티타늄 합금(Ti-6Al-4V)의 조직변화에 따른 피로수명 평가

The specific gravity of titanium alloy is 4.5 which is lighter than steel, however, its specific strength, heat and corrosion resistance are superior to steel. Therefore, it is used in spaceships, medicines, and so on. Ti-6Al-4V alloy is a kind of α+β phase titanium alloy, and mechanical properties are changed by alloy elements, shapes and distributions of microstructures. In this paper, the effect of microstructure on mechanical behavior for Ti-6Al-4V alloy was studied. Three different kinds of specimens are prepared under different heat treatments (rolled plate, 980℃, 1050℃) in order to produce different microstructures. Various kinds of mechanical tests such as hardness, tensile, fatigue and fretting fatigue tests are performed for evaluation of mechanical properties with the changes of microstructures. Through these tests, the following conclusions are observed: I) Microstructures are observed as equiaxed, bimodal and lamellar microstructures respectively. 2) Impact absorbed energy is superior for the bimodal microstructure, and the hardness and tensile strength are superior for the lamellar microstructure. 3) The fatigue endurance of lamellar structure shows higher value than that of the equiaxed and bimodal structures. 4) Fractal dimension depend on maximum stress and heat treatment temperature.