ISSN 0412-1961
CN 21-1139/TG
Started in 1956

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    Research Articles
    SUPERPLASTICITY OF ALUMINIUM SERIES INTERMETALLIC COMPOUND
    Acta Metall Sin, 2008, 44 (1): 1-7 . 
    Abstract   PDF (366KB) ( 886 )
    Based on basic conceptions of superplasticity and intermetallic compound, the significance of studying the supeplasticity of intermetallic compound is adressed. And recent advances in superplasticity in Ni-Al, Ti-Al and Fe-Al aluminium series intermetallic componund are reviewd.
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    GRAIN-SIZE DEPENDENCE OF COCIVITY OF NANOCOMPOSITE PERMANENT MAGNETS IN THREE PHASE-DISTRIBUTION MODELS
    Acta Metall Sin, 2008, 44 (1): 8-12 . 
    Abstract   PDF (185KB) ( 929 )
    Phase distribution and grain size are the key factors controlling the coercivity of nanocomposite permanent magnets. Assuming three simple physical models, we have calculated the dependence of coercivity on the grain size, phase distribution and volume fraction of two phases. The calculation results show that the different phase distributions lead to the variation of grain-interface fractions, and then make the intergrain exchange-coupling fluctuate randomly. Phase distribution influences the values of coeicivity of nanocomposites, but does not change the variation tendency of coercivity on hard grain size. High coercivity can be probably obtained by designing an ideal phase distribution and controlling the grain sizes.
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    VERIFICATION OF THREE 3D INDIVIDUAL GRAIN GROWTH RATES WITH LARGE-SCALE MONTE CARLO SIMULATION
    Acta Metall Sin, 2008, 44 (1): 13-18 . 
    Abstract   PDF (246KB) ( 1199 )
    Three existing topological dependence equations for the growth rate of three-dimensional individual grains have been testified using a new Potts model Monte Carlo simulation. The result shown that the volume change rate dVf/dt is related to the face number f by a curve, and thus, Rivier’s grain growth rate equation that predicts dVf/dt ∝f is not confirmed. Yu-Liu’s grain growth rate equation and MacPherson-Srolovitz’s grain growth rate equation are confirmed by mean of the simulation in the case of the face number f≥8. Yu-Liu’s grain growth rate equation and MacPherson-Srolovitz’s grain growth rate equation are not valid in the case of the face number f<8.
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    FIRST-PRINCIPLES INVESTIGATION OF β PHASE STABILITY AND ELASTIC PROPERTY OF Ti-Mo ALLOYS
    Acta Metall Sin, 2008, 44 (1): 19-22 . 
    Abstract   PDF (157KB) ( 1057 )
    The energetic, electronic structure and elastic property of the Ti-Mo binary alloys with Mo contents ranging from 4.17 at.% to 37.5 at.% were calculated using the method of supercell and augmented plane waves plus local orbitals within generalized gradient approximation. Based on the calculated results, the influences of Mo contents on the β phase stability and elastic property of Ti-Mo alloys were investigated. The results showed that the β phase stability, tetragonal shear constant C', bulk modulus, Young's modulus and shear modulus of Ti-Mo alloys increase monotonously with an increasing of Mo contents. The Ti-Mo alloy achieves low phase stability and low elastic modulus when the tetragonal shear constant C' reaches nearly zero.
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    Effect of heat treatment on transformation behavior of Ti-49.8Ni-1.0Co superelastic alloy
    Zhi-rong HE; Fang Wang
    Acta Metall Sin, 2008, 44 (1): 23-28 . 
