Papers

ICMCTF2010 Session G1-2: Innovations in Surface Coatings and Treatments

Monday, April 26, 2010 1:30 PM in Room Sunset

Monday Afternoon

Start	Invited?	Item
1:30 PM		G1-2-1 Nano-Structured Multi-Functional Composite Coatings and their Applications Xianting Zeng (Singapore Institute of Manufacturing Technology, Singapore) Surface engineering for nanocomposite coatings is offering a significant impact on product performance and quality because of their unique material properties and integrated multiple functionalities through nano-structuring and engineering. Such coatings containing nano-sized multi-phases in composition and multi- or nano-layers in structure render substantially improved mechanical, chemical and tribological properties as well as additional functions such as anti-sticking, self-lubricating, easy-to-clean or self-cleaning, corrosion and oxidation resistance, and environment- and bio-compatibility. In this paper, nano-phased hybrid multi-functional coating materials and deposition processes will be reviewed based on our research work in surface engineering using unbalanced magnetron sputtering and cathode arc, sol-gel and electro-chemical process technologies. Case studies in coating design, material selection and deposition processes will be shared and discussed for applications in precision engineering, aerospace and automotive as well as construction industries, with emphasis on PVD composite coatings for high temperature wear and oxidation protection and sol gel based composite coatings for corrosion protection and surface cleaning and maintenance.
2:10 PM		G1-2-3 Influence of Interface and Multi Layer Structure on Corrosion and Erosion Resistance of Thin Films (PVD) Joerg Ellermeier, Oliver Durst, Udo Depner, Torsten Trossmann, Herbert Scheerer, Christina Berger (TU Darmstadt, Zentrum für Konstruktionswerkstoffe, Germany) The research activities in the field of thin film PVD or CVD coatings are mainly focused on wear protection of tools or other machine parts. But these thin coatings are also relevant for applications where corrosion and erosion are present as single loading or as a superimposed loading. The main objective is to replace high alloyed and therefore expensive bulk materials with high corrosion resistance through low alloy steels thin film coated. That is the reason to investigate modern PVD multilayer structures with respect to the possibilities to protect against corrosion and erosion. The focus of this research project was to develop multi layer coatings which exhibit as few as possible defects. So to be done with the PVD HPPMS process (CrN/a-C). It was necessary to investigate the influence of alternating hardness and the plasma-nitriding of the substrate material (42CrMo4) to the interface bonding. Also the influence of the coating parameters (e.g. bias voltage, gas flow, target power, HPPMS parameters) to the bonding of the layers was determined. An alternating layer structure of the multi layer coating should avoid the growing of defects to obtain a dense coating with high corrosion resistance. The top layer must have a high hardness and adequate toughness to realize a sufficient resistance against erosion. Depending on the particle flow (perpendicular or parallel to the surface) therefore the erosion loading changes and different properties of the thin film are essential. The bonding between the layers is of prominent importance for the perpendicular flow of the erosion particles. For the parallel flow the hardness of the top layer is a significant factor. Besides the usual investigations like scratch test, Rockwell test, metallographic and SEM investigations for the characterization of the coatings, application orientated corrosion and erosion tests were carried out. With polarization curves of coated samples in artificial seawater the defects of the thin films can be detected. It was possible to produce thin films in multi layer structure which show a very low defect rate during the polarization test. For erosion-corrosion tests artificial seawater and demineralized water with additions of Al₂O₃ particles were used. The load of the thin films is quite higher with the superposition of corrosion and erosion than with erosion as dominant load. The resistance against erosion depends on the amount of defects in the thin films when the particle flow is nearly perpendicular to the surface.
2:30 PM		G1-2-4 Novel Materials for Thermal Compensated Strain Gauges Ralf Bandorf, Ulrike Heckmann, Mirjana Luebke, Martin Peters, Guenter Braeuer (Fraunhofer IST, Germany) For the measurement of stress and strain e.g. used for detecting loads or applied forces strain gauges are commonly used. While conventional polymer based strain gauges glued to the substrate show swelling and creep due to temperature and humidity thin film strain gauges avoid this problems. For improvement of the sensing properties of the material an increase in the gauge factor is required. For reliable measurement also a compensated temperature coefficient of resistivity TCR is beneficial. Investigations on the synthesis of new materials with compensated TCR, i.e. a TCR lower than 200 ppm/K were carried out on different material systems. It turned out that DLC based coatings using Ni as dopand are well suited to tailor the TCR and increase the gauge factor. A gauge factor exceeding 10 with a TCR close to zero was realised for films containing approximately 55 at% Ni. Another material class with high potential for high temperature use are the M-A-X coatings. For Ti-Si-C films sputtered from a stoichiometric Ti₃SiC₂ target also a TCR close to zero was found. The gauge factor of approximately 2.5 was close to conventional NiCr. In contrast to NiCr the Ti-Si-C films showed no modification of the properties with annealing up to 600°C.
