In-situ additive manufacturing of high strength yet ductility titanium composites with gradient layered structure using N_(2)

It has always been challenging work to reconcile the contradiction between the strength and plasticity of titanium materials.Laser powder bed fusion(LPBF) is a convenient method to fabricate innovative composites including those inspired by gradient layered materials.In this work,we used LPBF to selectively prepare Ti N/Ti gradient layered structure(GLSTi)composites by using different N_(2)–Ar ratios during the LPBF process.We systematically investigated the mechanisms of in-situ synthesis Ti N,high strength and ductility of GLSTi composites using microscopic analysis,TEM characterization,and tensile testing with digital image correlation.Besides,a digital correspondence was established between the N_(2) concentration and the volume fraction of LPBF in-situ synthesized Ti N.Our results show that the GLSTi composites exhibit superior mechanical properties compared to pure titanium fabricated by LPBF under pure Ar.Specifically,the tensile strength of GLSTi was more than 1.5times higher than that of LPBF-formed pure titanium,reaching up to 1100 MPa,while maintaining a high elongation at fracture of 17%.GLSTi breaks the bottleneck of high strength but low ductility exhibited by conventional nanoceramic particle-strengthened titanium matrix composites,and the hetero-deformation induced strengthening effect formed by the Ti N/Ti layered structure explained its strength-plasticity balanced principle.The microhardness exhibits a jagged variation of the relatively low hardness of 245 HV0.2 for the pure titanium layer and a high hardness of 408 HV0.2 for the N_(2) in-situ synthesis layer.Our study provides a new concept for the structure-performance digital customization of 3D-printed Ti-based composites.

Microstructural characterization and mechanical properties of(TiC+TiB)/TA15 composites prepared by an in-situ synthesis method

Titanium matrix composites reinforced with ceramic particles are considered a promising engineering material due to their combination of high specific strength,low density,and high modulus.In this study,the TA15-based composites reinforced with a volume fraction of 10% to 25%(TiB+TiC)were prepared using powder metallurgy and casting technique.Microstructural characterization and phase constitution were examined using optical microscopy(OM),scanning electron microscopy(SEM),and X-ray diffraction(XRD).In addition,the microhardness,room temperature(RT)and high temperature(HT)tensile properties of the composites were evaluated.Results revealed that the reinforcements are distributed uniformly even in the composites with a high volume of TiB and TiC.However,as the volume fraction exceeds 15%,TiB and TiC particles become coarsening and exhibit rod-like and dendritic-like morphology.Microhardness increases gradually from 321.2 HV for the base alloy to a maximum of 473.3 HV as the reinforcement increases to 25vol.%.Tensile test results indicate that a reinforcement volume fraction above 20% is beneficial for enhancing tensile strength and yield strength at high temperatures,but it has an adverse effect on room temperature elongation.Conversely,if the reinforcement volume fraction is below 20%,it can improve high-temperature elongation when the temperature exceeds 600℃.

Effects of temperature on fracture behavior of Al-based in-situ composites reinforced with Mg_2Si and Si particles fabricated by centrifugal casting

An aluminum-based in-situ composites reinforced with Mg2Si and Si particles were produced by centrifugal casting A1-20Si-5Mg alloy. The microstructure of the composites was examined, and the effects of temperature on fracture behavior of the composite were investigated. The results show that the average fraction of primary Si and Mg2Si particles in the composites is as high as 38%, and ultimate tensile strengths （UTS） of the composites first increase then decrease with the increase of test temperature. Microstructures of broken specimens show that both the particle fracture and the interface debonding affect the fracture behavior of the composites, and the interface debonding becomes the dominant fracture mechanism with increasing test temperature. Comparative results indicate that rich particles in the composites and excellent interface strength play great roles in enhancing tensile property by preventing the movement of dislocations.

Microstructure evolution and nitrides precipitation in in-situ Ti_2 AlN/TiAl composites during isothermal aging at 900°C

Microstructures of Ti2AlN/TiAl composites prepared by in-situ method were characterized in in-situ and aging treatment conditions and the nitride precipitation was investigated in Ti2AlN/TiAl composites aged at 900 ℃ for 24 h after being heat treated at 1400 ℃ for 0.5 h. The in-situ composites consist of γ＋α2 lamellar colonies, equiaxed y grains and Ti2AlN reinforcements. Matrix with nearly fully lamellar structure formed after solution and subsequently aging treatment. With the increase of Ti2AlN content, the nearly fully lamellar structure becomes instable for the aged composites. According to TEM study, fine Ti2AlN precipitates are found to distribute at the grain boundaries of lamellar colony. Needle-like Ti3AlN precipitates arrange in line with growing axis parallel to [001] direction of the γ-TiAl matrix and another needle-like Ti3AlN precipitates with lager size distribute at the dislocations. Key words：

