Accepted Manuscript Microstructure and mechanical characterization of continuous drive friction welded grade 2 seamless titanium tubes at different rotational speeds R. Palanivel, R.F. Laubscher, I. Dinaharan, D.G. Hattingh PII:
S0308-0161(16)30297-6
DOI:
10.1016/j.ijpvp.2017.06.005
Reference:
IPVP 3629
To appear in:
International Journal of Pressure Vessels and Piping
Received Date: 24 August 2016 Revised Date:
1 June 2017
Accepted Date: 5 June 2017
Please cite this article as: Palanivel R, Laubscher RF, Dinaharan I, Hattingh DG, Microstructure and mechanical characterization of continuous drive friction welded grade 2 seamless titanium tubes at different rotational speeds, International Journal of Pressure Vessels and Piping (2017), doi: 10.1016/ j.ijpvp.2017.06.005. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Microstructure and mechanical characterization of continuous drive friction welded Grade 2 seamless titanium tubes at different rotational speeds R. Palanivela*, R.F. Laubschera, I. Dinaharana, D.G. Hattinghb Department of Mechanical Engineering Science, University of Johannesburg, Auckland Park
Kingsway Campus, Johannesburg 2006, South Africa. b
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a
Department of Mechanical Engineering, Nelson Mandela Metropolitan University, Port
*
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Elizabeth 6001, South Africa. Corresponding author.
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E-mail addresses:
[email protected] (R. Palanivel),
[email protected] (R.F. Laubscher),
[email protected] (I. Dinaharan),
[email protected] (D.G. Hattingh). Abstract
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Friction welding is a near ideal process to join thin metallic tubes. Grade 2 titanium tubes of outer diameter 60 mm and wall thickness 3.9 mm were joined by friction welding. The effect of rotational speed on microstructure was evaluated for five different speeds. The process
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parameters were recorded during welding. The microstructure was observed using optical microscopy and electron back scattered diagram. The results revealed that the rotational speed
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had a significant effect on the process parameters, microstructure and joint integrity. An increase in rotational speed reduced the torque and rate of frictional power input and extended the welding duration. The rate of deformation increased with rotational speed and refined the grains in the weld zone. The grain size was observed to coarsen from the center of the weld zone towards the flash. The grain structure in the heat affected zone (HAZ) was identical to the parent
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metal. A maximum joint efficiency of 98.3 % was achieved at rotational speed of 2200 rpm. The details of microhardness, failure location and fracture surface are reported.
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Key words: Titanium; Tube; Friction Welding; Microstructure; Tensile Strength. 1. Introduction
Titanium and its alloys are extensively used in several industrial applications due to
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several desirable properties including high specific strength, low density, good creep resistance, biocompatibility and excellent corrosion resistance [1,2]. Tubular titanium products specifically,
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are finding more wide spread use in aerospace, marine, chemical, energy and transportation industries owing to those outstanding properties [3–5]. Since titanium has a lower specific gravity when compared to stainless steel and copper, it is possible to reduce the weight of selected components by up to 40% [6].The use of tubes in structural components usually requires
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joining. Conventional fusion welding techniques including gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), electron beam welding (EBW) and laser beam welding (LBW) can be used to join titanium tubes. These techniques may however suffer from certain drawbacks
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including: coarse microstructure, porosity, severe deformation and high residual stress [7,8]. The circular shape of the tubes makes it inconvenient to use fusion welding techniques due to poor
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weld bead formation. Thin walled tube welding is challenging and the success and joint properties is largely a function of operator skill [9]. Therefore, solid state welding processes shows promise, in certain applications, to significantly reduce the challenges associated with metals joining by melting. Friction welding has inherent benefits when it comes to joining thin walled metallic tubes [10,11]. It is a well-known joining method among the various solid state welding processes.
