Investigation of the microcrack evolution in a Ti-based bulk metallic glass matrix composite

AbstractThe initiation and evolution behavior of the shear-bands and microcracks in a Ti-based metallic-glass–matrix composite (MGMC) were investigated by using an in-situ tensile test under transmission electron microscopy (TEM). It was found that the plastic deformation of the Ti-based MGMC related with the generation of the plastic deformation zone in crystalline and shear deformation zone in glass phase near the crack tip. The dendrites can suppress the propagation of the shear band effectively. Before the rapid propagation of cracks, the extending of plastic deformation zone and shear deformation zone ahead of crack tip is the main pattern in the composite

Incorporating graphene oxide into biomimetic nano-microfibrous cellulose scaffolds for enhanced breast cancer cell behavior

Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10570-020-03078-w) contains supplementary material, which is available to authorized users.The impact of graphene oxide (GO) on normal cells has been widely investigated. However, much less is known on its effect on cancer cells. Herein, GO nanosheets were incorporated into electrospun cellulose acetate (CA) microfibers. The GO-incorporated CA (GO/CA) microfibers were combined with bacterial cellulose (BC) nanofibers via in situ biosynthesis to obtain the nano-microfibrous scaffolds. The GO/CA-BC scaffolds were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The GO/CA-BC scaffolds were used for breast cancer cell culture to evaluate the effect of GO on cancer cell behavior. Fluorescence images revealed large multicellular clusters on the surface of GO/CA-BC scaffolds. Compared to the bare CA-BC scaffold, the GO/CA-BC scaffolds not only showed enhanced mechanical properties but also improved cell proliferation. It is expected that the GO/CA-BC scaffolds would provide a suitable microenvironment for the culture of cancer cells which is necessary for drug screening and cell biology study.This work was supported by National Natural Science Foundation of China (Grant nos. 51572187, 51973058, 31660264, 31870963), the Key Research and Development Program of Jiangxi Province (No. 20192ACB80008), and the Youth Science Foundation of Jiangxi Province (No. 20181BAB216010), and Key Project of Natural Science Foundation of Jiangxi Province (No. 20161ACB20018).info:eu-repo/semantics/publishedVersio

Surface Modification of Q195 Structure Carbon Steel by Electrolytic Plasma Processing

In this study, we applied an emerging, environmentally friendly surface engineering technology, electrolytic plasma processing (EPP), for the surface modification of Q195 structure carbon steel surface pretreatment and further Zn coating. Treating the surfaces of Q195 structure carbon steel by EPP was a quite dynamic process, which was investigated using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The results shown that surface scale can be effectively remove after 40 s EPP treatment, and the EPP-treated Q195 structure carbon steel revealed a slight decrease in elastic modulus and hardness, but a substantial improvement in tensile (especially plastic) mechanical properties. Moreover, the further EPP modification conducted on the pretreated Q195 structure carbon steel sample for production of a layer of compact zinc coating with 15 μm thickness under an optimization EPP process. We also identified the modification mechanism of EPP to Q195 structure carbon steel, which may provide theoretical and practical guidance for future researchers and developers

Microstructure and phase transformations of ωo_o-Ti4_4Al3_3Nb based alloys after quenching and subsequent aging at intermediate temperatures

The existence of ω$_o$ (ordered ω) phase in TiAl alloys in different compositions at intermediate temperatures has been widely reported. In this study, the phase transformation behaviors of ω$_o$-based alloys at 750–900 °C were studied by electron microscopy. It is found that fine-grained microstructures mainly composed of $γ$+ω$_o$ and a tiny amount of $α_2$ phase precipitated in the alloys quenched from high temperature during aging. Twins form in $α_2$ phase after aging, which is analogous to observations reported in deformed TiAl alloys. The $γ$ phase precipitates originate from the stacking faults of $α_2$ laths and grow up by coarsening at 750 °C. Semi-coherent interfaces between $γ$ and ω$_o$ phases are formed and a high density of stacking faults can be observed inside the $α_2$ laths. At higher temperatures, the direct nucleation of $γ$ phase from the ω$_o$/β$_o$ matrix becomes active. Various orientation relationships are found between ω$_o$, $γ$ and $α_2$ phases, leading to a number of grain clusters having smooth interfaces in between. In addition, the effects of Ta, V and Zr on the microstructure are investigated. The effect of these elements on the stability of the ω$_o$ phase is not as obvious as reported for some other elements

Temperature and Crystalline Orientation-Dependent Plastic Deformation of FeNiCrCoMn High-Entropy Alloy by Molecular Dynamics Simulation

The effect of the crystallographic direction and temperature on the mechanical properties of an FeNiCrCoMn high-entropy alloy (HEA) is explored by molecular dynamics simulations. The calculated static properties are in agreement with the respective experimental/early theoretical results. The calculated compressive yield stress along the direction of a single crystal/polycrystal is the same in order of magnitude as the experimental results. The yield stress and Young’s modulus of the single crystal show strong anisotropy. Unlike the single crystal, the polycrystal behaves as an isotropic and has strong ductility. It is found that the dislocations produced in the plastic deformation process of the HEA are mainly 1/6 Shockley dislocations. The dislocations produced under normal stress loads are far more than that in the shearing process. FCC transformation into HCP does not occur almost until yield stress appears. The yield stress, yield strain, and Young’s modulus reduce gradually with increasing temperature. The modulus of the single/double crystal under compressive and tensile loads presents an obvious asymmetry, while there is only a small difference in the polycrystal. The strain point is found to be the same for stress yielding, FCC-HCP phase transition, and dislocation density, varying from slow to fast with strain at the considered temperature

