More Like this

1. Preferentially oriented growth of diamond films on silicon with nickel interlayer

   https://doi.org/10.1007/s42452-022-05092-y  

   K.C., Anupam ; Siddique, Anwar ; Anderson, Jonathan ; Saha, Rony ; Gautam, Chhabindra ; Ayala, Anival ; Engdahl, Chris ; Holtz, Mark W. ; Piner, Edwin L. ( July 2022 , SN Applied Sciences)

   A multistep deposition technique is developed to produce highly oriented diamond films by hot filament chemical vapor deposition (HFCVD) on Si (111) substrates. The orientation is produced by use of a thin, 5–20 nm, Ni interlayer. Annealing studies demonstrate diffusion of Ni into Si to form nickel silicides with crystal structure depending on temperature. The HFCVD diamond film with Ni interlayer results in reduced non-diamond carbon, low surface roughness, high diamond crystal quality, and increased texturing relative to growth on bare silicon wafers. X-ray diffraction results show that the diamond film grown with 10 nm Ni interlayer yielded 92.5% of the diamond grains oriented along the (110) crystal planes with ~ 2.5 µm thickness and large average grain size ~ 1.45 µm based on scanning electron microscopy. Texture is also observed to develop for ~ 300 nm thick diamond films with ~ 89.0% of the grains oriented along the (110) crystal plane direction. These results are significantly better than diamond grown on Si (111) without Ni layer with the same HFCVD conditions. The oriented growth of diamond film on Ni interlayers is explained by a proposed model wherein the nano-diamond seeds becoming oriented relative to the β₁-Ni₃Si that forms during the diamond nucleation period. The model also explains the silicidation and diamond growthmore »processes.

   High quality diamond film with minimum surface roughness and ~93% oriented grains along (110) crystallographic direction is grown on Si substrate using a thin 5 to 20 nm nickel layer.

   A detailed report on the formation of different phases of nickel silicide, its stability with different temperature, and its role for diamond film texturing at HFCVD growth condition is presented.

   A diamond growth model on Si substrate with Ni interlayer to grow high quality-oriented diamond film is established.

   « less
2. Mechanical Response of He-Implanted Amorphous SiOC/Crystalline Fe Nanolaminates

   https://doi.org/10.1038/s41598-019-41226-w  

   Zare, A. ; Su, Q. ; Gigax, J. ; Harriman, T. A. ; Nastasi, M. ; Shao, L. ; Lucca, D. A. ( March 2019 , Scientific Reports)

   This study investigates the microstructural evolution and mechanical response of sputter-deposited amorphous silicon oxycarbide (SiOC)/crystalline Fe nanolaminates, a single layer SiOC film, and a single layer Fe film subjected to ion implantation at room temperature to obtain a maximum He concentration of 5 at. %. X-ray diffraction and transmission electron microscopy indicated no evidence of implantation-induced phase transformation or layer breakdown in the nanolaminates. Implantation resulted in the formation of He bubbles and an increase in the average size of the Fe grains in the individual Fe layers of the nanolaminates and the single layer Fe film, but the bubble density and grain size were found to be smaller in the former. By reducing the thicknesses of individual layers in the nanolaminates, bubble density and grain size were further decreased. No He bubbles were observed in the SiOC layers of the nanolaminates and the single layer SiOC film. Nanoindentation and scanning probe microscopy revealed an increase in the hardness of both single layer SiOC and Fe films after implantation. For the nanolaminates, changes in hardness were found to depend on the thicknesses of the individual layers, where reducing the layer thickness to 14 nm resulted in mitigation of implantation-induced hardening.
3. Additive manufacturing of alumina-silica reinforced Ti6Al4V for articulating surfaces of load-bearing implants

   https://doi.org/doi.org/10.1016/j.ceramint.2021.03.227  

   Heer, Bryan ; Zhang, Yanning ; Bandyopadhyay, Amit ( July 2021 , Ceramics international)

   In this study, functional gradation via layer-wise additive manufacturing was coupled with Al2O3 and SiO2 ceramics' advantages to creating a composite of Ti6Al4V (Ti64) with improved hardness and wear resistance. It was hypothesized that with the addition of Al2O3 and SiO2 into Ti64, wear-resistance and hardness would increase when compared to the base Ti64 alloy. It was also hypothesized that if the structure could be created, an additional laser pass (LP) over the structure's top surface would further increase the hardness. Successfully fabricated composite structures were found to have varying phases of TiSi2 and Ti5Si3. Refined α-Ti grains were present in the composite region. The interface between the composite and pure Ti64 regions was crack-free, indicating a metallurgically sound bond. Dendritic microstructures were observed with the addition of LP on the composite top surface. Hardness was increased from 323.8 ± 9.6 HV in Ti64 substrate to 434.7 ± 7.3 HV and 677.1 ± 29.7 HV in 3D Printed Ti64 and the composite sample, respectively. An LP increased hardness further to 938.8 ± 57.5 HV, a 186% increase in hardness than the original Ti64 alloy. Wear resistance was also increased with the addition of Al2O3 and SiO2 by ~90%, indicating themore »potential processing variations placed on this material system to produce structures with site-specific functionality for biomedical applications, particularly in articulating surfaces of load-bearing implants.« less
4. Understanding process-microstructure-property relationships in laser powder bed fusion of non-spherical Ti-6Al-4V powder

   Mohammadreza Asherloo, Junghyun Hwang ( February 2023 , Materials characterization)

