Fabrication process of smooth functionally graded materials through a real-time inline control of the component ratio

Functionally graded materials (FGMs) play an essential role in tissue engineering because of their satisfactory histocompatibility and excellent mechanical performance. While traditional manufacturing methods allow production of simple FGMs, precise control of composition and customized property at transition between the dissimilar materials is still a challenge. Here, an extrusion-based functionally graded additive manufacturing (FGAM) platform was developed to generate smooth graded parts by thrusting out monolithic cylindrical filaments with high viscosity. Furthermore, the rheological properties, hydrodynamic behavior, and mixed homogeneity of the non-Newtonian fluids were studied. Therefore, the appropriate solid contents, alternative energy-efficient mixers, and optimized printing parameters were proved to be beneficial for an outstanding deposition effect of the suspension. Ultimately, an object with smooth gradient was successfully manufactured. The validity of this strategy was verified via optical microscopy combined with an image processing method to gauge homogeneity and a scanning electron microscope to investigate graded composition and microstructure.     

粉末注射成形钛合金的脱脂和烧结性能

应用粉末注射成形技术制备出高精度、高性能的异形钛合金零器件。通过多粒度粉末搭配,采用聚甲醛为主组元的多组元粘结剂,制备出高装载量催化脱脂型钛合金喂料,再经真空烧结获得制品。研究了催化脱脂工艺的影响因素以及喂料配比对烧结性能的影响。结果表明:当大（D₅₀=25.28 μm）、中（D₅₀=16.75 μm）、小（D₅₀=12.66 μm）颗粒按质量比17:6:2搭配时,钛合金混合粉末相对振实密度较大,为55%。喂料较佳的催化脱脂工艺为:脱脂温度120 ℃,N₂通入速率120 cm3·min?1,HNO₃气体通入速率1.5 cm3·min?1,脱脂时间6 h,粘结剂脱除率85%。采用全流程控制杂质含量技术,粉末注射成形钛合金制品的烧结性能可以达到相对密度95.9%,拉伸强度933 MPa,抗弯强度1282 MPa,延伸率7.5%,其中C质量分数为0.10%,O质量分数为0.21%。     

Experimental and theoretical research on interfacial reaction of solid Co with liquid Al

Interfacial reaction between solid Co and liquid Al was investigated with immersion tests and theoretical modeling. The microstructure characterization indicated that a Co₂Al₅ intermetallic layer was formed at solid–liquid interface during the immersion test. The modeling results indicated that the corrosion rate of a solid metal in a liquid metal was controlled by both the formation and dissolution of the intermetallic layer. In Co–Al reaction system, the formation and dissolution of the Co₂Al₅ layer reached an equilibrium state in a very short time, and the corrosion of the Co matrix was mainly dominated by the dissolution of the Co₂Al₅ layer.     

金属粉末特性对选区激光熔化工艺及其制件性能影响

高品质金属粉末是选区激光熔化（selective laser melting,SLM）制备高性能制件的重要基础。粉体特性对选区激光熔化技术的影响及其机理研究是理解选区激光熔化技术不可或缺的重要组成部分。本文从粉末物理和化学特性出发,论述了粉末特性对选区激光熔化工艺、制件微观组织与性能的影响。结果表明,粉末的物理特性,尤其是粉末形貌和粉末粒度分布能显著影响其流动性和粉末床堆密度等关键工艺特性;而粉末的化学成分,特别是杂质成分,是影响制件相组成和微观组织的重要因素。在此基础上,本文进一步介绍了选区激光熔化过程中高能量源与粉末颗粒的冶金作用机理研究进展。     

Effect of electromagnetic stirring and solution treatment on microstructure and properties of AZ31 magnesium alloy

Effect of electromagnetic stirring and solution treatment on the microstructural evolution and mechanical properties of AZ31 alloy are investigated in this study. Results show that the mechanical properties of AZ31 alloy are substantially increased after electromagnetic stirring and solution treatment. The tensile strength and elongation are 178 MPa and 19.6 % for AZ31 alloy prepared by electromagnetic stirring after solution treatment. A large number of twins and low angle boundaries are observed in the specimen after heat treatment, since the compressive stress on ( ) crystal plane become larger during quenching. The dislocation arrays, which produced by slip or climbing of dislocations, join together to form low angle boundaries.     

