Precipitation behavior of Ti in high strength steels

Precipitation behavior of Ti in high strength steels was investigated by means of the equilibrium solid solubility theory. The contributions of Ti content to yield strength were calculated. The calculated results were verified by the hot rolling experiment for C–Mn steel and C–Mn–Ti micro alloyed steel, respectively. The research results show that the precipitates are mainly Ti N at the higher temperature. With the decreasing temperature, the proportion of Ti C in precipitates increases gradually. When the temperature drops to 800 °C, Ti C will become predominant for the precipitation of Ti. When Ti content is less than 0.014%(mass fraction), Ti has little influence on the yield strength. When Ti content is in the range of 0.014%–0.03%(mass fraction), the yield strength of Ti micro alloyed steel is greatly increased, which leads to instability of the mechanical properties of the steel. Therefore, the design of Ti content in high strength steels should avoid this Ti content range. When Ti content is higher than 0.03%, the yield strength increases stably. In this experiment, when added Ti content was controlled in the range of 0.03%–0.05%, the contribution to the yield strength of Ti micro alloyed steel can reach about 92.44 MPa.

CALCULATION ON THE YIELD STRENGTH OF A PRECIPITATION STRENGTHENING Ni－BASE ALLOYS

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3 GPa超高强度马氏体时效钢组织性能

航空航天系统的小型化、轻量化发展趋势对动力轴材料的强塑性提出了更高的要求。为了开发3 GPa级的马氏体时效钢,设计一种高Co、Ni、Mo的马氏体时效钢,其成分为14Ni-15Co-9Mo-0.86Ti-0.35Al-Fe。通过锻比大于10的高温大塑性变形尽可能细化晶粒,并结合预拉伸变形及深冷+时效的热处理工艺调控,实验钢抗拉强度达到3.076 GPa,断后伸长率5.5%,表现出了优异的强塑性。通过对其显微组织进行分析表征,发现其基体组织为高位错密度的板条马氏体结构,平均晶粒尺寸为0.47μm。透射电镜及3DAP结果表明,基体中分布着大量的Ni3(Mo,Ti),析出相平均直径为6~7 nm。析出强化、细晶强化及位错强化是其主要的强化机制,保证了合金超过3 GPa的超高强度,同时极细的亚微米级晶粒保证了材料良好的塑性。

通过基体晶粒和颗粒分布异质结构的调控协同提升AlN_(p)/Al复合材料的强度-塑性

为了获得优异的强塑性能,采用液固反应结合后续的热机械处理方法制备了3种具有不同微观组织构型的异构AlNp/Al复合材料,详细研究了AlN颗粒分布和基体晶粒组织构型对拉伸强度和塑性的影响。结果表明,复合材料的强度和塑性同时提高。其中,具有较弥散颗粒分布的Uniformed-AlNp/Al复合材料表现出优异的极限抗拉强度(~387 MPa)和断裂伸长率(~9.1%)。与其他文献报道的颗粒增强铝基复合材料相比,该复合材料具有较好的比强度和延展性组合。此外,计算了异质变形诱导(HDI)应力。结果表明,在Uniformed-AlNp/Al复合材料中,HDI应力显著增加。揭示了HDI应力在提高AlNp/Al复合材料的强度和塑性中起着至关重要的作用。

高强β钛合金的发展现状与强化方法

钛合金是比强度最高的金属材料之一,广泛应用在航空航天领域。随着材料技术的进步,人们对高强钛合金的研究与开发也逐渐深入。综述了国内外高强β钛合金的发展现状与主要的强化方式。重点介绍了Ti-13-11-3、Ti-l023、Ti-5553以及Ti-55531等典型高强钛β合金。梳理了高强β钛合金的设计思路,指出了限制高强β钛合金向更优性能发展的瓶颈并提出了可能的解决途径。总结了固溶强化、析出强化、加工硬化、细晶强化以及增材技术等高强β钛合金的强化方法,以期为进一步提高高强β钛合金的强度、优化高强β钛合金综合性能提供指导。

