Influence of layer thickness on formation quality,microstructure,mechanical properties,and corrosion resistance of WE43 magnesium alloy fabricated by laser powder bed fusion

Laser powder bed fusion(L-PBF)of Mg alloys has provided tremendous opportunities for customized production of aeronautical and medical parts.Layer thickness(LT)is of great significance to the L-PBF process but has not been studied for Mg alloys.In this study,WE43 Mg alloy bulk cubes,porous scaffolds,and thin walls with layer thicknesses of 10,20,30,and 40μm were fabricated.The required laser energy input increased with increasing layer thickness and was different for the bulk cubes and porous scaffolds.Porosity tended to occur at the connection joints in porous scaffolds for LT40 and could be eliminated by reducing the laser energy input.For thin wall parts,a large overhang angle or a small wall thickness resulted in porosity when a large layer thicknesses was used,and the porosity disappeared by reducing the layer thickness or laser energy input.A deeper keyhole penetration was found in all occasions with porosity,explaining the influence of layer thickness,geometrical structure,and laser energy input on the porosity.All the samples achieved a high fusion quality with a relative density of over 99.5%using the optimized laser energy input.The increased layer thickness resulted to more precipitation phases,finer grain sizes and decreased grain texture.With the similar high fusion quality,the tensile strength and elongation of bulk samples were significantly improved from 257 MPa and 1.41%with the 10μm layer to 287 MPa and 15.12%with the 40μm layer,in accordance with the microstructural change.The effect of layer thickness on the compressive properties of porous scaffolds was limited.However,the corrosion rate of bulk samples accelerated with increasing the layer thickness,mainly attributed to the increased number of precipitation phases.

Microstructure and thermal properties of dissimilar M300–CuCr1Zr alloys by multi-material laser-based powder bed fusion

Multi-material laser-based powder bed fusion (PBF-LB) allows manufacturing of parts with 3-dimensional gradient and additional functionality in a single step. This research focuses on the combination of thermally-conductive CuCr1Zr with hard M300 tool steel.Two interface configurations of M300 on CuCr1Zr and CuCr1Zr on M300 were investigated. Ultra-fine grains form at the interface due to the low mutual solubility of Cu and steel. The material mixing zone size is dependent on the configurations and tunable in the range of0.1–0.3 mm by introducing a separate set of parameters for the interface layers. Microcracks and pores mainly occur in the transition zone.Regardless of these defects, the thermal diffusivity of bimetallic parts with 50vol% of CuCr1Zr significantly increases by 70%–150%compared to pure M300. The thermal diffusivity of CuCr1Zr and the hardness of M300 steel can be enhanced simultaneously by applying the aging heat treatment.

Lithiophilic Li-Si alloy-solid electrolyte interface enabled by high-concentration dual salt-reinforced quasi-solid-state electrolyte

Solid polymer electrolytes(SPEs)are urgently required to achieve practical solid-state lithium metal batteries(LMBs)and lithium-ion batteries(LIBs),Herein,we proposed a mechanism for modulating interfacial conduction and anode interfaces in high-concentration SPEs by LiDFBOP.Optimized electrolyte exhibits superior ionic conductivity and remarkable interface compatibility with salt-rich clusters:(1)polymer-plastic crystal electrolyte(P-PCE,TPU-SN matrix)dissociates ion pairs to facilitate Li+transport in the electrolyte and regulates Li^(+)diffusion in the SEI.The crosslinking structure of the matrix compensates for the loss of mechanical strength at high-salt concentrations;(2)dual-anion TFSI^(-)_(n)-DFBOP^(-)_(m)in the Li^(+)solvation sheath facilitates facile Li^(+)desolvation and formation of salt-rich clusters and is conducive to the formation of Li conductive segments of TPU-SN matrix;(3)theoretical calculations indicate that the decomposition products of LiDFBOP form SEI with lower binding energy with LiF in the SN system,thereby enhancing the interfacial electrochemical redox kinetics of SPE and creating a solid interface SEI layer rich in LiF.As a result,the optimized electrolyte exhibits an excellent ionic conductivity of9.31×10^(-4)S cm^(-1)at 30℃and a broadened electrochemical stability up to 4.73 V.The designed electrolyte effectively prevents the formation of Li dendrites in Li symmetric cells for over 6500 h at0.1 mA cm^(-2).The specific Li-Si alloy-solid state half-cell capacity shows 711.6 mAh g^(-1)after 60 cycles at 0.3 A g^(-1).Excellent rate performance and cycling stability are achieved for these solid-state batteries with Li-Si alloy anodes and NCM 811 cathodes.NCM 811‖Prelithiated silicon-based anode solid-state cell delivers a discharge capacity of 195.55 mAh g^(-1)and a capacity retention of 97.8%after 120 cycles.NCM 811‖Li solid-state cell also delivers capacity retention of 84.2%after 450 cycles.

