For the first time, the present study investigates the corrosion, surface, and subsurface properties of a shot-peened Ti6Al4V powder metallurgical alloy produced via pressure-assisted sintering. Shot ...peening yielded a fine-grained microstructure beneath the surface down to 100 microns, showing that it caused severe plastic deformation. XRD analysis revealed that the sizes of the crystallites in unpeened and shot-peened Ti6Al4V alloy samples were 48.59 nm and 27.26 nm, respectively, indicating a substantial reduction in crystallite size with shot peening. Cross-sectional hardness maps of shot-peened samples showed a work-hardened surface layer, indicating a ~17% increase in near-surface hardness relative to unpeened samples. Three-dimensional surface topographies showed that shot peening yielded uniform peaks and valleys, with a maximum peak height of 4.83 μm and depth of 6.56 μm. With shot peening, the corrosion potential shifted from −0.386 V to −0.175 V, showing that the passive layer developed faster and was more stable than the unpeened sample, improving corrosion resistance. As determined via XRD analysis, the increased grain refinement (i.e., the number of grain boundaries) and the subsequent accumulation of TiO2 and Al5Ti3V2 compounds through shot peening also suggested the effective formation of a protective passive layer. As demonstrated via electrochemical impedance spectroscopy, the formation of this passive film improved the corrosion resistance of the alloy. The findings will likely advance surface engineering and corrosion research, enabling safer and more productive shot peening in corrosion-critical applications.
Titanium alloys have been used in biomedical and aerospace applications owing to their excellent biocompatibility, high strength/weight ratio, and high corrosion resistance. The reactivity of contact ...surfaces of titanium alloys can be improved by roughening up the surface via grit blasting, which significantly improves the biocompatibility and the adhesion strength between substrate and coating for coating applications. This study investigates the effects of grit blasting parameters (grit size and blasting pressure) on the 3D surface topography, areal surface roughness, and surface morphologies of Ti6Al4V alloy. Ti6Al4V alloy specimens were blasted by various size garnet particles (20/40 and 180 mesh) under different blasting pressures (1.5, 3, and 4 bar) at constant particle impingement angle (90°). 3D optical microscope analyses and scanning electron microscopy analyses were carried out to determine the areal surface roughness, 3D surface topographies, and morphologies of the grit blasted specimens. The increases in particle size and blasting pressure increased the surface roughness of the specimens. The 3D surface topographies of grit blasted specimens were visualized and discussed. The 3D surface topographies and morphologies of the specimens were varied depending on both parameters. Finally, particle embedment was determined due to the grit blasting and detected via EDS analysis.
High-velocity air fuel (HVAF) coating processes have advantages over conventional high-velocity oxygen fuel (HVOF) processes, resulting in coatings with superior properties. The present review first ...provides a concise overview of HVAF coatings, highlighting their advantages over HVOF coatings. Then, the fundamentals of solid particle, slurry, and cavitation erosion are briefly introduced. Finally, the performance of HVAF coatings for erosion-resistant applications is discussed in detail. The emerging research consistently reports HVAF-coatings having higher erosion resistance than HVOF-coatings, which is attributed to their elevated hardness and density and improved microstructural features that inhibit the surface damages caused by erosion. The dominant wear mechanisms are mainly functions of particle impact angle. For instance, the removal of the binder phase at high impact angles causes the accumulation of plastic strain on hard particles (e.g., WC particles) in the matrix, forming micro-cracks between the hard particles and the matrix, eventually decreasing the erosion resistance of HVAF coatings. The binder phase of HVAF-coatings significantly affects erosion resistance, primarily due to their inherent mechanical properties and bearing capacity of hard particles. Optimizing spraying parameters to tailor the microstructural characteristics of these coatings appears to be the key to enhancing their erosion resistance. The relationship between microstructural features and erosion mechanisms needs to be clarified to process coatings with tailored microstructural features for erosion-resistant applications.
