ICMCTF2010 Session G6: Coatings, Pre-Treatment, Post-Treatment and Duplex Technology

Tuesday, April 27, 2010 1:30 PM in Pacific Salon 3

Tuesday Afternoon

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1:30 PM G6-1 Characterization of Duplex Layer Structures Produced by Plasma-Assisted Low Temperature Nitrocarburizing Treatment of Austenic Stainless Steel 316L
Yuanyuan Guo, Gregory Marcos, Thierry Czerwiec, Thierry Belmonte (Ecole des Mines de Nancy, France)

Austenitic stainless steels are attractive materials for various industrial applications where corrosion resistance especially in wet environment is a primary requirement. In order to improve their tribological properties, low thermochemical diffusion treatments as plasma assisted nitriding (PAN), plasma assisted carburizing (PAC) or their combination i.e. plasma assisted nitrocarburizing (PANC), are developed and improved since the 1980s.

PAN and PAC are treatments in which nitrogen and carbon atoms diffuse respectively in a metallic material from moderate to elevated temperatures. Below 420°C, a plasma assisted nitriding treatment of austenitic stainless steel produces a specific phase usually called expanded austenite, S phase, m phase or or ?N phase. Expanded austenite is a metastable nitrogen supersaturated solid solution with a disordered fcc structure and a distorted lattice. This phase is hard, wear resistant and a paramagnetic to ferromagnetic transition takes place for nitrogen contents higher than 14 at%. Other features of the expanded austenite are its high nitrogen content (from 10 to 35 at%) and compressive residual stress in the nitrided layer. Replacing nitrogen by hydrocarbon for conducting a low temperature PAC leads to a carburized layer containing the carbon expanded austenite phase ((?C). These two phases can be obtained simultaneously by combining hydrocarbon and nitrogen in the gas phase through a low temperature PANC.

We perform PAN and PAC treatments by using a multi-dipolar plasma, based on the Distributed Electron Cyclotron Resonance concept. The microwave power is supplied through eight microwave antennas arranged in a two-dimensional network. The resonant magnetic field is produced by permanent magnets located in front of the antennas. The resulting plasma mixture (N2/H2/Ar or C3H8/H2/Ar) diffuses towards the substrate-holder that can be independently heated and/or biased.

In this work, we show results obtained with sequential treatments: carburizing followed by nitriding and nitriding followed by carburizing. It was found that nitrogen and carbon atoms can simultaneously be dissolved into the austenite lattice during the nitrocarburising process, forming a dual layer structure with an extremely hard nitrogen-enriched layer near the substrate surface and above a hard carbon-enriched layer. Our investigations indicate that the carbon content is higher when carburizing is followed by nitriding. X-Ray Diffraction is used to identify the presence and structure of the expanded austenite. The layer thickness is observed by optical microscopy and the composition of the layers is determined by SNMS.

1:50 PM G6-2 Adaption of Chromium Interlayer Thickness to Cemented Carbide Substrates' Roughness for Improving the Adhesion of HPPMS PVD Films and the Cutting Performance
Konstantinos-Dionysios Bouzakis, Stylianos Makrimallakis, Georgios Katirtzoglou, Georgios Skordaris, Stefanos Gerardis (Aristoteles University of Thessaloniki, Greece / Fraunhofer PCCM, Germany, Greece); Emmanouil Bouzakis (Fraunhofer PCCM, Germany, Greece); Toni Leyendecker, Stephan Bolz, Werner Koelker (Cemecon AG, Germany)
High Power Pulsed Magnetron Sputtering (HPPMS) has been identified as a powerful tool for manufacturing hard and well-adherent coatings. Recent investigations have revealed the immense importance of the substrate pretreatments and of the adhesive nanointerlayers materials on the films’ adhesion and on the wear behavior of coated hardmetals. In this context, HPPMS techniques jointly with the deposition of a Cr-nanointerlayer can increase the film adhesion and consequently the coated tool life. These improvements depend on the roughness of the employed cemented carbide substrates. Considering these results, the investigations described in the present paper intent to explain the effect of Cr-interlayer thickness and substrate roughness on the coating adhesion and cutting performance. To attain various roughnesses, the applied cemented carbide inserts were superficially treated. These treatments were grinding at a medium roughness level, or grinding with subsequent polishing for enhancing the surface integrity and finally, in all cases, micro-blasting by fine Al2O3 grains. After Ar-ion etching, Cr adhesive layers with different thicknesses were deposited by HPPMS technology on the variously pretreated substrates. Subsequently, an approximately 3μm thick (Ti,Al)N film was deposited by HPPMS PVD on all used inserts. Rockwell C indentations and inclined impact tests were performed to assess qualitative and quantitative the films’ adhesion. The cutting performance of the coated tools was investigated in milling. FEM supported calculations of the developed stresses during the material removal process contributed in explaining the obtained tool wear results. In these calculations, the adhesion, dependent on the substrate roughness characteristics and on the adhesive interlayer thickness, was taken into account. The results revealed that the effectiveness of HPPMS adhesive Cr-nanointerlayer strongly depends on the substrate surface integrity and on the interlayer thickness. Thus, the film adhesion and consequently the cutting performance can be significantly improved if the interlayer thickness is adapted to the substrate roughness.
2:30 PM G6-6 Effect of Process Duration on Structure, Chemistry, and Mechanical Properties of Borided Low Carbon Steels
Guldem Kartal, Servet Timur (Istanbul Technical University, Turkey); Osman Eryilmaz, Ali Erdemir, Gregory Krumdick (Argonne National Laboratory)