Microstructure evolution and strengthening mechanism of high -performance powder metallurgy TA15 titanium alloy by hot rolling

Hot deformation of sintered billets by powder metallurgy(PM)is an effective preparation technique for titanium alloys,which is more significant for high-alloying alloys.In this study,Ti–6.5Al–2Zr–Mo–V(TA15)titanium alloy plates were prepared by cold press-ing sintering combined with high-temperature hot rolling.The microstructure and mechanical properties under different process paramet-ers were investigated.Optical microscope,electron backscatter diffraction,and others were applied to characterize the microstructure evolution and mechanical properties strengthening mechanism.The results showed that the chemical compositions were uniformly dif-fused without segregation during sintering,and the closing of the matrix craters was accelerated by increasing the sintering temperature.The block was hot rolled at 1200℃ with an 80%reduction under only two passes without annealing.The strength and elongation of the plate at 20–25℃ after solution and aging were 1247 MPa and 14.0%,respectively,which were increased by 24.5%and 40.0%,respect-ively,compared with the as-sintered alloy at 1300℃.The microstructure was significantly refined by continuous dynamic recrystalliza-tion,which was completed by the rotation and dislocation absorption of the substructure surrounded by low-angle grain boundaries.After hot rolling combined with heat treatment,the strength and plasticity of PM-TA15 were significantly improved,which resulted from the dense,uniform,and fine recrystallization structure and the synergistic effect of multiple slip systems.

Alloy design for laser powder bed fusion additive manufacturing:a critical review

Metal additive manufacturing(AM)has been extensively studied in recent decades.Despite the significant progress achieved in manufacturing complex shapes and structures,challenges such as severe cracking when using existing alloys for laser powder bed fusion(L-PBF)AM have persisted.These challenges arise because commercial alloys are primarily designed for conventional casting or forging processes,overlooking the fast cooling rates,steep temperature gradients and multiple thermal cycles of L-PBF.To address this,there is an urgent need to develop novel alloys specifically tailored for L-PBF technologies.This review provides a comprehensive summary of the strategies employed in alloy design for L-PBF.It aims to guide future research on designing novel alloys dedicated to L-PBF instead of adapting existing alloys.The review begins by discussing the features of the L-PBF processes,focusing on rapid solidification and intrinsic heat treatment.Next,the printability of the four main existing alloys(Fe-,Ni-,Al-and Ti-based alloys)is critically assessed,with a comparison of their conventional weldability.It was found that the weldability criteria are not always applicable in estimating printability.Furthermore,the review presents recent advances in alloy development and associated strategies,categorizing them into crack mitigation-oriented,microstructure manipulation-oriented and machine learning-assisted approaches.Lastly,an outlook and suggestions are given to highlight the issues that need to be addressed in future work.

Influence of heat treatment on microstructure,mechanical and corrosion behavior of WE43 alloy fabricated by laser-beam powder bed fusion

Magnesium(Mg)alloys are considered to be a new generation of revolutionary medical metals.Laser-beam powder bed fusion(PBF-LB)is suitable for fabricating metal implants withpersonalized and complicated structures.However,the as-built part usually exhibits undesirable microstructure and unsatisfactory performance.In this work,WE43 parts were firstly fabricated by PBF-LB and then subjected to heat treatment.Although a high densification rate of 99.91%was achieved using suitable processes,the as-built parts exhibited anisotropic and layeredmicrostructure with heterogeneously precipitated Nd-rich intermetallic.After heat treatment,fine and nano-scaled Mg24Y5particles were precipitated.Meanwhile,theα-Mg grainsunderwent recrystallization and turned coarsened slightly,which effectively weakened thetexture intensity and reduced the anisotropy.As a consequence,the yield strength and ultimate tensile strength were significantly improved to(250.2±3.5)MPa and(312±3.7)MPa,respectively,while the elongation was still maintained at a high level of 15.2%.Furthermore,the homogenized microstructure reduced the tendency of localized corrosion and favoredthe development of uniform passivation film.Thus,the degradation rate of WE43 parts was decreased by an order of magnitude.Besides,in-vitro cell experiments proved their favorable biocompatibility.

