*Supported by National Natural Science Foundation of China Nos. 51571052&51371044, Fundamental Research Funds for the Central Universities No. L1502027, Nature Science Foundation of Liaoning Province No. 2014020034.;
The effect of strain rate on the deformational behavior of laser welded joint of superalloy GH4169 was investigated, and the mechanism for strain rate sensitivity of the tensile deformation was discussed. The results show that the welded joints were more sensitive to the strain rate compared to the base material. The strain rate had little influence on the strength of welded joints at the strain rate range from 10-3 s-1 to 10-1 s-1. When the strain rate was higher than 100 s - 1, the yield strength and ultimate tensile strength of the welded joint increased with increasing strain rate, at the same time the yield strength had a much obvious increase. On the other hand, the plasticity of the welded joint tended to decrease with the increasing strain rate, however it increased while the strain rate changed from 101 s-1 to 102 s-1 and then reached the peak value of ductility by the strain rate of 102 s-1. The tensile failure location changed from the base material via the softened heat-affected zone to near the fusion zone with the increase of the strain rate. The strain rate sensitivity of deformation and fracture behavior of the welded joint under high strain rate was mainly caused by the difference of strain rate sensitivity of microstructures at different positions in the welded joint.
实验用GH4169合金的化学成分(质量分数, %)为: C 0.03, Fe 18.65, Cr 19.17, Mo 2.96, Al 0.52, Ti 1.03, Nb 5.05, Mn 0.011, P 0.002, S 0.002, B 0.003, Ni余量。采用真空感应(VIM)+真空电弧重熔(VAR)双联工艺冶炼出直径为508 mm的合金锭, 再经1160℃和1190℃两段式高温均匀化退火消除Laves相和Nb偏析后, 多火次锻造成截面为70 mm×210 mm的扁坯, 再精轧成24 mm×210 mm的扁坯供轧制板材成品。板材成品经多次冷轧和去应力退火轧, 制成厚度为1.4 mm的板材。
使用JHM-1GY-700型Nd: YAG多功能激光加工机对GH4169合金激光焊接。选用纯度为99.99%的Ar作为焊接保护气体, 气体流量为22 L/min, 聚焦镜焦距为100 mm, 离焦量为-3.1 mm, 脉宽为9.0 ms, 电流为89 A, 频率为9 Hz, 焊接速度为370 mm/min等工艺参数。
Fig.2
Macromorphologies of the welded joints of GH4169 alloy under different laser welding parameters (a) pulse width of 9.6 ms; (b) pulse width of 9.0 ms; (c) pulse width of 8.7 ms; (d) pulse current of 89 A; (e) pulse current of 93 A
固定脉冲宽度9.0 ms、脉冲频率9 Hz、离焦量-3.1 mm, 当脉冲电流强度为89A时焊点重合较好, 溶池样貌完整(图2d)。当脉冲电流强度由89 A升至93 A时焊缝表面出现气孔(图2e), 由此确定最佳电流强度为89 A。综上, 激光焊接1.4 mm厚 GH4169板材的优化参数为: 离焦量-3.1 mm, 脉宽9.0 ms, 电流强度89 A, 频率9 Hz, 焊接速度370 mm/min。
Fig.3
Microstructures of double side laser welded joint of GH4169 alloy (a) overview of the welded joint; (b) base material; (c) heat-affected zone; (d) columnar zone; (e) equiaxed zone; (f) remelting zone
Fig.5
Tensile properties of the base metal and laser welded joint of GH4169 alloy under various strain rates (welded joint: WJ; base material: BM) (a) yield strength; ultimate tensile strength; (b) elongation
MADexin, Development of single crystal solidification technology for production of superalloy turbine blades,Acta Metallurgica Sinica, 51(10), 1179(2015)
ZHUOu, LIYulong, ZHANGYan, CAOWei, LEILiming, Heat treatment process for single-crystal superalloys used in aeroengines,Foundry Technology, 34(9), 1137(2013)
DUSuigeng, WANGXifeng, GAOMan, Characteristics of the friction welding interface between single crystal superalloy DD3 and fine grained superalloy GH4169,Acta Metallurgica Sinica, 51(8), 951(2015)
Guo-QingChen, Bing-GangZhang, Tian-MinLÜ, Ji-CaiFeng, Causes and control of welding cracks in electron-beam-welded superalloy GH4169 joints,Transactions of Nonferrous Metals Society of China, 23, 1971(2013)
Welding joint of GH4169 alloy with a good formation was obtained. No macroscopic defects occurred in the joint. The weld had mainly a dendritic structure; the base metal was a solid solution of Ni, Cr, and Fe, and the strengthening-phase particles such as Ni3Nb were dispersively distributed along the grain boundary. The average tensile strength of the joint reached 743.7 MPa, and the Vickers hardness of the weld exceeded HV 300. Because of the segregation of the low-melting compound Ni3Nb at the grain boundary of the fusion zone, liquid cracks tended to occur as a result of welding stress. The formation of liquid cracks was inhibited by adding an alloying element, Mn, to the welding bath, because Mn diffused to the fusion zone and the high-melting phase Mn2Nb formed, and thus the overall properties of the joint were improved.
