Corrosion behavior of 2A97 Al-Cu-Li alloys in different thermomechanical conditions by quasi-in-situ analysis

As a promising material in the aircraft industry,2A97 Al-Cu-Li alloy exhibits high corrosion susceptibility that may limit its application.In the present work,to illustrate the influences of precipitate and grain-stored energy on localized corrosion evolution in 2A97 Al-Cu-Li alloy,cold working and artificial aging were carried out to produce 2A97 Al-Cu-Li alloys under different thermomechanical conditions.Quasi-in-situ analysis,traditional immersion test and electrochemical measurement were then conducted to examine the corrosion behavior of 2A97 alloys.It is revealed that precipitate significantly affects Cu enrichment at corrosion fronts,which determines corrosion susceptibility of alloys,whereas grain-stored energy distribution is closely associated with localized corrosion propagation.It is also indicated that quasi-in-situ analysis exhibits a consistent corrosion evolution with traditional immersion tests,which is regarded as a proper method to explore localized corrosion mechanisms by providing local microstructural information with enhanced time and spatial resolutions.

Microstructure characterization and mechanical properties of TC4-DT titanium alloy after thermomechanical treatment

Influence of thermomechanical treatments （mill annealing, duplex annealing, solution treatment plus aging and triple annealing） on microstructures and mechanical properties of TC4-DT titanium alloy was investigated. Results showed that thermomechanical treatments had a significant influence on the microstructure parameters and higher annealing and aging temperature and lower cooling rate led to the decrease of the volume fraction of primaryαand the size of prior-βand the increase of the width of grain boundary αand secondary α. The highest strength was obtained by solution treatment and aging due to a large amount of transformedβand finer grain boundaryαand secondaryαat the expense of slight decrease of elongation and the ultimate strength, yield strength, elongation, reduction of area were 1100 MPa, 1030 MPa, 13%and 53%separately. A good combination of strength and ductility has been obtained by duplex annealing with the above values 940 MPa, 887.5 MPa, 15%and 51%respectively. Analysis between microstructure parameters and tensile properties showed that with the volume fraction of transformedβphase and the prior-βgrain size increasing, the ultimate strength, yield strength and reduction of area increased, but the elongation decreased. While the width of grain boundary α and secondary α showed a contrary effect on the tensile properties. Elimination of grain boundaryαas well as small prior-βgrain size can also improve ductility.

Effect of thermomechanical treatment on microstructure and properties of Cu-Cr-Zr-Ag alloy

The effects of thermomechanical treatment on the properties and microstructure of Cu-Cr-Zr alloy and Cu-Cr-Zr-Ag alloy were investigated. Ag addition improves the mechanical properties of the alloy through solid solution strengthening and brings a little effect on the electrical conductivity of the alloy. A new Cu-Cr-Zr-Ag alloy was developed, which has an excellent combination of the tensile strength, elongation, and electrical conductivity reaching 476.09 MPa, 15.43% and 88.68% IACS respectively when subjected to the optimum thermomechanical treatment, i.e., solution-treating at 920℃ for 1 h, cold drawing to 96% deformation, followed by aging at 400℃ for 3 h. TEM analysis revealed two kinds of finely dispersed precipitates of Cr and CuaZr. It is very important to use the mechanisms of solid solution strengthening, work hardening effect as well as precipitate pinning effect of dislocations to improve tensile strength of the alloy without adversely affecting its electrical conductivity.

Effects of Thermomechanical Treatment on the Mechanical Properties and Microstructures of 6013 Alloy

The mechanical properties and microstructures of 6013 alloy after different thermomechanical treatments were investigated. The detailed dislocation configurations after deformation and morphologies of age hardening precipitates were examined through transmission electron microscopy （TEM）. The experimental results show that the thermomechanical treatment can significantly enhance the strength of 6013 alloy, and has a similar influence trend on single and two-step aging behaviors. With the increasing deformation ratio, the peak-hardness （HVmax） increases, the time to HV shortens, and the density of tangled dislocation network increases. The aging precipitates become larger and inhomogeneous by applying thernomechanical treatment.