    Abstract   PDF (195KB) ( 795 )
    The deformation characteristics of annealed Ti-49.8Ni-1.0Co (atomic percentage) alloy at room temperature were studied with differential scanning calorimetry (DSC) and tensile testing. The effects of annealing and aging processes on transformation behaviors of the alloy were systematically investigated by DSC. Ti-49.8Ni-1.0Co alloy shows superelasticity (SE) at room temperature. After replacing Ni with Co, the R phase (R) and martensitic (M) transformation temperatures, the transformation peak area, the SE stress and the SE loop area of the alloy are all decrease. The A→R→M/M→R→A (A-parent phase) type reversible transformation occurred in the 350-450℃ annealed alloy upon cooling / heating, the A→R→M/M→A type occurred in the 500-550℃ annealed alloy, and the A→M/M→A type occurred in above 600℃ annealed alloy. With increasing aging time, the transformation type of 300℃ aged alloy transforms from A→R→M/M→R→A to A→R→M/M→A, the one of 400℃ aged alloy transforms from A→R/R→A to A→R→M/M→R→A to A→R→M/M→A, and the one of 500℃ aged alloy is A→R→M/M→A constant. The influencing regularity of annealing temperature, annealing time, aging temperature and aging time on the R, M transformation temperature and temperature hysteresis were given out.
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    Phase Transitions of PLZT Ceramics near MPB Observed by In-situ Raman Spectroscopy
    CHENG Xuan
    Acta Metall Sin, 2008, 44 (1): 29-33 . 
    Abstract   PDF (227KB) ( 820 )
    In-situ Raman spectroscopy was employed to investigate PLZT ceramics (atomic ratio Zr/Ti=52/48, doped with small amount of La, Mn and Nb) at different temperatures. The observed Raman spectra were modified by the Bose population factor, and curve-fitted by the damped-harmonic-oscillator model and Gauss distribution function. Accordingly, the variations of Raman shifts and intensities of soft modes with temperatures were obtained. It confirmed that two types of phase transitions near morphotropic phase boundary (MPB) occurred at 240℃ and 360℃, respectively, when the temperatures increased from 47 to 600℃, indicating possible presence of mixed phases in PLZT ceramics. The effects of pre-polarization on phase transition are briefly discussed based on a comparison between the changes in Raman shift and intensity of soft mode observed with the unpoled powders and poled bulk specimens.
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    A Study on Thermal Stability of Nanocrystalline Pillars
    Zhou Nai-Gen
    Acta Metall Sin, 2008, 44 (1): 34-38 . 
    Abstract   PDF (285KB) ( 784 )
    Using nanocrystalline pillars as models of surface quantum dots, their structural stability has been studied. Molecular dynamics simulations of relaxation processes of aluminum nanocrystalline pillars of different sizes at different temperatures have been carried out. An EAM potential developed by Ercolessi was used to calculate of the inter-atomic forces. The results show that, for nanocrystalline pillars with near-square cross section and with {110} and {211} planes as side surfaces, there exists a critical size for stability transition. The nano-pillars with thickness lower than the critical size melt quickly and then re-crystallized, while those with thickness larger than the critical size have gradual structural reconfiguration by surface migration of atoms. The reconstructed stable structures, through either the melt-recrystallization or surface migration, are polyhedrons consisting of {111} and {100} surfaces, with only the relative ratio of the areas of the two types of surfaces differing from case to case. The critical size increases linearly with raising temperature. The simulations also show that the stability of the nanocrystalline pillars is insensitive to their height.
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    THE OBSERVATION AND ANALYSIS OF ε-Cu PHASE IN THE CU CONTAINING ANTIBACTERIAL AUSTENITESTAINLESS STEEL
    hengwu li
    Acta Metall Sin, 2008, 44 (1): 39-42 . 
    Abstract   PDF (235KB) ( 1045 )
    The paper presented Some results about ε-Cu phases formed during antibacterial treatment in the antibacterial stainless steel by LM,X-Ray, SEM,EPM and TEM, and then discussed form process ε-Cu phases.
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    EFFECTS OF ANNEALING TEMPERATURE ON INTENSITY AND DISTRIBUTION OF CRYSTAL TEXTURE IN Cu-12% Ag FILAMENTARY COMPOSITE
    Liang Meng
    Acta Metall Sin, 2008, 44 (1): 43-48 . 
