ICADME-2011papersfu-may14th

Modification of Microstrucure and Residual Stress on Friction Welding Surface of Titanium Alloy by Water-jet Cavitation PeeningDongying Ju1,a,Xinmao Fu2, b, Shun Na 2, c, Bing Han3, d, Xiaohu Deng4, e 1Department of Mechanical Engineering, Saitama Institute of Technology, Fukaya, Saitama,369-0293, Japan2Graduate School of Engineering Department, Saitama Institute of Technology, Fukaya, Saitama,3Department of Materials and Process, University of Science and Technology LiaoNing,185Qianshan Zhong Road, Anshan, Liaoning, China4Advanced Science Research Laboratory, Saitama Institute of Technology, Fukaya, Saitama,a dyju@sit.ac.jp, d ustl@Keywords: Cavitation Peening, Residual stresses, Fatigue Strength, Surface treatment, Grains, Dislocation.Abstract.In order to make titanium alloy friction welded joints stronger, titanium alloy is strengthened through water-jet cavitation peening. Take place the changes of residual stress and microstructure, before and after the occurrence of cavitation peening.Measuring residual stress of the base metal and friction welding while observing their microstructures. Through water-jet cavitation peening making analysis of the changes of material properties caused by the changes of residual stress and microstructure of the materials.IntroductionCavitation is a phenomenon of formation of vapours bubbles in a flowing liquid. In many cases, it is undesirable but cavitation peening can improve properties of the surface of metals and also strengthen the strain in ord er to harden the metal surface. What’s more, it can cause work hardening which is caused because of dislocation movements within the crystal structure of the material. This study is to improve mechanical strength of welding department of titanium alloy friction welding material used by the aerospace equipment through the change of residual stress before and after cavitation peening of titanium alloy friction welding, Changes in grain structure welding department is observed by the optical microscope and scanning electron microscope to analyze material properties. Experimental equipment and preparationWCP equipment (water-jet cavitation peening equipment) Refer with Fig. 1. Cavitation is produced in the tank by a high-pressure water pump The pressure of a high-pressure water pump is 30MPa and pump outlet flow is 16L/min. Air is added at the Jet and the air flow rate is 0.4L/min.The injection device is fixed on bottom plate of the sink The jet is up and perpendicular to the bottom plate and the pressure around the jet is determined through the pressure-sensitive paper.The impact pressure distributions with various fluxes of aeration induced by the bubble collapse are diverse in the vertical direction, and there is an obvious change rules between impact pressure of bubble collapse and the standoff distance. In order to obtain the optimal standoff distances with various fluxes of aeration. The color density can be evaluated by FPD-305E color indicator. By ht soft of FPS-307E, the pressure can be drawn out from the change of color density. In this study, a new high pressure measurement was adopted. The measurement pressure of the film ranges from 130 to 300MPa. The precision is less than 10%, and the time of retention at the pressure is 5s. The support of pressure sensitive film is installed in the center of the vertical-type test water tank bottom. An example of pressure sensitivefilm treated by WCP is also given in Fig. 2. When the fluxes of aeration are 0.4L/min, respectively, the impact pressure distributions are measured. It can be determined just above the pump nozzle between 70mm to 85mm is the strongest pressure. So experiment position is determined just above the pump nozzle department of 80mm.Fig. 1 WCP equipmentX ,m m Y,mm07.46914.9422.4129.8837.3444.8152.2859.7567.2274.6978.4282.1693.36104.6119.5Pressure,MPaFig. 2 peening pressure space distributionSpecimen and the cavitation peening methods In this experiment, Table 1 shows the chemical composition of the specimen material. Materials from the friction welding titanium alloy sheet, through the wire-electrode cutting into the specimen. Size as Fig. 3.Table 1 Chemical composition(wt.