2:50 PM		G1-2-5 SiBNCO PVD Coatings for High Performance Applications Joerg Vetter (Sulzer Metaplas GmbH, Germany); Masakazu Isaka, Takeshi Ishikawa, Kazuyuki Kubota (Hitachi Tool Engineering, Japan); Georg Erkens, Juergen Mueller, Jones Alami (Sulzer Metaplas GmbH, Germany) PVD coatings for high performance applications require at least one selected outstanding property like low friction, high hardness, high temperature stability or high oxidation stability. In the last decade a lot of high impact coatings were new developed and successfully introduced in industrial production of tools and components. Such coatings comprise TiSi-based and AlCr- based types (TiSiN, AlCrSiN). These coatings are belonging to the group of crystalline coatings and show a limit in the oxidation temperature of about 1000°C. The SiBNC0 coatings deposited by magnetron sputtering are able to withstand higher temperatures without a significant oxidation rate. The paper describes coating properties in dependence from the used reactive gases nitrogen, oxygen and carbon. Coating properties are high lightened by SEM, hardness measurement, EDX, X-ray diffraction and XPS. Tribological properties were investigated by Pin-On-Disc. Oxidation experiments were carried out up to 1000°C.
3:10 PM		G1-2-6 Ultra-Fast and Thick Boriding as a Novel Surface Treatment for Demanding Tribological Applications Ali Erdemir (Argonne National Laboratory); Guldem Kartal (Istanbul Technical University, Turkey); Osman Eryilmaz, Vivekanand Sista, Gregory Krumdick (Argonne National Laboratory); Servet Timur (Istanbul Technical University, Turkey) Increasingly more demanding and very stringent operating conditions of next-generation tribological systems will require much stronger and harder materials that can last for the duration of intended applications. Accordingly, there is an urgent need for the development of more robust surface engineering technologies that can meet such requirements for future tribological systems. In this study, we report an ultra-fast boriding technique that can results in very hard and thick boride layers in minutes. Specifically, the new technique produces 80-100 µm-thick boride layers on steel substrates in about 30 min., depending on the type of steel. Compared to conventional surface treatment methods (e.g., nitriding, carburizing, and pack-boriding which are used extensively by industry to achieve superior hardness and tribological properties in all types of steel components), novel ultra-fast boriding provides great advantages in terms of productivity, versatility, and environmental cleanliness. It is done in a molten salt electrolyte consisting of a mixture of natural borax and sodium carbonate at elevated temperatures. Work pieces to be borided are attached to a cathode, while the crucible that holds the electrolyte acts as an anode. The hardness of borided steel surfaces may range from 17 GPa to more than 20 GPa (depending on the steel type). The very thick boride layers produced on the surface has excellent resistance to wear, erosion, and corrosion. Under boundary lubricated sliding conditions, the boride layers provide low friction and extreme resistance to wear and scuffing. In addition to being ultra-fast, the new boriding technique is very cheap and produces no gaseous emissions and solid wastes. Overall, it may have significant positive impact on the heat treating and surface treatment fields.
