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
20 Jun 2013-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a defect-free friction stir processed (FSP'd) materials were evaluated by tensile tests on 2mm-thick Ti-6Al-4V sheets using various processing parameters including tool rotational speed (800-1000 RPM) and tool traverse speed (1 4 ).
Abstract: Friction stir processing (FSP) trials were performed on 2 mm-thick Ti–6Al–4V sheets using various processing parameters including tool rotational speed (800–1000 RPM) and tool traverse speed (1–4 IPM). A processing window was established with the W–1% La 2 O 3 tool to produce defect-free friction stir processed (FSP'd) materials. The stir zone (SZ) material of the FSP'd samples showed a fully β transformed microstructure characterized by typical basket-weave lamellar α/β structure. The prior β grains in the SZs contained multiple α variants, and the average sizes ranged from 12 μm to 38 μm influenced by the processing parameters. Based on metallurgical evaluation, the microstructural evolution in different regions from base material (BM) through heat-affected zone (HAZ) and thermomechanically affected zone (TMAZ) to SZ was established. The mechanical properties of the SZs were evaluated by tensile tests. Compared to the base material, the processed samples exhibit higher tensile strength and comparable ductility. The tensile strength was affected by the microstructure of the prior β grain size and α colony size, which are controlled by processing parameters. The lower tool rotational rate and/or higher traverse speed produced a lower peak temperature and a shorter dwell time above the β-transus temperature in the SZ, which resulted in finer prior β grains and smaller α colonies, leading to higher tensile strength.
72 citations
TL;DR: Friction stir welding of titanium alloy (Ti-6Al-4V) was demonstrated on 3, 6, 9 and 12 mm thickness square groove butt joints as mentioned in this paper, and complete microstructural and microhardness evaluations were conducted in addition to surface and subsurface examinations.
Abstract: Friction stir welding of titanium alloy (Ti–6Al–4V) was demonstrated on 3, 6, 9 and 12 mm thickness square groove butt joints. Complete microstructural and microhardness evaluations were conducted in addition to surface and subsurface examinations for each case. The 3 mm welds exhibited an extremely fine grained microstructure with evidence of processing temperatures below the beta transus temperature of the alloy. The 6, 9 and 12 mm samples possessed larger grains formed by a slower cooling rate from above the beta transus temperatures. The thick section weld exhibited a nearly uniform microhardness, while the thinner welds showed a slight, 6%, increase in hardness compared with the parent material.
71 citations
Journal Article•
TL;DR: In this paper, the authors describe results of application of thermography to evaluate the degree of fatigue degradation of epoxy-glass composites, which may be applied in the future in diagnostic procedures to nondestructive evaluation of high performance polymer composites.
Abstract: Purpose: The purpose of this paper was to describe results of application of thermography to evaluate the degree of fatigue degradation of epoxy-glass composites. Design/methodology/approach: Samples of epoxy-glass composite were subjected to fatigue degradation. During fatigue test, after defined number of cycles, samples were heated using infra-red heater and at the opposite side temperature increase was evaluated with thermovision camera. Findings: Analysis of achieved results allowed to elaborate relation between number of fatigue cycles and the degree of fatigue degradation. Such relation may be applied in diagnostic procedures. Research limitations/implications: Performed tests were of preliminary character and results will be applied to prepare research programme on thermographic testing of composites. Practical implications: Results of such tests may be applied in the future in diagnostic procedures to nondestructive evaluation of the degree of fatigue degradation of high performance polymer composites. Originality/value: Thermographic methods are applied up till now to non-destructive flaws detection. Proposed in the paper method may be applied to evaluate the degree of thermal and fatigue degradation in composites without any macroscopic flaws.
63 citations
TL;DR: In this paper, the peak temperatures during friction stir welding of Ti-6Al-4V alloy were determined as a function of the processing conditions such as tool rotation speed and feed rate.
Abstract: Experimental measurements were made to determine the peak temperatures during friction stir welding of Ti–6Al–4V alloy as a function of the processing conditions such as tool rotation speed and feedrate It was found that the spindle speed has a dominant effect on peak temperatures, while feedrate controls exposure time Low spindle speed conditions lead to peak temperatures near, or below, the beta transus temperature of the material, 1000°C (1800°F), while high spindle speed welds result in peak temperatures above 1200°C (2100°F) Weld microstructures were also evaluated as a function of the weld parameters Higher spindle speeds and lower federate lead to increased grain size
61 citations
TL;DR: In this article, the authors used a dual-beam focused ion beam device to evaluate the performance of investment-cast Ti-6Al-4V on four-point bend specimens and found that the fine-grained equiaxed structure has about a 12 pct higher compressive yield stress.
Abstract: Investment-cast titanium components are becoming increasingly common in the aerospace industry due to the ability to produce large, complex, one-piece components that were previously fabricated by mechanically fastening multiple pieces together. The fabricated components are labor-intensive and the fastener holes are stress concentrators and prime sites for fatigue crack initiation. The castings are typically hot-isostatically-pressed (HIP) to close internal porosity, but have a coarse, fully lamellar structure that has low resistance to fatigue crack initiation. The as-cast + HIP material exhibited 1- to 1.5-mm prior β grains containing a fully lamellar α + β microstructure consistent with slow cooling from above the β transus. Friction stir processing (FSP) was used to locally modify the microstructure on the surface of an investment-cast Ti-6Al-4V plate. Friction stir processing converted the as-cast microstructure to fine (1- to 2-μm) equiaxed α grains. Using micropillars created with a dual-beam focused ion beam device, it was found that the fine-grained equiaxed structure has about a 12 pct higher compressive yield stress. In wrought products, higher strength conditions are more resistant to fatigue crack initiation, while the coarse lamellar microstructure in the base material has better fatigue crack growth resistance. In combination, these two microstructures can increase the fatigue life of titanium alloy castings by increasing the number of cycles prior to crack initiation while retaining the same low-crack growth rates of the colony microstructure in the remainder of the component. In the current study, high-cycle fatigue testing of investment-cast Ti-6Al-4V was performed on four-point bend specimens. Early results show that FSP can increase fatigue strength dramatically.
51 citations