Fusion zone microstructure and fatigue crack growth behaviour in Ti-6Al-4V alloy weldments
TL;DR: In this paper, the fatigue crack growth resistance of α-β titanium alloys can be altered by microstructural modification during welding, the fusion zone microstructure depends on cooling rate.
Abstract: The fatigue crack growth resistance of α–β titanium alloys can be altered by microstructural modification. During welding, the fusion zone microstructure depends on cooling rate. In the present work, the alloy Ti-6Al-4V was welded over a range of heat inputs, using electron beam and gas tungsten arc welding. The weld microstructure varied from predominantly martensitic under rapid cooling conditions to a mixture of martensite and diffusional products on slower cooling. Post-weld heat treatment resulted in a basketweave α–β aggregate that coarsened with temperature and time. In all welded and heat treated conditions, the fusion zone exhibited a fatigue crack growth resistance superior to that of the base material, which was in part attributed to the lamellar microstructure of the fusion zone. Welding residual stresses also played a beneficial role in the as welded condition. Post-weld heat treatment eliminated the advantage resulting from the welding stresses but not that as a result of microstructure.
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15 Jan 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the effect of microstructural characteristics on high-cycle fatigue properties and fatigue crack propagation behavior of welded regions of an investment cast Ti-6Al-4V were investigated.
Abstract: The effect of microstructural characteristics on high-cycle fatigue properties and fatigue crack propagation behavior of welded regions of an investment cast Ti-6Al-4V were investigated. High-cycle fatigue and fatigue crack propagation tests were conducted on the welded regions, which were processed by two different welding methods: tungsten inert gas (TIG) and electron beam (EB) welding. Test data were analyzed in relation to microstructure, tensile properties, and fatigue fracture mode. The base metal was composed of an alpha plate colony structure transformed to a basket-weave structure with thin α platelets after welding and annealing. High-cycle fatigue results indicated that fatigue strength of the EB weld was lower than that of the base metal or the TIG weld because of the existence of large micropores formed during welding, although it had the highest yield strength. In the case of the fatigue crack propagation, the EB weld composed of thinner α platelets had a faster crack propagation rate than the base metal or the TIG weld. The effective microstructural feature determining the fatigue crack propagation rate was found to be the width of α platelets because it was well matched with the reversed cyclic plastic zone size calculated in the threshold Δ K regime.
100 citations
TL;DR: In this article, gas tungsten arc welding was carried out, during which transverse oscillations of the arc were induced through the use of an alternating external magnetic field, and considerable refinement of the fusion zone grain structure was achieved.
Abstract: In an effort to refine the weld metal grain structure in α–β titanium alloys, gas tungsten arc welding was carried out, during which transverse oscillations of the arc were induced through the use of an alternating external magnetic field. At optimum values of oscillation amplitude and frequency in both the alloys investigated, considerable refinement of the fusion zone grain structure was achieved. This could be attributed to factors that include enhanced fluid flow, reduced temperature gradients, and a continually changing weld pool size and shape owing to the action of the imposed magnetic field. The reduction in the prior β grain size was shown to result in a notable increase in fusion zone tensile ductility. Post-weld annealing increased ductility in all cases, but the magnetically treated material continued to show a higher elongation than that of the untreated material even after post-weld heat treatment.
71 citations
TL;DR: In this article, Fatigue crack growth behavior of Ti-6Al-2Zr-1.5V alloy was studied in lamellar, bimodal and acicular microstructural conditions.
34 citations
TL;DR: In this paper, the microstructure traits and structural integrity of Ti-6Al-4V welds of 5.5mm thickness were discussed using activated flux in the tungsten inert gas (ATIG) welding technique using the oxide surfactant.
27 citations
15 Feb 2010-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, three kinds of orientations were designed to study the influences of precrack orientations and locations on fatigue crack growth rate in as-weld welded joints, and the classical total-life fatigue performances of the joints were also studied.
