Laser Additive Manufacturing of 316L Stainless Steel Thin-wall Ring Parts

The process parameters of laser additive manufacturing have an important influence on the forming quality of the produced items or parts.In the present work,a finite element model for simulating transient heat transfer in such processes has been implemented using the ANSYS software,and the temperature and stress distributions related to 316L stainless steel thin-walled ring parts have been simulated and analyzed.The effect of the laser power,scanning speed,and scanning mode on temperature distribution,molten pool structure,deformation,and stress field has been studied.The simulation results show that the peak temperature,weld pool size,deformation,and residual stress increase with an increase in laser power and a decrease in the scanning speed.The scanning mode has no obvious effect on temperature distribution,deformation,and residual stress.In addition,a forming experiment was carried out.The experimental results show that the samples prepared by laser power P=800 W,V=6 mm/s,and the normal scanning method display good quality,whereas the samples prepared under other parameters have obvious defects.The experimental findings are consistent with the simulation results.

Laser Additive Manufacturing on Metal Matrix Composites: A Review

Important progresses in the study of laser additive manufacturing on metal matrix composites(MMCs)have been made.Recent efforts and advances in additive manufacturing on 5 types of MMCs are presented and reviewed.The main focus is on the material design,the combination of reinforcement and the metal matrix,the synthesis principle during the manufacturing process,and the resulted microstructures as well as properties.Thereafter,the trend of development in future is forecasted,including:Formation mechanism and reinforcement principle of strengthening phase;Material and process design to actively achieve expected performance;Innovative structure design based on the special properties of laser AM MMCs;Simulation,monitoring and optimization in the process of laser AM MMCs.

Design for Ti-Al-V-Mo-Nb alloys for laser additive manufacturing based on a cluster model and on their microstructure and properties

In this study,α+βTi-Al-V-Mo-Nb alloys with the addition of multiple elements that are suitable for laser additive manufacturing(LAM)were designed according to a Ti-6Al-4V cluster formula.This formula can be expressed as 12[Al-Ti12](AlTi2)+5[Al-Ti14]((Mo,V,Nb)2Ti),in which Mo and Nb were added into the alloys partially instead of V to give alloys with nominal compositions of Ti-6.01Al-3.13V-1.43Nb,Ti-5.97Al-2.33V-2.93Mo,and Ti-5.97Al-2.33V-2.20Mo-0.71Nb(wt.%).The microstructures and mechanical properties of the as-deposited and heat-treated samples prepared via LAM were examined.The sizes of theβcolumnar grains andαlaths in the Nb-containing samples are found to be larger than those of the Ti-6Al-4V alloy,whereas Mo-or Mo/Nb-added alloys contain finer grains.It indicates that Nb gives rise to coarsenedβcolumnar grains andαlaths,while Mo significantly refines them.Furthermore,the single addition of Nb improves the elongation,whereas the single addition of Mo enhances the strength of the alloys.The simultaneous addition of Mo/Nb significantly improves the comprehensive mechanical properties of the alloys,leading to the best properties with an ultimate tensile strength of 1,070 MPa,a yield strength of 1,004 MPa,an elongation of 9%,and micro-hardness of 355 HV.The fracture modes of all the alloys are ductile-brittle mixed fracture.

Role of laser scan strategies in defect control,microstructural evolution and mechanical properties of steel matrix composites prepared by laser additive manufacturing

Steel matrix composites(SMCs)reinforced with WC particles were fabricated via selective laser melting(SLM)by employing various laser scan strategies.A detailed relationship between the SLM strategies,defect formation,microstructural evolution,and mechanical properties of SMCs was established.The laser scan strategies can be manipulated to deliberately alter the thermal history of SMC during SLM processing.Particularly,the involved thermal cycling,which encompassed multiple layers,strongly affected the processing quality of SMCs.Sshaped scan sequence combined with interlayer offset and orthogonal stagger mode can effectively eliminate the metallurgical defects and retained austenite within the produced SMCs.However,due to large thermal stress,microcracks that were perpendicular to the building direction formed within the SMCs.By employing the checkerboard filling(CBF)hatching mode,the thermal stress arising during SLM can be significantly reduced,thus preventing the evolution of interlayer microcracks.The compressive properties of fabricated SMCs can be tailored at a high compressive strength(~3031.5 MPa)and fracture strain(~24.8%)by adopting the CBF hatching mode combined with the optimized scan sequence and stagger mode.This study demonstrates great feasibility in tuning the mechanical properties of SLM-fabricated SMCs without varying the set energy input,e.g.,laser power and scanning speed.

