion for the γN phase was confirmed by electrochemical polarization measurement in 3% NaCl solution. The protective passive film with a duplex character, iron hydroxide/oxides in the outer region and chromium hydroxide/oxides and iron oxides accompanying chromium and iron nitrides in the inner region, was by 2–3 times thicker than that of original stainless steel. The thick iron hydroxide/oxides region formed on the chromium hydroxide/oxides region due to the increase of alkalinity in the solution, leading to barrier against penetration of localized attack of the aggressive ions. The equivalent general corrosion resistance for the γN phase was observed in 0.5 mol/l H2SO4 solution relative to the original stainless steel. The passive film formed on the γN phase in 0.5 mol/l H2SO4 solution was similar to that of original stainless steel. The different role of nitrogen was proposed in pitting corrosion resistance and general corrosion resistance of austenitic stainless steel. [Copyright &y& Elsevier]

Abstract: Plasma-based low-energy ion implantation, including plasma source ion nitriding/carburizing and plasma source low-energy ion enhanced deposition of thin films, for surface engineering of metallic materials was emerged as low-temperature, low-pressure surface modification technique. Plasma source ion nitriding onto AISI 316L austenitic stainless steel produced a high nitrogen face-centered-cubic phase (γN) layer about 10μm thick at the temperature of 380°C during 4h with the high microhardness of HK0.1N 22.0GPa. The microhardness of the nitrided surface from the titanium nitride phase [(Ti,Al,V)N] layer on Ti6Al4V alloy at 750°C during 4 h achieved up to about HK0.1N 15.5GPa. No pitting corrosion in the Ringer’s solution at 37°C was detected by electrochemical polarization measurement for the nitrided AISI 316L stainless steel and Ti6Al4V alloy, respectively. Plasma source ion nitriding of the metallic materials provided the engineering surfaces with combined improvement in hardness and corrosion resistance. [Copyright &y& Elsevier]

Abstract: Plasma-based low-energy ion implantation, including plasma source ion nitriding/carburizing and plasma source low-energy ion-enhanced deposition, has emerged as a low-temperature surface engineering technique for steel and alloys. In this work, the effects of nitrogen alloying on the wear and corrosion resistance of the plasma source ion nitrided 1Cr18Ni9Ti austenitic stainless steel have been investigated in order to produce a combined improvement in wear and corrosion resistance. A high-nitrogen face-centered-cubic (f.c.c.) phase (γN) with the different nitrogen contents formed on the nitrided stainless steel was characterized using Auger electron spectroscopy, electron probe microanalysis, glancing-angle X-ray diffraction and transmission electron microscopy. The wear tests were performed on a pin-on-disc tribometer in which the γN-phase samples were rubbed against a hardened Cr12MoV high-alloy steel disc (HRC 62–63) under a normal load from 2.2 to 39 N using Cr2O3 powders in machine oil as the abrasive media. The corrosion resistance was analyzed in 1% NaCl and 0.5 mol l−1 H2SO4 solutions by the electrochemical polarization technology. The γN-phase samples have a high microhardness of about HK0.1N 22 GPa and a high load-bearing capability, leading to significant improvement in wear resistance, especially under the high normal loads. The high nitrogen content in the γN phase resulted in higher wear resistance through the formation of a thicker hardened layer. The γN-phase samples have a high pitting corrosion resistance and a similar general corrosion resistance compared with those of the original stainless steel. The nitrogen content in the γN phase mainly affected the pitting corrosion resistance and slightly affected the general corrosion resistance. [Copyright &y& Elsevier]

