690镍基合金焊接结晶裂纹形成机理分析

690镍基合金焊接结晶裂纹形成机理分析

薄春雨, 杨玉亭, 丑树国, 周世锋

(机械科学研究总院哈尔滨焊接研究所,哈尔滨 150080)

摘 要:采用横向可调拘束试验方法研究了690镍基合金焊带堆焊金属的结晶裂纹形成机理。结果表明,690镍基合金焊接结晶裂纹的形成与晶界(及亚晶界)偏析密切相关,Nb元素在其中有着重要影响:富Ni,Nb低熔点共晶相在晶界(及亚晶界)的偏析,导致堆焊金属的实际结晶温度降低,晶界(及亚晶界)处塑性储备减小、

690镍基合金焊接结晶裂纹形成机理分析

690镍基合金焊接结晶裂纹形成机理分析

形貌被改善,促使

结晶过程中裂纹萌生并沿平直晶界(及亚晶界)扩展。另外,Mn元素可通过抑制Nb元

素在晶界的偏析,削弱Nb的上述不利作用,增强690镍基合金抵抗结晶裂纹的能力。

关键词:690镍基合金;结晶裂纹;形成机理

中图分类号:TG115.28 文献标识码:A 文章编号:0253-360X(2007)10-069-04

薄春雨

0 序 言

690镍基合金(0Cr30Ni60Fe10)具有优异的耐应力腐蚀性能。近年来,该材料已在国外开始应用于压水堆核电站蒸汽发生器管板耐蚀层堆焊[1]。690合金的焊接性相对较差,其中最突出的问题是热裂纹敏感性较大。目前,国外对690合金焊接材料的研究已经取得了一定的成果,但就管板耐蚀层堆焊而言,焊接过程中的结晶裂纹问题仍是值得关注的技术关键;同时,对该材料结晶裂纹的形成机理亦没有统一的认识,这对于该材料安全可靠的使用是极为不利的。

试验采用国际上通用的可调拘束试验方法[2-4],对不同成分配比的690合金焊带堆焊金属进行了结晶裂纹敏感性研究;结合显微组织金相试验和扫描电镜断口试验等分析方法,探讨了690合金结晶裂纹的形成机理。

1 试 验

母材试板采用Q235A钢板,试板尺寸为330mm ×140mm×10mm。试验焊带经真空冶炼、轧制,规格为30mm×0.5mm,化学成分如表1所示。

试验在哈尔滨焊接研究所自行设计的HHR L—1

表1 试验焊带化学成分(质量分数,%)

Table1 Chemical compo sition of welding strip

材料编号Fe Cr Ni Mn Nb C S i S P Al T i余量

19.0~11.028.5~31.5基体 1.0~2.0≤0.5≤0.030≤0.20≤0.010≤0.010≤1.0≤1.0<0.5

29.0~11.028.5~31.5基体 1.0~2.0 1.0~2.0≤0.030≤0.20≤0.010≤0.010≤1.0≤1.0<0.5

39.0~11.028.5~31.5基体 1.0~2.0 2.0~3.0≤0.030≤0.20≤0.010≤0.010≤1.0≤1.0<0.5

49.0~11.028.5~31.5基体 3.0~5.0≤0.5≤0.030≤0.20≤0.010≤0.010≤1.0≤1.0<0.5

59.0~11.028.5~31.5基体 3.0~5.0 1.0~2.0≤0.030≤0.20≤0.010≤0.010≤1.0≤1.0<0.5

69.0~11.028.5~31.5基体 3.0~5.0 2.0~3.0≤0.030≤0.20≤0.010≤0.010≤1.0≤1.0<0.5

型可调拘束试验机上进行,试验过程如图1所示。试验前,采用电渣堆焊工艺对母材试板的梯形坡口进行堆焊,经机械矫形平整,加工至试验要求形状尺寸。试验过程中,采用TIG电弧沿堆焊金属纵向中心线自A点~C点进行焊接,焊接至B点时,对试板施加快速弯曲应变诱发裂纹。通过读数显微镜测量不同应变条件下产生的最大裂纹长度;重复上述焊接过程,采集并记录焊缝金属的结晶温度曲线。

第28卷第10期2007年10月

焊 接 学 报

TRANS ACTI ONS OF THE CHI NA WE LDI NG I NSTIT UTI ON

Vol.28 No.10

October 2007

收稿日期:2007-05-24

690镍基合金焊接结晶裂纹形成机理分析

图1 横向可调拘束试验示意图(mm)

