Microstructure and properties of ultra-high strength diffusion-bonded joint between TC21 titanium alloy and G50 steel
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摘要: 使用改进的真空扩散焊接方法制备了TC21钛合金及G50高强钢的超高强扩散焊接头。在刚性模具约束下，以V/Cu为过渡层，在915 ℃保温60 min进行焊接，焊接压力为20 MPa。与传统扩散焊工艺不同，待焊件接头处于三向压应力状态，使焊接界面处金属塑性流动及元素扩散更充分，可有效消除界面孔洞、微孔等缺陷，所制备的接头抗拉强度达752 MPa，为目前研究报道的钛钢接头强度最高值。界面分析显示，TC21/V、V/Cu界面处无析出相，Cu/G50界面处析出富铁相，拉伸时接头从富铁相处断裂。Abstract: An ultra-high strength joint between TC21 titanium alloy and G50 high-strength steel had been prepared by an improved diffusion bonding in this study. Under the constraints of a rigid mold, the diffusion bonding using the V and Cu as interlayers was carried out at 915 ℃ for 60 minutes with an axial load of 20 MPa. Unlike the traditional diffusion bonding processes where the joint was under unidirectional compressive stress, the bonded samples in this study were subjected to triaxial compressive stress state, which promoted more sufficient metal flow and elemental diffusion at the interfaces. This effectively eliminated interfacial defects such as voids and micro-pores. The tensile strength of the joint was as high as 752 MPa, which was so far the highest that have been reported in the literature for the joints between titanium and steel prepared by diffusion bonding. The interface analysis showed that there were no precipitates at the TC21/V and V/Cu interfaces, and Fe-rich precipitates were observed at the Cu/G50 interface. In the tensile test, the fracture occurred in the interface between Cu and G50, resulting from the Fe-rich precipitates.
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图 3 取样位置及试样尺寸（单位：mm)
（a）取样位置；（b）试样尺寸
Figure 3. The sampling position and dimension of tensile specimen
图 4 接头组织形貌
（a）接头金相图；（b）接头SEM图；（c）TC21/V界面放大图；（d）界面线扫结果；（e）V/Cu界面；（f）Cu/G50界面
Figure 4. The microstructure morphologies of the joint
图 6 TC21/V/Cu/G50扩散焊接头断口形貌
（a）宏观断口；（b）断口SEM图；（c）断口析出相形貌；（d）富铁析出相成分
Figure 6. Fracture morphology of TC21/V/Cu/G50 diffusion bonded joint
表 1 TC21钛合金及G50高强钢力学性能
Table 1. Tensile properties of the base metals of TC21 and G50
基材 抗拉强度/MPa 屈服强度/MPa 延伸率/% TC21 1262 1117 12.5 G50 1750 1510 12.3 
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表 2 TC21钛合金及G50高强钢基材化学成分
Table 2. Chemical compositions of the base metals of TC21 and G50
% 基材 Fe Ti Al Ni Nb Cr Mo Zr Sn Si Mn C TC21 Bal. 6.64 1.78 3.18 2.10 1.96 0.01 G50 Bal. 4.51 0.03 1.10 0.60 1.80 0.70 0.29
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表 3 TC21/V/Cu/G50扩散焊接接头力学性能
Table 3. Mechanical properties of TC21/V/Cu/G50 diffusion bonded joint
MPa 编号 抗拉强度 1# 756 2# 751 3# 749 平均值 752
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