Microstructure and mechanical properties of laser additive manufactured novel titanium alloy after heat treatment

A novel α+β titanium alloy with multi-alloying addition was designed based on the cluster formula 12[Al-Ti_(12)](AlTi_(2))+5[Al-Ti_(14)](AlV_(1.2)Mo_(0.6)Nb_(0.2))which was derived from Ti-6Al-4V.The nominal composition of this novel alloy was determined as Ti-6.83Al-2.28V-2.14Mo-0.69Nb-6.79Zr.In this study,the novel alloy and Ti-6Al-4V alloy samples were prepared by laser additive manufacturing.The microstructure,micro-hardness,room/high temperature tensile properties of the as-deposited samples were investigated.Compared to Ti-6Al-4V,the novel alloy has much higher room and high temperature(600℃)tensile strengths,which are 1,427.5 MPa and 642.2 MPa,respectively;however,it has a much lower elongation(3.2%)at room temperature because of the finer microstructure.To improve the elongation of the novel alloy,heat treatment was used.After solution at 960℃ or 970℃ for 1 h followed by air cooling and aging at 550℃ for 4 h followed by air cooling,a unique bi-modal microstructure which contains crab-like primaryαand residual β phase is obtained,improving the compression elongation by 80.9% compared to the as-deposited samples.The novel alloy can be used as a high-temperature and high-strength candidate for laser additive manufacturing.

Laser additive manufacturing of biodegradable Mg-based alloys for biomedical applications: A review

Metallic implants are widely used in internal fixation of bone fracture in surgical treatment.They are mainly used for providing mechanical support and stability during bone reunion,which usually takes a few months to complete.Conventional implants made of stainless steels,Ti-based alloys and CoCrMo alloys have been widely used for orthopedic reconstruction due to their high strength and high corrosion resistance.Such metallic implants will remain permanently inside the body after implantation,and a second surgery after bone healing is needed because the long-term presence of implant will lead to various problems.An implant removal surgery not only incurs expenditure,but also risk and psychological burden.As a consequence,studies on the development of biodegradable implants,which would degrade and disappear in vivo after bone reunion is completed,have drawn researchers’attention.In this connection,Mg-based alloys have shown great potentials as promising implant materials mainly due to their low density,inherent biocompatibility,biodegradability and mechanical properties close to those of bone.However,the high degradation rate of Mg-based implants in vivo is the biggest hurdle to overcome.Apart from materials selection,a fixation implant is ideally tailor-made in size and shape for an individual case,for best surgical outcomes.Therefore,laser additive manufacturing(LAM),with the advent of sophisticated laser systems and software,is an ideal process to solve these problems.In this paper,we reviewed the progress in LAM of biodegradable Mg-based alloys for biomedical applications.The effect of powder properties and laser processing parameter on the formability and quality was thoroughly discussed.The microstructure,phase constituents and metallurgical defects formed in the LAMed samples were delineated.The mechanical properties,corrosion resistance,biocompatibility and antibacterial properties of the LAMed samples were summarized and compared with samples fabricated by traditional processes.In addition,we have made some suggestions for advancing the knowledge in the LAM of Mg-based alloys for biomedical implants.

Effect of processing parameters on formability, microstructure, and micro-hardness of a novel laser additive manufactured Ti-6.38Al-3.87V-2.43Mo alloy

