PRECIPITATION OF TiC IN METASTABLE β-Ti ALLOY

本文研究了Ti-3.84Al-6.2Mo-10.43V-1.85Fe合金中TiC的析出行为.当合金经低于α+β→β转变温度加热淬火之后,在α/β相界面上存在TiC膜,其形貌与α-β双相合金中TiH_2界面相类似.TiC界面相提供了裂纹易扩展途径和裂纹萌生点.断口也与TiH_2界面相引起的相似.经β固溶处理后再等温时效,在有些试样的电子衍射花样中观察到了弧形衍射(2α相的特征衍射).根据合金成分和点阵常数分析,产生弧形衍射的质点可能是TiC,而非所谓的2α相.     

PRECIPITATION OF TiC IN METASTABLE β-Ti ALLOY

In order to clarify that the IFP and the “Type 2”α phase are also arising from TiC,ametastable β-Ti alloy was selected for investigation in this work.The results showed that af-ter heating the alloy just below the α+β→β transus temperature and quenching,the TiC lay-er existed at the α/β interface.The morphology of TiC is similar to that of the IFP arisingfrom TiH_2 in the α-β two-phase alloys.The IFP TiC also provided an easy crack path orthe crack initiation sites.The fracture is also identical to that caused by IFP TiH_2.The arceddiffractions(characteristic of “Type 2”α)were found in the selected area diffraction pat-terns of some specimens which had been isothermally aged after solid solution treatment.Theparticles which bring on the arced diffractions may be TiC on the basis of structure and lat-tice parameter analysis,not the so called “Type 2”α phase.     

PHASE TRANSFORMATION IN RAPIDLY SOLIDIFIED AI-Cu-Fe ALLOY

By means of rapid solidification, two Al_(65)Cu_(20)Fe_(15) powders were prepared with water and liquid N_2 as the respective cooling agent. Both powders are composed of a qnasicrystalline icosahedral phase and a crystalline hexagonal phase, with the water-cooled alloy having a higher crystalline phase content. In the isothermal an nealing process, the crystalline phase in the water-quenched alloy begins to decrease at 500℃ and then disap pears at 600～700℃. At about 800℃, new crystalline phases form, and at 900℃, the quasicrystalline phase disappears. Conversely, in the liquid N_2 quenched alloy, the quasicrystalline phase starts to decrease at about 500℃. and the hexagonal phase decomposes into new crystalline phases. At 700～800℃, the quasicrystalline phase disappears. For the water-cooled sample, the quenching at 100～200C makes the crystalline to quasicrystalline phase transformation start at a lower temperature and the crystallization of the quasicrystal occur at a higher temperature. For the liquid N_2 quenched alloy, the quenching at 100～400℃, did not affect its phase transformation at high temperature.     

ISOTHERMAL PHASE TRANSFORMATION IN Au-Si AMORPHOUS ALLOY

Electric resistivity measurements and X-ray diffraction analysis were performed to study theisothermal phase transformation in amorphous Au-Si ribbons with eutectic composition pre-pared using melt-spinning technique.A series of phase transformations take placespontaneously at room temperature and accelerate at elevated temperatures.Four stages ofthe transformation from amorphous state to the equilibrium state can be distinguished.Dis-cussion on the structural character of the metastable phases indicates that Hume-Rotheryelectron compounds and size factor compounds could form during isothermal aging.     

