Mechanical and Structural Properties of Joints of Stainless Steel and Titanium Brazed with Silver Filler Metals Containing Tin

Abstract

WŁAŚCIWOŚCI MECHANICZNE I STRUKTURALNE ZŁĄCZY STALI NIERDZEWNEJ I TYTANU LUTOWANYCH SPOIWAMI SREBRNYMI ZAWIERAJĄCYMI CYNĘJoining of titanium and its alloys with stainless steel by means of welding methods and obtaining joints characterised by good operation properties constitutes today a significant problem in relation to research and technology. Apart from specialised welding technologies, brazing is one of the basic methods applied for joining these having diversified physical and chemical properties material combinations. Brazing is especially recommendable in the production of systems and heat exchangers for chemical industry as well as subassemblies of nuclear reactors and aircraft engines and accessories. Similarly as in case of welded joints of stainless steel and titanium, the mechanical properties of brazed joints of the aforesaid materials are connected with the occurrence of hard and brittle intermetallic phases appearing in the form of continuous layers on braze boundaries.This work reports testing of strength properties and investigation of structures of vacuum-brazed joints of stainless chromium-nickel steel (X6CrNiTi18-10) and titanium (Grade 2) at 820÷900• C for 5÷20 min by means of silver brazing filler metals with tin grade B-Ag68CuSn-730/755 (Ag68Cu28Sn4) i B-Ag65CuSnNi-740/767 (Ag65Cu28Sn5Ni2). These filler metals assure better wettability of stainless steel hard to wettable in vacuum brazing.The structural tests were conducted taking advantage of optical microscopy; by means of a scanning electron microscope (SEM) and energy-dispersion spectrometer (EDS).The test results allowed to specify the most convenient brazing parameters of the tested material system from the mechanical properties point of view and to determine of qualitative and geometrical changes in joint structures depending on temperature and brazing times.

Brazing of Titanium with Aluminium Alloys

“…A clearly negative effect on the strength of joints is characteristic of hard and brittle intermetallic phases with titanium such as Ti-Cu, Ti-Fe (Ti-Fe-Cr, Ti-Fe-Ni), Ti-Ni, Ti-Cr and Ti-Al and well as solid solutions based on these phases. The lowest brittleness and hardness were characteristic of Ti-Ag type phases, which was also determined in tests previously conducted at Instytut Spawalnictwa and dedicated to the kinetics of the formation of intermetallic phases and their effect on the operational properties of brazed joints made of titanium and stainless steel using silver brazing metals [17,18].…”

“…The specimens were placed in special holders designed in a manner making it possible for the specimens to be subjected to shear forces only, without bending. Previous own research and information contained in reference publications indicate that a shear test performed in such a manner is advantageous for dissimilar joints, forming brittle intermetallic phases with the filler metal [16][17][18][19].…”

“…Such a specimen type enabled the economical disposal of base materials and filler metals. The use of appropriate tooling during strength tests enabled the obtainment of pure shearing and favoured an uninterrupted course of diffusion processes in a braze, ensuring high joint repeatability [16][17][18][19]. Directly before brazing, elements to be joined underwent chemical etching.…”

“…The research-related tests presented in the article are the continuation of previously conducted research related to brazing titanium with other metals [16][17][18].…”

Microstructure and Mechanical Properties of Joints of Titanium with Stainless Steel Performed using Nickel Filler

“…Such types of joints have applications in aerospace, chemical and nuclear industries [1][2][3][4]. Conventional fusion welding is not a feasible technique to join these materials due to the different problems like formation of stress concentration at the bond interface and development of chemical heterogeneities [5][6][7]. Hence, diffusion brazing offers a feasible solution to overcome these problems [8].…”