Stefanus Harjo

In situ neutron diffraction during tensile deformation of a ferrite-cementite steel

A fully pearlitic steel (specimen P1) was subjected to cold-drawing (P2) followed by aging at 423 K (P3) or 673 K (P4). Some drawn samples were annealed to make cementite particles spherical (P5). By using neutron diffraction, high compressive residual stress component parallel to the drawing direction was detected in the ferrite matrix of specimen P2, whereas this stress level was partly relaxed in P3 and mostly in P4. In situ neutron diffraction experiments performed during tensile tests have revealed different work hardening behaviors in these specimens. Based on the data provided by a profile analysis of diffraction spectra, i.e. microstrain related to dislocation density and block size, strength and work-hardening of these specimens are discussed. In particular, it is documented that the treatment of the specimen P4 which is equivalent to commercially Zn-plated steel wires produces the largest internal stress by tensile deformation leading to a good balance of strength and uniform elongation.

In situ neutron diffraction study of IF and ultra low carbon steels upon tensile deformation

Abstract Tensile behavior of an interstitial-free (IF) and an ultra low-carbon (ULC) steel bearing similar concentrations of carbon and nitrogen was studied by means of an in situ neutron diffraction technique. The (110), (200) and (211) lattice plane strains were determined as a function of the applied stress, revealing three deformation stages; (1) elastic deformation, (2) grain to grain yielding and (3) the stage III deformation. The microstrain associated with dislocation density (ρ) was increased with tensile straining and the increasing rate was higher in the ULC steel than in the IF steel, resulting in higher flow stress in the ULC steel due to dynamic strain aging. The estimated ρ was summarized as a function of strain (e); ρ = ρ0 + AeB, leading to the description of flow stress (σ); σ=120+0.89μb A1/2eB/2 MPa, where ρ0, A and B were constants, μ shear modulus, and b the magnitude of Burgers vector. The above constants were influenced by dynamic strain aging through the Bailey–Hirsch relation.

In situ neutron diffraction study of α–γ Fe–Cr–Ni alloys under tensile deformation

Abstract Neutron diffraction experiments were performed in situ upon tensile loading for five Fe–Cr–Ni alloys with different ferrite volume fractions ranging from 0 to 100%. The diffraction profiles were recorded along with the tensile deformation curves during temporary stops in a deformation machine (5 ks each) with the crosshead fixed. One reflection of each phase, (111) of austenite (γ) and (110) of ferrite (α), respectively, were measured simultaneously by using a position sensitive detector. Evolution of elastic lattice strains and dislocation densities in both constituent phases was evaluated from measured diffraction profiles as a function of external loading. Based on these experimental results, heterogeneous deformation behavior in the α–γ dual-phase alloys is discussed.

Measurements of thermal residual elastic strains in ferrite–austenite Fe–Cr–Ni alloys by neutron and X-ray diffractions

Abstract The thermal residual elastic strains in ferrite (α) and austenite (γ) phases in three kinds of α–γ Fe–Cr–Ni alloys generated by quenching specimens from 1273xa0K into water (273xa0K), have been measured by means of a neutron diffraction method. The phase-stresses are successfully determined by employing carefully prepared alloys with volume fractions of α in a range between 0% and 100%, whose chemical compositions are located on an equilibrium tie line of the Fe–Cr–Ni ternary phase diagram. The phase-stresses obtained are compressive for α phase and tensile for γ phase, showing good agreement with those predicted by Eshelby and Mori–Tanaka theories. The stress measurements for these alloys were also carried out by X-ray diffraction method. It is found that the conventional X-ray sin2 ψ method under the assumption of plane stress condition is not applicable. The phase-stresses obtained by a triaxial X-ray stress measurement method are in good agreement with those obtained by neutron diffraction method.

In situ neutron diffraction study of drawn pearlitic steel wires upon tensile deformation

Abstract The strengthening mechanism of heavily cold-drawn pearlitic steel wires was studied using the highresolution neutron diffraction experiment performed in situ upon tensile deformation. Microstructural parameters of lattice strain, microstrain and coherent block size, the evolution of which evidences the deformation mechanism of this ultrahigh strength steel, were extracted from the position, width and shape of the in situ recorded neutron diffraction profiles, respectively, using a newly proposed method of profile shape analysis. It was found that the deformation mechanism of cold-drawn pearlitic steel wires resembles the behavior of nanocrystalline materials.

