No abstract

With the development of additive manufacturing (AM), the Ti-6Al-4V alloy manufactured by laser powder bed fusion (LPBF) is becoming more widely studied. Fatigue fracture is the main failure mode of such components. During LPBF processing, porosity defects are unavoidable, which hinders the exploration of the relationship between fatigue performance and microstructure. In this study, a laser remelting method was used to reduce porosity defects inside the Ti-6Al-4V alloy. Three annealing treatments (AT) and three solution-aging treatments (SAT) were used to study the effect of the two-phase zone (α + β) microstructure on fatigue life and fatigue crack growth behavior. Fatigue life and crack growth rate (CGR) curves were obtained, and fatigue fracture surface and crack growth fracture surface were analyzed. The results show that microstructure influences fatigue life but has little effect on CGR. Compared with the as-built specimen, the fatigue life of the AT and SAT specimens increased significantly at 850℃ by 101 and 63.7 times, respectively. The thickness of the α lath and the location of crack nucleation together affect the fatigue life. In the stable growth stage, the layered microstructure of α colonies is the most resistant to crack growth.

During the last two decades, PT-based relaxor ferroelectric crystals such as (1−x)Pb(Zn 1/3 Nb 2/3 )O 3 -xPbTiO 3 (PZN-PT), (1−x)Pb(Mg 1/3 Nb 2/3 )O 3 -xPbTiO 3 (PMN-PT), and (1−x−y)Pb(In 1/2 Nb 1/2 )O 3 -yPb(Mg 1/3 Nb 2/3 )O 3 -xPbTiO 3 (PIN-PMN-PT or PIMNT) crystals, are widely studied due to their huge piezoelectric properties and super-high electro-mechanical coupling factors. They have excellent properties with compositions around the morphotropic phase boundary (MPB). It is gratifying that the PT-based relaxor crystals are replacing traditional PZT piezo-ceramics in many application fields. Most ferroelectrics with oxygen-octahedral structure, which show outstanding electro-mechanical properties, also have excellent optical performances. Ferroelectric single crystals with large electro-optic (EO) modulation are widely applied in laser communication devices. For the practical applications, the knowledge of detailed optical parameters is desirable. This paper tries to show a global review on the optical properties of PT-based relaxor ferroelectric crystals. In the present review, optical properties of the crystals are systematically summarized, including refractive index dispersion, transmittance, band gap, EO, acousto-optic, and photorefractive properties. These properties change with the crystal composition, orientation, and poling condition. The purpose of the review is to provide a resource for the researchers who are concerned with basic physical investigation or optical device applications of the PT-based relaxor ferroelectric crystals.