Microstructure And Element Diffusion Behavior Of Fine-grained Titanium Alloy After Superplastic Diffusion Bonding

Titanium alloy is an important metal materials in the 20^th century.High strength,low density and excellent corrosion resistance are the main properties that make titanium attractive for a variety of application.Superplastic diffusion bonding behavior of fine-grained TC4 alloy and TC21 alloy has been investigated.The diffusion bonding tests were carried out at different experimental parameters.Microstructure observation using optical microscope(OM),Scanning electron microscope(SEM) and electron probe microanalyzer(EPMA) was carried out to evaluate the superplastic diffusion bonding,microstructures,element distribution and fracture mechanism, etc.The results demonstrate that TC4 diffusion bonding joint have maximum shear bond strength at 920℃.Presents a mixture of plastic fracture and brittle fracture in bonding joint.It also shows that the TC4 alloy joint with finer grain size had much higher bonding rate.Microstructure analysis demonstrate that in superplastic diffusion bonding of TC4 alloy and TC21 alloy the samples with finer grain size always had a higher quality diffusion bonding joint.This result can be attributed to that the alloying elements diffused more easily through the grain boundaries in the sample with a finer grain size,which will result in a higher bonding rate.The fine-grained microstructure with equiaxed grains was appeared in the joint,because the joint experienced some plastic deformation under the applied pressure on the both sides,which induced the dynamic recrystallization.In the TC4 alloy element distribution analysis of the joint demonstrate that titanium elements transited smoothly and the distribution of aluminum,vanadium elements have a gradient variation across the bonding joint.Grads of aluminum elements was smaller than that of vanadium elements,which showed that aluminum elements diffused more easily.There were moreβphases distributed in the TC21 alloy diffusion bonding joint,which means that stable elements inβphases of TC21 alloy behaved actively and they had a high diffusion rate.