Mie Ota

The Development of High Performance Ti-6Al-4V Alloy via a Unique Microstructural Design with Bimodal Grain Size Distribution

The present work deals with the strengthening of Ti-6Al-4V alloy by creating a unique microstructure with bimodal grain size distribution, termed as “harmonic structure.” The Ti-6Al-4V compacts with harmonic structure design were successfully prepared via a powder metallurgy approach consisting of controlled mechanical milling and spark plasma sintering of the pre-alloyed Ti-6Al-4V powders. The microstructural evolution at each stage of processing has been investigated to establish a correlation between the processing conditions and the microstructural evolution. The Ti-6Al-4V compacts with heterogeneous harmonic structure exhibited better mechanical properties as compared to their homogeneous fine/coarse-grained counterparts. An attempt has also been made to explain the deformation mechanism of the harmonic-structured Ti-6Al-4V specimens with the help of the experimental evidences. The superior mechanical properties of the harmonic structure Ti-6Al-4V were found to be related to the peculiar topological distribution of strong fine-grained and ductile coarse-grained regions, which promotes uniform distribution of strain during plastic deformation and results in improved mechanical properties by avoiding the localized plastic deformation in the early stages of deformation.

Three-dimensionally gradient harmonic structure design: an integrated approach for high performance structural materials

ABSTRACT This paper presents an overview on the peculiar microstructural design, called ‘harmonic structure’ (HS), for improved mechanical performance of structural materials. A well designed powder metallurgy processing approach has been developed to create a unique three-dimensionally gradient HS with controlled bimodal grain size distribution in metals and alloys. The bulk materials with HS exhibited considerably higher strength and improved toughness as compared to coarse-grained structures. The unique HS design promotes uniformity of deformation by avoiding strain localization during plastic deformation. A possible mechanism of deformation behavior of HS has also been proposed based on the available experimental results. GRAPHICAL ABSTRACT

High performance Ti-6Al-4V alloy by creation of harmonic structure design

Ti-6Al-4V alloy is an advanced structural material having applications in a wide range of areas spanning from biomedical to aerospace sectors due to the excellent combination of mechanical and chemical properties. In the present work, a new tailored heterogeneous microstructural design with a specific topological distribution of fine and coarse grained areas, called harmonic structure, has been proposed for the strengthening of Ti-6Al-4V alloy to achieve improved performance of the components in service. It has been demonstrated that Ti-6Al-4V alloy with harmonic structure can be successfully prepared via a powder metallurgy route consisting of controlled severe plastic deformation of pre-alloyed powders via mechanical milling followed by their consolidation. The Ti-6Al-4V compacts with harmonic structure design exhibited significantly better strength and ductility, under quasi-static as well as rapid loading conditions, as compared to their homogeneous fine and coarse grained counterparts. It was found that the harmonic structure design has the ability to promote the uniform distribution of strain during plastic deformation, leading to improved mechanical properties by avoiding localized plastic instability.

Harmonic structure formation and deformation behavior in a (α + γ) two phase stainless steel

In the present work the harmonic structure design has been successfully applied for achieving a combination of high strength and high ductility, simultaneously, in a two-phase steel. The compacts of two-phase stainless steels with harmonic structure were prepared by controlling mechanical milling (MM) of pre-alloyed stainless steel powders followed by spark plasma sintering. The controlled MM leads to the formation of severely deformed shell region, wherein the subsurface region in the immediate vicinity of the powder surface consists of a nanocrystalline structure followed by the inner region consisting of dislocation cell structure. These severely deformed regions form fine-grained network during subsequent sintering, resulting in Harmonic structure. This networked structure displayed high strength, high ductility, and better uniform plastic deformation as compared to the homogeneous fine/coarse grained structure. Such a unique combination of properties in the two-phase stainless steel powder compacts was found to be associated with the ability of the harmonic structure to evenly distribute the strain during plastic deformation.

