Peculiarities of Structure of Electron Beam Welded Joints

Peculiarities of Structure of Electron Beam Welded Joints on Titanium Alloys (Ti-Si-X) with Disperse Strengthening Aim of the present work was investigation of the peculiarities of structure formation in joints of titanium alloys of Ti-Si-X system with disperse strengthening. Phase and chemical composition, structure and microstructure of base metal and welded joints, made by electron beam welding, were investigated. A local heat treatment was carried out for stabilizing of metal structure after welding. The objects of investigation were welded joints of three titanium alloys: № 1 – pseudo  (Ti-5,64Al-2,21Sn-3,53Zr-0,43Mo-0,95V-0,56Si); № 2 – pseudo  (Ti-5,22Al-3,33Sn-4,24Zr-0,77Nb-0,13Mo-0,61V-0,57Si); № 3 - α+β alloy: (Ti-4,29Al-4,39Sn-5,95Zr-4,26Nb-1,57Mo-0,68V-0,35Si); Facilities for electron beam welding HEAT TREATMENT OF pseudo  AND α+β TITANIUM ALLOYS Effect of LHT on the structure of the weld joint for example, α + β alloy before LHT after LHT Scheme of LHT Place temperature measurement Weld metal LHT increases structural homogeneity of the welded joints and reduces the probability of crack formation. It has beneficial effect on the mechanical properties For the investigated titanium alloys the following heat treatment was carried out: preliminary LHT till 2000C , welding → LHT till 7500C (aging 5 min) and cooling in a vacuum Microhardness of the titanium alloys weld joints alloy № 1 and №2 load of 100 g, 0.5 mm step alloy № 3 - load of 100 g, 1.0 mm step Before LHT After LHT Microhardness of the welded joints was investigated. It was determined, that the microhardness in weld metal is higher than that in HAZ and base metal due to increasing of amount of disperse particles and formation of  - phase which has high hardness and low ductility. ● top of weld center of weld ▲ - the root of the weld Mechanical properties Tested specimens for impact strength (a) and for tensile test (b) All investigated specimens were broken in a base metal zone. It indicates a high quality of the welded joints. Mechanical properties of welded joints and base metal of titanium alloys (Ti-Si-X system with disperse strengthening) Analysis of the results showed that mechanical properties of weld joints all investigated titanium alloys Ti-Si-X were about 93% of the base metal. The α + β Ti alloy has a maximum strength, but lower impact strength than the pseudo α - Ti alloys. Investigation of FRACTURE surface OF pseudo α TITANIUM ALLOYS №2 Mapping shows the distribution of reinforcing in the area Fractography image of pseudo α titanium alloy № 2: a - secondary electron image; b – f - characteristic mapping (b - Ti, c - Si, d- Al, e - V , f – Zr) The analytical range of particle composition The distribution of reinforcing disperse phases (Ti,Zr)5Si3 Complex silicides (Ti, Zr)5-Si3 with regular geometric shape and size from 0.1 to 0.7 microns were revealed by spectral analysis . They are randomly located in the metal. These particles are coherently linked to the matrix and enhance durability. CONCLUSIONS The formation of structural and chemical heterogeneity of the phase composition and mechanical properties of titanium alloys electron beam welded joints with fine dispersed phase strengthening were investigated It was determined that, formation by electron beam welding of narrow weld ( 3mm), small HAZ, and reduction of grain growth in these areas, increases of mechanical properties of the welded joints. The results revealed promising development of such alloys and the possibility of the developed technologies, in case of further research, in the manufacture of ANTONOV Company, KyAVO "AVIANT", SPA "Yuzhmash", JSC "Motor Sich", SPA "Star-Mashproekt" for the products of aerospace engineering, energy engineering, automotive industry (new generation engines for Ukrainian vehicles and helicopters). ▪ HV HV Tunyk V., Grigorenko S., Zadorozhnyuk O., Vrzhizhevsky E. E. O. Paton Electric Welding Institute of the NAS of Ukraine http://paton.kiev.ua; [email protected]