Alex Volinsky - Academia.edu (original) (raw)

Papers by Alex Volinsky

Coatings

Hydroxyapatite coatings were deposited for 1, 2, and 3 h on NiTi substrates using plasma-assisted... more Hydroxyapatite coatings were deposited for 1, 2, and 3 h on NiTi substrates using plasma-assisted radio frequency sputtering. The matrix consisted of NiTi B2 and NiTi B19’ phases and Ti2Ni, Ni3Ti, and Ni4Ti3 intermetallic compounds. The surface coating was monoclinic hydroxyapatite. Increasing the deposition time to 3 h made it possible to form a dense hydroxyapatite layer without visible defects. The phase contrast maps showed that the coating consisted of round grains of different fractions, with the smallest grains in the sample deposited for 3 h. The wettability tests showed that the coating deposited for 3 h had the highest surface energy, reflected in the proliferation density of the MCF-7 cell line.

$Research paper thumbnail of Mechanical characterization of high volume fraction Al7075-Al2O3 composite fabricated by semisolid powder processing$

The International Journal of Advanced Manufacturing Technology

The mechanical properties and physical characteristics of aluminum alloy composites can be signif... more The mechanical properties and physical characteristics of aluminum alloy composites can be significantly improved by adding reinforcing phases. However, the high loading of the reinforcement phase in Al7075-Al2O3 composites has not been thoroughly studied. In this work, a combination of semisolid metal powder processing and powder metallurgy is used to process and manufacture Al7075-Al2O3 composites with a high reinforcement fraction of > 40 vol.%. The effects of processing parameters on the microstructures and mechanical properties of the composite material are discussed in detail. The loading limits of the high volume Al2O3 reinforcement in Al7075 composites are identified and linked to the processing parameters. A methodology is introduced to estimate the consolidation temperature of Al7075 alloy using compaction testing. Al2O3 particles (the average particle size of 120 µm) were mechanically milled with Al7075 powder (the average particle size of 20 µm) for 10 min and 5 h usi...

Journal of Polymer Research

Engineering Failure Analysis, 2020

Scanning and transmission electron microscopy was used to characterize quantity, pattern, size, a... more Scanning and transmission electron microscopy was used to characterize quantity, pattern, size, and distribution of microstructure and precipitated phases in T91 steel exposed to high temperature in the subcritical unit superheater of a specific power plant. The materials were mechanically and electrochemically tested using a universal testing machine and an electrochemical workstation. The structure and performance of the original material and after the long-term service time were compared. The hardness and strength of T91 steel initially increased before they decreased during long-term service. It took 4000 h for the T91 steel to transform from the original to the service state, forming (Cr, Fe, V, Mo) 23 C 6 multi-component mixed phase, which delayed or inhibited the growth of the M 23 C 6-type carbides during the long-term high-temperature service. The MX-type carbide formation would pin dislocations and increase the strength. When the service time was between 4000 and 130,000 h, the carbide coarsening was obvious, and the effect of solid solution strengthening was reduced, the dislocation density was decreased, reducing the material's strength below the original state level. Electrochemical tests showed that longer service time degraded corrosion resistance of the T91 steel.

$Research paper thumbnail of Mechanical properties and fracture characteristics of cemented tungsten carbide with fine microstructure studied by nanoindentation$

International Journal of Surface Science and Engineering, 2008

This study systematically investigates the influence of hole shape on mechanical properties and f... more This study systematically investigates the influence of hole shape on mechanical properties and fracture characteristics of rocks containing a hole under uniaxial loading. First, combined with digital image correlation (DIC) and acoustic emission (AE) equipment, quantities of uniaxial compression tests on brittle prismatic sandstone samples containing a circular, inverted U-shaped, trapezoid, rectangular or square hole were conducted to study the strength, deformation and fracture characteristics. After that, the analytical solutions of stress for the five types of holes were derived using complex variable function theory. The experimental results suggest that the mechanical properties of the samples are greatly weakened by the existence of the holes, and the degradation degree depends on the hole shape. The stability order of these holes is ranked as: circle > inverted Ushape > trapezoidal > square > rectangle. According to the formation mechanism and sequence, four types of cracks, namely, primary tensile cracks, slabbing fractures, remote cracks and shear cracks, are formed around all the holes, but the crack sequence, initiation location and propagation characteristics of each hole are slightly different. The variation of AE signals matches well with the fracture evolution. The shear failure mode results from the coalescence of the shear cracks and V-shaped notches. Theoretical analysis shows that crack development mechanism can be well interpreted by the stress distributions around the holes. Moreover, the length of the primary tensile cracks is theoretically solved and compared, which is agreeable with the measured result.

SSRN Electronic Journal, 2021

Materials (Basel, Switzerland), Jan 20, 2017

In the current study, the properties of the CrxN coatings deposited on the Inconel 718 superalloy... more In the current study, the properties of the CrxN coatings deposited on the Inconel 718 superalloy using direct current reactive magnetron sputtering are investigated. The influence of working pressure on the microstructure, mechanical, and tribological properties of the CrxN coatings before and after high-temperature hydrogen exposure is studied. The cross-sectional scanning electron micrographs indicate the columnar structure of the coatings, which changes from dense and compact columns to large columns with increasing working pressure. The Cr/N ratio increases from 1.4 to 1.9 with increasing working pressure from 300 to 900 mPa, respectively. X-ray diffraction analysis reveals a change from mixed hcp-Cr₂N and fcc-CrN structure to approximately stoichiometric Cr₂N phase. After gas-phase hydrogenation, the coating deposited at 300 mPa exhibits the lowest hydrogen absorption at 600 °C of all investigated coatings. The results indicate that the dense mixed cubic and hexagonal structur...