In this study, we employed an ultra-fast boriding technique to grow hard, wear, and corrosion resistant boride layers on low carbon steel substrates using an induction furnace at 900°C. The technique utilizes an electrochemical cell in which it is possible to achieve 100 micrometer thick boride layers in about 30 minutes. The effect of the electrolysis time on boride layer thickness, composition, and structural morphology was investigated and an empirical equation was derived for the growth rate of boride layers. In depth analyses of the boride layers were carried out by microscopy and X-ray diffraction (XRD) which revealed that different boride phases (FeB, Fe2B, Fe3B) could be formed depending on the process duration. The growth rate of boride layers is nearly linear up to 30 minutes of treatment. However during much longer treatments, the growth rate has a parabolic character which can be represented with the equation (d = 1.4904 (t)0.5 + 11.712); where d (in µm) is the growth rate, t (in sec) is duration. The mechanical characterization of the borided surfaces in plane and in cross-sections has confirmed hardness values as high 19 GPa at or near the borided surface (where FeB phase is the most dominant) but gradual decrease in hardness to 14 to 16 GPa beneath the surface where Fe2B phase is present.

2:50 PM G6-9 Effect of Plasma Nitrocarburizing on Properties of AISI 4340 Steel Submitted to Different Heat Treatments
Vladimir Baggio-Scheid, Jorge Abdalla (Institute of Advanced Studies, Brazil)
The AISI 4XXX steel series are structural steels, widely used in the automobile and aerospace components. Plasma thermochemical treatments are commonly used when a hard case is also necessary in order to improve tribological and corrosion properties. In this work the AISI 4340 steel, treated by different heat treatments and by plasma nitrocarburizing process, has been characterized. Three different heat treatments were used. The steel samples were austenitized; austenitized, quenched in oil and tempered; and austenitized, quenched in salt bath and cooled in water (isothermic). After the heat treatments the samples were plasma nitrocarburized at 500°C for 3h. The samples were characterized by microhardness test, SEM, and XRD. Multphase structures predominantly bainitic and martensitic with hardness between 500 and 580 HV have been formed by the heat treatments. The nitrocarburizing process has resulted in a compound layer with 10 μm and hardness higher than 900 HV, containing predominantly the ε - {Fe2-3N] phase. A diffusion layer with a thickness of 130 mm has also been formed. The results concerning the influence of the plasma treatment on the microstructures of the samples are presented and analyzed.
3:10 PM G6-10 Duplex Plasma Technology for Aluminum
Sven Meier (Fraunhofer IWM, Germany)

An innovative approach to improving behavior of aluminum surfaces and meeting long-term durability requirements of aluminum devices is to design and develop novel systems incorporating duplex diffusion/plasma coating treatments. The composite layers consist of a N-diffusion zone obtained by rf-plasma nitriding, followed by a rf-plasma deposited DLC film. A PACVD processing technology is described that helps to overcome some of the most important limitations of existing technology to generate duplex coatings on technical aluminum substrates. Application of this technique to plasma assisted nitriding of pure aluminum and different aluminum alloys is demonstrated. The influence of the process parameters on the discharge characteristics was examined. Material properties and tribological testing results are shown.

3:30 PM G6-7 Plasma Modification of Al2O3 for Improved Adhesive Strength in Composite Materials
Andres Bujanda, Daphne Pappas, Christine Ho, Benjamin Stein, Robert Jensen (U.S. Army Research Laboratory)

Adhesive bond strength of ceramic components in composite systems is an area of growing interest due to the wide range of applications. The adhesive bond between the ceramic and the adhesive is, in many cases, the point where failure originates. In order to combat this debonding mode of failure, the surfaces of the ceramic materials are modified to promote strong, uniform bonding. The surface pretreatment regiment currently being used includes aggressive surface cleaning with alumina particles (grit blasting) in addition to chemical treatments such as priming and the application of silane coupling agents like glycidoxypropyltrimethoxy silane (GPS). Grit blasting, while effective at removing surface contaminants detrimental to adhesive bonding such as carbon, also acts to reduce flexural strength by exacerbating existing surface flaw populations. As an alternative to grit blasting, atmospheric plasma treatments were used to remove surface contamination and chemically functionalize the surface in one step. Atmospheric plasma processing of polymer systems removes the weak boundary layer residing on the surface, and chemically alters the surface of the material, improving surface wettability and chemical reactivity. It is postulated that ceramic surfaces subjected to a glow discharge would undergo similar improvements in wettability and surface reactivity.