氮对07Cr18Ni11Nb不锈钢组织和性能影响

通过热力学计算软件Thermo-Calc 2023a、场发射扫描电子显微镜(FESEM)等进行第二相析出模拟和金相、性能检测分析:氮含量在0.013%时,07Cr18Ni11Nb凝固时氮的析出相主要有Nb(CN)、(Cr∶Ni∶Si∶N)复合相和σ相。随着氮含量增加到0.055%时,氮的析出相主要有Nb(CN)、(Cr∶Ni∶Si∶N)复合相,Z相也出现,晶粒有逐渐减小的趋势。室温25℃和高温600℃下屈服强度和抗拉强度都有所增加,但是屈服强度增加的幅度较抗拉强度多。

Mg含量对w(Zn)=11%的超高强铝合金组织性能的影响

研究了Mg含量对w(Zn)=11%超高强铝合金组织性能的影响.超高强铝合金铸锭为网状枝晶组织,平均晶粒尺寸约170~240μm,铸锭组织中存在粗大的α(Al)+T(AlZnMgCu)共晶相.经均匀化退火后,w(Mg)<1.75%的合金组织中粗大的T相完全回溶,w(Mg)>2.0%的铸锭组织中还有少量T相残留.超高强铝合金挤压材固溶处理后,组织中T相完全回溶,组织为纤维组织,再结晶比例约1.2%~6.5%,纤维条带宽度约24.2~35.4μm.挤压材时效后,组织中分布高密度的析出强化相,主要为GP区和η'相,尺寸为2~5 nm.随Mg含量增加,合金的屈服强度由687 MPa升高到782 MPa,抗拉强度由717 MPa升高到795 MPa,伸长率从12.5%降低到9.3%.w(Zn)=11%的超高强铝合金中析出强化相的数量与Mg含量成正比,Mg含量增加,合金强度升高.

基于超声强化改性研磨时长的AlCoCrFeNi_(2.1)共晶高熵合金组织和力学性能影响研究

为提高室温下AlCoCrFeNi_(2.1)共晶高熵合金(EHEAs)的极限拉伸强度和延展性,通过光镜观察截面显微组织、维氏显微硬度计测量截面显微硬度、白光干涉仪分析表面三维形貌、拉伸试验机进行室温单轴拉伸试验,并绘制工程应力-应变曲线,利用扫描电镜分析断口形貌等仪器研究在不同时长(3、6、9 min)超声强化改性研磨(USG)处理下AlCoCrFeNi_(2.1)EHEAs显微组织和性能的变化规律。结果表明:与母材相比,超声强化改性研磨使AlCoCrFeNi_(2.1)EHEAs由外表至芯部形成厚度最高约120μm的强化层,表面三维形貌先增加到1.987μm后减少至1.490μm,表层显微硬度最高提升了30.40%,极限拉伸强度最高提升了25%,延展性最高提升至15.04%,且母材表层断口形貌特征为韧性断裂,经超声强化改性研磨处理后样件断口形貌特征均为韧-脆混合型断裂。可得结论:超声强化改性研磨可以有效提高AlCoCrFeNi_(2.1)共晶高熵合金的表层硬度和晶粒细化的强化层,从而协同提高其极限拉伸强度和延展性。

UHPC中钢纤维的增强机理:一种新的断裂相场模型

超高性能混凝土(UHPC)是一种具有巨大潜力的复合材料。为了降低UHPC的成本并获得更好的性能,有必要研究钢纤维在UHPC中的增强机理,实践中也需要一个有效的数值模型来促进UHPC的应用。钢纤维从UHPC中拔出时会产生新的裂纹面,进而需要消耗更多的能量。基于此,推导了新裂纹及其裂纹表面能的公式,提出了一种考虑钢纤维与UHPC基体之间界面断裂能的断裂相场模型。利用该模型,对含钢纤维的三维UHPC试样进行了单轴拉伸数值模拟;开展对比实验验证了所提模型的正确性。结果表明,模拟结果与实验结果吻合较好。通过分析不同试样的新裂纹面与拉伸强度间的关系,发现UHPC的抗拉强度和残余强度随钢纤维体积含量的增加而增加,随钢纤维直径的增加而降低。进一步分析发现,UHPC的抗拉强度与钢纤维的侧表面积成正比。理论分析、数值模拟和实验表明,钢纤维在UHPC中的增强机理为:钢纤维的加入使UHPC基体与钢纤维在断裂过程中产生了一些新的裂纹,这些新裂纹消耗了更多的能量。本文研究工作可为UHPC的性能设计和开发有效的UHPC数值模型提供理论依据。

