Effect of wire-arc directed energy deposition on the microstructural formation and age-hardening response of the Mg-9Al-1Zn(AZ91)alloy

In recent years,wire-arc directed energy deposition(wa DED),which is also commonly known as wire-arc additive manufacturing(WAAM),has emerged as a promising new fabrication technique for magnesium alloys.The major reason for this is the possibility of producing parts with a complex geometry as well as a fine-grained microstructure.While the process has been shown to be applicable for Mg-Al-Zn alloys,there is still a lack of knowledge in terms of the influence of the WAAM process on the age-hardening response.Consequently,this study deals with the aging response of a WAAM AZ91 alloy.In order to fully understand the mechanisms during aging,first,the as-built condition was analyzed by means of high-energy X-ray diffraction(HEXRD)and scanning electron microscopy.These investigations revealed a finegrained,equiaxed microstructure with adjacent areas of alternating Al content.Subsequently,the difference between single-and double-step aging as well as conventional and direct aging was studied on the as-built WAAM AZ91 alloy for the first time.The aging response during the various heat treatments was monitored via in situ HEXRD experiments.Corroborating electron microscopy and hardness studies were conducted.The results showed that the application of a double-step aging heat treatment at 325℃with pre-aging at 250℃slightly improves the mechanical properties when compared to the single-step heat treatment at 325℃.However,the hardness decreases considerably after the pre-aging step.Thus,aging at lower temperatures is preferable within the investigated temperature range of 250-325℃.Moreover,no significant difference between the conventionally aged and directly aged samples was found.Lastly,the specimens showed enhanced precipitation kinetics during aging as compared to cast samples.This could be attributed to a higher amount of nucleation sites and the particular temperature profile of the solution heat treatment.

Formation mechanism of inherent spatial heterogeneity of microstructure and mechanical properties of NiTi SMA prepared by laser directed energy deposition

Ni51Ti49 at.%bulk was additively manufactured by laser-directed energy deposition(DED)to reveal the microstructure evolution,phase distribution,and mechanical properties.It is found that the localized remelting,reheating,and heat accumulation during DED leads to the spatial heterogeneous distribution of columnar crystal and equiaxed crystal,a gradient distribution of Ni4Ti3 precipitates along the building direction,and preferential formation of Ni4Ti3 precipitates in the columnar zone.The austenite transformation finish temperature(Af)varies from-12.65℃(Z=33 mm)to 60.35℃(Z=10 mm),corresponding to tensile yield strength(σ0.2)changed from 120±30 MPa to 570±20 MPa,and functional properties changed from shape memory effect to superelasticity at room temperature.The sample in the Z=20.4 mm height has the best plasticity of 9.6%and the best recoverable strain of 4.2%.This work provided insights and guidelines for the spatial characterization of DEDed NiTi.

High-temperature tribological performance of functionally graded Stellite 6/WC metal matrix composite coatings manufactured by laser-directed energy deposition

Wear-driven tool failure is one of the main hurdles in the industry.This issue can be addressed through surface coating with ceramic-reinforced metal matrix composites.However,the maximum ceramic content is limited by cracking.In this work,the tribological behaviour of the functionally graded WC-ceramic-particlereinforced Stellite 6 coatings is studied.To that end,the wear resistance at room temperature and 400°C is investigated.Moreover,the tribological analysis is supported by crack sensitivity and hardness evaluation,which is of utmost importance in the processing of composite materials with ceramic-particle-reinforcement.Results indicate that functionally graded materials can be employed to increase the maximum admissible WC content,hence improving the tribological behaviour,most notably at high temperatures.Additionally,a shift from abrasive to oxidative wear is observed in high-temperature wear testing.

Pore Formation Mechanism in W-C Hard Coatings Using Directed Energy Deposition on Tungsten Alloy

Porosity is a common phenomenon and can significantly hinder the quality of the coating.Here,the pore formation mechanism and the characteristics of the single tracks of the W-C coating using directed energy deposition(DED)are systematically investigated.The forming quality of the tracks,the distribution of the pores,and the elemental distribution near the pores are analyzed by the observations of the cross-sections of the tracks.The temperature field of the melt pool is discussed comprehensively to reveal the pore formation mechanism.The results confirm that Ni and Co evaporated during the DED process due to the high temperature of the melt pool.Pores were continuously produced adjacent to the fusion line when the melt pool was about to solidify since the temperature at the solidification front was higher than the boiling point of Ni.The vaporization area at the fusion line was proposed,where Ni could also evaporate at the time the melt pool started to solidify.The relationship between the solidification rate,the size of the vaporization area and the DED parameters(laser power and scanning speed)was established to discuss the causes of severe pores above the fusion line.This work contains a practical guide to reduce or eliminate the porosity in the coating preparation process on the surface of the tungsten alloy.

