原位自生TiB含量对TiAl钎焊接头的影响

Effect of in-situ synthesized TiB content on TiAl brazed joint

采用TiH_(2)-65Ni(质量分数,%)+TiB_(2)粉末钎料在(1230℃,10 min)条件下钎焊连接Ti-47Al-2Nb-2Cr-0.15B(摩尔分数,%)合金,研究TiAl钎焊接头的界面组织、形成机制及其随原位自生TiB含量(体积分数0~40%)的演化过程,分析钎焊接头的界面组织与抗剪强度的内在联系,并探究TiB晶须在钎焊接头中的强化机制。结果表明:TiAl钎焊接头均由三个界面反应层组成,其主要物相为Al_(3)NiTi_(2)、Ti_(3)Al和TiB。随着TiB体积分数(0~20%)的增加,TiB晶须细化组织、强韧化作用增强,这有利于TiAl钎焊接头抗剪强度的提高,TiB体积分数为20%时接头抗剪强度达最大值332.54 MPa;当TiB体积分数分别增加至30%和40%时,TiAl钎焊接头脆化,产生孔洞,导致接头抗剪强度分别下降至206.75 MPa和170.43 MPa。TiAl钎焊接头均脆断于以连续块状的脆硬Al_(3)NiTi_(2)为主要物相的等温凝固层Ⅱ中。

TiH_(2)-65Ni(mass fraction,%)+TiB_(2)composite powder fillers were used to braze Ti-47Al-2Nb-2Cr-0.15B alloy at 1230℃for 10 min.The interfacial microstructure and formation mechanism of the TiAl brazed joint and its evolution process as a function of the in-situ synthesized TiB content(volume fraction of 0−40%)during brazing were investigated.Besides,the relationship between interfacial microstructure and shear strength of the TiAl brazed joint as well as the strengthening mechanism of in-situ synthesized TiB whiskers were analyzed.The results show that TiAl brazed joints are divided into three interfacial reaction layers and mainly consisted of Al_(3)NiTi_(2),Ti_(3)Al and TiB.The ability to refine microstructures as well as strengthening and toughening effects of TiB whiskers increase with increasing the in-situ synthesized TiB content(volume fraction of 0−20%),which is beneficial to improve the shear strength of the TiAl brazed joints.The maximum shear strength of 332.54 MPa is obtained when the in-situ synthesized TiB content is 20%.When the TiB whiskers content increases up to 30%and 40%,the TiAl brazed joints become embrittle and form microvoids,resulting in reduction of the shear strength to 206.75 MPa and 170.43 MPa,respectively.The brittle fracture occurs in the isothermal solidification layerⅡoccupied with continuous block brittle hard Al_(3)NiTi_(2)after shear tests for the TiAl brazed joints.