Metallurgical and Materials Transactions A最新文献

Triple-layer stainless-steel clad plate having 317L stainless steel (SS317L) as cladding layer and ASTM SA516 GR60 (GR60) as backing layer was successfully fabricated through vacuum hot roll bonding (VHRB) at 1373 K (1100 °C) temperature and strain rate regime of 1–5 s⁻¹, which were identified through process efficiency maps of the base materials (SS317L and GR60). The process efficiency maps were constructed by conducting isothermal compression tests within the temperature range of 1173 K (900 °C)–1473 K (1200 °C) and 0.1–50 s⁻¹strain rate regime. Effect of post-rolling heat treatments on the mechanical properties of clad plate was studied after solutionization at 1173 K (900 °C) for 1 h followed by cooling at different rates, i.e., water quenching, air cooling, and furnace cooling. As compared to other post-rolling heat treatments, the ultimate tensile strength, uniform plastic elongation, and maximum shear strength showed a significant change from 524 MPa, 0.46 and 519 MPa to 652 MPa, 0.36 and 410 MPa, when the normalized clad plate was solutionized at 1173 K (900 °C) and water quenched. A drastic change in shear fracture mode from gradual failure in normalized condition to catastrophic failure was also noticed after water quenching. These changes are essentially manifestation of the microstructural change in GR60 layer which led to the change in mechanical properties.

Circumferential near-neutral pH corrosion fatigue (C-NNpH-CF) is the result of the simultaneous impact of axial residual and applied stresses along with the near-neutral pH corrosive environment established on the external surface of the buried pipeline because of leakage through the protective coating. (This mechanism has previously been referred to as near-neutral pH stress corrosion cracking.) Since integrity management measures should be implemented before Stage III (rapid crack propagation to rupture), this study aims to evaluate the effect of bending residual stress (a suitable source of axial residual stress) and cyclic loading (simulated pipeline pressure fluctuations) on crack growth at Stage II. Based on the digital image correlation (DIC) method, the final stress distribution in length and thickness direction was used to analyze crack growth in various test parameters, including applied cyclic loading, initial notch depth/position, and bending angle/direction. As a result of stress gradients in the depth direction of bent pipelines, a new method was developed to obtain the stress intensity factor. A comparison of crack growth rates between circumferentially oriented and longitudinally oriented NNpH-CF was performed to reveal the growth mechanism. Crack growth was maximum at 1 mm depth initial notch, 20 deg bend (inward), and 50 pct cycling load.

In the present study, 3D non-woven needle-punched preform (NPP) C_f–SiC_m composite with 7.5 pct volume fraction of carbon fiber is prepared via liquid silicon infiltration technique and characterized for microstructure, phase formation and mechanical behaviors. Additionally, the composite is subjected to plasma arc jet tests for evaluation of ablation resistance under ultra-high temperature oxidation environment. The dense composite (density ~ 2.5 to 2.6 g/cm³) contains β-SiC phase due to the reaction between infiltrated molten silicon and carbon matrix surrounding the carbon fibers. The resultant C_f–SiC_m composite shows high hardness and high abrasion resistance due to a higher proportion of hard SiC matrix as well as exhibits various toughening mechanisms from the carbon fiber reinforcement causing a delay in fracture. It also contains excellent resistance to thermal shock and thermo-oxidative erosion resistance during plasma arc jet ablation test without any visible crack or damage on the exposed surface.

Graphical Abstract

The performance of modern dual hardening steels strongly relies on a well-controlled precipitation processes during manufacturing and heat treatment. Here, the precipitation of intermetallic β-NiAl in recently developed dual hardening steels has been investigated during aging using combined high-energy synchrotron X-ray diffraction and small-angle scattering. The effects of heating rate and aging temperature on the precipitation kinetics and lattice mismatch in two alloys (Hybrid 55 and Hybrid 60) were studied. Precipitation starts already during heating, typically in the temperature range 450 °C to 500 °C. The precipitation process is significantly faster at 570 °C compared to 545 °C for both steel grades, and the number density reaches its maximum already within 1 hours during aging at 545 °C and within 15 minutes during aging at 570 °C. The effect of heating rate is limited, but the precipitation during heating increases in Hybrid 60 when slower heating rate is used. This led to slightly higher volume fractions during subsequent aging, but did not affect the particle size. The lattice mismatch between β-NiAl and the matrix initially develops rapidly with time during aging, presumably due to a developing chemistry of the β phase, until a particle size of around 1.5 nm is reached, whereafter it saturates. After saturation, the lattice mismatch is small, but positive, and independent of temperature during cooling.