Friction Weldability of a High Nb Containing TiAl Alloy

The friction weldability of Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y alloy has been investigated by optimizing process parameters and analyzing the microstructures and tensile properties of the joints. The as-cast alloy with a nearly lamellar (NL) microstructure and the as-forged alloys with a duplex (DP) microstructure have been successfully welded. All the joints have a severe deformation zone (SDZ) and a transition zone (TZ) between the parent metal (PM) and SDZ. SDZ, showing a biconcave lens geometry, has a maximum thickness of hundreds of micrometers at the periphery. TZ is hundreds of micrometers thick. All SDZs have a fine-grained DP microstructure with a grain size of a few micrometers. For the joint of the as-cast alloy, the TZ consists of deformed lamellar colonies as the major constituent and partially recrystallized grains as the minor constituent. For the joint of the as-forged alloy, the TZ is similar to both the PM and SDZ, showing a DP microstructure. The grain size, volume fraction of γ grains, and the remnant lamellar colonies all increase with the distance from the SDZ. All joints presented perfect metallurgical bonding. The strengths of the joints are higher than those of the corresponding PMs. This indicates that the studied alloy has good friction weldability

Precipitation Behavior of ωo Phase in Ti-37.5Al-12.5Nb Alloy

Mutual transformation between α2 and ωo phases has been an interesting topic in recent years. In this study, martensitic α2 was obtained by air-cooling from 1250 °C in Ti-37.5Al-12.5Nb (at%) alloy while four ωo variants formed in the βo phase matrix during the cooling process. Nonetheless, only one ωo variant was observed at the periphery of the α2 plates in the βo phase and the orientation relationship between these two phases was [0001] α2//[({1overline{2}10})] ωo; (({11overline{2}0})) α2//(0002) ωo. Thin γ plates precipitated within the α2 phase and were thought to be related to the appearance of ωo phase. The redistribution of the compositions during the phase transformations was studied by energy dispersive X-ray spectroscopy analysis. The corresponding mechanisms of the phase transformations mentioned above are discussed

Evolution of Microstructure and Microsegregation of Ti-45Al-8Nb Alloy during Directional Solidification

High Nb-containing TiAl alloys have good oxidation resistance and mechanical properties, but the microstructure and the properties are substantially affected by the segregation. To quantitatively investigate the segregation behavior of Al during solidification, microstructures of directionally solidified (DS) Ti-45Al-8Nb (in atomic percent) alloy prepared at withdrawing rates of 30 μm/s and 200 μm/s and a temperature gradient of 4200 K/m were observed by optical microscope and electronic probe microanalyzer. The microsegregations were characterized by wave dispersive spectroscopy. The results show that the DS ingots include the no melting zone, directionally solidified zone with columnar grains, mushy zone, and quenched liquid zone. The primary dendritic arm spacings are 353 μm and 144 μm, respectively, for the two ingots. But the solidified microstructures of the ingots are large lamellar colonies, which contain a few B2 patches and γ bands induced by microsegregation. From dendritic zone to columnar zone, the volume fractions of B2 patches and γ bands decrease. The segregation extents of Al and Nb decrease with the increase of solidification rate. There exists an obvious back diffusion process of Al during solidification and cooling after solidification. According to evolution of Al concentration profiles from mushy zone to columnar grain zone, interdiffusion coefficient for Al in β-Ti at near solidus temperature is semiquantitatively calculated, and the value is (6 – 11) × 10−11 m2/s

Microstructure and Mechanical Properties of TiAl Matrix Composites Reinforced by Carbides

TiAl alloys have the potential to become a new generation of high-temperature materials due to their lightweight and high-strength properties, while the brittleness at room temperature and microstructure stability at elevated temperature are the key problems. The preparation of composite materials is an effective way to solve these problems, because the mechanical properties of TiAl matrix composites can be improved by the close combination of the reinforced phase and matrix. The preparation methods, microstructure, and mechanical properties of TiAl matrix composites reinforced by carbides are reviewed from the literature in this paper. A comprehensive summary of the effect of C on TiAl alloys can reveal the relationship between the microstructure and mechanical properties and provide guidance for subsequent experimental works. Two forms of C in TiAl matrix composites are reviewed: solid solutions in matrix and carbide precipitations. For TiAl alloys, the minimum carbon content for the carbide precipitation is about 0.5 at.% for low-Nb-containing TiAl alloys and about 0.8 at.% for high-Nb-TiAl alloys. An appropriate amount of C can improve the tensile properties and flexural strength of TiAl alloys. The hardness of the composites is higher than that of pure TiAl due to solution strengthening when the carbon content is low. The minimum creep rate of TiAl alloys can be reduced by one order of magnitude by adding C at the amount near the solubility limit