Jia-Hong Huang

Residual stress measurement in textured thin film by grazing-incidence X-ray diffraction

Measurements of residual stresses in textured thin films have always been problematic. In this article, a new experimental method using grazing-incidence X-ray diffraction is presented with its principles based upon the conventional sin c method. 2 Instead of using the Bragg–Brentano (B-B) or Seemann–Bohlin geometry, the proposed method utilizes an asymmetrical diffraction geometry for which the X-ray beam is incident at a grazing angle g to the sample surface, while the angle c is the tilt angle of the sample surface as defined by the conventional sin c method. Basicequations involved in the X-ray residual 2

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.

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.

Effect of hydrogen contents on the mechanical properties of Zircaloy-4

Abstract Zircaloy-4 plate specimens were gaseously hydrided up to 340 ppm H and then tested at 25, 100, 200 and 300°C. Notched tensile specimens were chosen to better understand the ductile-brittle transition associated with hydrogen content. The results showed that, at 25°C, a ductile-brittle transition occurred on the notched specimens of zircaloy-4 with hydrogen contents between 30 ppm and 140 ppm. The ductile-brittle transition became less distinct as temperature increased to 100°C and above. This was attributed to the improved ductility of the zirconium matrix by examining the temperature dependence of fracture surface and hydride morphology. Load serrations were observed on the hydrided, notched specimens tested at 200°C and above, which was related to dynamic strain aging. The stress-strain curves exhibited yield points on the specimens without hydriding. The yield points were suppressed on the hydrided specimens, which was explained by the mechanism that twinning-assisted slip may be hindered by hydrides.

Aging embrittlement and lattice image analysis in a Fe-Cr-Ni duplex stainless steel aged at 400°C

Abstract Aging embrittlement, normally observed in ferritic stainless steels, was found in a Fe-Cr-Ni duplex stainless steel thermally aged at 400°C for a long time. The ferrite content and composition of the duplex stainless steel was changed by varying the solution annealing temperature in order to investigate the effect of ferrite phase on the aging embrittlement. The material was aged at 400°C up to 10 000 h. Aging embrittlement was characterized by microhardness and other mechanical tests. The results show that the aging embrittlement of the duplex stainless steel was attributed to the degradation in ferrite phase. Microstructural studies in the ferrite phase indicated that spinodal decomposition and G-phase precipitation led to the degradation. High resolution electron microscopy (HREM) was utilized to analyze the lattice images of G-phase and ferrite matrix. The extent of embrittlement was found to be strongly dependent on the ferrite content and the composition in ferrite. The Ni content in ferrite seems to play an important role in aging embrittlement by promoting G-phase precipitation. As Ni content increased in the ferrite, the degradation of the material aged at 400°C became more severe.