Recent innovations in laser additive manufacturing of titanium alloys

Titanium(Ti)alloys are widely used in high-tech fields like aerospace and biomedical engineering.Laser additive manufacturing(LAM),as an innovative technology,is the key driver for the development of Ti alloys.Despite the significant advancements in LAM of Ti alloys,there remain challenges that need further research and development efforts.To recap the potential of LAM high-performance Ti alloy,this article systematically reviews LAM Ti alloys with up-to-date information on process,materials,and properties.Several feasible solutions to advance LAM Ti alloys are reviewed,including intelligent process parameters optimization,LAM process innovation with auxiliary fields and novel Ti alloys customization for LAM.The auxiliary energy fields(e.g.thermal,acoustic,mechanical deformation and magnetic fields)can affect the melt pool dynamics and solidification behaviour during LAM of Ti alloys,altering microstructures and mechanical performances.Different kinds of novel Ti alloys customized for LAM,like peritecticα-Ti,eutectoid(α+β)-Ti,hybrid(α+β)-Ti,isomorphousβ-Ti and eutecticβ-Ti alloys are reviewed in detail.Furthermore,machine learning in accelerating the LAM process optimization and new materials development is also outlooked.This review summarizes the material properties and performance envelops and benchmarks the research achievements in LAM of Ti alloys.In addition,the perspectives and further trends in LAM of Ti alloys are also highlighted.

Robust interface and excellent as-built mechanical properties of Ti–6Al–4V fabricated through laser-aided additive manufacturing with powder and wire

The feasibility of manufacturing Ti-6Al-4V samples through a combination of laser-aided additive manufacturing with powder(LAAM_(p))and wire(LAAM_(w))was explored.A process study was first conducted to successfully circumvent defects in Ti-6Al-4V deposits for LAAM_(p) and LAAM_(w),respectively.With the optimized process parameters,robust interfaces were achieved between powder/wire deposits and the forged substrate,as well as between powder and wire deposits.Microstructure characterization results revealed the epitaxial prior β grains in the deposited Ti-6Al-4V,wherein the powder deposit was dominated by a finerα′microstructure and the wire deposit was characterized by lamellar α phases.The mechanisms of microstructure formation and correlation with mechanical behavior were analyzed and discussed.The mechanical properties of the interfacial samples can meet the requirements of the relevant Aerospace Material Specifications(AMS 6932)even without post heat treatment.No fracture occurred within the interfacial area,further suggesting the robust interface.The findings of this study highlighted the feasibility of combining LAAM_(p) and LAAM_(w) in the direct manufacturing of Ti-6Al-4V parts in accordance with the required dimensional resolution and deposition rate,together with sound strength and ductility balance in the as-built condition.

Effect of quenching residual stress on precipitation behaviour of 7085 aluminium alloy

The quenching-induced residual stress in ultrahigh strength Al-Zn-Mg-Cu alloys has a great influence on their precipitation behaviour in subsequent heat treatment and the properties of the final products.In the present work,the cladding quenching method was employed for 7085 Al alloy slabs to tailor different quenching residual stresses.Then the effects of quenching residual stress on the precipitation behaviour of the 7085 Al alloy were investigated through finite element analysis,residual stress and hardness distri-bution measurements and microstructural examinations.The results indicate that the reduction in resid-ual stress increases with increasing cladding layer thickness.For a cladding layer thickness in the range of 1-1.4 mm,the residual stress is almost eliminated.The hardness at the surface of the aged sample with a large compressive residual stress is decreased,while the hardness at the centre of the sample with a large tensile residual stress is increased.The hardness is approximately identical between the aged sam-ples with little or no residual stress.The elastic lattice distortion caused by residual stress is found to promote the nucleation of precipitates during the artificial ageing process.The in-depth mechanisms for the effect of quenching residual stress on the precipitation of 7085 Al alloy are also discussed.