Micro-aluminum powder with bi-or tri-component alloy coating as a promising catalyst:Boosting pyrolysis and combustion of ammonium perchlorate

A novel design of micro-aluminum(μAl)powder coated with bi-/tri-component alloy layer,such as:Ni-P and Ni-P-Cu(namely,Al@Ni-P,Al@Ni-P-Cu,respectively),as combustion catalysts,were introduced to release its huge energy inside Al-core and promote rapid pyrolysis of ammonium perchlorate(AP)at a lower temperature in aluminized propellants.The microstructure of Al@Ni-P-Cu demonstrates that a three-layer Ni-P-Cu shell,with the thickness of~100 nm,is uniformly supported byμAl carrier(fuel unit),which has an amorphous surface with a thickness of~2.3 nm(catalytic unit).The peak temperature of AP with the addition of Al@Ni-P-Cu(3.5%)could significantly drop to 316.2℃ at high-temperature thermal decomposition,reduced by 124.3℃,in comparison to that of pure AP with 440.5℃.It illustrated that the introduction of Al@Ni-P-Cu could weaken or even eliminate the obstacle of AP pyrolysis due to its reduction of activation energy with 118.28 kJ/mol.The laser ignition results showed that the ignition delay time of Al@Ni-P-Cu/AP mixture with 78 ms in air is shorter than that of Al@Ni-P/AP(118 ms),decreased by 33.90%.Those astonishing breakthroughs were attributed to the synergistic effects of adequate active sites on amorphous surface and oxidation exothermic reactions(7597.7 J/g)of Al@Ni-P-Cu,resulting in accelerated mass and/or heat transfer rate to catalyze AP pyrolysis and combustion.Moreover,it is believed to provide an alternative Al-based combustion catalyst for propellant designer,to promote the development the propellants toward a higher energy.

Laser powder bed fusion additive manufacturing of NiTi shape memory alloys: a review

NiTi alloys have drawn significant attentions in biomedical and aerospace fields due to their unique shape memory effect(SME),superelasticity(SE),damping characteristics,high corrosion resistance,and good biocompatibility.Because of the unsatisfying processabilities and manufacturing requirements of complex NiTi components,additive manufacturing technology,especially laser powder bed fusion(LPBF),is appropriate for fabricating NiTi products.This paper comprehensively summarizes recent research on the NiTi alloys fabricated by LPBF,including printability,microstructural characteristics,phase transformation behaviors,lattice structures,and applications.Process parameters and microstructural features mainly influence the printability of LPBF-processed NiTi alloys.The phase transformation behaviors between austenite and martensite phases,phase transformation temperatures,and an overview of the influencing factors are summarized in this paper.This paper provides a comprehensive review of the mechanical properties with unique strain-stress responses,which comprise tensile mechanical properties,thermomechanical properties(e.g.critical stress to induce martensitic transformation,thermo-recoverable strain,and SE strain),damping properties and hardness.Moreover,several common structures(e.g.a negative Poisson’s ratio structure and a diamond-like structure)are considered,and the corresponding studies are summarized.It illustrates the various fields of application,including biological scaffolds,shock absorbers,and driving devices.In the end,the paper concludes with the main achievements from the recent studies and puts forward the limitations and development tendencies in the future.

Powder mixed electrochemical discharge process for micro machining of C103 niobium alloy

This work demonstrates the viability of the powder-mixed micro-electrochemical discharge machining(PMECDM) process to fabricate micro-holes on C103 niobium-based alloy for high temperature applications.Three processes are involved simultaneously i.e.spark erosion,chemical etching,and abrasive grinding for removal of material while the classical electrochemical discharge machining process involves double actions i.e.spark erosion,and chemical etching.The powder-mixed electrolyte process resulted in rapid material removal along with a better surface finish as compared to the classical microelectrochemical discharge machining(MECDM).Further,the results are optimized through a multiobjective optimization approach and study of the surface topography of the hole wall surface obtained at optimized parameters.In the selected range of experimental parameters,PMECDM shows a higher material removal rate(MRR) and lower surface roughness(R_(a))(MRR:2.8 mg/min and R_(a) of 0.61 μm) as compared to the MECDM process(MRR:2.01 mg/min and corresponding Raof 1.11 μm).A detailed analysis of the results is presented in this paper.