Improved mechanical properties and strengthening mechanism with the altered precipitate orientation in magnesium alloys

Aging prior to twinning deformation was proposed to alter the precipitate orientation of the plate-shapedβ-MgAlfrom(0002)basal planes(named basal plates)to■prismatic planes(named prismatic plates)in AZ31 Mg alloy.The experimental results showed that the compressive yield strength(CYS)of the sample containing prismatic plates increased 40 MPa and the compression ratio raised by 22%compared to that containing basal plates.The underlying strengthening mechanism was analyzed via a yield strengthen(YS)model with a function of grain size,precipitate characters(size,oritention,fraction)and Schmid factor(SF).It revealed that the improvement of CYS was mainly attributed to the altered precipitate orientation and refined grain size produced by twinning deformation.Particularly,the prismatic plates always have a stronger hardening effect on basal slip than basal plates under the same varites of precipitate diameter and SF.Besides,the decreased CRSS ratio of prismatic slip to basal slip revealed that the activity of non-basal slip in Mg alloy might be enhanced.More activated slip systems provided more mobile dislocations,contributing to the large compression ratio of the Mg rolled sheet with prismatic plates.

Effect of kaolin on tensile strength and humidity resistance of a water-soluble potassium carbonate sand core

Water soluble cores(WSCs) have been widely applied in manufacture of complex metal components with hollow configurations or internal channels. However, the WSCs without any additons have low tensile strength and low humidity resistance. The purpose of this study is to prepare a water-soluble potassium carbonate sand core with addition of kaolin by the hot-temping method. The effects of kaolin on tensile strength, humidity resistance, fracture mechanism, as well as the gas evolution and collapsibility of WSCs were investigated. Results show that both the crystal morphology and the fracture mechanism of the inorganic salt are changed under the participation of kaolin, contributing to the increase of the tensile strength and the humidity resistance of the core. With the addition of 3wt.% kaolin, the tensile strength could be increased by a factor of 2, reached 1.50 MPa and the hygroscopic rate could be decreased by 14%, achieved 0.559%(after stored for 8 h), respectively. As the addition amount of kaolin increases from 0wt.% to 3wt.%, the main fracture mechanism changes from a adhesive to a cohesive fracture mechanism. The water-soluble potassium carbonate core obtained has the low gas evolution and excellent collapsibility, which makes it suitable for casting low melting metal with complex cavities and crooked channels.

Improvement of humidity resistance of water soluble core by precipitation method

Water soluble core has been widely used in manufacturing complex metal components with hollow configurations or internal channels;however,the soluble core can absorb water easily from the air at room temperature.To improve the humidity resistance of the water soluble core and optimize the process parameters applied in manufacturing of the water soluble core,a precipitation method and a two-level-three-full factorial central composite design were used,respectively.The properties of the cores treated by the precipitation method were compared with that without any treatment.Through a systematical study by means of both an environmental scanning electron microscope(ESEM) and an energy dispersive X-ray(EDX) analyzer,the results indicate that the hygroscopicity can be reduced by 20% and the obtained optimal process conditions for three critical control factors affecting the hygroscopicity are 0.2 g·mL-1 calcium chloride concentration,4% water concentration and 0 min ignition time.The porous surface coated by calcium chloride and the high humidity resistance products generated in the precipitation reaction between calcium chloride and potassium carbonate may contribute to the lower hygroscopicity.