A novel Ti-6.38Al-3.87V-2.43Mo alloy was designed with a cluster formula of 12[Al-Ti12](V0.75Mo0.25Ti2)+4[Al-Ti12](Al3)by replacing Ti with Mo/V on the basis of the Ti-Al congruent alloy.The effects of laser power and scanning speed on the molten pool size,surface roughness,relative density,microstructure,and micro-hardness of single-track and bulk Ti-6.38Al-3.87V-2.43Mo samples prepared via laser additive manufacturing(LAM)were investigated.The results show that processing parameters significantly affect the formability,microstructure,and micro-hardness of the alloy.With decreasing laser power from 1,900 W to 1,000 W,the relative density is decreased from 99.86%to 90.91%due to the increase of lack-of-fusion;however,with increasing scanning speed,the relative density does not change significantly,but exceeds 99%.In particular,Ti-6.38Al-3.87V-2.43Mo samples of single-track and bulk exhibit a good formability under an input laser power of 1,900 W and a scanning speed of 8 mm·s_(-1),and display the lowest surface roughness(Ra=13.33μm)and the highest relative density(99.86%).Besides,the microstructure of LAM Ti-6.38Al-3.87V-2.43Mo alloy coarsens with increasing laser power or decreasing scanning speed due to the greater input energy reducing the cooling rate.The coarsening of the microstructure decreases the microhardness of the alloy.

Microstructure Evolution and Dynamic Mechanical Properties of Laser Additive Manufacturing Ti-6Al-4V Under High Strain Rate

The dynamic mechanical properties of the Ti-6Al-4V(TC4)alloy prepared by laser additive manufacturing(LAM-TC4)under the high strain rate(HSR)are proposed.The dynamic compression experiments of LAM-TC4 are conducted with the split Hopkinson pressure bar(SHPB)equipment.The results show that as the strain rate increases,the widths of the adiabatic shear band(ASB),the micro-hardness,the degree of grain refinement near the ASB,and the dislocation density of grains grow gradually.Moreover,the increase of dislocation density of grains is the root factor in enhancing the yield strength of LAM-TC4.Meanwhile,the heat produced from the distortion and dislocations of grains promotes the heat softening effect favorable for the recrystallization of grains,resulting in the grain refinement of ASB.Furthermore,the contrastive analysis between LAM-TC4 and TC4 prepared by forging(F-TC4)indicates that under the HSR,the yield strength of LAM-TC4 is higher than that of F-TC4.

Toward understanding the microstructure characteristics,phase selection and magnetic properties of laser additive manufactured Nd-Fe-B permanent magnets

Nd-Fe-B permanent magnets play a crucial role in energy conversion and electronic devices.The essential magnetic properties of Nd-Fe-B magnets,particularly coercivity and remanent magnetization,are significantly infuenced by the phase characteristics and microstructure.In this work,Nd-Fe-B magnets were manufactured using vacuum induction melting(VIM),laser directed energy deposition(LDED)and laser powder bed fusion(LPBF)technologies.Themicrostructure evolution and phase selection of Nd-Fe-B magnets were then clarified in detail.The results indicated that the solidification velocity(V)and cooling rate(R)are key factors in the phase selection.In terms of the VIM-casting Nd-Fe-B magnet,a large volume fraction of theα-Fe soft magnetic phase(39.7 vol.%)and Nd2Fe17Bxmetastable phase(34.7 vol.%)areformed due to the low R(2.3×10-1?C s-1),whereas only a minor fraction of the Nd2Fe14B hard magnetic phase(5.15 vol.%)is presented.For the LDED-processed Nd-Fe-B deposit,although the Nd2Fe14B hard magnetic phase also had a low value(3.4 vol.%)as the values of V(<10-2m s-1)and R(5.06×103?C s-1)increased,part of theα-Fe soft magnetic phase(31.7vol.%)is suppressed,and a higher volume of Nd2Fe17Bxmetastable phases(47.5 vol.%)areformed.As a result,both the VIM-casting and LDED-processed Nd-Fe-B deposits exhibited poor magnetic properties.In contrast,employing the high values of V(>10-2m s-1)and R(1.45×106?C s-1)in the LPBF process resulted in the substantial formation of the Nd2Fe14B hard magnetic phase(55.8 vol.%)directly from the liquid,while theα-Fe soft magnetic phase and Nd2Fe17Bxmetastable phase precipitation are suppressed in the LPBF-processed Nd-Fe-B magnet.Additionally,crystallographic texture analysis reveals that the LPBF-processedNd-Fe-B magnets exhibit isotropic magnetic characteristics.Consequently,the LPBF-processed Nd-Fe-B deposit,exhibiting a coercivity of 656 k A m-1,remanence of 0.79 T and maximum energy product of 71.5 k J m-3,achieved an acceptable magnetic performance,comparable to other additive manufacturing processed Nd-Fe-B magnets from MQP(Nd-lean)Nd-Fe-Bpowder.