Fig11 Trans2Vare straint te st

通过可调拘束试验方法,可得到多个裂纹参数

690镍基合金焊接结晶裂纹形成机理分析

,

但从不同的角度评定试验材料的裂纹敏感性,大都有一定的局限性。临界应变速率(critical strain rate for tem perature drop,简称CST)是表征结晶过程中焊缝塑性储备情况的物理量[5],而塑性储备是与材料抵抗裂纹的能力一一对应的,故研究选择CST作为结晶裂纹敏感性的评定判据。

2 试验结果及分析

2.1 试验结果

通过可调拘束试验得到各试验材料的CST值,如图2所示。结果表明,对690合金堆焊金属而言,随Nb含量的增加,CST值减小,裂纹敏感性增大,尤其是当Nb含量大于2.0%时,抗裂性显著下降;随Mn含量的增加,CST值增大,裂纹敏感性减小。

图2 试验材料的临界应变速率值比较

Fig12 CST of690alloy welding metal

690合金焊缝组织中,Nb元素结合Ni元素形成低熔点共晶相的倾向较大,这将导致结晶裂纹敏感性增大。然而,由于Nb元素在690合金中起着稳定焊缝、增强焊缝金属耐晶间腐蚀性能的重要作用,故该材料含有一定量的Nb元素是必须的。密道瓦尔指出[6],在镍基合金焊缝中加入一定含量的Mn元素,能够较大程度地抑制Nb元素对抗裂性的不利作用。

在各试样断口表面不同区域随机选取3组偏析相(每组3点,在同一区域),另随机选取基体的3个不同位置,采用电子能谱分析每组偏析相的平均Nb 含量,试验结果如图3所示。结果表明,当690合金堆焊金属的Nb含量处于低(1号,4号),中(2号,5号)水平时,Mn元素的加入将一定程度地对Nb元素的偏析产生抑制作用,其中,1

690镍基合金焊接结晶裂纹形成机理分析

号与4号两种材料Nb元素的平均偏析量分别为7.51%与2.66%,2号与5号两种材料Nb元素的平均偏析量分别为18.32%与8.78%。这与密道瓦尔的观点是一致的。但当690合金堆焊金属的Nb元素含量达高水平时, Mn元素的这种作用已不明显,3号和6号两种材料Nb元素的平均偏析量分别为18.72%和17.71%,差别很小。对比图2与图3可知,随着Nb,Mn含量的变化,试验材料的CST与其中Nb元素的平均偏析量有着相近的变化趋势,由此可见,690合金堆焊金属的塑性储备、抗裂性与Nb元素的偏析有着直接的联系。

图3 Mn元素对裂纹断面Nb元素偏析的影响

Fig13 E ffect of Mn on segregation of Nb in fracture

2.2 690合金焊带堆焊金属的结晶特性

图4所示为试验堆焊金属的显微组织及裂纹断口照片。由图4a可以看出,690合金堆焊金属显微组织中,奥氏体柱状晶粒表面较光滑,晶界平直。堆焊金属结晶过程存在一定的温度梯度,使组织具有很强的方向性,这可以从裂纹断口宏观形貌中得到反映(图4b),奥氏体柱状晶发达且方向性明显,其方向与热散失的方向是一致的。裂纹断口表现出明显的塑性断裂特征,这可从断口表面的韧窝组织得到反映(图4c)。

70

 焊 接 学 报第28卷

690镍基合金焊接结晶裂纹形成机理分析

图4 690合金焊带堆焊金属结晶特性

Fig 14 Solidification characteristics of 690alloy welding metal

2.3 690合金结晶裂纹的分布与形态

横向可调拘束试验条件下,

690镍基合金焊接结晶裂纹形成机理分析

裂纹宏观上围绕固

—液相界面分布,一般是焊道中心存在最大裂纹长度。这是由于焊缝结晶的方向性很强,沿热流方向的柱状晶生长的更快更多。因此,同热流方向基本一致的晶界在焊缝中占大多数,绝大部分结晶裂纹与固—液相界面基本垂直。随着裂纹向焊缝中心靠拢,脆性温度区间对应的长度增加,可能出现的裂纹长度相应增大,在焊道中心处产生最大裂纹。如裂