Investigation of the Laser Powder Bed Fusion Process of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si Alloy

Laser powder bed fusion(LPBF)is an advanced manufacturing technology;however,inappropriate LPBF process parameters may cause printing defects in materials.In the present work,the LPBF process of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy was investigated by a two-step optimization approach.Subsequently,heat transfer and liquid flow behaviors during LPBF were simulated by a well-tested phenomenological model,and the defect formation mechanisms in the as-fabricated alloy were discussed.The optimized process parameters for LPBF were detected as laser power changed from 195 W to 210 W,with scanning speed of 1250 mm/s.The LPBF process was divided into a laser irradiation stage,a spreading flow stage,and a solidification stage.The morphologies and defects of deposited tracks were affected by liquid flow behavior caused by rapid cooling rates.The findings of this research can provide valuable support for printing defect-free metal components.

Improving corrosion resistance of additively manufactured WE43 magnesium alloy by high temperature oxidation for biodegradable applications

Laser powder bed fusion(L-PBF)has been employed to additively manufacture WE43 magnesium(Mg)alloy biodegradable implants,but WE43 L-PBF samples exhibit excessively rapid corrosion.In this work,dense WE43 L-PBF samples were built with the relativity density reaching 99.9%.High temperature oxidation was performed on the L-PBF samples in circulating air via various heating temperatures and holding durations.The oxidation and diffusion at the elevated temperature generated a gradient structure composed of an oxide layer at the surface,a transition layer in the middle and the matrix.The oxide layer consisted of rare earth(RE)oxides,and became dense and thick with increasing the holding duration.The matrix was composed ofα-Mg,RE oxides and Mg_(24)RE_(5) precipitates.The precipitates almost disappeared in the transition layer.Enhanced passivation effect was observed in the samples treated by a suitable high temperature oxidation.The original L-PBF samples lost 40%weight after 3-day immersion in Hank’s solution,and broke into fragments after 7-day immersion.The casted and solution treated samples lost roughly half of the weight after 28-day immersion.The high temperature oxidation samples,which were heated at 525℃ for 8 h,kept the structural integrity,and lost only 6.88%weight after 28-day immersion.The substantially improved corrosion resistance was contributed to the gradient structure at the surface.On one hand,the outmost dense layer of RE oxides isolated the corrosive medium;on the other hand,the transition layer considerably inhibited the corrosion owing to the lack of precipitates.Overall,high temperature oxidation provides an efficient,economic and safe approach to inhibit the corrosion of WE43 L-PBF samples,and has promising prospects for future clinical applications.

Microstructures of Sintered Mo-Cu Alloys with Mechanically Activated Powder

Mechanical activation and liquid phase sintering were used to manufacture high performance Mo-Cu alloy and develop new processes. The microstructures and properties of the alloy were investigated. The experimental results showed that: (1) the ball milled Mo/Cu powder has lamellar structure, (2) the microstructures of the sintered Mo-Cu alloy were homogenous compound structures of adhesive phase Cu linking Mo grains, (3) Mo grains frequently strung or gathered in Cu phase, and (4) the full densities of Mo-Cu alloy was achieved through sintering and special densification process. As a result, the properties of the alloy are good enough to satisfy various requirements.

MICROSTRUCTURES OF TiAl BASED ALLOYS PREPARED BY HOT PRESSING ELEMENTAL POWDERS

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Improvement of Ductility of Powder Metallurgy Titanium Alloys by Addition of Rare Earth Element

Ti-4.5Al-6.0Mo-1.5Fe, Ti-6Al-1Mo-1Fe and Ti-6Al-4V alloys were prepared by blended elemental powder metallurgy （PM） process, and the effects of Nd on the microstructures and mechanical properties were investigated by scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and X-ray diffraction （XRD）. It was found out that the addition of Nd increased the density of sintered titanium alloys slightly by a maximum increment of 1% because small amount of liquid phase occurred during sintering. The addition of Nd shows little effect on the improvement of tensile strength, while the elongation is significantly improved. For example, the elongation of Ti-4.SAl-6.0Mo-1.5Fe can be increased from 1% without addition of Nd to 13% at a Nd content of 1.2 wt pct.