Effect of Ti-Si-Mg-Al wire on microstructure and mechanical properties of plasma arc in-situ welded joint of SiC_p/Al composites

The influence of Ti-Si-Mg-AI wire on microstructure and mechanical properties of SiCp/A1 metal matrix composite joints produced by plasma arc in-situ weld-alloying was investigated. Argon-nitrogen mixture was used as plasma gas and Ti-Si-Mg-A1 flux-cored wires as filled composites. Weldments were submitted to tensile test. Meanwhile, the macro morphology and microstructure of the joints were examined. The result shows that the formation ofneedie-like harmful phase A14C3 is effectively inhibited and the wettability of molten pool is improved by adding Ti-Si-Mg-A1 flux-cored wires. With 15Ti-5Si-5Mg-A1 flux-cored wire as filled composite, the maximum tensile strength of the welded joint is 267 MPa, which is up to 83% that of the matrix composites under annealed condition.

In-situ homogeneous synthesis of carbon nanotubes on aluminum matrix and properties of their composites

Using nickel catalyst supported on aluminum powders, carbon nanotubes （CNTs） were successfully synthesized in aluminum powders by in-situ chemical vapor deposition at 650 ℃. Structural characterization revealed that the as-grown CNTs possessed higher graphitization degree and straight graphite shell. By this approach, more homogeneous dispersion of CNTs in aluminum powders was achieved compared with the traditional mechanical mixture methods. Using the in-situ synthesized CNTs/Al composite powders and powder metallurgy process, CNTs/Al bulk composites were prepared. Performance testing showed that the mechanical properties and dimensional stability of the composites were improved obviously, which was attributed to the superior dispersion of CNTs in aluminum matrix and the strong interfacial bonding between CNTs and matrix.

Preparation and wear properties of TiB_2/Al-30Si composites via in-situ melt reactions under high-energy ultrasonic field

TiB2/Al-30Si composites were fabricated via in-situ melt reaction under high-energy ultrasonic field. The microstructure and wear properties of the composite were investigated by XRD, SEM and dry sliding testing. The results indicate that TiB2 reinforcement particles are uniformly distributed in the aluminum matrix under high-energy ultrasonic field. The morphology of the TiB2 particles is in circle-shape or quadrangle-shape, and the size of the particles is 0.1-1.5μm. The primary silicon particles are in quadrangle-shape and the average size of them is about 10μm. Hardness values of the Al-30Si matrix alloy and the TiB2/Al-30Si composites considerably increase as the high energy ultrasonic power increases. In particular, the maximum hardness value of the in-situ composites is about 1.3 times as high as that of the matrix alloy when the ultrasonic power is 1.2 kW, reaching 412 MPa. Meanwhile, the wear resistance of the in-situ TiB2/Al-30Si composites prepared under high-energy ultrasonic field is obviously improved and is insensitive to the applied loads of the dry sliding testing.

Effects of two modification methods on the mechanical properties of wood flour/recycled plastic blends composites: addition of thermoplastic elastomer SEBS-g-MAH and in-situ grafting MAH

The effect of maleic anhydride grafted styrene-ethylene- buty-lene-styrene block copolymer （SEBS-g-MAH） and in-situ grafting MAH on mechanical, dynamic mechanical properties of wood flour/recycled plastic blends composites was investigated. Recycled plastic polypro-pylene （PP）, high-density polyethylene （HDPE） and polystyrene （PS）, were mixed with wood flour in a high speed blender and then extruded by a twin/single screw tandem extruder system to form wood flour/recycled plastic blends composites. Results show that the impact properties of the composites were improved more significantly by using SEBS-g-MAH compatibilizer than by using the mixtures of MAH and DCP via reactive blending in situ. However, contrary results were ob-served on the tensile and flexural properties of the corresponding com-posites. In General, the mechanical properties of composites made from recycled plastic blends were inferior to those made from virgin plastic blends, especially in elongation break. The morphological study verified that the interfacial adhesion or the compatibility of plastic blends with wood flour was improved by adding SEBS-g-MAH or in-situ grafting MAH. A better interfacial bonding between PP, HDPE, PS and wood flour was obtained by in-situ grafting MAH than the addition of SEBS-g-MAH. In-situ grafting MAH can be considered as a potential way of increasing the interfacial compatibility between plastic blends and wood flour. The storage modulus and damping factor of composites were also characterized through dynamic mechanical analysis （DMA）.