EFFECT OF α-PHASE MORPHOLOGY ON STRENGTHENING AND FRACTURE BEHAVIOUR OF 47121 β-Ti ALLOY

用TEM,SEM,X射线衍射及拉伸试验等研究了47121β-Ti合金的拉伸性能与α相形貌及其断裂行为的关系。结果表明,低温时效由ω相转变成的弥散α相质点,随其体积分数增加,质点间共格应力场发生交叠,产生较强的内应力,在负荷作用下,导致宏观脆断,而微观断裂机制仍属于韧窝,因此可以把局部的内应力区认为是形成精细韧窝的核心。魏氏组织的α相具有强的加工硬化效应,位错切割α相是主要强化机制,但以孪生形变的α相片阻止位错切过。晶界两侧形成的无析出带,以及随后形成的羽毛状α相群,都使晶界区弱化,导致形成类似沿晶型断口。     

THE PHASE TRANSFORMATION OF δ-FERRITE IN A STRUCTURALLY DUPLEX IRON-ALUMINIUM-MANGANESE-MOLYBDENUM ALLOY

成分为0.07％C,4.6％Al,32.5％Mn,3.1％Mo的Fe-Al-Mn-Mo合金,于1100℃固溶处理后,具有γ+δ复相组织。用金相法研究了δ铁素体于950—450℃温度范围的组织转变过程,并对转变产物进行了结构与成分的相分析。以金相法测定了等温转变的开始动力学曲线,测量了等温转变过程中δ铁素体内显微硬度的变化。 研究表明:于950—750℃有δ→γ转变,650—550℃有δ→γ+M_(23)C_6转变。此二转变分别以完全扩散型及贝茵体型方式在相应的温度范围内同时进行。750—450℃有α-Mn型晶体结构的金属化合物X相宜δ铁素体中脱溶。X相平均化学式为Fe_(26)Mn_(16)Mo_8Al_8。     

CHARACTERISTICS OF INTERNAL FRICTION AND MODULUS ASSOCIATED WITH NON-EQUILIBRIUM DIFFUSION-TYPE PHASE TRANSFORMATION IN EUTECTOID Al-Zn ALLOY

The characteristics of the low frequency internal friction and the modulus effect associatedwith the non-equilibrium spinodal pretransformation and the following discontinuous trans-formation was investigated in an as-quenched eutectiod Al-Zn alloy.It was observed that theloss of the stability in the lattice,which corresponded to the large-amplitude long-wavelengthstatic concentration wave in the non-equilibrium spinodal pretransformation,did not induceany effect of localized soft modulus.Although there are two aging internal friction peaks inphase transformation which correspond to the appearance and disappearance of the coherencyin spinodal pretransformation and the maximum of the interface area in the discontinuoustransformation respectively,the effect of localized soft modulus did not take place yet.     

FORMATION OF QUASICRYSTALLINE PHASE IN RAPIDLY SOLIDIFIED Al-Fe-V-Si ALLOY

The icosahedral quasicrvstalline phase (i-phase)with the chemical composition of 82.4at%Al,8.8at?,3.6at%V and 5.2at%Si in melt spun Al-Fe-V-Si ribbons was found.It is suggested that the temperature and holding time of the melt prior to quenching are the important factors in the formation of the i-phase.     

IN SITU TEM OBSERVATION OF INITIATION AND PROPAGATION OF CRACKS IN NiAlF

ＩＮＳＩＴＵＴＥＭＯＢＳＥＲＶＡＴＩＯＮＯＦＩＮＩＴＩＡＴＩＯＮＡＮＤＰＲＯＰＡＧＡＴＩＯＮＯＦＣＲＡＣＫＳＩＮＮｉＡｌＦｅＩＮＴＥＲＭＥＴＡＬＬＩＣＳＹ．Ｘ．Ｌｕ；Ｃ．Ｈ．Ｔａｏ；Ｊ．Ｗ．Ｚｈａｎｇ；Ｍ．Ｌ．ＸｕｅａｎｄＤ．Ｚ．Ｙａｎｇ（Ｂｅｉｊｉ...     

