Multipass-friction Stir Processing (MFSP) of Ti-6Al-4V Alloy and Investigation of Flow Properties
08 Nov 2018-Vol. 422, Iss: 1, pp 012017
TL;DR: In this article, a multipass friction stir processing (MFSP) of the Ti-6Al-4V alloy was carried out at 600 tool rpm and 80 mm/min traverse speed, where the initial elongated α structure transformed to prior β grains, consisting of a mixture of acicular α'and very fine lamellar α colonies along with α layer grain boundary in stir zone (SZ).
Abstract: Multipass friction stir processing (MFSP) of the Ti-6Al-4V alloy was carried out at 600 tool rpm and 80 mm/min traverse speed. After first pass, the initial elongated α structure transformed to prior β grains, consisting of a mixture of acicular α'and very fine lamellar α colonies along with α layer grain boundary in stir zone (SZ). This subsequently transformed to equiaxed α grain via dynamic recrystallization (DRX) process. With the increase in the number of FSP passes the fraction of equiaxed α grains was found to increase, reaching almost fully equiaxed α structure in SZ upon completion of the fifth pass. Flow properties of MFSP Ti-6Al-4V alloy were investigated by differential strain rate test carried out at 927°C. There appears no significant variation in the strain rate sensitivity index (m ≥ 0.3) values between as received Ti-6Al-4V alloy and MFSP Ti-6Al-4V alloy specimens.
References
More filters
TL;DR: In this article, the α+β titanium alloy, Ti-6Al-4V, was friction stir welded at a constant tool rotation speed of 400-rpm to obtain defect-free welds with welding speeds ranging from 25 to 100mm/min.
96 citations
TL;DR: The most important factor responsible for superplastic behavior was found to be the very fine grain size as mentioned in this paper, which is in excellent agreement with the theory of grain boundary sliding accommodated by dislocation motion.
Abstract: The alloy Ti-6-Al-4V deforms superplastically in the temperature range 750 to 950° The most important factor which is responsible for superplastic behavior was found to be the very fine grain size. Strain rate has no direct effect on superplasticity, however when the strain rate is very low (approximately 2 × 10 s), prolonged exposure to high temperature causes grain growth and early failure. The strain rate sensitivity factorm = 0.5 and the apparent activation energyAH = 45,000 cal/mole, which is approximately the same as the activation energy for grain boundary self diffusion of titanium. Both values are independent of strain rate within the range 10 - 2.5 × 10 s. All the experimental points fall in a straight line when plotted as log (ekTd*
2/DgbGb3) vs log (σ/G) with a slopen = l/m = 2. This is in excellent agreement with the theory of grain boundary sliding accommodated by dislocation motion.
93 citations
TL;DR: In this paper, mill-annealed Ti-6Al-4V plates were successfully friction stir welded over a wide range of processing parameters using a tungsten-1/pct La2O3 tool.
Abstract: In this study, mill-annealed Ti-6Al-4V plates were successfully friction stir welded over a wide range of processing parameters using a tungsten-1 pct La2O3 tool Two K-type thermocouples embedded in the tool indicated that approximately 25 pct of the heat generated during welding was transferred out of the workpiece and into the tool The thermocouple data, combined with observations of the microstructure, indicated that the stir zone of all welds exceeded the β transus The microstructure and texture of two representative welds made just above and high above the β transus were investigated with scanning electron microscopy and electron backscatter diffraction (EBSD) The β phase orientations were reconstructed with a fully automated technique from the as-collected α phase data through knowledge of the Burgers orientation relationship The results suggest that the fine β grains in the stir zone are formed from the base material ahead of the advancing tool by dissolution of secondary and primary α phase, and there is no further recrystallization These grains subsequently deform by slip and rotate toward the orientations that are most stable with respect to the shear deformation induced by the tool In the highest temperature weld, diffusion tool wear in the form of periodically spaced bands provided an internal marker of the tool/workpiece interface during welding The flow patterns evident within the tungsten-enriched bands suggest that flow is considerably more chaotic on the advancing side than in the central stir zone
76 citations
25 Jun 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: The characteristics of microstructures at various locations behind the pin tool extraction site were studied in copper after FSP that had been conducted with continuous quenching to enhance cooling rates as discussed by the authors.
Abstract: The characteristics of microstructures at various locations behind the pin tool extraction site were studied in copper after FSP that had been conducted with continuous quenching to enhance cooling rates. The substructures initially formed around the pin tool consist of very small crystallites having sizes of a few tens of nanometers. It is proposed that the processing conditions result in formation of microband structures around pin tool in the presence of severe strain heterogeneity. The microbands appear as nano-scale elongated crystallites surrounded by high-angle boundaries. The elongated crystallites transform to nearly random oriented and equiaxed grain structures by shape adjustment during the initial stages of cooling from the peak temperature. Nanocrystalline structures ∼174 nm in size were produced in OFHC copper by FSP.
76 citations
TL;DR: In this article, the microstructural development of friction stir welding on an AZ91D magnesium alloy and the mechanical properties of the welds were investigated using optical and scanning electron microscopes.
Abstract: This study was carried out to grow an understanding of the microstructural development of friction stir welding on an AZ91D magnesium alloy and to evaluate the mechanical properties of the welds. AZ91D plates with the thickness of 4 mm were used, and the microstructural development of the weld zone was investigated using optical and scanning electron microscopes. Square butt welded joint with good quality was
76 citations