Influence of tungsten particle size on microstructure and mechanical properties of high strength and tough tungsten particle-reinforced nickel-based composites by laser-direct energy deposition

Tungsten(W)particle-reinforced nickel(Ni)-based composites were fabricated via laser-direct energy de-position(L-DED).The influence of the W particle size on the microstructure and mechanical properties of the deposited samples was systematically studied.The results indicate that refining the W particle size could refine theγ-Ni grains and subgrains,thin the(Ni,Cr)_(4)W interface layer,and increase the disloca-tion density of the intergranular matrix,thus improving the tensile strength and elongation of the L-DED samples.As W particle size decreased from 75 to 150μm to 6.5-12μm,the tensile strength and elonga-tion of the deposited samples increased by 150 MPa and 2.9 times to 1347.6±15.7 MPa and 17.5±0.4%,respectively.Based on the properties of the interface(Ni,Cr)_(4)W,a load-transfer efficiency factor suitable for this composite was proposed and the load-transfer strengthening formula was optimized.A quanti-tative analysis of the strengthening mechanisms was established considering load-transfer strengthening,Hall-Petch strengthening,thermal-mismatch strengthening,and solid-solution strengthening.The calcu-lated contribution of each strengthening mechanism to the yield strength and theoretical calculations were in good agreement with the experimental data.The article breaks the bottleneck of poor plasticity of W particle-reinforced Ni-based composites prepared by L-DED and provides a theoretical basis for the construction design of W particle-reinforced Ni-based composites with excellent mechanical properties.

Effect of hot isostatic pressure on the microstructure and tensile properties of γ'-strengthened superalloy fabricated through induction-assisted directed energy deposition

The microstructure characteristics and strengthening mechanism of Inconel738LC(IN-738LC) alloy prepared by using induction-assisted directed energy deposition(IDED) were elucidated through the investigation of samples subjected to IDED under 1050℃ preheating with and without hot isostatic pressing(HIP,1190℃,105 MPa,and 3 h).Results show that the as-deposited sample mainly consisted of epitaxial columnar crystals and inhomogeneously distributed γ’ phases in interdendritic and dendritic core regions.After HIP,grain morphology changed negligibly,whereas the size of the γ’ phase became increasingly even.After further heat treatment(HT,1070℃,2 h + 845℃,24 h),the γ’ phase in the as-deposited and HIPed samples presented a bimodal size distribution,whereas that in the as-deposited sample showed a size that remained uneven.The comparison of tensile properties revealed that the tensile strength and uniform elongation of the HIP + HTed sample increased by 5% and 46%,respectively,due to the synergistic deformation of bimodal γ’phases,especially large cubic γ’ phases.Finally,the relationship between phase transformations and plastic deformations in the IDEDed sample was discussed on the basis of generalized stability theory in terms of the trade-off between thermodynamics and kinetics.

High-performance martensitic stainless steel nanocomposite powder for direct energy deposition prepared by ball milling

Direct energy deposition(DED)has great potential for the production of stainless steel matrix nanocomposite parts.However,the propensity of nanoparticle agglomeration leads to the difficulty in realizing homogenous dispersion of nanoparticles in the matrix.In this study,a series of agglomeration-free nanoWC-Co-reinforced 420 stainless steel matrix nanocomposite powders with high flowability were prepared by ball milling under the optimal parameters.The effect of ball milling time on the properties of the composite powders was investigated.Excellent powder properties ensure the DED processing performance.Furthermore,the corresponding composites were fabricated by DED,and the effects of nano-WC-Co content on the properties of the composites were comprehensively investigated.The contact angles between the single pass cladding layer and the substrate change with increasing nano-WC-Co content(decrease from 127.38°to 113.07°).The different contact angles will significantly influence the quality of the multipass cladding layer.Furthermore,the addition of nanoWC-Co leads not only to further grain refinement but also to more pronounced isotropy of the micros tructure.With the increase in nano-WC-Co content,the corrosion resistance is significantly improved(62.28%lower corrosion current for 420-15 wt%nano-WC-Co than for 420).