Nd对压铸AZ91D合金组织与性能的影响

传统压铸获得AZ91D和AZ91D-1.11Nd两种合金试样,采用光学金相显微镜、扫描电子显微镜和X射线衍射仪分析了压铸态微观组织和相组成,并测试了其拉伸力学性能、硬度、导热性能和流动性能。结果表明,在AZ91D合金中添加1.11%Nd后,压铸态晶粒有所细化,形成较多弥散分布的细小颗粒状Al2Nd和少量针状Al₁₁Nd₃,原有的半连续网状分布的β-Mg₁₇Al₁₂数量有所减少。压铸态AZ91D-1.11Nd合金呈现良好的综合性能,室温抗拉强度、伸长率和热导率分别为272 MPa、12.0%和69.5 W/(m·K),与AZ91D合金相比分别提高14%、100%和14%;同时呈现与AZ91D合金相当的优异铸造工艺性能,流动长度达到1161 mm。     

时效温度对一种新型β钛合金组织演变及力学性能的影响

采用d-电子合金设计法设计了一种β钛合金,Ti-6Mo-5V-3Al-2Fe(wt.%)。在450℃~600℃范围内选取了多个时效温度进行时效处理,以研究时效温度对该合金组织演变及力学性能的影响。结果表明,当时效温度为500℃时,在ω辅助形核机制作用下,形成了尺寸和相间距更小的次生α相,在此细小的次生α相对β基体的强化作用下合金抗拉强度达到最大值,为1510MPa;同时,由于晶界α相的析出以及晶界无析出区的形成,导致合金的塑性极差,伸长率仅为4.6%。随着时效温度的升高,晶内细小的次生α相粗化。粗大的次生α相导致其相间距增大,并使可有效阻碍位错运动的α/β相界面减小。时效温度的升高使合金强度降低,但合金塑性提高。当时效温度升高至600℃,在β晶界处形成了向晶内平行生长的板条状次生α相,同时β晶粒内次生α相间距增大,使合金塑性明显提高,伸长率可达12.2%。     

YbB6 对Ti-6Al-4V钛合金组织和性能的影响

采用放电等离子烧结（SPS）制备了含YbB₆的Ti-6Al-4V钛合金,并研究了YbB₆对Ti-6Al-4V钛合金显微组织和力学性能的影响。结果表明,随着YbB₆含量的增加,复合材料的显微组织发生转变,晶粒明显细化,原位反应生成的TiB晶须和Yb₂O₃颗粒有利于复合材料力学性能的提高。此外,当添加0.6%（质量分数）YbB₆后,烧结样品的相对密度、显微硬度、屈服强度、极限拉伸强度和延伸率分别为99.43%、4030 MPa、903 MPa、1148 MPa和3.3%。与Ti-6Al-4V试样相比,其数值分别提高了0.37%、13.8%、38.07%和17.14%。强化机制主要是组织转变、晶粒细化和弥散强化。随着YbB₆含量的增加,断裂方式主要为韧性断裂和脆性断裂。     

In Situ Investigation of Si-Poisoning Effect in Al-Cu-Si Alloys Inoculated by Al-5Ti-1B

In situ synchrotron X-radiography was carried out on Al-13Cu and Al-13Cu-7Si alloys with and without addition of Al-5Ti-1B master alloy. The effects of Si content on grain growth and the solute-suppressed nucleation zone (SSNZ) were quantitatively studied. The average grain size can be refined to 164 μm of Al-13Cu alloy inoculated by Al-5Ti-1B. After addition of 7% Si content, a large number of TiB₂ sites in the melt lost the inoculating ability due to “Si poisoning.” The radius of the dendrite tip curvature of Al-13Cu is more than two times as large as that of Al-13Cu-7Si. The sharper tip is able to disperse the solute more effectively and thus grains can grow more rapidly. This causes that the dendrite arm growth rate with addition of 7% Si solute is about 2.6 times that of no Si addition. In addition, the solute enrichment in the SSNZ of Al-13Cu is faster, and the area change of SSNZ is slower than that of Al-13Cu-7Si. Thus more nucleation sites in the SSNZ cannot be activated with addition of Si. This study will shed light on the understanding of Si poisoning in casting Al-Cu-Si alloys.