Ge-Ping Yu

MECHANICAL PROPERTIES OF TIN THIN FILM COATINGS ON 304 STAINLESS STEEL SUBSTRATES

Titanium nitride (TiN) film was deposited on 304 stainless steel using a hollow cathode discharge ion-plating (HCD-IP) technique. Film thickness and N/Ti ratio were controlled. The depth profile of the composition was determined by secondary ion spectroscopy (SIMS). The results showed that the compositions of the films were uniform for the films deposited at the same deposition conditions. The purpose of this study is to investigate the variation of structure and mechanical properties of the TiN films with different film thickness. The preferred orientations of TiN films were determined using X-ray diffraction (XRD). The dominant preferred orientation of the TiN coatings for the deposition conditions was (111), especially for the films thicker than 1 μm. The residual stress of the TiN films was also measured by XRD using sin2 Ψ method. The residual stress was ranging from −5.93 to −2.70 GPa, varying with film thickness. Hardness of the films was measured by nanoindentation. The hardness values were ranging from 14.9 to 33.6 GPa, increasing with the film thickness. The ultimate interfacial shear stress between TiN/304SS was determined by in-situ strip tension of the TiN-coated specimens in a scanning electron microscope (SEM) chamber. The limiting thickness for the effective measurement of interfacial shear strength by the in-situ strip tension method is close to 0.5 μm. N/Ti ratios of the thin films were all at 0.8 measured using both X-ray photoelectron spectrometer (XPS) and Rutherford backscattering spectrometer (RBS). The packing factors of TiN films, calculated from the results of RBS, were 0.62–0.99, increasing with film thickness and leveling off at a thickness above 1.2 μm.

The effects of heat treatment on the chromium depletion, precipitate evolution, and corrosion resistance of INCONEL alloy 690

A series of heat treatments were performed to study the sensitization and the stress corrosion cracking (SCC) behavior of INCONEL Alloy 690. The microstructural evaluation and the chromium depletion near grain boundaries were carefully studied using analytical electron microscopy (AEM). The measured chromium depletion profiles were matched well to the calculated results from a thermodynamic/kinetic model. The constant extension rate test (CERT) was performed in the solution containing 0.001 M sodium thiosulfate (Na2S2O3) to study the SCC resistance of this alloy. The Huey test was also performed in a boiling 65 pct HNO3 solution for 48 hours to study the intergranular attack (IGA) resistance of this alloy. Both tests showed that INCONEL 690 has very good corrosion resistance. It is believed that the superior IGA and SCC resistances of this alloy are due to the high chromium concentration (≈30 wt pct). It is concluded in this study that INCONEL 690 may be a better alloy than INCONEL 600 for use as the steam generator (S/G) tubing material for pressurized water reactors (PWRs)

In situ observation of the cracking behavior of TiN coating on 304 stainless steel subjected to tensile strain

Abstract The validity of a periodic cracking model capable of evaluating the interfacial shear strength of a ceramic film on metal substrate system was tested in a highly residual-stressed TiN coating-304 stainless-steel substrate system. In situ observation of the cracking behavior of the coating was conducted while the TiN-coated tensile specimen was being pulled inside the chamber of a scanning electron microscope. Four sequentially developed morphologies of the crack and/or inter-crack-spacing of the coating, i.e. multiplication, stabilization, cross-linking and spallation, were observed. Inter-crack-spacings of the fragmented coating were analyzed and identified with their respective initiation mechanisms, thereby testing the claims made by the model. Stringent criteria for selecting the characteristic inter-crack-spacing were articulated to improve the accuracy of the calculated maximum interfacial shear stress. Lastly, a modified periodic cracking model, which incorporates the contribution from residual stress and the new rule for selecting the characteristic inter-crack-spacing, was presented. The interfacial shear strength of the subject system evaluated through the modified model is 0.65±0.06 GPa, which is of the order of magnitude of the substrates yield shear strength.

