Key Engineering Materials Vols. 353-358

Abstract: Yttria Stabilized Zirconia (YSZ) films were prepared by electron beam physical vapor deposition (EB-PVD) technique with a high deposition rate up to 1μm/min. An improved sin2ψ method was employed to analyze the residual stress of films by means of grazing incidence X-ray diffraction (GIXRD). The result of residual stress measurement reveals that residual stress of YSZ film is compressive stress and keeps a linear relationship with the deposition temperature, which is induced mainly by the thermal expansion mismatch between the film and substrate. The XRD result of films, prepared with different incident angles, demonstrates that the films show preferred orientation evidently. Furthermore, a parameter ωhkl was introduced from the inverse polar figure measurement theory to reveal the degree of preferred orientation clearly. The calculating result of ωhkl value indicates that the preferred orientation of different specimens changes with the incident angles, which is due to columnar growth pattern of films prepared by EB-PVD. In order to characterize the crystallographic texture visually, XRD with 2D detector system was used to analyze the texture of films. The result shows that Debye rings appear asymmetric intensively, which denotes the existence of preferred orientation directly and agrees with the calculating result of ωhkl value.

Abstract: Temperature rise has two-edged influences on chemical mechanical polishing (CMP) process: temperature-rise facilitates the chemical activity and the motion of the nano particles contained in the slurry through which material removal ratio (MRR) is enhanced; to the other side of the same coin, however, it will soften the pad surface and subsequently reduce the MRR. Thus the research on temperature distribution of CMP process will be conducive to discovering the mechanism of polishing, and acquiring stable MRR and improving surface quality. With the help of the knowledge of tribology, hydrodynamics, and thermodynamics, flow equation considering the temperature variation in the fine step of CMP process, wherein high surface quality is the main concern and usually operates in contact free state, is set up, based on which the temperature field in contact is investigated in detail by taking advantage of the simulation technique, and the heat energy production and transition relations are obtained. Due to the slurry used, a small viscous heating effect is acknowledged by simulated results, and the temperature rise is negligible in contact-free flows, which is very conducive to the promotion of the final polished wafer/disk surfaces. The research will surely shed some lights in the mechanism of CMP and lay a feasible foundation for possible future utilization.

Abstract: Improved corrosion resistance of carbon fiber reinforced aluminum (Cf/Al) matrix composites can be achieved by applying appropriate coatings, and the electroless plating nickel-phosphor (Ni-P) coatings on the Cf/Al composites was provided in this paper. It has been founded that the pretreatment with zinc dipping solution for the electroless plating Ni-P can be approved perfect coatings on the Cf/Al composites. The EDS lines scanning results that the length of Ni-P coating is about 12 +m. In zinc dipping bath, matrix Al alloy surface could catch hold of action points for depositing Ni-P with substitution reaction, however, carbon fibers surface only have adsorption action points from zinc dipping bath, then, Ni-P alloys could deposit on the Al surface or carbon fibers. The uncoated and coated composites samples immersed in 3.5 wt % NaCl solution to contrast. The pitting corrosion behavior of the uncoated composites destroyed materials, therefore, the coated sample appeared pitting only on the surface. The corrosion resistance mechanisms of Ni-P coatings came from inhabiting the formation of the classical galvanic corrosion, additionally, the Ni-P coating was amorphous structure, there was not grains boundary which is sensitive for the corrosion reaction, so the corrosion resistant of Cf/Al composites were improved.

Abstract: Hydroxyapatite (HA) active coatings on Titanium were prepared using Spark Plasma Sintering (SPS). This study focused on the effects of the composition and thickness of coating on its bonding strength and the fracture appearance. The results showed that the Ti20wt%HA80wt% coating on Titanium could be well sintered, and bonding strength was improved from 12 MPa to 29 MPa and to 36 MPa along with the reduction of the coat thickness from 0.3mm to 0.2mm and to 0.1mm respectively. When the coating was treated by passivation, the bonding strength of interface increased largely to 48MPa and 64MPa respectively for HA coating and Ti20wt%HA80wt% coating on Titanium body, which the HA did not disassemble, and metallurgical combination between coating and metal was realized at 1180K.

