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.

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.

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.

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.

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.

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。

TC4_(f)/LA91热压复合制备与组织性能研究

通过热压层合工艺制备TC4_(f)/LA91复合材料,并对其复合界面显微组织和力学性能进行研究,为拓展Mg-Li合金复合材料应用提供一定的理论与技术支持。分别用金相显微镜(Optical Microscopes,OM)、扫描电镜(Scanning Electron Microscope,SEM)观察复合材料的微观形貌,使用能谱仪(Energy Dispersive Spectrometer,EDS)检测元素分布情况、X射线衍射(X-ray Diffraction,XRD)分析复合材料的相组成,通过拉伸试验测试复合材料的力学性能。结果表明,TC4_(f)/LA91复合材料界面具有扩散效应,基体中的主要元素Mg、Li、Al与增强体中的主要元素Ti、Al、V相互扩散,并随温度增加能够形成具有一定宽度(2~3μm)且形状完整、轮廓清晰的扩散层,实现界面复合效果,界面处物相稳定,无新相产生。TC4_(f)/LA91复合材料的抗拉强度对温度和增强体分数敏感,基本不随保温时间变化,有明显屈服现象。在510℃保温45 min工艺条件下、10 vol.%体积分数的抗拉强度为297 MPa,相比LA91基体抗拉强度增加50.76%,强化效果明显。在拉伸过程中,由于界面复合紧密,TC4纤维未被拔出,其断口呈颈缩,LA91合金基体未发生明显开裂。

Fabrication of Ti/Al/Mg laminated composites by hot roll bonding and their microstructures and mechanical properties

Ti/Al/Mg laminated composites were successfully fabricated by hot roll bonding.The effects of the rolling reduction on the microstructural evolution and mechanical properties of the composites were explored.The results show that Ti/Al/Mg laminated sheets exhibit good interfacial bonding.The rolling reduction has a significant effect on the deformation inhomogeneity through the thickness of the Al layer.The initial grains of the Al layer near the Ti/Al interface are fragmented into fine equiaxed grains,and the grains at the center and near the Al/Mg interface are elongated.The R-cube shear texture of the Al layer forms near the Ti/Al interface and permeates into the center layer in the samples with greater rolling reductions.The b-fiber rolling texture of the Al layer is observed near the Al/Mg interface and increases with the increase of rolling reduction.The stress–strain curves indicate that the fracture appears first in the Mg layer.With the increasing rolling reduction,the ultimate tensile and yield strength values increase,and the elongation up to the Mg layer fracture decreases.

Effect of Annealing on Microstructure and Mechanical Properties of Ultrafine-Grained Low-Carbon Medium-Manganese Steel Produced by Heavy Warm Rolling

An ultrafine-grained(UFG) low-carbon medium-manganese steel was fabricated by the heavily warm rolling(HWR) and subsequent quenching, and the effects of annealing temperatures on microstructure and mechanical properties of the UFG HWRed steel were investigated. The results show that the HWRed steel exhibits simultaneous improvements in strength,uniform elongation and work hardening, which is mainly attributed to the refinement of martensitic microstructures. The HWRed steels comprise only a-phase when annealing at lower temperatures below to 550 °C and at higher temperatures above to 700 °C. Whereas, UFG c-austenite is formed by reverse transformation when the HWRed steel was annealed at intermediate temperatures from 550 to 700 °C and the volume fraction increases with increasing annealing temperatures,consequently resulting in a dramatic increase in ductility of the annealed HWRed steels. It was found that the transformed UFG austenite and ferrite remained ～500 nm and ～800 nm in size when the HWRed steel was annealed at 650 and700 °C for 1 h, respectively, showing an excellent thermal stability. Moreover, the HWRed steel annealed at 650 °C exhibits high strength-ductility combinations with a yield strength of 906 MPa, ultimate tensile strength(UTS) of1011 MPa, total elongation(TEL) of 51% and product of strength and elongation(PSE: UTS 9 TEL) of 52 GPa%. It is believed that these excellent comprehensive mechanical properties are closely associated with the UFG austenite formation by reverse transformation and principally attributed to the transformation-induced plasticity(TRIP) effect.