Emulating the Ni-base superalloy (gamma ) + (gamma ^{prime }) microstructure in BCC–B2 refractory alloys is a promising design strategy to achieve high temperature strength and ductility. Ru-base B2 precipitates have shown exceptional thermal stability but can be difficult to solutionize, making high cooling rate solidification pathways like additive manufacturing (AM) a promising approach for synthesis of more homogeneous microstructures. Using single track laser experiments on aged bulk substrates, five representative refractory alloys with varying Ru-base B2 precipitates (AlRu, HfRu, TiRu) and matrix constituents (Mo, Nb) were investigated for their solidification behavior and defect susceptibility under laser melting conditions. Susceptibility to solidification cracking, solid-state cracking, and keyhole formation was found to be highly dependent on the matrix composition. Characterization of the melt pools by scanning and transmission electron microscopy shows evidence for disordered BCC upon solidification, enabling tailoring of the B2 precipitates that are thermodynamically stable above 1300 °C. The B2 precipitate morphologies in the melt tracks after aging treatments are influenced by the partitioning behavior of Ru from laser melting. Results from these single track experiments provide guidance toward design strategies for fabricable refractory BCC–B2 alloys.

In this study, the influence of various mechanical and chemical surface treatments on the adhesion strength and surface properties of sodium alginate coatings electrophoretically deposited (EPD) on 316L stainless steel substrates was investigated. XPS and TEM results revealed the presence of oxide layers containing elements from the substrates, with thicknesses varying from 1 to 45 nm, depending on the treatment used. Most substrates exhibited high roughness and hydrophilic properties (CA with water 62.8–82.6 deg). Sodium alginate coatings with uniform morphology were deposited with the same process parameters, i.e., 5 V and 300 s. The surface topography of the coatings was closely related to that of the substrate on which they were deposited. All coatings exhibited higher hydrophilicity (CA with water 29.5–49.7 deg) compared to the substrates (CA with water 62.8–82.6 deg). The coatings on the etched and anodized substrates demonstrated the highest adhesion strength (class 4B), attributed to the very low oxide layer thickness and the specific substrate surface topography. Mechanical interlocking was identified as the primary adhesion mechanism for these coatings. This work provides insight into optimizing surface treatments for improved adhesion of sodium alginate coatings to stainless steel substrates widely used for temporary bone implants. The results obtained will also be helpful in providing high adhesion of sodium alginate-based composite coatings to steel substrates.

The application of low carbon micro-alloyed steel sheets in chassis and frame parts of automobiles demands high formability during hot or cold forming operations to produce various intricate shapes. In view of the forming applications, stretch flangeability is considered as one of the most important critical parameters for these steel grades. The stretch-flangeability of micro-alloyed steels, with three different types of microstructure consisting of mainly single-phase ferrite, ferrite-pearlite and ferrite-bainite micro-constituents, is evaluated in this investigation based on hole expansion ratio (HER). The desired microstructures of the low carbon steels micro-alloyed with Nb, Nb-V and Nb-V-Ti steels were obtained at three different coiling temperatures by systematically varying the plant operating process parameters. While Micro-alloying elements largely affect the mechanical strength and ductility of the steel, its direct impact on HER value and fracture behavior are not correlated. The correlation of microstructure with tensile strength and ductility have been attempted for the studied low carbon micro-alloyed steels and described in this paper. It is observed that single-phase steel consisting of soft ferritic matrix as well as steel with 5 to 15 pct pearlite uniformly distributed in ferrite matrix has better stretch flangeability and strength to hole expansion ratio correlation in comparison to ferrite-bainite steel.

