Ti-Ni-Nb钎料钎焊βNb-Ti合金接头的微观组织及力学性能

Microstructure and Mechanical Properties of βNb-Ti Joints Brazed with Ti-Ni-Nb Filler Metal

采用65Ti-25Ni-10Nb (%,质量分数)钎料对体心立方结构的βNb-Ti固溶体合金进行钎焊,研究了钎焊条件对接头微观组织和力学性能的影响规律。研究发现,接头焊缝组织主要由{(Nb,Ti)+TiNi}共晶组织、(Nb,Ti)固溶体相、 TiNi相、 Ti2Ni相和富Ti相组成。随着钎焊温度的升高和钎焊时间的延长,钎焊过程中钎料和基体中的合金元素发生互扩散,焊缝组织中的{(Nb, Ti)+TiNi}共晶组织和TiNi相逐向Ti2Ni相转变,并在Ti2Ni相内部逐渐析出富Ti相。同时,基体中的其他合金元素如Al, V和Cr元素向钎料中扩散。随钎焊温度的升高或保温时间的延长,钎焊接头的剪切强度呈先增加后降低的趋势。这主要是由于Ti2Ni相具有较高的剪切模量,其含量的增加使钎焊接头的剪切强度增加,但随后Ti2Ni相内部析出富Ti相使焊缝内应力增加,导致钎焊接头的剪切强度迅速降低。在1150℃钎焊15 min时, 65Ti-25Ni-10Nb/Nb-Ti钎焊接头的室温剪切强度可达到617.7 MPa。

The 65 Ti-25 Ni-10 Nb(%, mass fraction) brazing alloy is used to join bcc structure βNb-Ti solid solution alloy, the effects of brazing condition on the microstructure and mechanical properties were investigated. It was found that the brazing joint mainly consisted of the eutectic {(Nb,Ti)+TiNi} phase,(Nb,Ti) solid solution, TiNi, Ti2Ni and Ti-rich phases. With the increasing of brazing temperature and holding time, the alloy elements in the brazing alloy and the substrate diffused to each other during the brazing process. The microstructure of brazing joint was transformed from {(Nb,Ti)+TiNi} eutectic phase and TiNi intermetallic compound to Ti2Ni phase, and then the Ti-rich phase was precipitated in the Ti2Ni phase. Meanwhile, the elements in the substrate, such as Al, V and Cr diffused into the brazing alloy. With the increasing of brazing temperature and holding time, the shear strength of brazing joint increased first and then decreased. The increase of strength was mainly attributed to the increasing of Ti2Ni content because of its high shear modulus. However, the shear strength of brazing joint was decreased as the rich-Ti phase precipitated in Ti2Ni phase, which increased the internal stress of the joint. The room temperature shear strength of 65 Ti-25 Ni-10 Nb/Nb-Ti brazing joint reached 617.7 MPa at 1150 ℃ holding for 15 min.