    Abstract   PDF (430KB) ( 858 )
    Cu-12% Ag (mass fraction) strengthened by double-phase filamentary composite was prepared by heavy drawing. The effect of annealing temperature on the intensity and distribution of crystal texture in both Cu and Ag phases was investigated by annealing the composite at different temperatures. With the increase of annealing temperature up to 400 °C, the <111> component intensity decreases and the <100> component intensity increases in Cu phase while the <111> component intensity in Ag phase changes insignificantly. Annealing at temperatures higher than 400 °C enhances the texture intensities in both Cu and Ag phases. The texture formed by heavy drawing in Ag phase is more stable than that in Cu phase for the composite annealed at lower temperatures. The interface migrating, structure aggregating, fiber glomerating, and grain propagating from recover and recrystallization in annealing process generally change the intensities of the texture components formed by heavy drawing to form annealing texture. Therefore, the annealing texture components have the same orientation indexes as the deformation texture components.
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    EFFECT OF ROLLING PROCESS ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF 7050 ALUMINUM ALLOY
    Acta Metall Sin, 2008, 44 (1): 49-54 . 
    Abstract   PDF (751KB) ( 1837 )
    The effect of rolling reduction and temperature on the microstructure and mechanical properties of 7050 aluminum alloy was investigated. For the sample with a rolling deformation of 30%, most of dendritic structure remained. When the rolling reduction increased to 70%, the cast structure disappeared with the microstructure being characterized by the subgrains and recrystallized grains. Some coarse phases were identified to be Al7Cu2Fe and Al2CuMg by DSC and EDS. The Al7Cu2Fe with a cluster distribution did not dissolve into the matrix, whereas the globular shape of the Al2CuMg phase suggested partial dissolution during the heat treatment. The fraction of the recrystallized grains in the samples rolled under a reduction of 70 and 90% was 1.25 and 12.4%, respectively. The sample rolled under a rolling reduction of 70% exhibited the highest strength and hardness. The sample rolled at 300oC had a lot of recrystallized grains. At 430oC, improved material flow and the occurrence of dynamic recovery reduced stored deformation energy, thereby decreasing the amount of recrystallized grains. In this case, the sample exhibited the highest strength and hardness.
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    INFLUENCE OF CYCLIC EXTRUSION AND COMPRESSION ON THE MECHANICAL PROPERTIES OF ZK60 ALLOY
    LIN Jin-bao; Wang Qudong; Peng Liming; Chen Yongjun
    Acta Metall Sin, 2008, 44 (1): 55-58 . 
    Abstract   PDF (221KB) ( 1099 )
    Effects of cyclic extrusion and compression (CEC) deformation on the microstructure, texture and mechanical properties of ZK60 Mg alloy were investigated. The strengthening mechanism of CECed ZK60 Mg alloy was discussed in detail. Results shown, after subjected to CEC deformation 8 passes at 350℃, the microstructure of ZK60 alloy is dramatically refined and uniformed, the average grain size is decreased from ~20µm to ~1.5µm, the initial fiber texture is vanished and revealed a {10-13}<30-32>+{10-11}<15-43> texture. With the microstructure refining and texture changing, the compression yield stress of ZK60 alloy increased dramatically and the tension yield stress decreased slightly. As a result, the strength-differential effect (SDE) of ZK60 alloy is eliminated. At the same time, the ductility of ZK60 alloy is enhanced, especially under compression, the elongation is increased up to 38% from 15%.
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    INFLUENCE OF THE MELT SUPERHEATING TREATMENT ON SOLIDIFICATION MICROSTRUCTURE OF DD3 Ni-BASE SINGLE CRYSTAL SUPERALLOY
    ZOU Min-Ming; Jun Zhang; Lin LIU
    Acta Metall Sin, 2008, 44 (1): 59-63 . 
    Abstract   PDF (408KB) ( 979 )
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    The influence of hydrogen on ultra-high cycle fatigue properties of high strength spring steel 50CrV4
    Yongde LI; shou xin LI
    Acta Metall Sin, 2008, 44 (1): 64-68 . 