Globularization Mechanism and Near Isotropic Properties in Subcritical Heat‑Treated Ti6Al4V Fabricated by Directed Energy Deposition

Microstructure with globularαphase is desirable as it contributes to preferable comprehensive mechanical properties for titanium alloys.However,titanium alloys fabricated by directed energy deposition(DED)are mainly characterized by the lamellarαphase within the basket-weave microstructure,which often leads to severe anisotropy and inferior low cycle fatigue(LCF)properties.To address this,the subcritical annealing and the cyclic annealing were applied to DED Ti–6Al–4V in order to achieve the transformation from the lamellarαphase to the globularαphase.The microstructural characteristics and the globularization behavior ofαphase during heat treatment were investigated.The results show that the aspect ratio ofαis significantly decreased with the subcritical annealing due to the coarsening of lamellarα.Furthermore,the globularαis obtained with the cyclic annealing as a combination result of the termination dissolution and the side surface growth of the lamellarα.These contribute to a pronounced reduction of 85.4%in the ductility anisotropy,compared with the as-built specimens,and superior comprehensive mechanical properties including LCF are achieved with the formation of globularα.

Microstructure and Mechanical Properties of an Ultrahigh-strength Titanium alloy Ti-4.5Al-5Mo-5V-6Cr-1Nb Prepared Using Laser Directed Energy Deposition and Forging:A Comparative Study

The application of titanium alloys in aerospace put forward the requirement for higher strength.Additive manu-facturing is a promising method for the efficient and economical processing of titanium alloys.However,research on the additive manufacturing of ultrahigh-strength titanium alloys is still limited.The mechanisms of microseg-regation for high alloying elements and poor plasticity are still not clear.In this study,an ultrahigh-strength titanium alloy Ti-4.5Al-5Mo-5V-6Cr-1Nb(TB18)was prepared using two methods:laser direct energy deposi-tion(LDED)and forging.The LDEDed alloy contains three zones with similar grain morphologies but different microstructure.The microsegregation of the alloy is limited due to the rapid solidification and almost eliminated after the thermal cycle and solution treatment.With stress relief treatment,the LDEDed alloy exhibits anisotropic mechanical properties.After solution and aging treatments,its ultimate strength is enhanced;however,its plas-ticity is relatively lower than that of the wrought alloy with equally high strength.The excellent balance of the strength and plasticity of the wrought alloy can be ascribed to the formation of𝛼WGB and multiscale𝛼laths,which provides enlightenment for optimizing the properties of the LDEDed alloy.

Effect of Aging Parameters on Inconel 718 Fabricated by Laser Directed Energy Deposition

Inconel 718 is a nickel-based superalloy of high interest in high temperature applications such as turbine parts.To be used in such applications,heat treatments are commonly applied to dissolute Laves phase and to achieve𝛾γ′phase.However,conventional heat treatment methods for wrought Inconel 718 may not be suitable for Inconel 718 fabricated by laser directed energy deposition(LDED)due to its unique microstructure formed during the rapid solidification process.There has been a lack of investigation in heat treatments for Inconel 718 fabricated by this process,specifically around the impact of aging parameters on this alloy.In this study,the effects of aging parameters were studied by performing seven different heat treatments,including solutionising and aging treatments.Our results indicate that for LDED Inconel 718,a high temperature solution treatment of 1100℃for 1 h followed by single aging at 650℃for 20 h achieved a tensile strength and elongation of 1247 MPa and 23%,respectively.Further,results indicated that even with a shorter aging time of 10 h,γ′phase was found to be of comparable size to the standard double aged treatment.

Investigation on the Cracking Mechanism of Melt Growth Alumina/Aluminum Titanate Ceramics Prepared by Laser Directed Energy Deposition

Oxide melt growth ceramics(OMGCs)exhibit excellent performance and microstructure stability near their melt-ing point and are expected to become a new structural material for long-term stable service in extremely high-temperature water-oxygen environments.Owing to its unique advantages of high efficiency,flexible manufac-turing,and near-net shaping,laser directed energy deposition(LDED)has become a promising technology for the rapid preparation of high-performance OMGCs.However,owing to the limited understanding of the crack-ing mechanism,the severe cracking problem that hinders OMGCs-LDED towards engineering applications has not been resolved.Alumina/aluminum titanate(Al_(2)O_(3)/Al_(x)Ti_(y)O_(z),A/AT)ceramics are prepared using an LDED system and their cracking characteristics are investigated.Subsequently,numerical simulations are conducted to reveal the dominant factors and influencing mechanisms of the cracking behavior.The results demonstrate that the cracking nucleation process is mainly controlled by solidification defects,whereas the cracking propagation process is determined primarily by both the microstructure and stress level.This study provides a theoretical basis for the development of appropriate cracking suppression methods for OMGCs-LDED.

