Papers

ICMCTF2001 Session E3-1: Coatings Resistant to Severe and Unusual Environments

Monday, April 30, 2001 10:30 AM in Room California

Monday Morning

Start	Invited?	Item
10:30 AM		E3-1-1 TiN Coating Improves the Corrosion Behavior of a Superelastic NiTi Surgical Alloy D. Starosvetsky, I. Gotman, E.Y. Gutmanas (Technion, Israel) The key to the biocompatibility of NiTi surgical devices resides in the improvement of the material's corrosion resistance. To protect the surface of NiTi from corrosion, an original PIRAC nitriding method was proposed. In the present work, the corrosion and electrochemical properties of NiTi samples annealed under a low pressure of highly reactive nitrogen at 900 and 1000°C for 0.5, 1.5, 3.5 and 6.0 hours were studied. The microstructure of PIRAC coatings was characterized employing XRD, SEM/EPMA and High Resolution SEM, and was found to consist of a hard TiN outer layer followed by a Ti2Ni(N) layer. Electrochemical tests were performed in Ringer's solution on coated and uncoated NiTi samples, both upon immersion in deaerated solution and after long term exposure (400 h) under aeration at open circuit potential (OCP). PIRAC nitriding treatment was found to significantly improve the corrosion resistance of NiTi alloy. Protective characteristics of PIRAC coatings became pronouncedly stronger with increasing treatment time and temperature. No pitting corrosion was observed on NiTi specimens PIRAC nitrided at 900°C with annealing times longer than 3.5 h. When PIRAC treatment was performed at 1000°C, a short 0.5 h exposure was sufficient to prevent pitting. A very low anodic current in the passive region and exceedingly low metal ion release rate were measured on PIRAC coated samples. Relationship between the nitriding parameters (annealing time, temperature, etc.) and corrosion protective properties of PIRAC coatings has been established, and the role of the outer and inner surface layers in the improvement of NiTi corrosion resistance is discussed. PIRAC nitriding treatment seems to be very promising for NiTi protection from corrosion, since the thin TiN layers are believed to be able to sustain large deformations associated with the material's superelasticity.
10:50 AM		E3-1-2 Control of Porosity through Plasma Induced Polymerization or Deposition M.J. Neumann (Univeristy of Illinois at Urbana-Champaign); J.E. Norman, D.N. Ruzic (University of Illinois at Urbana) A multifunctional plasma reactor is used to treat a variety of polymers. The plasma is produced in a commercial PlasmaQuest 256 fitted with a Mori 200 helicon source. Plasma densities and temperatures are in the range of 1 to 10 x 10¹¹ cm^-3 and 2 to 5 eV. Plasma treatment modifies the cross-linking of surface atoms and permits modifications of surface properties. In some cases this modification is limited to the surface of the polymer, while leaving the underlying bulk material unchanged. Thus, while surface interaction properties can the modified, the overall properties of the bulk polymer remain constant. Other treatments can permeate through the bulk of the material and alter the entire sample. The polymer films can be altered significantly. Destruction, etching, polymerization, deposition, or hard coating applications can be produced by merely changing the gas species in the reactor. The changes of porosity and surface characteristics of the polymers are investigated through the use of mass spectrometry and SEM. Plasma properties are measured with a Langmuir probe and optical emission spectroscopy. Potential applications of these processing techniques include many uses in biomaterial engineering including protein-fouling, drug engineering, drug delivery systems, reduction of friction and wear-resistance applications.
11:10 AM		E3-1-3 Corrosion Resistance of Boroaluminized Layers on Steel R. Petrova (New Jersey Institute of Technology); Z. Zahariev, D. Cristakieva (Bulgarian Academy of Sciences, Bulgaria); M. Marinich (Ukrainian Academy of Sciences, Ukraine) Abstract The corrosion resistance in 10% H₂SO₄, NaOH+Na₂S (pH=10), 10% KOH, and Al₂(SO₄)₃ (100g/l) of boronized, boroaluminized, and aluminized diffusion layers on plain-carbon steel (C=0.45%; Si=0.20%; Mn=0.60%; Cr=0.25%; Ni=0.25%), obtained by a BOROZAR composition has been investigated. The layers obtained are compared with stainless steel (Cr=18.0%; Ni=9.0%; Ti=0.7%; C=0.12%, and Si=0.8%) regarding their corrosion resistance. The microstructure, phase composition, and thickness of the diffusion layers obtained are presented. The comparative corrosion tests are based on the weight loss of the samples or are performed potentiometrically. The results obtained on the corrosion rate in the presence of a corrosive medium have been shown that the boroaluminized layer is stable in an Al₂(SO₄)₃ medium, exceeds boronized layers in corrosion resistance and can be used instead of stainless steel. The boroaluminized layers passivate usual carbon steel in a NaOH+Na₂S (pH=10) medium, have better qualities than the boronized layers and can be used instead of stainless steel. In 10% H₂SO₄, the boroaluminized layers are not interior to the boronized and better than aluminized with respect to their corrosion resistance.
