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.     

ELECTRON RADIATION INDUCED VOID SWELLING AND GRAIN BOUNDARY SEGREGATION IN AN Fe-Cr-Mn AUSTENITIC ALLOY

The behavior of void swelling and segregation in Fe-15Cr-xMn alloys and an alloy con-taining small amount of W and V was investigated by electron-irradiation.The compositionalanalysis in the irradiated regions including grain boundaries was performed.The resultdts showthat there are many common features of irradiuation tehavior in the Fe-Cr-Mn andFe-Cr-Ni systems while there are some significant differences,In the Fe-Cr-Mn alloy sys-tems void swelling was rematrkably suppressed and at the same time the radiation-inducedsegregation was also retarded,furthermore,the segregation was strongly retarded in anFe-15Cr-15Mn alloy containing small amount of W and V.The results also show that Ni re-placed by Mn does not in general confer immunity from either swelling or phase instabilities.The phase instability is due to the different diffusion behavior of Ni and Mn in reponse to theoperation of the inverse-Kirkendall effecr.Fe segregates to the microstructural sinks in theFe-Cr-Mn alloys.The segregation of Fe often leads to the formation of ferrite.This fact isbeneficial to reducing the swelling rate and segregation on the grain boundaries.     

电子辐照Fe-Cr-Ni奥氏体合金的空洞体胀与诱起晶界偏析的研究

本文用超高压电镜(HVEM)作为电子束源,研究了Fe-15％Cr-30％Ni合金电子辐照后,合金空洞体胀和诱起晶界偏析.实验结果证明:723K,最大剂量15dpa条件下,体胀量为0.62％.在晶界发生Cr贫化、Ni富化.随着辐照温度提高,晶界偏析程度增加,723K时Cr,Ni在晶界出现最大偏析峰,相应空洞体胀量也最大.结果表明,空洞形成和晶界偏析密切相关,本文提出了辐照诱起晶界偏析模型.     

Role of chromium on mechanical properties of Fe-Mn-Ni-Mo-Ti maraging steels

This experiment investigated the role of chromium in the mechanical properties of Fe-5Mn-9Ni-5Mo-1.5Ti maraging steels containing up to 3% chromium. Remarkable age-hardening responses were observed in the Fe-5Mn-9Ni-5Mo-1.5Ti and Cr-bcaring alloys. A ductile-brittle-ductile transition occurred in the Cr-bearing alloys during isothermal aging below 510°C. This was due to the segregation of titanium and manganese to prior austenite grain boundaries and their subsequent desegregation into the matrix. The addition of chromium to the base alloy considerably improved its ductility after aging at 520°C. From microstructure and AES analyses, it is suggested that chromium addition augments the volume fractions of (Fe,Mn)₂Mo and η-Ni₃Ti precipitates in the Fe-5Mn-9Ni-5Mo-Cr alloys, which act as sinks of manganese and titanium in the matrices. This resulted in the reduction of the alloying elements concentration in the matrix, which is followed by the reduction in the segregation level of the elements at prior austenite grain boundaries, and consequently enhanced intergranular fracture strength. The optimum combination of strength and ductility was obtained in the Fe-5Mn-9Ni-5Mo-3Cr-l.5Ti alloy aged at 520°C for 2 hr. and was σ_{0 2}=1721 MPa, σ_LS=1756 MPa. and ε,= 10.2%.     

晶界非平衡偏聚与晶体缺陷构型的关系

对Ｆｅ－３０％Ｎｉ合金和超低碳贝氏体钢在高温进行不同方式变形和保温,通过变形、回复、与再结晶,获得秒同的晶体缺陷数量与构型（主要是位错分布形态）。用硼径迹显微照相技术研究了 空冷过程中硼向晶界的非平衡偏聚及与不同形态晶体缺陷的关系。结果表明,在再结晶新晶粒冷却时晶界偏聚明显。晶界附近会出现较显著的贫硼现象,而变形并回复后的原始晶粒中此现象不明显,高温回复阶段形成的多边形化亚晶界（位错墙）对冷却时硼     

Effect of alloying elements on fracture behavior of Fe-18Ni-2Ti-(8Co) alloys

Effect of alloying elements on fracture behavior of Fe-18Ni-2Ti-(8Co) alloys has been investigated in the light of grain boundary segregation of alloying elements. During isothermal aging at 540°C, hardness level in the cobalt-bearing alloy was higher than that in the cobalt-free alloy, which is attributed to the solid solution hardening of cobalt, and the bigger hardness difference after overaging was due to the relatively fine precipitates in the cobalt-bearing alloy. The grain boundary segregation behavior of the elements was similar in two alloys, regardless of the cobalt addition. In two alloys, the fracture behavior before and after the maximum tensile strength is mainly governed by two factors: titanium at the grain boundaries and over-aging. Up to the aging time corresponding to the maximum tensile strength, the intergranular fracture strength was roughly inversely proportional to the titanium level at the grain boundaries, and after the time the tensile strength decreased with restoring ductility. Nickel or cobalt was not effective on the grain boundary strengthening of the iron-based alloys.     