CRYSTALLOGRAPHIC ANALYSIS OF THE LATH MARTENSITE TRANSFORMATION IN Fe-Ni-Mn ALLOY

1.IntroductionBased on the concept of an invariant plane strain (IPS), phenomenological theory of martensite transformation (PTMT) is established[1-3]. In this case, an invariant plane is obtained by self-accommoda-tion effect between different martensitic variants, and the formula which reveals this self-accommoda-tion effect can be written as …     

IN-SITU OBSERVATION OF δ→γ PHASE TRANSFORMATION OF AN AISI304 STAINLESS STEEL

利用共焦激光扫描显微镜原位观察了AISl304不锈钢冷却过程中高温铁素体(δ)→奥氏体(γ)相变的过程及其特征.结果表明,γ相优先在δ晶界处形成;冷却速率影响γ相的生长形态,典型形态分为块状、圆形、树枝状等;"游离"γ枝晶发生粗化,并和周围的γ枝晶聚合;相同冷却条件下,δ晶界处的γ枝晶聚合程度明显高于δ晶粒内部;二次枝晶在冷却过程中粗化,并竞争生长.利用ThermoCalc计算C元素在δ→γ相变过程中的偏析系数,以此求解δ→γ相变数学模型.     

PHASE TRANSFORMATION UNIT OF BAINITIC FERRITE AND ITS SURFACE RELIEF IN LOW AND MEDIUM CARBON ALLOY STEELS

The lath-or plate-shaped bainitic ferrite of low and medium carbon alloy steels consists ofpackets of ferrite sublaths which are composed of many finer and regular ferrite blocks.Theyare uniform shear growth units of bainitic phase transformation.No carbide is precipitatedfrom them.The bainitic O-carbides are precipitated from γ-α interface or carbon-richaustenite.The mode of arrangement of the units in ferrite sublath packet is in uni-or bi-di-rection.Single surface relief is produced by the accumulation of uniform shear strains with allthe ferrite units arranged unidirectionally in a sublath packet,while tent-shaped surface reliefis formed by the integration of the uniform shear strains of two groups with ferrite units pilingup in two directions and growing face to face;whereas if they grow back to back,the integra-tion will be responsible for invert-tent-shaped surface relief.The interface trace between twogroups of ferrite units in a sublath packet is shown as“midrib”.     

MECHANISMS OF α_2→α_2/γ PHASE TRANSFORMATION IN A TiAL ALLOY

ＭＥＣＨＡＮＩＳＭＳＯＦα_２→α_２／γＰＨＡＳＥＴＲＡＮＳＦＯＲＭＡＴＩＯＮＩＮＡＴｉＡＬＡＬＬＯＹＸＵＱｉａｎｇ；ＬＥＩＣｈａｎｇｈｕｉ（ＢｅｉＪｉｎｇＬａｂｏｒａｔｏｒｙｏｆＥｌｅｃｔｒｏｎＭｉｃｒｏｓｃｏｐｙ．ＣｈｉｎｅｓｅＡｃａｄｅｍｙｏｆ...     

PHASE COMPOSITION AND TRANSFORMATION STRESS OF PRIMARY LAMELLAR STRUCTURE IN γ-TiAl-BASED DUPLEX ALLOY DURING ISOTHERMAL DECOMPOSITION

应用Ｘ射线衍射测定了过饱和α２单相的Ｔｉ－４５％Ａｌ合金在９５０℃等温分解过程中,初生片层形成时的γ相转变分数及２和γ相晶格参数的变化。结果表明,初生片层中α２和γ相晶格参数的变化,结果表明,初生片层中α２相是亚稳相,其成分可以由自由能成分曲线的亚稳态α２相与γ相自由能成分曲线公切线的切点稳定,该成分的确定对定量计算合金自由能及发生不连续粗化的转变驱动有十分重要的作用;     

IN-SITU OBSERVATION OF NUCLEATION AND GROWTH OF HIGH-TEMPERATURE δ PHASE DURING AUSTENITE → FERRITE+LIQUID PHASE TRANSFORMATION IN AN AISI304 STAINLESS STEEL

