Al−Si−Fe−Mn合金熔体保温过程中富铁相的三维形态特征和生长行为

采用扫描电子显微镜、透射电子显微镜、热力学计算和同步辐射X射线成像技术研究Al−7.0Si−1.0Fe−1.2Mn合金熔体保温过程中富铁相的形态演变和生长行为。结果表明,随着保温温度的降低,富铁相的形态由粗大的星形和多边形状转变成细小的汉字状以及汉字和多边形的耦合结构。富铁相的三维形貌显示,星形富铁相由多个多分支的初生相和衍生的不规则次生相组成;耦合结构由多面体和枝晶组成;单一汉字相则由枝晶组成。随着保温温度的降低,富铁相的数量、体积分数以及最大富铁相的体积和连通性显著降低。原位同步辐射X射线结果显示,在凝固过程中形成了两类初生富铁相,其中尺寸较小的初生富铁相保留在熔体中,并成为耦合共晶结构富铁相的形核质点。

High-throughput studies and machine learning for design of β titanium alloys with optimum properties

Based on experimental data,machine learning(ML) models for Young's modulus,hardness,and hot-working ability of Ti-based alloys were constructed.In the models,the interdiffusion and mechanical property data were high-throughput re-evaluated from composition variations and nanoindentation data of diffusion couples.Then,the Ti-(22±0.5)at.%Nb-(30±0.5)at.%Zr-(4±0.5)at.%Cr(TNZC) alloy with a single body-centered cubic(BCC) phase was screened in an interactive loop.The experimental results exhibited a relatively low Young's modulus of(58±4) GPa,high nanohardness of(3.4±0.2) GPa,high microhardness of HV(520±5),high compressive yield strength of(1220±18) MPa,large plastic strain greater than 30%,and superior dry-and wet-wear resistance.This work demonstrates that ML combined with high-throughput analytic approaches can offer a powerful tool to accelerate the design of multicomponent Ti alloys with desired properties.Moreover,it is indicated that TNZC alloy is an attractive candidate for biomedical applications.

双重异质结构对AZ91挤压板力学性能的影响

研究晶粒尺寸和析出相的双重异质结构对小挤压比制备的AZ91挤压板材力学性能的影响。与挤压比(ER)为12.8的样品(即ER12.8样品)相比,ER3.9和ER6.4样品呈现明显的粗细晶粒层和异质分布的细小弥散的析出相。此外,在ER3.9样品的细晶层中还观察到大量带状析出相。由于异质变形诱导(HDI)力和析出相的平衡,ER6.4样品呈现良好的强度和塑性结合。尽管ER3.9样品表现出最高的HDI力和基面滑移施密特因子,改善了塑性,但更多的带状析出相对恶化其力学性能仍起主导作用。

Revealing effect of aluminum alloying on work hardening and impact behaviors of low-density Fe-18Mn-1.3C-2Cr-(4,11)Al casting steel

The present study designed two kinds of Fe-18Mn-1.3C-2Cr-(4,11)Al(wt.%)low-density steels.Tensile and impact tests were carried out to evaluate the work hardening and impact toughness properties via aluminum(Al)alloying control.Meanwhile,microstructure evolution and fracture morphology were investigated by X-ray diffraction(XRD),a scanning electron microscope(SEM)equipped with electron backscatter diffraction(EBSD),a transmission electron microscope(TEM),and a stereo-optical microscope(OM).It is found that the Al addition obviously promotes the dislocation planar slipping,resulting in cleavage and brittle impact fracture in 11wt.%Al steel.Besides,the microband-induced plasticity(MBIP)mechanism is found in 4wt.%Al containing steel,introducing considerable work hardening capacity and impact toughness of 156.8±17.4 J.The present study provides a direct illustration of the relationship between work hardening and impact toughness behaviors of these two low-density steels for potential application as impact-resistant components.

Effect of Ti−6Al−4V particle reinforcements on mechanical properties of Mg−9Al−1Zn alloy

Mg−9Al−1Zn(AZ91)magnesium matrix composites reinforced by Ti−6Al−4V(TC4)particles were successfully prepared via powder metallurgical method.The yield strength(YS),ultimate tensile strength(UTS),and elongation(EL)showed a mountain-like tendency with the increase of the TC4 content.The mechanical properties of AZ91 magnesium matrix composites reached the optimal point with TC4 content of 10 wt.%,realizing YS,UTS,and EL of 335 MPa,370 MPa,and 6.4%,respectively.The improvement of mechanical properties can be attributed to the effective load transfer from the magnesium matrix to the TC4 particles,dislocations associated with the difference in the coefficient of thermal expansion,good interfacial bonding between the Mg matrix and TC4 particles,and grain refinement strengthening.