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Components to be joined are rotated or moved in contact with each other. The relative motion at the faying surfaces produces frictional heat which plasticizes the material. Coalescence of materials is finally achieved upon the application of a compressive force. It is relatively simple to
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automate the process. The welding is accomplished in solid state without melting the materials to be joined. Since no filler metal is used, it eliminates the undesirable effects of low temperature eutectic segregation and problems with poor filler metal selection. High reliability joints may be
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achieved with appropriate process design. It is a low cost energy efficient process and may significantly reduce the extent of the heat affected zone (HAZ) [12,13]. It is mostly used to
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fabricate essential parts such as engine valves, drive shafts, axle housing etc [14]. Some studies on joining of metallic tubes using friction welding have been reported in the literature [15–22]. Singh and Gill [15] joined galvanized steel tubes and developed a fuzzy model to predict the tensile strength.Faes et al. [16] developed a new method to join carbon steel
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tubes using friction welding. They used a rotating intermediate ring between the pipes to generate the necessary heat to realize the weld. Shin et al. [17] joined dissimilar zirconium based bulk metallic glass tubes and recorded the temperature distribution during welding. They carried
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out microstructural characterization and X-ray diffraction analysis on the weld cross section.
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Kimura et al. [18] joined AISI310S austenitic stainless steel and studied the effect of process parameters on microstructure and tensile strength of the joints in detail. Theyfurther analyzed the effect of various tube thicknesses on the joint properties. Kumar and Balasubramanian [19] joined SUS304HCu austenitic stainless steel tubes. They identified various regions within the joint and reported the microstructure. The welded zone exhibited higher hardness compared to the base material. Kimura et al. [20] joined dissimilar AA6061 aluminum alloy bar and cast AlSi12CuNi Alloy tube and investigated the influence of forge pressure and friction time on the
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joint properties. Rovere et al. [21] joined supermartensitic stainless steel by modified friction welding process and determined the corrosion properties of the joints based on electrochemical tests. Kimura et al. [22] joined dissimilar AA6063 aluminum alloy and AISI 304 austenitic
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stainless steel tubes and proposed a new method to minimize significant deformation on the aluminum side. They described the effect of friction time on the joint properties.
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It is inferred from the short literature survey that it is possible to join various metallic tubes by friction welding. However, no investigations have specifically focused on joining of
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titanium tubes by friction welding. Therefore the objective of the present work is to join titanium tubes by friction welding and to report the variation of microstructure and joint integrity as a function of selected process parameters. 2. Experimental procedure
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Grade 2 commercially pure titanium tubes were used in this research work. The tubes have an outer diameter of 60 mm, wall thickness of 3.9 mm and length of 75 mm. The ratio of outer diameter to wall thickness is 15.4 which implies a thin tube classification. Friction welding
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was carried out by using a process development system for friction processing (M/s Profile Tooling, Port Elizabeth) at Nelson Mandela Metropolitan University as shown in Fig. 1a. It is a
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fully automatic machine with a computer interface. Parameters such as torque (T), rotational speed (N), axial force (F) and axial shortening were recorded during welding. Coefficient of friction (µ), power input (P) and energy (E) were calculated according to the following expressions. µ = P=
(1) π
(2)
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E=
P
(3)
Where R – effective radius of the tube, ti- weld start time, tf – weld finish time. A fixture (see Fig. 1b) was specially designed to hold the titanium tubes securely in
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position during welding and to minimize misalignment between the rotating and stationary tubes. Argon gas shielding was provided to avoid oxidation of the titanium during welding. The faying surfaces were thoroughly cleaned with acetone prior to welding. The titanium tubes were welded
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at rotational speeds of 1600, 1900, 2200, 2500 and 2800 rpm. Other process parameters were kept constant. A friction force of 20 kN, forging time of 22 s and forging force of 30 kN were
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used. Braking was applied after a preset axial shortening of 0.6 mm was reached. The friction time for each experiment was estimated based on the recorded welding cycle to calculate E. The range of rotational speed was chosen based on obtaining an acceptable joint displaying symmetric bead without major defects. Fig. 2 presents typical defects including cold welding,
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excessive flash, incomplete forging and insufficient plasticization that were obtained in the trail welds. An example of a friction welded tube (2200 rpm) is shown in Fig. 3. Specimens were machined perpendicular to the welding direction for metallographic
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analysis. They were mounted (STRUERS Citopress), polished (STRUERS Labopol) and etched with Kroll’s reagent. The etched specimens were observed using an optical microscope
