Cu-2.0Ni-0.5Si合金时效析出动力学研究

研究了不同时效温度和时间对Cu-2.0Ni-0.5Si合金组织和性能的影响,合金经不同温度和时间时效处理后,第二相呈弥散分布,并可获得较高的显微硬度及导电率。通过该合金在500℃时效过程中的导电率变化,同时根据导电率与新相的转变量之间的关系计算出了时效过程中新相的转变比率,从而确定了该合金不同温度下时效时的Avrami相变动力学方程及导电率方程。该合金时效析出过程中以Orowan机制为主,实际强化的结果与采用Orowan强化机制计算的结果非常接近。     

Cu-3.0Ni-0.75Si合金时效析出动力学分析

为研究Cu-3.0Ni-0.75Si合金时效过程中沉淀相的析出与长大规律,及其对合金硬度的影响,采用涡流电导仪和布氏硬度计分别测量合金的电导率和硬度,根据导电率与新相析出量之间的关系分析合金的时效析出动力学过程.结果表明,在350℃下时效,合金硬度随时效时间的延长,先升高后趋于平缓;在450℃、550℃下时效,合金硬度随时效时间的增加快速上升,到达峰值后缓慢下降;时效温度越高,合金硬度峰值越低,但硬度达到峰值所需的时间越短.温度一定,随时效时间的增加,合金电导率在时效初期快速升高,至峰值后趋于平缓.根据Cu-3.0Ni-0.75Si合金在450℃时效过程中电导率的变化,通过Avrami方程推导出相应的相变动力学方程及电导率方程分别为f=1-exp(-0.052 2t0.717 61)和σ=15.2+16.3[1-exp(-0.052 2t0.717 61)],采用相关系数检验法及F检验法对电导率方程的可信性进行检验,结果说明时效析出动力学方程和电导率方程具有一定的可靠性.对比由电导率经验方程得出的电导率理论值与测量得出的实验值,该理论值与实验值有良好的吻合度.     

高温退火和时效处理对Ni47Ti44Nb9合金显微组织和马氏体相变的影响

本文用金相显微镜，电子探针和电阻率－温度曲线测试仪研究了高温退火和时效对Ｎｉ４７Ｔｉ４４Ｎｂｇ合金显微组织和马氏体相变的影响。结果表明，加热温度高于１０５０℃时，β－Ｎｂ相粒子聚集长大，但对马氏体相变并不产生明显影响。与富Ｎｉ的近等原子比Ｔｉ－Ｎｉ合金不同，Ｎｉ４７Ｔｉ４４Ｎｂｇ合金在时效过程中没有时效析出和时效硬化现象。Ｎｂ加入Ｔｉ－Ｎｉ合金中抑制了时效析出和Ｒ相变，从而降低了马氏体相变温度受热     

热处理对Ti-50.8Ni合金相变行为和拉伸性能的影响

采用Pyis Dyiamond差热分析仪和电子万能试验机,研究了固溶、固溶加时效对Ti-50.8Ni合金的相变行为和拉伸性能的影响。结果表明:热处理制度对Ti-50.8Ni合金的相变温度和相变行为有明显影响,Ti-50.8Ni合金在时效过程中产生析出相,导致相变温度和相变行为发生改变,进而对室温拉伸性能产生影响。     

Ni36CrTiAl弹性合金晶界不连续析出相变动力学的研究

本文对高弹性合金NI_(36)CrTiAl的晶界不连续析出相变进行了动力学研究.动力学分析指出:在特定条件下,不连续析出相变的总体动力学不符合动力学定律(Avrami方程),而是符合与纤维组织发展相对应的线性动力学。     

预时效对CuAlNi单晶相变温度的影响

根据有序化理论,提出了预时效概念,并用无析出物形成的预时效处理研究了Cu-13.4Al-4. 0Ni单晶相变温度随预时效工艺的变化,结合DSC和偏光金相分析探讨了预时效与时效的界限.淬冷状态的Cu-Al-Ni单晶其相变温度可以根据需要进行预时效处理,经预时效后,其M s为淬冷态的Ms+0～70 ℃,As为淬冷态的As+0～90 ℃可调. 预时效温度应为淬冷态的Ms+100～200 ℃. 经过预时效的合金在马氏体状态下其相变温度保持稳定. 在高出淬冷态合金Ms点300 ℃以上随着保温温度的升高或保温时间的增长,处理后的 Ms、As等转变温度向高温移动,并且相应的β′1相的数量也会降低,γ′1 相量增加. 尽管此时没有析出物产生,但是单一β′1相转变为β′1+γ′1后,由于γ′1相很差的原位再现性而导致降低形状记忆行为和超弹行为.     

