钛合金针状焊缝组织的超塑性变形机理

焊 接 学 报

TRANSACTIONS OF THE CHINA WELDING INSTITUTION

Vol.39(9):065 − 070September 2018

钛合金针状焊缝组织的超塑性变形机理

江训焱， 程东海， 陈益平， 胡德安

(南昌航空大学 航空制造工程学院，南昌　330063)

摘 要： 钛合金激光焊缝是非理想的针状组织，对其超塑性变形机理的研究可进一步推进钛合金LBW/SPF技术的实际应用，也对材料成形机理的发展具有一定意义. 研究结果表明，TC4钛合金激光焊接试样具有良好的超塑性变形能力，在变形过程中，焊缝发生两次重要的组织转变，即针状组织片层化和片层组织等轴化的组织转变. 片层组织在应力作用下，通过断裂、解体和等轴化的过程而转变成等轴晶粒. 片层断裂的主要机制是动态再结晶和应力挤压作用；片层解体的主要机制是晶界滑动和转动作用，接头组织的塑性流动机理为晶粒滚动和晶界滑动机理.关键词： 钛合金；激光焊；变形机理；超塑性变形

中图分类号：TG 456.3 文献标识码：A doi：10.12073/j.hjxb.2018390226

0 序　　言

钛合金的焊接/超塑成形组合工艺是一种低成本、高效益、近无余量的组合成形技术，是构件加工制造中的重要技术之一. 激光焊/超塑成形组合工艺更是具有自动化程度高，尺寸控制精确，可制造复杂结构零件等优点，在航空等领域具有很好的应用前景. 目前，国内外关于激光焊/超塑成形组合工艺(LBW/SPF)的研究已经证实了它的可行性，钛合金激光焊接接头具有较好的超塑性变形能力

[3-4]

[2]

[1]

焦，焦距为190.5 mm. 焊接工艺选取参数：离焦量为–0.5 mm；激光功率为1 300 W；焊接速度为3.0 m/min.

采用高温拉伸试验研究TC4钛合金激光焊接试样的超塑性变形行为，拉伸试验在高温MTS810拉伸试验机上进行，高温拉伸规范如图1所示. 变形温度为870~920 ℃，初始应变速率为10~10 s，高温拉伸试样尺寸如图2所示.

–1–3–1

.

但由于焊缝组织为针状的网篮组织，其超塑性变形过程中的组织演变机理存在其自身的特点，不完全适用通常理想组织材料的超塑性变形机制.

文中系统性的研究了TC4钛合金激光焊缝的超塑性变形行为，在观察激光焊缝在超塑性变形过程中组织演变的基础上，着重分析了针状组织在超塑性变形过程中的机理，为激光焊/超塑成形组合工

温度 T/℃设定温度保温 5 min拉伸

降温时间 t/s

[5]

加热速度 (1 ℃/s)

图 1 高温拉伸规范

Fig. 1 High temperature tensile specification

20

艺的实际应用提供理论依据.

1 试验方法

试验材料为细晶TC4钛合金板材，厚度为0.8 mm.激光焊接设备使用Lase 4000 CO2轴流激光器，额定输出功率为4 kW，光束模式为TEM01，透射镜聚

收稿日期：2017 − 05 − 01

基金项目：国家自然科学基金资助项目(51465042)

f 420R 1515565

图 2 激光焊接试样高温拉伸试样尺寸(mm)

Fig. 2 Dimensions of laser welded specimens at

elevated temperature

为了评价接头在变形过程中焊缝的应力行为，采用式(1)进行计算，即

66

焊 接 学 报

第 39 卷

σ−σm·SmWb=FS(1)W式中：F是焊接试样截面所承受的力(N)；Sm为焊接试样截面母材承载面积(mm2

)；Sw为焊缝承载面积(mm2

)；σMb为母材峰值应力(MPa)；σWb为焊缝峰值应力(MPa)；σm为焊接试样峰值应力时的应变所对应的母材应力(MPa).

2 试验结果及分析

2.1 力学行为

图3所示为TC4钛合金激光焊接试样超塑性变形前后部分试样的宏观照片. 可以看出，试样超塑性变形后可以得到较高的断后伸长率，并且平行段变形均匀. 实物观察中可以看到试样边缘呈锯齿状，表明变形过程中试样发生了颈缩与抗颈缩的典型超塑性变形过程.