Effect of substrate cooling on the epitaxial growth of Ni-based single-crystal superalloy fabricated by direct energy deposition

The columnar-to-equiaxed transition(CET)or the formation of stray grains in the laser melting deposition is the least desirable for the repair of single-crystal blades.In this work,the forced water-cooling was conducted on a single-crystal Rene N5 substrate during the direct energy deposition(DED).The single track remelting,one-layer,two-layer,and eight-layer depositions were investigated to explore the grain growth mechanism.The solidification conditions of the DED process,including temperature field,temperature gradient,and solidification speed,were numerically analyzed by a finite element model.The single-track remelting results showed that the fraction of columnar crystal regions increases from55.81%in the air-cooled sample to 77.14%in the water-cooled one.The single-track deposits of one-and two-layer have the same trend,where the proportion of columnar crystal height was higher under the forced water-cooled condition.The electron backscattered diffraction(EBSD)grain-structure maps of an eight-layer deposit show that the epitaxial growth height increases from 1 mm in the air-cooling sample to 1.5 mm in the water-cooling one.The numerical results showed that the tempe rature gradient in[0011 direction was significantly increased by using forced water-cooling.In conclusion,the in-situ substrate cooling can become a potential method to promote epitaxial growth during DED via the influence on CET occurrence.

Effect of ultrasonic micro-forging treatment on microstructure and mechanical properties of GH3039 superalloy processed by directed energy deposition

In this work,ultrasonic micro-forging treatment(UMFT)was introduced to achieve homogeneous microstructure,reduce defects and improve mechanical properties of GH3039 superalloy cladding layer processed by directed energy deposition(DED).The microstructure,defects and mechanical properties of the cladding layers treated by UMFT with different ultrasonic powers(UIPs)were investigated.Results revealed a gradient structure as equiaxed grains distributed at the top,a columnar-to-equiaxed transition(CET)region that mixed of columnar dendrites and equiaxed grains distributed at the middle and columnar dendrites at the bottom of the cladding layer was formed.After UMFT,the proportion of equiaxed grains was increased,the average size of equiaxed grains was refined to 10μm from 16μm,the orientation of grains was more uniform and the phases enriched of Al,Ti,C,Nb and Mo were precipitated.The grain refinement can be attributed to the fracture of columnar dendrites induced by the ultrasonic vibration during solidification.Besides,the porosity of the cladding layer was reduced after UMFT.The microhardness of the cladding layers exhibited a depth-dependent gradient at the top region.The microhardness of the top surface was the highest and showed an increasing trend with the increase of UIP.The microhardness of different grain morphologies exhibited no substantial difference.However,due to grain refinement and precipitation of strengthening phase induced by UMFT,the microhadness of some local locations were improved.These results indicated UMFT has a significant effect on improving the microstructure,defects and mechanical properties of the deposited cladding layer.

Microstructural features of Ti-6Al-4V manufactured via high power laser directed energy deposition under low-cycle fatigue

Laser additive manufacturing(LAM)technique has unique advantages in producing geometrically complex metallic components.However,the poor low-cycle fatigue property(LCF)of LAM parts restricts its widely used.Here,the microstructural features of a Ti-6 Al-4 V alloy manufactured via high power laser directed energy deposition subjected to low-cycle fatigue loading were studied.Before fatigue loading,the microstructure of the as-deposited parts was found to exhibit a non-homogeneous distribution of columnar prior-βgrains(200-4000μm)at various scanning velocities(300-1500 mm/min)and relatively coarseα-laths(1.0-4.5μm).Under cyclic loading,fatigue microcracks typically initiated within the alignedαphases in the preferred orientation(45°to the loading direction)at the surface of the fatigue specimens.Fatigued Ti-6 Al-4 V exhibited a single straight dislocation character at low strain amplitudes(<0.65%)and dislocation dipoles or even tangled dislocations at high strain amplitudes(>1.1%).In addition,dislocation substructure features,such as dislocation walls,stacking faults,and dislocation networks,were also observed.These findings may provide opportunities to understand the fatigue failure mechanism of additive manufactured titanium parts.