In-situ deposition of apatite layer to protect Mg-based composite fabricated via laser additive manufacturing

Biodegradable magnesium(Mg) and its alloy show huge potential as temporary bone substitute due to the favorable biocompatibility and mechanical compatibility. However, one issue deserves attention is the too fast degradation. In this work, mesoporous bioglass(MBG)with high pore volume(0.59 cc/g) and huge specific surface area(110.78 m^(2)/g) was synthesized using improved sol-gel method, and introduced into Mg-based composite via laser additive manufacturing. Immersion tests showed that the incorporated MBG served as powerful adsorption sites, which promoted the in-situ deposition of apatite by successively adsorbing Ca2+and HPO42-. Such dense apatite film acted as an efficient protection layer and enhanced the corrosion resistance of Mg matrix, which was proved by the electrochemical impedance spectroscopy measurements. Thereby, Mg based composite showed a significantly decreased degradation rate of 0.31 mm/year. Furthermore,MBG also improved the mechanical properties as well as cell behavior. This work highlighted the advantages of MBG in the fabrication of Mg-based implant with enhanced overall performance for orthopedic application.

Investigation into machining performance of microstructurally engineered in-situ particle reinforced magnesium matrix composite

Magnesium and magnesium in-situ composites have significant potential in the application of design and manufacturing for automotive and aerospace industries because of their high specific strength and reduced fuel consumption.But there are many challenges for machining of Mg based alloys and composites because of the high tendency of fire and oxidation.These challenges can be minimized through microstructural engineering.In this present study,the machining performances of AZ91 Mg alloy and in-situ hybrid TiC+TiB_(2)reinforced AZ91 metal matrix composite was investigated.The effectβ-Mg_(17)Al_(12)phases and grain refinement with and without in-situ particles on machinability were studied through microstructural engineering via aging and friction stir processing.The end milling operation was carried out at different cutting speeds ranging from 25 mm/min to 90 mm/min under dry environment by using an AlTiN-coated tungsten carbide tool.The optimum cutting speed for machining was found to be 75 mm/min based on the surface roughness values of all conditioned materials.The base material with dendritic microstructure was found to have poor machinability in terms of inadequate surface finish and edge-burrs formation.The combined effect of in-situ TiC+TiB_(2)particles addition and grain refinement enhanced the machining performance of the material with superior surface finish,negligible edge-burr formation and better tool wear resistance.The influence of in-situ TiC+TiB_(2)particles,β-Mg_(17)Al_(12)phases and grain refinement on machining characteristics are explained based on the tool wear mechanisms,chip behavior and machining induced affected zone.

In-situ fabrication of particulate reinforced aluminum matrix composites under high-frequency pulsed electromagnetic field

Pulsed magnetic field is generated when imposing pulse signal on high-frequency magnetic field. Distribution of the inner magnetic intensity in induction coils tends to be uniform. Furthermore oscillation and disturbance phenomena appear in the melt. In. situ Al2O3 and Al3Zr particulate reinforced aluminum matrix composites have been synthesized by direct melt reaction using AlZr（CO3）2 components under a foreign field. The size of reinforced particulates is 2-3 μm. They are well distributed in the matrix. Thermodynamic and kinetic analysis show that high-frequency pulsed magnetic field accelerates heat and mass transfer processes and improves the kinetic condition of in-situ fabrication.

In-situ interfacial passivation and self-adaptability synergistically stabilizing all-solid-state lithium metal batteries

The function of solid electrolytes and the composition of solid electrolyte interphase(SEI)are highly significant for inhibiting the growth of Li dendrites.Herein,we report an in-situ interfacial passivation combined with self-adaptability strategy to reinforce Li_(0.33)La_(0.557)TiO_(3)(LLTO)-based solid-state batteries.Specifically,a functional SEI enriched with LiF/Li_(3)PO_(4) is formed by in-situ electrochemical conversion,which is greatly beneficial to improving interface compatibility and enhancing ion transport.While the polarized dielectric BaTiO_(3)-polyamic acid(BTO-PAA,BP)film greatly improves the Li-ion transport kinetics and homogenizes the Li deposition.As expected,the resulting electrolyte offers considerable ionic conductivity at room temperature(4.3 x 10~(-4)S cm^(-1))and appreciable electrochemical decomposition voltage(5.23 V)after electrochemical passivation.For Li-LiFePO_(4) batteries,it shows a high specific capacity of 153 mA h g^(-1)at 0.2C after 100 cycles and a long-term durability of 115 mA h g^(-1)at 1.0 C after 800 cycles.Additionally,a stable Li plating/stripping can be achieved for more than 900 h at 0.5 mA cm^(-2).The stabilization mechanisms are elucidated by ex-situ XRD,ex-situ XPS,and ex-situ FTIR techniques,and the corresponding results reveal that the interfacial passivation combined with polarization effect is an effective strategy for improving the electrochemical performance.The present study provides a deeper insight into the dynamic adjustment of electrode-electrolyte interfacial for solid-state lithium batteries.