Wire-feed laser additive manufacturing of dissimilar metals via dual molten pool interface interlocking mechanism

Intermetallic compounds produced in laser additive manufacturing are the main factors restricting the joint performance of dissimilar metals.To solve this problem,a dual molten pool interface interlocking mechanism was proposed in this study.Based on a dual molten pool interface interlocking mechanism,the dissimilar metals,aluminum alloy and stainless steel,were produced as single-layer and multilayer samples,using the wire-feed laser additive manufacturing directed energy deposition technology.The preferred parameters for the dual molten pool interface interlocking mechanism process of the dissimilar metals,aluminum alloy and stainless steel,were obtained.The matching relationship between the interface connection of dissimilar metals and the process parameters was established.The results demonstrated excellent mechanical occlusion at the connection interface and no apparent intermetallic compound layer.Good feature size and high microhardness were observed under a laser power of 660 W,a wire feeding speed of 55 mm/s,and a platform moving speed of 10 mm/s.Molecular dynamics simulations demonstrated a faster rate of aluminum diffusion in the aluminum alloy substrate to stainless steel under the action of the initial contact force than without the initial contact force.Thus,the dual molten pool interface interlocking mechanism can effectively reduce the intermetallic compound layer when dissimilar metals are connected in the aerospace field.

Collaborative optimization design of process parameter and structural topology for laser additive manufacturing

High-resolution laser additive manufacturing(LAM)significantly releases design free-dom,promoting the development of topology optimization(TO)and advancing structural design methods.In order to fully take advantage of voxelated forming methods and establish the quantitative relationship between the mechanical properties of printing components and multiple process factors(laser-and process-parameters),the concurrent optimization design method based on LAM should cover the process-performance relationship.This study proposes a novel artificial intelligence-facilitated TO method for LAM to concurrently design microscale material property and macroscale structural topology of 3D components by adopting heuristic and gradient-based algorithms.The process–structure–property relationship of selective laser sintering is established by the back propagation neural network,and it is integrated into the TO algorithm for providing a systematic design scheme of structural topology and process parameter.Compared with the classical optimization method,numerical examples show that this method is able to improve the mechanical performance of the macrostructure significantly.In addition,the collaborative design method is able to be widely applied for complex functional part design and optimization,as well as case studies on artificial intelligence-facilitated product evaluation.

Direct fabrication of single-crystal-like structure using quasi-continuous-wave laser additive manufacturing

The synchronously periodic re-melting of molten pool was firstly introduced in additive manufacturing to promote the epitaxial growth of columnar structure using a novel quasi-continuous-wave(QCW)laser.The epitaxial growth of columnar structure was intensified and the single-crystal-like sample with highly oriented "zigzag" columnar grains was produced.The modified molten-pool geometry and the synchronously high-frequency re-melting of the molten pool contribute to the formation of singlecrystal-like structure.This work reports a new route to promote the continuously epitaxial growth of dendrites for fabrication of single-crystal-like sample.

Solidification Microstructure of Laser Additive Manufactured Ti—6Al—2Zr—2Sn—3Mo—1.5Cr—2Nb Titanium Alloy

Solidification microstructure of powder fed laser additive manufactured Ti-6Al--2Zr--2Sn--3Mo--1.5Cr--2Nb titanium alloy was investigated, The results showed that by deliberately increasing the powder feed rate, partially melted powders were retained at the top of the molten pool, which can promote heteroge- neous nucleus. Thus, each cladding layer is composed of two regions： （i） randomly orientated cellular structure region caused by partially melted powders at the top of each cladding layer; and （ii） epitaxial cellular structure region adjacent to the fusion line. Usually, randomly orientated cellular structure region was totally remelted for a wide range of process conditions. The remelting effect ensures the continuity of epitaxial growth of cellular structure and leads to the formation of columnar β grains, In order to obtain equiaxed grains the scanning velocity and powder feed rate should be carefully selected to enlarge the randomly orientated cellular structure region,

Laser additive manufactured high-performance Fe-based composites with unique strengthening structure