DongyunZhang, WenNiu, XuanyangCao, ZhenLiu, Effect of standard heat treatment on the microstructure and mechanical properties of selective laser melting manufactured Inconel 718 superalloy,Materials Science & Engineering A, 644, 32(2015)
ABSTRACT Inconel 718 superalloy has been fabricated by selective laser melting technology (SLM). Its microstructure and mechanical properties were studied under solution+aging (SA) standard heat treatment, homogenization+solution+aging (HSA) standard heat treatment and as-fabricated conditions. Precipitated phases and microstructures were examined using OM, SEM, TEM and X-ray analysis methods. The fine dendrite structures with an average dendrite arm spacing of approximately 698 nm accompanying some interdendritic Laves phases and carbide particles can be observed in the as-fabricated materials. After standard heat treatments, dendrite microstructures are substituted by recrystallization grains, and Laves phases also dissolve into the matrix to precipitate strengthening phases and δ particles. The test values of all specimens meet Aerospace Material Specification for cast Inconel 718 alloy, and the transgranular ductile fracture mode exists for the three conditions. The strength and hardness of heat-treated SLM materials increase and are comparable with wrought Inconel 718 alloy, whereas their ductility decreases significantly compared with the as-fabricated material. This is because of the precipitation of fine γˊ and γ〞strengthening phases and needle-like δ phases. For the as-fabricated alloy, the formation of finer dislocated cellular structures that develop into a ductile dimple fracture shows excellent ductility. Due to dislocation pinning from γˊ and γ〞strengthening phases and the impediment of dislocation motion caused by the needle-like δ phases, the ductility of the SA materials decreases and causes a transgranular fracture, compared with the as-fabricated samples.
TiejunMa, MingYan, XiaweiYang, WenyaLi, Y.J. Chao, Microstructure evolution in a single crystal nickel-based superalloy joint by linear friction welding,Materials & Design, 85, 613(2015)
Linear friction welding (LFW) was used with a single crystal nickel-based superalloy to produce sound welds. Microstructural examination shows that the joint has a distinct weld zone (WZ) and thermomechanically affected zone (TMAZ). In the WZ, the microstructure has recrystallized polycrystals instead of a single crystal. In the TMAZ, the amount of γ′ phase increased from the TMAZ/WZ interface to the parent material (PM) and decreased from the periphery to the centre along the weld creating a U-shaped microhardness profile in the TMAZ. The microhardness is however lower than that in the WZ. The average tensile strength was found to be 837.502±025002MPa, comparable to the PM (88002MPa [26]).
