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A subgridding unconditionally stable finite-element time-domain method based on local eigenvalue solution (SUSL-FETD) is proposed to solve multiscale modeling. In this method, subgridding elements are used to discrete a multiscale computational domain, and the explicit central-difference method is applied for temporal discretization. Compared with traditional elements, the subgridding elements have a more complex distribution of edges and nodes. Therefore, an efficient subgridding scheme is given to form the element matrix for each subgridding element. Such system matrices assembled by all element matrices are symmetric. The subgridding FETD (S-FETD) is then further developed into the subgridding unconditionally stable FETD (SUS-FETD) by filtering spatial unstable modes. It is time-consuming to obtain the unstable modes by global eigenvalue decomposition. In this article, the local eigenvalue decomposition is proposed to get the unstable modes, which further reduces the memory storage and computing time. Numerical examples certify that the proposed SUSL-FETD has high accuracy and efficiency.

The extension of the cosmic-ray spectrum beyond 1 petaelectronvolt (PeV; 1015 electronvolts) indicates the existence of the so-called PeVatrons—cosmic-ray factories that accelerate particles to PeV energies. We need to locate and identify such objects to find the origin of Galactic cosmic rays1. The principal signature of both electron and proton PeVatrons is ultrahigh-energy (exceeding 100 TeV) γ radiation. Evidence of the presence of a proton PeVatron has been found in the Galactic Centre, according to the detection of a hard-spectrum radiation extending to 0.04 PeV (ref. 2). Although γ-rays with energies slightly higher than 0.1 PeV have been reported from a few objects in the Galactic plane3–6, unbiased identification and in-depth exploration of PeVatrons requires detection of γ-rays with energies well above 0.1 PeV. Here we report the detection of more than 530 photons at energies above 100 teraelectronvolts and up to 1.4 PeV from 12 ultrahigh-energy γ-ray sources with a statistical significance greater than seven standard deviations. Despite having several potential counterparts in their proximity, including pulsar wind nebulae, supernova remnants and star-forming regions, the PeVatrons responsible for the ultrahigh-energy γ-rays have not yet been firmly localized and identified (except for the Crab Nebula), leaving open the origin of these extreme accelerators. Observations of γ-rays with energies up to 1.4 PeV find that 12 sources in the Galaxy are PeVatrons, one of which is the Crab Nebula.

Due to their high hardness and high strength, VC reinforced hard materials such as high vanadium high-speed steel (HVHSS) are not suitable for machining to obtain complex shape with low cost. Therefore, 3D gel printing (3DGP) was employed to print HVHSS parts, using highly loaded slurry with 60% solid content as printing slurry. After printing parameters optimization, the printing sample had good surface quality, and obvious printing lines were observed. The extruded filament was in-situ cured, thus enough to maintain the designed shape. Uniform sintering shrinkage with a shrinkage rate of about 15% was obtained in the as-sintered sample with relative density of 99%. The surface roughness decreased from 6.5 µm to 3.8 µm. Fine carbides (

The VHE component from at least two GRBs, i.e., GRB180720B and GRB190114C, has been detected in the afterglow phase. We systematically analyzed 199 GRBs detected by Fermi-LAT during 2008-2019. If an additional high-energy component exists in the afterglows of Fermi-LAT GRBs, the best-fit spectral model could be a broken power-law (BPL) model with an upturn above a break energy. We compare the afterglow spectra using PL and BPL representations. Out of the 30 GRBs with >10GeV photons that arrived after T90, 25 GRBs are tentatively or significantly detected at 0.1-200 GeV after 2*T90. The spectrum of GRB131231A shows an upturn above a break of 1.6+-0.8~GeV, supporting the BPL model. For GRB131231A, we performed a modeling of its X-ray and gamma-ray spectra, and found that the SSC model can explain the upturn with acceptable parameter values. In the cases of GRBs 190114C, 171210A, 150902A, 130907A, 130427A, and 090902B, the improvement of the BPL fit compared to the PL fit is tentative or marginal. There is no conclusive evidence that an additional higher energy component commonly exists in Fermi-LAT GRB afterglows, except for a group of Fermi-LAT GRBs mentioned above. Such an additional high-energy component may be explained by the synchrotron self-Compton mechanism. Current and future VHE observations will provide important constraints on the issue., A\&A in press. arXiv admin note: substantial text overlap with arXiv:2002.08734

