Question

11. (a) Describe the challenges in obtaining dissimilar weld joints of e.g. stainless steel and [5 marks] titanium (b) From the phase diagram shown in Figure 4, what are the typical intermetallic phase(s) that will form during fusion welding of steel and titanium, and what are their typical chemical compositions? [3 marks] 1700 1670 Liquid (L) 1536 1500 LFe2Ti 7° L+FezTi L+aFe 1317 1300bcc (aFe10 12 89 27.6 35-2 49-7 L+ BTi 16 L+FeTi 1085 525 1100 bcc (ATi) Fe2TiFeTi aFe Fe2Ti 900 BTi FeTi 882 BTi+ aTi FeZTi (A) Fe Ti- 700 590 FeTi (aTi) 500l Fe 10 20 30 40 50 70 Ti 60 80 90 Atomic Percent Titanium Fig.4 Phase diagram of Fe-Ti. Temperature,c

Answer 1

Nickel-base alloys such as Monel and Inconel can be successfully welded to low-alloy steel by using the Monel analysis of filler material when using any of the arc welding processes. In the case of Inconel to mild or low-alloy steel the Inconel base electrode would be used. The same situation applies also to the welding of Inconel or Monel to stainless steels. Here the Inconel or Monel type electrode is used.

Intermetallic compounds (IMC) are generally considered detrimental to joint properties. They are usually very brittle and their thermo-mechanical properties are often different; their low thermal coefficient weakens the bond between the IMC and the alloy whereas their high electrical resistivity can lower a joint electrical conductivity. For some dissimilar material combinations the formation of intermetallic compounds is unavoidable during cooling from their liquid state

Key Findings

Joining of titanium directly to stainless steel by friction welding is not immediately suitable for industrial application as welds fail due to brittle fracture with joint tensile strengths below 85% of parent values. A study on single interlayers was carried out.