Fractography

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

Fracture behaviors and microstructural failure mechanisms of laminated Ti–TiBw/Ti composites

Abstract: A range of laminated Ti–TiBw/Ti composites with layer thicknesses of 300 μm, 400 μm and 500 μm were successfully fabricated by reaction hot pressing. The stress–strain curve of the laminated composites with 300 μm layer thickness exhibits superior tensile elongation (24.5%) and similar strength compared with the laminated composites with 400 μm and 500 μm layer thicknesses. The higher elongation is characterized by a prolonged strain softening stage and “non-catastrophic fracture” behavior. The fractography of laminated Ti–TiBw/Ti composites comprises two fracture modes; Ti layers exhibit shear fracture with many shear bands accompanying with micro-voids. However, TiBw/Ti composite layers reveal ductile fracture initiated by nucleation, growth and coalescence of micro-cracks. The difference on fracture mechanisms between Ti layer and TiBw/Ti composite layer is determined by the TiBw reinforcement, while high elongation of the laminated Ti–TiBw/Ti composites with thinner layer thickness is probably attributed to the effective size effect. Meanwhile, with the increase of stress and strain during the plastic deformation process, Ti layer and TiBw/Ti composite layer reveal interaction and mutual competing fracture damage behaviors.

The morphology and growth of creep cavities in α-iron

Abstract: Electron fractography has been used to study the intergranular cavities formed in alpha-iron during slow tensile deformation at high temperatures. A minimum in ductility is observed at about 700° C: this coincides with conditions where grain-boundary sliding makes a maximum contribution to the overall deformation and where the morphology of the cavities tends to be dendritic and finely terraced. This is explained in terms of the gradient of chemical potential for vacancies which may develop at the cavity periphery during grain-boundary sliding. Under other testing conditions, planar growth is observed and the cavity surface is often faceted.

Effect of bimodal grain size distribution on fatigue properties of Ti-6Al-4V alloy with harmonic structure under four-point bending

Abstract: Titanium alloy (Ti-6Al-4V) with a bimodal harmonic structure, which is defined as a coarse-grained structure surrounded by a network structure of fine grains, was fabricated using powder metallurgy to improve both the strength and ductility. The microstructure of the sintered compacts was characterized using electron backscattered diffraction (EBSD). The areal fraction of the fine-grained structure in the harmonic structure tended to increase with the milling time. Tensile tests and four-point bending fatigue tests at a stress ratio of 0.1 were performed in air at room temperature. The tensile strength, 0.2% proof stress and fatigue limit of Ti-6Al-4V alloy with harmonic structure tended to increase as the areal fraction of the fine-grained structure increased. In contrast, elongation decreased due to the formation of a high areal fraction of the fine-grained structure (79.0%), which resulted in a reduction of the fatigue life with a low cycle regime. Thus, titanium alloy with high strength, ductility and fatigue resistance can be formed by optimization of the milling conditions. Furthermore, the mechanism for fatigue fracture of the Ti-6Al-4V alloy with a harmonic structure is discussed with respect to fractography and crystallography. A fatigue crack was initiated from the α-facet of the coarse-grained structure in the harmonic structure.

Mechanical properties of ZrB2–SiC ceramic composites: room temperature instantaneous behaviour

Abstract: The mechanical properties of ZrB2–30 wt-%SiC ultra high temperature ceramic composites have been studied. The composite was processed by hot pressing at 2100°C, 30 MPa and 45 min dwell time to achieve a good densification. Young’s modulus, single edge V notch beam fracture toughness, hardness, stress–strain deformation, four-point bending strength and Weibull parameters were measured. Fractography and microstructure analyses of ZrB2–30 wt-%SiC ceramic composite were also performed.

Fractographic analysis of fatigue crack initiation and propagation in CP titanium with a bimodal harmonic structure

Abstract: Commercially pure (CP) titanium with a bimodal harmonic structure, which is defined as coarse grained regions surrounded by a network of fine grains, was fabricated by consolidating mechanically milled powders to improve both strength and ductility. In order to determine the fatigue properties of bimodal harmonic structured CP titanium, four-point bending fatigue tests were conducted at a stress ratio of 0.1 under ambient conditions. The fracture surfaces were analyzed by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) to identify the mechanisms of small fatigue crack initiation and propagation on the basis of fractography and crystallography. The fatigue crack initiation resistance was increased compared to sintered compacts fabricated from as-received initial powders, which was attributed to grain refinement during mechanical milling. Transgranular fracture occurred from coarse grains with a basal plane perpendicular to the loading direction. The fatigue crack path in harmonic structured CP titanium was not influenced by the microstructure.