We report the discovery of a new unidentified extended $\gamma$-ray source in the Galactic plane named LHAASO J0341+5258 with a pre-trial significance of 8.2 standard deviations above 25 TeV. The best fit position is R.A.$=55.34^{\circ}\pm0.11^{\circ}$ and Dec$=52.97^{\circ}\pm0.07^{\circ}$. The angular size of LHAASO J0341+5258 is $0.29^\circ \pm 0.06^\circ_{stat} \pm0.02^\circ_{sys}$. The flux above 25 TeV is about $20\%$ of the flux of Crab Nebula. Although a power-law fit of the spectrum from 10 TeV to 200 TeV with the photon index $\alpha=2.98 \pm 0.19_{stat} \pm 0.02_{sys}$ is not excluded, the LHAASO data together with the flux upper limit at 10 GeV set by the Fermi LAT observation, indicate a noticeable steepening of an initially hard power-law spectrum %($\alpha \leq 1.75$) spectrum with a cutoff at $\approx 50$ TeV. We briefly discuss the origin of UHE gamma-rays. The lack of an energetic pulsar and a young SNR inside or in the vicinity of LHAASO J0341+5258 challenge, but do not exclude both the leptonic and hadronic scenarios of gamma-ray production., Comment: Accepted by APJL

Titanium (Ti) and its alloys are attracting special attention in the field of dentistry and orthopedic bioengineering because of their mechanical adaptability and biological compatibility with the natural bone. The dental implant is subjected to masticatory forces in the oral environment and transfers these forces to the surrounding bone tissue. Therefore, by simulating the mechanical behavior of implants and surrounding bone tissue we can assess the effects of implants on bone growth quite accurately. In this study, dental implants with different gradient pore structures that consisted of simple cubic (structure a), body centered cubic (structure b) and side centered cubic (structure c) were designed, respectively. The strength of the designed gradient porous implant in the oral environment was simulated by three-dimensional finite element simulation technique to assess the mechanical adaptation by the stress-strain distribution within the surrounding bone tissue and by examining the fretting of the implant-bone interface. The results show that the maximum equivalent stress and strain in the surrounding bone tissue increase with the increase of porosity. The stress distribution of the gradient implant with a smaller difference between outer and inner pore structure is more uniform. So, a-b type porous implant exhibited less stress concentration. For a-b structure, when the porosity is between 40 and 47%, the stress and strain of bone tissue are in the range of normal growth. When subject to lingual and buccal stresses, an implant with higher porosity can achieve more uniform stress distribution in the surrounding cancellous bone than that of low porosity implant. Based on the simulated results, to achieve an improved mechanical fixation of the implant, the optimum gradient porous structure parameters should be: average porosity 46% with an inner porosity of 13% (b structure) and outer porosity of 59% (a structure), and outer pore sized 500 μm. With this optimized structure, the bone can achieve optimal ingrowth into the gradient porous structure, thus provide stable mechanical fixation of the implant. The maximum equivalent stress achieved 99 MPa, which is far below the simulation yield strength of 299 MPa.