233%273%320%

353%

图 3 TC4钛合金激光焊缝超塑性变形后宏观照片Fig. 3 Macroscopic photographs of laser welding of TC4

titanium alloy after superplastic deformation

图4所示为焊接试样和母材在超塑性变形过程中的典型应力–应变曲线. 由图4可以看出，超塑性变形过程中发生了颈缩与抗颈缩的典型超塑性

24焊板20aPM16/σ母材 力12应840020406080100 应变 δ (%)图 4 焊接试样与母材在超塑性变形过程中的应力-应变曲线Fig. 4 Stress strain curves of welded specimens and

base metal during superplastic deformation

变形特征，应力–应变曲线呈锯齿状；在相同变形条件下焊接试样流动应力大于母材.

焊接试样在超塑性变形过程中，由于焊缝内部存在粗大柱状晶和呈网篮状分布的针状马氏体组织. 这种组织属于非理想超塑性变形组织，相对于母材的等轴晶粒而言，接头组织更容易发生加工硬化而难以发生超塑性变形. 一方面，钛合金的马氏体形态为针状，不利于滑动或滚动，容易引起应力集中. 而且钛合金的马氏体组织是一种富位错组织，在变形过程中容易引起位错的塞积和钉扎，也会加强焊缝组织的加工硬化效果；另一方面，接头组织的软化作用将受到组织转变和位错运动的影响而被减弱. 因此，相对于母材的应力–应变曲线，焊接试样的流动应力更大.

图5a、图5b分别为计算后焊缝和母材的峰值流动应力. 可见，相同变形条件下，接头峰值应力明显大于母材. 变形温度920 ℃、初始应变速率为10–3

s–1

时，母材的峰值应力为7.5 MPa，而对应的焊缝峰值应力达到21.5 MPa. 这是由于接头中存

在大量针状马氏体组织，相对母材的等轴组织更难以变形. 但是，在较低初始应变速率时(10–3 s–1

)接头具备了低变形应力的特征. 接头的流动应力随变

180 10−1 s−1 10−2 s−1a150P 10−3 s−1M/σ120 力应90值峰60300870880890900910920温度 T/℃(a) 焊缝峰值应力150 10−1 s−1120 10−2 s−1aP−3M 10 s−1/σ90 力应值60峰300870880890900910920温度 T/℃ (b) 母材峰值应力图 5 焊缝及母材的峰值流动应力

Fig. 5 Peak flow stress of welded bead and base metal

第 9 期江训焱，等：钛合金针状焊缝组织的超塑性变形机理67

形工艺参数的变化趋势与母材相同，即流动应力峰值随温度的升高而减小、随初始应变速率的增加而增加. 但是随变形温度的升高或初始应变速率的降低，接头峰值应力的变化幅度大于母材的变化幅度，约是两倍关系. 说明变形工艺的优化对接头的影响大于母材，由于接头显微组织是非理想超塑性变形组织，在超塑性变形过程中要发生一系列的组织转变，如动态再结晶，使得组织向理想超塑性变长大，且试样容易被氧化，造成材料断后伸长率的下降. 由图6b可见，随初始应变速率的增加，应力集中得不到及时缓解，材料内部变形来不及协调，接头断后伸长率不断减小.

与母材TC4钛合金的超塑性变形类似，接头在高温拉伸时同样具有很好的变形能力，在900 ℃、10 s时断后伸长率可达到最大397%. 变形温度及初始应变速率是影响焊缝变形能力的主要因素，–3

–1

形组织——等轴组织转变，说明变形工艺优化对于非理想超塑性变形组织的影响大于理想超塑性变形组织.

