Effects of Sinusoidal Vibration of Crystallization Roller on Composite Microstructure of Ti/Al Laminated Composites by Twin-Roll Casting

A new,innovative vibration cast-rolling technology of “electromagnetic stirring+dendrite breaking+asynchronous rolling” was proposed with the adoption of sinusoidal vibration of crystallization roller to prepare Ti/Al laminated composites,and the effect of sinusoidal vibration of crystallization roller on composite microstructure was investigated in detail.The results show that the metallurgical bonding of titanium and aluminum is realized by mesh interweaving and mosaic meshing,instead of transition bonding by forming metal compound layer.The meshing depth between titanium and aluminum layers (6.6μm) of cast-rolling materials with strong vibration of crystallization roller (amplitude 0.87 mm,vibration frequency 25 Hz) is doubled compared with that of traditional cast-rolling materials (3.1μm),and the composite interfacial strength(27.0 N/mm) is twice as high as that of traditional cast-rolling materials (14.9 N/mm).This is because with the action of high-speed superposition of strong tension along the rolling direction,strong pressure along the width direction and rolling force,the composite linearity evolves from "straight line" with traditional casting-rolling to "curved line",and the depth and number of cracks in the interface increases greatly compared with those with traditional cast-rolling,which leads to the deep expansion of the meshing area between interfacial layers and promotes the stable enhancement of composite quality.

Microstructure and mechanical behavior of Ti/Cu/Ti laminated composites produced by corrugated and flat rolling

Ti/Cu/Ti laminated composites were fabricated by corrugated rolling(CR) and flat rolling(FR) method.Microstructure and mechanical properties of CR and FR laminated composites were investigated by scanning electron microscopy, numerical simulation methods, peel and tensile examinations. The effect of CR and FR was comparatively analyzed. The results showed that the CR and FR laminated composites exhibited different effective plastic strain distributions of the Ti layer and Cu layer at the interface. The recrystallization texture, prismatic texture and pyramidal texture were developed in the Ti layer by CR, while the R-Goss texture and shear texture were developed in the Cu layer by CR. The typical deformation texture components were developed in the Ti layer and Cu layer of FR laminated composites. The CR laminated composites had higher bond strength, tensile strength and ductility.

Interfacial Microstructure and Mechanical Properties of Al Alloy/Mg Alloy Laminated Composite Plates Fabricated by Equal Channel Angular Processing

KAl（7075）alloy/Mg（AZ31）alloy laminated composite plates were successfully fabricated by the equalchannelangular processing（ECAP）by using route A for 1,2,and 3 passes at 573 K,respectively.After fabrication,the 1-pass ECAPed laminated composite plates were annealed at different temperatures.The microstructure evolution,phase constituent,and bonding strength near the joining interface of Al（7075）alloy/Mg（AZ31）alloy laminated composites plates were evaluated with scanning electron microscopy,X-ray diffraction,and shear tests.The experimentalresults indicated that a 20 μm diffusion layer was observed at the joining interface of Al（7075）alloy/Mg（AZ31）alloy laminated composites plates fabricated by the 1-pass ECAP,which mainly included Al_3Mg_2 and Mg_（17）Al_（12） phases.With the increase of passes,the increase of diffusion layer thickness was not obvious and the form of crack in these processes led to the decrease of bonding strength.For 1-pass ECAPed composites,the thickness of diffusion layer remained unchanged after annealed at 473 K,while the bonding strength reached its maximum value 29.12 MPa.However,after elevating heat treatment temperature to 573 K,the thickness of diffusion layer increased rapidly,and thus the bonding strength decreased.

Fabrication, microstructure and properties of electron beam-physical vapor deposited TiAl sheet and TiAl/Nb laminated composites

The TiAl-based alloys sheet with 150 mm×100 mm×0.4 mm and the TiAl/Nb laminated composites with 150 mm×100 mm×0.2 mm were fabricated by using electron beam-physical vapor deposition(EB-PVD) method, respectively. The microstructure and properties of the sheet were investigated by AFM, SEM and EDS. The results show that the TiAl based alloys sheet has a good surface quality, and its microstructure is columnar crystal. The component of the alloys indicates a regular and periodical gradient change which leads to the spontaneous delamination along the normal direction of substrate. In the TiAl/Nb laminated composites alternating overlaid by TiAl of 24 layers and Nb of 23 layers, the interface of each layer evenly distributed throughout the cross-section is transparent, and the interlayer spacing is about 8μm. The component of TiAl layers also changes regularly along the normal direction of substrate, but no delamination phenomenon is found. The TiAl/Nb laminated composites have better ductility than the TiAl-based alloys sheet.