M.Pouranvari, A.Ekrami, A.H.Kokabi, Solidification and solid state phenomena during TLP bonding of IN718 superalloy using Ni-Si-B ternary filler alloy,Journal of Alloys & Compounds, 563, 143(2013)
This paper addresses solidification and solid state precipitation phenomena during transient liquid phase (TLP) bonding of wrought IN718 nickel base superalloy using Ni–4.5Si–3.2B (wt.%) ternary filler alloy. The solidification sequence of the residual liquid in the joint centerline was found to be (1) formation of proeutectic γ, followed by (2) γ/Ni 3 B eutectic reaction, followed by (3) ternary eutectic of γ/Ni 3 B/Ni 6 Si 2 B. Extensive fine Ni 3 Si formed within the eutectic-γ via solid state precipitation during cooling. Extensive Cr–Mo–Nb rich boride precipitates were formed in the substrate region due to boron diffusion into the base metal during bonding process. The implications of the phase transformations on the mechanical properties, corrosion resistance and aging behavior of the joint, which are pertinent to the development of an optimum post bond heat treatment, are highlighted.
FeiYan, ChunmingWang, YajunWang, XiyuanHu, TianjiaoWang, JianminLi, GuozhuLi, A study of the mechanism of laser welding defects in low thermal expansion superalloy GH909,Materials Characterization, 78, 21(2013)
In this paper, we describe experimental laser welding of low-thermal-expansion superalloy GH909. The main welding defects of GH909 by laser in the weld are Equation cracks and porosities, including hydrogen and carbon monoxide porosity. The forming mechanism of laser welding defects was investigated. This investigation was conducted using an optical microscope, scanning electron microscope, energy diffraction spectrum, X-ray diffractometer and other methodologies. The results demonstrated that porosities appearing in the central weld were related to incomplete removal of oxide film on the surface of the welding samples. The porosities produced by these bubbles were formed as a result of residual hydrogen or oxygenium in the weld. These elements failed to escape from the weld since laser welding has both a rapid welding speed and cooling rate. The emerging crack in the heat affected zone is a liquation crack and extends along the grain boundary as a result of composition segregation. Laves-Ni2Ti phase with low melting point is a harmful phase, and the stress causes grain boundaries to liquefy, migrate and even crack. Removing the oxides on the surface of the samples before welding and carefully controlling technological parameters can reduce welding defects and improve formation of the GH909 alloy weld. (C) 2013 Elsevier Inc. All rights reserved.
Bing-QingChen, Hua-PingXiong, Bing-BingSun, Bo-RuiDu, Zhen-WeiWei, BoChen, Dissimilar joining of Ti3Al-based alloy to Ni-based superalloy by arc welding technology using gradient filler alloys,Materials & Design, 87, 732(2015)
In this study, Ti–Al–Nb, Ti–Ni–Nb and Ni–Cr–Nb system alloys were designed and incorporated in order to construct a gradient structure at the surface of the joined Ti 3 Al base material. And the Ti 3 Al-based alloy and Ni-based superalloy were successfully joined together using gas tungsten arc (GTA) welding technology. The microstructure evolution, mechanical properties and fractured behaviors of the joints were investigated. The gradient structure remarkably decreased the formation tendency of brittle phases within the joints compared with a single filler alloy and thus improved the joint strength effectively. The average room-temperature tensile strength of the Ti 3 Al/In718 dissimilar joint reached 35302MPa, and the strength value at 87302K was 24502MPa. At the Ti–Ni–Nb/Ni–Cr–Nb interface, some Ni 3 (Nb, Ti)02+02(Nb, Ti)Cr 2 and TiNi 3 phases were detected in the Ti–Ni–Nb matrix. It was believed that their presence decreased the room-temperature strength of the Ti–Ni–Nb alloy but improved its high-temperature strength.
M.Khakian, S.Nategh, S.Mirdamadi, Effect of bonding time on the microstructure and isothermal solidification completion during transient liquid phase bonding of dissimilar nickel-based superalloys IN738LC and Nimonic 75,Journal of Alloys & Compounds, 653, 386(2015)
Joining of dissimilar nickel base superalloys IN738LC to Nimonic 75 by use of transient liquid phase bonding with Ni–15Cr-3.5B interlayer (MBF-80) was carried out at temperatures of 1080°C, 1120°C, 1150°C and 1180°C for different bonding times. Joint microstructure was surveyed by optical and scanning electron microscopy. Microstructural examinations showed those in short bonding times, the joint microstructure consists of continuous eutectic intermetallic phases and longer times lead to eutectic free microstructure. It was shown that bond shear strength increases with holding time increment. Fick's equations were used for prediction the time required for completion of isothermal solidification. It was seen that there was a good correspondence between the results of modeling and experimental data.