超塑性变形时，变形温度和初始应变速率对接头断后伸长率有显著影响，如图6所示. 从图6a中可看出，高初始应变速率下，温度的提高有助于断后伸长率的增加，而在10–3 s–1

的初始应变速率下则应选择合适的变形温度以得到较高的断后伸长率.这是由于高初始应变速率下，再结晶和材料内部变形的协调来不及进行，应变硬化不能充分消除，而温度的升高有助于促进晶界滑移及扩散蠕变能力的提高，并加强了动态软化作用，从而促进应变硬化的消除，有利于断后伸长率的提高. 在低初始应变速率下，随温度的升高，试样拉伸时间过长，晶粒

900)750%( A 600率长伸450后断30010−1 s−115010−2 s−110−3 s−10870880890900910920温度 T/℃(a) 母材断后伸长率90010−1 s−175010−2 s−1)%10−3 s−1( A600 率长450伸后断3001500870880890900910920温度 T/℃ (b) 焊缝断后伸长率图 6 焊缝及母材的断后伸长率Fig. 6 Elongation of weld and base metal

它们通过改变试样内部晶粒的长大程度以及再结晶程度对断后伸长率产生影响. 随着初始应变速率的降低，焊缝断后伸长率增加. 焊缝组织为细小的针状马氏体α′ 相，超塑性变形过程中将发生α′→α+β的转变，同时针状组织转变成片层状再又向等轴组织转变. 初始应变速率越低，焊缝具有越充足的时间进行组织转变，同时再结晶也进行得越彻底，焊缝断后伸长率也就更大.

从图6a可以看出，随着变形温度的升高，断后伸长率总体是上升的趋势，仅在初始应变速率为10–3 s–1

、断后伸长率在920 ℃时略有回落. 处于较高温度时，激光焊缝会被软化，温度越高软化程度越大. 随温度的升高，热激活作用增强，可降低临界切变应力并提高原子的自由能，促进晶界滑移及扩散蠕变能力的提高，此外动态回复及动态再结晶引起的软化程度也随温度的升高而增大，从而导致试样的变形能力总体上具有增强的趋势. 然而，变形过程中的晶粒长大将对焊缝的变形能力造成负面影响，并且温度越高变形速率越低时晶粒长大越严重，从而

造成焊缝断后伸长率在10–3 s–1

，900 ℃达到最大值397%，当温度升到920 ℃时反而降到387%. 因此，TC4钛合金激光焊接接头超塑性变形的最佳工艺为900 ℃，10–3

s–1

.2.2 组织演变

TC4钛合金母材及焊缝的组织如图7所示. 试验所用TC4钛合金母材原始组织是由密排六方点

10 μm10 μm (a) 母材显微组织(b) 焊缝显微组织图 7 TC4钛合金母材及焊缝的组织

Fig. 7 Microstructure of TC4 titanium alloy base metal

and weld

68焊 接 学 报第 39 卷

阵结构的α相和体心立方点阵结构的β相两相组织组成，晶粒平均尺寸在5 μm左右. 焊缝快速冷却过程中原始β晶粒内部发生马氏体相变，生成针状马氏体α′相，形成了典型的网篮状组织. 针状马氏体对焊缝产生界面强化，使焊缝强硬度升高，塑韧性略有降低.

图8为900 ℃，10–3 s–1

条件下超塑性变形后，不同变形量下焊缝的显微组织. 从图中可以清晰看出各组织的分布形态，当变形量较小时，焊缝显微组织为网篮状分布的片层组织. 这是由于原始焊缝中的针状马氏体α′相是合金元素在α相中的过饱和固溶体. 在高温作用下，焊缝中合金元素扩散速度增加，保温一段时间之后，焊缝内部相组成发生α′→α+β的相变，即是说超塑性变形后焊缝内部相组成已由原来的α′相转变成了α+β相，同时针状组织长大为片层状，如图8a所示. 当变形继续到143%时，由于应力及变形的作用，长片状组织被打碎而生成一些短小片层甚至等轴晶粒(图8b)，而更细小的组织由于塑性流动而具备了长大的空间，此时片层间的差距被缩小，但仍有大小长短之分，且组织取向的分布已杂乱无章，原始大β晶粒晶界消失. 随着变形的继续，变形量达到229%时，由图8c可以看出焊缝内有部分片层组织断成几段，在片层中间有不少等轴晶粒出现，说明此时在焊缝中发生了明显的动态再结晶，动态再结晶的发生是变形畸变能达到一定程度的结果，其发生将大大促进片层等轴化的进程，是焊缝组织等轴化的主要机制. 当变形量达到断裂时的318%时，如图8d所示，焊缝

10 μm10 μm(a) 43%(b) 143%10 μm10 μm (c) 229%(d) 318%图 8 900 ℃，10–3

s–1

条件不同变形量下的焊缝显微组织Fig. 8 Microstructure of weld under different deforma-tion of 900 °C and 10–3s

–1

内部组织已经大部分是等轴晶粒，且晶粒细小，分布均匀，即在断裂之前焊缝变形已完成动态再结晶，使得焊缝组织等轴化.