Heat-affected zone (HAZ) of welding joints critical to the equipment safety service are commonly repeatedly welded in industries. Thus, the effects of repeated welding up to six times on the microstructure and mechanical properties of HAZ for AISI 304N austenitic stainless steel specimens were investigated by a Gleeble simulator. The temperature field of HAZ was measured by in situ thermocouples. The as-welded and one to five times repeated welding were assigned as-welded (AW) and repeated welding 1–5 times (RW1–RW5), respectively. The austenitic matrices with the δ-ferrite were observed in all specimens by the metallography. The δ-ferrite content was also determined using magnetic and metallography methods. The δ-ferrite had a lathy structure with a content of 0.69–3.13 vol.%. The austenitic grains were equiaxial with an average size of 41.4–47.3 μm. The ultimate tensile strength (UTS) and yield strength (YS) mainly depended on the δ-ferrite content; otherwise, the impact energy mainly depended on both the austenitic grain size and the δ-ferrite content. The UTS of the RW1–RW3 specimens was above 550 MPa following the American Society of Mechanical Engineers (ASME) standard. The impact energy of all specimens was higher than that in ASME standard at about 56 J. The repeated welding up to three times could still meet the requirements for strength and toughness of welding specifications. [ABSTRACT FROM AUTHOR]

AISI 304 L austenitic stainless steel was modified by using the plasma-based low-energy nitrogen ion implantation (PBLEII) at a process temperature of 400 °C for a processing time of 4 h in order to improve the corrosion-fatigue resistance of the austenitic stainless steel. A single high-nitrogen face-centered-cubic phase (γ N ) layer with a maximal nitrogen concentration of about 25 at.% was formed on the nitrogen-modified austenitic stainless steel. Compared with the original austenitic stainless steel, the γ N phase layer on the austenitic stainless steel possessed a significant improvement in corrosion resistance in the borate buffer solution with a pH value of 8.4. The corrosion-fatigue properties of the γ N phase layer on the austenitic stainless steel were examined by the push–pull fatigue experiments with a ratio R of tensile and compression of − 1 in the borate buffer solution. The γ N phase layer has an increased corrosion-fatigue strength up to 230 MPa from 180 MPa of the original austenitic stainless steel with an apparent increase of about 28%. The corrosion-fatigue crack initiation in the γ N phase layer was found as a controllable stage in the fracture process at the interface between the γ N phase layer and the austenitic stainless steel matrix with the arc corrosion-fatigue source. Some tiny corrosion-fatigue striations were obtained on the corrosion-fracture surfaces of the γ N phase layer. The high density of slip bands and dislocations in the γ N phase layer was able to prevent the crack initiation and propagation, leading to improvement of the corrosion-fatigue properties in the borate buffer solution. [ABSTRACT FROM AUTHOR]

A recent investigation of the nitriding response of austenitic Fe-Cr-Ni alloys with various compositions showed that the surface adjacent zone generally identified as expanded austenite consists of a duplex structure. In the near-surface part, with the highest N content, long-range ordering (LRO) among the nitrogen atoms occurs in addition to short-range ordering (SRO) of N and Cr atoms; and in the near-matrix part, with a lower N content, only SRO of N and Cr atoms is encountered. These zones are dubbed γ' N and γ N , respectively. In the present contribution, a pragmatic model is presented to effectively describe the nitrogen arrangements in γ N and γ' N and the transition of one into the other by changing the Cr and N contents. The model considers the occupancy of octahedral interstices surrounded by more than one Cr atom and, depending on the number of Cr atoms constituting the octahedron, distinguishes between strong and weak interactions between the octahedral sites and N atoms. In order to account for the competition between Cr-N SRO and Fe 4 N-like LRO, the occupancy of neighboring interstices with N surrounding a central metal atom is taken into consideration. The distribution of N atoms over differently coordinated interstices is obtained by pragmatically fitting the model to experimental data. The model is validated by comparison of the predicted distributions of occupied interstices to literature data for Mössbauer spectroscopy and Extended X-ray Absorption Fine Structure, respectively. Furthermore, the model provides a consistent interpretation of thermodynamics and diffusion data for nitrogen-stabilized expanded austenite. [Display omitted] [ABSTRACT FROM AUTHOR]