Effect of thermomechanical treatment on microstructure and hardness behavior of AZ63 magnesium alloy

Due to their high specific strength and low density, magnesium alloys are widely used in many weight-saving applications. This research is aimed at investigating the microstructure and hardness of commercial AZ63 alloy specimens subjected to two different thermomechanical treatments （TMTs）. For the first TMT, after solution treated at the temperature of 380 ℃ for 20 h, AZ63 alloy specimens were 5% cold worked by rolling process followed by ageing at the temperatures of 150 ℃and 250 ℃ for 3, 9 and 25 h. In the second TMT, the specimens were solution treated at the temperature of 380 ℃ for 20 h, underwent 2% cold worked and quenched in water of 0 ℃. Half of the specimens were then 2% cold worked whilst the rest were rolled to 8% cold worked. All the specimens were then aged at the temperatures of 150 ℃ and 250 ℃ for 3, 9 and 25 h. Optical microscope was used to analyze the microstructures of the specimens. Hardness test was too conducted to measure the effect of the treatments on the specimens. Results show that two-step aging enhances the hardness of the specimens due to the distribution of fine β-phase （MglTA112） in the alloy matrix. The results also reveal that, the best hardness from the first TMT was produced by specimen that was pre-aged at 150 ℃ whereas, in the second TMT, aging at 250 ℃ exhibited the best hardness values.

Effect of thermomechanical cyclic quenching and tempering treatments on microstructure,mechanical and electrochemical properties of AISI 1345 steel

Thermomechanical cyclic quenching and tempering(TMCT)can strengthen steels through a grain size reduction mechanism.The effect of TMCT on microstructure,mechanical,and electrochemical properties of AISI 1345 steel was investigated.Steel samples heated to 1050℃,rolled,quenched to room temperature,and subjected to various cyclic quenching and tempering heat treatments were named TMCT-1,TMCT-2,and TMCT-3 samples,respectively.Microstructure analysis revealed that microstructures of all the treated samples contained packets and blocks of well-refined lath-shaped martensite and retained austenite phases with varying grain sizes(2.8–7.9μm).Among all the tested samples,TMCT-3 sample offered an optimum combination of properties by showing an improvement of 40%in tensile strength and reduced 34%elongation compared with the non-treated sample.Nanoindentation results were in good agreement with mechanical tests as the TMCT-3 sample exhibited a 51%improvement in indentation hardness with almost identical reduced elastic modulus compared with the non-treated sample.The electrochemical properties were analyzed in 0.1 M NaHCO_(3) solution by potentiodynamic polarization and electrochemical impedance spectroscopy.As a result of TMCT,the minimum corrosion rate was 0.272 mm/a,which was twenty times less than that of the nontreated sample.The impedance results showed the barrier film mechanism,which was confirmed by the polarization results as the current density decreased.

Low cycle fatigue improvement of powder metallurgy titanium alloy through thermomechanical treatment

A low-cost β type Ti-1.5Fe-6.8Mo-4.8Al-1.2Nd (mass fraction, %)(T12LCC) alloy was produced by blended elemental powder metallurgy(P/M) method and subsequent thermomechanical treatment. Low cycle fatigue(LCF) behavior of P/M T12LCC alloy before and after thermomechanical treatment was studied. The results show that the LCF resistance of P/M titanium alloy is significantly enhanced through the thermomechanical treatment. The mechanisms for the improvement of LCF behavior are attributed to the elimination of residual pores, the microstructure refining and homogenization.