Steel matrix composites(SMCs),reinforced by ceramic particles,have received a consistent attention in recent years.Using conventional methods to prepare SMCs is generally challenging,and the mechanical properties of conventionally fabricated SMCs are limited.In this study,we successfully fabricated highperformance SMCs by laser powder bed fusion(LPBF)of a composite powder consisting of Fe-based alloy powder and submicron-sized WC particles.The effect of laser energy density on the phase formation,microstructural evolution,overall density and resulting mechanical properties of LPBF-fabricated composites was investigated.The present results show that a novel Fe_(2)W_(4)C carbidic network precipitates in the solidified microstructure entailing segregations along the boundaries of cellular sub-grains.The presence of this carbidic network hampers the growth of sub-grains even at elevated temperatures,and hence,stabilizes the grain size though prepared at a broad range of different energy densities.The exact distribution of the Fe_(2)W_(4)C carbides depends on the employed laser energy densities,as for instance they are more uniformly distributed at higher energy input.The density of LPBF samples reaches the maximum value of 99.4%at 150 J/mm^(3).In this parameter set,high microhardness of~753 HV,compression strength of~3350 MPa and fracture strain of~24.4%are obtained.The enhanced mechanical properties are ascribed to less metallurgical defects,higher volume fraction of the martensitic phase and increasing pile-up dislocations resulting from the pinning effect by Fe_(2)W_(4)C carbide.

Ultrashort-time liquid phase sintering of high-performance fine-grain tungsten heavy alloys by laser additive manufacturing

Liquid phase sintering(LPS)is a proven technique for preparing large-size tungsten heavy alloys(WHAs).However,for densification,this processing requires that the matrix of WHAs keeps melting for a long time,which simultaneously causes W grain coarsening that degenerates the performance.This work develops a novel ultrashort-time LPS method to form bulk high-performance fine-grain WHAs based on the principle of laser additive manufacturing(LAM).During LAM,the high-entropy alloy matrix(Al_(0.5)Cr_(0.9)FeNi_(2.5)V_(0.2))and W powders were fed simultaneously but only the matrix was melted by laser and most W particles remained solid,and the melted matrix rapidly solidified with laser moving away,producing an ultrashort-time LPS processing in the melt pool,i.e.,laser ultrashort-time liquid phase sintering(LULPS).The extreme short dwell time in liquid(-1/10,000 of conventional LPS)can effectively suppress W grain growth,obtaining a small size of 1/3 of the size in LPS WHAs.Meanwhile,strong convection in the melt pool of LULPS enables a nearly full densification in such a short sintering time.Compared with LPS WHAs,the LULPS fine-grain WHAs present a 42%higher yield strength,as well as an enhanced susceptibility to adiabatic shear banding(ASB)that is important for strong armor-piercing capability,indicating that LULPS can be a promising pathway for forming high-performance WHAs that surpass those prepared by conventional LPS.

Laser Additive Manufacturing of Bio-inspired Metallic Structures

High-performance/multifunctional metallic components primarily determine the service performance of equip-ment applied in the aerospace,aviation,and automobile industries.Organisms have developed structures with specific properties over millions of years of natural evolution,thereby providing inspiration for the design of high-performance structures to satisfy the increasing demands of modern industries.From the perspective of manufacturing,the ability of conventional processing technologies is inadequate for fabricating these complex structural configurations.By contrast,laser additive manufacturing(AM)is an effective method for fabricating complex metallic bio-inspired structures owing to its layer-by-layer deposition advantage.Herein,recent devel-opments in the laser AM of bio-inspired cellular,plate,and truss structures,as well as the materials used in laser AM for bio-inspired printing are briefly reviewed.The organisms being imitated include butterfly,Norway spruce,mantis shrimp,beetle,and water spider,which expand the diversity of multifunctional structures for laser AM.The mechanical properties and functions of laser-AM-processed bio-inspired structures are discussed.Additionally,the challenges,possible outcomes,and directions of utilizing laser AM technology to fabricate high-performance/multifunctional metallic bio-inspired structures in the future are outlined.