CALCULATION OF YIELD STRENGTH IN NICKEL BASE SINGLE CRYSTAL SUPERALLOYS

In this article, a quantitative equation was established to determine the relationship between yield strength and composition in nickel base SC superalloys based on Copley Kear precipitation strengthening model. The yield strength of two well known commercial SC superalloys calculated by this equation was compared with experimental data. It was found that the calculated yield strength of these two alloys was fairly correspondent with experimental results reported in the references. This model accurately described the solution strengthening of alloying elements and precipitation strengthening of γ′ phase. Yield strength of SC superalloys can be successfully predicted by this equation.

In-situ Observation of Dark Phase Precipitation during Heating and Soaking Process of a High Nickel Steel

In-situ observation of microstructural evolution during heating and soaking process was carded out for a high nickel steel using HTCLSM. Dark phases were observed when soaking at 900℃. Results showed that the number of the dark phases culminated in about 50 s during soaking at 900℃. With the increase of soaking time the area proportion of the dark phases increased and reached the maximum value in about 3 min, When temperature rose from 900 ℃, the dark phases remained steady initially, but started to dissolve into the matrix at about 1 060 ℃ and completely disappeared at 1 132℃. When the specimen soaked at 900 ℃ was cooled down to room temperature （RT）, the dark phases kept stable. Energy spectrum analysis results showed that the dark phases contained much more Cr and Mn elements than the matrix and,were also rich in V. Tensile test results showed that the dark phase strengthened the steel with the maximum tensile strength obtained after soaking at 900 ℃ for 3 minutes.

Effect of Precipitating Phases on Tensile Strength and Microstructural Stability of a Spray-Deposited Al-Si-Fe-Mn-Cu-Mg Alloy

Spray deposition is a novel process which is used to manufacture rapidly solidified bulk and near-net-shape preforms. In this study, AI-20Si-5Fe-3Mn-3Cu-1Mg alloy was synthesized by spray deposition technique. The aging process of the alloy was investigated by differential scanning calorimetry (DSC) analysis and transmission electron microscopy (TEM). The results show that two kinds of phases, i.e. S(Al2CuMg) and σ(Al5Cu6Mg2), precipitate from matrix and improve the tensile strength of the alloy efficiently at both the ambient and elevated temperatures (300℃). In addition, the σ-Al5Cu6Mg2 is a relatively stable phase which improves microstructural stability of the alloy.

新能源汽车驱动电机用高强无取向硅钢力、磁性能调控研究进展

新能源汽车能够有效缓解传统汽车行业对化石燃料的严重依赖和全球所面临的环境问题,是未来发展的必然趋势.驱动电机作为新能源汽车的动力核心,不仅需要具有优异的磁性能提高能源转换效率,同时需要具有高强度来抵抗高速运转时的离心力.然而,无取向硅钢的强度和磁性能难以兼顾,因此无取向硅钢力、磁性能的协同调控是新能源汽车驱动电机发展过程中的一个关键科学问题.本文综述了国内外有关高强无取向硅钢力学性能和磁性能调控的相关研究现状,分析了不同强化方式对无取向硅钢磁性能的影响,指出了新能源汽车驱动电机用高强无取向硅钢力学性能和磁性能协同调控的未来发展趋势,即多种强化方式共同作用或利用细小弥散的纳米共格析出相实现高强无取向硅钢力、磁性能的最佳匹配,为新能源汽车驱动电机用高强无取向硅钢的发展提供借鉴.

Difference in extrusion temperature dependences of microstructure and mechanical properties between extruded AZ61 and AZ91 alloys

