Review on laser directed energy deposited aluminum alloys

Lightweight aluminum(Al)alloys have been widely used in frontier fields like aerospace and automotive industries,which attracts great interest in additive manufacturing(AM)to process high-value Al parts.As a mainstream AM technique,laser-directed energy deposition(LDED)shows good scalability to meet the requirements for large-format component manufacturing and repair.However,LDED Al alloys are highly challenging due to their inherent poor printability(e.g.low laser absorption,high oxidation sensitivity and cracking tendency).To further promote the development of LDED high-performance Al alloys,this review offers a deep understanding of the challenges and strategies to improve printability in LDED Al alloys.The porosity,cracking,distortion,inclusions,element evaporation and resultant inferior mechanical properties(worse than laser powder bed fusion)are the key challenges in LDED Al alloys.Processing parameter optimizations,in-situ alloy design,reinforcing particle addition and field assistance are the efficient approaches to improving the printability and performance of LDED Al alloys.The underlying correlations between processes,alloy innovation,characteristic microstructures,and achievable performances in LDED Al alloys are discussed.The benchmark mechanical properties and primary strengthening mechanism of LDED Al alloys are summarized.This review aims to provide a critical and in-depth evaluation of current progress in LDED Al alloys.Future opportunities and perspectives in LDED high-performance Al alloys are also outlined.

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.

Microstructure and mechanical properties of Al-Si-Ni coating on Cu-Cr substrate prepared by multi-permeation and friction stir processing

The surface of copper-chromium alloy was processed by Al-Si-Ni multi-permeation and friction stir processing,and the microstructure and mechanical properties of the surface layer were tested by scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),microhardness tester and friction testing machine.The results show that Al,Si and Ni elements are fully permeated into the surface of copper-chromium alloy after multielement co-infiltration and friction stir processing.In the observation of the microstructures,we found that the reticular structure is fragmented and distributed in the stir zone region.Microstructure becomes finer and grains refinement.The micro hardness of the copper-chromium alloy increased to 129 HV,44.9%higher than that of the original matrix.The main reasons of microhardness enhancement are solid solution strengthening,fine grains strengthening and dispersion strengthening.The friction test results show that the friction coefficient is basically stable at 0.69 and the wear mass is only 0.0017 g after 10 min of friction test.The improvement of wear resistance was attributed to the increase of microhardness of the alloy surface.

Influence of rare earth oxides on microstructure and mechanical properties of nickel-based superalloys fabricated by high energy beam processing:A review

In this paper,the effects of rare earth oxides on the micro structure and mechanical properties of nickelbased superalloys prepared by high-energy beam processing technology were critically studied.The focus is on the optimal amount of rare earth oxides that can produce ideal results.Special attention was paid to their main strengthening mechanisms,including solid solution strengthening mainly in the form of solid solution dissolved in the nickel-based alloy and improving the microstructure of the alloy by grain refinement or fine grain strengthening produced by homogenizing the distribution phase.Y_(2)O_(3),La_(2)O_(3) and CeO_(2) rare earth oxides can also improve the fluidity of the alloy molten pool and reduce the segregation of alloying elements.These advantages can significantly improve the mechanical properties of the alloy.Thereafter,this paper outlines the future research directions of rare earth oxides,aiming to expand their application potential.

Microstructure and Mechanical Properties of Selective Laser Melted Al–2.51Mn–2.71Mg–0.55Sc–0.29Cu–0.31Zn Alloy Designed by Supersaturated Solid Solution

Selective laser melting(SLM)of aluminium alloys for lightweight application is arousing widespread interest,but the available alloy compositions are limited due to unsatisfactory mechanical performances.The rapid solidifi cation of SLM provides a pathway to design a novel alloy composition with extended solubility.This strategy is demonstrated by an additively manufactured novel Al–2.51 Mn–2.71 Mg–0.55 Sc–0.29 Cu–0.31 Zn alloy with the supersaturated solid solution in the present study.The microstructure of as-build sample is characterized with multi-modal grains with the fi ne equiaxed grain(FEG,~800 nm)at molten pool boundaries,coarse equiaxed grain(CEG,~2μm)and columnar dendrites(CD,~4μm)inside the molten pool,which relates to the precipitations type and distribution.It is observable that Al 3(Sc,Zr)precipitation particles with the size of~50 nm are dispersed in the FEG zone,while the interior of CEG shows no Al3(Sc,Zr)particle which only exists at the CEG boundaries.Regardless of FEG,CEG or CD,the slender Al6 Mn precipitation with the length of~500 nm is distributed along the grain boundaries.Meanwhile,a lot of vacancies and thickness fringes are detected in the FEG zone,which confi rms the supersaturated solid solution in laser rapid solidifi cation.The ultimate tensile strength and yield strength of the as-printed sample are~380 MPa and~330 MPa,respectively,with elongation~14%,which increase to~440 MPa and~410 MPa with a reduction of elongation to~9%after heat treatment.

