尖锐晶界角对柱状晶铜排伸长率的显著影响及机理（英文）

研究柱状晶铜排在小变形量冷拉拔后伸长率显著下降的原因。通过温型连铸技术制备铜排,在多个应变量停止拉伸测试以探测裂纹源,采用电子背散射衍射(EBSD)技术分析位错滑移带。研究发现,铸态铜排中存在与连铸方向近平行的尖锐晶界角,拉拔后铜排的伸长率由铸态的68.8%骤降至拉拔态的18.8%。在尖锐晶界角附近发生更剧烈的塑性变形,局部应力集中甚至使Schmid因子低至0.17的位错滑移系启动。尖锐晶界角附近塑性变形的集中促使裂纹萌生和扩展,最终导致拉拔态铜排伸长率的显著降低。

Crystallography of precipitates in Mg alloys

Crystallography of precipitates in Mg alloys is indispensable to explain and predict alloy microstructures and properties.In order to obtain a global understanding of diversified experimental results,a general theory of singular interface is introduced,which provides the physical base and calculation methodology for interpreting precipitate morphology and orientation relationship(OR),especially useful for understanding irrational facets and ORs.Guided by the theory,recent experimental findings are systematically summarized,including thermally stable and metastable precipitates with various crystal structures.Then,theoretical advances inspired by the findings are introduced,which deepens our understanding on OR selection and preference of irrational facets.At last,future research directions in this field are proposed.

300 MPa grade biodegradable high-strength ductile low-alloy(BHSDLA)Zn-Mn-Mg alloys:An in vitro study

300 MPa grade biodegradable Zn-(0.6,0.8)Mn-(<0.1)Mg alloys with yield strengths>300 MPa and elongations>15%have been developed,which are designated as Zn06Mn006Mg(HE)and Zn08Mn005Mg(HE)in as-extruded state.They are the newest members of a small group of biodegradable Zn alloys with mechanical properties beyond the generally accepted benchmark for orthopedic implants.Immersed in simulated body fluid for 30 days,Zn06Mn006Mg(HE)and Zn08Mn005Mg(HE)exhibit corrosion rates of 38 and 53μm y^(-1),respectively.They show high antibacterial rates of 93%-97%against E.coli.In 25%-75%extracts of both the alloys,MC3T3-E1 cell viabilities for 1 day and 3 days are all over 100%,indicating complete cytocompatibility.In 100%extracts for 3 days,both alloys show non-toxicity.After a longtime room temperature storage of 72 weeks,natural embrittling alike Zn-Mg alloys does not happen.The Zn-Mn-Mg alloys still have mechanical properties exceeding the benchmark by a large margin.The in vitro study shows the newly developed BHSDLA Zn-Mn-Mg alloys are promising candidates for orthopedic implants.

Biodegradable Zn-0.5Li alloy rib plate:Processing procedure development and in vitro performance evaluation

Trauma kills more than four million people worldwide each year,with chest trauma accounting for 25%of these deaths.Rib fractures are the main manifestation of chest trauma.Biodegradable Zn alloys offer a new option to overcome clinical problems caused by permanent rib fracture internal fixation mate-rials,e.g.,long-term stress masking and secondary surgery.In this study,the fabrication procedure of biodegradable Zn-0.5Li alloy rib plates is successfully developed,which consists of casting,hot-warm rolling,cutting,and pressing sequentially.Biomechanical three-point bending performance of the Zn al-loy rib plates is comparable to that of commercial pure Ti rib plates,much higher than that of pure Zn rib plates.In addition,the Zn alloy exhibits the best antibacterial ability against E.coli and S.aureus among the three materials.Although the Zn alloy exhibits a weaker MC3T3 cytocompatibility than pure Ti,it is better than pure Zn.This study provides a foundation for the future development of various biodegrad-able Zn alloy rib plates.

Zn-0.8Mn alloy for degradable structural applications:Hot compression behaviors,four dynamic recrystallization mechanisms,and better elevated-temperature strength

Environmentally degradable Zn-0.8Mn alloy is highly ductile,which lays the foundation for developing high-performance Zn-Mn-based alloys.However,not only constitutive equation of this alloy is unknown,but also its dynamic recrystallization(DRX)behavior is unclear,which makes optimization of hot pro-cessing parameters of this alloy almost dependent on trial-and-error.This work aims to tackle these prob-lems.The constitutive equation was deduced to be˙ε=1.38×10^(12)×[sinh(0.009σ)]^(8)exp(-135150/RT).A processing map of the alloy was obtained for the first time,which shows that it has excellent hot formability with narrow instability zones.At a final true strain of 0.8,the volume fraction of DRX grains increased from 37%to 79%with temperature increasing from 150℃to 350℃and strain rate decreas-ing from 10 s^(−1)to 10^(-3)s^(−1).Discontinuous DRX(DDRX),continuous DRX(CDRX),twinning-induced DRX(TDRX),and particle stimulated nucleation(PSN)were activated during hot compressions.DDRX was al-ways the main mechanism.TDRX was completely suppressed at 300℃and above.PSN arose from dis-persed MnZn 13 particles.Furthermore,Zn-0.8Mn alloy exhibited elevated-temperature strengths better than pure Zn and Zn-Al-based alloys.At 300℃and 0.1 s^(−1),its peak stress was 1.8 times of pure Zn,owing to MnZn 13 particles of 277±79 nm impeding the motion of grain boundaries and dislocations.