The effects of extrusion temperature on the microstructure and tensile properties of extruded AZ61 and AZ91 alloys are investigated by subjecting them to hot extrusion at 300 and 400℃.Although the average grain size of the extruded AZ61 alloy slightly increases from 9.5 to 12.6μm with increasing extrusion temperature,its resultant microstructural variation is insignificant.In contrast,the average grain size of the extruded AZ91 alloy significantly increases from 5.7 to 22.5μm with increasing extrusion temperature,and the type of Mg17Al12 precipitates formed in it changes from fine dynamic precipitates with a spherical shape to coarse static precipitates with a lamellar structure.As the extrusion temperature increases,the tensile yield strength of the extruded AZ61 alloy increases from 183 to 197 MPa while that of the extruded AZ91 alloy decreases from 232 to 224 MPa.The tensile elongations of the extruded AZ61 and AZ91 alloys decrease with increasing extrusion temperature,but the degree of decrease is significant in the latter alloy.These different extrusion temperature dependences of the tensile properties of the extruded AZ61 and AZ91 alloys are discussed in terms of their microstructural characteristics,strengthening mechanisms,and crack initiation sites.

镁含量对高锌Al-9Zn-xMg-1Cu合金时效沉淀相及其强化作用的影响

采用硬度测试和室温拉伸测试,结合透射电镜、高分辨透射电镜及几何相位分析技术,定量研究了Mg含量(1%~3%,质量分数)对高锌Al-9Zn-xMg-1Cu合金在120℃人工时效时沉淀相的影响,并探讨了强化作用。结果表明:当Mg含量从1%增至2%时,合金的屈服强度大幅增加,增加率约为37.7%;当Mg含量继续增至3%时,合金的屈服强度小幅增加,增加率仅为9.1%。Al-9Zn-1Mg-1Cu合金的强化相为η’相,Al-9Zn-2Mg-1Cu和Al-9Zn-3Mg-1Cu合金的强化相都为η’相和T’相。T’相引起的应变大于η’相,其强化效果更好;Mg含量变化对两种强化相引起的最大应变值影响不大。随着Mg含量增加,η’相的体积分数、数量密度及其比例减小,T’相的变化则相反,沉淀相的总数量密度和体积分数增大。基于η’相和T’相的尺寸、体积分数和数量密度,计算和分析了它们对沉淀强化的贡献,计算结果与实验结果基本一致。

典型耕作土壤团聚体力稳性的区域分异特点及其影响因素

土壤团聚体力稳性直接影响根系生长和农业耕作等过程。为探究不同类型土壤团聚体力稳性的区域分异规律,自北向南选取典型农业种植区耕作土壤(黑土、褐土、红壤和砖红壤),通过抗压试验测定不同粒径团聚体(1~2、3~5、>5~8、>8~10 mm)的抗张强度、破碎能量和易碎性指数,分析其与土壤理化性质和气候因子间关系。结果表明:抗张强度和破碎能量自北向南逐渐减小,并随团聚体粒径增大而减小,但具体变化特征因土壤类型而异。易碎性指数自北向南先增大后减小,其中红壤最大(0.87),黑土最小(0.47);相比温带地区黑土和褐土,亚热带和热带的红壤和砖红壤易碎性指数的粒径分异更为明显,表现为其小粒径团聚体易碎性指数(1.10和0.76)显著高于大粒径团聚体(0.65和0.58)。抗张强度和破碎能量与蛭石呈极显著正相关关系(r=0.73和0.70,P<0.01),与年均降水量呈极显著负相关关系(r=-0.72和-0.72,P<0.01);易碎性指数与年均降水量呈极显著正相关关系(r=0.66,P<0.01),与蛭石、碳氮比、非晶形氧化锰呈极显著负相关关系(r=-0.75~-0.66,P<0.01),表明在区域尺度上气候因子通过黏土矿物控制团聚体力稳性的空间分异。研究结果为不同区域农业土壤质量的评估与改良提供了理论依据。

550MPa级低合金高强钢的试制

文章详细阐述了550 MPa级低合金高强钢的关键试制方案,包括化学成分、热轧工艺、冷轧工艺、退火工艺。研究了合金元素、生产工艺对产品组织及性能的影响。试制结果表明,550 MPa级低合金高强钢微观组织主要由铁素体与弥散分布的TiC析出相组成,其主要强化机制为细晶强化与析出强化。试制钢带屈服强度为556~581 MPa,抗拉强度为622~653 MPa,延伸率为14.0%~16.5%,满足相关标准及产品应用要求。