Interface analysis of 7B52 Al alloy laminated composite fabricated by hot-roll bonding

The bonding interface of 7B52 Al alloy laminated composite （ALC） fabricated by hot rolling was investigated using optical microscopy （OM）, transmission electron microscopy （TEM）, scanning electron microscopy （SEM）, ultrasonic flaw detection （UFD）, and bonding strength tests. The results show that metallurgical bonding is achieved at the interface after composite rolling. The TEM analysis and tensile tests indicate that the 7B52 ALC plate combines high strength of the hard individual layer and good toughness of the soft individual layer. However, UFD technology and SEM analysis prove that the defects （thick oxide films, acid washed residues, air, oil and coarse particles） existing in the bonding interface are harmful to the bonding strength. To sum up, the composite roiling process is suitable for 7B52 ALC plate, and the content and size of the defects should be controlled strictly. Advanced surface treatment of each individual layer would be beneficial to further improve the bonding quality.

Progress on the glassy-crystal laminates:From design,microstructure to deformation and future solutions

The development of new design strategies to create innovative structural materials,refine existing ones,and achieves compatible combinations of strength and plasticity remains a worldwide goal.Promising alloys,such as shape memory alloys(SMAs),bulk metallic glasses(BMGs),high entropy alloys(HEAs),and heterogeneous pure metals such as Cu,have excellent mechanical responses,but they still fall short of meeting all the requirements of structural materials due to specific flaws,such as lack of tensile de-formation for BMGs and low yielding strength for HEAs.To address these shortcomings,proposals such as integrating glassy matrices and crystallized alloys,such as HEAs/SMAs,have been suggested.However,these solutions have unresolved issues,such as the challenging control of B2 phase formation in BMG composites.Recently,glass-crystal(A/C)laminated alloys with alternating layers have been reported to exhibit improved mechanical properties and activated work-hardening behaviors,but they still face press-ing issues such as bonding interfaces and unknown deformation mechanisms.This review focuses on design routes such as the selection of alloy components and processing techniques,exploration of micro-structural evolution and deformation modes with an increase in strain,and future solutions to address pressing and unsolved issues.These prominent advantages include diversified deformation mechanisms,such as deformation twinning,martensitic phase transformation,and precipitation hardening,as well as tuned interactive reactions of shear bands(SBs)near the A/C interfaces.Thus,this review provides a promising pathway to design and develop structural materials in the materials field community.

Fabrication of ultrafine-grained AA1060 sheets via accumulative roll bonding with subsequent cryorolling

Ultrafine-grained(UFG)AA1060 sheets were fabricated via five-cycle accumulative roll bonding(ARB)and subsequent three-pass cold rolling(298 K),or cryorolling(83 K and 173 K).Microstructures of the aluminum samples were examined via transmission electron microscopy,and their mechanical properties were measured via tensile and microhardness testing.Results indicate that ultrafine grains in ARB-processed sheets were further refined by subsequent rolling,and the grain size became finer with reducing rolling temperature.The mean grain size of 666 nm in the sheets subjected to ARB was refined to 346 or 266 nm,respectively,via subsequent cold rolling or cryorolling(83 K).Subsequent cryorolling resulted in ultrafine-grained sheets of higher strength and ductility than those of the sheets subjected to cold rolling.

Elastic and Plastic Behaviors of Laminated Ti-TiBw/Ti Composites

The novel laminated Ti-TiBw/Ti composites composed of pure Ti layers and TiBw/Ti composite layers have been successfully fabricated by reactive hot pressing. Herein, two-scale structures formed： the pure Ti layer and TiBw/Ti composite layer together constructed a laminated structure at a macro scale. Furthermore, TiBw reinforcement was distributed around Ti particles and then formed a network microstructure in TiBw/Ti composite layer at a micro scale. The laminated Ti-TiBw/Ti composites reveal a superior combination of high strength and high elongation due to two-scale structures compared with the pure Ti, and a further enhancement in ductility compared with the network structured composites. Moreover, the elastic modulus of the laminated composites can be predicted by H-S upper bound, which is consistent with the experimental values.

