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

本研究的目的是为了弄清钛与钢扩散结合过程中结合特性与中间层形成之间的关系。深入研究了氮对基体钢的影响，即与TiN层形成的扩散键合，以及Ti-6Al-4V合金、Fe-Si合金、Fe-Cr合金等插入金属的影响。研究结果如下：1。由于扩散结合Ti/钢接头在Ti侧形成Kirkendall空洞，降低了接头的结合强度。扩散键合Ti/软氮化钢和Ti/离子氮化钢接头在界面处形成锡层。然而，在这种情况下，粘结强度的提高是无法实现的。由于TiN层抑制Fe或Ti向其他贱金属以及TiC的扩散，因此TiN层具有防止脆性β -Ti和Ti-Fe金属间化合物形成的作用。扩散键合Ti-6Al-4V合金/S20C接头的界面处形成TiC层，而在1000^ C处形成TiC层和TiFe_2层。接头的抗拉强度随温度的升高而升高，但随温度的升高而降低。这说明TiFe_2层与TiC层共存对接头强度的影响要大于单独形成的TiFe_2层。在0.8kgf/mm^2的温度下，在1000^ cc下结合30min的Ti/Fe-2%Si合金接头的结合强度达到了27 kgf/mm^2。这解释了TiC层的形成和Kirkendall空洞的预防的显著影响。在0.8kgf/mm^2的温度下，在1000^ cc下焊接30min的Ti/Fe-30Cr合金接头的最大结合强度为34 kgf/mm^2。得到较高结合强度的原因可能是850^ C时未结合面积的减小和1000^ C时中间层生长的抑制。

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.