Study On The Uniformity Of Structure And Mechanical Properties Of Tc4-Dt Alloy Deposited By Cmt Process

TC4-DT alloy is developed based on TC4 alloy, with medium strength and high damage-tolerance, showing a great promise to be widely used in aerospace field. However, the traditional method to fabricate large and complicated parts has the problems of hot working difficulty, long processing cycle, low "buy-to-fly" ratio and high-cost. Additive manufacturing (AM) technology is a good alternative and has been used to manufacture titanium parts since year 2006. Compared to other AM technologies, cold metal transfer mode wire and arc additive manufacturing (CMT WAAM), as a kind of gas metal arc welding (GMAW) technology, has several advantages like simple structure, good spatial accessibility and high efficiency. In this study, a TC4-DT deposit was fabricated by CMT WAAM method. The macrostructure and microstructure, texture, and tensile properties in the overlapping zone and ordinary deposition zone were investigated and compared. The bottom of the ordinary deposition zone consisted of columnar and equiaxed prior beta grains, and in higher zone the coarse equiaxed prior beta grains were in the majority. The microstructure of the ordinary deposition zone was mainly characterized by basketweave alpha phase platelets. Microstructure of both sides of the overlapping line was characterized by a mixture of fine basketweave, lamellar and coarse basketweave a phase due to temperature gradient. Transformed alpha texture from {001}(beta)//Z silk texture existed in different zones, and the texture of overlapping zone was complicated due to the complexity of heat dissipation conditions, including transformed a texture and other complicated texture. EBSD results showed that there was a strong < 0001 >(alpha)//X texture at the overlapping line, resulting in low Schmid factors for both prismatic slip and basal slip at the overlapping line, hindering the slip of dislocation. Combined with the Hall-Petch relationship, it was concluded that the prior beta grain boundary and the overlapping line were main factors affecting the uniformity of mechanical properties. The average effective dislocation slip distances in different zones had the following relationship: overlapping zone.