Investigation Of Fatigue Properties Of Ti-6Al-4V Alloy Fabricated By Electron Beam Melting

Electron Beam Melting?EBM?is one of the most rapidly advanced manufacturing technologies,and it is widely used in medical,aviation,automotive and other fields.In this paper,the different sizes of the Ti-6Al-4V alloy samples were produced by EBM using Ti-6Al-4V ELI power in order to study the microstructure of the Ti-6Al-4V alloys.EBM Ti-6Al-4V alloy mainly consists of?lamellas.There is a small amount of?phase among?lamellas.The hot isostatic pressing treatment and heat treatment can lead to?lamella thicker.However,after hot isostatic pressing treatment,the porosity defects can be closed and it can improve the density of the samples.And these samples were carried out the fatigue crack growth test,fatigue notch sensitivity test and fracture toughness experiment in order to find the influencing factors.From the result of the fatigue crack growth test,we can find the influencing factors of fatigue crack growth.In stress intensity factor??K?<18MPa·m^1/2 stage,the fatigue crack growth rates of two different samples were different,because the thickness of?lamella and porosity defects replacing the plastic zone size ahead of fatigue crack tip become the main factors.However,the influence of the thickness of?lamella and the pore detects on the crack growth tare decreases with the increasing of?K.It is worth noting that the pore detects become the mainly influencing factor.From the result of the fatigue notch sensitivity test,we can find the influencing factors of fatigue notch sensitivity.Compared to the as-fabricated samples,the HIPed samples are more sensitive to notch.There are two reason leading to his phenomenon.One is that after hot isostatic pressing treatment,the porosity defects can be closed,which can avoid the formation of the crack source directly in the pores for the smooth samples,so it can improve the fatigue strength of smooth samples.The other is that after hot isostatic pressing treatment,the thickness of?lamella will be increasing,the number of?lamella will decrease at the certain distance,which can decrease the fatigue strength of notch samples.Because the as-fabricated samples have the porosity defects that can lead to the secondary crack.And then it can decrease the fatigue crack growth rate in the as-fabricated samples,so the fatigue strength of the as-fabricated notch samples can be improved.From the result of the fracture toughness tests,we can find that the main factors affecting the fracture toughness are the microstructure and the plasticity rather than the proof-ultimate strength difference and the plastic zone ahead of fatigue crack tip in the fracture toughness test of Ti-6Al-4V alloy fabricated by EBM by contrast.However,in test of the effect of hot isostatic pressing on fracture toughness by contrast,the plasticity became the main factor at the effect of the hot isostatic pressing treatment on fracture toughness.