Corrosion and wear behavior of harmonic structured SUS304L austenitic stainless steel

P is a common chronic inflammatory skin disease, characterized by abnormal differentiation and proliferation of keratinocytes, angiogenesis and infiltration of inflammatory cells that secrete Th1 and Th17 associated cytokines in the skin lesion, such as TNF-α, IL-17 and IL-20. Although mRNAs that encode cytokines are short-lived mRNAs in eukaryotes, the premRNAs, which contain AU-Rich Elements (AREs) in their 3’-untranslated regions, are recognized and stabilized by Human Antigen R (HuR), an RNA-binding protein, for post-transcription. Previous studies have suggested that HuR is involved in the stabilization of mRNAs in the psoriatic skin. HuR binds to and regulates IL-20 mRNA and relocalizes to the cytoplasm of psoriatic keratinocytes. Furthermore, HuR can bind numerous transcripts involved in the pathogenesis of psoriasis. Therefore, HuR may be a potential therapeutic target for psoriasis. In the present study, we tested several novel oligopeptides that targeted the RNA binding site of HuR as therapeutic agents for psoriasis. A mouse model of imiquimod (IMQ)-induced psoriasis-like dermatitis was generated in BALB/c mice by daily topical application of IMQ cream on the ear from days 0 to 9. The mice were treated with oligopeptides from days 5 to 10. The pathological features of psoriasis were scored daily using the thickness gauge and clinical Psoriasis Area and Severity Index (PASI). We found that the oligopeptide JS-1 could significantly ameliorate psoriasis pathogenesis in a dose-dependent manner. The oligopeptide affected the HuR downstream signaling pathway. Collectively, this study may provide an alternative therapeutic strategy for psoriasis.W are looking forward to the simple but strong method to enhance a sensitivity and responsibility of Graphene Oxide (GO) by forming a self-corrugated surface of GO. The self-corrugated surface was formed by the reaction of graphene oxide with Gallium chloride. The surface of GO is more corrugated with the concentration of gallium hydroxide during the dry of GO powder. The graphene oxide structure was distorted due to the three hydroxyl groups of gallium hydroxide. The properties of wrinkled GO were investigated by scanning electron microscope, energy dispersive spectroscopy, X-ray diffraction, Raman spectroscopy and atomic force microscope, respectively. This self-corrugated GO have superior advantages over normal GO for a higher sensitivity and responsibility for sensor applications.I in developing alternative energy sources is increasing due to depletion of oil resources and global warming. Therefore, fuel cells, which are new energy conversion and storage devices with low emission of pollutants, are emerging as an alternative. The process of producing hydrogen as a fuel of fuel cells requires a great deal of cost. Therefore, researches are being studying on reforming catalysts for converting natural gas rich in reserved into hydrogen energy and for use in fuel cells. In general, a transition metal (Ni, Co, Cu) or a noble metal (Ru, Pd, Pt) is used as a methane steam reforming catalyst. The noble metal catalyst has excellent catalytic activity and resistance to carbon deposition. But it is becoming a stumbling block to commercialization due to expensive cost. Ni-based catalysts are less expensive than noble metals and have a simple manufacturing process, but the problem of degradation due to carbon deposition and grain growth is pointed out as a disadvantage. In this study, Ni/MgO composite reforming catalyst activated Ni catalyst by exsolution was manufactured to improve durability. The size and amount of precipitated Ni particles were controlled by the reducing temperature and time. The catalytic activity and durability of the catalysts prepared as above were evaluated. The conversion rate of methane was measured and evaluated in the temperature range of 250-750oC and methane:water vapor = 1:2 atmospheres with catalyst in fixed bed reactor. The microstructure and distribution of the produced catalyst were confirmed by XRD and SEM.A well-defined 3D bicontinuous network structure in nanoscopic regular array has attracted considerable attention because of its potential applications such as photonic crystals, meta-materials, energy devices and superconductor. In this study, the asymmetric polystyrene-block-poly (methyl methacrylate) (PS-b-PMMA) thin