%)Fig. 3 Dimension of the specimenCFe N O H Al V 0.005 0.192 0.007 0.143 0.005 6.295 4.180 ********Gas flowmeter Aeration pump Test specimen Jet nozzle Test water tank Plunger pump Feed pump Reservoir tank 87654321In order to observe the surface, it was polished to a mirror with 50-60μm emery paper. In order to use optical microscope, the surface is eroded in 5%HF+15%HNO3 +85% H2O solution for 5 seconds. Observe the microstructural evolution with WCP duration at a same point, an experimental design involving an in-situ observation function was conducted as Fig. 4. First, the same specimens A and B were ground and polished, and adjoining plane were eroded. The microstructure photos were recorded by Optical microscope. As shown in this Fig, the same specimens A B were joined by the special clamp and treated with 15 min duration. After the WCP treatment, the microstructures at the same points were again recorded by Optical microscope and SEM. Repeat the last two steps, in this method, microstructural evolution were recorded at 15, 30, 45, 60 min WCP duration.Fig. 4WCP experimental procedureFig. 5 depicts a schematic of the test specimen and clamp. The special clamp depicted in Fig. 5 was used to ideally combine the specimens A and B into one part. The key process conditions of WCP include aeration flux, standoff distances, and WCP duration. All of these attributes significantly impact the degree of enhancement of the process, and therein, it is necessary to determine ideal process conditions prior to treating the test specimens.the specimens were treated by WCP in the bottom center of the test water tank. WCP durations of 15min,30min,45min,and60min were investigated in this study.Fig. 5An experimental design involving an in-situ observation function Microstructure observationFig. 6 shows the in-situ observation results of titanium alloy base metal by Optical microscope. Fig.6 (a) is typical microstructure of titanium alloy, from Fig.6(b-e), The density and quantity of deformation twinning increase gradually with increasing WCP duration. For each sample, the density and quantity of deformation twinning decrease gradually with increasing layer depth. The depth of deformation twinning reaches about 40μm. The trend in micro structural change is similar to results of the residual stress. Fig. 7 shows the in-situ observation results of titanium alloy base metal SEM. It can get the same conclusion with Fig. 6.Fig. 6Optical microscope fractography titanium alloy base metal by WCP test specimen with the timeFig. 7 SEM fractography titanium alloy base metal by WCP test specimen with the time.Fig. 8 SEM fractography titanium alloy soldered joint by WCP test specimen with the timeBecause of friction welding, the grain refinement is produced at the welding department, resulting in the hardness of welds larger than the base metal. Therefore, the dislocation of welds is not very clear. Fig.8 (a) is microstructure of titaniumalloy, it shows the needle-like stripes become more than before, from Fig.8 (b-e).Residual stress methods and analysisTitanium alloy x-ray of stress measurement ray is small, seems to be not enough now fully examined as a measurement, x-ray stress measurement, x-ray of the measurement range the diffraction angle of the measuring device and ray tube In the diffraction intensity curve obtained Diffraction peaks. TC4 is a two-phase metallic materials from the construction phase and β phase α, stress measurement conditions are different for each phase, where the lattice constant of a dense hexagonal α phase c =4.68 Å and a = 2.92Å for X 2θ diffraction angle normal stress measurement system can be applied to specific line = 120 ~ 160deg examined the range of diffraction conditions, Co-Ka characteristic x-ray (λ wavelength = 1.789 Å) and a combination of diffraction plane Lattice spacing d and the plane index (hkl) can be found in the Diffraction angle 2θ diffraction results were calculated using the 211 diffraction condition of the equation. Table2 is the x- ray determination of the conditions of stress.Table 2 Determination of residual stress conditionsIn-situ x-ray stress measurement method to measure stress distribution of