THE INFLUENCE OF TEMPERATURE AND TIME OF PRESSURE WELDING ON THE FORMATION OF A JOINT BETWEEN THE TITANIUM ALLOY AND Ni-2 %Cr ALLOY

The authors studied the solidphase joining of the PT3V (Ti-4.2Al-1.6V) titanium alloy and 12H18N10T stainless steel through the nanostructured interlayer of Ni-2 % Cr alloy. In the process of joining at the temperatures of 650, 700, 750 and 800 °C, the Ti₂Ni, TiNi and TiNi₃ intermetallic layers are formed in the contact zone. It is known, that during pressure welding of the titanium alloy and nickel, the solid layers of these intermetallides are formed at the bond interface. The destruction occurs just along these layers. The most probable cause of destruction is a jump of the coefficient of thermal expansion (CTE) during the austenitic-martensitic transformation with the TiNi layer formation, which results in the cracks in the adjacent brittle Ti₂Ni and TiNi₃ layers at the stage of cooling from the welding temperature. The alloying of TiNi with chromium within 1–2 % leads to the significant decrease in the temperature range of austenitic-martensitic transformation.

At the TiNi₃/Ni-2 % Cr interface, a thin TiCr₂ layer is formed, which prevents the diffusion of chromium and nickel into the Ti₂Ni, TiNi, and TiNi₃ intermetallic layers. This leads to the formation of thinner layers of intermetallides at the PT3V/Ni-2 % Cr contact zone. The application of Ni-2 % Cr alloy led to the alloying of TiNi intermetallic chromium in the amount of 0.2–0.6 at % that lowered the temperature of austenitic-martensitic transformation below the room temperature and changed the appearance and location of cracks in the weld seam. When applying the Ni-2 % Cr alloy interlayer the greatest tensile strength of 390±20 MPa is achieved after welding at T=700 °C during 20 min. The increase of holding time at the temperature of 700 °C or the increase of temperature lead to the strength reduction.