材料状态对NiTi形状记忆合金相变行为的影响

用金相显微镜观察了冷加工和固溶状态的显微组织形貌,用示差热量扫描法(DSC)系统研究了冷加工、固溶和时效处理对近等原子比的NiTi形状记忆合金的相变温度的影响。试验结果表明,冷加工态NiTi合金组织形态呈纤维状,固溶处理后组织形态呈等轴状。冷加工带来的大量变形缺陷抑制了热弹性马氏体的相变;冷加工态NiTi合金直接进行时效发生了P→M相变;经固溶处理后再进行时效则发生了P→R→M相变。NiTi合金在不同的热处理条件下发生了不同类型的热弹性马氏体相变。分析认为,应力、位错密度及析出相对NiTi合金热弹性马氏体的相变行为有重要的影响。     

TiNi形状记忆合金中富镍相的析出及其对机械行为的影响

本文评述了近年来有关 TiNi 形状记忆合金的时效及其对合金机械行为的影响方面的文献资料,系统地综述了 TiNi 形状记忆合金时效过程中富镍相的析出行为、析出相的结构及晶体学关系,探讨了富镍相对合金预马氏体相变及马氏体相变、伪弹性及记忆效应影响的机理,并提出了尚待解决的问题。     

TiNi基高温形状记忆合金的马氏体相变与形状记忆效应

综述了Ti-Ni基高温形状记忆合金中的马氏体相变和形状记忆效应最近研究进展。Ti-Ni基高温形状记忆合金主要包括用Ti-Ni-Pd,Ti-Ni-Pt,Ti-Ni-Zr和Ti-Ni-Hf等。对Ti-Ni基高温形状记忆合金体材料、薄带和薄膜中的马氏体相变、组织结构、形状记忆效应以及超弹性性能等进行了评述和归纳。值得注意的是,通过适当的时效处理可调节相变温度,显著改善Ti-Ni-Hf高温形状记忆合金的开头记忆效应和超弹性性能,其主要原因在于时效的Ti-Ni-Hf合金中析出纳米级析出相导致基体强度升高。采取适当的制备和加工方法,提高合金的马氏体相变温度,改善合金的开头记忆效应,是当前TiNi基形状记忆合金研究的主要发展趋势。     

快速凝固Cu-Cr-Zr-Mg合金时效析出与再结晶的交互作用及其对性能的影响

本文研究了快速凝固Cu-Cr-Zr一Mg合金在时效过程中,析出与再结晶的交互作用及其对显微硬度的影响.研究结果表明:形变使得快速凝固合金时效析出相更加细小弥散,析出过程先于再结晶过程,并对再结晶的形核和长大过程产生阻碍作用.使得冷变形后的合金在较高温度下时效,仍可达到较高的硬度,如冷变形40%的合金在500℃时效30min,其显微硬度值可达Hv220.     

Aging Kinetics in a CuNiSiCr Alloy

The aging precipitation behavior in solution treated Cu-Ni-Si-Cr alloy has been studied in terms of the analyses of the variations in electrical conductivity. On the basis of the linear relationship between the electrical conductivity and the volume fraction of the precipitates, the phase transformation kinetics equation was deduced from the Avrami empiricai formula. On the basis of this equation, transformation kinetics curves corresponding to 5% and 50% transformation were established.     

LD7铝合金淬火敏感性及相变动力学规律

通过分级淬火的方法,结合所测LD7铝合金淬火态电导率和时效态硬度拟合出合金的时间-温度-转化率(TTT)曲线和时间-温度-性能(TTP)曲线。利用透射电镜(TEM)和Johnson-Mehl-Avrami(JMA)方程研究了铝合金等温淬火过程中的组织变化和相变动力学规律。结果表明:LD7铝合金TTT和TTP曲线的鼻尖温度均为350℃,孕育期约为2s,淬火敏感区间为290~410℃;等温保温过程中过饱和固溶体析出第二相粒子,鼻尖温度附近析出速率最快;随保温时间的延长,第二相富集长大且粗化,无沉淀析出区域变宽,晶界第二相连续化,导致合金强化效果下降;根据相变动力学方程拟合出的S曲线,解释了合金在350℃附近淬火敏感性最大以及淬火敏感区间合金第二相主要以针状形态析出的规律。     

Differential scanning calorimetry and energy dispersive spectrometry studies of phase transformations in supersaturated Al–39·5 at.-%Zn alloy

Abstract

The transformation processes in a supersaturated Al–39·5 at.-%Zn solid solution have been studied and characterised by using an SEM equipped with an energy dispersive spectroscopy (EDS) elemental composition microanalyser and a differential scanning calorimetry analyser. With the aid of the SEM examinations of the alloy after various specific aging temperatures, the EDS analysis showed that a transformation, solid solution α_ss phase → spherical Zn precipitates → ZnAl precipitates with an average Zn concentration of 70·5 at.-%, had taken place as a result of increasing the aging temperature. On the basis of the Johnson–Mehl–Avrami equation and assuming diffusion controlled continuous transformation processes, it was concluded that the above transformations were controlled by the three-dimensional mechanism. The average overall activation energy associated with the first precipitation process is determined as 28·13 kJ mol^-1. The other transformation processes are not dominated by their reaction kinetics but are dominated by their temperature dependent thermodynamic equilibrium.     