    Abstract   PDF (305KB) ( 982 )
    The influence of hydrogen on ultra-high cycle fatigue (UHCF) properties of high strength spring steel was discussed in this study. Three groups of specimens with different hydrogen content (CH) were obtained from three different heat treatment procedures: quenched and tempered (specimen QT), annealed at 380℃ in a vacuum after QT (specimen VA) and treated by High-pressure Thermal Hydrogen Charging (HPTHC) after QT (specimen HPTHC). It was observed by SEM that the crack initiation site was internal inclusion clusters for a high cycle fatigued specimen . The fatigue strength (σw) decreased according to σ0-аexp(CH)law with the increase of CH. Basquin exponent--b in Basquin Eq. decreased gradually with the increase of CH.
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    THE EXPERIMENTAL APPARATUS OF THE COUPLING OF FORCE, TEMPERATURE AND MAGNETIC FIELD
    Acta Metall Sin, 2008, 44 (1): 69-73 . 
    Abstract   PDF (211KB) ( 714 )
    The research on the coupling effect of force, temperature and magnetic field on material is one of front branches of material science. The paper introduces the principle and structure of the experimental apparatus of the coupling of force, temperature and magnetic field. The principle and structure of heating outside the furnace and dynamically sealing are advanced. According to this, the inert gases sealed in the furnace may effectively prevent the oxygenation of the specimen and the friction between the furnace mouse and pull bar. While applying the coupling effect of temperature and magnetic field, it is solved that the heated circular resistance wires interfere in the magnetic field of exciting coil. And so a new experiment means is provided for the research on the plasticity and superplasticity.
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    Study on the micro structure and residual stress of nanocrystalline diamond film
    Dunwen Zuo; Wenzhuang Lu; Min Wang
    Acta Metall Sin, 2008, 44 (1): 74-78 . 
    Abstract   PDF (299KB) ( 891 )
    Nanocrystalline diamond film is obtained at the grid and substrate bias current in the self-made double bias HFCVD system. The micro structure of the film is analyzed by Raman, SEM and AFM, and elastic modulus and residual stress are investigated by nano-indentation and XRD method. The results show that the increasing of grid and substrate bias current will cause the decreasing of grain size and the increasing of sp2 non-diamond content in the film. The grid and substrate bias current lead to the decreasing of elastic modulus and thermal stress in the diamond film. The non-diamond impurity induces the compression intrinsic stress in the film. The grid bias current results in the increasing of intrinsic stress as the increasing of grain boundary. But the substrate bias current leads to the weak ability of resistance to deformation as a lot of non-diamond content in the grain boundary, which results in the decreasing of intrinsic stress.
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    Numerical Simulation for the Interfacial Behavior of Steel and Slag in a Slab Continuous Casting Mold with Blowing Argon Gas
    Na CAO
    Acta Metall Sin, 2008, 44 (1): 79-84 . 
    Abstract   PDF (520KB) ( 1036 )
    A mathematical model to describe the interfacial behavior between fluid steel and molten slag layer in a slab continuous casting mold with blowing argon gas was developed, and the prediction was validated by the water model. The influences of casting speed, argon gas volume flowrate, mold width, submergence depth of SEN (Submerged Entry Nozzle) and bubble size on interfacial behavior were numerically investigated. The results show that given a casting speed 1.8m/min, the upper circulating flow in the mold gradually disappears and the interfacial uneven disturbed by argon bubbles is gradually evident with the increasing argon gas flowrate. Raising the casting speed from 1.2m/min to 2.2m/min leads to the deeper penetration of bubbles and less influence of argon bubbles on the flow pattern and interfacial profile with a given argon gas flowrate. Increasing the submergence depth of SEN can effectively restrain interfacial oscillations in mold, while mold width has little effect on it. Bubble size has a remarkable influence on the interfacial behavior of molten steel and slag in mold.
