Joining Of Titanium And Steel Dissimilar Materials By Laser Additive Manufacturing

Laser melting deposition(LMD),as a main additive manufacturing technology,is one of the most suitable technologies for manufacturing dissimilar materials.It has become an important method to manufacture new new materials due to its advantages in achieving complex structures,precision molding and reducing material waste.At present,laser additive manufacturing technology has been applied in the fabrication of titanium alloy and steel.However,few researches have been carried out on the joining of titanium and steel.In this paper,direct joining of titanium and steel,and joining of titanium and steel using interlayers,such as Ni,Cu and its alloys,have been investigated using LMD technology with medium carbon low alloy steel as the substrate.The influence of laser process parameters on the titanium/steel interface has been studied.Suitable laser additive manufacturing joining parameters,including laser power,scanning speed and powder feeding rate,were determined based on the interfacial reactions and joining properties.The results show that for the direct joining of titanium and steel samples,the metallurgical reaction between Ti and Fe elements produces a hard and brittle Ti-Fe intermetallic compound at the interface,which leads to the interface cracking under the thermal stress generated during the laser additive manufacturing process.The effective joining of titanium/steel dissimilar materials cannot be achieved.When Ni and Cu are used as interlayers,Ni and Cu can both bond well with the steel substrate,and the strength of the Cu/steel interface can even reach 470 MPa.However,the Ni/Ti and Cu/Ti interfaces usually cannot achieve good bonding,especially when a single layer of metal is used as the interlayer,during which the diffusion of Fe and Ti cannot be avoided,resulting in a brittle interface,which fractures during the cooling process after fabrication.When a double layer of Cu alloy is used as the interlayer,the Ti and Fe elements can be effectively isolated and a Cu/steel interface free of obvious holes and crack defects can be obtained.At the same time,the microstructures are significant different between the two layers of the cu alloy interlayer.The first layer shows a fine equiaxed grain structure due to the heterogeneous nucleation of the formed Fe-rich particles,while the second layer shows a slightly coarser columnar grain structure due to the directional heat flow.