纹扩展至焊缝表面,则无金属光泽(图5a ),这是由于裂纹暴露在空气中,高温条件下在表面形成氧化物所致。金相分析表明,大部分裂纹沿晶开裂。多数裂纹的形态是一端较粗钝而另一端较尖锐,如图5b 所示。另外,在金相试验中发现曲折晶界的存在。图5c 很好地说明了晶界曲折的作用:晶界曲折打破了裂纹的连续性,故细化晶粒或打乱柱状晶的方向性对改善奥氏体焊缝的抗裂性能有较好的效果。

图5 690合金焊接结晶裂纹的分布与形貌

Fig 15 Distribution and appearance s of solidification cracking in 690welding metal

2.4 结晶裂纹的形成特性

研究发现,690合金焊接结晶裂纹的形成与结

晶过程中的偏析现象有着密切的联系。焊缝金属结晶速度较快,结晶过程中易于形成晶界或晶内偏析。690合金中,Ni 含量较高,致使富Ni 共晶相的形成趋势增大。研究表明,共晶相在晶界(及亚晶界)处的偏析较为严重。图6a 所示为断口表面晶界颗粒状析出物,从图中可见,颗粒状析出物弥散分布于柱状晶界,较为密集。电子能谱分析结果表明,这些析出物是富Ni ,Nb 的。有研究表明,Ni 2Nb 共晶相的

熔点较低,平衡条件下仅为1175℃[7]

,在非平衡的焊接条件下则更低。可以确定,这些颗粒状析出物是低熔点共晶相在固态下的存在形式。结晶过程中,由于偏析所造成的焊缝组织不均匀性,表现为晶界上覆盖的低熔点共晶薄膜。图6b 所示为裂纹断

口表面局部区域覆盖的白色薄膜。电子能谱分析结果表明,薄膜的Nb ,Ni 含量较焊缝基体高。可以认为,该薄膜为裂纹产生后仍残留在晶界表面的残余相,是低熔点共晶相在液态下的存在形式。就诱发裂纹而言,薄膜的量是充足的,薄膜厚度较厚。

低熔点共晶相形成元素含量相对较低时,焊缝金属中的偏析程度相应较小。图6c 所示为Mn ,Nb 含量处于低水平的690合金焊缝裂纹断口低温段形貌。从图中可见,断面较为平坦,基体上弥散分布着少量的点状析出物;电子能谱分析表明,该析出物的Nb 含量仅为2.09%,此时Ni 2Nb 共晶相的形成倾向较低,焊缝金属的实际熔点相对较高。

随着共晶相形成元素含量的增加,富Ni 低熔点共晶相的数量将增加。图6d 所示为Nb 含量处于高水平的690合金焊缝裂纹断口低温段形貌。从图中

第10期薄春雨,等:690镍基合金焊接结晶裂纹形成机理分析71

 

图6 典型试样裂纹断口局部形貌

Fig16 Fracture appearance of typical te st specimens

可见,由于Ni,Nb等元素含量较高,使断口表面在冷却至低温段后仍残留有较多的共晶花样,这正是共晶液膜处断裂后在低温时的形貌;电子能谱分析表明,共晶花样的Nb含量水平达27.67%,Ni2Nb共晶相的量较多。

综上所述,690合金焊缝结晶裂纹的形成与结晶过程中的偏析现象有着直接联系:低熔点共晶相在结晶过程中偏析于晶界(及亚晶界),使焊缝金属的成分过冷度增大,实际结晶温度区间变宽,促使柱状晶粒长大,晶界(及亚晶界)光滑平直;当焊缝金属中大部分已结晶完成后,晶界(及亚晶界)处的残留低熔点液相趋向于以液态薄膜的形态铺展,成为焊缝金属中的薄弱地带;在焊缝结晶过程中产生的拉应力作用下,薄膜铺展处产生开裂,而此时的液相含量之少使之已无法填塞愈合裂纹,从而裂纹将萌生并沿平直晶界扩展。

3 结 论

(1)690合金中,Nb对于抗裂性是不利的。Mn 的加入则可通过抑制Nb在晶界的偏析,削弱Nb的这种不利作用,增强690合金堆焊金属抵抗结晶裂纹的能力。

(2)690合金结晶裂纹宏观上垂直固—液相界面分布,表面无金属光泽;微观上沿晶分布,大多数裂纹呈一端尖锐一端粗钝的形态。

(3)690合金结晶裂纹的形成与焊缝结晶过程中的偏析现象有着密切的联系。焊缝金属结晶过程中,富Ni2Nb低熔点共晶相在结晶过程中偏析于晶界(及亚晶界),当焊缝金属中大部分已结晶完成后,晶界(及亚晶界)处的低熔点共晶相趋向于以液态薄膜的形态铺展,在焊缝结晶过程中产生的拉应力作用下,薄膜铺展处产生裂纹,而此时的液相含量之少已不足以填塞愈合裂纹,由此裂纹将萌生并沿平直晶界扩展。

