摘要
采用Cu41.83Ti30.21Zr19.76Ni8.19(at.%)非晶钎料对Ti48Al2Cr2Nb合金与ZrB2-SiC陶瓷进行真空钎焊连接,通过扫描电镜、能谱分析、X射线衍射以及万能试验机对接头的微观组织和力学性能进行研究。结果表明:TiAl合金与ZrB2-SiC陶瓷钎焊接头的界面结构为TiAl/Ti2Al/AlCuTi/(Ti,Zr)2(Cu,Ni)+TiB+TiCu/Ti5Si3/ZS。当钎焊温度为910 ℃,随着保温时间的延长,靠近ZrB2-SiC一侧反应层宽度逐渐增大,接头中弥散分部的TiB和TiCu聚集长大。接头剪切强度随着保温时间的延长先上升后降低,当钎焊温度为910 ℃,保温20 min时,接头剪切强度最大,为187 MPa,通过对各工艺的接头断口分析,发现接头均断裂在陶瓷侧,断裂方式为脆性断裂。
TiAl合金作为一种能够替代镍基合金的轻质高温合金,拥有高强度、良好的抗腐蚀性和高弹性模量等优点,这些优异的性能使得其在飞机涡轮叶片上得到广泛的应
LI
ZrB2-SiC复合陶瓷(为了叙述方便简称为ZS)作为一种高温材料广泛地应用在航空航天中,ZrB2陶瓷自身具有良好的导电性,高硬度以及耐高温性,SiC的加入提高了ZrB2陶瓷的韧
所选用的TiAl合金名义成分为Ti48Al2Cr2Nb(原子分数),通过用高纯度Ti,Al和Cr金属以及Nb-Al中间合金进行电弧熔炼来制备。为了确保成分的均匀性,将合金锭重复熔融至少四次。随后,在Ar气氛中,在1 380 ℃下热处理30 min,以消除残余应力和降低收缩孔隙
采用电火花线切割技术将TiAl合金切割成尺寸为4 mm见方和10 mm×10 mm×4 mm的样品,将ZS陶瓷切割成尺寸为4 mm见方的样品。钎焊前使用SiC砂纸将待焊母材打磨至光滑,再将待焊样品置于存有无水乙醇的超声波清洗机中清洗3 min,随后将母材与钎料装配成三明治结构,将两个4 mm见方的母材按照

图1 TiAl/CuTiZrNi/ZS钎焊接头示意图
Fig.1 Schematic illustration of the TiAl/CuTiZrNi/ZS brazed joint

图2 TiAl/CuTiZrNi/ZS钎焊工艺示意图
Fig.2 Brazing process of TiAl/CuTiZrNi/ZS brazed joint

(a) 钎焊接头整体形貌

(b) 金属侧

(c) 陶瓷侧
图3 钎焊温度910 ℃、保温10 min接头微观组织形貌
Fig.3 Microstructure of joint brazed at 910 ℃ for 10 min
对析出相进行EDS分析,结果如

图4 钎焊温度910 ℃、保温10 min钎缝XRD分析
Fig.4 XRD patterns of fracture of joint brazed at 910 ℃ for 10 min

(a) 保温10 min接头整体形貌
(b) 保温10 min ZS侧放大形貌

(c) 保温20 min接头整体形貌
(d) 保温20 min ZS侧放大形貌

(d) 保温30 min接头整体形貌
(e) 保温30 min ZS侧放大形貌
图5 钎焊温度910 ℃、不同保温时间下接头界面微观形貌
Fig.5 Microstructure of joints at different holding time and temperature of 910 ℃
结合上述分析可以发现,当钎焊过程刚开始时,加热温度较低,钎料未融化,未发生元素扩散现象。随着加热过程继续进行,钎焊温度升高,当炉内温度达到钎料熔点时,钎料开始融化并润湿母材。由于浓度梯度的存在,母材中元素向熔融钎料扩散,同时,熔融钎料中的Cu、Ti、Zr、Ni元素也向母材扩散。随着钎焊温度的继续上升,钎料完全融化,原子扩散速率加剧,TiAl合金中的Ti、Al元素继续扩散,由文献[

图6 钎焊910 ℃不同保温时间下获得的接头剪切强度
Fig.6 Variation of room temperature shear strength with different holding time

(a) 10 min宏观断口形貌

(b) 20 min宏观断口形貌

(c) 30 min宏观断口形貌

(d) 10 min微观断口形貌

(e) 20 min微观断口形貌

(f) 30 min微观断口形貌
图7 钎焊温度910 ℃、不同保温时间接头断口形貌
Fig.7 Appearance of joint fracture at different holding time of 910 ℃
从图中可以看到不同工艺条件下接头均断裂在陶瓷侧,在断口微观形貌中并未观察到韧窝等形貌,接头呈现典型的脆性断裂。裂纹一般是由脆性相萌生,随着外应力作用裂纹逐渐延伸至母
(1)采用Cu41.83Ti30.21Zr19.76Ni8.19非晶钎料成功实现了TiAl/ZS真空钎焊连接,接头结合良好,并未发现孔洞和裂纹等缺陷。典型的接头界面结构为:TiAl/Ti2Al/AlCuTi/(Ti,Zr)2(Cu,Ni)+TiB+TiCu/Ti5Si3/ZS。
(2)钎焊工艺影响接头微观结构和力学性能,随着保温时间的延长,Ⅰ区和Ⅲ区宽度逐渐增大,Ⅱ区宽度逐渐较小,中心反应区中TiCu和TiB相尺寸增大,接头力学性能先上升后下降。当钎焊温度910 ℃、保温20 min接头力学性能达到最大值为187 MPa。对各工艺参数下TiAl/ZS接头断口进行分析,发现断口均断裂在陶瓷侧,属于脆性断裂。
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