Crack propagation behavior of inhomogeneous laminated Ti-Nb metal-metal composite

In order to investigate the real-time cracking behavior of each component of a composite with strong interfacial bonding among lamellae, Ti-18 Nb(at.%) composite was prepared by spark plasma sintering(SPS), followed by hot-rolling, annealing, and quenching. The microstructure and mechanical properties were characterized by scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), micro-region X-ray diffractometry(MRXRD), nanoindentation, and in-situ scanning electron microscopy tensile testing. The results show that the Ti-18 Nb consists of Ti-enriched, diffusion and Nb-enriched zones, and the sharp Nb gradient across different zones leads to inhomogeneous distribution of phase and mechanical properties. A remarkable finding is that the diffusion zones not only enable the cooperative deformation between the brittle Ti-enriched zones and the ductile Nb-enriched zones but also act as the crack-arresters to prevent the local cracks in the Ti-enriched zones from further propagating across the composite.

Variation of the uniaxial tensile behavior of ultrafine-grained pure aluminum after cyclic pre-deformation

To explore the influence of cyclic pre-deformation on the mechanical behavior of ultrafine-grained（UFG）materials with a high stacking fault energy（SFE）,UFG Al processed by equal-channel angular pressing（ECAP）was selected as a target material and its tensile behavior at different pre-cyclic levels D（D=N_i/N_f,where N_i and N_f are the applied cycles and fatigue life at a constant stress amplitude of 50 MPa,respectively）along with the corresponding microstructures and deformation features were systematically studied.The cyclic pre-deformation treatment on the ECAPed UFG Al led to a decrease in flow stress,and a stress quasi-plateau stage was observed after yielding for all of the different-state UFG Al samples.The yield strengths_（YS）,ultimate tensile strengths_（UTS）,and uniform straineexhibited a strong dependence on D when D≤20%;however,when D was in the range from 20%to 50%,no obvious change in mechanical properties was observed.The micro-mechanism for the effect of cyclic pre-deformation on the tensile properties of the ECAPed UFG Al was revealed and compared with that of ECAPed UFG Cu through the observations of deformation features and microstructures.

Electron Beam-Physical Vapor Deposited TiAl-based Laminated Composite Sheet with Nb Layer Toughening

The TiAl-based laminated composite sheet of 150 mm × 100 mm × 0.2 mm, with 24 TiAl layers and 23 Nb layers laid alternately one on another, was successfully fabricated using the electron beam-physical vapor deposition （EB-PVD） method. The microstructure and properties of the sheet were investigated on an atomic force microscope （AFM）, a scanning electron microscope （SEM） and a tensile testing machine. The results indicate that the evenly distributed Nb layers are well joined with the TiAl layers, and the interfaces between layers are transparent, and every interlayer spacing is of about 8μm. The fractures appear to be a mixture of intergranular fractures and somewhat ductile quasi-cleavage ones. Despite its slight influence on ultimate tensile strength, the inserts of Nb layers efficiently increase the room temperature ductility of TiAl-based alloys due to the crack deflection effect.

Enhanced mechanical properties of a carbon and nitrogen co-doped interstitial high-entropy alloy via tuning ultrafine-grained microstructures

C-N co-doped interstitial high entropy alloy(iHEA)was reported to have high strength and ductility.However,iHEA with fully recrystallized ultrafine grains(UFGs)and underlying thermally activated pro-cesses associated with dislocation slip,twinning,and solute drag have not been reported yet.In this work,a C-N co-doped iHEA with nominal composition Fe_(48.5)Mn_(30)Co_(10)Cr_(10)C_(0.5)N_(1.0)(at.%)was prepared,and the microstructures were tuned by cold-rolling and annealing treatments to improve mechanical properties.Upon cold-rolling with a strain of 1.74,the main microstructures in the iHEA are composed of nano-grains,nano-twins,HCP laminates,and high density of dislocations,leading to ultrahigh hardness of 466.7 HV and tensile strength of 1730 MPa at the expense of ductility(2.44%).Both the nanostructures and the high hardness of the iHEA can be maintained up to an annealing temperature of 600℃(462.5 HV).After annealing at 650℃ for 1 h,the UFG microstructures are obtained in the iHEA,containing re-crystallized grains with an average grain size of 0.91μm and nanoprecipitates with an average diameter of 90.8 nm.The combined strengthening and hardening effects of UFGs,nanoprecipitates,twinning,and solutes contribute to high strain hardening(n=0.81),gigapascal yield strength(984 MPa),and good duc-tility(20%).The C-N co-doping leads to a strong drag effect on dislocation slip,resulting in a nano-scale mean free path of dislocation slip λ(1.44 nm)and much small apparent activation volume V^(∗)(15.8 b^(3))of the UFG iHEA.

