Tribological properties of HVOF-sprayed WC-Co coatings deposited from Ni-plated powders at elevated temperature

Jafari, Majid,Han, Jong-Chan,Seol, Jae-Bok,Park, Chan-Gyung Elsevier Sequoia 2017 Surface & coatings technology Vol.327 No.-

<P><B>Abstract</B></P> <P>WC-Co coatings with low degree of WC decomposition were deposited from electroless Ni-plated micro- and nano-structured feedstock powders using high velocity oxygen fuel (HVOF) spraying. Dry sliding friction and wear behavior of the resultant coatings, referred to as Ni/mc-WC and Ni/nc-WC, were investigated by using sintered alumina (Al<SUB>2</SUB>O<SUB>3</SUB>) as the mating material at 700°C. For the purpose of comparison, similar experiments were carried out on conventional micro- and nano-structured coatings, denoted as mc-WC and nc-WC. The worn scars were examined by field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectroscopy (EDS). The wear resistance of Ni/mc-WC and Ni/nc-WC coatings at 700°C was found to be 45% and 72% greater than that of mc-WC and nc-WC coatings, respectively. Moreover, Ni/mc-WC and Ni/nc-WC coatings exhibited a significantly lower friction coefficient with negligible fluctuations as compared to mc-WC and nc-WC. The microscopic analyses of mc-WC and nc-WC worn surface revealed the presence of plastically deformed and discontinuous tribofilms, made up of a mixture of MWO<SUB>4</SUB>/WO<SUB>3</SUB> (M=Co) and Al<SUB>2</SUB>O<SUB>3</SUB>, severe cracking and delamination especially at the interface of tribofilm and the underlying surface. In contrast, examination of Ni/mc-WC and Ni/nc-WC substantiated that a large area of the coatings surface is covered by a dense and adhered MWO<SUB>4</SUB>-type oxide layer (M=Co, Ni), which provides a more protection against wear at elevated temperature.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Wear resistance of Ni/mc-WC at 700°C was enhanced by 45% compared to mc-WC coating. </LI> <LI> Ni/nc-WC showed 72% improvement in wear resistance at 700°C relative to nc-WC. </LI> <LI> Type of oxide layer formed on wear track at 700°C has a key role on wear resistance. </LI> <LI> For mc-WC and nc-WC, tribofilm was comprised of a mixture of CoWO<SUB>4</SUB>/WO<SUB>3</SUB> and Al<SUB>2</SUB>O<SUB>3</SUB>. </LI> <LI> For Ni/mc- and Ni/nc-WC, dense and adhered MWO<SUB>4</SUB> oxide formed on wear track at 700°C. </LI> </UL> </P>

Comparative Study of Poly(L-Lactic Acid) Scaffolds Coated with Chitosan Nanoparticles Prepared via Ultrasonication and Ionic Gelation Techniques

Majid Salehi,Mahdi Naseri-Nosar,Mahmoud Azami,Saeedeh Jafari Nodooshan,Javad Arish 한국조직공학과 재생의학회 2016 조직공학과 재생의학 Vol.13 No.5

In this study, an attempt was made to develop bi-functional constructs serving both as scaffolds and potential delivery systems for application in neural tissue engineering. The constructs were prepared in two steps. In the first step, the bulks of poly (L-lactic acid) (PLLA) in 1, 4-dioxane/water (87:13) were fabricated using liquid-liquid thermally induced phase separation technique. In the next step, the prepared bulks were coated with chitosan nanoparticles produced by two different techniques of ultrasonication and ionic gelation by grafting-coating technique. In ultrasonication technique, the chitosan solution (2 mg/mL) in acetic acid/sodium acetate buffer (90:10) was irradiated by an ultrasound generator at 20 kHz and power output of 750 W for 100 s. In ionic gelation technique, the tripolyphosphate in water solution (1 mg/mL) was added to the same chitosan solution. The physicochemical properties of the products were characterized by Scanning Electron Microscopy, Attenuated Total Reflection Fourier Transform-Infrared, liquid displacement technique, contact angle measurement, compressive and tensile tests, as well as zeta potential and particle size analysis using dynamic light scattering. Moreover, the cell proliferation and attachment on the scaffolds were evaluated through human glioblastoma cell line (U-87 MG) and human neuroblastoma cell line [BE (2)-C] culture respectively. The results showed that the samples coated with chitosan nanoparticles prepared by ultrasonication possessed enhanced hydrophilicity, biodegradation and cytocompatibility compared with pure PLLA and PLLA coated with chitosan nanoparticles prepared by ionic gelation. This study suggests successful nanoparticles-scaffold systems which can act simultaneously as potential delivery systems and tissue engineering scaffolds.

