触变注射成形AZ91D的固溶和时效热处理

对触变注射成形AZ91D固溶和时效处理后的组织和硬度变化进行了研究.结果表明,固溶处理过程中,溶质扩散、溶解和固溶体熟化相继发生.而固溶体的硬度受固溶强化的影响,随固溶温度的升高而升高.时效处理过程中,β-Mg17Al12首先在α-Mg的晶界处非连续析出,随后在α-Mg晶内连续析出.受沉淀强化影响,α-Mg的硬度值随着时效时间的延长和时效温度的提高逐渐增大.     

Mg-5Gd-1Mn-0.3Sc合金铸态的显微组织及其异常热处理行为

研究了Mg-5Gd-1Mn-0.3Sc合金铸态显微组织及在520 ℃固溶处理不同时间后的组织结构演变行为.结果表明,合金铸态组织表现为粗大的枝晶结构,晶界上或枝晶之间都分布着大量的富溶质相,其中相当数量的GdMg3相在非平衡凝固过程中生成,而在固溶处理中并未消除.合金经520 ℃不同时间固溶处理,晶粒尺寸变化异常.固溶14 h后晶粒尺寸减小到铸态的1/3,继续延长固溶时间,晶粒尺寸重新变大.因此控制固溶温度和时间,可获得试验合金晶粒细化的效果.     

固溶处理工艺对V-5(Al-5Ti-1B)氢分离合金显微组织、硬度和轧制性能的影响

在真空电弧炉中熔炼制备V-5(Al-5Ti-1B)合金（V-5ATB合金）,采用光学显微镜、X射线衍射仪、硬度测试和轧制性能测试技术,研究固溶处理温度和时间对V-5ATB合金的显微组织、硬度和轧制性能的影响。研究结果表明：V-5ATB合金在800和900℃固溶处理,随着温度升高,TiB相逐渐溶入V基固溶体（Vss）,晶粒随之长大。合金TiB第二相析出强化及细晶强化的效应减弱程度大于固溶强化效应的增加程度,导致合金硬度随温度升高而降低。而在1000℃固溶处理时,合金中TiB相几乎完全溶入Vss中,固溶强化效应占主导使合金硬度值出现回升。V-5ATB合金在900℃固溶处理随着时间延长,TiB相逐步溶入到Vss中,晶粒随之长大。合金第二相析出强化及细晶强化的效应减弱程度大于固溶强化效应的增加程度,导致合金固溶处理后的硬度随时间延长而降低。V-5ATB合金较适宜的固溶处理工艺参数为900℃/2 h。固溶处理态合金的轧制性能相比于铸态的提升了约24%。     

热处理温度对含纳米Si C的快冷镁合金固溶组织影响

采用铜模喷铸与等温热处理相结合,制备出纳米SiC参与下快冷镁合金细晶组织,研究热处理温度对非平衡凝固镁合金固溶组织转变的影响及其高温晶粒长大行为。结果表明:提高冷速与添加纳米SiC可实现镁合金的复合细化,有利于形成细小花瓣状组织。经320、370和400℃等温处理2 h后,快冷AZ91+2%纳米SiC合金从不完全固溶向完全固溶发生转变,溶质偏析程度降低,同时,晶界β-Mg_(17)Al_(12)相不断消失,最终获得多边形等轴晶组织。由于纳米SiC对晶界迁移起到良好的抑制作用,亚稳细晶组织的高温晶粒长大行为得到有效控制,其中经400℃固溶8 h后的平均晶粒尺寸仅为13μm,快冷合金的热稳定性得到显著提高。     