Microstructure and Mechanical Behavior of Mg-Based Bimetal Plates with High Formability Sleeve by Co-extrusion

In this study,microstructure and mechanical behavior of two types of Mg-based bimetal plates with a high formability sleeve were systematically studied,with a great emphasis on the effect of the interface characteristic and the sleeve fraction on the plasticity of composite plates.The rule of mixtures(ROM)for elongation was also addressed.The results show that when there is no or thin diffusion layer with thickness of about 3μm,Mg-based bimetal plates have a good plasticity with elongation of about 19-24%,and the ROM predicted elongations are very close to the experimental ones.In contrast,with a diffusion layer about 95-155μm thick,Mg-based bimetal plates exhibit a poor plasticity with elongation of about 11-17%,and the experimental elongations largely deviate from the ROM predictions.The plasticity of Mg-based bimetal plates increases with increasing sleeve fraction.This study provides new insights on the plastic deformation of Mg-based bimetal composites with a high formability sleeve.

Effect of Ti Particles on the Microstructure and Mechanical Properties of AZ91 Magnesium Matrix Composites

Spherical micro-Ti particle(TiP)-reinforced AZ91 magnesium alloy composites were fabricated by semi-solid stirring assisted ultrasonic vibration,which were then subjected to hot extrusion.The microstructure results showed that the addition of Ti particles refined the grain size and decreased the texture intensity of the as-extruded AZ91 alloy.An Al3Ti phase with a thickness of 100 nm formed at the Ti/Mg interface,which had a non-coherent relationship with the magnesium matrix.The as-extruded 1 vol.%TiP/AZ91 composite exhibited the best comprehensive mechanical properties,with yield strength,ultimate tensile strength,and elongation at break of 366 MPa,456 MPa,and 14.6%,respectively,which were significantly higher than those of the AZ91 alloy.Therefore,the addition of Ti particles can improve the strength and ductility of the AZ91 alloy,demonstrating the value of magnesium matrix composites for commercial applications.

Corrosion and impact-abrasion-corrosion behaviors of quenching- tempering martensitic Fe-Cr alloy steels

The corrosion and impact-abrasion-corrosion behaviors of quenching-tempering Fe-Cr martensitic steels for ball mill liner were investigated in the corrosive slurry of a copper mine compared with high manganese steel.It is found that the corrosion resistance and the protectiveness of the passive film of Fe-Cr martensitic steels became worse when the carbon content increased.The quenching-tempering Fe-Cr martensitic steel showed better impact-abrasion-corrosion resistance in the corrosive slurry compared with the high manganese steel,especially the alloy steel with the carbon content of 0.3 wt.%.The synergistic effect between mechanics and corrosion has also been analyzed to further reveal the impact-abrasion-corrosion mechanism of the steels.The damage from pure mechanics accounted for the largest percentage(over 65%)for all steels,demonstrating that mechanical damage played the most important role in the impact-abrasion-corrosion behaviors of the steels.The impact and cracking resistance of the steel should also be paid special attention during the development of new materials for ball mill liner.

Strengthening Mechanism and Microstructure of Deformable Ti Particles Reinforced AZ91 Composite

In this study,the deformable titanium(Ti)particles reinforced AZ91 composite was successfully prepared by powder metallurgy and subsequent extrusion.The mechanical properties and microstructural evolution of pure AZ91 and 5 Ti/AZ91 composite were studied.The yield strength,ultimate tensile strength,and elongation of 5 Ti/AZ91 composite are measured to be 212 MPa,323 MPa,and 10.1%,respectively.Microstructure analysis revealed that Ti particles are elongated along the extrusion direction,forming a discontinuous strip Ti particles,fine precipitated Mg_(17)Al_(12) phase inhibits dynamic recrystallization(DRX)behavior through Zener pinning effect and hinders the growth of matrix grains,resulting in refiner grains of 5 Ti/AZ91 composite.Heterogeneous deformed Ti particles and magnesium(Mg)matrix to generate additional heterogeneous deformation-induced(HDI)strengthening.Heterogeneous deformation-induced strengthening mainly contributed to the increment of yield strength for 5 Ti/AZ91 composite.

Effects of Ni content and tempering temperatures on microstructure and properties of medium-carbon cast steel

The microstructure evolution and properties of medium-carbon cast steel alloyed with different Ni contents after tempering at various temperatures have been investigated.The addition of 0.47-1.59 wt.%Ni content results in the formation of 16%-36% retained austenite(RA).The blocky and irregular-polygonal RA mainly forms along the prior austenite grain boundaries,and the tempering temperature does not affect the RA content.The hardness of medium-carbon cast steel is affected by the precipitation of carbides and the hardness of martensite.Excessive RA content is the main cause of intergranular impact rupture and low impact energy.The long-strip carbides formed after tempering at 320℃ would further reduce the impact energy of medium-carbon cast steel.When tempering at 220 and 380℃,the increase in impact energy is attributed to the formation of rod-like and spherical carbides and the low-carbon martensite.For the medium-carbon cast steel with high impact energy,its impact-abrasive wear resistance is more excellent.Micro-cutting and delamination are the primary wear mechanisms.