• Real-time nanostructure of passive film on γ N phase is characterized by TEM/EDS. • All passive films composed of defect spinels are epitaxially growing on γ N phase. • n -type inner (Fe,Cr) 3 (N,O) 4 and p -type outer γ -Fe 2 (N,O) 3 region in passive films. • Low-defective passive film inhibits absorption of aggressive ion. • Nanostructure of dense passive film limits migration of Cr3+ ion and anion vacancy. The real-time composition and structure of the passive film formed on a high nitrogen face-centered-cubic phase (γ N) layer at the characterized transient corrosion currents from the electrochemical noise analyses in the borate buffer solution with the pH = 7.7 are investigated by the transmission electron microscope (TEM) with energy dispersion X-ray spectrum (EDS) using the focused ion beam (FIB) sampling. The thicker passive film of the γ N phase layer on the nitrided AISI 304L in the borate buffer solutions is observed as two regions structure of O enriched n -type defect spinel γ -Fe 2 (N,O) 3 and hydroxides in the outer region and Cr and N enriched p -type defect spinel (Fe,Cr) 3 (N,O) 4 in the inner region, although few β -(Fe,Cr)OOH compounds are detected due to dehydration. The defect spinel in directions of < 112 >, < 213 > and < 110 > is epitaxially growing on the γ N phase matrix during the passivation up to 8 h with a decreasing lattice mismatch from 5.9 to 1%, which is attributed to lattice expansion of the γ N phase and the defect spinel. The lattice expansion of the γ N phase at the interface with growing passive film is affected by dissolving nitrogen outward to the borate buffer solution. The dissolving nitrogen in the defect spinel induces its lattice expansion by hydrolysis at the interface. The dense and low-defective passive films on the γ N phase layer have a significant effect on the corrosion resistance due to inhibition of the absorption of aggressive ion and limitation of the carrier density. [Display omitted] [ABSTRACT FROM AUTHOR]

The fracture toughness of TiAlN thin films on AISI 304 austenitic stainless steel was inversely investigated by combining nanoindentation experiment with finite element method (FEM) and extended FEM (XFEM) simulation. The TiAlN thin films were deposited by deep oscillation magnetron sputtering (DOMS) with the oscillation pulse on and off times of 12 μs and 30 μs at a peak power of 136.1 kW. A completely dense TiAlN thin film with the thickness of 1500 nm has a face-centered-cubic microstructure with (200) preferred orientation. The displacements of the nanoindenter were intentionally interrupted by 1200 nm and 1800 nm, latter is thin film-crossing to induce an apparently cracking. The cross-sectional samples of TiAlN thin films with the cracks were fabricated by focused ion beam. The experimental crack number and position in the cross-sectional samples were observed by scanning electron microscopy. The maximum damage initiating stress (σ max) and corresponding crack separation distance (δ c) in the Griffith–Irwin relationships were fitted using the XFEM calculation based on the crack morphology to match the crack number and position of TiAlN thin films. The fracture toughness of TiAlN thin films on AISI 304 austenitic stainless steel was calculated to be 1.09 MPa m1/2 according to the fitted parameters of 5.5 GPa for σ max and 1.5 nm for δ c. Therefore, an alternative method by the nanoindentation morphology and the inversely calculation fitting was developed to estimate the fracture toughness of thin films. 1. TiAlN thin films were deposited on steel by deep oscillation magnetron sputtering. 2. Fracture toughness was evaluated by extended finite element method and experiments. 3. Key fracture parameters of TiAlN thin films were solved as an inverse problem. 4. Crack separation distance and maximum damage initiating stress were key parameters. 5. Experimental and calculated similarity in crack number and position was established. [ABSTRACT FROM AUTHOR]