In this study, surface modification of aluminum oxide (Al2O3)) specimens due to helium (He), helium-oxygen (He-O2), and helium-nitrogen (He-N2) dielectric barrier discharges was compared to that of as-received and grit blasted specimens. Contact angle goniometry, x-ray photoelectron spectroscopy (XPS) were used to track chemical changes on the surface, while atomic force microscopy (AFM), and flexural strength testing were used to track surface roughness and surface damage, respectively. Wettablility tests showed an improvement in the hydrophilic character of the ceramic surface as the water contact angle decreased by 24% with the He-O2 plasma. XPS results show a reduction in surface carbon similar for both grit blasted and He-O2 plasma treated surfaces. Flexural strength data show no measurable reduction in strength due to plasma exposure, while grit blasting reduces the characteristic strength by ~10%.

3:50 PM G6-11 Improvement of the Cavitation Erosion Resistance of UNS 31803 Stainless Steel by Duplex Treatment
Dairo Mesa (Technological University of Pereira, Colombia); Carlos Pinedo (Heat Tech Ltd., Brazil); André Tschiptschin (University of São Paulo, Brazil)

A duplex surface treatment consisting of a High Temperature Gas Nitriding (HTGN) followed by a Low Temperature Plasma Nitriding (LTPN) was carried out in an UNS 31803 stainless steel. HTGN was performed at 1,200ºC for 8 hours, in a 1 atm N2 atmosphere while LTPN was carried out in a 75% N2:25% H2 atmosphere, at 400ºC for 12 hours. A duplex structure consisting of a ~12 µm thick expanded austenite gN layer with 1,400 HV0.025 hardness was formed on top of a 1.0 mm thick fully austenitic layer, with 350 HV. The HTGN layer was intended to give mechanical support to the more hard and brittle expanded austenite layer. A less steep hardness gradient was obtained between the expanded austenite layer and the UNS 31803 stainless steel matrix. The duplex treated specimens were tested in vibratory cavitation erosion testing equipment. The incubation time for the onset of cavitation for the duplex treated steel was 1.5 times higher than the HTGN UNS 31803 steel and 20 times higher than the UNS 31803 untreated steel. The mass loss rates decreased from 1.5 mg/h for the untreated stainless steel to 0.25 mg/h for the HTGN steel and 0.15 mg/h for the duplex treated steel.

4:10 PM G6-12 Low Temperature Plasma Carburizing of AISI F51 Duplex Stainless Steel
Carlos Pinedo (Heat Tech Ltd., Brazil); José Bressan (State University of Santa Catarina, Brazil); André Tschiptschin (University of São Paulo, Brazil)

Duplex stainless steels are nowadays being used in a variety of applications within the refining and petrochemical industry, where high corrosion resistance and mechanical properties are required. The surface properties of these steels may be optimized in order to attain better performance in highly stressed tribological systems. AISI F51 (EN 1.4462) duplex stainless steel was DC-Plasma carburized at 480 oC, using CH4 as carbon carrier gas. Although the carburized layer showed an apparently duplex structure inherited from the matrix, XRD results, using the Rietveld method, showed only peaks of expanded austenite. The carburized layer attained a surface hardness of 1600 HV0.05 and XRD results showed that this strong hardening effect is related to the formation of a highly stressed carbon expanded austenite on the surface of the specimens. When tested in a ball on disk tribometer in dry conditions wear coefficients as low as 4 x 10-15 m3/(N m) were obtained. The corrosion resistance of the expanded austenite layer in 10% HCl solution was two-fold better than the uncoated F51 steel.