12Cr1MoV高温时效过程的动力学研究

对低碳低合金耐热钢12Cr1MoV在高温时效过程中,合金元素贫化以及从晶内向晶界扩散迁移、晶粒长大和脱溶沉淀的碳化物粒子粗化等成分、组织结构变化进行了研究,运用扩散理论、相变热力学和动力学理论对这些转变的规律进行分析和处理,并获得与实验相符合的结果.结果表明,合金元素的贫化和晶粒长大分别符合ΔC=K.t3/2和Dt=C.t1/2规律;通过Larson-Miller(P=T(C+lgt)热强参数的统一描述,指出了12Cr1MoV钢高温时效是持续而又缓慢的成分和组织结构逐渐变化(退化)的过程.     

Conversion between non-isothermal and isothermal transformation kinetics of γ to α for C–Mn and Nb microalloyed steels

Abstract

In the present paper, austenite γ to ferrite α transformation kinetics of steels at different cooling rates has been measured by thermal dilatation. The relationship between lnln[1/(1 ? X)] and ln(|C _R|) (C _R: cooling rate) was plotted using the data at early stage of cooling, which well fitted a linear relationship for the calculation of exponential values of n in the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation for isothermal kinetics using the method developed by Rios. The values of k in the JMAK equation obtained with the Rios method, however, have led to big discrepancies when the isothermal equations were used to predict the transformation kinetics during cooling. By assuming a Gaussian function of temperature, k was calculated using an optimisation method based on the rule of additivity. The isothermal transformation model was used to predict the transformation kinetics during cooling, showing good agreement with the measured data. It has been proved that even though the rule of additivity has to be relaxed to take into account the effects of cooling rates, precise conversion between non-isothermal and isothermal kinetics can still be realised.     

Isothermal Aging Kinetics in CuZnAl Shape Memory Alloy

Isothermal aging behaviours of a CuZnAl shape memory alloy have been investigated by means ofdilatometry.The length of the specimens during isothermal aging from 190 to 280℃ increases withthe aging time at each temperature.The isothermal aging kinetics fits in Avrami equation and thetime exponent n decreases with the increase in aging temperature.The apparent activation energyfor the isothermal aging process was measured to be 109.0kJ/mol,which is about equal to that of arelaxation internal friction peak at about 200℃ (f≈1 Hz) in the alloy.     

Decomposition of Zn–Al alloys on quench–aging

Abstract

The aging behaviour of quenched Zn–Al alloys containing small additions of copper was studied using metallography, hardness measurements, and quantitative X-ray diffraction. The kinetics of decomposition of supersaturated α/α′ and β phases were determined and related to structural changes. It was found that the Avrami or Johnson–Mehl equation may be used to analyse the kinetics of decomposition of β phase with an acceptable degree of accuracy. However, the kinetics of zinc formation were more complex and did not obey any known rate equation.

MST/1082     

基于动力显式算法的热成形数值模拟预测

考虑金属热处理相变动力学模型,建立了适用于高强度钢板热成形的热、力、相变多场耦合本构方程。基于大变形动力显式有限元算法及上述多场耦合本构方程,建立了热成形动力显式有限元方程。并将板料相变潜热释放引入到热成形温度场分析过程中。在自主开发的商业化金属成形CAE软件KMAS(King Mesh Analysis System)基础上开发了热成形动力显式分析模块,可用于预测热成形过程中零件的厚度变化、温度变化、微观组织各相的体积分数以及硬度分布。随后采用该模块对一款汽车B柱的热成形过程及最终力学性能进行数值模拟预测,并与试验结果进行对比,对比的一致性证明了所建立的多场耦合本构方程及KMAS热成形动力显式分析模块的正确性。     

有机防护涂层综合加速试验老化动力学模型的建立

为了预测舰船航空飞行器有机防护涂层的服役寿命,模拟了其海洋服役环境:紫外光照射-周期浸润-温度冲击。采用电化学交流阻抗技术进行了综合加速试验,研究有机防护涂层的老化动力学过程,以交流阻抗低频模值为涂层性能的参数,建立了有机防护涂层的老化动力学方程。结果表明:在综合因素加速作用下,有机防护涂层的老化过程可以分为涂层完好、被腐蚀介质渗透、失去防腐蚀作用3个阶段;所建的涂层老化动力学模型有助于确定有机防护涂层的服役寿命和耐久性能,为其使用和维护提供了依据。