基于社会功能假说探讨应激对传染性哈欠的影响

看到周围有人打哈欠,我们自己可能也会跟着打哈欠,这种由他人哈欠诱发的哈欠被称为传染性哈欠.传染性哈欠在生活中很常见,但原因和机制的分析还非常有限.哈欠的社会功能假说认为,哈欠可能具有交流功能,用以传递威胁或预警信息,使得哈欠的传染具有一定的适应意义.然而,该假说更多的基于动物观察推测而来,少有实证探讨,在人类群体中相关考察更是稀少.基于这一假说,研究对60名大学生采用社会压力任务激活应激状态,监测心电反应并通过正性负性情绪量表中文版与放松状态主观评定问卷对自己当前的情绪状态进行自我评定,采用眼中读心任务测量心理理论,同时采用匹兹堡睡眠质量指数和斯坦福嗜睡量表控制睡眠状况和警觉程度,考察心理应激与传染性哈欠的关系及其影响因素.结果发现,心理应激会显著增强传染性哈欠,却不会影响自发性哈欠.同时,被试的心率变异性越高,对应影响越不明显;心理理论越高,对应影响则越明显.上述结果为哈欠的社会功能假说提供了支撑,提示传染性哈欠在漫长的演化过程中可能承担着重要的交流功能,有着特定的适应意义.

Corrosion–wear behavior of a biocompatible magnesium matrix composite in simulated body fluid

Magnesium matrix composites are a new generation of biocompatible implant materials,but they will inevitably undergo simultaneous wear and corrosion in the human body.In this study,hydroxyapatite(Ca10(PO4)6(OH)2,HA)is used in a magnesium matrix composite to study its effects on the corrosion–wear behavior.Two samples(a magnesium alloy composed of Mg,Zn,and Zr(ZK60)alloy and ZK60/10HA composite)were fabricated using the powder metallurgy(PM)process.Their corrosion–wear behavior was investigated using the sliding wear test in a simulated body fluid(SBF).At all the sliding velocities tested,the corrosion–wear resistance of ZK60/10HA was superior to ZK60.At a sliding velocity of 942.5 mm/min,ZK60/10HA demonstrated a 42%improvement in corrosion–wear resistance compared to ZK60.For ZK60,the main wear mechanism under dry conditions was abrasion,while the wear mechanisms in the SBF were abrasion and corrosion.For ZK60/10HA,the wear mechanisms under dry conditions were abrasion and delamination,while in SBF they were mainly abrasion and corrosion,accompanied by slight delamination.The results indicated that HA particles can be used as an effective corrosion–wear inhibitor in biocompatible magnesium matrix composites.

Revealing the decomposition mechanisms of dislocations and metastableα’phase and their effects on mechanical properties in a Ti-6Al-4V alloy

The metastableα’phase and dislocation characteristics(e.g.,density and constituents)are of vital importance for the mechanical responses of(α+β)titanium alloys.In this work,to reveal the in-depth decomposition mechanisms of dislocations and metastableα’and their influences on mechanical properties in a Ti-6Al-4V(α+β)alloy,the thermal stability of different microstructures tailored by various cooling approaches were investigated utilizing scanning electron microscope,electron backscattered diffraction,transmission electron microscope and X-ray diffraction line profile analysis.The results showed that the initial characteristics ofα’andαlaths and dislocation density were influenced by the cooling methods remarkably.The thermal stability of Ti-6Al-4V alloy increased with decreasing cooling rate.The improvement in thermal stability can be ascribed by the decrement in dislocations,partitioning of the alloying elements and grain orientations variation of theα’lath andαphase.It is also found that the plastic strain accommodation ofβ→α’transformation was dominated by dislocations.During stabilization annealing treatments,the,and dislocations simultaneously decomposed.The decomposition of dislocations and metastableα’phase during various stabilization annealing and the particular twins and stacking faults microstructures formed during quenching have a great influence on the properties of the studied Ti-6Al-4V alloy.

Recent progress in graphene-reinforced aluminum matrix composites

Recent years witnessed a growing research interest in graphene-reinforced aluminum matrix composites(GRAMCs).Compared with conventionalreinforcements of aluminum matrix composites(AMCs),graphene possesses manyattractive characteristics such as extremely high strength and modulus,unique self-lubricating property,high thermal conductivity(TC)and electrical conductivity(EC),andlow coefficient of thermal expansion(CTE).A lot of studies have demonstrated that theincorporation of graphene into Al or Al alloy can effectively enhance mechanical andphysical properties of the Al matrix.The purpose of this work is aimed to trace recentdevelopment of GRAMCs.Initially,this paper covers a brief overview of fabricationmethods of GRAMCs.Then,mechanical,tribological,thermal and electrical properties ofrecently developed GRAMCs are presented and discussed.Finally,challenges andcorresponding solutions related to GRAMCs are reviewed.