利用共焦激光扫描显微镜原位观察AISI304不锈钢加热过程中高温占相的形核与生长．结果表明，130m-1400℃之间δ相在，γ晶界处优先析出，而δ相在γ晶粒内“爆炸”形成需在1410℃以上；δ相形成主要受控于Ni原子的扩散；提高升温速率有利于δ晶粒细化，促使δ／γ平界面失稳并出现二次枝晶．δ相析出时以非小平面为主，另可见少量的小平面δ晶体；随着相变进行，小平面状δ相呈现出边缘钝化、向非小平面转变的趋势．利用平直界面稳定临界扰动理论探讨了δ相生长界面失稳的机制，并从结晶动力学对δ相生长方式转变的原因进行了分析．     

MARTENSITE TRANSFORMATION OF A TiNiCu ALLOY

ＭＡＲＴＥＮＳＩＴＥＴＲＡＮＳＦＯＲＭＡＴＩＯＮＯＦＡＴｉＮｉＣｕＡＬＬＯＹ￥Ｚｈａｎｇ，Ｙｉ；Ｊｉｎ，Ｊｉａｌｉｎｇ；Ｊｉ，Ｚｈｉｑｉａｎｇ（ＳｈａｎｇｈａｉＩｒｏｎａｎｄＳｔｅｅｌＲｅｓｅａｒｃｈＩｎｓｔｉｔｕｔｅ，Ｓｈａｎｇｈａｉ２００９４０）...     

TRANSFORMATION KINETICS AND COARSENING OF LAMELLAR STRUCTURE IN γ-TiAl ALLOY

研究了Ｔｉ－４７．８ａｔ．－％Ａｌ合金从α相区冷至室温再在双相区时效后，层状组织的转变机理及不连续粗化．层状组织转变过程与时效温度和形成过饱和α＿２单相时的冷却速度有关．建立了层状组织转变的动力学模型．层状组织的稳定性随片间距减小而降低，表现为时效时发生不连续粗化．     

ADIABATIC SHEARING PHENOMENON OF β-Ti ALLOY AT HIGH STRAIN RATE

对高应变率下变形的β-钛合金,用光学显微镜和扫描电镜观察研究了其绝热剪切带的显微组织。表明随变形的增加,依次有三种类型的绝热剪切带,即:形变带,具有细条状微晶结构和具有等轴微晶结构的转变带。在大形变量时,均沿绝热剪切带出现裂纹。在讨论绝热剪切判据时区分绝热剪切变形,绝热剪切断裂和热塑失稳是重要的。     

PRECIPITATION AND GROWTH OF δ''- PHASE IN 8090 Al-Li ALLOY

通过热处理，透射电镜分析、图像分析等手段，对８０９０Ａｌ－Ｌｉ合金中δ’相的析出长大行为进行了研究。结果表明，合金在１６０℃时效时，δ’相半径的３次方与时效时间不成直线关系，δ’相的析出长大存在快速和渐缓两个阶段。分析认为，随时效进行合金中过饱和空位浓度的减少造成ＬＳＷ理论模型中ｋ值的减小。     

AN ELECTRON DIFFRACTION STUDY OF γ" PHASE IN Ni-Fe-Cr-Nb ALLOY

<正> Ni-Fe-Cr-Nb合金中γ″(Ni_3Nb) 相沿{100}_γ以三种可能的取向共格析出。γ″通常是弥散的细小析出相,选区电子衍射谱是这三种取向γ″的电子衍射谱的迭加。对于某些晶带衍射,由于两种取向的γ″电子衍射谱与基体完全相重,而被基体衍射所覆盖,其中一种取向的γ″有时又可能不形核,这样对判断这两种取向γ″的存在带来一定困难。为此,本文研究了γ″和γ基体电子衍射谱的相重规律,以选择适当晶带衍射来判定相关取向γ″成核与否,并研究了基体衍射上或其周围的条纹花样或“卫星”斑点对于判断各种取向γ″存在的作用。