The tungsten (W)-plated diamond process was explored and optimized. A dense and uniform tungsten coating with a thickness of 900 nm was successfully prepared by the powder covering sintering method. The Diamond-WC-Cu composite with high density and high thermal conductivity were successfully prepared by cyclic vacuum pressure infiltration. The microstructure and composition of the W-plated diamond particles were analyzed. The effect of tungsten coating on the microstructure and thermal conductivity of the Diamond-WC-Cu composite was investigated. After calculation, the interface thermal resistance of the composite forming the tungsten carbide transition layer is 2.11 × 10−8 m2∙K∙W−1. The thermal conductivity average value of the Diamond-WC-Cu composite with a diamond volume fraction of 60% reaches 874 W∙m−1∙K−1, which is close to the theoretical prediction value of Hasselman-Johnson (H-J) model and differential effective medium (DEM) model. Moreover, the Maxwell-Eucken (M-E) model, H-J model, and DEM model were used to evaluate the thermal conductivity of the Diamond-WC-Cu composite.

The Gamma-Ray Integrated Detectors (GRID) is a space mission concept dedicated to monitoring the transient gamma-ray sky in the energy range from 10 keV to 2 MeV using scintillation detectors onboard CubeSats in low Earth orbits. The primary targets of GRID are the gamma-ray bursts (GRBs) in the local universe. The scientific goal of GRID is, in synergy with ground-based gravitational wave (GW) detectors such as LIGO and VIRGO, to accumulate a sample of GRBs associated with the merger of two compact stars and study jets and related physics of those objects. It also involves observing and studying other gamma-ray transients such as long GRBs, soft gamma-ray repeaters, terrestrial gamma-ray flashes, and solar flares. With multiple CubeSats in various orbits, GRID is unaffected by the Earth occultation and serves as a full-time and all-sky monitor. Assuming a horizon of 200 Mpc for ground-based GW detectors, we expect to see a few associated GW-GRB events per year. With about 10 CubeSats in operation, GRID is capable of localizing a faint GRB like 170817A with a 90% error radius of about 10 degrees, through triangulation and flux modulation. GRID is proposed and developed by students, with considerable contribution from undergraduate students, and will remain operated as a student project in the future. The current GRID collaboration involves more than 20 institutes and keeps growing. On August 29th, the first GRID detector onboard a CubeSat was launched into a Sun-synchronous orbit and is currently under test., accepted for publication in Experimental Astronomy

This paper provides a new method for preparing refractory metal diboride by reducing refractory metal oxide with Calcium hexaboride (CaB6), which is prepared using B4C and calcium as raw materials. For refractory metal powders (M = Ti, Zr, Hf, V, Nb, Ta, Cr) which are expensive and hard to be produced by a simple route, it is more cost-effective to directly use refractory metal oxide to prepare its boride. After reacting at 1473 K for 4 h, CaB6 and refractory metal oxide could completely react to form MB2, CaO and B2O3. The single-phase product with the particle size of sub-micron was obtained after acidic leaching, filtration and drying. CaB6 could be used as a universal reducing agent to prepare metal boride.

In the current work, we first reported the fabrication of mesoporous SiCNO fibers by electrospun polyureasilazane and polyvinylpyrrolidone precursor followed with a microwave-assisted pyrolysis process. The resulting product was characterized by field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), nitrogen adsorption-desorption, X-ray diffraction (XRD), Raman spectrometer (Raman) and Fourier Transform infrared spectroscopy (FTIR). The as-prepared SiCNO fibers have uniform diameter and high morphological purity. It is found that the elemental compositions and BET specific surface area in the resulted SiCNO fibers could be controlled by adjustment the pyrolysis temperature.

W Ti alloy, which is a candidate of the gasket material used for the neutron high pressure diffraction, was proposed and fabricated by the powder metallurgy method in this paper. The laser particle size analyzer, scanning electron microscope, and transmission electron microscope were used to study the effects of milling time on the particle size distribution and the microstructure. The results show that with the extension of milling time, the particle size of the milled powders decreases, and the grain size of the sintered alloys also decreases. However, the oxygen content increases, and the αTi phase gradually appears and its amount increases with the increase of the milling time. The microstructure is composed of the W-rich (βTi,W) phase, the αTi phase and the eutectic phase before the milling time of 2 h, and after that the eutectic phase disappears. Oxygen coming from the milling gets rich in titanium so that it makes more and stable αTi phase. This is because, with the extension of milling time, the oxygen content is so high that the αTi phase can be very stable and the diffusion of W into Ti at the high temperature is suppressed. Moreover after 0.5 h ball milling, the maximum strength of the alloy is 3323 MPa due to the uniform microstructure.