films on the two different substrate with highmolecular-weight were prepared to be exposed a neutral solvent vapor to generate a hexagonal (HEX) cylindrical morphology to long-range ordered Gyroid (GYR). The interfacial interaction by different substrate interaction induced the two distinct GYR, [211] and [111] planes, which were directed from cylinders, like the parallel and perpendicular orientation on the selective and neutral substrate, respectively. Moreover, we further performed coarse-grained simulations of a block copolymer model to provide the molecular mechanisms. Our results based on experiments and simulations suggest a simple route for the controlled and well-defined GYR structures.T Fe-Mo based double perovskites have attracted much attention in the field of materials science due to their multiverse fascinating physical properties which make them suitable candidates for several technological applications. In the present work, the Sr2-xNdxFeMoO6 (0.0≤x≤0.3) samples have been investigated for their structural, magnetic and magnetocaloric properties. Polycrystalline Sr2-xNdxFeMoO6 (0.0≤x≤0.3) samples were prepared by using the conventional solid-state reaction method. To achieve the target double perovskite phase and to minimize the undesirable secondary phases, the samples were sintered in a reducing atmosphere, created by a gas mixture of 5% H2/95% Ar. The structure, microstructure and phase purity of the samples were investigated by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). XRD study confirmed the formation of tetragonal structure with Fm3m space group in all the synthesized samples. The Arrott plots and magnetization measurements showed a second order of ferromagnetic phase transition in all the fabricated samples. All the samples went through a paramagnetic to ferromagnetic phase transition at the Curie temperature (TC). A magnetocaloric effect was calculated in terms of isothermal magnetic entropy change. The value of the Relative Cooling Power (RCP) was observed to decrease with the increasing Nd content. A significant variation in the magnetocaloric properties of the samples was observed with the increasing Nd concentration. This investigation suggests that Sr2-xNdxFeMoO6 samples can be used as potential magnetic refrigerants for magnetocaloric applications.Purpose: Vorinostat (SAHA) is the most representative histone deacetylase inhibitor and a widely used anticancer drug, SAHA is applied in the treatment of hematological malignancies and most solid tumors. SAHA is challenging due to poor water solubility, low bioavailability and rapid elimination of drugs in vivo. In this study, we will prepare SAHA-Pluronic F127 Nanoparticles and investigated whether this could improve drug solubility, the effect of sustained release and inhibitory effect on cancer cells.C nanotube/polytetrafluoroethylene composite polymer targets (abbreviated as composite target) are proposed for use in the fabrication of plasma polymer fluorocarbon (abbreviated as PPFC) thin films using the mid-range frequency sputtering process. Large-area PPFC thin films were fabricated on roll-type PET substrate (polyethylene terephthalate, width 700 mm, thickness 100 μm) by a pilot-scale roll-to-roll sputtering system. The PPFC thin films exhibit an amorphous phase with a smooth surface and show a high water contact angle, optical transmittance and bendability. Mechanical property of PPFC thin films were studied using nanoindentation method and analyzed using X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. As the carbon nanotube concentration in the composite target increases, a carbon cross-linked structure was formed which enhanced the film hardness and the modulus of the PPFC thin films.T monolayer graphene-Ag nanoparticles hybrids system is fabricated as the electro-optical coordinated controlled substrate of Surface-Enhanced Raman Scattering (SERS) spectroscopy. Plasmon-exciton coupling interactions of this hybrid system are systemically investigated and applied in the field of surface catalytic reactions, manipulated by the electrooptical synergy. Our experimental results demonstrate that plasmon-exciton coupling interaction co-driven surface catalytic reactions can not only be controlled via plasmon-exciton coupling, but also by gate voltages and electric current (or bias voltage). The gate voltage can tune the Density of State (DOS) of hot electrons and electric