Fe—Cr—Mn（W,V）合金焊接热影响区的辐照损伤及诱发的晶界元素偏析

采用电子束辐照研究裂变－聚变混合反应堆预选结构材料Ｆｅ－Ｃｒ－Ｍｎ（Ｗ,Ｖ）合金的焊接热影响区（ＨＡＺ）组织损伤,测定损伤组织和晶界处的合金元素浓度变化。实验结果表明：低温下剂达１０ｄｐａ,合金奥氏体组织稳定,未发现空洞形成和第二相析出;然而在高温下,剂量达４．８ｄｐａ就明显出现低密度微小空洞,并出现晶界移植现象。其次,在低温下,晶界附近大尺寸溶质原子Ｃｒ和Ｍｎ贫化,而小尺寸原子Ｓｉ,Ｖ,Ｎｉ,Ｗ     

Sc,La对Al-Mg焊料中杂质元素偏聚的调控作用

采用金相显微镜、扫描电镜、能谱分析和X射线衍射仪,研究了添加微量钪、镧对铝镁焊料中杂质元素偏聚的调控作用. 结果表明,在铝镁焊料合金凝固过程中,铁、硅等杂质元素在晶界有偏聚效应,添加微量钪、镧可以降低铁、硅杂质在晶界的偏聚浓度. 钪与镧减轻杂质元素在晶界偏聚的效果存在差别,添加钪的合金比添加镧的合金晶界处杂质元素偏聚强度明显减弱. 造成这种差别的原因是,钪、镧对杂质元素偏聚的调控机制不同.     

关于Fe－28Al合金中的析出相

用磁性分析、显微组织观察和Ｘ射线衍射对淬火态Ｆｅ—２８Ａｌ合金的结构进行了研究．结果表明，合金从Ｂ２区淬火后沿晶粒边界可有第二相析出，已初步确定它是Ｆｅ和Ａｌ的碳化物Ｆｅ_３ＡｌＣ_ｘ（ｋ相）．     

关于Fe—28Al合金中的析出相

用磁性分析、显微组织观察和Ｘ射线衍射对淬火态Ｆｅ—２８Ａｌ合金的结构进行了研究．结果表明，合金从Ｂ２区淬火后沿晶粒边界可有第二相析出，已初步确定它是Ｆｅ和Ａｌ的碳化物Ｆｅ_３ＡｌＣ_ｘ（ｋ相）．     

原位TiC颗粒对喷射成形Al-Fe-V-Si合金组织和性能影响

通过扫描电镜和透射电镜分析研究了原位反应生成的TiC颗粒对喷射成形态及挤压态的Al-8.5Fe-1.4V-1.7Si合金显微组织的影响,并对合金的力学性能进行了测试。结果表明,原位反应生成的TiC颗粒均匀地分布在合金基体中并细化了基体合金的晶粒,提高了合金的高温组织稳定性;喷射成形Al-8.5Fe-1.4V-1.7Si 3.0TiC合金挤压态的室温和高温强度明显高于喷射成形Al-8.5Fe-1.4V-1.7Si合金挤压态的强度,而且塑性也有明显的提高。     

Fe-Cr-Mn奥氏体合金的辐照体胀与诱起晶界偏析行为的研究SCIEI

本文采用电子束辐照,研究了Fe-15Cr-xMn合金以及添加W,V合金的孔洞体胀和诱起晶界偏析行为,并对包含晶界在内的辐照区进行成分分析。结果表明,在Fe-Cr-Mn系合金中孔洞体胀孕育期可以被强烈抑制,晶界偏析也减少。特别是,合金中添加W,V效果更加明显。用Mn代替Ni,通常要发生体胀和相的不稳定性,由于反Kirkendall效应导致Ni和Mn的扩散行为不同,使Fe富集在尾闾处,局部地区形成铁素体,有利于减少体胀和晶界偏析。     

硅含量对Fe-Cr基减振合金微观组织和内耗性能的影响

制备了含硅量分别为0%、0.2%、0.5%、0.9%和1.2%的5种Fe-12.8Cr合金,并研究了这5种合金在淬火状态下的微观组织特征和阻尼性能,解释了硅含量对Fe-Cr合金阻尼性能的影响。研究结果表明,当含硅量为0.6%左右时,Fe-12.8Cr减振合金具有适当的晶粒尺寸,阻尼性能最好。     