固溶处理温度对高硅锰铬镍奥氏体不锈钢晶间腐蚀的影响

利用光学显微镜(OM)、扫描电镜(SEM)及能谱仪(EDS)等对不同温度下固溶处理高硅锰奥氏体不锈钢(UNS S21800钢)的晶间腐蚀进行了研究,分析了固溶处理和固溶+敏化处理两种工艺下进行晶间腐蚀试验后试样的组织形貌及晶间腐蚀倾向。研究结果表明:固溶处理后进行晶间腐蚀的试样中,表面均未发现裂纹,900℃固溶处理试样其晶界处存在较多的第二相,在950℃时第二相颗粒数量明显减少,当温度达到1200℃时,晶界附近已难以观测到第二相颗粒;经固溶处理+675℃敏化处理后进行晶间腐蚀试验的试样中,900℃固溶处理试样表面观测到有晶间裂纹存在,而固溶温度在950℃及其以上温度的试样未出现晶间裂纹。形成晶间裂纹原因是由于900℃固溶处理试样经过敏化处理后晶界处析出了更多的球状和长条状的富Cr碳化物,使得晶界附近区域形成了贫铬区,发生了晶间腐蚀;而950～1200℃固溶处理+敏化处理试样由于在固溶过程中第二相已大量溶入基体,虽然在敏化过程有部分析出,但不足以形成贫铬区,因此在该温度区间内难以发生晶间腐蚀行为。     

固溶处理对一种新型亚稳定β型钛合金组织与力学性能的影响

研究了固溶处理对一种亚稳β型Ti-10Mo-6Zr-4Sn-3Nb钛合金组织与力性能的影响。结果表明:经(α+β)固溶后的组织为拉长的β晶粒,晶界和晶内析出球状初生α相;时效后,晶内β基体上均匀析出细小针状的次生α相。β单相区固溶后的组织为等轴β晶粒;时效后,晶界析出取向相近的次生α相片层,晶内析出针状、平行交叉的次生α相。随固溶温度的升高,初生α相体积分数减少,β晶粒度增加。经(α+β)固溶+时效后,析出的次生α相细小;经β单相区固溶+时效后,析出的次生α相较粗大;经固溶后,合金拥有较高的强度和塑性,且随固溶温度的升高,强度减小,塑性增加;(α+β)固溶时效强化大于β单相区固溶时效强化,二者差约60 MPa。     

热处理对T-250钢电子束焊接头组织的影响

T-250马氏体时效钢电子束焊接头经850℃、950℃、1 050℃和1 150℃等不同温度固溶1 h,再经4h 500℃的回火处理后,材料的组织结构产生明显差异.在相对较低温度下固溶处理,焊缝组织中逆转奥氏体含量较高,奥氏体组织以浅色衬度池塘形态分布于晶界.而经高温固溶处理,焊缝区的胞状晶组织消失,焊缝区发生奥氏体化再结晶,淬火后成为单一的马氏体组织,奥氏体含量很低,表明高温均质化完全,焊缝区溶质元素晶界偏析现象消失而不利于奥氏体形成.固溶处理温度稍高于再结晶温度可有效改善焊缝组织.     

热机械处理对Al-10.78Zn-2.78Mg-2.59Cu-0.22Zr-0.047Sr铝合金固溶时效态组织及力学性能的影响

以固溶-时效和热机械处理(TMT)(固溶-过时效-热压缩)-固溶-时效加工的超高强铝合金Al-10.78Zn-2.78Mg-2.59Cu-0.22Zr-0.047Sr为实验对象,分别采用电子背散射衍射(EBSD)、X射线衍射(XRD)、硬度测试和拉伸试验研究合金组织晶粒晶界特征分布、内部的位错密度和力学性能,并定量计算位错强化和晶界强化值。结果表明:热机械处理对合金晶粒细化影响不显著,平均晶粒尺寸从7.30μm减小至6.04μm,晶界角度从21.45?下降到21.04?,小角度晶界比例从0.588下降到0.546;TMT使峰时效硬度从2146 MPa(120℃/48 h)提高到2268 MPa(100℃/48h),但对强度影响较小,二者屈服强度均为600 MPa左右,拉伸断口均为沿晶和撕裂混合断裂。合金分别经固溶及TMT-固溶后,晶界位错密度均为零,TMT使位错强化与晶界强化的总强化从58.8 MPa下降到57.4 MPa。     

在线固溶及离线热处理对压铸AZ91D镁合金组织及硬度的影响(英文)