4:30 PM G6-13 Mechanical and Corrosion Properties of Duplex Treated AISI301 Stainless Steel
Marwan Azzi, Moushab Benkahoul, Jolanta Klemberg-Sapieha, Ludvik Martinu (Ecole Polytechnique de Montreal, Canada)
Plasma nitriding is a very common technique used to increase the surface hardness of stainless steels, and consequently to improve their tribological properties. It is also used to create an interface between soft stainless steel and hard coatings to improve adhesion. This paper reports on the mechanical and corrosion properties of AISI301 stainless steel (SS) after a duplex treatment consisting of plasma nitriding followed by the deposition of hard CrSiN films prepared by magnetron sputtering. More specifically, we investigated the effect of deposition parameters, such as nitriding temperature and substrate bias, on the mechanical and corrosion characteristics of the duplex-treated SS. Mechanical properties of the deposited films such as hardness (H) and reduced Young’s modulus (Er) were measured using depth-sensing indentation. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were applied to evaluate the resistance to localized and general corrosion, respectively. The corrosion behavior is correlated with the microstructure and the composition of the surface layers determined by complementary characterization techniques including XRD, EDS, and SEM. The CrSiN layers exhibited an H value of 23 GPa, whereas the nitrided layer was shown to present a gradual increase of the H value from 5 GPa (for the non-nitrided SS) to almost 14 GPa at the surface. Electrochemical results revealed that the nitriding temperature is a critical parameter defining the corrosion properties of the duplex-treated SS. At relatively high temperatures (673 K), the nitrided layer exhibited poor corrosion resistance due to the precipitation of chromium nitride compounds and the depletion of Cr in the stainless steel matrix. This, in turn, leads to a poor corrosion performance of the duplex-treated SS since the pores and defects in the CrSiN film were the potential sites for pitting. On the contrary, at relatively low temperatures (573 K), the nitrided interface exhibited excellent corrosion resistance due to the formation of compound-free diffusion layer. The latter effect is shown to favor passivation of the material at the electrode/electrolyte interface of the duplex-treated SS.
4:50 PM G6-5 Improvement of Press Dies Used for the Production of Diamond Composites by Means of DUPLEX-PVD-Coatings
Wolfgang Tillmann, Evelina Vogli, Siavash Momeni (TU Dortmund, Germany)

In the machining of hard materials such as glass or stone, cemented carbides have been recently replaced by diamond tools, consisting of a metallic carrier, on to which diamond segments are brazed. One of the most economic ways for the production of diamond segments is the cold compaction of the mixture of a metallic powder and diamond particles. Due to a highly abrasive sliding contact between diamond particles and the die walls, the wear rate of the press dies is very high. As a result of a low lifetime of the press dies, they must be replaced in short time periods. To avoid the costly and time-consuming substitution of the press dies, in this work PVD-coatings were deposited on the inner surface of the pre-plasma nitrided press dies (DUPLEX treatment). Thereby, various high and low alloy tool steels were treated by means of plasma nitriding process. Subsequently, a nanocomposite PVD coating, titanium aluminum supernitride, was deposited by means of a high ionization magnetron sputtering device on nitrided and non-nitrided steel substrates. The mechanical and tribological properties of these coating systems were studied by means of several standard tests such as nanoindentation, ball-on-disc and scratch test. The most wear resistant coating system was chosen to employ on the inner surface of the press dies. The wear resistance of the press dies developed in this study was tested under real loading condition during compaction of the mixture of diamond particles and cobalt powder. It was revealed that employing plasma nitrided tool steels coated with titanium aluminum supernitride enhances the lifetime of the press dies up to 500%. Furthermore it was shown that the press dies with different surface treatments possess different failure modes during the compaction process.

5:10 PM G6-4 Effects of Post Deposition Annealing on Resistive Switching Characteristics of SrZrO3 Thin Films
Meng-Han Lin, Ming-Chi Wu, Shih-Wei Jan, Yi-Han Huang (National Chiao Tung University, Taiwan); Chen-Hsi Lin (Windbond Electroncs Corporation, Taiwan); Tseung-Yuen Tseng (National Chiao Tung University, Taiwan)

In this paper, the effects of post deposition annealing (PDA) in O2, N2, and Ar at 600oC for 1 min on the resistive switching characteristics of SrZrO3 (SZO) thin films were investigated. The SZO resistive memory devices exhibited the large dispersion of resistive switching parameters such as turn-on voltage and high resistance state (HRS) current, further restricting their development in the future nonvolatile memory (NVM) applications. The severe dispersion is more greatly reduced by O2 600oC- PDA than N2 and Ar 600oC- PDA owing to that the suppression of the oxygen vacancies in thin films could be significantly enhanced by O2 600oC- PDA . Furthermore, device yield is dramatically increased to 90% by O2 600oC- PDA in comparison to the other devices. T he oxygen-annealed SZO memory devices can be successively switched between HRS and low resistance state (LRS) by applying voltage signal over 150 times, and the resistive ratio of LRS and HRS is still kept more than 1000 . The retention characteristics of both HRS and LRS are stable up to 106 s at room temperature (RT) and 85oC. Besides, the resistive ratio of HRS and LRS still remains nearly 1000 more than 14000 s under successive reading voltage stress at RT and 85oC. The oxygen-annealed SZO memory device with its superior memory characteristics is a promising candidate for the next-generation NVM applications.

Time Period TuA Sessions | Abstract Timeline | Topic G Sessions | Time Periods | Topics | ICMCTF2010 Schedule