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(OLYMPUS BX51M). The grain size was measured according to ASTM E112 − 10 using ImageJ software. The macrograph was recorded using a stereo microscope (OLYMPUS SZX16). The microstructure of selected welded tubes was further characterized using electron back scattered diagram (EBSD). The microhardness was recorded according to ASTM E140 − 12b using a Vickers microhardness tester (MITUTOYO HM-220). Indentations were made at the center of the wall thickness across the joint. A total of 30 indentations were made on either side
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from the centre of the weld zone at a spacing of 0.1 mm. A load of 500 gm was applied for 15 s. Tensile specimens as per ASTM E8M-04 standard having a gauge length 40 mm and gauge width 6 mm were machined from the welded tubes using water jet cutting. Examples of the
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machined tensile specimens are presented in Fig. 4.The flash was machined prior to tensile
testing. The ultimate tensile strength (UTS) was estimated using a computerized tensile tester
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(INSTRON 1195). The fracture surfaces were viewed using SEM (TESCAN VEGA 3). 3. Results and discussions
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3.1. Process analysis
Fig. 5 shows typical friction welding cycle which was recorded for rotational speed of 2200 rpm. The variation in the friction welding parameters and responses are shown against welding time. The welding cycle looks similar to the established welding cycle for continuous
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drive friction welding [13]. There are four stages indentified in the welding cycle and marked clearly using arrows. These stages are known as initial friction stage (0–5 s), friction stage (5–37 s), braking stage (37–38 s) and forging stage (38–60 s). The rotational speed (2200 rpm) and the
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axial force (20 kN) reached the preset values during initial stage. The rise in rotational speed causes the torque to reach an initial peak value. The resistance to rotation is initially high which
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cause the value of torque to reach a peak value. During the friction stage the rotational speed and the axial force is maintained at the preset values. The initial peak torque reduces to some extend and fluctuates within a band throughout this stage. This toque value was considered as equilibrium torque. As time lapses the resistance to rotation reduces and maintains which is reflected in the torque trend. This stage continues till a predetermined axial shortening is reached. The spindle drive is then disengaged and brake is applied to stop the rotation. The torque value reaches another peak which is taken as peak torque. The increased resistance to
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rotation during braking increases the torque value. The axial force is increased to the predetermined value (30 kN) for forging to commence. The axial shortening rises sharply due to the application of forge force and rotation stoppage. The axial force is maintained at a preset
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value during forging stage to consolidate the frictionally heated material. The axial force is rapidly reduced to zero at the end of the forging stage and the weld is completed.
The impact of rotational speed on various parameters of the friction welding process is
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shown in Fig. 6. The increase in rotational speed decreases the peak and equilibrium torque values (Fig. 6a). The peak toque is 324 Nm at 1600 rpm and 188 Nm at 2800 rpm while the
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equilibrium torque is 194 Nm at 1600 rpm and 112 Nm at 2800 rpm. The friction coefficient between the rubbing surfaces plays an important role to influence the torque generated. The variation in torque can be correlated to the variation in friction coefficient at different rotating speeds. The rotating speed is analogous to sliding velocity of wear test conducted in a pin-on-
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disc configuration. Li et al. [23] reported that the friction coefficient of titanium and its alloys decreases with an increase in sliding velocity. The variation of friction coefficient with the increase in rotational speed is shown in Fig. 6b.The friction coefficient is higher at low rotational
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speed which leads to higher torque values. The decrease in friction coefficient with an increase in rotational speed lowers the torque value. This result suggests that an increase in rotational speed
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does not promote an increase in available average frictional power input. This observation is confirmed in Fig. 6c. The calculated frictional power input decreases with increase in rotational speed. The higher average frictional power input at lower rotational speed increases the rate of deformation during frictional stage. The rate of heating affects the welding time as depicted in Fig. 6d. The increase in rotational speed prolongs the welding duration due to reduction in torque and average frictional power input. Similar observation was reported by Chander et al. [24]. The
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decrease in heating rate increases the time to reach the preset axial shortening at higher rotational speed. The volume of metal affected by the frictional heat is less at lower rotational speed due to higher heating rate. The rate of frictional heat generation is higher compared to the rate of
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conduction of frictional heat at lower rotational speed. The volume of material heated to forging temperature is low which is expelled in the form of flash and the cycle is repeated. Therefore, a shorter weld time is observed at lower rotational speed. On the other hand, the lower heating rate
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consumes high amount of time to attain forging temperature at high rotational speed. The longer heating time causes more frictional heat to be conducted axially to the adjacent metal from the
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weld interface [25]. Larger volume of metal is softened at higher rotational speed due to higher energy (Fig. 6e). Hence, more plasticized material is for forging stage compared to lower rotational speed. Eventually more material is expelled by the axial force as flash during the
3.2. Macrostructure
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forging stage and increases the axial shortening at higher rotational speed (Fig. 6f).