Wire Oscillating Laser Additive Manufacturing of 2319 Aluminum Alloy: Optimization of Process Parameters, Microstructure, and Mechanical Properties

In this study,a wire oscillating laser additive manufacturing(O-WLAM)process was used to deposit 2319 aluminum alloy samples.The optimization of the deposition process parameters made it possible to obtain samples with smooth surfaces and extremely low porosities.The effects of the deposition parameters on the formability and evolution of the microstructure and mechanical properties before and after heat treatment were studied.The oscillating laser deposition of 2319 aluminum alloy,especially the circular oscillation mode,significantly reduced the porosity and improved the process stability and formability compared with non-oscillating laser deposition.There were clear boundaries between the deposition units in the deposition state,the interior of which was dominated by columnar crystals with many rod-and point-shaped precipitates.After the heat treatment,theθphase was significantly dissolved.The residual dot-and rod-shapedθ'phases were dispersedly distributed,exhibiting an obvious precipitation-hardening effect.The samples in the as-deposited state had a tensile strength of 245–265 MPa,an elongation of approximately 12.6%,and an 87 HV microhardness.After heat treatment at 530°C for 20 h and aging at 175°C for 18 h,the tensile strength,elongation,and microhardness reached 425–440 MPa,approximately 10%,and 153 HV,respectively.The performance improved significantly without significant anisotropy.Compared with the samples produced by wire arc additive manufacturing(WAAM),the tensile strength increased by approximately 10%,and the strength and microhardness were significantly improved.

Interfacial Features of Stainless Steel/Titanium Alloy Multi-metal Fabricated by Laser Additive Manufacturing

Laser additive manufacturing(LAM)is promising for fabricating multi-metallic component,but the mechanism of microstructural evolution at the interface of two metals is still needed to research further.In this study,a 316L stainless steel/Ti6Al4V alloy multi-metal was fabricated by LAM,and the mechanism of intermetallic phase transformation was deeply investigated.Results show that a strong reaction zone(SRZ)can be induced at the interface of the multi-metal.The phase constituents at the SRZ vary fromχ(Ti_(5)Fe_(17)Cr_(5))+Fe_(2)Ti+α′-Ti+β-Ti or FeTi to Fe_(2)Ti+χwhen the laser power is increased.When the scanning speed is further decreased,the thickness of the SRZ is significantly increased,andα′-Ti phase is also formed at this region besides Fe_(2)Ti andχphases.Moreover,the micro-hardness at the SRZ is increased,caused by the intermetallic phase transformation and elemental interdiffusion at the interface.

Effect of thermal deformation on microstructure and properties of TC18 titanium alloy produced by laser additive manufacturing

Grain boundary of α phase damaged ductility of laser melting-deposited TC18 titanium alloy and grain boundary of α phases were difficult to break by nominal heat treatment. An extra thermal deformation was introduced to break the grain boundary of α phase with the improved mechanical property of TC18 titanium alloy fabricated by laser melting deposition technique.Results indicated that after thermal deformation, β grains in alloy seriously elongated. When sample was deformed at temperatures from 750 to 850 ℃, α phase exhibited both rod and irregular morphologies with discontinuous distribution at grain boundary, and the subsequent heat treatment would lead to spheroidization of the α phase. However, after deformation at 900 ℃, α phase transferred into β phase and the subsequent heat treatment would make continuous grain boundary of α phase reappear. The suitable hot deformation can effectively break the continuous grain boundary in laser melting-deposited TC18 alloy with respected improved ductility.

Laser additive manufacturing of ductile Fe-based bulk metallic glass composite

Laser additive manufacturing(LAM)is a promising technology for processing bulk metallic glass(BMG)with freeform geometries or unlimited size.However,the inherently brittle Fe-based BMGs produced by LAM have always been plagued by the micro-cracking induced by the large thermal stresses during the LAM process.To solve this dilemma,316L stainless steel(SS)with excellent toughness and similar elemental composition was carefully selected as the second phase to form Fe-based BMG composites(BMGCs).The obtained Fe-based BMGCs are equipped with a heterogeneous structure,i.e.,the 316L SS phase is wrapped by the metallic glass and forms a unique"fishbone"structure with a micron-scale.Excitedly,the special structure nicely improves a plastic strain of the Fe-based BMGC with a strength of 2355 MPa to~17%,achieving a record-breaking achievement among Fe-based amorphous with critical dimensions over 1mm.