Report on an Investigation of Brittle Nuggets in Spot Welds of Titanium with Other Metals, Especially Stainless Steel

摘要

The investigation comprised a microscopical study of spot welds made between titanium and stainless steel (and some other metals), together with a survey of the literature with the hope of finding an explanation of the brittle weld nuggets encountered. The outstanding features of the brittle spot welds were: (1) Melting had largely, if not wholly, been concentrated in the titanium and while melted titanium had penetrated into the stainless steel (or other second metal) no evidence of the reverse action was seen. (2) The nugget metal had evidently been very mobile, which suggested that it was not a high-melting point intermetallic compound. (3) The general etching behavior and cracking mode of the nugget metal suggested that it might well be titanium which had been embrittled by absorption of an interstitial element by diffusion and most probably was alpha-titanium stabilized by oxygen. If titanium is to be welded successfully to other metals such as stainless steel, special techniques need development. Possible means include welding to an easily deoxidized intermediary. Aluminum and magnesium appear generally not to be recommended because of their low melting temperatures. Silver recommends itself because of its auto-deoxidation characteristics. Iron thoroughly deoxidized, using first mild deoxidants and then excess of magnesium or calcium silicide should serve equally and would have the additional advantage of discouraging alpha stabilization, even if oxygen still reached the titanium in dangerous amounts. (Author)