The formation of a metastable and nitrogen-supersaturated f.c.c. interstitial solid solution layer on Fe–Cr–Ni austenitic stainless steel at a moderate temperature around 650–720 K is not entirely understood. In the present work, three groups of austenitic Fe–Cr–Ni alloys, containing systematic variations of chromium, nickel and iron contents were nitrided by plasma-based low-energy ion implantation at 653 K for 4 h and investigated with light-optical microscopy (LOM), electron probe microanalysis (EPMA), (grazing incidence) X-ray diffraction (XRD) and transmission electron microscopy (TEM). Commercial AISI 304L was included for comparison. For the austenitic alloys with a Cr content below 12 wt.%, a duplex layer is observed in the nitrided case where the interface between the top layer, consisting of γ'-Fe 4 N like ordered γ' N , and the disordered γ N (nitrogen enriched austenite) zone underneath is associated with a decrease in N content. For the alloys with a Cr-content over 12 wt.%, a featureless continuous zone is observed with LOM and a gradual decrease in nitrogen content is measured with EPMA. Nevertheless, a similar duplex structure of outer γ'-Fe 4 N like ordered γ' N and inner γ N is confirmed by XRD and TEM for all nitrided alloys, irrespective of the Cr content. The results are discussed in terms of the short-range order (SRO) promoted by the Cr–N interaction and long-range order (LRO) caused by the Fe–N interaction. Image 1 [ABSTRACT FROM AUTHOR]

A carburizing treatment of AISI 304L austenitic stainless steel was performed at a low temperature of 450 °C using the low-pressure hollow cathode plasma source technique. The hollow cathode plasma was produced in a cathodic cage made of stainless steel screen inlaid with a stainless steel tubes array. A pulsed high voltage power, with a peak voltage of 800 V and a pulse frequency of 30 kHz, was applied at a low gas pressure of 50 Pa. The austenitic stainless steel samples were carburized with a direct current bias of −200 V under the CH 4 /H 2 ratio changing in a range from 0.11 to 9, for a carburizing time of 4 h. Under the lower CH 4 /H 2 ratio of 0.11, a diamond-like carbon film of approximately 260 nm thick formed on the stainless steel surface. As the CH 4 /H 2 ratio increased to 0.67 and 1, both carburizing cases possessed a similar thickness of about 11 μm, with the surface carbon concentration being 6 to 6.5 at.%. A layer of carbon supersaturated face-centered-cubic (γ C) phase formed, together with carbon-rich (Fe,Cr) 5 C 2 carbide precipitation. Under the highest CH 4 /H 2 ratio of 9, a single γ C phase layer was obtained in a carburizing case of similar thickness, with a high surface carbon concentration of 7.5 at.%. The maximum surface hardness value of HV 0.25 N 7.1 GPa occurred on the single γ C phase layer. No pitting corrosion occurred on the single γ C phase in the polarization curve. The higher passive film resistance and the lower donor and acceptor concentrations and flat band potential indicated that a more compact passive film is grown on the γ C phase layer. The (Fe,Cr) 5 C 2 carbide precipitates in the γ C phase matrix degraded the passivity of the γ C phase layer due to the reduced compactness of the passive film. A carbon transport competition mechanism between carbon adsorption onto the surface and carbon inward diffusion that was mainly dependent on the heavier CH n + ion bombardment, was proposed to explain the transition with increasing CH 4 /H 2 ratio from carbon film deposition, to a carburizing case composed of ae single γ C phase, with both increased hardness and higher corrosion resistance. • Low-pressure hollow cathode plasma source carburizing of AISI 304 stainless steel • Transition from the DLC film to carburizing case composed of the single γ C phase • Surface hardness maximum value of the γ C phase layer was HV 0.25 N 7.1 GPa. • No pitting corrosion in NaCl solution was observed on the γ C phase layer. • Carbon transport competition mechanism depended on CH n +/H+ ions bombardment. [ABSTRACT FROM AUTHOR]