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作者简介:薄春雨,男,1981年出生,硕士,助理工程师。主要从事镍基和不锈钢焊接材料的研究与开发。发表论文2篇。Email:bcyhit@http://m.wendangku.net/doc/4b3efe06b52acfc788ebc905.html

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690镍基合金焊接结晶裂纹形成机理分析

high2temperature tensile test;endurant tensile test

Welding process of micro2alloying cast iron electrode ZH AI Qiuya,ZH AI Bo,T ANG Zhen,X U Jin feng(School of Materials Science and Engineering,X i’an University of T echnology,X i’an 710048,China).p53-56

Abstract: Using a micro2alloying cast iron electrode the rela2 tionship between preheat temperature and microstructure and proper2 ties of joint were investigated by backing welding with low2current and then continuous welding with high2current.The results showed that the micro2alloying cast iron electrode has strong graphitizing a2 bility and the weld metal had a little chilling tendency.The applied welding process can effectively decrease the depth of fusion zone and suppress the precipitation of cementite in fusion zone at a great ex2 tent.Thus the welding with the micro2alloying cast iron electrode can be realize at ambient temperature.When the preheated temperature is less than200℃,the hom ogeneous weld can be obtained which has the same microstructure and properties as base metal.With the increase of the preheat temperature,the graphite m orphology in weld changes from spotted graphite to rosette graphite to flake graphite. The contents of graphite and ferrite increase,while the hardness of the weld decreases.I f the preheated temperature reaches to200℃, the microstructure of the weld consists of pearlite,ferrite,flaky graphite and rosette graphite,and the microstructure of fusion zone consists of pearlite,small shiver ferrite and undercooled graphite. The welded joint has excellent mechamical properties.

K ey w ords: micro2alloying cast iron electrode;iron casting; ambient temperature welding;microstructure and properties of joint

Analysis of ch aracteristic of vertical position laser w elding for a2 luminum alloys MI AO Y ugang,CHE N Y anbin,LI Liqun,W U Lin(S tate K ey Laboratory of Advanced Welding Production T echnol2 ogy,Harbin Institute of T echnology,Harbin150001,China).p57-60

Abstract: The experiments of vertical and flat position laser welding for4mm2thick5A06aluminum alloys were implemented, and the characteristics of weld dimension and porosity in the vertical position laser welding for aluminum alloys were investigated.The re2 sults show that the concave value and excessive penetration value of vertical welding is less than those of flat welding.Further,with the increase of heat input,the difference of vertical and flat welding be2 comes obvious.The weld appearance and dimension of the vertical welding and flat welding were slightly different.When the heat input is increased to a great extent,the weld depth of vertical welding is m ore than that of flat welding.H owever,the weld width of vertical welding is less than that of flat welding.The porosity of vertical posi2 tion laser welding for aluminum alloys is composed of the large and irregular porosity or hole.It is not obviously different during vertical welding and flat welding,and a great deal porosity concentrates in the upper and middle part of weld section,which can be indicatied from the distributing position and shape of porosity.The number of porosity in vertical welding was slightly less than that of flat welding for the same welding parametors.

K ey w ords: aluminum alloys;vertical position laser weld2 ing;flat welding;characteristic E ffect of aluminizing and diffusion treatment on adhesive strength of arc2sprayed coatings W ANG Qiang,LAN D ongyun,X UAN Zhaozhi,LI U Chenghui(C ollege of Materials Sci2 ence and Engineering,Jilin University,Changchun130025,Chi2 na).p61-64

Abstract: C orrosion2resisting and heat2resisting coatings of 1828stainless steel were made by arc spraying,aluminizing and dif2 fusion treatment on cast iron.The microstructures and chemical com2 positions of coatings with aluminizing and diffusion treatment were studied by optical microscope,scanning electron microscope and X2 ray diffraction.And the adhesive strength of coatings was evaluated by thermal fatigue tests.The results show that there is s ome regions with metallurgy bonding on the interface between coatings and sub2 strates through aluminizing and diffusion treatment,therefore,the adhesive strength of coatings were improved greatly.And a long pe2 riod of aluminizing time is adverse to the adhesive strength of coat2 ings,s o aluminizing time should be controlled well.