Thermomechanical treatment of super high strength Cu-8.0Ni-1.8Si alloy

The microstructures and properties of Cu-8.0Ni-1.8Si alloy subjected to different heat treatments were examined by mechanical and electrical properties measurements,optical and transmission electron microscopes observation. The results show that the precipitation process during aging can be accelerated by the cold deforming before aging. As the Cu-8.0Ni-1.8Si alloy is subjected to solution treatment at 970 ℃ for 4 h,cold rolling to 60% reduction,and then aging at 450 ℃ for 60 min,its properties are σb=1 050 MPa,σ0.2=786 MPa,δ=3.2% and conductivity 27.9%(IACS). The strengthening mechanisms of the alloy include spinodal decomposition strengthening,ordering strengthening and precipitation strengthening. The precipitation of the alloy is nano-scale Ni2Si phase.

Properties improvement and microstructure changes during thermomechanical treatment in sintered Cu-Au alloy

The changes in hardness, microhardness, electrical conductivity and microstructure of the sintered Cu-4%Au （mole fraction） alloy during thermomechanical treatment were studied. Following the primary strain hardening, an annealing of rolled alloy in the temperature range of 60-350 ℃ provided additional strengthening due to the anneal hardening effect. An increase in properties took place in two stages, and the best combination of properties was achieved in the alloy pre-rolled with 40% reduction after annealing at 260 ℃. Significant microstructural changes followed the changes of properties in the course of the thermomechanical treatment.

Thermomechanical treatment of austempered ductile iron

The production of lightweight ferrous castings with increased strength properties became unavoidable facing the serious challenge of lighter aluminum and magnesium castings. The relatively new ferrous casting alloy ADI offers promising strength prospects, and the thermo-mechanical treatment of ductile iron may suggest a new route for production of thin-wall products. This work aims at studying the influence of thermomechanical treatment, either by ausforming just after quenching and before the onset of austempering reaction or by cold rolling after austempering. In the first part of this work, ausforming of ADI up to 25% reduction in height during a rolling operation was found to add a mechanical processing component compared to the conventional ADI heat treatment, thus increasing the rate of ausferrite formation and leading to a much finer and more homogeneous ausferrite product. The kinetics of ausferrite formation was studied using both metallographic as well as XRD-techniques. The effect of ausforming on the strength was quite dramatic （up to 70% and 50% increase in the yield and ultimate strength respectively）. A mechanism involving both a refined microstructural scale and an elevated dislocation density was suggested. Nickel is added to ADI to increase hardenability of thick section castings, while ausforming to higher degrees of deformation is necessary to alleviate the deleterious effect of alloy segregation on ductility. In the second part of this work, the influence of cold rolling （CR） on the mechanical properties and structural characteristics of ADI was investigated. The variation in properties was related to the amount of retained austenite （7~） and its mechanically induced transformation. In the course of tensile deformation of ADI, transformation induced plasticity （TRIP） takes place, indicated by the increase of the instantaneous value of strain-hardening exponent with tensile strain. The amount of retained austenite was found to decrease due to partial transformation of 7~ to martensite under the CR strain. Such strain-induced transformation resulted in higher amounts of mechanically generated martensite. The strength and hardness properties were therefore increased, while ductility and impact toughness decreased with increasing CR reduction.