Abstract: A continuum model of the evolution of air ingestion and entrainment for open-ended squeeze film dampers is proposed in this paper. Hydrodynamic lubrication theory is extended to lubrication with mixture of a Newtonian liquid and an ideal gas. The solution to the universal Reynolds equation is determined numerically using a control volume method (Elrod algorithm) and the forth-order Range-Kutta method. This method conserves mass throughout the computational domain including air ingestion and entrainment. Excellent agreement is found with the experimental works of Diaz and San Andrès for the squeeze film damper [1, 2].

Abstract: The corrosion surface of hot-dip galvanized steel is regarded to be fractal and contains abundant self-similar information. In most cases, the corrosions of surface are not uniform as considered. For such an uneven eroded surface, regional fractals are introduced here in order to improve the analysis accuracy for local corrosions. Basing on the singular value decomposition of surface image, fractal dimensions of the energy norm along with the energy scale are analyzed. Combining energy norm of singular values and wavelet transform, the corrosion surfaces are described in different scales and decomposed levels.

Abstract: The interface bonding between the carbides and the solid solution matrix is studied in surfacing welding metal of Fe-Nb-Ti-V-C alloy system. Both the quenched welding droplets and the deposited metal are investigated by means of SEM and TEM. In the deposited metal, the carbides are dispersed, and the matrix is low carbon martensite. According to welding metallurgical characteristics, it is deduced that the carbides are formed during the droplets stage and then transmit into the welding pool. When the welding pool solidify, the carbides serve as nucleation site, so the interface between the carbides and the matrix is clean and free from other reactants. The selected area electron diffraction (SAED) analysis reveals that the mismatch between the two phase is δ= (6.1~8.3)%, and there exist a crystal parallel relationship at the interface: (002)α-Fe // (220)(NbTiV)C. The metallurgical bonding between the carbides and the matrix favors to prevent the carbides to detach from the matrix during wear process, so the surfacing welding metal can achieve good wear-resistance.

Abstract: A type of wear resistance coating material composed by ternary-boride-based (TBB) cermet coating and steel 65Mn substrate has been developed successfully by in-situ reaction synthesis. The TBB cermet coating has been formed by the in-situ reactions among the mixed raw metal powders during the process of casting. Microstructure has been studied using X-Ray Diffraction (XRD) and scanning electron microscopy (SEM). Results show that the main composition of the coating is ternary boride base hard phase Mo2FeB2 and ferrous base binder phase α-Fe, both of them distribute uniformly in the coating. There is element diffusion in the interface of coating and steel substrate. The bonding at the interface of coating and steel substrate is excellent which has been confirmed by the three-point bend tests.

Abstract: Ti/TiN multilayer films were synthesized on 17-4PH stainless steel using unbalanced magnetron sputtering. The modulation periods is ranged from 100nm to 350 nm. The microstructure of the multilayer films was analyzed by X-ray diffraction. The cross-section views of the multilayer films were studied by scanning electron microscope (SEM). The microhardness and wear resistance of the films were measured by a HXD-1000 microhardness tester and ball-on-disk wear tester. The corrosion resistance of the multilayer films was evaluated by potentiodynamic polarization scans in a 3% NaCl solution. The results showed that there was TiNx intergradation layer in the films. The microhardness and the wear resistance of the multilayer films increased with the layer number. The Ti/TiN multilayer can improve the corrosive resistance of the 17-4PH stainless steel.

Abstract: In order to prevent stress corrosion cracking (SCC) of austenitic stainless steel weldment, a novel technique -laser peening- has been introduced which is able to convert surface tensile stresses in the weldment to surface compressive stresses. In this paper, water-immersed welded specimens of type 304 stainless steel are peened by Q-switched Nd: glass laser with a wavelength of 1.06μm. A residual compressive layer is produced on the specimen surface by scanning laser pulse to cover the heat affected zone (HAZ) along the weld line. The residual compressive stress value based on X-ray measure is significant enough to prevent the initiation of stress corrosion cracking that is also validated by the finite element analysis. The SCC accelerated tests for comparing the potential against SCC of the specimens, which are unpeened and peened by laser pulse with different laser spot coverage, are carried on. The results show that stress corrosion cracks on the surface of unpeened specimen occur after immersion for 25 hours in boiling 42% MgCl2 solutions at 143°C. In contrast, the specimen with 45% laser spot coverage cracks after immersion for 300 hours, while, cracks are observed on the surface of laser-peened specimen with 80% laser spot coverage after 985 hours of testing. The results show that laser peening is an effective technique for improving the residual stress distribution and the SCC resistance of 304 stainless steel weldment.