The macrographs of the welded joints at different rotational speeds are presented in Fig.
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7. No major defects such as pores or irregularities are observed at the weld interface. The welding is complete. It is evident from the macrographs that rotational speed remarkably
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influenced the geometry of the weld zone and the morphology of the flash. The biconcavity of the weld zone and the size of the flash increase with rotational speed. The overall width of the weld zone reduces with an increase in biconcavity. The material flow lines are axially curved from the central weld section to the peripheral section. The friction heat generated at the faying surfaces increases the temperature of the rotating tubes at the rubbing interface. The increase in interface temperature reduces the flow stress of the material. Subsequently, the material is unable to withstand the applied axial compressive force and flows plastically outwards resulting in the
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formation flashes. The flash carries away any oxides or contaminant present in the weld interface. The friction welded tubes have flashes both in the inside and outside of the tube after welding. The outer flash is easily removable while the inner flash is difficult to machine out. The
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residual strain in the flashes is usually higher compared to other regions within the weld zone [26]. Too small or too big flash is undesirable for friction welded tubes. The increase in flash size and reduction in weld zone geometry can be attributed to the amount of heated and
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plasticized material available prior to forging stage. As discussed in the previous section, the amount of deformed material is increased with an increase in rotational speed. Hence, more
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material is expelled at higher rotational speed. This is reflected in reduction in axial shortening as provided in Fig. 6d. The symmetry between inner and outer flash is lost at a rotational speed of 2800 rpm. The outer flash is bigger than the inner flash. This indicates that excess amount of material at elevated temperature is extruded out from the weld interface which is unhealthy for
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the joint quality. The high centrifugal force throws more extruded material outwardly. The flash in friction welding of metal and alloys usually has a lip like structure at the end. It is interesting to observe that such lip like structure is absent in the present work. Titanium has high hot
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strength compared to other nonferrous metals and grades of steel. If can be inferred that the combination of process parameters employed did not cause too much deformation of titanium at
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the elevated temperature to form lip like structure. 3.3. Microstructure
The optical micrographs of the various zones of the welded tubes at rotational speed of
2200 rpm are depicted in Fig. 8. The optical micrograph of the as received titanium (Fig. 8a) shows fine equiaxed grains. The average grain size was 10.2 µm. The transition zone of welded joint (Fig. 8b) shows weld zone (WZ) and heat affected zone (HAZ). WZ is also known as
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recrystallized zone (RZ) or transformed and recrystallized zone (TRZ). The formation of various zones can be related to the frictional heat input and degree of plastic deformation. Kumar and Balasubramanian [19] observed four distinct zones in friction welded austenitic stainless tubes
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which are namely weld zone (WZ), deformed zone (DZ), partially deformed zone (PDZ) and parent metal (PM). DZ and PDZ are not present in the welded titanium tube as seen in Fig. 8b. Those zones were not formed during friction welding. The transition from WZ to HAZ is abrupt
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without an intermediate zone and a linear transition boundary separated these regions. Da Silva et al. [25] noticed a narrow HAZ between the WZ and PM in friction welded Ti–6Al–4V/TiC
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composites. They did not report any presence of DZ. Avinash et al. [27] observed HAZ which contained coarse grains next to WZ in friction welded Ti–6Al–4V rods. In the present work, the grain size of HAZ (Fig. 8b) resembles the grain size of PM (Fig. 8a). No coarsening of grains is noticed in HAZ. Similar observations were recorded in all joints at different rotational speeds.
