https://pureadmin.qub.ac.uk/ws/files/2742312/Effect_of_microstructure_on_the_fatigue_properties_of_Ti_6Al_4V_titanium_alloys.pdf

Effect of microstructure on the fatigue properties of Ti-6Al-4V titanium alloys

In this paper, a comparative study of high-cycle fatigue tests (T=650 °C, f=110 Hz, R=0.1, Kt=1) were carried out with wrought Inconel 718 and LAMed Inconel 718. The results show that the influences of the Laves phases on high-cycle fatigue properties are based on the applied stress amplitudes. At a low stress amplitude, most of the Laves phases held their original morphologies. The fatigue cracks stopped in front or detoured around them, which means that the unbroken Laves phases play an important role in hindering crack propagation. In this way, the high-cycle fatigue life of LAMed Inconel 718 was superior to that of wrought Inconel 718. However, at a high stress amplitude almost all of the Laves phases in the crack propagation region splintered into smaller fragments, parts of which separated from the austenite matrix. Microscopic holes or cracks were formed at the interface, which provided passages for the fatigue cracks to propagate. In this case, the Laves phases were harmful, leading to the degradation of fatigue performance in LAMed Inconel 718 compared with wrought Inconel 718.

The influence of Laves phases on the high-cycle fatigue behavior of laser additive manufactured Inconel 718

Surface characteristics and fatigue behavior of shot peened Inconel 718

Cryogenics is an exciting, important and inexpensive technique that already has led to main discoveries and holds much future assurance. Cryogenic processing is the treatment of the materials at very low temperature around 77 K. This technique has been proven to be efficient in improving the physical and mechanical properties of the materials such as metals, alloys, plastics and composites. It improves the wear, abrasion, erosion and corrosion resistivity, durability and stabilizes the strength characteristics of various materials. Cryogenic refines and stabilizes the crystal lattice structure and distribute carbon particles throughout the material resulting a stronger and hence more durable material. In present paper, we have reviewed the effect of cryogenic treatment on some metals, alloys, plastics and composites.

Cryogenic Processing: A Study of Materials at Low Temperatures

Strain-rate effects on the mechanical behavior of the AISI 300 series of austenitic stainless steel under cryogenic environments

High-cycle fatigue properties at 4 K, 77 K and 293 K were investigated in forged-INCONEL 718 nickel-based superalloy with a mean gamma (� ) grain size of 25 mm. In the present material, plate-like delta phase precipitated atgrain boundaries and niobium (Nb)-enriched MC type carbides precipitated coarsely throughout the specimens. The 0.2% proof stress and the ultimate tensile strength of this alloy increased with decreasing temperature, without decreasing elongation or reduction of area. High-cycle fatigue strengths also increased with decreasing temperature although the fatigue limit at each temperature didn't appear even around 10 7 cycles. Fatigue cracks initiated near the specimen surface and formed faceted structures around crack initiation sites. Fatigue cracks predominantly initiated from coarse Nb-enriched carbides and faceted structures mainly corresponded to these carbides. In lower stress amplitude tests, however, facets were formed through transgranular crack initiation and growth. These kinds of distinctive crack initiation behavior seem to lower the high-cycle fatigue strength below room temperature in the present material.

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High-Cycle Fatigue Properties at Cryogenic Temperatures in INCONEL 718 Nickel-based Superalloy

Tensile, fracture toughness, and high cycle fatigue tests were done at 293, 77, and 4 K for Ti-6Al-4V alloys with three levels of oxygen content. The alloys were investigated both in as-forged condition and in the rolled condition. Rolling did not necessarily make α grains finer, but changed the shape from plate-like to globular. Strengths depended mainly on the oxygen content; the lower content produced lower strengths. The alloy with lowest oxygen content showed the best ductility at 4 K. The fracture toughness at cryogenic temperature was also enhanced by the reduction of oxygen. In the lowest oxygen alloy, no drop in the fracture toughness was observed between 293 and 4 K. Fatigue properties were influenced by the forming process. The rolled materials had higher fatigue strength than the forged materials. The difference was accentuated at 4 K. This is believed to be due to the difference in the morphology of α grains. The lowest oxygen alloy showed the highest fatigue strength at 4 K.

Cryogenic mechanical properties of Ti-6Al-4V alloys with three levels of oxygen content

Effect of welding structure and δ-ferrite on fatigue properties for TIG welded austenitic stainless steels at cryogenic temperatures

S-N curves of Ti-5Al-2.5Sn ELI alloy were determined at liquid helium temperature (4K) for both the base and welded materials.The base material had a longer fatigue life at 4K than at 77K. Welding deteriorated the fatigue properties at 4K. Internal crack initiation was seen at lower cyclic stress in both the base and the welded materials. For the base material, internal crack initiation occurred at 4K, and there were no obvious defects near the initiation sites. On the other hand, fatigue cracks generally initiated at porosity in the weldment. Internal crack initiation is considered one of the causes of reduced fatigue life.High cyclic frequency brought about a large temperature increase in the specimen, making the testing temperature uncertain in fatigue tests at cryogenic temperature.

Tetsumi Yuri

Papers

High-Cycle Fatigue Properties at Cryogenic Temperatures in INCONEL 718 Nickel-based Superalloy

Cryogenic mechanical properties of Ti-6Al-4V alloys with three levels of oxygen content

Effect of welding structure and δ-ferrite on fatigue properties for TIG welded austenitic stainless steels at cryogenic temperatures

Fatigue Fracture of Ti-5Al-2.5Sn ELI Alloy at Liquid Helium Temperature

High-cycle Fatigue Properties of Alloy718 Base Metal and Electron Beam Welded Joint