Fractography

About: Fractography is a research topic. Over the lifetime, 5043 publications have been published within this topic receiving 86068 citations.

Effect of microstructure and strength on the fracture behavior of AA2219 alloy

Abstract: The plane strain fracture toughness, K J I c and crack growth toughness in terms of the non-dimensional tearing modulus, TR of Al–Cu alloy were evaluated following the J-integral method. An empirical relation is proposed for estimating the fracture toughness from the tensile properties. The estimated fracture toughness values from the empirical relation are found to be in good agreement with the measured fracture data. The microstructural as well as strength variations in the subject alloy were examined through different aging treatments (viz., under aging (UA), natural aging (NA), peak aging (PA) and over aging (OA)). The microstructural observations in different aging conditions were made through transmission electron microscopy (TEM) to understand the type of phase or intermediate stages of the phase present (GP zones, θ″, θ′ or θ). Fracture toughness testing has been carried out on 14 mm thick compact tension (CT) specimens and estimated the crack extension by unloading compliance technique. It was noted that the yield strength increases and fracture toughness decreases with the increase in the degree of aging from NA to PA condition. On overaging the alloy to a yield strength level as that of UA, it was not possible to retain the UA level of fracture toughness. The highest crack growth toughness is exhibited by the NA temper. The fractography analysis revealed that the fracture mode was predominantly transgranular dimpled rupture. Fracture initiation occurred by void nucleation at the second phase particles. The differences in the fracture toughness of the alloy in different aging conditions were shown to be dependent on the differences in the matrix deformation behavior and the strength differential.

Microstructure and Mechanical Properties of Inconel 718 Produced by SLM and Subsequent Heat Treatment

Abstract: The article presents results of selective laser melting of Inconel 718 superalloy. It was studied phase microstructure of the material obtained by selective laser melting and also the material after heat treatment. The phase composition of the initial powder material, the specimens after selective laser melting before and after heat treatment was studied. The effect of heat treatment on microstructure and mechanical properties of the specimens was shown. It was studied the mechanical behavior of the manufactured specimens before and after heat treatment at room and elevated temperatures as well. The results of impact tests and fractography of the specimens are presented. Mechanical tests showed that the specimens after heat treatment have decent mechanical properties comparable to hot-rolled material. Fractography showed that the obtained material is characterized by ductile failure mode with local elements of brittle fracture.

Fractography, mechanical properties, and microstructure of commercial silicon nitride-titanium nitride composites

Abstract: Commercial-grade Si3N4–TiN composites with 0, 10, 20, and 30 wt% TiN content have been characterized. Submicrometer grain-size Si3N4 was reinforced with fine TiN grains. Density, Young's modulus, coefficient of thermal expansion, and fracture toughness increased linearly with TiN content. Increased strength was observed in the Si3N4+20 wt% TiN, and Si3N4+30 wt% TiN composites. Fractography was used to characterize the different types of fracture origins. Improvements in toughness and strength are due to residual stresses in the Si3N4 matrix and the TiN particles. A threefold improvement in dry wear resistance of the Si3N4+30 wt% TiN composite over the Si3N4 matrix was observed.

Effects of Ti addition on cleavage fracture in Nb-Cr-Ti solid-solution alloys

Abstract: The fracture toughness of Nb-Cr-Ti solid-solution alloys has been shown to be greatly improved by Ti addition, but the mechanism of toughness enhancement has not been established. In this study, critical experiments were performed on the tough Nb-Cr-Ti alloy to characterize the crack-tip fracture process and to investigate the origin of fracture toughness. In addition, theoretical calculations of the unstable stacking energy (USE) and the Peierls-Nabarro (P-N) energy and stress were performed as a function of Ti content in the Nb-Cr-Ti alloys. The experimental results indicate that the fracture toughness in the tough Nb-Cr-Ti alloy originates from extensive dislocation emission that suppresses cleavage crack propagation from the crack tip. The theoretical calculation indicates that Ti addition lowers the P-N energy and stress, but has little effect on the USE. These results are used to elucidate the effects of Ti addition on cleavage fracture in Nb-Cr-Ti alloys by considering the influence of the P-N energy and stress values on (1) dislocation mobility, (2) crack-tip dislocation emission, (3) fracture toughness, and (4) brittle-to-ductile fracture transition. It is concluded that dislocation emission in the Nb-Cr-Ti alloys appears to be controlled by the P-N energy, which influences dislocation mobility, rather than by the USE, which influences dislocation nucleation. Ti increases the fracture toughness of Nb-Cr-Ti alloys by increasing dislocation mobility and dislocation emission from the crack tip through a reduction of the P-N energy and stress.