X.Chen, F. Q.Xie, T. J.Ma, W. Y.Li, X. Q.Wu, Microstructure evolution and mechanical properties of linear friction welded Ti2AlNb alloy,Journal of Alloys & Compounds, 646, 490(2015)
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XinYe, XuemingHua, MinWang, SongnianLou, Controlling hot cracking in Ni-based Inconel-718 superalloy cast sheets during tungsten inert gas welding,Journal of Materials Processing Technology, 222, 381(2015)
The pre-welding condition of the base metal, the welding heat input, and the state of the interlayer in multi-layer welding are examined to identify means of controlling the hot cracking in Inconel-718 cast sheets during tungsten inert gas (TIG) welding. A finite element method (FEM) incorporating the cast microstructure and alloy chemical composition was used to calculate the welding stresses and predict crack initiation. The crater crack, weld-seam center longitudinal solidification crack, and the weld toe compound crack mixed with the transversal solidification crack and the heat-affected zone (HAZ) liquation crack are discussed. A pre-welding homogenization heat treatment, lower welding heat input, and post-welding crater grinding of each individual welding seam can decrease its hot cracking susceptibility.
GuangyiMa, DongjiangWu, FangyongNiu, HelinZou, Microstructure evolution and mechanical property of pulsed laser welded Ni-based superalloy,Optics and Lasers in Engineering, 72, 39(2015)
For evaluating the microstructure evolution and mechanical property of Ni-based Hastelloy C-276 weld joint by the pulsed laser welding, the influence of pulsed laser welding on the microstructure and mechanical property of the weld joint is investigated by the analysis of the microstructure morphology, microhardness, phase structure and tensile property. The results indicate that, in the fusion zone three sections are divided on the basis of the patterns of grain structures. In the weld joint, the element segregation is found, but the trend of brittle phase's formation is weakened. The weld microhardness presents just a little higher than that of base metal, and there is no obvious the softened heat affected zone. Meanwhile in the weld joint, the phase structure is still the face-center cubic with the tiny shift of peak positions and widened Full Width at Half-Maximum. The yield strength of weld joint is the same as that of base metal, and the tensile strength is nearly 90% of that of base metal. The decreased tensile strength is mainly attributed to the dislocation piling-up.
LongfeiNie, LiwenZhang, ZhiZhu, WeiXu, Microstructure evolution modeling of FGH96 superalloy during inertia friction welding process,Finite Elements in Analysis and Design, 80, 63(2014)
In order to investigate the microstructure evolution of inertia friction welding process of FGH96 ring part, the dynamic recrystallization kinetic model of FGH96 superalloy was established and a two-dimensional axisymmetric coupled thermo-mechanical finite element model was developed using the MSC.Marc software. By the second development of MSC.Marc, the dynamic recrystallization kinetic model was integrated into the finite element model to simulate the microstructure evolution of inertia friction welding process of FGH96 superalloy. The distributions of dynamic recrystallized fraction and average grain size during the inertia friction welding process were obtained and analyzed. The inertia friction welding experiments of FGH96 ring parts were carried out. The comparison results show that the simulated results agree well with the measured ones. (C) 2013 Elsevier B.V. All rights reserved.
M.Pouranvari, A.Ekrami, A.H.Kokabi, TLP bonding of cast IN718 nickel based superalloy: Process-microstructure-strength characteristics,Materials Science & Engineering A, 568, 76(2013)
This paper aims at addressing the microstructure–strength characteristics relationship during transient liquid phase (TLP) bonding of cast IN718 nickel based superalloy using Ni-7Cr-4.5Si-3Fe-3.2B (wt%) amorphous interlayer. The progress of the isothermal solidification at different temperatures for different times is analyzed using a Larson–Miller parameter (LMP). It was found that there is direct relationship between isothermal solidification zone (ISZ) size and LMP. Results showed that in situation where isothermal solidification has not been completed, the ratio of athermal solidification zone (ASZ) size to the width of the total solidified zone is the controlling factor for shear strength of the TLP bonds. After completion of isothermal solidification, the shear strength of the joint is controlled by the hardness of ISZ, which in turn is governed by transport of solid solution strengthening elements (more effectively Cr, Nb and Mo) via dissolution of the base metal and inter diffusion between base metal and bond region during isothermal solidification.