current can make the hot electrons with higher kinetic energy. Both of them can significantly promote plasmon-exciton co-driven surface catalytic reaction. Our electro-optical device based on plasmon-exciton coupling can be potentially applied in the fields of sensor, catalysis, energy and environment.C thin film coatings present unique optical properties. In this study, structural, chemical bonding and optical properties of the thin films in relation to the composition of reaction gas via sputtering process were investigated. All the thin films exhibited a polycrystalline character with cubic fluorite-structure for cerium dioxide along (111), (200) and (222) orientations. XPS analysis revealed that two oxidation states of CeO2 and Ce2O3 are present in the films prepared at lower argon-oxygen flow ratios, whereas the films are totally oxidized into CeO2 as the aforementioned ratio increases. Optical parameters (α, ε1, ε2, n and k) derived from UV-Vis reflectance data indicate that the thin films have indirect optical band gaps in the range of 2.25-3.1 eV. Density Functional Theory (DFT+U) implemented in the Cambridge Serial Total Energy Package (CASTEP) has been employed to model some optical properties of CeO2 cluster at ground state. The simulated electronic Density of State (DOS) of the relaxed structure of CeO2 demonstrates a band gap, agrees well with the measured optical band gap. The experimental and calculated absorption coefficient (α), have analogous trends and to some extent a similar range of values in the wave length. All in all, our theoretical findings consistently support the experimental results.A neuronal growth underlies the prefrontal cortical (PFC) pathology of many neurodegenerative disorders. Current treatments are inadequate and commonly cause severe side effects. Importantly, conventional pharmacotherapy strategies have limited efficacy in treating PFC dis-regulation in neurodegenerative disorders. Electrical stimulation is a modern treatment method which can include electroconvulsive therapy, Deep-Brain Stimulation (DBS) and epidural stimulation, etc. Previous studied showed that the application of electrical stimulations promotes neuritis outgrowth resulted to inter neuronal networking. Wide range of metallic microelectrodes composed of gold, steel, platinum etc. have been previously utilized to perform electrical stimulation however, rigidity, incompatible mechanical properties, high initial impedance and low chargetransfer capacity limit their application. Graphene and its derivatives are an exciting class of materials, which are utilized in microelectrodes due to having excellent mechanical stability, electrical conductivity, biocompatibility, flexibility and ability to fabricate and scale up. This work develops three-dimensional (3D) flexible electrode composed of 3D printed Reduced Liquid Crystalline Graphene Oxide (rLCGO) on a polyurethane (PU) substrate. The flexible conducting electrode is used as Host Template for Human Neural Stem Cells (hNSCs) development during proliferation and differentiation. The application of electrical stimulation on hNSC using graphene/PU electrodes revealed promising results to improve neurites guidance through 3D printed lines and enhanced cell-cell communication and networking.P method is superior in the fabrication of ultra-high-temperature ceramics with the designable composition and structure, low sintering temperature and easy densifying process. In this study, three kinds of hybrid precursors for ZrC/C, ZrC/SiC and ZrC/SiBNC multinary ceramics were synthesized via radical polymerization. ZrC/C ceramic precursor was synthesized using Cp2Zr (CH2CH=CH2) as monomer ZrC/SiC or ZrC/SiBNC precursor is obtained by further adding low molecular weight polycarbosilane (LPCS) or polyborosilazane (LPBSZ) for copolymerization. By controlling the preparation procedure, these hybrid polymers can dissolve in most organic solvent, which is essential to construct CMCs in complicated shapes and large sizes. After pyrolyzing at 1400oC, the synthesized precursors can convert into Zr-containing multinary ceramics, with ZrC nanoparticles finely dispersed in C, SiC or SiBNC matrix depending on the hybrid polymer. All of the three Zr-containing multinary ceramics can remain finely phase distribution at 1600oC, especially for ZrC/C and ZrC/SiC multinary ceramics, which can have a stabilized microstructure and little mass loss (less than 1.5 wt%) up to 2000oC in inert atmosphere. As for ZrC/SiBNC, the introduction of ZrC phase can restrict the decomposition of SiBNC matrix at 1800oC. Although the SiC and SiBNC components improve the oxidation resistance of ZrC, the oxidation weight increase of these multinary ceramics at about 500oC is still up to 5%.W synthesized cationic, one-dimensional fibril assemblies formed from coil-sheet poly(L-lysine)-block-poly(Lthreonine) (PLL-b-PLT) block co-polypeptides as anticancer agents. The 1D fibril assemblies can efficiently interact with negatively charged cellular and mitochondrial membranes via electrostatic interactions, leading to cell necrosis through membrane lysis and apoptosis via the lytic effect of mitochondria. This effect is similar to that of one-dimensional drug carriers that exhibit enhanced cell penetration. Compared to free PLL chains, PLL-b-PLT fibril assemblies exhibited more selective cytotoxicity against cancer cells, lower hemolytic activity, higher membranolytic activity and a different apoptotic pathway, which may be due to differences in the peptide-membrane interactions. The fibril assemblies significantly inhibited tumor growth, improved survival and suppressed tumor metastasis to the lung in C57BL/6 mice bearing syngeneic LL2 lung tumors. An additive antitumor activity was also observed when the tumor bearing mice were treated with PLL-b-PLT in combination with the common chemotherapeutic drug cisplatin. Collectively, these results support the feasibility of using one-dimensional fibril assemblies as potential anticancer therapeutics.C Vapor Deposition (CVD) synthesis of Carbon Nanotubes (CNTs) was carried out in a self-assembled apparatus consisting of a hot tube furnace. Magnesium oxide supported iron catalyst samples, containing varied proportions of iron loadings were prepared using impregnation method and spread uniformly over copper strips. Ceramic boats were placed in the furnace so as to expose the catalyst-loaded copper strips to industrial gases such as nitrogen, methane and hydrogen. Usage of horizontal tube furnace instead of conventional CVD reactor not only reduced the cost but also added to the simplicity of the apparatus. Additionally, ceramic boats are at least 50% cheaper than the commonly used quartz boats. FESEM tests on the resultant samples revealed that the CNTs ranged between 19.78 nm and 30.36 nm in diameter, which validates the nanotube structures. We demonstrate that increasing the iron loading in the catalyst samples enhanced the probability of CNT formation: 0% iron loading yielded no CNTs, while increasing the loading to 6.5% gave way to formation of Multi-Walled Carbon Nanotubes (MWCNTs). This study opens up an economical route for the mass production of MWCNTs.H structured materials consist of a bimodal structure with a periodic or harmonic distribution of fine and coarse grains allowing optimum combination of high strength and ductility to be attained. Harmonic structured materials have potential in variety of applications, where high wear and corrosion resistance are required. Therefore, effect of harmonically distributed fine and coarse grains on the corrosion and wear behavior of a SUS304L austenitic stainless steel was studied and compared with a non-harmonic structured SUS304L and a conventional 304 stainless steel. The corrosion study was performed using linear, potentiodynamic and cyclic polarization techniques as well as salt fog exposure test for 30 days in 3.5% NaCl solution. Improved pitting corrosion resistance was found in case of the harmonic structured steel as compared to that of the non-harmonic and the conventional 304 stainless steel. Harmonically distributed fine grained structure, less porosity and higher fraction of passive α-FeOOH are attributed to the improvement in corrosion resistance of the harmonic structured steel. The wear study was performed using fretting wear tests at varying loads under ball-on-flat contact configuration. Coefficient of friction and wear volume were found to be minimum at intermediate normal load of 5 N, whereas maximum at 10 N in case of the harmonic stainless steel compared to other two steels. Harmonically distributed fine grained structure attributes to the higher wear rate of the harmonic structured steel because of hard and soft interaction of the ball with the harmonically distributed fine and coarse grains.A Solid Oxide Electrolyzer Cells (SOECs) is an electrochemical device for producing hydrogen by electrolysis water vapor at a high temperature. SOEC is that they can operate reversibly as solid oxide fuel cells, producing electricity with high efficiency by consuming stored hydrogen. It can also be used in next-generation power generation and storage systems that produce hydrogen using surplus power. SOEC have disadvantage to provide high temperature/high-pressure water vapor to the hydrogen electrode and since oxygen is released very quickly at the air electrode, deterioration of cells and stacks is larger than SOFC and it is a stumbling block to commercialization. In this study, the effect of operating conditions on hydrogen electrode performance and deterioration of SOEC was investigated. To improve the durability of the hydrogen electrode the material technology for inhibiting oxidation of Ni/YSZ was studied. The polarization resistance and J-V characteristics are evaluated in both SOFC/SOEC. The partial pressure of water vapor is changed to 10, 30 and 50%. The change of voltage is observed under the condition of applying current density of 0.1 mA/cm2 to the cell. And the durability of the cell is evaluated by measuring the voltage change according to the SOFC-SOEC switching operation. In addition, to suppress the oxidation of the hydrogen electrode (Ni/YSZ) in a steam atmosphere, a composite hydrogen electrode was fabricated by applying anticorrosion technology and the possibility of oxidation suppression is examined.Methods: Morphology was studied by Transmission Electron Microscopy (TEM). 5 μl of freshly prepared micellar dispersions were placed on Formvar and allowed to dry for 5 min. To unveil the usefulness of such formulations concerning physical stability, formulations FM1-FM5 and meloxicam were dissolved in enteric and gastric medium. After 1 and 2 h we quantified meloxicam in gastric medium and after 3 and 4 h we quantified meloxicam in enteric medium. Quantification was performed using an UV spectrophotometer and absorbance taken at 363 nm. To determine encapsulation efficiency, FM1-FM5 was quantified immediately after preparation. Later on, micellar suspensions were centrifuged at 3000 g for 15 min using Amicon® Ultra 4 Centrifugal filter units, the supernatant was quantified and EE calculated based on the following equation: Finally, cytotoxicity of formulations was assessed in Caco-2 cells by Alamar Blue assay, performing a screening of crescent concentrations (0.625%, 1.25%, 2.5%, 5% and 10%) for each formulation.G Multiforme (GBM) is an aggressive brain tumor with poor prognosis, mainly because standard treatment is not always effective enough in reaching tumor cells. Blood-Brain Barrier (BBB) is pointed out as one of great challenges in this field. Considering the negative charge of BBB surface and its restricted permeability to small compounds, positively-charged nanoparticles have been developed to facilitate the transport of drugs through the BBB. This work aimed at studying the interaction of different cationic surfactants used in Lipid Nanoparticle (LN) formulations with BBB, using atomistic simulations. Surfactants incorporating natural structural motifs, specifically serine, were chosen instead of the conventional synthetic surfactants, due to the lower cytotoxicity and higher biodegradability, thus being environmental friendly. Molecular dynamics simulations were performed on 4 systems containing different serine-based surfactants, two of them are monomeric (16SerTFA and 12SerTFA) and the other two are dimeric ((12ser)2CON12 and (12ser)2N5), in a fully hydrated palmitoyloleoylphosphatidylcholine (POPC) lipid model, intended to mimic cell membranes of both the BBB and tumor. The systems were evaluated in terms of effects induced by the surfactants in this type of membranes and rationalize the interactions at molecular level. The results showed an integration of all surfactants into the POPC membrane. Longer chain length surfactants tended to induce the highest membrane stabilization, as evidenced by 16serTFA. Conversely, the dimeric (12ser)2CON12 led to the greater disturbance in the membrane structure, probably due to bridging phenomena. This may anticipate a better BBB cross ability of LN containing (12ser)2CON12. Overall, this computational study suggests the viability of cationic serine-based surfactants as appealing compounds in LN formulations for targeted GBM therapy.