Graphite flake/Cu composites with Zr element introduced into the matrix were successfully fabricated by vacuum hot pressing. The influence of Zr addition on the phase composition, microstructure and properties were investigated. The results indicate that the bending strength in X-Y plane gradually rises with the Zr content increasing from 0 to 2.0 wt%, nearly doubled from 50 MPa to 95 MPa. The thermal conductivity in X-Y plane initially increases and then decreases, yielding a maximum of 640 W m−1 K−1 at 1.0 wt% Zr. This improvement is ascribed to the formation of carbide interfacial layer at the graphite flake/Cu interface. Due to the simple preparation process and excellent thermal conductivity, the graphite flake/Cu composites with moderate Zr addition can be a highly promising candidate for thermal management materials.

There have been substantial improvements on Fermi Large Area Telescope (LAT) data and analysis tools since the last analysis by Auchettl et al. on the intermediate-aged supernova remnant (SNR) Kes 79. Recent multiwavelength studies confirmed its interaction with molecular clouds. About 0.°36 north from Kes 79, a powerful pulsar, PSR J1853+0056, also deserves our attention. In this work, we analyze the 11.5 yr Fermi-LAT data to investigate the γ-ray feature in/around this complex region. Our result shows a more significant detection (∼34.8σ in 0.1–50 GeV) for this region. With ≥5 GeV data, we detect two extended sources: Src-N (the brighter one; radius ≈0.°31) concentrated at the north of the SNR while enclosing PSR J1853+0056, and Src-S (radius ≈0.°58) concentrated at the south of the SNR. Their spectra have distinct peak energies (∼1.0 GeV for Src-N and ≲0.5 GeV for Src-S), suggesting different origins for them. In our hadronic model that includes the leaked cosmic rays (CRs) from the shock-cloud collision, even with extreme values of parameters, SNR Kes 79 can by no means provide enough CRs reaching clouds at Src-N to explain the local GeV spectrum. We propose that the Src-N emission could be predominantly reproduced by a putative pulsar wind nebula powered by PSR J1853+0056. On the other hand, our same hadronic model can reproduce a majority of the GeV emission at Src-S with typical values of parameters, while the three known pulsars inside Src-S release a total power that is too low to account for half of its γ-ray emission.

In the present work, we reported the fabrication of CdS decorated mesoporous SiC hollow nanofibers for efficient visible-light-driven photocatalytic hydrogen production. The mesoporous SiC hollow nanofibers were firstly fabricated by electrospinning, followed by hydrothermal treatment to introduce the CdS nanoparticles decorated on the preformed fiber matrix, The resultant CdS/SiC hybrid photocatalysts were systematically characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) and N2 adsorption. The as-fabricated CdS/SiC hybrids exhibited a robust stability with a release rate up to ~ 124.65 µmol h−1 g−1 for photocatalytic H2 evolution driven by visible light, which was profoundly enhanced for more than 16 times to that of pristine SiC counterparts, and comparable to the state-of-the-art one of SiC-based photocatalysts.

Sub-solvus dynamic recrystallization (DRX) mechanisms in an advanced &gamma, &gamma, &rsquo, nickel-based superalloy GH4151 were investigated by isothermal compression experiments at 1040 &deg, C with a strain rate of 0.1 s&minus, 1 and various true strain of 0.1, 0.3, 0.5, and 0.7, respectively. This has not been reported in literature before. The electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) technology were used for the observation of microstructure evolution and the confirmation of DRX mechanisms. The results indicate that a new dynamic recrystallization mechanism occurs during hot deformation of the hot-extruded GH4151 alloy. The nucleation mechanism can be described as such a feature, that is a primary &gamma, (Ni3(Al, Ti, Nb)) precipitate embedded in a recrystallized grain existed the same crystallographic orientation, which is defined as heteroepitaxial dynamic recrystallization (HDRX). Meanwhile, the conventional DRX mechanisms, such as the discontinuous dynamic recrystallization (DDRX) characterized by bulging grain boundary and continuous dynamic recrystallization (CDRX) operated through progressive sub-grain merging and rotation, also take place during the hot deformation of the hot-extruded GH4151 alloy. In addition, the step-shaped structures can be observed at grain boundaries, which ensure the low-energy surface state during the DRX process.

