Γ-phase Matrix Research Articles

Tension-Compression Asymmetry in Plasticity Modeling of a Single Crystal Superalloy Using a "Unit Cell" Approach

The [001] tensile and compressive flow behavior of a single crystal superalloy CMSX-4 was simulated using a “unit-cell” mesh to represent the γ/γ′ microstructure. The simulation results showed a tension-compression (T-C) asymmetry, where the magnitude of the flow stress is larger in the elastic-plastic transition regime in tension, and is larger in compression in the plastic (flow softening) regime. The T-C flow behavior was related to the flow response of the γ-phase matrix under the geometric and kinematic constraint of the γ/γ′ unit cell.

Observation of Patterns by Magnetic Force Microcopy in Fe-alloys with Shape Memory Effect

ABSTRACTIn this study, we investigated the magnetic domains of a FeMnSiNiCr stainless steel sample using Magnetic Force Microscope (MFM). We compared the magnetic patterns obtained by scanning the sample with three coated probes with different magnetic properties: Medium magnetic moment (MM), low magnetic moment (LM), and low coercivity (LC). The probe-surface separation was varied between 25 to 300 nm in order to quantify the magnetic microstructure of the sample. A simple model for the probe-sample interaction was used to interpret the contrast change as a function of the probe-surface separation. The experiment showed that the average maximum frequency decreases with the probe-surface separation and the intensity of the frequency is the strongest for the MM probe. X ray diffraction experiments were used to identify the different phases present in the sample. The X-ray diffraction experiments together with the MFM showed that α-phase islands surrounded by a γ-phase matrix are responsible for the magnetic properties of the sample.

Effects of grain shape and texture on the yield strength anisotropy of Al-Li alloy sheet

Inconel 625 and Hastelloy C-276 nickel-based alloy coatings were prepared on 304 stainless steels by cold metal transfer (CMT), aiming at improving the resistance to corrosion, cavitation erosion and wear. The synergistic cavitation erosion-corrosion (SCE-C) effect of the coatings was also revealed in 3.5 wt% NaCl solution. Experimental results show that the Inconel 625 coating was composed of γ-phase matrix and MC-type carbide precipitates dominated by NbC, while the Hastelloy C-276 coating exhibited γ-phase matrix and Mo-rich p phase. Both corrosion resistance and cavitation erosion resistance of the Hastelloy C-276 coating and Inconel 625 coating were higher than that of 304 substrate, and the Hastelloy C-276 coating possessed higher corrosion resistance and cavitation erosion resistance than Inconel 625 coating as indicated by higher polarization resistance (152.95 kΩ cm2) and lower mean depth erosion rates (1.3 ± 0.15 μm/h). The carrier concentration ND of passivation film for Hastelloy C-276 coating (4.05 ± 0.01 × 1022 cm−3) was lower after 10h-cavitation erosion compared to Inconel 625 coating, indicating its passive film showing a stronger passivation behavior and protective ability. The Hastelloy C-276 coating also exhibited a higher wear resistance, and the wear mechanism was adhesive-abrasive comprehensive wear dominated by adhesive wear in the linear reciprocating wear test with Al2O3 as the friction pair. The wear resistance of Inconel 625 coating and Hastelloy C-276 coating was about 1.3 and 1.5 times that of 304 substrate, respectively. The Hastelloy C-276 coating fabricated in the present study exhibited a great potential as flow-passing parts in marine engineering fields due to the desirable resistance to corrosion, cavitation erosion and wear.

Effect of plasma on nitriding of Fe-18Cr-9Ni alloy

The plasma nitriding behaviour of Fe-18Cr-9Ni alloy was compared with gas nitriding. The alloy was nitrided under the following conditions: specimen temperature: 823 K, nitriding time: mainly 108 ks, total pressure: 0.4–0.7 kPa, mixture ratio of N2 and H2∶ 0.25, discharge voltage: 350–450 V, current: 0.8–1.1 A. Formation of a surface layer of iron nitrides was not observed. Formation of a homogeneous internal nitriding layer, consisting of small precipitates of CrN and the γ-phase matrix, was, however, noted. The lattice constant at the specimen surface was smaller than that at greater depth. This may have been because the sputtering effect decreased the dissolved nitrogen content at the specimen surface. The sputtering of iron nitrides at the specimen surface by the plasma was experimentally confirmed through γ′-Fe4N formation on Si beside an alloy specimen. The characteristics of the plasma nitriding mentioned above are discussed in relation to the sputtering.

室温付近におけるSUS 304鋼中の水素の拡散および溶解

An investigation of diffusivity and solubility of hydrogen in both annealed and as-cold-rolled specimens of an austenitic Type 304 steel has been carried out at room temperature by means of an electrochemical permeation method. Especially, the effect of formation of the “foreign phases”, such as hydride phases (γH, εH) and hydrogen-induced martensitic transformation ones (ε+α′) in the cathodic surface on the hydrogen permeation behavior is discussed. Results obtained were as follows:(1) The linear relation of log(t1⁄2·Jt) vs 1⁄t in the hydrogen permeation transients was valid at the beginning of the permeation process. The results were explained by a model in which the rate-determining step of the permeation is a hydrogen-diffusion process in the remaining γ-phase matrix of annealed specimen or in the remaining (γ+α′) phase matrix in the case of as-cold-rolled specimen, accompanying the phase transition of the γ or (γ+α′) phase matrices to the γH, εH hydride phases and/or hydrogen-induced transformation (ε+α′) martensite phases during permeation.(2) The apparent diffusion coefficient of hydrogen determined from the theoretical permeation transient derived under the condition of the homogeneous medium throughout the specimen is equivalent to the true diffusion coefficient in the remaining matrix phase. However, the apparent hydrogen concentration directly beneath the cathodic surface determined by the theoretical solution of a homogeneous medium corresponds to the phase equilibrium hydrogen concentration of the matrix phase in the phase boundary related to the moving rate parameter of the phase boundary. Therefore, in order to determine strictly the concentration of hydrogen in the matrix phase at the interface of the foreign/matrix phase, especially in the case of higher cathodic current density for hydrogen introduction, it should be desired to use the heterogeneous medium solution related to the moving rate parameter of the interface.(3) The diffusivity (D) and apparent solubility (C) of hydrogen in the annealed specimen obtained in the temperature range from 311 to 332 K, at ic=50 A·m−2 can be described as follows:D(m2·s−1)=(4.41±0.92)×10−7exp[−53510±750(J·mol−1)⁄RT] and C(mol·m−3)=(6.11±2.17)×105exp[−10170±1050(J·mol−1)⁄RT].These values were in agreement with those previously obtained from the gas [phase method at high temperature. While, compared with the annealed specimen, the as-cold-rolled one had the higher diffusivity and the low activation energy for hydrogen diffusion, due to the pre-existence of cold worked α′-martensite. The apparent solubility of hydrogen in the as-cold-rolled specimen was higher than that in the annealed one and the hydrogen absorption occurred by the exothermic reaction.

Concerning the Origin of Uniaxial Magnetic Anisotropy in Electrodeposited Permalloy Films

Experimental evidence is adduced to suggest that electrodeposited iron-nickel alloys may contain α-phase regions in a γ-phase matrix. This observation is taken as evidence of large variations in composition on a scale of 1000 Å or less, and calculations are presented which show that it may be feasible to explain the observed uniaxial anisotropy in electrodeposited iron-nickel alloys in terms of a magnetostrictive mechanism even though the average plating composition be that of a zerostrictive material.