Bo-WunHuang, Effect of number of blades and distribution of cracks on vibration localization in a cracked pre-twisted blade system,International Journal of Mechanical Sciences, 48, 1(2006)
A number of several blades can be grouped at their tips to increase their stiffness. This work examines how the effect of number of grouped blades and distribution of cracks affect the mode localization of a mistuned blade system. The pre-twisted blade and the effect of twist angle on localization are also considered in this article. Dynamic characteristics of blades in a blade system are focused to study. Periodically coupled pre-twisted beams were used to approximate shrouded blades. The Euler-Bernoulli beam model was employed to characterize the tapered pre-twisted blade. The mode localization equations associated with the local blade crack defects in the rotating grouped blade system were formulated using Hamilton's principle. The Galerkin method was used to discretize the localization equations of the mistuned system. The numerical results herein reveal that the number of grouped blades and the distribution of multi-disorders in a rotating blade system may markedly affect the localization phenomenon.
X.Fang, J.Tang, E.Jordan, K.D.Murphy, Crack induced vibration localization in simplified bladed-disk structures,Journal of Sound and Vibration, 291, 395(2006)
In this paper, we study the effect of a crack on the vibratory response of a simplified aero-engine bladed-disk model, which consists of cantilevered beams (blades) coupled with springs (inter-blade internal coupling). Our goal is to obtain qualitative understandings of the unique dynamic behavior of such structure with crack, i.e., the occurrence of vibration localization and its level. A fracture mechanics based approach is employed to evaluate the crack induced stiffness loss on a single beam. By taking advantage of the structural periodicity or near-periodicity, using the U-transformation approach we then develop analytical solutions to the free and forced vibrations of the bladed-disk with a single crack. It is identified that, while the stiffness loss on a single beam could be small and may not cause a significant frequency change, it could lead to the free and forced vibration localization in a periodic structure. The intrinsic relation between the response amplitudes and various system parameters such as internal coupling, crack severity, excitation patterns and number of blades is systematically investigated.
JINTao, ZHOUYizhou, WANGXinguang, LIUJinlai, SUNXiaofeng, HUZhuangqi, Research process on microstructural stability and mechanical behavior of advanced Ni-based single crystal superalloys,Acta Metallurgica Sinica, 51(10), 1153(2015)
JianjunWang, Wei-GuoGuo, YuSu, PingZhou, KangboYuan, Anomalous behaviors of a single-crystal Nickel-base superalloy over a wide range of temperatures and strain rates,Mechanics of Materials, 94, 79(2016)
This study is concerned with the plastic behaviors of a newly developed single-crystal Nickel-base superalloy over a temperature range of 293–1273K and over a strain-rate range of 0.001–4000/s. Both static and dynamic loading tests were conducted to study the true stress–true strain behaviors of the superalloy along the nominal orientation [001]. Anomalous high temperature peak of the flow stress and the property of tension/compression asymmetry were noticed in the tests. Investigation on the experimental results was carried out to study the strain-rate effect on the temperature-dependent anomalies of the flow stress. It was found that the peak of the flow stress shifts to a higher temperature as the applied strain rate increases. Subsequent study of the temperature-dependent rupture property of the material revealed that the path of the crack propagation is dependent on the temperature. The strengthening and failure mechanisms of the material were established based on the experimental observations. Finally, a constitutive model was developed to describe the temperature and strain-rate effects on the material's yield behavior. The model is able to capture the anomalous temperature peak of the yield strength, which is dependent on the applied strain rate. It was demonstrated that the yield behavior of the superalloy can be adequately predicted over a wide range of temperatures and strain rates.