K ey w ords: arc spraying;aluminizing;diffusion;adhesive strength

Microstructure and melting property of Sn22.5Ag20.7Cu2XG e solder ME NG G ongge1,Y ANG Tuoyu2,CHE N Leida1 (1.School of Material Science&Engineering,H arbin University of S cience and T echn ology,H arbin150040,China;2.Anhui S cience and T echn ology University,Bengbu,233100,Anhui,China).p65-68 Abstract: The3composition Sn22.5Ag20.7Cu2XG e lead2 free s olders were studied by scanning electron microscope and differ2 ential scanning calorimetry equipments.The result indicates that the microstructure is cobblestone2like pro2eutectic grain and scattered long narrow piece and small pellet eutectic mixture.With0.5%or 1.0%element G e,the microstructure m orphology does not change. But the intermetallic compounds of Ag3Sn and Cu6Sn5tend to be fine,and their dispersion tends to be well2distributed,and Ag3Sn phase tends to be fine needle from long narrow piece.By adding ele2 ment G e,the temperatures of the melting beginning,the melting peak and the melting finish all reduce correspondingly.And in the melting curve,the endothermic peak changes is narrow,and the melting finish part is long,but the melting temperature zone varies a little.

K ey w ords: lead2free s older;microstructure;melting prop2 erty

Solidification cracking mech anism of690nickeil2b ased alloy sur2 facing metal BO Chunyu,Y ANG Y uting,CH OU Shuguo, ZH OU Shifeng(Harbin Welding Institute,China Academy of Ma2 chinery Science and T echnology,Harbin150080,China).p69-72 Abstract: T rans2varestraint test was used to investigate the s olidification cracking mechanism of690nickel2based alloy surfacing metal.Results show that,the s olidification cracking susceptibility of 690nickel2based alloy surfacing metal is closely correlated with the segregation process during welding,which is greatly in fluenced by Nb.The s olidification temperature of690nickel2based alloy surfac2 ing metal falls when the Ni,Nb2rich phases segregate on the grain boundary or subgrain boundary,which induces that the ductility de2 creases and the appearance is fined.Then,cracking initiates and

Ⅳ M AI N T OPICS,ABSTRACTS&KEY W ORDS 2007,Vol.28,No.10

expands along the finer grain boundary or subgrain boundary during the s olidification process.Furtherm ore,in690nickel2based alloy surfacing metal,Mn weakens the negative in fluence of Nb on s olidi2 fication cracking resistance to s ome extent by restraining the segrega2 tion effect of Nb,and then the cracking resistance is improved.

K ey w ords: 690nickel2based alloy;s olidification cracking; mechanism

Ch aracterization on strength and toughness of w elded joint for ultra2low carbon b ainitic steel G UO Aimin1,2,LI U Jibin2, MI AO K ai2,DONG Hanxiong2,Z OU Dehui2,HE X inlai1(1.School of Materials Science and Engineering,Beijing University of Science and T echnology,Beijing100083,China;2.Research and Develop2 ment Institute,Wuhan Iron and S teel(G roup)C ompany,Wuhan 430080,China).p73-76

Abstract: The weldability was investigated on ultra low2car2 bon bainitic steel with therm omechanical control process by utilizing shielded metal arc welding,submerged arc welding and welding thermal simulation test.Results showed that hardness is a little dif2 ferent in the heat affected zone(H AZ).The maximum hardness in the heat affected zone was less than60H V.C ompared with the same class of low alloy high strength steels,the uniformity of strength in H AZ increases remarkably.The heat affected zone has high tough2 ness.The impact abs orbing energy at-40℃reaches above60J in the simulated coarse2grained zone when the heat input was56k J/ cm.The impact abs orbing energy at-40℃reached above100J in shielded metal arc welding,and submerged arc welding.