3:30 PM		G1-2-7 Using Electroless Plating Cu Technology for TFT-LCD Application Yi-Teh Chou, Po-Tsun Liu, Chih-Yu Su (National Chiao Tung University, Taiwan); Hung-Ming Chen (Liquide Laboratories, Japan) With the trend of increasing size for active matrix liquid crystal display (AMLCD) development, the requirement of low-resistivity metallization to release resistivity-capacity delay (RC delay) problems becomes more and more critical. Copper (Cu) interconnection architecture, for this reason, attracts lots of attention for its low resistivity below 3μΩ-cm. However the conventional copper deposition technology, such as sputtering, almost needs vacuum systems which need high maintaining and process cost. Other methods like electroplating methods still face poor uniformity issues, limiting its application in AMLCD. In this study, we applied a novel electro-less plating (ELP) method to form Cu film no need of any vacuum system. With the control of process temperatures, the highly uniform copper film on glass substrate can be easily achieved. Successful fabrication of amorphous silicon thin film transistors (a-TFTs) with ELP Cu electrodes also indicates the capacity of this proposed technology for AMLCD applications. In this study, a layer of NiP film was first formed by ELP method to serve as a great adhesion layer between the subsequent copper film and glass substrate as well as to prevent copper diffusion. The chemical solution mixed with NiSO₄ and NaH₂PO₂ were served as precursors of Ni and P for the NiP film deposition. Also, the chemical SnCl₂, PdCl₂ and NaH₂PO₂ were used to catalyze and condition the base surface after pre-cleaning and macro-etching the glass substrate. After catalyzing the seed layer of NiP film, the copper film was deposited with self-alignment on the NiP surface by immersing the samples in CuSO₄ solution. All ELP processes were done in the ambient free of any vacuum system. The resistivity of ELP as-deposited Cu film is about 2.6μΩ-cm. XRD results indicated the ELP Cu film is of polycrystalline structure. The surface morphology was analyzed in this work as well. Following the conventional a-TFT manufacturing process with ELP Cu as gate electrode, the electrical characteristics were measured by Keithley 4200 semiconductor analyzer comprehensively. The threshold voltage (V_th) and mobility (μ) were extracted about 3.55V and 0.56, respectively, at V_D=7.67V. Besides, the electrical stability of the a-TFT with ELP Cu gate electrodes also was discussed by DC and AC bias stress under a variety of measurement temperatures for 10⁴ sec. Compared to the typical a- TFT with MoW gate electrode, experimental results have shown the proposed ELP Cu-gate a-TFT possesses superior electrical performance and good stability for realistic AMLCD applications.
3:50 PM		G1-2-8 Etching Properties of Si and HfO₂in an Inductively Coupled Plasma Etcher Sang Lee, Breandan O'Shaughnessy (University of Texas at Dallas); K.J. Park, Y.H. Joh (DMS, Korea); Keum Jee Chung (Hanyang University, Korea); Gil Lee, Jiyoung Kim, Moon Kim (University of Texas at Dallas) The etch rate behaviors of Si and HfO₂ in an inductively coupled plasma etcher are studied. CHF₃(40 sccm)/Ar(10 sccm) gases are used at 10 mTorr chamber pressure. Ion flux and bombarding energy, which are two key factors of adjusting plasma-surface interactions and etch properties, are controlled by source power and bias power respectively. Source power and bias power are varied over a wide range (200 W ~ 900 W for source power and 10 W ~ 100 W for bias power) to investigate dry etching characteristics. Boron doped p-type (100) Si wafers and HfO₂ films deposited on the Si wafers using an atomic layer deposition system are utilized to investigate etching properties. While the attempt of etching for Si and HfO₂ resulted in the polymer deposition at low bias power, both materials are etched at higher bias power. While both source power and bias power affect etch rate of Si, the etch rate of HfO₂ mainly depends on bias power for all etch conditions in this study. Different behaviors of HfO₂ films are attributed to higher bombarding energy required to trigger the etching process, which is consistent with the slow etch rate. In the case of Si etching, the amount of polymer deposition decreases and etch rate continuously increases with bias power. Nonetheless, HfO₂ shows step-like etch rates as bias power increases: first the amount of polymer deposition on the HfO2 surface decreases, then its etch rate is kept nearly constant, until the bias power reaches 50W where the etch rate starts increasing. The step-like behavior is a result of the competition between polymer deposition and etching. The effect of the distance of the sample from the plasma source is also investigated. As the distance increases from 4 mm to 14 mm, ions experience more collisions which results in lower ion flux near the sample surface. The ion flux decreases to 15~28% at longer distance (14 mm) from that at a shorter distance (4 mm) which is measured with an in-situ measurement. The etch rate is expected to be lower at the same source power and bias power with a longer distance from plasma source due to the smaller ion flux. In case of Si, the etch rate decreases to ~16 % at longer distance compared to shorter distance at lower source power (where the source power dominantly affects the etch rate) while little change is observed at high source power (where bombarding energy dominates etch rate). However, the etch rate of HfO₂ does not change much at longer distance because that of HfO₂ is mainly affected by bombarding energy, which is controlled by bias power, rather than ion flux controlled by source power.