Journal of Materials Engineering and Performance, 2016

MRS Proceedings, 2000

ABSTRACTIn this study, film interfacial fracture is induced by nanoindentation to quantify the pr... more ABSTRACTIn this study, film interfacial fracture is induced by nanoindentation to quantify the practical work of adhesion of a post-CMP copper film to an amorphous silicon nitride passivation film. Poor adhesion of electrodeposited copper to SiN passivation is observed following CMP due to copper oxide growth prior to plasma enhanced silicon nitride deposition. Four point bend testing has shown that failure by brittle fracture of test structures occurs at the Cu/CuO interface. Hydrogen, ammonia, and nitrogen plasma treatments of the post-CMP copper surface can be used to remove the oxide, shown by auger electron spectroscopy, and to increase the surface roughness of copper, shown by atomic force microscopy. Both effects can be used to improve the Cu/SiN adhesion. Nanoindentation with a conical indenter (1.59 μm tip radius) was used to induce SiN film delaminations from Cu, the sizes of which were measured and correlated with the practical work of adhesion.[1,2] In order to more reli...

RSC Advances, 2014

The catalytic effects of CoFe2O4 nanoparticles on the hydrogen storage properties of LiAlH4 prepa... more The catalytic effects of CoFe2O4 nanoparticles on the hydrogen storage properties of LiAlH4 prepared by ball milling were investigated.

NATO Science for Peace and Security Series C: Environmental Security, 2009

This paper reviews tecrrniques for measurement of basic mechanical properties of thin films. Emph... more This paper reviews tecrrniques for measurement of basic mechanical properties of thin films. Emphasis is placed on the adaptations needed to prepare, handle, and characterize thin films, and on adaptaiions of fracture mechanics for adhesion strength. The paper arso describes a recent deveropment, the use of electrical current as a controlled means of applying thermo_ mechanical stresses to electrical conductors to characterir" itr"i. fatigue behavior.

MRS Proceedings, 2008

ABSTRACTThe addition of water results in the higher wear rate of gold compared to experiments per... more ABSTRACTThe addition of water results in the higher wear rate of gold compared to experiments performed in the ambient environment (approximately 60% humidity). This higher wear rate in water has been observed with the AFM, Hysitron Triboindenter, and additionally in single pass scratch tests performed with the Taber Shear/Scratch tester. These tests were preformed using silicon nitride cantilevers on the AFM and a conical diamond tip in the Taber instrument. Tests performed in the ambient atmosphere resulted in slightly reduced surface roughness, while much higher wear rate was observed in the wear tests performed in water. Ambient scratch tests produced slightly shallower scratch trenches than wet scratches consistently as a function of the varied normal load. Single scan lines provide valuable information about the mechanisms and progression of the nanoscale wear. The different components of scratch friction are investigated to explore the main contributors to the nanoscale scrat...

MRS Proceedings, 2007

There is a technological need for hard thin films with high elastic modulus and fracture toughnes... more There is a technological need for hard thin films with high elastic modulus and fracture toughness. Silicon carbide (SiC) fulfills such requirements for a variety of applications at high temperatures and for high-wear MEMS. A detailed study of the mechanical properties of single crystal and polycrystalline 3C-SiC films grown on Si substrates was performed by means of nanoindentation using a Berkovich diamond tip. The thickness of both the single and polycrystalline SiC films was around 1-2 μm. Under indentation loads below 500 μN both films exhibit Hertzian elastic contact without plastic deformation. The polycrystalline SiC films have an elastic modulus of 457 GPa and hardness of 33.5 GPa, while the single crystalline SiC films elastic modulus and hardness were measured to be 433 GPa and 31.2 GPa, respectively. These results indicate that polycrystalline SiC thin films are more attractive for MEMS applications when compared with the single crystal 3C-SiC, which is promising since g...

Thin Solid Films, 2013

Diamond-like carbon (DLC) thin films were deposited on p-type Si (100) substrates by RF hollow ca... more Diamond-like carbon (DLC) thin films were deposited on p-type Si (100) substrates by RF hollow cathode method under different RF power and pressure, using ethane as the precursor gas. The deposition rate of 45 nm/min was achieved, almost 4 times higher than by conventional radio frequency plasma enhanced chemical vapor deposition. The mechanism of fast DLC films deposition is attributed to high plasma density in RF hollow cathode method, discussed in this paper. Scanning electron microscopy and Raman spectroscopy were used to investigate the microstructure of DLC films. The film hardness and Young's modulus were measured by nanoindentation.

Journal of Materials Research, 2004

This paper describes the nanoindentation technique for measuring sputter-deposited Au and Cu thin... more This paper describes the nanoindentation technique for measuring sputter-deposited Au and Cu thin films’ mechanical properties at elevated temperatures up to 130 °C. A thin, 5-nm Pt layer was deposited onto the Cu film to prevent its oxidation during testing. Nanoindentation was then used to measure elastic modulus and hardness as a function of temperature. These tests showed that elastic modulus and hardness decreased as the test temperature increased from 20 to 130 °C. Cu films exhibited higher hardness values compared to Au, a finding that is explained by the nanocrystalline structure of the film. Hardness was converted to the yield stress using both the Tabor relationship and the inverse method (based on the Johnson cavity model). The thermal component of the yield-stress dependence followed a second-order polynomial in the temperature range tested for Au and Pt/Cu films. The decrease in yield stress at elevated temperatures accounts for the increased interfacial toughness of Cu...