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    EFFECT OF CONTACT MODEL ON NUMERICAL SIMULATION OF FRICTION STIR WELDING
    Acta Metall Sin, 2008, 44 (1): 85-90 . 
    Abstract   PDF (301KB) ( 916 )
    Two contact models, including the classical Coulomb contact model and the modified Coulomb contact model, are used in a fully coupled thermo-mechanical numerical model of friction stir welding to study the effect of the different contact models on the simulation of friction stir welding process. Results indicate that there are little differences between the numerical results of the two contact models for friction stir welding in low rotating speed. But for the friction stir welding in high rotating speed, the classical Coulomb contact model fails to simulate the friction stir welding process due to no limit of shear stress at the interface, which is not considered to be a problem when the modified Coulomb contact model is used. The increase of the rotating speed does not change the nature of solid joining in friction stir welding. When higher rotating speed is adopted, the material deformations on the top and bottom surfaces become more similar, which lead to more uniform microstructures. So, it is recommended to adopt higher rotating speed in a real friction stir welding.
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    The investigation of the oriented precipitate-free zone in high strength aluminum alloy welds
    许良红 Xu Liang-Hong; tian zhiling Tian
    Acta Metall Sin, 2008, 44 (1): 91-97 . 
    Abstract   PDF (491KB) ( 934 )
    The microstructure in the partially melted zone of an arc-welded 20mm thickness 2519-T87 high strength aluminum alloy is investigated, an oriented precipitate-free zone is found behind the grain boundary, and this zone is not uniformly surrounding the grain, but usually oriented toward the fusion line. The formation mechanism of this zone is also studied. Results indicate that the mechanism of grain boundary liquid film migration is favored the formation of the precipitate free zone, the driving forces include coherency strain energy, the differential strain energy between the two grains induced by the elastic stresses generated during welding and differential surface energy due to grain boundary curvature. And with the increase of heat input, the thickness of the precipitate free zone increase. The precipitate free zone is harmful to the mechanical property of partially melted zone, and the fractography of PMZ showing the intergranular fracture.
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    RESEARCH ON DYNAMIC MECHANICAL PROPERTIES OF 0Cr18Ni10Ti WELDED JOINT AT ELEVATED TEMPERATURES AND HIGH STRAIN RATES
    XU Ze-Jian
    Acta Metall Sin, 2008, 44 (1): 98-104 . 
    Abstract   PDF (519KB) ( 840 )
    Dynamic mechanical behaviors of base and weld materials for an important reactor engineering pipeline material, 0Cr18Ni10Ti, are studied at elevated temperatures and high strain rates with split Hopkinson pressure bar (SHPB), which is installed with heating and synchro assembly system. The tests are carried out at loading rates ranging from 200 to 3800/s and temperatures ranging from 25 to 600ºC, and different stress-strain curves are obtained correspondingly for each condition. Emphasis is put on the study of strain rate and temperature sensitivity of plastic flow stress, and the Johson-Cook (J-C) models are obtained for both the materials. The results show that the base and the weld materials both have evident heat softening effect and strain hardening effect, but the effect of strain rate hardening is comparatively weaker. Meanwhile, these effects are also effected by temperature, and the hardening effects of both the materils by strain and strain rate are weakened at higher temperature. With the increase of strain, the flow stress of both the materials even begin to decrease at a certain deformation. The intrinsic mechanism is discussed according to the thermally activated dislocation motion theory. Optical microstructures of the materials are observed. Bright slipping bands formed under shear stress along the diagonal lines of the longitudinal section of the specimen for the base material, and the material at the center of the specimen deformed most seriously. Distorted dendrite structure is observed on the profile of the weld material after load, while no obvious slipping band is found.
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    RESIDUAL STRESS AND ITS INFLUENCING FACTOR ANALYSIS FOR BRAZED STAINLESS STEEL PLATE-FIN STRUCTURE
    Wen-Chun JIANG
    Acta Metall Sin, 2008, 44 (1): 105-111 . 