Laser-based directed energy deposition of novel Sc/Zr-modified Al-Mg alloys:columnar-to-equiaxed transition and aging hardening behavior

The control of grain morphology is important in laser additive manufacturing(LAM),as grain morphology further affects the hot cracking resistance,anisotropy,and strength–ductility synergy of materials.To develop a solidification-control solution and achieve columnar-to-equiaxed transition(CET)in Al-based alloys during LAM,Sc-and-Zr-modified Al-Mg alloys were processed via directed energy deposition(DED).CET was achieved by introducing high potent primary Al_(3)(Sc,Zr)nucleation sites ahead of the solidification interface.Furthermore,the relationship between the solidification control parameters and precipitation behavior of primary Al_(3)(Sc,Zr)nucleation sites was established using the time-dependent nucleation theory.Then,the CET was studied according to the Hunt criterion.The results indicated that coarse columnar grain structure was still obtained at the inner region of the molten pool at low Sc/Zr contents owing to the effective suppression of the precipitation of the primary Al_(3)(Sc,Zr)nucleation sites via rapid solidification during DED.In addition,the relatively low melt temperature at the fusion boundary unavoidably promoted the precipitation of primary Al_(3)(Sc,Zr)nucleation sites,which resulted in a fine equiaxed grains band at the edge of the molten pool.As the Sc/Zr content increased,the solidification cooling rate was not sufficient to suppress the precipitation of the primary Al_(3)(Sc,Zr)nucleation sites,and a fully equiaxed grain structure was obtained.Furthermore,the effect of the layer-by-layer manufacturing process on the subsequent precipitation strengthening of secondary Al_(3)(Sc,Zr)precipitates was discussed.Both the remelting and subsequent aging during thermal cycling should be considered to achieve greater precipitation strengthening.

Interfacial characteristics and mechanical properties of additive manufacturing martensite stainless steel on the Cu-Cr alloy substrate by directed energy deposition

Copper/steel is a typical bimetal functional material,combining the excellent electrical and thermal conductivity of copper alloy and the high strength and hardness of stainless steel.There has been recent interest in manufacturing copper/steel bimetal by directed energy deposition(DED)due to its layer-bylayer method.However,cracks tend to form on the copper/steel interface because of the great difference in thermal expansion coefficient and crystal structure between copper and steel.In this work,interfacial characteristics and mechanical properties of the copper/steel bimetal were studied from one layer to multilayers.The laser power has a great influence on the Cu element distribution of the molten pool,affecting the crack formation dramatically on the solidification stage.Cracks tend to form along columnar grain boundaries because of the Cu-rich liquid films and spherical particles in the cracks.Crack-free and good metallurgical bonding copper/steel interface is formed at a scanning velocity of 800 mm/min and the laser power of 3000 W.The ultimate tensile strength(UTS)and the break elongation(EL)of the vertically combined crack-free copper/steel bimetal are 238.2±4.4 MPa and 20.6±0.7%,respectively.The fracture occurs on the copper side instead of the copper/steel interface,indicating that the bonding strength is higher than that of the Cu-Cr alloy.The UTS of the horizontally combined crack-free copper/steel bimetal is 746.7±22.6 MPa,which is 200%higher than that of the Cu-Cr alloy substrate.The microhardness is 398.6±5.4 HV at the steel side and is 235.3±64.1 HV at the interface,which is400%higher than that of the Cu-Cr alloy substrate.This paper advances the understanding of the interfacial characteristics of heterogeneous materials and provides guidance and reference for the fabrication of multi-material components by DED.

Microstructure and room-temperature tensile property of Ti-5.7Al-4.0Sn-3.5Zr-0.4Mo-0.4Si-0.4Nb-1.0Ta-0.05C with near equiaxed β grain fabricated by laser directed energy deposition technique

Near-equiaxed β grain was achieved in the near-α Ti60(Ti-5.7Al-4.0Sn-3.5Zr-0.4Mo-0.4Si-0.4Nb-1.0Ta-0.05C) titanium alloy via laser directed energy deposition(LDED). The microstructural evolution along the building direction and the room-temperature tensile properties along the horizontal and vertical directions(building direction) were systematically studied through SEM and OM. EBSD and XRD were utilized to accurately demonstrate the texture of the α and β phases. The results showed that the α phase presented a low texture intensity, which was ascribed to the weak textured β grain with near-equiaxed morphology, since there are Burgers orientation relationships during the β →α transition. In addition, numerical simulation, combined with the CET curve of Ti60 alloy considering the effect of multi-composition,was utilized to elucidate the formation mechanism of the near-equiaxed β grains. Furthermore, according to the solidification theory, we proposed that the solidification temperature range ΔTfwas more accurate than the growth restriction factor Q in predicting the formation tendency of equiaxed β grain in different titanium alloys. Tensile results showed that the horizontal and vertical samples had similar strength,while the former exhibited larger elongation than the latter. The effect of the near-equiaxed β grain and the internal α phase on mechanical properties were revealed at last.

