Influence of Heating Media on Mechanical and Microstructural Properties of CP Titanium Alloy

Commercially pure titanium alloys are used as structural materials in aerospace industry. These alloys are mainly exposed to stress relief after forming operations. Heat treating of commercially pure (CP) titanium alloys are generally carried out in air, atmosphere-controlled and vacuum atmospheres. This study investigates the effect of heating media on mechanical and microstructural features of CP titanium alloys. The samples have been subjected to stress relief treatment by different heating media. The heating media are vacuum and atmosphere-controlled atmospheres. Discoloration has been observed in atmosphere-controlled heating media. The microstructure has not been influenced by heating media neither near the surface and at core. Although, discoloration has been detected, alpha case formation is not noticed. The samples heat-treated in vacuum atmosphere showed approximately 7 % higher tensile and yield strength whereas elongation % has not been changed. Fatigue test has been performed at 310, 350 and 370 MPa stress levels. The fatigue life has been decreased at all stress levels. When stress level is increased up to 375 MPa, fatigue life has been decreased nearly by 40 %. Impurity content of samples has been examined within the scope of hydrogen and oxygen content. Oxygen and hydrogen contents have not been changed so much in vacuum heat-treated samples whereas oxygen content has been increased by 50 ppm and hydrogen content by 20 ppm. Increment in hydrogen content decreased mechanical properties.