George Z.Voyiadjis, FaridH.Abed, A coupled temperature and strain rate dependent yield function for dynamic deformations of bcc metals,International Journal of Plasticity, 22, 1398(2006)
A coupled temperature and strain rate microstructure physically based yield function is proposed in this work. It is incorporated along with the Clausius鈥揇uhem inequality and an appropriate free energy definition in a general thermodynamic framework for deriving a three-dimensional kinematical model for thermo-viscoplastic deformations of body centered cubic (bcc) metals. The evolution equations are expressed in terms of the material time derivatives of the elastic strain, accumulated plastic strain (isotropic hardening), and the back stress conjugate tensor (kinematic hardening). The viscoplastic multipliers are obtained using both the Consistency and Perzyna viscoplasticity models. The athermal yield function is employed instead of the static yield function in the case of the Perzyna viscoplasticity model. It is found that the static strain rate value, at which the material shows rate-independent behavior, varies with the material deformation temperature. Computational aspects of the proposed model are addressed through the finite element implementation with an implicit stress integration algorithm. Finite element simulations are performed by implementing the proposed viscoplasticity constitutive models in the commercial finite element program ABAQUS/Explicit [ABAQUS, 2003. User Manual, Version 6.3. Habbitt, Karlsson and Sorensen Inc., Providence, RI] via the user material subroutine coded as VUMAT. Numerical implementation for a simple compression problem meshed with one element is used to validate the proposed model implementation with applications to tantalum, niobium, and vanadium at low and high strain rates and temperatures. The analysis of a tensile shear banding is also investigated to show the effectiveness and the performance of the proposed framework in describing the strain localizations at high velocity impact. Results show mesh independency as a result of the viscoplastic regularization used in the proposed formulation.
Marc A.Meyers, Vitali F.Nesterenko, Jerry C.Lasalvia, QingXue, Shear localization in dynamic deformation of materials: microstructural evolution and self-organization,Materials Science & Engineering A, 317, 204(2001)
ABSTRACT The plastic deformation of crystalline and non-crystalline solids incorporates microscopically localized deformation modes that can be precursors to shear localization. Shear localization has been found to be an important and sometimes dominant deformation and fracture mode in metals, fractured and granular ceramics, polymers, and metallic glasses at high strains and strain rates. Experiments involving the collapse of a thick walled cylinder enable controlled and reproducible application of plastic deformation at very high strain rates to specimens. These experiments were supplemented by hat-shaped specimes tested in a compression Hopkinson bar. The initiation and propagation of shear bands has been studied in metals (Ti, Ta, Ti-6A1-4V, and stainless steel), granular and prefractured ceramics (Al2O3 and SiC), a polymer (teflon) and a metallic glass A fine recrystallized structure is observed in Ti, Cu, Al-Li, and Ta, and it is becoming clear that a recrystallization mechanism is operating. The fast deformation and short cooling times inhibit grain-boundary migration; it is shown, for the first time, that a rotational mechanism, presented in terms of dislocation energetics and grain-boundary reorientation, can operate within the time of the deformation process. In pre-fractured and granular ceramics, a process of comminution takes place when the particles are greater than a critical size ac. When they are smaller than ac, particle deformation takes place. For the granular SiC, a novel mechanism of shear-induced bonding was experimentally identified inside the shear bands. For all materials, shear bands exhibit a clear self-organization, with a characteristic spacing that is a function of a number of parameters. This self-organization is analyzed in terms of fundamental material parameters in the frame of Grady-Kipp (momentum diffusion), Wright-Ockendon, and Molinari (perturbation) models.
WurongWang, MengLi, ChangweiHe, XichengWei, DazhiWang, HanbinDu, Experimental study on high strain rate behavior of high strength 600-1000 MPa dual phase steels and 1200 MPa fully martensitic steels,Materials and Design, 47, 510(2013)
As one of high grade advanced high strength steels (AHSSs), dual phase (DP) steel sheets and fully martensitic (MS) steel sheets have been successfully used in automotive crash-resistance components for its great benefit in reducing vehicle weight while improving car safety as well as their advantage in cost saving through cold forming instead of hot forming. The strain rate sensitivity of 600/800/1000 MPa DP and 1200 MPa MS were studied in this paper through a split Hopkinson tensile bar (SHTB) setup and compared with each other. The experiments showed that all dual phase (DP) AHSS ranging from 600 MPa to 1000 MPa are of positive strain rate sensitivity. While for the tested 1200 MPa MS, negative strain rate sensitivity has been found. Possible reason for the difference has been investigated through metallo-graphical observation and their microstructures. (C) 2013 Elsevier Ltd. All rights reserved.