The objectives of this study were to compare the fracture strength of endocrown restorations fabricated with different preparation depth and various CAD/CAM ceramics, and to assess the fracture ...types. Endodontically treated 100 extracted human permanent maxillary centrals were divided into two preparation depth groups as short (S : 3-mm-deep) and long (L : 6-mm-deep) , then five ceramic subgroups, namely : feldspathic-ceramic (Vita Mark II-VM2) , lithium-disilicate glass-ceramic (IPS e.max CAD-E.max) , resin-ceramic (LAVA Ultimate-LU) , polymer infiltrated ceramic (Vita Enamic-VE) and monoblock zirconia (inCoris TZI-TZI) (n=10/subgroup) . The endocrowns were fabricated by CAD/CAM and were cemented with resin cement (RelyX U200) . The teeth were thermally cycled (5,000cycles) and fracture tests were performed at 45° angle to the teeth. The data were statistically analyzed (Kruskal-Wallis, Mann Whitney U) , failure modes were evaluated with stereomicroscopy. Zirconia group provided the statistically highest fracture strength, but also exhibited non-repairable failures. Preparation depth has an effect on the fracture strength only for feldspathic ceramic.
The present study reveals for the first time the dry sliding wear behavior of a powder metallurgical pure titanium alloy (Cp-Ti) modified by shot peening. Cp-Ti samples were manufactured via powder ...metallurgy, and then their surface and subsurface features were modified using a custom-made, fully automated shot-peening system. The texture isotropy rate and the highest orientation angle of the shot-peened samples were 71.5% and 36°, respectively. The Abbott curves of the shot-peened surfaces revealed that the most common areal roughness value was 5.177 μm, with a frequency of 8.1%. Shot-peened surfaces exhibited an ~20% lower wear rate than unpeened surfaces under dry sliding wear, whereas the coefficient of friction was the same for both surfaces. Micro-ploughing, micro-cutting, oxidation, and three-body abrasion wear mechanisms were observed on the shot-peened and unpeened surfaces. High resolution 3D surface topographies of worn unpeened and shot-peened surfaces revealed micro-scratches and inhomogeneities along wear tracks, which are indicative of three-body abrasion mechanisms during contact. In addition, vertical and horizontal microcracks were visible just beneath the wear track, suggesting a clear indication of plastic deformation during contact. The cross-sectional hardness maps of shot-peened samples revealed the formation of a work-hardened surface layer with shot peening, which improved the wear resistance. These findings support that shot peening can be a useful tool to modify the surface and tribological properties of powder metallurgical Cp-Ti alloys.
The process of machining micro surface patterns on a workpiece to improve various performance
aspects of engineering materials, including wear resistance, corrosion resistance,
and biocompatibility, ...has been a hot topic of research in recent years. Due to the restricted
machinability of titanium and its alloys, it is very challenging to process micro surface patterns
with exact surface geometries using traditional machining methods. Consequently,
non-traditional processing techniques, such as laser, electro-erosion, and chemical etching,
may overcome these obstacles. In the present study, electrical discharge machining (EDM)
is used to form micro surface patterns on Cp-Ti alloy samples. First, graphite electrodes
with several channels were manufactured, and then square-shaped surface patterns were
processed onto Cp-Ti samples using EDM. To evaluate the machining performance of the
process and surface features of the obtained micro surface patterns, the surface morphology
and topography of the processed samples were investigated by scanning electron microscopy
(SEM) and three-dimensional (3D) optical profilometry, respectively. The average
widths of the square-shaped surface patterns along the X and Y axes were 663.7±8 μm and
609.5±4 μm, respectively. For micro surface designs with square geometry, dimensional
consistency was obtained with exceedingly small amounts of variation. However, a limited
number of microcracks were observed due to rapid cooling during the processing of the
surface patterns. The 3D surface topographies revealed that square-shaped micro surface
patterns were successfully processed on the samples, indicating that micro surface patterns
can be processed on Cp-Ti samples by using the proposed methodology, which has the
potential for obtaining tailor-designed surface features, particularly for biomedical and tribological
applications.