K ey w ords: ultra2low carbon bainitic steel;welding;heat affected zone;toughness

B razing process of high temperature brazing filler metal BCo45NiCrWB LI U Enze1,2,S UN Shuchen1,T U G an feng1, ZHE NG Zhi2,T ong Jian2,G uo Y i2(1.School of Materials and Met2 allurgy,N ortheastern University,Shenyang110004,China;2.Su2 peralloys Division,Institute of Metal Research Chinese Academy of Sciences,Shenyang110016,China).p77-80

Abstract: Wettability and flow2ability experiments of a high temperature brazing filler metal BC o45NiCrW B were studied.Dy2 namic analysis of brazing process was studied by a ST M D2300surface tension test apparatus.Microstructures of brazed joint with different brazing processes were studied.Microstructure of brazed joint was analyzed by optical microscope.The element distribution of brazed joint was analyzed by electron microprobe.Rupture life of brazed joint at the condition of980℃/132MPa was tested.The best braz2 ing process of BC o45NiCrW B alloy was established.The brazing pa2 rametens are1220℃/2h,+1080℃/4h+900℃/16h,all by arg on quench.Results show that the high temperature brazing alloy BC o45NiCrW B has excellent process brazeability.At the condition of 980℃/132MPa the rupture life is m ore than60hours.

K ey w ords: brazing;wettability;flow2ability;rupture life

E ffect of therm al cycles of DSAW on microstructure in lowalloy high strength steel ZH ANG Huajun,ZH ANG G uangjun, W ANGJunheng,W U Lin(S tate K ey Labortory of Advanced Weld2 ing Production T echnology,Harbin Institute of T echnology,Harbin 150001,China).p81-84

Abstract: According to the low alloy high2strength steel thick plate welding,a new high efficiency technique which does not need back chipping-double2sided double arc welding(DS AW)was pro2 vided.Backing run with double2sided double pulsed gas metal arc welding,and other passes with double2sided double gas metal arc welding.The temperature fields of single TIG(tungsten inert2gas) welding and DS AW near the bond area were measured by the method of hiding thermal2couple in drilled hole.C ompared the thermal cy2 cles of tw o methods,the t8/5and t8/3of DS AW are higher.In DS AW,fore pass provides the rear pass with a preheat action and rear pass provides the fore pass with a postheat treatment.In single TIGwelding,microstructure of weld and coarse grain zone is coarse martensitic,but in DS AW weld contains a few of acicular ferrilite besides of martensitic.M oreover,microstructure of coarse grain zone is smaller than that of single TIGwelding.Microhardness distribution results indicated that hardness of DS AW was lower than that of single TIG welding.

K ey w ords: double2sided double arc welding;temperature field;T joint;low alloy high strength steel

E ffects of heat treatment on microstructure and properties of electron beam w elded TC4titanium alloy G U Baolan,DI NG Dawei,W ANG Li,X U Xuedong(Institute of Microstructure and Properties of Advanced Material,Beijing University of T echnology, Beijing100022,China).p85-88

Abstract: F or electron beam welding(E BW)of T C4titanium alloy with different preheat treatments and post2weld heat treatment, microstructure and phase composition characteristics of these welds of T C4were studied by means of optical microscope and X2ray diffrac2 tion.T ension and impact test were carried out at room temperature. The results indicated that the microstructure of tw o kinds of base metals is the mixture ofαphasse andβphase,but their state and distribution are different.The post2weld s olution and aged operation carried out in the case of annealed welds leads to a coarsening and hom ogenous of the acicularα,the microstructures is typically reticu2 lar structure.The welds in s olid s olution state were given a relief an2 nealed after welding,whose microstructure at FZ is tempered martensiteαin side priorβgrains and at grain boundaryα.It induced that the ultimate tensile strength(UTS)of annealed state welds is less than that of s olution treated welds,but the impact toughness of the former is greater than that of the latter.H owever,the UTS and impact toughness of these tw o kinds of welds are greater that that of base metal.

K ey w ords: T C4titanium alloy;electron beam welding;mi2 crostructure;mechanical properties

Finite element analysis simulations of life prediction for PBG A soldered joints under therm al cycling T ONG Chuan,ZE NG Shengkui,CHE N Y unxia(Reliability Research Institute,Beihang University,Beijing100083,China).p89-92

Abstract: A typical plastic ball grid array(P BG A)compo2 nent was selected and the plastic ball grid array packaging was m od2 eled as a tri2layer structure composed of encapsulation,die and sub2 strate.Visco2plastic m odel was used to describe the behavior of SnPb

2007,Vol.28,No.10 TRANS ACTI ONS OF THE CHI NA WE LDI NG I NSTIT UTI ON Ⅴ

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