Study on in-situ WC particles/tungsten wire reinforced iron matrix composites under electromagnetic field

By applying electromagnetic field to a system consisting of tungsten wires and grey cast iron melt,the grey cast iron matrix composite reinforced by either in-situ WC particles or the combination ofin-situ WC particles and the residual tungsten wire was obtained.By means of differential thermal analysis(DTA),the pouring temperature ofiron melt was determined at 1,573 K.The microstructures of the composites were analyzed by using of X-ray diffraction(XRD),scanning electron microscopy(SEM) equipped with an energy dispersive spectrum(EDS) and pin-on-disc abrasive wear test.The obtained results indicated that,with the enhancing frequency of electromagnetic field,the amount ofin-situ WC particles gradually increases,leading to continuous decrease of the residual tungsten wires.When the electromagnetic field frequency was up to 4 kHz,tungsten wires reacted completely with carbon atoms in grey cast iron melt,forming WC particals.The electromagnetic field appeared to accelerate the elemental diffusion in the melt,to help relatively quick formation of a series of small FeW-C ternary zones and to improve the kinetic condition ofin-situ WC fabrication.As compared with the composite prepared without the electromagnetic field,the composite fabricated at 4 kHz presented good wear resistance.

Microstructures and mechanical properties of in-situ TiB2/Al−xSi−0.3Mg composites

In-situ 2 vol.%TiB2 particle reinforced Al−xSi−0.3Mg(x=7,9,12,15 wt.%)composites were prepared by the salt−metal reaction,and the microstructures and mechanical properties were investigated.The results show that the TiB2 particles with a diameter of 20−80 nm and the eutectic Si with a length of 1−10μm are the main strengthening phases in the TiB2/Al−xSi−0.3Mg composites.The TiB2 particles promote grain refinement and modify the eutectic Si from needle-like to short-rod shape.However,the strengthening effect of TiB2 particles is weakened as the Si content exceeds the eutectic composition,which can be attributed to the formation of large and irregular primary Si.The axial tensile test results and fractography observations indicate that these composites show more brittle fracture characteristics than the corresponding alloy matrixes.

Research on properties of hollow glass microspheres/epoxy resin composites applied in deep rock in-situ temperature-preserved coring

Deep petroleum resources are in a high-temperature environment.However,the traditional deep rock coring method has no temperature preserved measures and ignores the effect of temperature on rock porosity and permeability,which will lead to the distortion of the petroleum resources reserves assessment.Therefore,the hollow glass microspheres/epoxy resin(HGM/EP)composites were innovatively proposed as temperature preserved materials for in-situ temperature-preserved coring(ITP-Coring),and the physical,mechanical,and temperature preserved properties were evaluated.The results indicated that:As the HGM content increased,the density and mechanical properties of the composites gradually decreased,while the water absorption was deficient without hydrostatic pressure.For composites with 50 vol%HGM,when the hydrostatic pressure reached 60 MPa,the water absorption was above 30.19%,and the physical and mechanical properties of composites were weakened.When the hydrostatic pressure was lower than 40 MPa,the mechanical properties and thermal conductivity of composites were almost unchanged.Therefore,the composites with 50 vol%HGM can be used for ITPCoring operations in deep environments with the highest hydrostatic pressure of 40 MPa.Finally,to further understand the temperature preserved performance of composites in practical applications,the temperature preserved properties were measured.An unsteady-state heat transfer model was established based on the test results,then the theoretical change of the core temperature during the coring process was obtained.The above tests results can provide a research basis for deep rock in-situ temperature preserved corer and support accurate assessment of deep petroleum reserves.