阳极氧化AlCoCrFeNi高熵合金用于高效碱性电解水

碱性水电解(AWE)作为一种具有工业应用前景的绿色制氢方法,能够用来改善能源短缺和环境污染问题.然而,由于电极材料昂贵且效率低下,这种方法生产氢气的效率比较低.本文采用块状AlCoCrFeNi高熵合金作为碱性电解水的有效电极.研究发现通过快速阳极氧化(5 min)处理的高熵合金可以同时对析氢和析氧反应(HER和OER)具有超高的催化活性,只需要880和845 m V的过电位就可以达到-500 mA cm-2(HER)和500 mA cm-2(OER)的电流密度.特别地,该催化剂只需要3.00 V就可以达到500 mA cm-2的全解水电流密度,并且在此电流密度下表现出超过100小时的出色稳定性.我们的研究表明,阳极氧化的块体AlCoCrFeNi高熵合金作为高效催化剂在工业水电解制氢中具有广阔的应用前景,有望用于缓解环境问题和能源危机.

Microstructure and Mechanical Properties of TiC-Reinforced Al–Mg–Sc–Zr Composites Additively Manufactured by Laser Direct Energy Deposition

In order to refine the microstructure and improve the performance of direct energy deposited(DED)additively manufactured Al–Mg–Sc–Zr alloy,TiC-modified Al–Mg–Sc–Zr composites were prepared by DED and the effect of TiC content on the microstructure and performance was studied.In the absence of TiC particle,the microstructure of Al–Mg–Sc–Zr alloy prepared by DED consisted of fine grains with average size of 8.36μm,and well-dispersed nano-Al;(Sc,Zr)particles inside the grains and Mg;Si phase along the grain boundaries.With the addition of 1 wt%TiC,the microstructure of TiC/Al–Mg–Sc–Zr prepared by DED became finer apparently compared with that without TiC;while the further increase of TiC content to 3 wt%,the microstructure of TiC/Al–Mg–Sc–Zr prepared by DED became coarser with appearance of a new kind of needle-like(Ti,Zr);Si;phase.Also,the addition of TiC decreased the porosity of Al–Mg–Sc–Zr prepared by DED.Simultaneously,after the addition of TiC,the tensile strength increased from 283.25 MPa to 344.98–361.51 MPa,and the elongation increased from 3.61%to 9.58–14.10%.The potential mechanism of the microstructure evolution and strength improvement was discussed.This research will provide new insights into the available metal matrix composites by laser additive manufacturing(LAM).

A Comparative Study on the Microstructure and Properties of ITO Targets and Thin Films Prepared from Two Different Powders

With the rapid development of indium tin oxide(ITO)in the electronic display industry,choosing which raw powders to prepare high-quality ITO targets has always been a controversial topic.In the work,in order to clearly understand the effect of the raw powders on the microstructure and properties of ITO targets and thin films,tin-doped indium oxide(dITO)and In_(2)O_3-SnO_(2)mixed(mITO)powders were chosen to prepare ITO targets for depositing the films and a comparative study on their microstructure and properties was conducted.It is found that,(1)dITO targets possess a higher solid solubility of tin in indium oxide and more uniform elemental distribution,while there are a higher density,a finer grain size and a higher mass ratio of In_(2)O_3 to SnO_(2)for the mITO targets;(2)dITO films with more coarser columnar grains and a rougher surface prefer to grow along the[100]direction in an Ar atmosphere;(3)the conductive property of ITO films only depends on the doping amount of tin and is independent of the raw powders and the preparation process of the target source;(4)dITO films possess the superior optical property and narrower optical band gap;(5)the etching property of mITO films is superior to that of dITO films due to the lower solid solubility of tin in indium oxide.

Microstructures and Mechanical Properties of Al-Mg-Sc-Zr Alloy Additively Manufactured by Laser Direct Energy Deposition

An Al-Mg-Sc-Zr alloy was additively manufactured by laser direct energy deposition(DED)under different laser powers,and the microstructures and mechanical properties of the as-deposited samples were investigated.The samples showed a fully equiaxed grain structure with grain sizes of 2–30μm.Most of the blocky primary Al3(Sc,Zr)-precipitated phases(<5μm)were arranged along the grain boundaries.A small amount of fine granular secondary Al3(Sc,Zr)phases(<0.5μm)were precipitated owing to the cyclic heat treatment during the DED forming process.According to the EBSD(Electron backscatter diffraction)results,the texture index and strength of the sample were only slightly greater than 1,indicating that the material structure exhibited a certain but not obvious anisotropy.The sample in the horizontal direction had better yield strength,tensile strength,and elogation properties(399.87 MPa,220.96 MPa,9.13%)than that in the building direction(385.40 MPa,219.40 MPa,8.24%),although the sample in the〈XOZ〉plane had the finest equiaxed grains.The ductility of the〈XOZ〉sample deteriorated as the number of pores increased.