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The propagation of friction heat along the axial direction of the welded tubes increases with an increase in rotational speed as discussed in Sec. 3.1. Although there is no noticeable change in grain size in HAZ, this region might have possibly encountered softening. Moreover, titanium
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has very low thermal conductivity (16.4 W/mK) which might have restricted the propagation of friction heat to a longer distance away from WZ and avoided the formation of DZ and PDZ [28].
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EBSD maps in Fig. 9 show the grain structure of titanium and weld zone in detail. Large
number of twins is visible (Fig. 9a) in the grain structure of titanium. The twins are hardly observed in WZ (Fig. 9b). This can be attributed to the frictional heat which exceeds a certain value for a particular strain present in the weld zone [29]. The grain size in WZ is refined considerably after friction welding. Dynamic recrystallization is the cause for extensive grain refinement. The rubbing and forging action result in severe plastic deformation of the material at
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the interface. The density of the dislocations is increased to a critical level needed for nucleation of fresh grains. New grains originate due to recrystallization. Those new grains undergo a cycle of repeated deformation and recrystallization until the weld is completed. Subsequently, the fine
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grains are retained in the WZ.
The variation in WZ grain size with different rotational speeds is shown in the optical micrographs in Fig. 10a–e. These micrographs were captured at the geometric center of the WZ.
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The influence of rotational speed on the grain size is quantitatively presented in Fig. 10f. The average grain size was measured to be 2.5 µm at 1600 rpm and 1.2 µm at 2800 rpm. The grain
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size became finer and finer with an increase in rotational speed. This observation agrees to the findings of Etesami et al. [30]. The available quantity of frictional heat and the rate of deformation are the two key factors which influence the grain size predominantly. Both the factors have opposite effect on grain size to each other. The increase in frictional heat supply
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causes the grains to grow and coarsen. On the other contrary, the increase in deformation rate restricts grain growth and assists to fragment the formed grains. Therefore, the grain size is the resultant effect of frictional heat and the rate of deformation. Both the frictional heat generated
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and rate of deformation increase with an increase in rotational speed [24,31]. The reduction in the grain size with an increase in rotational speed indicates that the effect of rate of deformation
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dominates over the effect of frictional heat. The grain growth is inhibited and grains are refined more and more.
The optical micrographs of the WZ (welded at 2200 rpm) at different radial distance from
the center of WZ to flash are presented in Fig. 11. It is interesting to observe that the grain size varies radially towards the flash. The grain size was constant up to ± 0.8 mm from the center of WZ. The grains coarsen continually with further increase in radial distance. The plasticized
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material is squeezed out of the weld interface under the application of axial force during the forging stage. The expelled material expands in the radial direction to form the flash and stops when the weld is completed. The increase in grain size begins at a distance of 0.8 mm from the
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center of WZ. This is the location where the expansion of plasticized material is well
pronounced. The width of the WZ is nearly constant up to ± 0.8 mm from the center of WZ in Fig. 7c. Therefore, an increase in grain size occurs at the instant of commencement of expansion.
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The effect of expansion process is the reverse of extrusion process where the expanding high temperature material results in significant grain coarsening. The flash has the largest grain size.
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Since the flash is removed, it does not affect the tensile test results. But the regions of various grain sizes may be strained differently during tensile loading. There is a possibility that failure may originate from the region having highest grain size. The grain size in Fig. 11c is higher excluding flash which is recorded near the edges of the wall. This region is susceptible to
3.4. Mechanical properties
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premature failure during tensile test.
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The variation in the microhardness profiles of the welded joints with different rotational speeds is presented in Fig. 12. The hardness of the WZ is higher compared to the PM. This can
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be ascribed to the formation of fine grains in the WZ due to dynamic recrystallization. It is evident from Fig. 12 that the hardness of the WZ increases with an increase in rotational speed. The reduction in grain size with rotational speed increases the hardness of the WZ according to Hall–Petch relation. The WZ is strengthened with an increase in rotational speed. The change in hardness from PM to WZ is instant. This indicates that there is no intermediate zone between PM and WZ and softening of material outside WZ. The range of peak hardness in WZ reduces with rotational speed due to reduction in the width of the WZ.