以上分析表明，TC4钛合金激光焊缝在超塑性变形过程中发生了两次重要的组织转变，其中在变形初期完成针状组织转变成片层组织；而后在变形过程中逐渐进行片层组织的等轴化. 片层组织的等轴化过程是焊缝超塑性变形的重要特征，其进程对焊缝的超塑性变形能力也有重要影响.2.3 超塑性变形机理

经分析表明，TC4钛合金激光焊缝在高温状态下发生了针状组织向片层组织转变. 其发生过程示意图如图9所示，首先在高温作用下，马氏体中的过饱和合金元素向外扩散，导致原始焊缝中的针状马氏体α′相(图9a)将转变为α相(图9b). 在内应力作用下发生片层的断裂，从而形成接头的一次转变组织(图9c).

α′αα βββ图 9 针状马氏体一次组织转变示意图

Fig. 9 Schematic diagram of acicular martensite

transformation

图10为焊缝中一次转变组织的形成过程，焊缝中的原始针状组织转变为片层组织，而热影响区由原始的等轴晶和短小针状组织转变为等轴晶、微小等轴晶和短小片层的混合组织.

20 μm20 μm (a) 变形前(b) 变形后图 10 焊缝一次转变组织的形成

Fig. 10 Formation of primary transformation of weld

随着超塑性变形的进行，片层组织将发生等轴化，将超塑性变形过程中后期，这种在应力和高温

共同作用下转变得到的组织称为“二次转变组织”. 片层在演化过程中经过断裂、解体(即晶粒从片层上分离出来)和球化过程才能最终实现等轴化.

片层的断裂是片层组织等轴化的关键步骤，它

第 9 期江训焱，等：钛合金针状焊缝组织的超塑性变形机理69

主要有两种方式进行：动态再结晶和片层间应力挤压.

动态再结晶对于片层的等轴化是一个不可缺少的过程，已往的研究表明在钛合金高温变形或超塑性变形过程中，α晶内都出现了动态再结晶. 片层受到剪切应力而发生剪切变形. 在这一过程中，处于与施加应力有利位向的片层α相首先加入到剪切变形中，同时相邻的处于不利位向的片层α相发生转动；而后片层α相内沿剪切线产生位错；同时变形过程发生动态回复，导致相交滑移面上的异号位错相互消，剩下的同号位错沿剪切线形成界面. 图11所示为片层组织的动态再结晶过程的透射电镜照片.

2 μm图 11 片层组织动态再结晶

Fig. 11 Lamellar structure dynamic recrystallization

应力挤压也是片层组织断裂的重要机制. 在超塑性变形过程中，焊缝将发生大变形，其内部组织必然存在较大的应力作用，且各片层之间的分布杂乱，很容易在某些位置产生应力集中而导致片层的断裂. 在超塑性变形的高温下，焊缝片层内部发生相变而成为两相混合物，在超塑性变形应力的作用下，细小的片层状组织容易受到剪切而发生断裂和破碎，而在片层内部也容易在α相和延展性更好的β相界面上出现滑移，片层组织在α相晶粒边界破碎，这些断裂和破碎出来的组织容易形成大致等轴的晶粒，同时也为再结晶提供了更多的形核位置而使得组织等轴化；另一方面，在高温拉伸及相变过程中，β相会楔入α片层内的晶界，在α片层表面形成沟槽，若沟槽深度等于片层厚度的一半，则β相会贯穿整个片层，也会导致片层解体，促进组织的球化，此外β相楔入使界面面积增加，使得晶界滑动更易于进行，促进了切应力下片层组织的破碎，从而有利于组织球化. 如图12所示即为焊缝片层在应力剪切和晶界滑动作用下断裂的微观照片. 因

此，在超塑成形过程中，焊缝由原始的针状组织逐渐发展成为球状+片层状组织，从而有助于焊缝超塑性变形的进行.

10 μm图 12 焊缝片层间应力挤压断裂Fig. 12 Interlaminar stress fracture

超塑性变形过程中，片层发生断裂后，在变形应力的作用下将发生解体，或者片层断裂和解体同时进行(图13). 片层断裂后，新的晶界已经形成，晶界滑动是片层解体的主要机制之一.