Abstract: Ti–6Al–4V lamella microstructure obtained by β annealing, which had slow fatigue crack propagation rate and high propagation resistance, was used as base metal and welded by tungsten-inert-gas welding (TIG). Three kinds of orientations were designed to study the influences of precrack orientations and locations on fatigue crack growth rate in as-weld welded joints. In comparison, the classical total-life fatigue performances of the joints were also studied. The results showed that, no matter the precrack was initiated in the center of the weld, near the fusion-line or in HAZ, the fatigue crack propagation rates in the initial stage were all slower than that of the base metal. The fatigue crack in the central region of the weld seam propagated by striation mechanism in the initial propagation stage, and the weld metal exhibited lower fatigue crack propagation rate and higher threshold stress intensity than the base metal and the other joint specimens.
21 citations
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TL;DR: In this paper, the authors analyzed the FD growth behavior of five beta-annealed alloys and found significant effects of microstructure upon the logarithmic plot of fatigue crack growth rate (da/dN) vs stress-intensity range (ΔK).
127 citations
42 citations
TL;DR: In this article, the effects of Widmanstatten and basket weave microstructures on the fracture toughness and fatigue crack growth behavior of Ti-24Al-11 Nb are reported.
Abstract: The results of a recent study of the effects of Widmanstatten and basket weave microstructures on the fracture toughness and fatigue crack growth behavior of Ti-24Al-11 Nb are reported Intrinsic and extrinsic toughening components due to crack blunting and bridging by the β phase, crack deflection, and microcracking are computed from existing crack-tip shielding models. Predictions of fracture toughness and fatigue thresholds obtained by the superposition of extrinsic toughening components are compared with measured values obtained from compression precraked single edge notch (SEN) bend specimens. The results indicate that the continuity of the β matrix between the α2 laths is important for the effectiveness of crack-tip blunting mechanisms. Widmanstatten microstructures obtained by annealing solely in the α2 + β phase field are shown to promote crack deflection and unstable room-temperature fatigue crack growth rates.i.e., crack growth rates that increase after further thermal exposure in the α2 + β and field. Basket weave microstructures produced by two-stage annealing (TSA) in the β and α2 + β phase fields are shown to promote crack bifurcation and deflection and significant improvements in fatigue crack growth resistance when the β anneal is followed by a furnacecool. The article highlights the significant role of microcracking in the fatigue propagation mechanism. The micromechanisms of fatigue and fracture are also discussed for the microstructures examined.
23 citations
TL;DR: In this article, the effects of stress ratio and temperature on the near-threshold fatigue crack growth characteristics of Ti-8Al-1Mo-1V were investigated, and a unique value of fatigue crack growing rate threshold, ΔK th was observed for all of the test conditions when crack closure was accounted for in the data analysis.
22 citations
Journal Article•
TL;DR: In this paper, the effects of Widmanstätten and basket weave microstructures on the fracture toughness and fatigue crack growth behavior of Ti-24Al-11 Nb are reported.
Abstract: The results of a recent study of the effects of Widmanstätten and basket weave microstructures on the fracture toughness and fatigue crack growth behavior of Ti-24Al-11 Nb are reported Intrinsic and extrinsic toughening components due to crack blunting and bridging by the β phase, crack deflection, and microcracking are computed from existing crack-tip shielding models. Predictions of fracture toughness and fatigue thresholds obtained by the superposition of extrinsic toughening components are compared with measured values obtained from compression precraked single edge notch (SEN) bend specimens. The results indicate that the continuity of the β matrix between the α2 laths is important for the effectiveness of crack-tip blunting mechanisms. Widmanstätten microstructures obtained by annealing solely in the α2 + β phase field are shown to promote crack deflection and unstable room-temperature fatigue crack growth rates.i.e., crack growth rates that increase after further thermal exposure in the α2 + β and field. Basket weave microstructures produced by two-stage annealing (TSA) in the β and α2 + β phase fields are shown to promote crack bifurcation and deflection and significant improvements in fatigue crack growth resistance when the β anneal is followed by a furnacecool. The article highlights the significant role of microcracking in the fatigue propagation mechanism. The micromechanisms of fatigue and fracture are also discussed for the microstructures examined.
21 citations