The correlation between the peak spectra energy ($E_p$) and the equivalent isotropic energy ($E_{\rm iso}$) of long gamma-ray bursts (GRBs), the so-called Amati relation, is often used to constrain the high-redshift Hubble diagram. Assuming Lambda cold dark matter ($\Lambda$CDM) cosmology, Wang et al. found a $\gtrsim 3\sigma$ tension in the data-calibrated Amati coefficients between low- and high-redshift GRB samples. To reduce the impact of fiducial cosmology, we use the Parameterization based on cosmic Age (PAge), an almost model-independent framework to trace the cosmological expansion history. We find that the low- and high-redshift tension in Amati coefficients stays almost the same for the broad class of models covered by PAge, indicating that the cosmological assumption is not the dominant driver of the redshift evolution of GRB luminosity correlation. Next, we analyze the selection effect due to flux limits in observations. We find Amati relation evolves much more significantly across energy scales of $E_{\rm iso}$. We debias the GRB data by selectively discarding samples to match low-$z$ and high-$z$ $E_{\rm iso}$ distributions. After debiasing, the Amati coefficients agree well between low-$z$ and high-$z$ data groups, whereas the evidence of $E_{\rm iso}$-dependence of Amati relation remains to be strong. Thus, the redshift evolution of GRB luminosity correlation can be fully interpreted as a selection bias, and does not imply cosmological evolution of GRBs., Comment: 5 pages, 4 figures; significant modification

We investigate the nature of the unidentified very-high-energy (VHE) gamma-ray object, HESS J1832-093, in a multi-wavelength context. Based on X-ray variability and spectral index ($\Gamma_X\sim\,1.5$), and its broad-band spectrum (which was remarkably similar to HESS J0632+057, a confirmed gamma-ray binary), HESS J1832-093 has been considered to be a strong gamma-ray binary candidate in previous works. In this work, we provide further evidence for this scenario. We obtained a spectrum of its IR counterpart using Gemini/Flamingo, finding absorption lines that are usually seen in massive stars, in particular O stars. We also obtained a rather steep ATCA spectrum ($\alpha=-1.18^{+1.04}_{-0.88}$) which prefers a gamma-ray binary over an AGN scenario. Based on spatial-spectral analysis and variability search, we found that 4FGL J1832.9-0913 is possible to be associated with SNR G22.7-0.2 rather than with HESS J1832-093 only., Comment: 9 pages, 5 figures, submitted

The composite of low alloy steel reinforced with TiC particles (36 wt%) was prepared by the powder metallurgy (PM) process in this paper. The effects of the chromium content and the total carbon content on the composites were studied. The scanning electron microscopy (SEM) was used to observe the microstructure and such properties as porosity, hardness, transverse rupture strength (TRS) and fracture morphology of the samples were tested. The results show that the optimum sintering temperature decreases with the increase of chromium content. The porosity of sintered samples decreases with increasing the total carbon content, and increases with increasing the chromium content. The TRS and hardness of samples increase with the increase of the carbon content. With the increase of the chromium content, the TRS of the sample gradually decreases, and the hardness firstly increases and then decreases a little. This results from the combined effects of the martensite amount and the shape, size and composition of precipitated chromium carbides in the steel matrix.