10 μm图 13 晶界滑移导致α片层解体

Fig. 13 Decomposition of a lamellar struc caused by

grain bamdary sliding

材料在超塑性状态下发生了软化，在应力作用下必然发生晶粒的滑动和转动. 晶界滑动对超塑性变形有两方面的作用. 一方面晶界滑移使得新生的二次转变组织离开原始相对位置，减小或消除变形应力的作用，对超塑性变形起协调作用；另一方面，二次转变组织通过晶界滑移的方式运动过程实际上是在应力的作用下运动的，运动的总体趋势是延纵向伸长、截面收缩. 因此，晶界滑动和转动对超塑性变形有直接的贡献.

大片层解体为若干小片层后，小片层最初一般不具有等轴状，还需要进一步的球化才能最终完成等轴化. 球化过程主要由两部分原因，一方面是Gibbs-Thomson效应发生作用的结果. 由于原子浓

70焊 接 学 报第 39 卷

度不同而发生晶粒边缘原子不均匀扩散，从而推动了晶粒的等轴化进程，所涉及的原子扩散过程如图14所示；另一方面是由于变形过程中，晶粒在变形应力作用下发生滑动和转动，而等轴晶粒处于较低的能量状态，更容易运动，晶粒的等轴化将降低系统的总体能量，根据最小能量定理，晶粒将逐渐等轴化(图15).

A1 原子迁移方向向β向方方移子α移迁迁子 原 原VV A1 原子迁移方向图 14 小片层球化的原子扩散过程示意图

Fig. 14 Schematic diagram of the atom diffusion

process in a small layer

10 μm图 15 焊缝片层组织解体、球化

Fig. 15 Lamellar disintegration and spheroidization

3 结　　论

(1) TC4钛合金激光焊接接试样有良好的超塑性变形能力，在10–3

~10–2

s–1

的初始应率870~920 ℃的变形温度范围内，具有12.5~69 MPa的低峰值流动应力和233%~318%的高断后伸长率. 在超塑性变形过程中，焊缝发生两次重要的组织转变，即针状组织片层化的组织转变和片层组织等轴化的组织转变.

(2) 针状组织片层化转变主要是由于在高温作

用下原始焊缝中的针状马氏体在元素扩散过程中长大，并在应力作用下破碎原始粗大β晶界，从而细化原始接头组织，生成片层组织；片层组织等轴化是由于在应力作用下，通过断裂、解体和等轴化的过程而转变成等轴晶粒. 其中片层断裂的主要机制是动态再结晶和应力挤压作用；片层解体的主要机制是晶界滑动和转动作用，接头组织的塑性流动机理为晶粒滚动和晶界滑动机理.

参考文献：

[1]郭和平, 曾元松, 韩秀全, 等. 飞机钛合金整体结构的超塑成形/

焊接组合工艺技术[J]. 焊接, 2008(11): 41 − 45, 71.

Guo Heping, Zeng Yuansong, Han Xiuquan, et al. Superplasticforming/welding combination technology of titanium alloy integ-rated structure of aircraft[J]. Welding & Joining, 2008(11): 41 −45, 71.

[2]程东海, 黄继华, 陈益平. 激光焊接头超塑性变形组织特征[J]. 焊

接学报, 2012, 33(7): 89 − 92.

Cheng Donghai, Huang Jihua, Chen Yiping. Laser welding charac-teristics superplastic deformation[J]. Transactions of the ChinaWelding Institution, 2012, 33(7): 89 − 92.

[3]Will Jeffrey, D Kistner, G Matthew. Fabrication of laser beam wel-ded superplastically formed multi-sheet structure using advanced ti-tanium alloys[J]. International SAMPE Technical Conference,1996, 28(4-7): 651 − 663.

[4]程东海, 陈益平, 胡德安, 等. TC4钛合金激光焊对接接头超塑变

形显微组织[J]. 焊接学报, 2011, 32(9): 81 − 84, 117.

Cheng Donghai, Chen Yiping, Hu Dean, et al. Microstructure ofTC4 titanium alloy laser welded butt joint under superplastic de-formation[J]. Transactions of the China Welding Institution, 2011,

32(9): 81 − 84, 117.