specimen a stress analyzer based on single exposure technique with one position sensitive proportional counter is used in the biaxial loading test system. As a brief theoretical development and a nondestructive method, x-ray stress measurement is presented emphasizing practical engineering applications of the pane-stress Tube type Tube voltage Current Slit diameter Diffractive planeMeasurement angle ψ Cr-K α 40Kv 30mA 1.0mm α-Fe (211) 144˚ 0˚,18.4˚,26.6˚,33.8˚,39.2˚,45˚ 02θmodel, which requires no external standard. All diffractions based on stress analysis utilize the distance between atomic planes of a crystalline specimen an an internal strain gage for any reflection can be determin ed from m of the appropriate diffraction peak through bragg’s law.Shows the diffraction of a monochromatic beam of x-rays at a high diffraction angle from the surface of a stressed sample for two orientations of the sample relative to the x-ray beam. Fig. 9shows the location of the stress measurement points. Point A is in the department of friction welding. Point B is base metal. Residual stress measurement was recorded at 0, 15, 30, 45, 60 min WCP duration.Stress σwas obtained by the following equations :2(2)''(sin )K M K θσψ∂=⋅=⋅∂Fig. 9 Determination of the location of residual stressR e s i d u a l s t r e s s ,M P a WCP time,minFig. 10 Residual stress changes at 0, 15, 30, 45, 60 min WCP duration at point A,BFig.10 shows over time WCP sample surface residual stress became compressive stress, while compressive stress increases with time.ConclusionsThe experimental results with the in-situ observation function indicate that WCP process can induce deformation twinning and high density dislocations in the strengthening layer of titanium alloy base metal and friction soldered joint. The dislocation sources in crystal grains are continuously induced in the near-surface of specimens due to the shear stresses. The dislocation density increases gradually, and many dislocation pile-ups form. When plastic deformation occurs, deformation twinning is induced at the location of the dislocation block due to the low number of slip systems. The microstructure changes verify the existence of micro-plastic strain in WCP processing. The generation mechanism of residual stress is related to the activity of deformation twinning and dislocations.AcknowledgementsWe would like to show gratefulness to the continuous support from the High-Tech Research Center at the Saitama Institute of Technology.References[1] D.Y.Ju,H.Tsuda,Vincent Ji,T.Uchiyama and R.Oba,Surface Improvement of A Quenched Gear Using Water Peening by a Cavitation Jet Technique, ATEM’03, JSME-MMd, Sep. 10-12, pp.248-263(2003)[2] Bing Han. Studies on Generation Mechanism of Residual Stress and Material Strengthening by Water-jet Cavitation Peening. Doctor paper. Saitama Institute of Technology. (2009)[3] Jangang Wang. Study on evolution technology of anisotropic mechanical properties and microstructure evolution of metal thin plate under complex stress condition. Doctor paper. Saitama Institute of Technology. March, (2011)[4] Nasun. Study on improvement of fatigue strength of friction welded Cavitation Peening Method. Master paper. Saitama Institute of Technology. (2010)[5] A. Sahaya Grinspan, R.Gnanamoorthy, Surface modification by oil jet peening in aluminum alloys AA6063-T6 and AA601-T4: surface morphology, erosion and mass. Loss. Appl.Surf.Sci.253 (2006) 997-1006[6] D. Salko, Peening by water. Proceeding of 2nd International Conference on Shot Peening, Chicago, USA, May, 1984, 37-38[7] Z. Sun, X. Q. Kang, X. H. Wang, Experimental system of cavitation erosion with water-jet. Mater. Des. 26 (2005) 59-63[8] M. Qin, Improvement on the process capability of water cavitation peening by aeration. D. Y. Ju, R. Oba, Surf. Coat. Tech. 200 (2006) 5364-5369[9] H. Soyama, Introduction of compressive residual stress using a cavitating Jet in Air. ASME J. Fluids Eng. 127(2005) 1095-1101[10] F. G. Hammitt, M. K. De, Cavitation damage prediction. Wear 52(1979)243-262[11] Y. L. Chen, T. Kuhl, Mechanism of Cavitation Damage in Thin Liquid Films: Collapse Damage versus Inception Damage. J. Israelachvili, Wear 153(1992) 31-51。