研究在线固溶处理、离线固溶处理和时效处理对压铸AZ91D镁合金组织及硬度的影响。结果表明:在线淬火和离线时效处理可提高压铸AZ91D合金的布氏硬度,但是离线固溶处理使合金的硬度下降。通过X射线物相分析、光学显微组织分析、差热分析、扫描电镜及能谱分析,发现在线固溶和时效处理后合金的组织与压铸AZ91D的基本相同,仍由α-Mg及β-Al12Mg17组成。在压铸镁合金冷却过程中,在线固溶处理使温度急剧降低从而阻止了β-Al12Mg17相的继续析出,增强了Al元素固溶强化的效果。时效处理后,Al12Mg17从Mg的过饱和固溶体中析出并细化组织,改善了细晶强化的效果。离线的固溶处理使Al12Mg17分解,导致其固溶强化效果得到增强但是晶界强化相大幅度减少,从而使合金的硬度降低。     

固溶处理对注射成形0Cr17Mn11Mo3N钢组织性能的影响

采用金属粉末注射成形工艺制备出了0Cr17Mn11Mo3N高氮无镍奥氏体不锈钢(含氮0.78wt%),研究了固溶处理对力学性能和组织的影响.结果表明,固溶处理能极大改善材料组织和性能,未固溶处理试样组织主要为奥氏体、铁素体以及在晶界连成网状的Cr2N析出物,固溶处理后得到了均一的全奥氏体孪晶组织;固溶处理后力学性能大大提高,抗拉强度和伸长率分别为885MPa和26.0%,为未固溶试样的1.3倍和2.2倍;未固溶处理试样断口为沿晶和韧窝断裂特征,固溶处理试样为韧窝延性断裂特征.     

Phase field crystal model of solute drag

The atomic scale interaction of solute with a migrating grain boundary has been studied using a binary phase field crystal (PFC) model. This model bridges between atomistic and continuum simulation techniques as it operates on diffusive timescales but at atomistic length scales. For this study, a two-dimensional channel containing two grains separated by a flat grain boundary has been constructed that allows for a channel length on the order of one micrometer. A new formalism has been developed to allow for the application of an external driving pressure for the growth of one grain. These simulations account for solute/grain boundary interactions, resulting in a solute drag effect on the grain boundary motion. The PFC simulations show good agreement with classical solute drag theory, though deviations due to the atomic scale nature of the interface exist.     

Study on Influence of Solute Atoms on Grain Boundary Character Distribution with Internal Friction Method

Based on the relationship between parameters of grain boundary internal friction peak(GBP)andgrain boundary character distribution(GBCD),and the internal friction results of Al-Mg,Al-Ga,Al-Cu andAl-Zn alloys,the addition of different kinds of solute atoms has different effects on GBCD.Among them,Mg atoms are able to concentrate and stabilize GBCD in AI-Mg alloys.The origin of these effects of soluteatoms on GBCD is also discussed.     

NON-EQUILIBRIUM SEGREGATION OF SOLUTE TO GRAIN BOUNDARIES

In consideration of the local equilibrium among vacancies,solute atoms and vacancy-soluteatom complexes and the influence of equilibrium grain boundary segregation,theoretical dy-namic formulas for non-equilibrium grain boundary segregation of solute have been derivedon the basis of the vacancy-dragging mechanism.Theoretical calculation by computer hasbeen carried out for the non-equilibrium segregation of boron to austenitic grain boundariesduring isothermal holding and continuous cooling after heating at high temperatures.The re-suits agree well with those obtained from experiments.     

Effects of High Density Electropulsing Treatment on Aging Kinetics of GH4199 Alloy

GH4199 alloy was treated by high density electropulsing for different time, and the microstructure evolution and tensile properties were examined. The results show that the diffusion of solute atoms in GH4199 alloy can be strongly accelerated by electropulsing. The growth activation energy of γ′ phase of 89.86 kJ/mol in the alloy electropulsing-treated, decreases by 64.31 % compared with that normally aged, which accelerates the precipitation and the growth of both the γ′ phase and carbides on the grain boundary of the alloy. The strength of GH4199 alloy increases with increasing of electropulsing treatment time, and the plasticity has no obvious change. The growth of γ′ phase and the precipitation of carbides on the grain boundary is the main reason for obstructing the dislocation motion and improving the plastic deformation resistance of the alloy. The piled-up dislocations can go through the grain boundary across the gap of carbides which is distributed on the grain boundary in chainlike form, and no degradation of the plasticity of GH4199 alloy appears.     