[5]程东海, 黄继华, 杨　静, 等. TC4钛合金激光焊接接头超塑性变

形力学行为研究[J]. 稀有金属材料与工程, 2010, 39(2): 277 −280.

Cheng Donghai, Huang Jihua, Yang Jing, et al. Superplastic de-formation mechanical behavior of laser welded joints of TC4 titani-um alloys[J]. Rare Metal Materials and Engineering, 2010, 39(2):277 − 280.

作者简介：江训焱，男，1992年出生，硕士生. 主要从事高能束焊接

及超塑性成形方面研究的工作. Email: 912193523@qq.com

通讯作者：程东海，男，副教授. Email: 70269@nchu.edu.cn

2018, Vol. 39, No. 9TRANSACTIONS OF THE CHINA WELDING INSTITUTIONIII

relative motion；microcosmic evolution

Investigation of brazing joints of Al2O3 ceramics to Kovaralloys by Ti+Nb/Mo metallization XIN Chenglai， LINing， YAN Jiazhen (School of Manufacturing Science andEngineering, Sichuan University, Chengdu 610065, China). pp45-48

Abstract: Ti+Nb/Mo thin films were deposited ontoAl2O3 ceramic by magnetron sputtering with a subsequentnickel-plating to ensure the robust brazing of Al2O3 ceramic toKovar alloy using the filler of AgCu28. Microstructures of themetallization layer and the brazing joints of Al2O3/Kovar wereinvestigated systematically by scanning electron microscopy(SEM) and energy dispersive X-ray (EDS). The results showthat the interfacial reaction layers are created between filleralloys and base materials. Interdiffusion of Ni and Cu at theinterface of AgCu/Kovar resulted in the formation of thereaction layer. The metallization layer plays an important rolein hindering the formation of intermetallic compounds andrelieving residual thermal stress at Al2O3/AgCu interface. Inaddition, the presence of eutectic region arising from nickel-plating can improve the thickness of the brazing seam andtherefore a good bonding betweenAl2O3 ceramic and Kovarwas achieved.

Key words: Al2O3 ceramics；metallization；brazejoint

；magnetron sputtering

Microstructural evolution of Cu/Sn/Cu joints and effect oftemperature on three-dimensional morphology of IMCs inpackaging technology LIANG Xiaobo， LI Xiaoyan，YAO Peng， LI Yang (College of Materials Science andEngineering,Beijing university of technology, Beijing 100124,China). pp 49-54

Abstract: A 4 μm thick Sn film was deposited on thecopper substrate by electroplating. Two copper substrates withelectroplated Sn were constituted of a Cu/Sn/Cu structure. 240°C and 1 N were chosen as soldering temperature and pressureto be soldered for different time to investigate the law ofmicrostructural evolution of IMCs. The three-dimensionalmorphology of Cu6Sn5 and Cu3Sn under different solderingtemperature(240, 270, 300 °C) were fabricated, Investigate theeffect of temperature on three-dimensional morphology. Theresults show Cu6Sn5 was planar after soldered for 30 min andturned into scallop-like with the increase of soldering time.Cu3Sn in the bottom of scallop was thicker than that in bottomof scallop on both sides. Sn was reacted with the increase ofsoldering time, Cu6Sn5 in the two side merged into a wholegradually. Increase more soldering time, Cu6Sn5 continued tobe transformed into Cu3Sn. The three-dimensional of Cu6Sn5transformed from polyhedron shape to procumbent and the sizeof Cu3Sn grains decreased gradually with the increase ofsoldering temperature.

Key words: Cu/Sn/Cu joints；Cu3Sn；Cu6Sn5；micro-structural evolution

；three-dimensional morphology

Thermal characteristics and weld formation of double-electrode micro-plasma arc welding LI Ting1

Jiankang1， HANG

， CHEN Xiujuan2， YU Shurong2， FAN Ding1

(1.State Key Laboratory of Advanced Processing and Recycling

of Non-ferrous Metals, Lanzhou University of Technology,Lanzhou 730050, China；2. School of Mechanical andElectronical Engineering, Lanzhou University of Technology,Lanzhou 730050, China). pp 55-60

