Effects of Nitrogen in Steel and Insert-metals on Diffusion Bonding Characteristics of Titanium to Steel Joint

点击翻译按钮获取中文摘要

The purpose of the present investigation is to make clear the between the bonding characteristics and the formation of interlayer in the diffusion bonding of titanium to steel. We have thoroughly the problem of 1) effect of nitrogen in base metal steel, that is the diffusion bonding with the format ion of TiN layer, and 2) effect of insert-metals, such as Ti-6Al-4V alloy, Fe-Si alloy and Fe-Cr alloy. The results are as follows :1. Since Kirkendall voids are formed at the Ti side in the diffusion bonded Ti/steel joint, the bond strength of the joint is lowered.2. Tin layer is formed at the bond interface in diffusion bonded Ti/soft-nitriding steel and Ti/ion-nitriding steel joints. Improvement of the bond strength, however, cannot be accomplished in this case. Since the TiN layer suppresses the diffusion of Fe or Ti into the other base metals as well as TiC, the TiN layer has the effect of preventing the formation of the brittle beta-Ti and Ti-Fe intermetallic compounds.3. TiC layer is formed at the bond interface in diffusion bonded Ti-6Al-4V alloy/S20C joint bonded at 850^ﾟC, but TiC and TiFe_2 layers are formed at 1000^ﾟC. The tensile strength of joints increased with bonding temperature below 900^ﾟC, but above 900^ﾟC decreased with rise in bonding temperature. This fact suggests that the TiFe_2 layer coexisting with the TiC layer had more harmful effect on the joint strength than those formed individually.4. Higher bond strength of 27 kgf/mm^2 was obtained in Ti/Fe-2%Si alloy joint bonded at 1000^ﾟC for 30min under 0.8kgf/mm^2. This accounts for the pronounced effects of the formation of the TiC layer and the prevention of the Kirkendall voids.5. The maximum bond strength of 34 kgf/mm^2 was obtained in Ti/Fe-30Cr alloy joint bonded at 1000^ﾟC for 30min under 0.8kgf/mm^2. The reason why higher bond strength has obtained may be due to the effect of the decrease of unbonded area at 850^ﾟC and the depression of the growth of the interlayers at 1000^ﾟC.