Formation regularity of phases in nanometer powders of Al-Fe alloy prepared by gas evaporation

Nanometer powders of Al Fe alloy were prepared by gas evaporation. The formation regularity of the phases in the as prepared powders and the morphology of the particles were examined. The experimental results show that chemical composition of the master alloy is the key factor which controls the chemical composition of the compound phases in nanometer powders at given evaporating temperature, the compound phases with high Fe mole fraction will form with increasing of Fe content in master alloy. Only Al 13 Fe 4, FeAl 2 and Al 2Fe compound phases form in nanometer powders in present experiment, changing of the pressure of Ar can only alter relative amounts of the compound phases in the powders. Nanometer particles with inhomogeneous tissue were obtained, which is very different from that of pure Al and Fe nanometer particles. When mole fraction of Fe in particles increases, the inhomogeneity is enhanced. [

CHARACTERISTICS OF FATIGUE SURFACE MICROCRACK GROWTH IN VICINAL INCLUSION FOR POWDER METALLURGY ALLOYS

Inclusion flaw is one of the worst flaws of powder metallurgy.The inclusion flaw plays an important role in the failure of high temperature turbine materials in aircraft components and automotive parts,especially fatigue failure.In this paper,an experimental investigation of fatigue microcrack propagation in the vicinal inclusion were carried out by the servo-hydraulic fatigue test system with scanning electron microscope(SEM).It has been found from the SEM images that the fatigue surface microcrack occurs in the matrix and inclusion.According to the SEM images,the characteristics of fatigue crack initiation and growth in vicinal inclusion for powder metallurgy alloys are analyzed in detail.The effect of the geometrical shape and material type of surface inclusions on the cracking is also discussed with the finite element method(FEM).

SYNTHESIS OF Ti-47Al-2Cr-2Nb ALLOY THROUGH ELEMENTAL POWDER METALLURGY

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Influence of B source materials on the synthesis of TiB_2-Al_2O_3 nanocomposite powders by mechanical alloying

An Al2O3-TiB2 nanocomposite was successfully synthesized by ball milling of Al, TiO2 and two B source materials of B2O3 （system （1）） and H3BO3 （system （2））. Phase identification of the milled samples was examined by Xray diffraction. The morphology and microstructure of the milled powders were monitored by scanning electron microscopy and transmission electron microscopy. It was found that the formation of this composite was completed after 15 and 30 h of milling time in systems （1） and （2）, respectively. More milling energy was required for the formation of this composite in system （2） due to the lubricant properties of HaBO3 and also its decomposition to HBO2 and B2O3 during milling. On the basis of X-ray diffraction patterns and thermodynamic calculations, this composite was formed by highly exothermic mechanically induced self-sustaining reactions （MSR） in both systems. The MSR mode took place around 9 h and 25 h of milling in systems （1） and （2）, respectively. At the end of milling （15 h for system （1） and 30 h for system （2）） the grain size of about 35-50 nm was obtained in both systems.

Synthesis of nanocrystalline NiCrC alloy feedstock powders for thermal spraying by cryogenic ball milling

Nanocrystalline NiCrC alloy powders with a qualified particle size distribution for thermal spraying were synthesized using the cryogenic ball milling （cryomilling） method. The morphology, microstructure, size distribution, and phase transformation of the powders were characterized by scanning electron microscopy （SEM）, laser scattering for particle size analysis, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. After cryomilling for 20 h, the average grain size of the as-milled powders approached a constant value of 30 nm by XRD measurement. The average particle size slightly increased from 17.5 to 20.3 μm during the 20-h milling. About 90vol% of the powders satisfied the requirement for thermal spraying with the particle dimension of 10-50 μm, and most of the powders exhibited spherical morphology, which were expected to have good fluidity during thermal spraying. The Cr2O3 phase formed during the cryornilling process as revealed in the XRD spectra, which was expected to enhance the thermal stability of the as-milled powders during the followed thermal spraying or other heat treatment.

Microstructure and Properties of W-Cu Alloys Prepared with Mechanically Activated Powder

W-15% Cu (mass fraction) alloys were sintered with mechanically activated powder in order to develop new preparing processes and improve properties of alloys. The microstructures of the activated powder and the sintered alloy were observed. Properties such as density were measured. The results show that through mechanical activation, the particle size of the powder becomes finer to sub-micron or nanometer level, some copper was soluble in tungsten, and high density W-Cu alloys can be obtained by mechanically activated powder for its action to the activation sintering.