The Effect Of Interstitial Elements (H, N, O) On The Microstructure And Mechanical Properties Of The Casting Titanium Alloy

Compared with the wrought titanium alloy, the casting titanium alloy can increase the utilization efficiency of the raw material and reduce the cost significantly. Especially, when the hot isostatic pressing technology is applied in the products of the casting titanium, the mechanical properties and the production stability of the titanium alloy improve greatly, which lead to the wide application of the casting titanium production. However, during the foundry production, the titanium casting is inevitably contaminated by the interstitial element (H, N, O). So in the present investigation, the effect of interstitial elements (H, N, O) on the microstructure and mechanical properties of the casting titanium alloy was studied by vacuum self-consuming arc melting furnace and hydrogen-charging treatment. That provides the experience for the controlling of the interstitial elements in reasonable amount, and then contributes to fabricate the casting titanium production with low content of interstitial elements.The study on the effect of hydrogen on the casting titanium alloy shows that the influence of hydrogen on the titanium alloy with a phase is rather greater than that on the titanium alloy withα+βstructure. After hydrogenation, TiH₂ phase is formed in the ZTA1 and ZTA7 alloy, and the amount of the TiH₂ precipitates increase with the increase of the amount of the hydrogen, but there is no new phase precipitates in the ZTC4 and ZBT22 alloy. With the increase of the hydrogen content, the tensile strength improves significantly, but the elongation and contraction of area decrease.The research on the effect of nitrogen reveals that the TiN_0.3 phase appears in the ZTA1 alloy, when the nitrogen content comes to 0.08 wt%. There is no new phase formation in the ZTC4 alloy, if the nitrogen content is less than 0.072 wt%. With the increase of the nitrogen content, the tensile strength and yield strength improve simultaneous, but the elongation and the contraction of area decrease obviously.The investigation on the influence of the oxygen shows that when the oxygen content in the ZTA1 and ZTC4 alloy is less than 0.38 wt% and 0.35 wt% respectively, the effect of oxygen on the microstructure of the alloy is very little. The tensile strength and yield strength of the ZTA1 and ZTC4 alloy improve obviously, but the elongation and the contraction of area decrease, with the increase of the oxygen content.Because the oxygen and nitrogen both can stabilize the a phase, in the present investigation the oxygen equivalent is introduced in the alloy to study the effect of the element on the mechanical properties of the titanium alloy. The results reveal that the casting titanium production can obtain well balance between strength and ductility, when the oxygen content is in the range of 0.13%～0.18%.