NON-EQUILIBRIUM SOLUTE SEGREGATION TO AUSTENITIC GRAIN BOUNDARY IN FERRUM-NICKLE ALLOY

1. IntroductionNon-equilibrium segregation of solute atoms at grain boundaries has been fOund inmany alloy systems and always been an interesting study topic. The non-equilibriumsegregation of boron at austenitic grain boundaries in low carbon steel is a typical example.A series of experimental studies indicate that the alloy system, the type and concentratiollof solute atoms, the binding energy of solute atoms with vacancies, heat treatment history,heating temperature and cooling rate have le…     

Effect of Boron on the Structure and Properties of Disk Forgings from High-Temperature Alloy KhN73MBTYu-VD (ÉI98-VD)

Boron segregation on the boundaries and in near-boundary volumes of alloy ÉI698-VD bearing up to 0.005% B and 0.01% B is investigated. The structure of fracture surfaces of impact specimens and the nature and distribution of boron carbides and borides on conventional and wide grain boundaries are described. Statistical analysis of controllable properties of production forgings with boron content in the supplied bars varying from at most 0.005% to at most 0.008% is performed.     

Grain refinement of primary silicon in hypereutectic Al-Si alloys by different P-containing compounds

The grain refinement behavior of Si-3 P,Si-25 Mn-10 P,and Al-10 Si-2 Fe-3 P master alloys on hypereutectic Al-24 Si alloy was studied.Microstructure analysis indicates that the P-containing compounds in the three master alloys are Si P,Mn P,and Al P,respectively.The coarse flower-like primary silicon in the Al-24 Si alloy transforms into smaller,well-distributed blocks with the addition of various master alloys.When pouring at 840°C,the average grain size of the primary silicon refined by Si-25 Mn-10 P master alloy with a holding time of 30 min is about 18μm,which is significantly smaller than those refined by Si-3 P and Al-10 Si-2 Fe-3 P master alloys.The grain size shows an increasing trend when the holding time is further prolonged.Higher holding temperature has a positive effect on the grain refinement of Si-25 Mn-10 P master alloy.The grain refinement mechanism of the three master alloys was also discussed.     

Grain-boundary segregation of impurities in iridium and effects on mechanical properties

Impurity effects were investigated in an Ir alloy of nominal composition Ir–0.3 W–0.006 Th–0.005 Al¹. The impurities that were added included Fe, Ni, Cr, Al, and Si, at levels ranging from 50 to 5000 ppm. Of the elements investigated (impurities as well as alloying additions), only Si and Th were found to segregate to the grain boundaries. In alloys doped with low levels of Si (<200 ppm), both Si and Th segregated to the grant boundaries. In addition, Th-containing precipitates were identified in these alloys, but not Si-containing precipitates. When added at higher bulk levels, Si displaced (beneficial) Th from the boundaries. This caused the segregated Th at the boundaries to decrease (to practically zero) when the amount of grain-boundary Si increased (to its saturation level). Silicon also reacted with Th to form Ir–Th–Si precipitates and promoted the formation of a low-melting eutectic on the grain boundaries of the highest Si alloys. As for the other elements, not only did they not segregate to the grain boundaries, but they also did not affect Th segregation. Together, these results explain why Fe, Ni, Cr, Al (and Si at low levels) do not embrittle iridium, whereas Si at high levels causes severe embrittlement.     

GRAIN BOUNDARY FEATURE AND CREEP BEHAVIOR OF Fe-15Cr-25Ni ALLOYS

Creep behavior of Fe-15Cr-25Ni alloys with different grain boundary features has been in-vestigated at 850 and 950℃ and in stress range of 14.7～78.5 MPa.The single phase alloyexhibits typical recovery creep characteristics,and for the alloy in which M_(23)C_6 carbidesdensely precipitate at grain boundaries,the creep rate dramatically decreases and creep behav-ior is also significantly different from the single phase alloy.When the carbides precipitate atgrain boundaries,the dislocation density are higher and the size of subgrains near grainboundaries are smaller than those of single phase alloy.The creep mechanisms for two grainboundary features have been discussed.     

镁偏析对铝合金晶界性能影响的计算机模拟

采用嵌入原子法对铝晶界上Mg的偏析性质及其对晶界性能的影响进行了计算机模拟。结果表明 ,Mg的晶界偏析具有自发性 ,并且降低基体的电荷密度和空位形成能 ,从而导致晶界脆化。     

ANTIMONY GRAIN BOUNDARY SEGREGATION AND ITS SUPPRESSION BY CERIUM IN Fe—2Mn—Sb STRUCTURAL STEELS

Antimony grain boundary segregation in Fe-2%Mn-Sb structure steels has been studied through measurements of the ductile-brittle transition temperature in conjunction with scanning electron microscopy, Auger electron spectroscopy and secondary ion mass spectroscopy. The research result reveals that during tempering or ageing after quenching at 980℃, Sb segregates to grain boundaries with both equilibrium and non-equilibrium natures and brings about temper embrittlement in the steels. Cerium can relieve temper embrittlement of the steels and its segregation to grain boundaries may play an important role in reducing this embrittlement.