Grain coarsening inhibited by solute segregation

It will be shown that grain boundaries are in a metastable thermodynamic equilibrium in the presence of solute atoms and, therefore, grain coarsening is stopped as there is no driving force. This is in contradiction to a generally accepted interpretation, where solute drag, i.e. zero mobility of the boundaries, stops grain coarsening. Based on the empirical relation between terminal solubility of a solute and its grain boundary segregation it can be shown that a two-phase mixture with solute atoms agglomerating in a precipitated phase will be the stable thermodynamic equilibrium state. However, if precipitation is kinetically hindered, the metastable equilibrium with a certain grain boundary area and a zero grain boundary energy is attained. Changes in this grain boundary area or grain size respectively are calculated as a function of temperature and compared with experimental findings.     

GRAIN-BOUNDARY PRECIPITATION UNDER IRRADIATION IN DILUTE BINARY ALLOYS

Irradiation-induced grain boundary segregation of solute atoms frequently bring about grain boundary precipitation of a second phase because of its making the solubility limit of the solute surpassed at grain boundaries. Until now the kinetic models for irradiation-induced grain boundary precipitation have been sparse. For this reason, we have theoretically treated grain boundary precipitation under irradiation in dilute binary alloys. Predictions of γ' -Ni3Si precipitation at grain boundaries are made for a dilute Ni-Si alloy subjected to irradiation. It is demonstrated that grain boundary silicon segregation under irradiation may lead to grain boundary γ'-Ni3Si precipitation over a certain temperature range.     

微量Ce对工业纯铝铸态组织的影响

研究了微量Ce对工业纯铝铸态组织的影响,分析了Ce对微观组织的细化作用及变质机理。结果表明,微量Ce会使铝熔体成分过冷和增大溶质不稳定扰动,并释放大量潜热,导致界面稳定性下降,促使组织晶粒细化;Ce具有较高的化学活性,易形成新的α相核心,促进晶粒细化;界面上形成的含稀土化合物会填补界面表面缺陷,促使杂质相转变成球粒状,并促使杂质原子在晶界富集。     

电脉冲固溶对Al-22％Si-1．5％Cu合金组织的影响

利用光学显微镜观察及显微硬度测量等方法研究了在脉冲电流作用下，Al-22％Si-1．5％Cu合金经过固溶、时效后其显微组织及基体性能的变化。结果表明，采用短时间高密度脉冲电流作用于A1．22％Si-1．5％Cu合金固溶过程前期（作用时间为120S），可明显改善该合金初生硅相及Al2Cu相的形态和分布、显著提高基体的显微硬度。在固态相变经典形核理论的基础上，本文讨论了其作用机理。分析后认为脉冲电流影响了溶质原子的非平衡扩散过程，提高了固态相变的驱动力场从而降低扩散能垒，强化了溶质粒子扩散过程。     

直流磁场对7075铝合金组织结构的影响

研究了在直流磁场下凝固的7075铝合金晶内溶质含量及凝固组织的变化。试验结果表明：与未施加磁场的试样相比，经过直流磁场处理后，7075铝合金中Zn、Mg、Cu3种溶质元素在晶粒内部的含量均增加。此外，直流磁场作用下，试样宏观组织的变化不明显，而晶内析出相的形貌和尺寸发生了显著变化，由无磁场时的粗大针状组织变为细小均匀的结构。探讨了磁场的作用机制。认为电磁场作用使得各溶质粒子对基体铝产生了相对运动，这种运动增强了溶质粒子在铝中的扩散，从而导致了晶内溶质含量的增加。     

金属退火硬化现象及机理的研究进展

通常金属进行退火时都会发生软化现象,而对于一些特殊的金属或者合金,将出现退火硬化的反常现象。对纯金属、铜合金、镍钨合金、锌铝合金和铝合金等体系中退火硬化现象及机理进行了总结与分析。铝钪、铝镱和铝锆系合金中存在铸态直接退火硬化现象,而其它合金体系需要进行冷变形才会出现退火硬化现象。退火硬化的机理主要包括:晶界溶质偏析、晶界弛豫、第二相颗粒的晶界钉扎、位错源限制硬化、溶质偏析对孪晶边界迁移或位错滑动的钉扎效应、退火孪晶、第二相纳米粒子强化等。