Cavitation Behaviors in a Tetragonal Zirconia Polycrystal Subjected to Superplastic Deformations Measured by SANS Method

3Y-TZP specimens were pulled at temperatures ranging from 1623 to 1723 K with strain rates ranging from 3.3×10 to 6.7×10 s to various nominal strains. Characterization of cavities was conducted for gauge section of deformed specimens by SANS method and conventional ones including density measurement method and scanning electron microscopy analysis. The volume fraction of cavities and the evolution of cavity shapes were evaluated from the SANS results as a function of nominal strain for deformations carried out under the same superplastic condition. These behaviors were also discussed with the change in deformation condition. It is found that the SANS method is the most excellent technique for cavity characterization: the SANS method can measure the characteristics of cavities with better statistics and can measure flat cavities or fine defects which are quite difficult to identify by the conventional methods.

Superplastic deformation characteristics of 3Y-TZP after Zr ion irradiation

Abstract The effects of Zr-ion irradiation on the superplastic deformation behavior of a 3 mol% yttria containing tetragonal zirconia polycrystals (3Y-TZP) were studied. The specimens were irradiated by Zr11+ ions with 130 MeV at fluence levels of 3.5xa0×xa01012 and 2.1xa0×xa01013 ions/cm2 in the TANDEM accelerator at Tokai Research Establishment of JAERI. The TRIM simulation indicated that the maximum irradiation damage emerged at the depth of about 10 μm. The mechanical and superplastic properties of the irradiated specimens were examined by the bending test at elevated temperatures. It was found that the activation energy for the superplastic deformation was increased with increasing the irradiation fluence. One of the possible causes of this increase is that excess Zr ions, implanted in the irradiation surface region, prevented the diffusion of constitutive ions and hence restrained diffusion controlled accommodation process for grain boundary sliding.

Radiation damage effects in superplastic 3Y-TZP irradiated with Zr ions

Abstract The 3 mol% yttria stabilized tetragonal zirconia polycrystals (3Y-TZP) were irradiated using 130 MeV Zr11+ ions in the TANDEM accelerator facility at Tokai Research Establishment, JAERI. Irradiation was performed with the fluence of 3.5xa0×xa01012 and 2.1xa0×xa01013 ions/cm2. Residual stresses and changes in mechanical properties caused by the ion irradiation and the effects of the subsequent annealing are studied. The occurrence of compressive residual stress and increases in hardness and fracture toughness were found at the surface regions of as-irradiated specimens. It was found from the subsequent annealing that these quantities were decreased gradually with raising the annealing temperature and returned to those of un-irradiated state at around 1173 K. A most probable cause of the increases in the hardness and fracture toughness after the irradiation may, therefore, be the residual compressive stress left in the irradiated surface region.

Progress in Bulk Texture Measurement Using Neutron Diffraction

Quantum Beam Science Center, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan; J-PARC Center, Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan; Research Center for Neutron Science and Technology, Comprehensive Research Organization for Science and Society, Tokai, Ibaraki, 319-1106, Japan; Department of Neutron Application Technology, Radiation Application Development Association, Tokai, Ibaraki, 319-1106, Japan; College of Engineering, Ibaraki University, Hitachi, Ibaraki, 316-8511, Japan; Department of Materials Engineering and Industrial Technologies, University of Trento, 7738123 Trento, Italy.

Thermal Strain in Superconducting Nb3Sn Strand at Cryogenic Temperature

Large superconducting cables consisting of Nb3Sn strands are essential components of the experimental fusion reactor built under the ITER project. [1] The presence of strains in the Nb3Sn is well known to affect superconducting properties [2], and therefore thermal strains at its use conditions (cryogenic temperatures) are necessary to be determined. Measurements of thermal strains in the superconducting constituent (Nb3Sn phase) in Nb3Sn strand were performed using BL19 Takumi of MLF, J-PARC. Lattice parameters of Nb3Sn phase in Fig. 1(a) change continuously with increasing temperature. To avoid the thermal expansion effect, lattice parameters of the filaments (extracted from the strand) measured at the same temperatures were used to estimate the thermal strains in Nb3Sn phase. As shown in Fig. 1(b), thermal strains for axial direction below 50 K are kept roughly constant at large compressive values, while the values are much lower (the difference is ~0.13%) than that measured at room temperature [3].