【作者】 马海军；

【导师】 李亚江；

【作者基本信息】 山东大学 ， 材料加工工程， 2009， 博士

【摘要】 Fe₃Al金属间化合物独特的性能使其具有很好的应用前景,但由于Fe₃Al属脆硬材料,其熔焊具有很大难度。本文采用填丝钨极氩弧焊（TIG）和焊条电弧焊（SMAW）针对Fe₃Al以及Fe₃Al/18-8钢和Fe₃Al/Q235钢的焊接性进行试验研究。以扫描电镜（SEM）、透射电镜（TEM）、高温差示扫描量热仪（DSC）和ANSYS有限元分析软件等为主要研究手段,以钨极氩弧焊（TIG）接头为研究重点,揭示Fe₃Al焊接区微观组织结构与接头性能的内在联系。系列工艺性试验结果表明,钨极氩弧焊（TIG）采用Cr23-Ni13填充材料,焊接热输入5.5-6.9 kJ/cm;焊条电弧焊（SMAW）采用E310-16型焊条,焊接热输入9.8-11.5kJ/cm,可获得组织性能良好的Fe₃A1焊接接头。其中,Fe₃Al/Q235接头的剪切强度最大（591.1MPa）,Fe₃Al/18-8接头次之,Fe₃Al/Fe₃Al接头最小（127.3MPa）。以接头特征区域划分为主线,展开显微组织、微观结构、裂纹和断口的针对性研究。Fe₃Al接头特征区域包括均匀混合区（HMZ）、不均匀混合区（PMZ）、部分熔化区（PFZ）和热影响区（HAZ）。Fe₃Al/18-8和Fe₃Al/Q235的HMZ以γ为基体,晶界上有片状先共析铁素体析出。Fe₃Al/18-8接头PMZ存在残余δ、ML和Fe₃Al小岛:宽约30μm的富奥氏体带以50-70°的角度沿PFZ分布。Fe₃Al/Fe₃Al的HMZ由大块α-Fe（Al）固溶体组成,PMZ形成Fe₃Al熔化滞留层。Fe₃Al焊接裂纹起源于PFZ,并沿PFZ及HAZ扩展。Fe₃Al/18-8和Fe₃Al/Q235钢接头剪切断口以穿晶解理断裂为主,Fe₃Al/Fe₃Al接头断口为沿晶断裂。Fe₃Al/18-8接头区的相结构由Fe₃Al、γ-（Fe,C）、FeAl、α-Fe（Al）、Ni₃Al和（Cr,Fe）₇C₃组成;Fe₃Al/Q235接头区的相结构包括Fe₃Al、FeAl、Fe₄Al₁₃、α-Fe（Al）、NiAl和（Fe,Cr）:Fe₃Al/Fe₃Al接头区相结构相对简单。Fe₃Al/18-8接头HMZ中上贝氏体α相内部具有高密度位错亚结构,α板条宽度在0.3μm左右,α相和γ相之间存在（110）α//（111）_γ、[001]_α//[101]_γ的位相关系。下贝氏体α相板条宽度在0.2-0.5μm之间。PMZ中的ML板条宽度约为40nm,残余γ薄膜宽度为10-20nm。Fe₃Al/Fe₃Al接头PMZ中α-Fe（Al）相和Fe₃C相之间存在（100）_Fe3C//（110）_{α-Fe（Al）};[100]_Fe3C//[110]_{α-Fe（Al）}的位相关系。揭示焊接条件下Fe₃Al B2与DO₃有序结构转变的两种模式:位错密度较大处为间隔转变模式;位错密度较低处DO₃结构从B2结构中呈球形析出转变模式,并以间隔转变模式为主。DO₃-B2相变温度和热焓变化焊后出现不同程度的降低,且焊接热输入越小,降低幅度越大,DO₃-B2转变逐渐向低温发展。在表征分析、热力学分析的基础上,建立DO₃-B2转变的数学模型,通过控制焊接热输入,可获得DO₃与B2结构比例不同的Fe₃Al接头,适用不同的工作条件。在组织结构分析的基础上,对Fe₃Al/18-8接头的应力分布进行研究。将Fe₃Al/18-8接头应力区划分为应力突变区、应力过渡区和应力稳定区,分析熔合区、焊缝及热影响区不同截面的应力分布。Fe₃Al侧熔合区为应力集中区域,在应力突变区主要受σ_y拉应力作用,σ_y峰值约为σ_x峰值的2倍;在应力稳定区主要承受σ_x拉应力;焊缝应力突变区主要承受σ_y压应力,应力稳定区主要受σ_x拉应力作用:Fe₃Al热影响区应力突变区主要承受σ_y拉应力,应力稳定区则主要为σ_x压应力。本文解决了Fe₃Al脆性材料熔焊时的裂纹问题,特别是在不预热条件下的焊接裂纹问题,为Fe₃Al金属间化合物的应用打下良好试验和理论基础。本文提出焊接区组织结构与应力分析相结合,以特征区域为研究主线的研究思路,采用表征分析、热力学分析与数学分析相结合的研究手段,为高脆性材料的焊接研究提供思路。更多还原