A new method was proposed to fabricate diamond/Cu composites. Double-layer diamond particles were directly compressed at ultra-high pressure to prepare the preform and then sintered in a vacuum equipment for densification. The raw diamond particles were coated with zirconium carbide by magnetron sputtering for the inner layer and then deposited with copper by chemical method for the outer layer. Prepared with these particles, the composites had good interface bonding and homogeneously distributed particles in the copper matrix. The thermal conductivity of 65 vol% diamond/Cu composite was as high as 720 W m−1 K−1. When the diamond content increased to 70 vol%, the coefficient of thermal expansion was extremely low (4.33 × 10−6/K). With superb thermal–physical performance, diamond/Cu composites are potentially applicable to electronic packaging.

Zirconium carbide (ZrC) coatings were deposited on graphite substrates by chemical vapor deposition from the Zr-Br 2 -C 3 H 6 -H 2 -Ar system. The influence of total pressure on the growth of ZrC was investigated in the range of 5–60 kPa. As the total pressure increased, the deposition rate increased evidently, and the preferential orientation of ZrC coatings changed from the (200) plane to the (220) plane. The growth mechanism changed from a mass transport reaction to a surface reaction at the total pressure of 20–40 kPa. At the total pressure below 20 kPa, the deposition was dominated by crystal growth, so the coatings were composed of well-faceted pyramidal-shaped crystals growing along the direction. At the total pressure above 60 kPa, the growth of ZrC coatings was controlled by the nucleation mechanism, so the coatings were cluster-like crystals rapidly growing along the direction. In addition, low pressure was conducive to the formation of near-stoichiometric ZrC without free carbon. These variations of ZrC coatings can mainly be attributed to gas supersaturation and remarkably changed transport diffusion coefficients with increasing total pressure.

The supernova remnant (SNR) HESS J1731-347 is a young SNR which displays a non-thermal X-ray and TeV shell structure. A molecular cloud at a distance of 3.2 kpc is spatially coincident with the western part of the SNR, and it is likely hit by the SNR. The X-ray emission from this part of the shell is much lower than from the rest of the SNR. Moreover, a compact GeV emission region coincident with the cloud has been detected with a soft spectrum. These observations seem to imply a shock-cloud collision scenario at this area, where the stalled shock can no longer accelerate super-TeV electrons or maintain strong magnetic turbulence downstream, while the GeV cosmic rays (CRs) are released through this stalled shock. To test this hypothesis, we have performed a detailed Fermi-LAT reanalysis of the HESS J1731-347 region with over 9 years of data. We find that the compact GeV emission region displays a spectral power-law index of -2.4, whereas the GeV emission from the rest of the SNR (excluding the cloud region) has an index of -1.8. A hadronic model involving a shock-cloud collision scenario is built to explain the -ray emission from this area. It consists of three CR sources: run-away super-TeV CRs that have escaped from the fast shock, leaked GeV CRs from the stalled shock, and the local CR sea. The X-ray and -ray emission of the SNR excluding the shock-cloud interaction region is explained in a one-zone leptonic model. Our shock-cloud collision model explains well the GeV-TeV observations from both cloud regions around HESS J1731-347, i.e. from the cloud in contact with the SNR and from the more distant cloud which is coincident with the nearby TeV source HESS J1729-345. We find however that the leaked GeV CRs from the shock-cloud collision do not necessarily dominate the GeV emission from the clouds, due to a comparable contribution from the local CR sea., Comment: 20 pages

GRB 190114C is an unusual gamma-ray burst (GRB) due to its detection at sub-$TeV$ energies by MAGIC, seen at redshift z = 0.42. This burst is one of the brightest GRB detected by \fermi. A joint GBM-LAT analysis of the prompt emission reveals the presence of sub-$GeV$ spectral cutoff when the LAT \emph{low-energy events} (LLE) data is also examined. A similar high-energy cutoff was likewise reported in GRB 160509A and GRB 100724B earlier, as well as handful of other sources. The cutoff can be explained by the intrinsic opacity due to pair production within the emitting region. GRB 190114C shows a transition from non-thermal to a quasi-thermal-like spectrum and a radiation component that can be attributed to afterglow. Based on spectral analysis, we constrain the site of the prompt emission and $Lorentz$ factor. Knowing that sub-$TeV$ photons are detected in MAGIC, we perceive that the observed spectrum is indeed an overlap from two emission sites, where the emission observed in \fermi is more consistent with prompt emission produced via photospheric dissipation along with a concurrent component from the external shock., Comment: Revised and accepted for publication in the ApJ