Competitive grain boundary segregation of phosphorus and carbon governs delamination crack in a ferritic steel

Han, Jong-Chan,Seol, Jae-Bok,Jafari, Majid,Kim, Ju-Eun,Seo, Seok-Jong,Park, Chan-Gyung Elsevier 2018 Materials characterization Vol.145 No.-

<P><B>Abstract</B></P> <P>The present study aims at unveiling the influence of trace amounts of phosphorus on the macro-scale delamination in a ferritic steel. Two different steels with trace amounts of phosphorus were examined to reveal the cause: One was made by long-time high temperature holding to maximize the phosphorus segregation, and the other one was made by short-time high temperature holding to minimize the phosphorus segregation. The atom probe results at the grain boundaries ahead of the delamination-related cracks provide a strong evidence that phosphorus-enrichment and carbon-depletion for the long-time high temperature holding induces a larger degree of delamination as compared to the short-time high temperature holding. Reasons for the different segregation tendency were discussed by correlating the isothermal holding time at high temperature and the competitive segregation between phosphorus and carbon.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Trace amounts of P in the steel cause delamination in case of Lt-high Temp. holding. </LI> <LI> Anisotropic microstructure did not affect the delamination in this study. </LI> <LI> Crack-linked GBs in Lt-high Temp. steel had higher P and lower C segregation. </LI> <LI> Crack-interrupt GBs in St-high Temp. steel had lower P and higher C segregation. </LI> <LI> Competitive segregation controlled by high Temp. holding time affects delamination. </LI> </UL> </P> <P><B>Graphical Abstract</B></P> <P>[DISPLAY OMISSION]</P>

Inbreeding affected differently on observations distribution of a growth trait in Iranian Baluchi sheep

Binabaj Fateme Bahri,Farhangfar Seyyed Homayoun,Jafari Majid 아세아·태평양축산학회 2021 Animal Bioscience Vol.34 No.4

Objective: Initial consequence of inbreeding is inbreeding depression which impairs the performance of growth, production, health, fertility and survival traits in different animal breeds and populations. The effect of inbreeding on economically important traits should be accurately estimated. The effect of inbreeding depression on growth traits in sheep has been reported in many breeds. Based on this, the main objective of the present research was to evaluate the impact of inbreeding on some growth traits of Iranian Baluchi sheep breed using quantile regression model. Methods: Pedigree and growth traits records of 13,633 Baluchi lambs born from year 1989 to 2016 were used in this research. The traits were birth weight, weaning weight, six-month weight, nine-month weight, and yearling weight. The contribution, inbreeding and co-ancestry software was used to calculate the pedigree statistics and inbreeding coefficients. To evaluate the impact of inbreeding on different quantiles of each growth trait, a series of quantile regression models were fitted using QUANTREG procedure of SAS software. Annual trend of inbreeding was also estimated fitting a simple linear regression of lamb’s inbreeding coefficient on the birth year. Results: Average inbreeding coefficient of the population was 1.63 percent. Annual increase rate of inbreeding of the flock was 0.11 percent (p<0.01). The results showed that the effect of inbreeding in different quantiles of growth traits is not similar. Also, inbreeding affected differently on growth traits, considering lambs’ sex and type of birth. Conclusion: Quantile regression revealed that inbreeding did not have similar effect on different quantiles of growth traits in Iranian Baluchi lambs indicating that at a given age and inbreeding coefficient, lambs with different sex and birth type were not equally influenced by inbreeding. Objective: Initial consequence of inbreeding is inbreeding depression which impairs the performance of growth, production, health, fertility and survival traits in different animal breeds and populations. The effect of inbreeding on economically important traits should be accurately estimated. The effect of inbreeding depression on growth traits in sheep has been reported in many breeds. Based on this, the main objective of the present research was to evaluate the impact of inbreeding on some growth traits of Iranian Baluchi sheep breed using quantile regression model.Methods: Pedigree and growth traits records of 13,633 Baluchi lambs born from year 1989 to 2016 were used in this research. The traits were birth weight, weaning weight, six-month weight, nine-month weight, and yearling weight. The contribution, inbreeding and co-ancestry software was used to calculate the pedigree statistics and inbreeding coefficients. To evaluate the impact of inbreeding on different quantiles of each growth trait, a series of quantile regression models were fitted using QUANTREG procedure of SAS software. Annual trend of inbreeding was also estimated fitting a simple linear regression of lamb’s inbreeding coefficient on the birth year.Results: Average inbreeding coefficient of the population was 1.63 percent. Annual increase rate of inbreeding of the flock was 0.11 percent (p<0.01). The results showed that the effect of inbreeding in different quantiles of growth traits is not similar. Also, inbreeding affected differently on growth traits, considering lambs’ sex and type of birth.Conclusion: Quantile regression revealed that inbreeding did not have similar effect on different quantiles of growth traits in Iranian Baluchi lambs indicating that at a given age and inbreeding coefficient, lambs with different sex and birth type were not equally influenced by inbreeding.

