Assessment of titanium metallization thin film deposited on alumina substrate: Microstructure and nano-indentation.

Surface titanium (Ti) metallization was conducted on alumina (Al2O3) through chemical vapor deposition (CVD) method derived from non-contact pack cementation. The effects of different deposition temperature (1000 °C, 1050 °C, and 1100 °C) were examined in this scenario. The morphology, phase composition, and interfacial defects of the resulting films were systematically investigated through scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction. The nanomechanical characterization of the proposed thin films was evaluated by conducting nano-indentation tests at different depths. The results revealed that uniform Ti films were coated on the Al2O3 substrate. During coating, the atoms on the matrix surface were driven to form different structure due to different deposition temperature, leading to disparate morphologies of the surface and the interface, which consequently influenced the binding force between the film and the substrate. Moreover, the nanomechanical properties were found to be related to the internal and interface structure. Decreased modulus and hardness were obtained for metallization films treated at 1050 °C, and plastic deformation was the main deformation pattern.

Quasi-static and dynamic experimental studies on the tensile strength and failure pattern of concrete and mortar discs.

As concrete and mortar materials widely used in structural engineering may suffer dynamic loadings, studies on their mechanical properties under different strain rates are of great importance. In this paper, based on splitting tests of Brazilian discs, the tensile strength and failure pattern of concrete and mortar were investigated under quasi-static and dynamic loadings with a strain rate of 1-200 s-1. It is shown that the quasi-static tensile strength of mortar is higher than that of concrete since coarse aggregates weaken the interface bonding strength of the latter. Numerical results confirmed that the plane stress hypothesis lead to a lower value tensile strength for the cylindrical specimens. With the increase of strain rates, dynamic tensile strengths of concrete and mortar significantly increase, and their failure patterns change form a single crack to multiple cracks and even fragment. Furthermore, a relationship between the dynamic increase factor and strain rate was established by using a linear fitting algorithm, which can be conveniently used to calculate the dynamic increase factor of concrete-like materials in engineering applications.

Strain-induced phase transformation behavior of stabilized zirconia ceramics studied via nanoindentation.

To study the tetragonal-to-monoclinic (T-M) phase transformation behavior under different strain rates and indentation depths, nanoindentation tests were performed on stabilized zirconia ceramics with Continuous Stiffness Measurements. The results indicate decreased phase transformation velocities at both lower and higher strain rates, but increased velocity under medium strain rate during loading. The phase transformation process is sensitive to P/P but the final volume fractions are almost identical (45%). Furthermore, most of the phase transformation is completed during a short initial time followed by slight linear increase of the M-phase volume fraction with holding time. The phase transformation continuously slowed with increasing indentation depth when indented with a constant strain rate.

Spherical and cylindrical cavity expansion models based prediction of penetration depths of concrete targets.

The cavity expansion theory is most widely used to predict the depth of penetration of concrete targets. The main purpose of this work is to clarify the differences between the spherical and cylindrical cavity expansion models and their scope of application in predicting the penetration depths of concrete targets. The factors that influence the dynamic cavity expansion process of concrete materials were first examined. Based on numerical results, the relationship between expansion pressure and velocity was established. Then the parameters in the Forrestal's formula were fitted to have a convenient and effective prediction of the penetration depth. Results showed that both the spherical and cylindrical cavity expansion models can accurately predict the depth of penetration when the initial velocity is lower than 800 m/s. However, the prediction accuracy decreases with the increasing of the initial velocity and diameters of the projectiles. Based on our results, it can be concluded that when the initial velocity is higher than the critical velocity, the cylindrical cavity expansion model performs better than the spherical cavity expansion model in predicting the penetration depth, while when the initial velocity is lower than the critical velocity the conclusion is quite the contrary. This work provides a basic principle for selecting the spherical or cylindrical cavity expansion model to predict the penetration depth of concrete targets.

Microstructure, corrosion and tribological and antibacterial properties of Ti-Cu coated stainless steel.

A Ti-Cu coated layer on 316L stainless steel (SS) was obtained by using the Closed Field Unbalanced Magnetron Sputtering (CFUBMS) system to improve antibacterial activity, corrosion and tribological properties. The microstructure and phase constituents of Ti-Cu coated layer were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and glow discharge optical emission spectrometry (GDOES). The corrosion and tribological properties of a stainless steel substrate, SS316L, when coated with Ti-Cu were investigated in a simulated body fluid (SBF) environment. The viability of bacteria attached to the antibacterial surface was tested using the spread plate method. The results indicate that the Ti-Cu coated SS316L could achieve a higher corrosion polarization resistance and a more stable corrosion potential in an SBF environment than the uncoated SS316L substrate. The desirable corrosion protection performance of Ti-Cu may be attributable to the formation of a Ti-O passive layer on the coating surface, protecting the coating from further corrosion. The Ti-Cu coated SS316L also exhibited excellent wear resistance and chemical stability during the sliding tests against Si3N4 balls in SBF environment. Moreover, the Ti-Cu coatings exhibited excellent antibacterial abilities, where an effective reduction of 99.9% of Escherichia coli (E.coli) within 12h was achieved by contact with the modified surface, which was attributed to the release of copper ions when the Ti-Cu coatings are in contact with bacterial solution.