Titanium alloy, Ti–6Al–2.2Mo–1.4Cr–0.4Fe–0.3Si (BT3-1), is a two phase α + β alloy developed for applications in rocket engines, gas turbine engines, and aircraft frames for service up to a temperature of 450 °C. The hot workability of this alloy has been studied through isothermal hot compression testing in the temperature and strain rate ((dot{varepsilon })) range of 800 °C to 1000 °C and 10⁻³ to 10 s⁻¹, respectively, in a thermomechanical simulator. Processing maps using dynamic material model has been generated and different regions of the map were correlated with microstructural observations. The flow stress data were fitted in Arrhenius strain-compensated model and constitutive equations were developed. Optical microstructures revealed elongated grains, kinking of α phase, flow localisation, and adiabatic shear bands at lower temperatures. Super-plasticity was found to be operative at low temperature of 850 °C and (dot{varepsilon }) 10⁻³ s⁻¹, whereas dynamic recrystallization (DRX) was dominating at high temperatures of 950 °C to 1000 °C and (dot{varepsilon }) of 10⁻³ s⁻¹. Finite element analysis showed the flow localization in the unstable regions of processing map. Enhanced hot workability was achieved above 950°C in the (dot{varepsilon }) of 10⁻²−10⁻³ s⁻¹ due to initiation of DRX in view of an increase in the β phase fraction.

Graphical Abstract

We show that rhenium can be sintered from powders to nearly full density (99.96 pct) by directly injecting electrical current into dogbone shaped specimens. The current was increased at a rate of 1 A s⁻¹. The specimen sintered abruptly after about 30 seconds when its temperature had risen to 900 °C. The experiments were carried out without furnace heating, within a glove box in Ar atmosphere. The following in-operando measurements are reported, (i) shrinkage strain with a rapid rate camera, (ii) resistivity measured by voltage and current, (iii) temperature measured with a pyrometer, and (iv) electroluminescence spectra measured with a spectrometer. The sintering cycle, the first, during which the sample sintered to full density, was followed by two more flash cycles with the same specimen. In the first cycle, the change in resistance exhibited a peak arising from abatement of interparticle interface resistance; the peak was absent in the second and third cycles. The rapid sintering is attributed to the generation of defects in the form of vacancy-interstitial (Frenkel) pairs. The concentration of the Frenkels was estimated from in-situ calorimetry, where the difference between the electrical input energy, and the energy lost to radiation, convection and specific heat, was attributed to an endothermic reaction for defect generation. In this way we calculated a concentration of ∼ 10 mol pct of Frenkel pairs. The resistance of the flash sintered specimens was higher than literature values, presumably due to these defects. The very low sintering temperature and the anonymously high defect concentrations mean that flash sintering of metals is a far-from-equilibrium phenomenon.

Annealing treatment in a mild magnetic field has been investigated on the mechanical and magnetic properties of the FeCo-2V alloy. Samples were annealed at 750 °C and 880 °C for various holding times (3, 6, or 9 hours) with an external magnetic field (0, 3300 or 5500 A/m). The mechanical strength, magnetic properties, and grain size of annealed samples were measured. The results show that the magnetic-field-annealing (MFA) treatment retards the grain growth, and the small grains result in an increase in the mechanical strength. Moreover, there is a significant improvement in the magnetic properties. The unusual correlation between the small grains and improved magnetic properties is explained through grain shape anisotropy. Moreover, MFA is found to be more effective in improving the magnetic properties of FeCo-2V alloy than extending the holding time. The 880-6-5500 samples exhibit a high maximum permeability of about 35000, the lowest core loss and coercivity with 34.4 W/kg and 85.9 A/m, respectively at 2.0 T/400 Hz. The finding reveals a practical route to improve the mechanical and magnetic performance of electric machines by annealing under a weak magnetic field.