Microstructure Evolution and Microhardness of Ultrafine-grained High Carbon Steel during Multiple Laser Shock Processing

Surface microstructure and microhardness of （ferrite＋ cementite） microduplex structure of the ultrafine- grained high carbon steel after laser shock processing （LSP） with different impact times were investigated by means of scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD） and microhardness measurements. Equiaxed ferrite grains were refined from 400 to 150 nm, and the cementite lamellae were fully spheroidized, with a decrease of the particle diameter from 150 to 100 nm as the impact times increased. The cementite dissolution was enhanced significantly. Correspondingly, the lattice parameter of α-Fe and microhard- hess increased with the impact times.

Microstructure,fracture behavior,in vitro corrosion resistance,and cytotoxicity of Zn-Mg/Mg-Zn-HAp laminated composites produced by spark plasma sintering

Ideal biodegradable materials exhibit suitable degradation rates and sufficient mechanical properties for their specific application.With these parameters in mind,Zn-Mg/Mg-Zn-hydroxyapatite(HAp) laminated composites were designed and fabricated by spark plasma sintering.This paper describes the structure,mechanical properties,in vitro corrosion resistance,and cytotoxicity of the Zn-Mg/Mg-Zn-HAp laminated composites.The compressive strength and elastic moduli of the laminated composites matched that of cortical bone and could effectively reduce the stress shielding effect as an implant with good biomechanical compatibility.Analysis of the fracture path and morphology after fracture toughness tests indicated that the Zn-Mg/Mg-Zn-HAp laminated composites exhibited significant capacity to prevent crack propagation,improving the fracture toughness.In vitro degradation experiments showed that the design of the laminated structure can provide a gradient degradation rate for the material.Furthermore,the laminated composites exhibited excellent biocompatibility and are promising candidates for orthopedic implants.

Effect of processing parameters on the microstructure and mechanical properties of TiAl/Ti_(2)AlNb laminated composites

In order to improve the intrinsic brittleness of TiAl alloys,Ti_(2)AlNb alloys with outstanding ductility and toughness at room temperature,and good high-temperature performance are competitive candidates in constructing the TiAl-based laminated composites.In this work,TiAl/Ti_(2)AlNb laminated composites are successfully synthesized by vacuum hot pressing combined with the foil-foil(sheet)metallurgy.Under the pressure of 65 MPa,different holding time and temperature of hot pressing are tried and the optimized fabrication parameter is acquired as 1050℃/120 min/65 MPa.Along with the changes of processing parameters,the defect,microstructure,interface,phase transformation and the corresponding mechanical properties are detailly discussed.The results show that the TiAl/Ti_(2)AlNb laminated composite fabricated at 1050℃ for 2 h achieves a good metallurgical interface bonding.The corresponding interface microstructure is composed of region I and region II.The region I consists of O,α_(2)and B2/βphase,and region II is made up ofα2.Subsequently,the tensile tests indicate that the composite synthesized at 1050℃ for 2 h possesses a maximum strength of 812 MPa and a total elongation of 1.31%at room temperature,and a strength of 539.71 MPa and the highest total elongation of 10.34%at 750℃.The well synergistic deformation ability between the interface and the two base alloys endows the composite an excellent tensile performance.Moreover,the composite processed at 1050℃ for 2 h behaves the best fracture toughness in both arrester orientation and divider orientation with the value of 32.6 MPa.m^(1/2)and 30.1 MPa.m^(1/2),respectively.The Ti_(2)AlNb alloy in the laminated structure effectively release the stress around the crack tip and plays a role in toughening.Further,crack deflection,crack bridging,crack blunting and fragmentation also make contributions to enhance the fracture toughness of the laminated composites.

Microstructure Characteristics in Ultrafine-grained Commercially Pure Aluminium after Laser Shock Processing

The aim of this paper was to address the effect of laser shock processing (LSP) on the microstructure of ultrafine-grained commercially pure aluminium which was produced through severe cold rolling and annealing. The microstructure characteristics of ultrafine-grained commercially pure aluminium were experimentally investigated by TEM during ultra-high strain rate loading. The results show that microstructure was obviously refined due to ultra-high plastic strain induced by a single pass LSP impacts. The grain sizes decrease from 0.6 μm after severe cold rolling and annealing to 0.3 μm at the center of the laser shock wave after a single pass LSP. There is a distinct increase in the dislocation density at the edge of the laser shock wave. These experiments have guide meaning to the practical engineering applications of LSP technique.