    Abstract   PDF (260KB) ( 781 )
    Micro Plate-fin heat exchanger (PFHE) is the typical candidate for the miniaturization of macro heat exchanger. A serious problem faced is that large residual stress generates during the vacuum brazing. This paper performed residual stress and its influencing factor analysis for brazed stainless steel plate-fin structure using finite element code-ABAQUS. Nine influencing factors were discussed such as brazing temperature, material mismatch, pressure load, brazing gap, fin height, fin pitch, fin thickness, fin layers and plate thickness. The results show that large residual stress generates in brazed joint due to mechanical properties mismatch between base metal and filler metal. Material mismatch, brazing gap, pressure load, fin pitch, fin thickness and plate thickness are the main influencing factors and have great effect on residual stress while the brazing temperature, fin height, fin layers have little influence. This work provides a reference for optimizing of brazing procedure for stainless steel plate-fin structure.
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    ANALYSIS OF COOLING EFFECT IN TWO-STAGE SLITLESS MOLD FOR SOFT CONTACT ELECTROMAGNETIC CONTINUOUS CASTING
    Bai-Gang JIN
    Acta Metall Sin, 2008, 44 (1): 112-118 . 
    Abstract   PDF (310KB) ( 839 )
    In order to know the cooling effect of two-stage slitless mold used in soft contact electromagnetic continuous casting (SC-EMC), heat transfer in two-stage SC-EMC mold and thickness of initial solidified shell were analyzed through numerical simulation method. The results showed that the thickness of initial solidified shell in two-stage mold was thinner about 0.4 mm than that in conventional mold. The temperature of strand surface increased about 2.5 K and the initial solidified point descended about 9 mm in two-stage mold. They would bring the effect of hot-top mold, which was good to improve the surface quality of strand. The thickness of initial solidified shell descended with the length of top half of mold increasing, as resulting in serious scouring of molten metal on the connection of two-stage mold. The length of top half of mold 120 mm was thought as the better parameter to meet the requirement of continuous casting industrial production. In the present research condition, the heat-resisting strength on two-stage mold wall was satisfied with the requirement of safe production.
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    Micro-mechanical properties of ceramic coating fabricated by plasma electrolytic oxidation on steel substrate
    Zhen-qiang Wu; Yuan xia; Guang Li; Fang-tao Xu; Guang-yao Yin
    Acta Metall Sin, 2008, 44 (1): 119-124 . 
    Abstract   PDF (358KB) ( 810 )
    Micro-mechanical properties such as nanohardness, elastic modulus, fracture toughness, etc. of composite coatings which consist of Al2O3 layer, Al layer and FeAl layer were evaluated by using nanoindentation method. The micrographs of nanoindentation were observed using a scanning electron microscopy (SEM). The effect of pores on Load-displacement response and crack propagation was investigated. The results show that there are some pores at micron scale or sub-micron scale within ceramic coatings. Elastic modulus and hardness of ceramic coating are about 226.4Gpa, 19.6Gpa, respectively. Mechanical properties of ceramic coatings are very discrete when the nanoindentatin depth is set as 250nm. The resistance of crack propagation of Al2O3 layer is large than that of FeAl layer. Radial crack emerges from the corner of residual impression of FeAl layer and propagates along straight line. Radial crack and lateral crack appear at nanoindentation of PEO coating and the cracks’ paths are deflected.
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    A Novel Method for Determining the Residual Stresses of Hard Coatings
    Sheng-Sheng ZHAO
    Acta Metall Sin, 2008, 44 (1): 125-128 . 
    Abstract   PDF (358KB) ( 986 )
    A new method was put forward to determine the residual stresses of hard coatings. A set of optical lever system was designed to measure accurately the curvature of the sample bended by the stresses of the films, and then the residual stress can be calculated. Through detecting the error of the measuring equipment and testing the residual stresses in (Ti,Al)N films deposited using by arc ion plating, the effectiveness of the method was exhibited.
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