A Correlative Approach for Identifying Complex Phases by Electron Backscatter Diffraction and Transmission Electron Microscopy

Na, Seon-Hyeong,Seol, Jae-Bok,Jafari, Majid,Park, Chan-Gyung Korean Society of Microscopy 2017 Applied microscopy Vol.47 No.1

A new method was introduced to distinguish the ferrite, bainite and martensite in transformation induced plasticity (TRIP) steel by using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). EBSD is a very powerful microstructure analysis technique at the length scales ranging from tens of nanometers to millimeters. However, iron BCC phases such as ferrite, bainite and martensite cannot be easily distinguished by EBSD due to their similar surface morphology and crystallographic structure. Among the various EBSD-based methodology, image quality (IQ) values, which present the perfection of a crystal lattice, was used to distinguish the iron BCC phases. IQ values are very useful tools to discern the iron BCC phases because of their different density of crystal defect and lattice distortion. However, there are still remaining problems that make the separation of bainite and martensite difficult. For instance, these phases have very similar IQ values in many cases, especially in deformed region; therefore, even though the IQ value was used, it has been difficult to distinguish the bainite and martensite. For more precise separation of bainite and martensite, IQ threshold values were determined by a correlative TEM analysis. By determining the threshold values, iron BCC phases were successfully separated.

Effect of Al Content, Substrate Temperature and Nitrogen Flow on the Reactive Magnetron Co-sputtered Nanostructure in TiAlN Thin Films Intended for Use as Barrier Material in DRAMs

Reza Jalali,Mojtaba Parhizkar,Hasan Bidadi,Hamid Naghshara,Seyd Reza Hosseini,Majid Jafari 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.6

TiAlN thin films were deposited by using the reactive magnetron co-sputtering method whitindividual Ti and Al targets, where the Ti and the Al targets were simultaneously powered by usingDC and RF sources, respectively. the electrical resistivity and the structural and microstructuralproperties of the deposited TiAlN thin films and the effects of Al content, substrate temperatureand nitrogen gas flow rate on those properties were investigated. At a low flow rate of nitrogen gas(0.51 sccm), the electrical resistivity of the films was found to increase with increasing AC power,but at a high flow rate of nitrogen gas, it was found to decrease. The structural and microstructuralanalyses performed by using X-ray diffraction and scanning electron microscopy (SEM) showed thatwith increasing substrate temperature from room temperature to 400◦C, the films prepared at 400◦C have a crystalline structure while those prepared at room temperature had an amorphous nature. Also, the SEM analysis revealed that with decreasing AC power and increasing nitrogen flow rate,the size of the grains in the prepared films become larger.

Direct Three-Dimensional Observation of Core/Shell-Structured Quantum Dots with a Composition-Competitive Gradient

Chae, Byeong Gyu,Lee, Jun Ho,Park, Seongyong,Lee, Eunha,Kwak, Chang Min,Jafari, Majid,Jeong, Young Kyu,Park, Chan Gyung,Seol, Jae Bok American Chemical Society 2018 ACS NANO Vol.12 No.12

<P>Synthesizing semiconductor nanoparticles through core/shell structuring is an effective strategy to promote the functional, physical, and kinetic performance of optoelectronic materials. However, elucidating the internal structure and related atomic distribution of core/shell structured quantum dots (QDs) in three dimensions, particularly at heterostructure interfaces, has been an overarching challenge. Herein, by applying complementary analytical techniques of electron microscopy and atom probe tomography, the dimensional, structural, topological, and compositional information on commercially available 11.8 nm-sized CdSSe/ZnS QDs were obtained. Systematic experiments at high resolution reveal the presence of a 1.8 nm-thick Cd<I><SUB><I>x</I></SUB></I>Zn<SUB>1</SUB><I><SUB>-<I>x</I></SUB></I>S inner shell with a composition gradient between the CdSe core and the ZnS outermost shell. More strikingly, the inner shell shows compositional variation because of competitive atomic configuration between Cd and ZnS, but it structurally retains a zinc-blende crystal structure with the core. The inner shell may grow through the decreased reactivity of S with Cd, followed by atomic diffusion-related processes. The composition-competitive gradient inner shell alleviates lattice misfit strain at heterostructure interfaces, thereby enhancing the quantum yield and photostabilty to a greater extent than those of other single-shell structures. Thus, this precise measurement approach could offer a potential pathway to develop a wide variety of three-dimensional core/shell-structured materials.</P> [FIG OMISSION]</BR>