In-situ formation of Al-CaB_6 composites with low resistivity

In this work, in-situ CaB6 reinforced aluminum matrix composites were fabricated, and the microstructure, resistivity, microhardness and coefficient of thermal expansion (CTE) of Al-CaB6 composites were studied. It is found that CaB6 compounds can be formed by reducing reaction occurred in the Al melt: . CaB6 exhibits a hexahedron morphology and distributes uniformly in the Al alloy matrix. The resistivity of Al-CaB6 composites is 3.02*10-8 Ω·m, which is close to that of pure Al and lower than that of 6063Al/Ga composites. The average microhardness of Al-CaB6 composites can reach 1270 MPa, 259.8% higher than that of pure Al. Compared to pure Al, the CTE of Al-CaB6 composites is much lower.

Friction and wear properties of casting in-situ silicon particle reinforced ZA27 composites

The effects of silicon particle content and testing temperature on friction and wear properties of casting in-situ silicon particle reinforced ZA27 composites were investigated.The wear mechanisms were mainly discussed by observations of both worn surfaces and their side views.The results indicated that the variations of wear resistance with increasing of silicon particle content,at all of the testing temperatures applied,showed a similar tendency with a manner of non-monotonous change.It was surprised that the wear resistance decreased with the increase of silicon particle content from 2 vol.%to 5 vol.%,while it increased when the content was less than 2 vol.%or more than 5 vol.%.Similarly,the friction coefficient also did not change monotonously.The dominative wear mechanism changed from a relatively severe regime of plastic deformation accompanied by adhesion wear to a mild regime of smear,then to a very severe regime of severe plastic deformation induced wear,and finally again to a relatively mild regime of smear accompanied by abrasive wear as the silicon content increased.The wear resistance always decreased with elevating testing temperature,but the decrease ranges were different for the composites with different silicon contents.The friction coefficients changed irregularly for the different composites with the increase of testing temperature.Correspondingly,the wear mechanism alternated from a mild regime of smear accompanied by abrasive wear to a severe regime of plastic deformation accompanied by adhesion wear.

Thermodynamics and Kinetics of in-situ Formation of TiAl_3/7075 Composites

The thermodynamics and kinetics of the reaction between Titanium powder and 7075 aluminum alloy were investigated to assess the possibility of preparing TiA1J7075 composites by in-situ synthesis method. Results show that Ti and A1 melt can form TiA13 spontaneously, which is considered as a reinforced phase of the matrix. Measurements such as XRD, SEM, and EDX were performed to characterize the as-synthesized samples, and results confirmed the formation of TiA13 in aluminum matrix composites. The reactive kinetics was controlled by three main factors, which are the system temperature, particle size of Ti, and the thickness of external diffusion layer.

Microstructure Characteristic of In-situ Ti/TiC Composites

TiC reinforced titanium composites has been produced with different Al content and C content by XDTM. The results have shown that TiC particles are of two different morphologies f coarse dendritical primary TiC and short bar-shape eutectic TiC. Al content has great effects on the morphology of TiC. With the increasing of Al content, the morphology of primary TiC changes from coarse developed dendrite into short bar-shape or plate--shape TiC with 35%Al. Meanwhile, the structure of the matrix changes from single Ti to Ti and Ti3Al, and to Ti3Al and TiAl. However, the C content has no influence on the microstructure of matrix. When the C content is less than 1.2%, the dendrite TiC disappears and only short bar-shape or plate-shape TiC exists in the composites. In addition, the effect of he3t treatment on the morphology of TiC has also Studied.

In-situ Micro-CT analysis of deformation behavior in sandwich-structured meta-stable beta Ti−35Nb alloy

Beta Ti−35Nb sandwich-structured composites with various reinforcing layers were designed and produced using additive manufacturing(AM)to achieve a balance between light weight and high strength.The impact of reinforcing layers on the compressive deformation behavior of porous composites was investigated through micro-computed tomography(Micro-CT)and finite element method(FEM)analyses.The results indicate that the addition of reinforcement layers to sandwich structures can significantly enhance the compressive yield strength and energy absorption capacity of porous metal structures;Micro-CT in-situ observation shows that the strain of the porous structure without the reinforcing layer is concentrated in the middle region,while the strain of the porous structure with the reinforcing layer is uniformly distributed;FEM analysis reveals that the reinforcing layers can alter stress distribution and reduce stress concentration,thereby promoting uniform deformation of the porous structure.The addition of reinforcing layer increases the compressive yield strength of sandwich-structured composite materials by 124%under the condition of limited reduction of porosity,and the yield strength increases from 4.6 to 10.3 MPa.