The composite of 35CrMo high-strength steel matrix reinforced with TiC reinforcement (50 wt.%) has been produced by conventional powder metallurgy (PM). The sintering temperature and process for heating treatment were discussed. The scanning electron microscopy (SEM) revealed the morphology and distribution of the reinforcement phase. Density, hardness, and transverse rupture strength (TRS) of the samples were analyzed. The results showed that the optimal sintering process for the composite is sintering at 1430 °C for 1 h and heat treatment process is annealing at 850 °C/30 min, quenching at 880 °C/30 min and then tempering at 560 °C/60 min. The composite after heat treatment has excellent mechanical properties with a relative density of 99.7%, hardness of 65 HRC, TRS of 1850 ± 20 MPa, respectively, and will be used as refractory moulds, cold work moulds and some gaskets, etc.

•Si addition to Al matrix can reduce the unwanted reactions of Al4C3.•12 wt.% Si addition to Al matrix between diamond and Al can form SiC with a high TC.•The diamond/Al–12.2Si composite has a high TC (558 W/mK) and a low CTE (8.9 × 10−6/K).•The diamond/Al–40Si composite has a very low CTE of 4.5 × 10−6/K.•The mixing of the diamond powders can enhance the TC and reduce the CTE.

Porous Ti–4Mo alloy was prepared by indirect selective laser sintering and investigated with focuses on its porous structure, microstructural characteristic, mechanical properties and corrosion behavior. The results indicate that as the porous alloy is sintered from 1000 to 1200 °C, the pore morphology changes gradually from interconnected to closed pores, meanwhile the porosity level and pore size reduce in the ranges 54–20 % and 103–35 μm, respectively. A laminar microstructure composed of dominant α and minor β phases is observed in pore walls together with slight α precipitations. Elastic modulus and yield strength increase with decreased porosity in the ranges 2.56–10.8 GPa and 47.0–162.4 MPa, respectively. The relationship between the relative mechanical properties and relative density obeys a power law relation. All the polarization curves exhibit an obvious passive characteristic despite different pore features, and the passive film could protect the porous alloy against corrosion in simulated body fluids. Overall, the porous Ti–4Mo alloy may be a potential candidate material for biomedical implants.

Solution plus ageing leads to the precipitation of finer and more homogeneous γ′ precipitates in comparison to direct ageing. Solution treatment at 1220 °C eliminates the large primary γ′ phase and replaces them with homogeneous secondary γ′ precipitates. Coarsening of γ′ particles according to Ostwald ripening mechanism is confirmed. An increase of the critical resolved shear stress (CRSS) is observed for the under-aged specimens, followed by a maximum of CRSS at γ′ particle size of around 100 nm and a decrease of CRSS for the over-aged specimen. This result agrees well with the highest yield strength and microhardness of the 750 °C × 24 h aged specimens.

Cu matrix composites reinforced with flake graphite and diamond particles were prepared by a powder hot pressing process. In this paper, we assess the influence of particle size and the powder composition of the raw material on the microstructure and thermal properties of (Gf + Diamond)/Cu composites. Our results show that Cu powders with small particle sizes that are close to the size of the diamond beneficially increase the performance of prepared composites because their improved flowability allows parallel arrangement of the flake graphite during pressing. The optimum Cu powder composition has an equal volume of the matrix alloy to the combined volume of diamond and flake graphite. Additionally, we compared the experimentally determined thermal conductivity with the theoretically calculated value.