B. L.Boyce, M. F.Dilmore, The dynamic tensile behavior of tough, ultrahigh-strength steels at strain-rates from 0.0002 s-1 to 200 s-1,International Journal of Impact Engineering, 36, 263(2009)
<h2 class="secHeading" id="section_abstract">Abstract</h2><p id="">The present study examines the strain-rate sensitivity of four high-strength, high-toughness steels at strain-rates ranging from 0.0002 s<sup>−1</sup> to 200 s<sup>−1</sup>: AerMet 100, modified 4340, modified HP9-4-20, and a recently developed Eglin AFB steel alloy, ES-1c. A newly developed dynamic servohydraulic method was employed to perform tensile tests over this entire range from quasi-static to near split-Hopkinson or Kolsky bar strain-rates. Each of these alloys exhibits only modest strain-rate sensitivity. Specifically, the semi-logarithmic strain-rate sensitivity factor <em>β</em> was found to be in the range of 14–20 MPa depending on the alloy. This corresponds to a ∼10% increase in the yield strength over the 6-orders of magnitude change in strain-rate. Interestingly, while three of the alloys showed a concomitant ∼3–10% drop in their ductility with increasing strain-rate, the ES-1c alloy actually exhibited a 25% increase in ductility with increasing strain-rate. Fractography suggests the possibility that at higher strain-rates ES-1c evolves towards a more ductile dimple fracture mode associated with microvoid coalescence.</p>
XiangyuWang, ChuanzhenHuang, BinZou, HanlianLiu, HongtaoZhu, JunWang, Dynamic behavior and a modified Johnson-Cook constitutive model of Inconel 718 at high strain rate and elevated temperature,Materials Science & Engineering A, 580, 385(2013)
Abstract Constitutive model is very important in finite element simulation of Inconel 718 cutting process. However, there are few constitutive models for Inconel 718 which are suitable for the cutting process. In this research, firstly, dynamic behavior of Inconel 718 at high strain rate and elevated temperature of the same order as the practical cutting process was obtained using SHPB(Split Hopkinson Pressure Bar) test. In the tests, the strain rate was 5000-11000 s(-1), and the temperature was 500-800 degrees C. Secondly, thermal and strain rate effect were discussed. Strain rate softening effect was found at high strain rate and discussed, and it was temperature dependent. Finally, a modified Johnson-Cook model was established.
L. X.Tian, C. L.Ma, Strain rate dependence of the yield stress and strain hardening rate of a single crystal superalloy at intermediate temperature,Materials Science & Engineering A, 620, 198(2015)
The effect of temperature and strain rate on the yield stress and deformation mechanism of the DD6 single crystal is investigated. The results show that the strain rate has very limited effect on the yield stress and strain hardening rate at 87302K, but has strong effect on both properties at 107302K. The situation at 87302K is similar with the single phase γ00. At 107302K, the strong strain rate dependence of yield stress is due to the operation of stalking faults. The strain rate dependence of strain hardening rate at 107302K is attributed to the difference of the dislocation density in the matrix channels.
E.Chlebus, K.Gruber, B.Kuźnicka, J.Kurzac, T.Kurzynowski, Effect of heat treatment on microstructure and mechanical properties of Inconel 718 processed by selective laser melting,Materials Science & Engineering A, 639, 647(2015)
ABSTRACT Microstructural and mechanical properties of Inconel 718 were determined on the specimens manufactured by selective laser melting (SLM) of prealloyed powder. High density (99.8%) cylindrical specimens were built with four orientations (0°, 45 °, 45°×45° and 90°) in relation to the building and scanning directions. Because of directional, dendritic-cellular grain growth, microstructure of the as-built specimens was characterized by columnar grains of supersaturated solid solution with internal microsegregation of Nb and Mo, demonstrated by fractions of Laves eutectic or its divorced form in interdendritic regions. Such a heterogeneous microstructure is unsuitable for direct post-process ageing and makes the alloy sensitive to subsolidus liquation during rapid heating to the homogenizing temperature. In homogenized and aged condition, the alloy received a very good set of mechanical properties in comparison with the wrought material. In heat-treated condition, like in as-built condition, weak anisotropy of properties was found, manifested by lower Young's modulus, yield strength and tensile strength of the specimens extended along the build direction in comparison to the values for the other variants of the specimens. This is attributed to the fact that the grains maintained their geometric and crystallographic texture obtained during solidification.