300 MPa grade highly ductile biodegradable Zn-2Cu-(0.2-0.8)Li alloys with novel ternary phases

Although a few high-strength biodegradable Zn alloys with yield strengths(YSs)over 300 MPa in rolled state have been developed,their elongations(ELs)are generally less than 30%.This study developed rolled Zn-2Cu-x Li(x=0.2 wt.%,0.5 wt.%,0.8 wt.%)alloys with YSs of 316-335 MPa and ELs of 44%-61%.Three-dimensional atom probe(3DAP)and time of flight secondary ion mass spectrometry(TOF-SIMS)were employed to characterize Li distribution.Three kinds of Zn-Cu-Li ternary phases are identified,which are blockyε′-(Cu_(0.5),Li_(0.5))Zn 4,blockyβ′-(Li_(0.9),Cu_(0.1))Zn 4,and small roundγparticles with high Li content in the annealed state.Other identified phases are Zn,β-LiZn 4,andε-CuZn 4 phases.With the increase of Li content in the alloys,ε′phase with 6.50 at.%Cu transforms intoβ′phase with 2.12 at.%Cu,i.e.,the average level in the alloys.Withinε′phase,there exist nano-scale Li clusters andεphase,resulting inε′/εstructure.Dense Zn laths precipitate fromβ′phase,resulting inβ′/Zn lamellar structure.The lamel-lar structure is the matrix of Zn-2Cu-0.8Li and leads to near-isotropic plasticity.Electrochemistry tests show that degradation rates fall in the range of 153-196μm/year,which decrease with Li content.All the alloys exert positive effects on the growth of MC3T3-E1 cells with 10%extract.This research reveals how microstructure evolves in Zn-2Cu-x Li alloys,which lays the foundation for their future applications.

High-performance hot-warm rolled Zn-0.8Li alloy with nano-sized metastable precipitates and sub-micron grains for biodegradable stents

Fabricated through a newly developed hot-warm rolling process,Zn-0.8 Li(wt%)alloy has ideal strength and ductility far beyond the mechanical benchmark of materials for biodegradable stents.Precipitation of needle-like Zn in primary p-LiZn4 phase is observed in Zn-Li alloy for the first time.Orientation relationship between them can be described as[1-213]β//[2-1-10](Zn),(10-10)βabout 4.5°from(0002)(Zn).Zn grains with an average size of 640 nm exhibit strong basal texture,detected by transmission electron back-scatter diffraction.Li distribution is determined by three-dimensional atom probe,which reveals the formation of nano-sized metastableα-Li2Zn3 precipitates with a number density of 7.16×10^22 m^-3.The fine lamellar Zn+β-LiZn4 structure,sub-micron grains and the nano-sized precipitates contribute to the superior mechanical properties.

Design biodegradable Zn alloys: Second phases and their significant influences on alloy properties

Alloying combined with plastic deformation processing is widely used to improve mechanical properties of pure Zn.As-cast Zn and its alloys are brittle.Beside plastic deformation processing,no effective method has yet been found to eliminate the brittleness and even endow room temperature super-ductility.Second phase,induced by alloying,not only largely determines the ability of plastic deformation,but also influences strength,corrosion rate and cytotoxicity.Controlling second phase is important for designing biodegradable Zn alloys.In this review,knowledge related to second phases in biodegradable Zn alloys has been analyzed and summarized,including characteristics of binary phase diagrams,volume fraction of second phase in function of atomic percentage of an alloying element,and so on.Controversies about second phases in Zn-Li,Zn-Cu and Zn-Fe systems have been settled down,which benefits future studies.The effects of alloying elements and second phases on microstructure,strength,ductility,corrosion rate and cytotoxicity have been neatly summarized.Mg,Mn,Li,Cu and Ag are recommended as the major alloying elements,owing to their prominent beneficial effects on at least one of the above properties.In future,synergistic effects of these elements should be more thoroughly investigated.For other nutritional elements,such as Fe and Ca,refining second phase is a matter of vital concern.