   Powder feedstock is a major cost driver in metal additive manufacturing (AM). Replacing the spherical powder with the cost-efficient non-spherical one can reduce the feedstock cost up to 50% and attract more interest to adopt AM in production and new alloy development. Here, a comprehensive study was conducted to understand process-microstructure-property relationships in laser powder bed fusion of hydride-dehydride Ti-6Al-4V powder. We demonstrated that variation of laser scan speed had a significant impact on the grain structure, pore evolution and properties compared to laser power. Dynamic X-ray radiography showed that with decreasing scan speed at a constant laser power, a transition from conduction to keyhole mode laser processing occurred, in which a deeper melt pool at lower scan speed intensified texture. In other words, an increase in laser scan speed resulted in formation of the refined prior  grains with shape factor of ~5, lowering the anisotropy. The degree of variant selection was evaluated based on the analyzed texture as a function of laser power and scan speed. With increasing laser scan speed, the dominant α/α boundary type was altered from type 2 to 4 and the degree of variant selection was noticeably decreased. On the other hand, increasing lasermore »power left the morphology of prior  grains, their size, and the dominant α/α boundary (type 4) unchanged, while the texture and anisotropy were intensified, and the degree of variant selection was slightly decreased. Finally, dependency of surface roughness and microhardness were discussed as a function of laser processing parameters.« less
5. Developing Bioactive-Nanograined Metals With Bacterial Biofilm Inhibition Properties For Orthopedic Devices

   Kelkar, Shaunak ; Saleh, Bahram ; Yusa, Fumie ; Suzuki, Yohei ; Komatsu, Takafumi ; Webster, Thomas ( January 2021 , Orthopaedic Research Society)

   INTRODUCTION: Orthopedic implants are important therapeutic devices for the management of a wide range of orthopedic conditions. However, bacterial infections of orthopedic implants remain a major problem, and not an uncommon one, leading to an increased rate of osteomyelitis, sepsis, implant failure and dysfunction, etc. Treating these infections is more challenging as the causative organism protects itself by the production of a biofilm over the implant’s surface (1). Infections start by the adhesion and colonization of pathogenic bacteria such as Staphylococcus aureus (SA), Staphylococcus epidermidis (SE), Escherichia coli (E. coli), Methicillin-Resistant Staphylococcus aureus (MRSA), and Multi-Drug Resistant Escherichia coli (MDR E. coli) on the implant’s surfaces. Specifically, Staphylococcus comprises up to two-thirds of all pathogens involved in orthopedic implant infections (2). However, bacterial surface adhesion is a complex process influenced by several factors such as chemical composition, hydrophobicity, magnetization, surface charge, and surface roughness of the implant (3). Considering the intimate association between bacteria and the implant surface, we measured the effect of stainless-steel surface properties on bacterial surface attachment and subsequent formation of biofilms controlling above mentioned factors. METHODS: The prominent bacteria responsible for orthopedic implant infections (SA, SE, E. coli, MRSA, and MDR E. coli) were used inmore »this study. We were able to control the grain size of medical grade 304 and 316L stainless steel without altering their chemical composition (grain size range= 20μm-200nm) (4). Grain size control affected the nano-topography of the material surfaces which was measured by an Atomic Force Microscope (AFM). Grain sizes, such as 0.2, 0.5, 1, 2, 3, 9, and 10 μm, were used both polished and non-polished. All the stainless-steel samples were cleaned by treating with acetone and ethanol under sonication. Triplicates of all polished and non-polished samples with different grain sizes were subjected to magnetization of DM, 0.1T, 0.5T, and 1T, before seeding them with the bacteria. Controls were used in the form of untreated samples. Bacterial were grown in Tryptic Soy Broth (TSB). An actively growing bacterial suspension was seeded onto the stainless-steel discs into 24-well micro-titer plates and kept for incubation. After 24 hours of incubation, the stainless-steel discs were washed with Phosphate Buffer Saline (PBS) to remove the plankton bacteria and allow the sessile bacteria in the biofilm to remain. The degree of development of the bacterial biofilms on the stainless-steel discs were measured using spectrophotometric analysis. For this, the bacterial biofilm was removed from the stainless steel by sonication. The formation of biofilms was also determined by performing a biofilm staining method using Safranin. RESULTS SECTION: AFM results revealed a slight decrease in roughness by decreasing the grain size of the material. Moreover, the samples were segregated into two categories of polished and non-polished samples, in which polishing decreased roughness significantly. After careful analysis we found out that polished surfaces showed a higher degree for biofilm formation in comparison to the non-polished ones. We also observed that bacteria showed a higher rate for biofilm formation for the demagnetized samples, whereas 0.5T magnetization showed the least amount of biofilm formation. After 0.5T, there was no significant change in the rate of biofilm formation on the stainless-steel samples. Altogether, stainless steel samples containing 0.5 μm and less grainsize, and magnetized with 0.5 tesla and stronger magnets demonstrated the least degree of biofilm formation. DISCUSSION: In summary, the results demonstrate that controlling the grain size of medical grade stainless steel can control and mitigate bacterial responses on, and thus possibly infections of, orthopedic implants or other implantable devices. The research was funded by Komatsuseiki Kosakusho Co., Ltd (KSJ: Japan) SIGNIFICANCE/CLINICAL RELEVANCE: Orthopedic implants that more than 70% of them are made of metals (i.e., stainless steel, titanium, and cobalt-chromium alloys) are failing through loosening and breakage due to their limited mechanical properties. On the other hand, the risk of infection for these implants and its financial burden on our society is undeniable. We have seen that our uniformly nanograined stainless steel shows improved mechanical properties (i.e., higher stiffness, hardness, fatigue) as compared to conventional stainless steel along with the reduction of biofilm formation on its surface. These promising results made us to peruse the development of nanograined titanium and cobalt-chromium alloys for resolving the complications of orthopedic implants.« less