• Passive film thickening derived from transits current and photocurrent on γ N phase. • Passive films momentarily dissolved in borate buffer solutions with Ph = 6.5–7.7. • Passive films continuously grew in the solutions with pH = 8.1–8.9 up to 8 h. • Formation and dissolution kinetics on γ N phase were simulated and explained by PDM. • Transporting N in oxygen anion vacancy hydrolyzed to ammonia then to ammonium. The passive film thickening on a high nitrogen face-centered-cubic phase (γ N) layer in a series of borate buffer solutions is in-situ characterized by the transient corrosion current and potential with the structure evolution in the photoelectrochemistry and electrochemical noise analyzes. The real-time nitrogen effect on the passivation is intended by controlling the proton concentration of the borate buffer solutions at the pH values of 6.5–8.9 with the immersion time up to 8 h. The γ N phase layer on the nitrided AISI 304L austenitic stainless steel has a transitional maximum thickness with the firstly immersion time, and then gradually achieves a steady thickness value. Seven components, such as α-Fe 2 O 3 , FeO, Cr(OH) 3 , γ-FeOOH, CrOOH, Cr 2 O 3 and γ-Fe 2 O 3 , are observed with 8 h, although no CrN x and FeN x compounds are detected due to lack of references in photoelectrochemistry. The nitrogen dissolving from the γ N phase layer in the borate buffer solutions is clarified, according to the real-time photocurrent and transient corrosion current at the controllable pH values. The passivation transition period dependent on the nitrogen dissolving in the borate buffer solutions is proposed by the point defect model. The nitrogen hydrolysis to ammonia with a fast reaction rate is determined by the nitrogen concentration on the surface of the γ N phase layer. The ammonia is further hydrolyzed to ammonium with a lower reaction rate which is mainly affected by proton concentration in the solutions. Therefore, the two-step nitrogen hydrolysis from the γ N phase layer is in - situ discovered as an effect mechanism in the borate buffer solutions. [Display omitted] [ABSTRACT FROM AUTHOR]

A low-pressure hollow cathode plasma source carburizing was developed as a novel surface treatment technique based on the active screen plasma carburizing combined with hollow cathode sources. The cylindric cathodic cage with array holes was made of pure graphite, where the hollow cathode graphite tubes were inlaid on. A pulsed high voltage power with a peak voltage of 800 V and a pulse frequency of 30 kHz was supplied to ignite the hollow cathode discharge inside graphite tubes at a low pressure less than about 300 Pa using a gas mixture of CH 4 + 90%H 2. The hollow cathode plasma source together with the pulsed high voltage power realized a high biasing current on the carburized samples at low pressure, and produced an enhanced heating except the thermal radiation by the cathodic cage. The graphite cathode as a carbon source besides the gas precursor provided an additional carbon potential. The AISI 304L austenitic stainless steel was carburized at a low temperature of 450 °C for a treatment time of 6 h with a bias of 200 V under the carburizing pressure of 50 Pa and 300 Pa, respectively. It was observed that the carburizing case at 50 Pa was about 13 μm with a higher surface carbon concentration of about 6.5 at.% and a higher hardness of about HV 0.25 N 8.5 GPa compared with that at 300 Pa. The carbon-expanded austenite (γ C) phase was observed by the x-ray diffraction of both the carburizing cases. The metastable high carbon carbide Fe 5 C 2 only appeared at 50 Pa, which was attributed to high carbon potential at the lower pressure. Therefore, an increased carburizing efficiency at the low temperature was obtained by the low-pressure hollow cathode plasma source carburizing technique using a pulsed high voltage power. • Hollow cathode plasma source is utilized in low temperature plasma carburizing. • Pulsed high voltage is used in graphite hollow cathode discharge at low pressure. • High sample biasing current with enhanced heating is realized by plasma source. • Graphite cathode provides additional carbon potential besides the gas precursor. • Thick carburizing case with metastable carbide and high hardness is obtained. [ABSTRACT FROM AUTHOR]