Abstract: To solve the limitation about deposition rateand welding current can not be decoupled of the traditionalmicro-plasma arc welding, double-electrode micro plasma arcwelding is proposed.The article added a bypass current into thefiller wire to make a bypass arc is appeared between the wireand the tungsten. Though this method to realize the decouplingof the heat of melting base material and the heat of meltingwire. Thus, the melting speed of the filler wire is increasedwhile the current of melting base material keeps stable.Theexperimental study was carried out on the deposition rate, theheat input of the base metal and the weld formation quality ofthe double-electrode micro plasma arc welding. The double-electrode micro plasma arc welding not only maintains theadvantages of the conventional micro plasma arc welding, butalso improves the deposition rate and reduces the heat input ofthe base metal; When the other welding parameters remainunchanged, , the weld penetration and dilution rate decreaseand the forming coefficient increases with the increase of thebypass current.

Key words: double-electrode micro plasma arc weld-ing

；bypass current；heat input

Detection of non-groove butt joint feature based on cornerprinciple WANG Wenchao， GAO Xiangdong， DINGXiaodong， ZHANG Nanfeng (Guangdong Provincial WeldingEngineering Technology Research Center, GuangdongUniversity of Technology, Guangzhou 510006, China). pp 61-64

Abstract: A method for detecting and tracking thenon-groove butt joint by using the principle of corner detectionbased on line structured light vision sensing is studied. It isdifferent from the traditional line structured light sensingmethod to detect the weld position according to thedeformation feature. The proposed method applies for the factthat the laser stripe has obvious gray gradient variation in theweld. The morphological image processing method is adoptedto extract the feature of weld center. The gray value of eachcolumn in the image is calculated, and the region of interest isextracted by the central difference method. According to theprinciple of the corner detection method, the sub-pixelcoordinates of the weld center can be determined accurately.The actual position deviation of the weld is obtained by using asimple and fast system calibration. Experimental results showthat the average error can be kept within 0.1 mm by tracking abutt joint whose width is about 0.2 mm, which can meet therequirement of seam tracking precision.

Key words: seam tracking；line structured light；buttjoint weld

；non-groove；corner detection

Superplastic deformation mechanism of acicular weldmicrostructure of titanium alloy JIANG Xunyan，CHENG Donghai， CHEN Yiping， HU Dean (AviationManufacturing and Engineering College, Nanchang HangkongUniversity, Nanchang 330063, China). pp 65-70

Abstract: Laser welding seam of titanium alloy is a

IVTRANSACTIONS OF THE CHINA WELDING INSTITUTION2018, Vol. 39, No. 9

non-ideal acicular structure. The research on its superplasticdeformation mechanism can promote the application oftitanium alloy LBW/SPF technology, and also have benefits ofsignificance to the development of material formingmechanism. The results show that the laser welding of TC4titanium alloy after welding have good superplasticdeformation ability. During the deformation process, twoimportant microstructure changes are taken placed in the weld,that is, the microstructure transformation of the acicularstructure lamellae and the lamellar tissue equiaxed. Under theaction of stress, the lamellar structure is transformed intoequiaxed grains through the process of fracture, disintegrationand equiaxed. The dynamic recrystallization and compressionis the main mechanism of the lamellar fracture; the mechanismof the lamellar disintegration is grain boundary sliding androtation, the plastic flow mechanism of the weld joint is grainboundary sliding and rolling mechanism.

Key words: titanium alloy；laser welding；deformationmechanism

；superplastic deformation

Interfacial investigation and mechanical properties of Al-glass-Al anodic bonding process CHEN Daming， HULifang， XUE Yongzhi， CHEN Shaoping， WANG Wenxian (Department of Materials Science and Engineering, TaiyuanUniversity of Technology, Taiyuan 030024, China). pp 71-75

Abstract: The Al-glass-Al joint was successfullybonded by the two-step anodic bonding process. The bondingcurrent in each step of the two-step bonding process wasinvestigated. Scanning electron microscopy (SEM ) wasperformed on the interface for the Al-glass surface. Theelement profile of the transitional layer was investigated byglow discharge optical emission microscopy (GD-OES).Atomic force microscopy analysis (AFM) was done toinvestigate the surface roughness on Al-glass. Tensile testswere executed to evaluate the bonding strengths of thespecimens. The results indicated that all Al-glass jointsdisplayed a homogeneous microstructure without voids orcracks. There were no differences for the interfacialmicrostructure between the two sides of the Al. It was also

found that Al migrated into the Na+

depletion region, the

quantification of Na+

along the depth direction of Al(1)-glasswas larger than the Al(2)-glass. Atomic force microscopymapping results indicated that sodium precipitated from theback of the glass, which makes the roughness of the surfacebecome coarse. The fracture occurred at the glass-Al(2)interfacial area and the Al was destroyed.