湿热处理对豆粉营养品质及面团物化特性的影响

采用湿热处理研究不同豆粉抗氧化、营养特性及面团性质的影响。结果表明:随着湿热处理时间的延长,红豆粉和豌豆粉的总酚、黄酮含量及其抗氧化能力呈先增加后降低的趋势,分别在0.5 h和1.0 h时达到最大,而白芸豆粉总酚、黄酮含量呈增加趋势,在8.0 h达到最大;湿热处理对2,2’-联氮双-(3-乙基苯并噻唑啉-6-磺酸)阳离子自由基清除率和1,1-二苯基-2-三硝基苯肼自由基清除率趋势与总酚、黄酮含量一致;3种豆粉的主要脂肪酸种类分别为棕榈酸、硬脂酸、亚油酸、顺-11-二十碳一烯酸和油酸;湿热处理2.0 h及以上,对白芸豆粉中油酸、亚油酸和顺-11-二十碳一烯酸含量有显著影响;湿热处理后红豆粉和白芸豆粉中游离氨基酸参与美拉德反应,含量显著下降,而豌豆粉中更多结合态的氨基酸游离出来,使其含量升高;扫描电子显微镜观察微观结构结果显示,随着湿热处理时间延长,蛋白质变性和部分淀粉发生糊化,出现孔洞、黏附等现象;淀粉的重结晶使得豆粉的峰值黏度、谷值黏度和回生值下降,抗剪切力变差;面团水分分布测定结果显示,湿热处理后红豆粉的弛豫时间T_(21)、T_(22)增加,红豆粉成团性优于其他面团;湿热处理使混合豆粉热机械特性中的蛋白弱化度增强,抑制了淀粉的回生,降低了老化度,有益于提升产品品质。

形变热处理对Ti-Nb-Zr合金组织及超弹性行为的影响

Ti-Nb-Zr合金具有低弹性模量、高强度以及优异的生物相容性,在生物医用材料领域备受关注。Ti-Nb-Zr合金的超弹性归因于β↔α″相变。综述了Ti-Nb-Zr合金的弹性模量和超弹性的影响因素及变化规律。通过添加合金元素来调整相变温度和滑移临界应力,应力诱发马氏体相变更易发生,β相塑性变形延迟出现,获得更大的相变应变和恢复应变。总结了Ti-Nb-Zr合金的形变热处理与超弹性效应之间的关系和作用机制。冷轧后短时间热处理可以增加位错滑移的临界应力、避免其他相(ω或α相)的生长,保持β相的稳定性、提高合金的恢复应变和超弹性。

形变热处理对Cu-Ni-Si合金组织性能的影响

借助扫描电镜、电子万能试验机、维氏硬度计和数字涡流金属电导仪等研究了冷轧变形量和时效对Cu-Ni-Si合金组织与性能的影响。结果表明:冷轧态合金变形量越大,显微组织中晶粒沿着轧制的方向被拉得越长和越扁。当时效温度或时效时间增加到一定程度时,冷变形晶粒发生了回复再结晶,时效时间继续延长再结晶晶粒逐渐长大。冷轧态合金主要以脆性断裂为主,时效态合金以韧性断裂为主。当冷轧变形量为80.0%及经500℃×1 h时效后合金的综合性能最佳,电导率为46.37%IACS,显微硬度为236.14 HV0.1,抗拉强度为638.24 MPa,屈服强度为581.55 MPa,伸长率为5.77%。

双相多主元合金热机械处理的进展

双相多主元合金作为一种新型金属结构材料,一经提出便受到广泛关注和研究。作为金属材料,热机械处理是调控其微观组织,提升综合力学性能的重要方法。本文综述了国内外有关双相多主元合金热机械处理的研究现状,从轧制工艺、时效参数、多级处理等方面讨论了热机械处理对双相多主元合金微观组织的调控作用,进而总结了热机械处理对其力学性能的影响,以期对双相多主元合金的热机械处理研究提供参考。

球磨处理对小米-小麦粉混合面团流变学及热机械学特性的影响

以小米为原料通过球磨处理制备球磨小米粉,再将小米粉与小麦粉按照一定比例混合制备混合面团,研究不同球磨处理对混合面团流变学及热机械学特性的影响。结果表明:在球磨时间4.0 h、球磨转速450 r/min、球料质量比3∶1时,混合面团的流变学特性最佳且热机械学特性较佳,说明适当的球磨处理可以改善小米-小麦粉混合面团的流变学和热机械学特性。