Additive manufacturing of copper-stainless steel hybrid components using laser-aided directed energy deposition

Combining dissimilar materials in a single component is an effective solution to integrate diverse material properties into a single part.Copper-stainless steel hybrid components are attracting more and more attention since the high thermal conductivity of copper can greatly enhance the thermal performance of stainless steel,which benefits its applications in many industries.However,direct joining of copper and stainless steel such as SS316 L is challenging since they preserve significant dissimilarities in physical,chemical,and thermo-mechanical properties.This paper aims to fabricate well-bonded copper-SS316 L hybrid parts using a laser-aided directed energy deposition(DED) process.A nickel-based alloy Deloro22(D22) is introduced between copper and SS316 L to address the detrimental issues in copper-SS316 L direct joints.Using this technique,defect-free interfaces are achieved at both the D22-SS316 L and copper-D22 transition zones.Tensile testing of Cu-D22-SS316 L and D22-SS316 L hybrid parts shows the fracture occurs at pure copper and SS316 L region,respectively,indicating an excellent bonding at the interfaces.Ascending in the building direction,a transition of grain structure is observed.A significant diffusion zone is obtained at both the D22-SS316 L and the Cu-D22 interfaces.The large diffusion distance results in a smooth variation in microhardness over the dissimilar materials.The microhardness increases from SS316 L to D22 with the highest value of 240 HV and then decreases from D22 to Cu with the lowest value of 63 ± 4 HV.Testing of thermophysical properties of the Cu-D22-SS316 L system indicates there is a ~300 % increase in thermal diffusivity and a ~200 % increase in thermal conductivity when compared to pure SS316 L.The significant increase in thermal diffusivity and conductivity validates the enhanced thermal performance of SS316 L when it is joined with pure copper.

Microstructural banding of directed energy deposition-additively manufactured 316L stainless steel

The microstructures of 316L stainless steel created by rapid solidification are investigated by comparing the similar microstructures of individual hatches of directed energy deposition additive manufacturing(DED-AM)and those of single,laser surface-melted tracks formed on a solid plate.High recoil pressure,which is exponentially dependent on the laser beam power density,induces convection of the melt pool,which causes formation of microstructural bands in the as-solidified microstructure.The microstructural bands are associated with changes in the chromium concentration and are a significant component of the inhomogeneous microstructure of DED-AM.

Tailoring grain morphology in Ti-6Al-3Mo through heterogeneous nucleation in directed energy deposition

A common challenge in direct energy deposition(DED)is eliminating the anisotropy in mechanical performance associated with microstructure and the formation of coarse columnar grains.In this work,a heterogeneous nucleation mechanism was introduced into the melt pool,and,from this mechanism,an almost fully equiaxed grain morphology was obtained in the DED of Ti-6 Al-3 Mo.Three types of grain morphologies in DED Ti-6 Al-3 Mo,including full columnar grains,near-equiaxed grains and almost fully equiaxed grains were obtained from premixed and satellite powder blends from Ti,6 wt.%Al and 3 wt.%Mo,respectively.Combined with the analysis of the interactions between powder particles and the melt pool in DED,the formation mechanism of the equiaxed grains caused by the incomplete melting of high melting point Mo particles was revealed.As the prior-βgrains transformed from coarse columnar grains to fine-equiaxed grains,the strong<100>fiber texture along the deposition direction was weakened,while the size of theα-laths in the prior-βgrains slightly decreased,and the selection ofα-variants was weakened.Due to the transformation of the prior-βgrains from coarse columnar grains to fine-equiaxed grains,the tensile strength of the deposited samples increased from 982 MPa to 1082 MPa,while the yield strength increased from 840 MPa to 922 MPa,and the elongation of the as-deposited alloy also increased from 9.0%to 9.8%,which confirmed that the presence of fine-equiaxed grains is beneficial to the strength and plasticity of the DED alloy.This work further demonstrates the role that satelliting powders can play in terms of enhancing the columnar to equiaxed transition(CET)behavior associated with DED.