Deposition of TiN thin films on Si(100) by HCD ion plating

Titanium nitride (TiN) films were deposited on Si(100) substrates using a hollow cathode discharge ion plating (HCD-IP) technique. Based on previous experimental results, the optimum deposition conditions were chosen. The thickness of the TiN film and the angle between the specimen surface and the evaporating source (coating angle) were selected as the variable parameters. The purpose of this study is to investigate the effect of these two processing parameters on the properties of TiN films. After deposition, the thin film structure was characterized by X-ray diffraction (XRD), cross-sectional transmission electron microscopy (XTEM), and field-emission-gun scanning electron microscopy (FEG-SEM). N/Ti ratios of the thin films were determined using both X-ray photoelectron spectrometer (XPS) and Rutherford backscattering spectrometer (RBS). The resistivity of the TiN films was measured by a four-point probe. The hardness of the thin films was obtained from nanoindentation tests. An atomic force microscope (AFM) was used to measure the roughness of the thin films. The results showed that (111) was the dominant preferred orientation in the TiN films for most of the deposition conditions and for all coating angles, especially for film thicknesses greater than 1 μm. Hardness values of TiN films were approximately 28 GPa for film thicknesses close to 0.5 μm and above, and did not vary with the coating angle. The hardness can be correlated to the (111) preferred orientation of the TiN film. The hardness increased with the (111) texture coefficient and leveled off as the texture coefficient approached 1. The packing factor had a linear relationship with the film thickness. Resistivity decreased with increasing thickness and increasing packing factor for all coating angles. At a similar thickness or packing factor, specimens coated at angles different from 0° had a much higher resistivity than those coated at 0°.

Corrosion resistance of ZrN films on AISI 304 stainless steel substrate

Abstract The corrosion resistance of ion-plated Zr, ZrN and ZrN/Zr films on commercial AISI 304 stainless steel has been investigated by electrochemical measurement. The electrolyte, 0.5 M H 2 SO 4 containing 0.05 M KSCN, was used for the potentiodynamic polarization. The potentiodynamic scan was conducted from −800 to 800 mV (SCE) with scan rate ranging from 10 to 600 mV/min. The N/Zr ratios of the ZrN films determined by X-ray photoelectron spectroscopy (XPS) were essentially stoichiometric. The composition depth profiles measured by secondary ion mass spectrometry (SIMS) indicated that the compositions in the ZrN films were uniform from the film surface to the 304 stainless steel substrate. Experimental results showed that the corrosion current density I corr and passive current density I p increased with increasing polarization scan rate for the bare AISI 304 stainless steel specimens. Compared with the bare substrate, the I corr and I p for the coated specimens decreased at least 1 order of magnitude. The bi-layer ZrN/Zr coating possessed the highest corrosion resistance among the three coated-specimens. Because of the cathodic control of the galvanic corrosion, the corrosion potential of the coating specimens was slightly higher than that of bare metal substrate. The corrosion power Q , i.e. the integrated electric charge per unit area of the specimen during potentiodynamic polarization test, was an effective index to evaluate the corrosion resistance of the coated stainless steel substrate. The pinhole density played a significant role in corrosion resistance of the transition metal nitride coatings. Normalized critical passive current density ( NI crit ) was closely related to the exposure area, and a linear relationship between Q and NI crit was held.

A tensile-film-cracking model for evaluating interfacial shear strength of elastic film on ductile substrate

Abstract The stress distribution associated with the film cracking model originally proposed by Agrawal and Raj is further investigated through the use of the finite element analysis (FEA) technique. The result of the FEA analysis indicates that the interfacial shear stress can be approximated by a quarter segment of an elliptical function, rather than by a sine function of a full wavelength as employed in the original model. A modified model related to the maximum interfacial shear stress is thus proposed. The validity of the new model has been tested in a TiN coating–304 stainless steel system. It is demonstrated that the interfacial shear strength evaluated through the new model is of the same order of magnitude as that of the yield shear strength of the substrate.