Fabrication and characterization of novel biodegradable Zn-Mn-Cu alloys

Zn-Mn-Cu alloys with micro-alloying of Mn and Cu in Zn are developed as potential biodegradable met- als. Although the as-cast alloys are very brittle, their ductilities are significantly improved through hot rolling. Among the as-cast and the as-hot-rolled alloys, as-hot-rolled Zn-0.35Mn-0.41 Cu alloy has the best comprehensive property. It has yield strength of 198.4 ± 6.7 MPa, tensile strength of 292.4 ± 3.4 MPa, elongation of 29.6 ±3.8% and corrosion rate of 0.050-0.062 mm a^-1. A new ternary phase is characterized and determined to be MnCuZn18, which is embedded in MnZn13, resulting in a coarse cellular/dendritic MnZna3-MnCuZn18 compound structure in Zn-0.75 Mn-0.40Cu alloy. Such a coarse compound structure is detrimental for wrought alloy properties, which guides future design of Zn-Mn-Cu based alloys. The preliminary research indicates that Zn-Mn-Cu alloy system is a promising candidate for potential cardiovascular stent applications.

Hierarchical microstructure and two-stage corrosion behavior of a high-performance near-eutectic Zn-Li alloy

In order to improve mechanical and corrosion properties of biodegradable pure Zn,a knowledge-based microstructure design is performed on Zn-Li alloy system composed of hard β-LiZn_(4) and soft Zn phases.Precipitation and multi-modal grain structure are designed to toughen β-LiZn_(4) while strengthen Zn,resulting in high strength and high ductility for both the phases.Needle-like secondary Zn precipitates form in β-LiZn4,while fine-scale networks of string-like β-LiZn4 precipitates form in Zn with a tri-modal grain structure.As a result,near-eutectic Zn-0.48 Li alloy with an outstanding combination of high strength and high ductility has been fabricated through hot-warm rolling,a novel fabrication process to realize the microstructure design.The as-rolled alloy has yield strength(YS) of 246 MPa,the ultimate tensile strength(UTS) of 395 MPa and elongation to failure(EL) of 47 %.Immersion test in simulated body fluid(SBF) for 30 days reveals that Li-rich products form preferentially at initial stage,followed by Zn-rich products with prolonged time.Aqueous insoluble Li_(2) CO_(3) forms a protective passivation film on the alloy surface,which suppresses the average corrosion rate from 81.2 μm/year at day one down dramatically to 18.2 μm/year at day five.Afterwards,the average corrosion rate increases slightly with decrease of Li2 CO_(3) content,which undulates around the clinical requirements on corrosion resistance(i.e.,20 μm/year) claimed for biodegradable metal stents.

Microstructure quantification of Cu-4.7Sn alloys prepared by two-phase zone continuous casting and a BP artificial neural network model for microstructure prediction

Microstructures of Cu-4.7Sn(%) alloys prepared by two-phase zone continuous casting(TZCC)technology contain large columnar grains and small grains.A compound grain structure,composed of a large columnar grain and at least one small grain within it,is observed and called as grain-covered grains(GCGs).Distribution of small grains,their numbers and sizes as well as numbers and sizes of columnar grains were characterized quantitatively by metallographic microscope.Back propagation(BP) artificial neural network was employed to build a model to predict microstructures produced by different processing parameters.Inputs of the model are five processing parameters,which are temperatures of melt,mold and cooling water,speed of TZCC,and cooling distance.Outputs of the model are nine microstructure quantities,which are numbers of small grains within columnar grains,at the boundaries of the columnar grains,or at the surface of the alloy,the maximum and the minimum numbers of small grains within a columnar grain,numbers of columnar grains with or without small grains,and sizes of small grains and columnar grains.The model yields precise prediction,which lays foundation for controlling microstructures of alloys prepared by TZCC.

Oxidation resistant low-alloyed Ti alloys with good ductility

Oxidation resistance enhancement of pure Ti often comes at the cost of reduced ductility,which is frequently the problem through alloying with sole Al,Si,W,Mo and B.To overcome the short coming of single element alloying,this paper proposes a multi-element low-alloying strategy to take advantage of synergistic effects and resolve the conflict between oxidation resistance and ductility.It demonstrates that the addition of a small quantity of Ta(0.51wt%)can boost both oxidation resistance and ductility in comparison to pure Ti.Furthermore,the combined addition of a small amount(0.54 wt%)of Ta,Nb and Si not only preserves good ductility of pure Ti,but also reduces mass gains to 14%-67%of pure Ti during 100 h oxidation at 650-850℃in air.This indicates even better oxidation resistance than that obtained through the use of Ta,Nb,or Nb+Ta additions.The Ta+Nb+Si alloying creates an oxide layer that is less porous and more resistant to stratification and spalling.Consequently,a 3-μm N-rich layer can form in the Ti substrate beneath the oxide scale,in which phase transformation generates coherent Ti_(2)N with(0001)_(Ti)as the habit plane,with N atoms prefers to diffuse along■than along[0001]_(Ti).The completely transformed Ti_(2)N region or partially transformed Ti+Ti_(2)N region can effectively impede oxygen invasion.Therefore,the multielement low-alloying strategy is promising for enhancing both oxidation resistance and mechanical properties of metallic materials in the future.