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The effect of rotational speed on UTS is shown in Fig. 13. The optical macrographs of the tensile tested specimens and SEM micrographs of the fractured specimens are presented in Fig. 14 and 15 respectively. The UTS was measured to be 283 MPa at 1600 rpm and increases to
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338 MPa at 2200 rpm. The UTS decreases with further increase in rotational speed. It was found to be 251 MPa at 2800 rpm. The UTS of as received titanium was tested to be 344 MPa. The joint efficiency was 98.3 % at 2200 rpm. The variation in UTS can be correlated to the
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microstructural and fracture surface observations. The tensile specimen at 1600 rpm failed at the WZ (Fig. 14a). The available quantity of plasticized material is low at 1600 rpm which leads to
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poor consolidation at forging stage. Although no porosities are observed in the macrograph (Fig. 7a), the fracture surface at 1600 rpm reveals (Fig. 15a) presence of pores. Those pores reduce the cross sectional area to bear the tensile load and act as crack initiation sites. Hence, the lower UTS at 1600 rpm is the result of poor consolidation of material and presence of pores. The
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tensile specimen at 2200 rpm failed at the PM (Fig. 14b). The WZ was intact. The consolidation of the material is proper. The increase in rotational speed increases the available plasticized material and adequate material is available for proper consolidation during forging. Hence, the
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tensile specimen failed at PM and the joint strength reached a peak value. The fracture surface (Fig. 15b) revealed large population of fine dimples which indicate ductile mode of fracture. The
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tensile specimen at 2800 rpm failed at the WZ (Fig. 14c). The fracture surface (Fig. 15c) shows relatively flat surface compared to other fracture surfaces (Fig. 15a and b). Although some dimples are spotted, they did not grow fully and distributed throughout the fracture surface. This indicates that the failure was rapid. The increase in rotational speed beyond 2200 rpm increases the quantity of plasticized material more than optimum for consolidation. As a result, more amount of material at high temperature is expelled out of the interface. The grain size in WZ near
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the edges of the tube wall was very high as discussed in Sec 3.3 which leads to differential straining of WZ during tensile loading. This coarse grain region at both the end of the WZ yields to the tensile load and failure proceeds at higher pace in the WZ. Hence, the UTS is lower at
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2800 rpm. 4. Conclusions
rotational speeds. The following conclusions are derived:
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In the present work, titanium tubes were successfully joined using friction welding at different
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The increase in rotational speed decreased the peak and equilibrium torque. The peak toque was 324 Nm at 1600 rpm and 188 Nm at 2800 rpm while the equilibrium torque was 194 Nm at 1600 rpm and 112 Nm at 2800 rpm. The downward torque trend indicated that the heating rate was high at lower rotational speed and vice versa.
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The weld time was 46 s at 1600 rpm and 70 s at 2800 rpm .The increase in rotational speed increased the weld time due to reduction in heating rate to reach the preset axial shortening.
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The axial shortening was 1.1 mm at 1600 rpm and 2.2 mm at 2800 rpm .The increase in rotational speed increased the axial shortening due to increased expulsion of higher
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amount of plasticized material. The increase in rotational speed reduced the geometry of the weld zone and increased the
size of the flash due to increased amount of heated and plasticized material available prior to forging stage.
All the welded joints had three zones namely weld zone (WZ), heat affected zone (HAZ) and parent metal (PM). The grain structure in HAZ was identical to PM.
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The average grain size in WZ was measured to be 2.5 µm at 1600 rpm and 1.2 µm at 2800 rpm. The reduction in grain size was due to increased rate of deformation which dominated the coarsening effect of frictional heat.
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The grain size in WZ increased radially from the center towards the flash due to expansion of plasticized material at high temperature during forging stage.
The hardness of the WZ increased with an increase in rotational speed due to grain
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refinement. The average grain size in WZ was measured to be 175 Hv at 1600 rpm and 205 Hv at 2800 rpm.
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The joint strength was high at rotational speed of 2200. The lower joint strength at 1600 rpm and 2800 rpm was respectively ascribed to the presence of pores and coarsened grain regions in the WZ.