Effect of Harmonic Microstructure on the Corrosion Behavior of SUS304L Austenitic Stainless Steel

Corrosion behavior of a harmonic structured SUS304L austenitic stainless steel was examined and compared with nonharmonic structured SUS304L stainless steel and conventional 304 stainless steel in 3.5 pct NaCl solution. The study was performed using linear polarization, potentiodynamic polarization, cyclic polarization, and a salt fog exposure test for 30 days. Characterization was accomplished using a scanning electron microscope, an electron probe microanalyzer, and Raman spectroscopy. Improved pitting corrosion resistance was found in the case of the harmonic structured steel as compared to that of the nonharmonic and the conventional 304 stainless steel. Harmonically distributed fine-grained structure, less porosity, and higher fraction of passive α-FeOOH are attributed to the improvement in corrosion resistance of the harmonic structured steel.

Microstructure Evolution and Deformation Mechanisms of Harmonic Structure Designed Materials

This paper presents the novel microstructure design, called Harmonic Structure, which gives structural metallic materials outstanding mechanical properties through an innovative powder metallurgy process. Homogeneous and ultra-fine grain (UFG) structure enables the materials high strength. However, such a “Homo-“ and “UFG” microstructure does not, usually, satisfy the need to be both strong and ductile, due to the plastic instability in the early stage of the deformation. As opposed to such a “Homo-and UFG“ microstructure, “Harmonic Structure” has a heterogeneous microstructure consisting of bimodal grain size together with a controlled and specific topological distribution of fine and coarse grains. In other words, the harmonic structure is heterogeneous on micro-but homogeneous on macro-scales. In the present work, the harmonic structure design has been applied to pure metals and alloys via a powder metallurgy route consisting of controlled severe plastic deformation of the corresponding powders by mechanical milling or high pressure gas milling, and subsequent consolidation by SPS. At a macro-scale, the harmonic structure materials exhibited superior combination of strength and ductility as compared to their homogeneous microstructure counterparts. This behavior was essentially related to the ability of the harmonic structure to promote the uniform distribution of strain during plastic deformation, leading to improved mechanical properties by avoiding or delaying localized plastic instability.

Microstructure Formation of High Pressure Torsion Processed (α + γ) Two Phase Stainless Steel

(α + γ) two phase stainless steel (Fe-21%Cr-4.8%Ni-1.5%Mo) powder was processed by high pressure torsion (HPT) and consolidation at room temperature. The received powder had fully α single phase due to the rapid cooling during gas atomizing process. Specimens after HPT process were heat treated at 1173K for 3.6ks. It was revealed that the decomposition of α phase to γ took place during the heat treatment. Detailed microstructure observation showed that an equiaxed (α + γ) micro-duplex structure was developed and its average grain size was approximately 3.2 micrometers. The same heat treatment given to the material without HPT resulted in a coarse two phase microstructure.Therefore, it is considered that an ultra fine grained microstructure was caused by increasing of nucleation sites for γ phase due to severe plastic deformation (SPD) of HPT process. Electron backscatter diffraction patterns (EBSD) analysis indicated that α phase has a {110}/ND strong texture, that is, the α phase seems to have single orientated coarse grain structure. The γ precipitates indicated a {111}/ND strong texture, and the crystallographic orientation relationship of Kurdjumov-Sachs was observed.

Harmonic structure design of Ti-6Al-4V alloy by High-pressure gas milling process

Abstract Ti-6Al-4V alloy has been widely used for biomedical and aerospace applications, due to the excellent combination of mechanical and chemical properties. In this study, a new heterogeneous bimodal microstructure design, termed as harmonic structure design, consisted of coarse-grained area (Core) enclosed in a three-dimensional continuously connected network of fine-grained structure (Shell), is proposed for the strengthening of Ti-6Al-4V alloy to achieve improved performance of components. A novel high-pressure gas milling process, called jet milling, followed by spark plasma sintering has been proposed to create bimodal harmonic structure. The sintered Ti-6Al-4V alloy compacts with harmonic structure exhibited a significantly better combination of strength and toughness, as compared to their homogeneous fine- and coarse-grained counterparts.

Application of High-pressure gas milling process to pure Titanium for harmonic structure design

Abstract In this study, a new heterogeneous microstructural design based on bimodal grain size distribution, termed as harmonic structure, is proposed for the strengthening of Pure Ti to achieve improved mechanical performance. Moreover, to ensure contamination-free high purity Ti compacts, a new high pressure gas milling process, called Jet milling, has been proposed for the controlled mechanical milling. The resulting milled powder exhibited bimodal microstructure consisting of nanosized grains in the near-surface region and micron-sized coarse grains in the centre of powder particle. The spark plasma sintering of milled powder led to the full density Ti compacts with harmonic structure. The harmonic pure Ti compacts exhibited significantly better combination of strength and toughness as compared to the homogeneously coarse-grained compacts prepared from initial powder.