退火处理对热轧Al/Mg/Al复合板界面微观组织与性能的影响

采用1 mm Al+3 mm Mg+1 mm Al的组坯方式,轧制温度为400℃,压下率为35%,热轧得到6061/AZ31B/6061复合板。在退火温度为200℃的条件下,研究了不同退火时间对复合板拉伸性能、界面结合、微观组织以及表面残余应力的影响。在保温时间分别为0、0.5、1和1.5 h情况下,分别进行拉伸实验、能谱分析、微观组织观察和残余应力测试。结果表明,当轧制压下率为35%时,6061铝合金和AZ31B镁合金能够通过热轧方法得到很好的复合;随着退火时间的增加,6061/AZ31B/6061复合板的拉伸强度、伸长率和界面扩散厚度显著增加,且铝合金表面残余应力也增大。

烧结温度对Ti(C,N)-HfN/Ti(C,N)-WC层状陶瓷微观组织和力学性能的影响

以Ti(C,N)为基体相,HfN和WC为不同层的增强相,金属Ni和Mo为粘结相,采用交替铺层法制备素坯,并利用真空热压烧结技术制备Ti(C,N)-HfN/Ti(C,N)-WC层状陶瓷,研究了烧结温度对层状陶瓷微观组织和力学性能的影响。结果表明:随着烧结温度的升高,材料中的晶粒逐渐长大,在烧结温度为1350℃和1400℃时,材料的晶粒较小但分布不均匀,且存在较多的微缺陷;在烧结温度为1450℃和1500℃时,材料中的晶粒相对均匀(粒径~1μm),微缺陷较少;在烧结温度达到1550℃时,材料中出现了大量粗大晶粒(粒径~2μm)。随着烧结温度的升高,层状陶瓷的抗弯强度、维氏硬度和断裂韧度均先增大后减小。在1450℃下所制备的Ti(C,N)-HfN/Ti(C,N)-WC层状陶瓷具有较好的综合力学性能,其抗弯强度、维氏硬度和断裂韧度分别为(1263.6±17.1)MPa、(18.5±0.3)GPa和(8.2±0.1)MPa·m1/2。此外,Ti(C,N)-HfN/Ti(C,N)-WC层状陶瓷在断裂时表现为穿晶与沿晶并存的断裂模式。

航空发动机GH3230高温合金层板结构TLP扩散焊接制备及力学性能研究

随着更高推重比需求的不断提高,航空发动机热端部件不仅需要耐高温材料,更需要冷却效率更高的结构形式,本文采用自主研制的KNiCr–5中间层在1200℃保温4 h的工艺条件下TLP扩散焊接制备了GH3230高温合金多孔层板冷却结构,测试了层板结构模拟件的焊接质量和接头力学性能。超声检测结果表明,层板模拟件所有柱形结构(扰流柱)与底板(冲击板)焊接完好,未发现任何缺陷。焊缝形成了均匀的固溶体组织,无任何化合物相、裂纹和孔洞缺陷存在。室温/950℃高温拉伸测试结果表明,层板板柱结构模拟件和GH3230高温合金棒材对接结构全部断裂在GH3230高温合金基体,焊缝强度均明显高于GH3230高温合金。高温拉伸断裂试件的延伸率高达52%,薄板焊缝90°三点弯曲后无开裂,微观观察无裂纹等缺陷,表明了焊缝具有优异塑性。优异的焊接质量和性能保证了焊缝结构承受高温载荷时能达到GH3230高温合金基体的传热和承力性能,避免了焊缝成为整个层板结构薄弱环节。

层厚对TiC-HfN/TiC-HfC层状陶瓷微观组织及力学性能的影响

以TiC为基体相、Hf N和HfC分别为各层的增强相、Ni和Co为金属相,利用微叠层装置进行叠层,采用真空热压烧结技术,在1500℃下制备了不同层厚的TiC-Hf N/TiC-HfC层状陶瓷,其层厚分别为0.25、0.30、0.35、0.40mm,研究了层厚对该材料微观组织和力学性能的影响。研究结果表明:在不同层厚下,材料的断口形貌基本相似,且晶粒的尺寸均在5μm左右;随着层厚的增大,材料的相对密度、硬度和抗弯强度先增大后减小,层面断裂韧度基本保持不变,而层间断裂韧度不断减小;当层厚为0.30 mm时,材料具有相对较好的综合力学性能,此时其硬度为(19.6±0.24)GPa、抗弯强度为(841.1±20) MPa、层面断裂韧度为(6.5±0.18)MPa·m^(1/2)和层间断裂韧度为(8.3±0.27)MPa·m^(1/2)。