共晶高熵合金研究进展

共晶高熵合金是凝固过程中发生共晶转变的多组元合金,具有优异的液态充型能力和机械性能,适用于生产形状复杂、对力学性能要求较高且不能进行热机械处理的零件。共晶高熵合金具有4种及以上元素,且相组成和组织形貌对合金成分变化不敏感,因此具有很大的性能调控空间及工艺窗口。通过调控共晶高熵合金的相组成及组织形貌可使其叠加各种优异性能。本文从设计方法、制备工艺、组织结构、力学及理化性能等方面综述了共晶高熵合金的研究现状,并对共晶高熵合金未来的发展进行展望。

轧制形变热处理对Cu-Ni-Si系合金性能和微结构的影响

对比了Cu-Ni-Si合金二次固溶态(790℃×120 min)和大变形冷轧(98.42%累积变形量)+二次时效态(420℃×480 min)的强度、硬度、导电率等性能的变化规律,分析了两种不同形变热处理工艺状态下合金的显微组织和断口形貌。结果表明:大变形冷轧+二次时效工艺条件下制备的合金平均晶粒尺寸为4.28μm;析出相主要由Cr3Si与Ni2Si构成,平均尺寸分别为65 nm和11 nm,呈弥散分布,且合金内出现大量纳米孪晶。累积大变形产生的形变强化和弥散分布的纳米级析出相形成的析出强化,以及大量纳米孪晶的形成,是Cu-Ni-Si合金力学性能显著提升的主要因素。大变形冷轧+二次时效处理后的合金导电率、硬度、抗拉强度、屈服强度分别为27.2%IACS,HV 231.98,707 MPa,703MPa,较二次固溶态合金分别提升了32.60%,94.67%,204.74%,575.96%。二次固溶态合金断口形貌主要由大而深的韧窝组成,大变形冷轧+二次时效态合金断口形貌主要由小而浅的韧窝组成,数量较多,分布致密。

形变热处理工艺(TMTP)对T91钢显微组织的影响

在Gleeble 1500热模拟实验机上采用热压缩实验方法,研究了形变热处理工艺即在奥氏体未再结晶区变形后直接淬火对T91铁素体耐热钢微观组织的影响。结果表明:形变热处理工艺明显优化了T91钢的组织结构,使T91钢的马氏体板条趋于细化,并且能生成更多纳米级碳氮化物颗粒来进一步进行组织强化,从而论述了采用形变热处理工艺来提高铁素体耐热钢耐热温度的可行性。

CoCrFeNi系高熵合金的力学性能研究现状

高熵合金因其高强度、高硬度、耐辐照性和优异的高温稳定性等成为近年来材料领域里的研究热点。CoCrFeNi合金以其室温下优异的塑性受到广泛关注,而通过适当的元素成分调控改善合金的微观组织可以增加CoCrFeNi合金的强度。综述了CoCrFeNi系高熵合金的力学性能研究现状;阐述了元素掺杂、热机械处理等对CoCrFeNi合金微观组织和力学性能的影响。

热机械处理Al-Co-Fe-Ni共晶高熵合金组织性能研究

共晶高熵合金具有优异的强塑性匹配,同时还兼具传统共晶合金良好的铸造性能,对高熵合金的实际化应用有着重大的意义。而如何进一步提升共晶高熵合金的强塑性能,成为了高熵合金领域的研究热点。本文以Al-(21)Co_(19.5)Fe_(9.5)Ni_(50)共晶高熵合金为研究对象,探究了热机械处理对合金微观组织和拉伸力学性能的影响规律。并结合合金微观组织和相结构对合金应变硬化能力的影响,阐明了热机械处理条件下合金的变形机制及其对合金力学性能的影响。结果表明,经过热机械处理后合金由共晶层片组织转变为近完全等轴晶组织,且FCC相中析出L1_(2)相。热机械处理后合金在拉伸变形过程中,随着应变量的增加FCC相内位错密度增加,B2相发生应力诱发马氏体相变而形成具有相互交错孪晶结构的L1_(0)相,最终在FCC相与B2相双重强化机制下,表现出更高的屈服强度(551 MPa)和断裂伸长率(10.2%),加工硬化率曲线出现显著变化。