Diffusion Bonding Between TZM Alloy And WRe Alloy By Spark Plasma Sintering

By using Spark Plasma Sintering(SPS),two experimental programs,high-temperature direct diffusion and low-temperature indirect diffusion with addition of titanium(Ti)interlayer,were emloyed to realize the effective connection of the dissimilar high-temperature structural materials,TZM alloy and WRe alloys in the present work dissimilar such high temperature structural materials.The microstructure and mechanical properties of bonded joints were analyzed by Sscanning Electron Microscopy(SEM),Energy Dispersive Spectrometry(EDS),Strength Test and other means.The best process parameters were determined and the mechanism was also explored.Without adding any interlayer,the best bonding parameters were found by analyzing the morphology,mechanical property and thermal fatigue of the joint of the disc test specimens,and successfully applied to the bonding experiment of tensile test specimens,structural test specimens and ignition test specimens.For disc test specimens,the effective connection of the TZM and WRe alloys was realizd at temperature ranges of 1300~1600 ~oC for 30 min with 20 MPa.The bonding interface is smooth,and cracks and no bonding areas are not found.The diffusion depth(Mo and W)increases with the increasing bonding temperature.And at the same bonding temperature,the diffusion depth of Mo to the WRe alloy is greater than that of W and Re to the TZM alloy.The EDS spectral lines are continuous and smooth in the TZM/WRe interface,which means the formation of molybdenum-tungsten solid solution.When the bonding temperature is 1500 ~oC,the shearing strength of the joints reached the maximum,and shear strength and three point bending strength were 497±50 MPa and 910±65 MPa,respectively;for the tensile test specimens,the WRe/TZM joint obtained by SPS diffusion bonding has good mechanical properties,and the room temperature tensile strength is 475±33 MPa;for structural test specimens,the joints interface is smooth and level,and no cracks appeared after 1500times thermal shock.It speculates that the TZM/WRe joint has excellent high temperature properties.The influence of SPS diffusion bonding temperature and the initial state of Ti interlayer on the microstructure and mechanical properties of TZM/Ti/WRe joints was studied in the present work.Experimental results show that the additions of Ti foil(Ti_f)and Ti powders(Ti_p)as the intermediate transition layer both realize the solid-state diffusion bonding of TZM and WRe alloys below the recrystallization temperature of the base metals.The TZM/Ti and Ti/WRe interfaces are free from discontinuities or microcracks at the bonding temperature range of 800~1000oC.Mo and W diffuse to the Ti interlayer and form solid solutions,and the diffusion distance increases with the increasing bonding temperature.The diffusion distance of Mo in the Ti interlayer is greater than that of W in the Ti interlayer at the same bonding temperature.In contrast to the Ti foil,the spreading of Ti powders on the bonding surface affects the physical contact between the powders and bonding surface,leading to an inhomogeneous diffusion of Mo and W in the Ti_p interlayer.When the bonding temperature is 900oC,the TZM/Ti/WRe joints obtain the maximum shearing strength at room temperature,and the shear failure occurs on the Ti/WRe interfaces by intergranular fracture and transgranular cleavage fracture.At the lower bonding temperature than 900oC,the TZM/Ti/WRe joint fracture on the Ti/WRe interface due to the insufficient diffusion of W in the Ti interlayer,and the corresponding fracture surface is even and smooth,accompanied by intergranular fracture.When the bonding temperature is higher than 900oC,however,Mo concentrate on the grain boundaries of Ti interlayer,resulting that the fracture of TZM/Ti/WRe joint occurs on the TZM/Ti interface.The shearing strength of TZM/Ti_f/WRe joint is greater than that of TZM/Ti_p/WRe joint at the same bonding temperature.