11:30 AM		E3-1-4 Dissolution and Soldering Behavior of Nitrided Hot Working Steel with Multilayer LAFAD PVD Coatings R. Shivpuri, V. Joshi (The Ohio State University); R.S. Bhattacharya, S.J. Dikshit (UES, Inc.); A. Srivastava (The Ohio State University) Soldering and corrosive dissolution are the primary causes of failure of dies in permanent mold and die casting production of net shape parts for transportation industry. At worst these corrosive reactions result in core pin or sprue dissolution and at the least, some soldered cast metal remains behind when the casting is ejected. Typically the cast metal aluminum or zinc in die casting which has affinity with the metal molds which are of H-13 hot working die steel. The objective of this investigation was to investigate the thermo-chemical reactions occuring at the cast metal- die steel interface and to explore the possibility of surface engineering the die steel surface in order to provide an effective barrier to the dissolution and soldering mechanisms. Single layer hard ceramic coatings applied by the arc process were found to act as effective barrier for medium corrosive environment. However, they failed in more severe environment due to surface pitting. This paper presents a duplex surface treatment which consists of nitrided steel substrate coated by multi-layer titanium based coatings applied by the Large Area Filtered Arc Deposition which has been found to be very effective preventer of thermo-chemical surface corrosion. Details of the coating process, the cyclic testing scheme which consists of alternate dipping in liquid aluminum and water, and the reasons for the coating's effectiveness are included. Also included is the hypothesis that nitriding of the substrate acts to reduce the surface wettability which reduces the chemical reactions. The nitriding case was varied to quantify this effect. Basedon this investigations the duplex coating system is being evaluated in actual die casting environment. Results of these industrial trials will also be included.
11:50 AM		E3-1-5 Microstructural Analysis of Corrosion in a Nitrided AISI-SAE 4140 Steel. A. Medina (Instituto de Investigación Nuclear, México); J. Bernal (ITESM. CEM., México); J. Ascencio (ININ., México); P. Santiago (ININ, México); J. Oseguera (ITESM. CEM., México) In this work, the nitrided zone of a AISI-SAE 4140 steel was characterized using various microstructural analysis techniques. The 4140 steel pieces were nitrided in the post-discharge flow of a microwave generated plasma at temperatures above and below the eutectoid point. The corrosion behavior was evaluated by the anodic polarization technique. Results of power dynamics polarization indicate a corrosion potential of E_corr =-599 Mv_sce for the nitrided steel and E_corr=-500 Mv_sce for the nitrided material. The nitrided products were characterized by X-Ray Diffraction (XRD) to identify phases, Scanning Electron Microscopy (SEM) to establish the morphology of nitrides and depth, and Energy Dispersive Spectrometry (EDS) to determine the elemental distribution in the nitrided region. Microhardness profiles were also obtained from the samples. The results of this work indicate that post-discharge nitriding of the 4140 steel produce a nitrided layer that provide good corrosion resistance respect untreated material. Molecular Simulation techniques are also applied to optimize the analysis .
12:10 PM		E3-1-6 Corrosion Behavior of Zirconium Nitrides Film Coated on 304 Stainless Steel G.-P. Yu, W.-J. Chou (National Tsing Hua University, Taiwan, ROC); J.-H. Huang (National Tsing Hua University, Taiwan, R.O.C.) The corrosion resistance of ion-plated Zr, ZrN, Zr/ZrN films on commercial AISI 304 stainless steel has been investigated by electrochemical measurement. The electrolyte, 0.5M H2SO4 containing 0.05M KSCN, was used for the potentiodynamic polarization scan conducting from â€“800mV to 800mV (SCE) with different scan rate from 10 to 600mV/min. The ZrN layer was essentially stoichiometric for XPS measurement. According to the SIMS composition depth profile, the compositions are very uniform through the film surface to the 304 stainless steel substrate. The corrosion current density and passive current density increase with increasing potentiodynamic polarization scan rate for bare 304 stainless steel. Comparing to the bare substrate and coated specimens, the Icorr and Ip decreased at least one order, and the bi-layer Zr/ZrN coating showed the highest corrosion resistance than other two single layer coatings. Because of the cathodic control of the galvanic corrosion, the corrosion potential of the coating specimens is slightly higher than that of the bare metal substrate. The corrosion power Qs is an effective index to evaluate the corrosion resistance of film coated on metal substrate. The porosity or pinhole density plays a significant role in the transition mental nitride protection coatings. Normalized critical passive current density was closely related to the exposure area, and a linear relationship between Qs and NIc holds.