YangLiu, DanyangDong, LeiWang, XiChu, PengfeiWang, MengmengJin, Strain rate dependent deformation and failure behavior of laser welded DP780 steel joint under dynamic tensile loading,Materials Science & Engineering A, 627, 296(2015)
Laser welded DP steel joints are used widely in the automotive industry for weight reduction. Understanding the deformation and fracture behavior of the base metal (BM) and its welded joint (WJ), especially at high strain rates, is critical for the design of vehicle structures. This paper is concerned with the effects of strain rate on the tensile properties, deformation and fracture behavior of the laser welded DP780 steel joint. Quasi-static and dynamic tensile tests were performed on the WJ and BM of the DP780 steel using an electromechanical universal testing machine and a high-speed tensile testing machine over a wide range of strain rate (0.0001鈥1142 s). The microstructure change and microhardness distribution of the DP780 steel after laser welding were examined. Digital image correlation (DIC) and high-speed photography were employed for the strain measurement of the DP780 WJ during dynamic tensile tests. The DP780 WJ is a heterogeneous structure with hardening in fusion zone (FZ) and inner heat-affected zone (HAZ), and softening in outer HAZ. The DP780 BM and WJ exhibit positive strain rate dependence on the YS and UTS, which is smaller at lower strain rates and becomes larger with increasing strain rate, while ductility in terms of total elongation (TE) tends to increase under dynamic loading. Laser welding leads to an overall reduction in the ductility of the DP780 steel. However, the WJ exhibits a similar changing trend of the ductility to that of the BM with respect to the strain rate over the whole strain rate range. As for the DP780 WJ, the distance of tensile failure location from the weld centerline decreases with increasing strain rate. The typical ductile failure characteristics of the DP780 BM and WJ do not change with increasing strain rate. DIC measurements reveal that the strain localization starts even before the maximum load is attained in the DP780 WJ and gradual transition from uniform strains to severely localized strains occurs at high strain rates. The diffuse necking of the DP780 WJ occurs earlier during the tensile deformation process at higher strain rates under dynamic loadings.
Woei-ShyanLee, Chi-FengLin, Tao-HsingChen, Hong-WeiChen, Dynamic mechanical behaviour and dislocation substructure evolution of Inconel 718 over wide temperature range,Materials Science & Engineering A, 528, 6279(2011)
Abstract A compressive split-Hopkinson pressure bar and transmission electron microscope (TEM) are used to investigate the mechanical behaviour and microstructural evolution of Inconel 718 at strain rates ranging from 1000 to 5000s611 and temperatures between 61150 and 550°C. The results show that the flow stress increases with an increasing strain rate or a reducing temperature. The strain rate effect is particularly pronounced at strain rates greater than 3000s611 and a deformation temperature of 61150°C. A significant thermal softening effect occurs at temperatures between 61150 and 25°C. The microstructural observations reveal that the strengthening effect in deformed Inconel 718 alloy is a result primarily of dislocation multiplication. The dislocation density increases with increasing strain rate, but decreases with increasing temperature. By contrast, the dislocation cell size decreases with increasing strain rate, but increases with increasing temperature. It is shown that the correlation between the flow stress, the dislocation density and the dislocation cell size is well described by the Bailey–Hirsch constitutive equations.
Effect of bonding time on the microstructure and isothermal solidification completion during transient liquid phase bonding of dissimilar nickel-based superalloys IN738LC and Nimonic 75,
0
2015
Microstructure evolution and mechanical properties of linear friction welded TiAlNb alloy,
, 王磊, 李妨