Acknowledgements
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The authors are grateful to Dr. V. Balasubramanian, Center for Materials Joining and Research at Annamalai University for technical inputs, Dr. I. Samajdar, OIM and Texture Lab at
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Indian Institute of Technology Bombay for EBSD characterization, Mr. Riaan Brown, Facilities Engineer at Nelson Mandela Metropolitan University for operating the friction processing
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platform, Mr. J. P. De Kock at Resolution Circle and Mr. D. Walter, Manufacturing Research Centre at University of Johannesburg for assisting in specimen preparation. References
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Welding Between Solid Bar of 6061 Al Alloy and Pipe of Al-Si12CuNi Al Cast Alloy. J Mater Eng Perform 2015;24:4551–60. 21. Rovere CAD, Aquino JM, Ribeiro CR, Silva R, Alcântara NG, Kuri SE. Corrosion behavior of radial friction welded supermartensitic stainless steel pipes. Mater Des 2015;65:318–27.
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22. Kimura M, Kusaka M, Kaizu K, Nakata K, Nagatsuka K. Friction welding technique and joint properties of thin-walled pipe friction-welded joint between type 6063 aluminum alloy and AISI 304 austenitic stainless steel. Int J Adv Manuf Technol 2016;82:489–99.
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Mechanical Properties of Dissimilar Metal AISI 304-AISI 4140 Continuous Drive Friction
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and flash formation of 45# steel in continuous drive friction welding. Trans Nonferrous Met Soc China 2012;22:s528–33.
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Mechanical Behaviuor of Rotary Friction Welded Titanium Alloys. Proc World Acad Sci Eng Technol 2007;26:426–8.
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28. Zhou L, Liu HJ, Liu QW. Effect of rotation speed on microstructure and mechanical properties of Ti–6Al–4V friction stir welded joints. Mater Des 2010;31:2631–6. 29. Nasser SN, Guo WG, Cheng JY. Mechanical properties and deformation mechanisms of a commercially pure titanium. Acta Mater 1999;47:3705–20.
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friction-welded AISI 304L to 4340 steel. Mater Des 2007;28:301–7.
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Fig. 1. (a) Friction processing platform and (b) a close up view of fixture. Fig. 2. Typical defects obtained during the friction welding of the titanium tubes; (a) cold weld, (b) excessive flash, (c) incomplete forging and (d) insufficient plasticization.
Fig. 4. Example of the machined tensile specimens.
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Fig. 3. An example of a friction welded tube at 2200 rpm rotational speed.
Fig. 5. Friction welding cycle recorded at rotational speed of 2200 rpm (1– Initial friction
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stage, 2– Friction stage, 3– Braking stage and 4– Forging stage).
Fig. 6. Effect of rotational speed on; (a) torque, (b) coefficient of friction, (c) power input, (d)
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weld time, (e) energy and (f) axial shortening.
Fig. 7. Optical macrograph of welded joint at rotational speed of; (a) 1600 rpm, (b) 1900 rpm, (c) 2200 rpm, (d) 2500 rpm and (e) 2800 rpm.
Fig. 8. Optical micrograph of welded joint at rotational speed of 2200 rpm; (a) parent metal
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and (b) transition zone.
Fig. 9. EBSD (IPF + grain boundary) map of welded joint at rotational speed of 2200 rpm; (a) parent metal and (b) weld zone.
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Fig. 10. Optical micrograph of weld zone at rotational speed of; (a) 1600 rpm, (b) 1900 rpm, (c) 2200 rpm, (d) 2500 rpm and (e) 2800 rpm and (f) effect of rotational speed on grain size.
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Fig. 11. Optical micrograph of weld zone using rotational speed of 2200 rpm at a radial distance of; (a) 0 mm (b) 0.8 mm, (c) 1.9 mm and (d) 2.3 mm from center. Fig. 12. Effect of rotational speed on microhardness. Fig. 13. Effect of rotational speed on UTS. Fig. 14. Optical micrograph of tensile failed specimens at rotational speed of; (a) 1600 rpm, (b) 2200 rpm and (c) 2800 rpm. Fig. 15. SEM micrograph of fracture surface of tensile failed specimens at rotational speed of; (a) 1600 rpm (pores are encircled), (b) 2200 rpm and (c) 2800 rpm.
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Torque and average frictional power reduced with increased rotational speed. Grain size of heat affected zone and weld zone were identical.
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Grain size was varying across the radial direction in the weld zone.