【Abstract】 The particular performance of Fe₃Al intermetallic makes it a luciferous prospect. However,Fe₃Al is difficult to fusion welded due to the hard brittleness of this material.In this paper,the weldability of Fe₃Al as well as Fe₃Al/18-8 and Fe₃Al/Q235 steels was studied via filler TIG and SMAW.The research methods of SEM,TEM,high-temperature DSC and ANSYS finite element software were used to reveal the relationship of microstructure with the performance.And the emphasis was put upon TIG joint zone.The results of series welding experiments indicated that a Fe₃Al joint with good performance was obtained under the condition of welding heat input 5.5-6.9 kJ/cm, filler Cr23-Ni13 alloy via TIG and welding heat input 9.8-11.5kJ/cm,electrode E310-16 via SMAW.The shear strength of Fe₃Al/Q235 joint was largest（591.1MPa）, Fe₃Al/18-8 joint the secondary and Fe₃Al/Fe₃Al joint the least（127.3MPa）.The analysis of microstructure,cracks and fracture of Fe₃Al joint were carried out based on the division of character zones.Fe₃Al joint character zones included a homogeneous mixture zone（HMZ）,a partial mixture zone（PMZ）,a partially fused zone（PFZ） and a heat-affected zone（HAZ）.The matrix of Fe₃Al/18-8 and Fe₃Al/Q235 HMZ wasγaustenite and pro-eutectoid ferrite（PF） precipitated along theγgrain boundary.The retainedδ,LM and Fe₃Al isle existed in Fe₃Al/18-8 PMZ. A 30μm wide austenite rich band distributed along PFZ with an angle of 50-70°.The Fe₃Al/Fe₃Al HMZ was composed of bulkα-Fe（Al） solid solutions and the fusion residence layer was formed in PMZ.Fe₃Al welding cracks originated in the PFZ and extended along the PFZ and HAZ.The shear fracture of Fe₃Al/18-8 and Fe₃Al/Q235 joint were mostly transgranular cleavage,and the fracture of Fe₃Al/Fe₃Al joint was in intergranular mode.The phase constituents Fe₃Al/18-8 joint were composed of Fe₃Al,γ-（Fe,C）, FeAl,α-Fe（Al）,Ni₃Al and（Cr,Fe）₇C₃.The phase structure of Fe₃Al/Q235 joint constituted of Fe₃Al,FeAl,Fe₄Al₁₃,α-Fe（Al）,NiAl and（Fe,Cr）.The phase constituents of Fe₃Al/Fe₃Al joint were relatively simple.The density of the dislocation inαphase was very high for upper bainite（B_u） in Fe₃Al/18-8 HMZ,and theαplate was 0.3μm wide.The lattice orientation between a and y phases was（110） _α//（111）_γ,[001]_α//[101]_γ.The width of a plate in lower bainite（B_l） was 0.2-0.5μm. The lath martensite（ML） was 40nm in width in PMZ,and the width of retainedγmembrane was 10-20nm.The lattice orientation betweenα-Fe（Al） and Fe₃C phases was（100）_Fe3C//（110）_{α-Fe（Al）},[100]_Fe3C//[110]_{α-Fe（Al）} in Fe₃Al/Fe₃Al PMZ.Two kinds of transformation models for Fe₃Al B2 and DO₃ ordered structure were revealed:the alternation model in the zones with higher dislocation density and precipitation transformation model in the zones with lower dislocation density in which globular DO₃ domains precipitated from the B2 structure.And alternation model was the major model for the DO₃-B2 transformation.The DO₃-B2 transition temperature and enthalpy changes reduced in different degrees after welding.The less the welding heat input,the larger the reduction range was.The DO₃-B2 transformation occurred gradually to lower temperature.On the basis of characterization and thermodynamics analysis,the mathematic models of DO₃-B2 transformation were found.The Fe₃Al joint containing different proportion of DO₃ and B2 structure was obtained by controlling the welding heat input to satisfy various running conditions.The stress fields of Fe₃Al/18-8 joint were studied based on the analysis of microstructure.The stress regions of Fe₃Al/18-8 joint were divided into three character zones of stress jump zone,stress transition zone and stress stable zone to analysed the stress distribution of fusion zone,weld and HAZ in different cross-sections,respectively.The Fe₃Al side fusion zone was the stress concentration zone.The stress jump zone was mainly affected byσ_y tensile stress,and the peak value ofσ_y was twiceσ_x.The stress stable zone was mostly affected byσ_x tensile stress.The weld was mainly affected byσ_y compression stress in stress jump zone andσ_x tensile stress in stress stable zone.The Fe₃Al HAZ was mainly affected byσ_y tensile stress in stress jump zone andσ_y compression stress in stress stable zone.The welding cracks problem of Fe₃Al brittle material was solved in this paper, especially without pre-heat treatment,which provided experimental and theoretical basis for improving the application of Fe₃Al intermetallic.This paper presented the combination analysis of the microstructure and stress distribution,character zones division as the research main line and combination of characterization, thermodynamics and mathematics methods,which was a consideration to the welding research for high brittle materials.更多还原