铝板水热碳吸附工艺制备APC/Al层状复合材料的显微组织、力学性能和摩擦学性能

采用铝板水热碳吸附工艺(HTCAP)和真空热压烧结工艺(VHPS)制备无定形碳(APC)/Al层状复合材料,研究葡萄糖溶液浓度对其显微组织、力学性能和摩擦学性能的影响。结果表明,APC在层间分布均匀,并且通过Al的扩散与基体形成良好的界面结合。随着葡萄糖溶液浓度的增加,层间硬度、极限抗拉强度(UTS)和伸长率先增大后减小,而磨损率则呈现相反的趋势,摩擦因数(COF)逐渐减小。当葡萄糖溶液浓度为0.3 mol/L时,伸长率最大,为16.4%,磨损率最小,为0.344×10^(-5)mm^(3)/(N·m)。粘着磨损是APC/Al层状复合材料的主要磨损机制。耐磨性的提高是由于在磨损表面形成均匀的APC润滑膜。

钛合金扩散连接技术及其层合结构疲劳裂纹扩展研究进展

本文主要对钛合金的扩散连接及层合结构疲劳裂纹扩展行为的研究进展进行了综述,总结了扩散连接钛合金界面的微观组织演变和疲劳裂纹扩展特性。首先概述了超塑成形/扩散连接技术的应用背景和优势,以及提高钛合金扩散连接界面质量的辅助技术(如添加中间层、热氢处理、脉冲电流加热和表面改性)。从钛合金扩散连接和钛合金与其他合金扩散连接两方面综述了界面组织和力学性能,指出组织演变严重依赖界面处合金元素种类和元素相互扩散能力。扩散连接技术可用来制备同种和异种合金的层合结构,且可灵活控制界面焊合与未焊合区域的形状与分布。最后,简述了同种或异种钛合金扩散连接层合结构可降低疲劳裂纹扩展速率,从而优化钛合金构件的疲劳损伤容限性能。

Bulk ultrafine grained microstructures with high thermal stability via intragranular precipitation of coherent particles

Producing ultrafine-grained(UFG)microstructures with enhanced thermal stability is an important yet challenging route to further improve mechanical properties of structural materials.Here,a high-performance bulk UFG copper that can stabilize even at temperatures up to 750℃(∼0.75 T m,T m is the melting point)was fabricated by manipulating its recrystallization behavior via low alloying of Co.Addition of 1 wt.%–1.5 wt.%of Co can trigger quick and copious intragranular clustering of Co atoms,which offers high Zener pinning pressure and pins the grain boundaries(GBs)of freshly recrystallized ul-trafine grains.Due to the fact that the subsequent growth of the coherent Co-enriched nanoclusters was slow,sufficient particles adjacent to GBs remained to inhibit the migration of GBs,giving rise to the UFG microstructure with prominently high thermal stability.This work manifests that the strategy for pro-ducing UFGs with coherent precipitates can be applied in many alloy systems such as Fe-and Cu-based,which paves the pathway for designing advanced strain-hardenable UFGs with plain compositions.

Effects of heat treatment on microstructures and properties of a heterostructured alloy with dissimilar components fabricated by WAAM

Heat treatment significantly influences homogeneous material microstructures and mechanical properties,which can be improved by an optimal heat treatment process.However,heat treatment application to heterogeneous materials presents significant challenges due to compositional and microstructural heterogeneities.Herein,a laminated heterostructured alloy comprising alternating316L stainless steel(SS)and 18Ni300 maraging steel(MS)layers fabricated using wire and arc additive manufacturing was investigated.A solution treatment was applied at900℃for 0.5 h.Subsequently,the solution-treated and asfabricated(AF)samples were aged at 500℃for 4 h;these samples were denoted SA and AT,respectively.The AT phase compositions and orientations were similar to those of AF.The SA 316L SS layer resembled that of AF,but the SA 18Ni300 MS layers exhibited a reduced austenite phase fraction and refined grain size,attributable to solid-state transformation.In the AT sample,aging induced the formation of nanoscale acicularωphase and ellipsoidal Ni_(3)Ti,Fe_(2)Mo,and X precipitates in the 18Ni300 MS layers.Conversely,the SA precipitates contained acicular Fe Ni_(2)and ellipsoidalω,Ni_(3)Ti,and X precipitates,and their fractions were lower than those in AT precipitates.The18Ni300 MS layer microhardness in the heat-treated samples increased due to nanoprecipitation,but the 316L SS layer microhardness resembled that of AF.The AT and SA ultimate tensile strengths increased to(1360±50)and(1473±41)MPa,respectively,attributable to precipitation strengthening.The SA 316L SS layer exhibited a high stress-induced martensite fraction,enhancing the ductility of heated samples.