Key words: anodic bonding；Al-glass-Al；glow dis-charge optical emission spectrometry

；MEMS

Effect of microalloying elements on the microstructuralevolution and mechanical properties of weld joints of

centrifugally cast furnace tubes LIU Chunjiao1

Bin1， CHEN Xuedong1， QIAN， CHEN Tao1， CHEN Wenhong2

(1.Hefei General Machinery Research Institute Co., ltd., NationalEngineering & Technical Research Center on Pressure Vesselsand Piping Safety, Sinopec Inspection and Assessment Centeron Furnace Tube, No. 888 West Changjiang Road, Hefei,Anhui, P. R. China, 230031；2. SINOPEC MaomingCompany, Maoming 525000, China). pp 76-82

Abstract: Microstructural evolution and mechanical

properties of weld joints of centrifugally cast furnace tubeswith different contents of Ti and W are investigated via fieldemission scanning electron microscopy (FESEM) equippedwith energy-dispersive X-ray spectroscopy, tensile testingmachine and creep testing machine. The results show that hightemperature performance of weld joints of 25Cr35NiNb+MA(micro alloy) and 35Cr45NiNb+MA furnace tube with additionof Ti and W is significantly higher than that of the weld jointswithout Ti and W. Micro alloying element Ti significantlyaffects the microstructures of weld joints. The microstructureof the original welded joints with high Ti content is NbTiC, andit partially transformed to G phase (Ni16Nb6Si7) during aging,which has poor creep resistance. Both NbTiC and NbC arepresent in the original welded joints with low Ti content, whichtotally transformed to G phase after high temperature aging.Micro alloying element W could improve high temperatureperformance of weld joints by solid solution strengthening.

Key words: micro alloying；Ti；W；weld joint；25Cr35NiNb+MA

；35Cr45NiNb+MA

Application of Snake model and genetic algorithm in

special weld seam extraction WU Xin11

Bojin2

， LI Qiang， QI

(1. School of mechanical and electronic controlengineering, Beijing Jiaotong University, Beijing 100044,China；2. School of Mechanical Engineering & Automation,Beihang University, Beijing 100191, China). pp 83-89

Abstract: Aimed at the weld vision detection problemof arc welding robot in CCD directly photographed image, analgorithm for the extraction of special weld seam track withlarge discontinuity, sharp turning point and more interferencewas proposed. The algorithm firstly use wavelet transform tosmooth the weld edge line to get the initial weld track that isvery close to the final weld, and then use Snake model andgenetic algorithm to get accurate matching and extraction ofspecial welds. Experimental results demonstrate that thealgorithm can improve the precision of special weld trackrecognition and detection, and has strong adaptability, and canalso provide some technical reference for further improving theintelligent vision detection of arc welding robot.

Key words: arc welding robot；image processing；wavelet transform

；Snake model；genetic algorithm

Microstructure and mechanical property of Cf/SiBCNcomposite joint brazed with Cu-Pd-V filler alloy LI

Wenwen1， XIONG Huaping1， CHEN Bo1， ZOU Wenjiang1

，

LIU Wei2

(1. Welding and Plastic Forming Division, BeijingInstitute of Aeronautical Materials, Beijing 100095, China；2.Science and Technology on Advanced High TemperatureStructural Materials Division, Beijing Institute of AeronauticalMaterials，Beijing 100095, China). pp 90-94

Abstract: Cu-Pd-V filler alloy was used to joinCf/SiBCN composite. Its dynamic wettability on the compositewas studied with the sessile drop method. After heating at1 170 °C for 30 min, the filler alloy showed a contact angle of57°. The microstructure and phase confirmation of the jointwere analyzed by SEM and XRD, respectively. When brazedat 1 170 °C for holding time of 10 min, the interfacial reactionsresulted in resulted in the formation of V(C,N) reaction bandwith the thickness of 1 μm at the surface of Cf/SiBCNcomposite, and the microstructure in the central part of the joint