Bias effect of ion-plated zirconium nitride film on Si(100)

Abstract Zirconium nitride (ZrN) films were deposited on Si(100) substrates using the hollow cathode ion-plated (HCD-IP) technique. The deposition conditions were designed to deposit stoichiometric ZrN films, and the thickness of the film was also controlled. The substrate bias was selected as the controlling parameter ranging from floating to −300 V. The purpose of this study is to investigate the effect of bias on the structure and properties of ZrN film. The results showed that (111) orientation was the dominant preferred orientation in ZrN films deposited at the bias voltage ranging from 0 to −250 V. The (220) orientation became the preferred orientation for ZrN films deposited at bias voltage of −300 V. Hardness values of ZrN film ranged from 22∼32 GPa. The optimum condition of the negative substrate bias was close to 50 V. At this condition, the specimen showed the lowest resistivity of 56 μΩ cm, the highest packing factor of 0.99, the lowest roughness of 0.66 nm, the highest brilliance of 87.2, and a relatively high hardness of 30.63 GPa. Resistivity increased with increasing bias and with decreasing packing factor. The brilliance increased linearly with increasing packing factor. The relationships between ZrN film properties and bias were successfully developed.

Mechanical properties of ion-plated TiN films on AISI D2 steel

Abstract TiN films were deposited on AISI D2 steel substrates without and with a titanium intermediate layer using a hollow cathode discharge (HCD) ion plating technique. The structure of the film was determined by X-ray diffraction (XRD) and the composition was measured by X-ray photoelectron spectroscopy (XPS). The microhardness and adhesive strength of the as-deposited coatings were measured as well. The results of X-ray diffraction and X-ray rocking curves showed that the TiN film exhibited a (111) preferred orientation. The hardness of coatings was found to be related to the N/Ti composition ratio and the porosity in the TiN films. The results of scratch test show that the high critical load is a measure of the adhesion of the TiN film, while the low critical load can be used as a qualitative measure of the toughness of the TiN film. The interfacial diffusion depth increased with the average substrate temperature during the ion plating process. From the results of scratch test and the depth profiles of secondary ion mass spectrometry (SIMS), the adhesive strength of the coating/substrate interface increased with increasing interdiffusion depth. Moreover, the results indicated that the Ti interlayer can enhance the adhesion strength of the coatings.

Microstructure and Hardness of Hollow Cathode Discharge Ion-Plated Titanium Nitride Film

Titanium nitride (TiN) films were deposited on 304 stainless steel substrate by hollow cathode discharge (HCD) ion-plating technique. The preferred orientation and microstructure were studied by x-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. Microhardness of the TiN film was measured and correlated to the microstructure and preferred orientation. The results of TEM study showed that the microstructure of TiN film contains grains with nanometer scale. As the film thickness increases, the grain size of TiN increases. The x-ray results show that TiN(111) is the major preferred orientation of the film. The hardness of TiN film is primarily contributed from TiN(111) preferred orientation.

Effect of heat treatment on the structure and properties of ion-plated TiN films

Abstract Heat treatment processes were widely applied to improve the properties of hard coatings. However, the mechanisms that enhance thin film properties are still unclear. In this study, titanium nitride (TiN) films were deposited on 304 stainless steel using a hollow cathode discharge ion-plating technique. The specimens were heat-treated at 400 and 700 °C for 1 h under controlling atmosphere to reduce the oxidation of the thin films. After heat treatment, the microstructure and packing factor inside the TiN thin films were not significantly changed; however, the surface grain size was enlarged and surface roughness decreased. The variation of texture coefficient was more distinct at 700 than 400 °C. The hardness of heat-treated specimens increased 10–30% more than the as-deposited specimens with corresponding thickness. The 400 °C-treated specimens were all slightly harder than those treated at 700 °C, except one specimen. This can be attributed to the fact that the specimens treated at 400 °C have higher residual stress than those treated at 700 °C. The higher residual stress may be from the insufficient supply of thermal energy at 400 °C such that the rearrangement of atoms is incomplete in the processing time, which may lead to the poor accommodation of the atoms, and thereby increasing the residual stress.