Metals and Materials International最新文献

In this study, the effects of Cu and Zn addition on the microstructure, mechanical properties, and intergranular corrosion (IGC) resistance of Al-5.5Mg alloys are examined. With increasing Cu addition in as-cast alloy, the primary phases change from lamellar T-Al₆Mg₄Cu phase to blocky S-Al₂CuMg and T-Al₆Mg₄Cu phases, which are reticulately distributed alongside grain boundaries. The lump T-Mg₃₂(Al, Zn)₄₉ phase is formed by introducing Zn. In Cu-containing alloys, the mechanical properties are optimal for the alloy with 1.5 wt% Cu, with a yield strength (YS) of 348 MPa, an ultimate tensile strength (UTS) of 452 MPa, and an elongation (EL) of 12.4%, due to the synergistic strengthening effect of the S phase, dislocation, and solid solution. The alloy with 3 wt% Zn exhibits the highest level of tensile properties, with a YS of 441 MPa, an UTS of 508 MPa, and an EL of 10.9%. This is attributed to the higher number density and finer dispersion of the spherical T phase, which effectively impedes the movement of dislocations. For corrosion properties, all Cu-containing alloys exhibit significant IGC susceptibility, while the IGC resistance of Zn-containing alloys increase with Zn content. The alloy containing 3 wt% Zn demonstrates uniform corrosion and exhibits excellent IGC resistance, with a maximum corrosion depth of 68.1 μm.

This study systematically investigates the effect of process parameters of laser powder bed fusion (LPBF) on the forming quality of polycrystalline γ-TiAl alloy at microscopic level through molecular dynamics (MD) simulation. By changing the laser power (152–320 µW) and scanning speed (0.2-1 Å/ps), the effects of different parameters on the evolution of the forming process and the microstructure of crystallization were elucidated. The results indicate that increasing the laser power and decreasing the scanning speed both increase the temperature peak width and prolong the duration of the molten pool, which promotes the diffusion of powder particle atoms. However, both high power and low scanning speed increase the total energy input of the molten pool, promoting the accumulation of heat. Ultimately, this leads to a higher proportion of HCP structures in the powder bed. Furthermore, lower scanning speed and laser power both result in higher crystallinity, with scanning speed having a more remarkable regulatory influence on the crystallinity. Grain analysis indicates that with the increase of laser power and the decrease of scanning speed, the grain width of the formed alloy gradually increases, and the grains transform from fine equiaxed crystals or short columnar crystals to coarse long columnar crystals. Tensile testing reveals that both laser power and scanning speed present a nonlinear relationship on the tensile strength of TiAl alloy, which is the result of the combined action of factors such as grain size, dislocations and residual stress. During stretching, the FCC and HCP structures of the stretching block undergo mutual transformation, and the dislocation entanglement at the grain boundaries formed by laser forming could impede slip, thereby enhancing the tensile strength.

Graphical Abstract

Process parameters determine the quality characteristics of additively manufactured (AMed) parts. During Laser-based Directed Energy Deposition (DED-LB), an elaborated parametric analysis is required to control the materials’ behaviour precisely. This work deals with the effect of process parameters on process stability in terms of consistent melt pool geometrical features, such as aspect ratio of the bead and dilution, formation of pores, and ductility of super duplex stainless steel (SDSS) during pulsed laser and powder DED-LB. Independent variables including laser power, deposition speed, pulse frequency, and flow rate of the shielding gas were selected as controlling factors to deposit single tracks and plates of SDSS. Experiments have been designed and conducted according to L16 orthogonal array of Taguchi methodology. Relative density was estimated using Archimedes method. Ductility was estimated by tensile testing of the builds. For geometrical evaluation, phase characterization, and microstructural assessment, specimens were subjected to optical and Scanning Electron Microscopies, and Electron Backscattered Diffraction. Overall results were interpreted and explained using the Taguchi approach and analysis of signal-to-noise ratio. Single objective parameter-property relationships were achieved and discussed. Conclusive parametric remarks under the multi-attribute optimization were derived using weighted Grey Relational Analysis. A desirable parametric combination was extracted, and the associated quality responses were verified by the satisfying confirmatory deposition. The key role of parameters on the process stability, microstructure, and mechanical behaviour was further discussed. This work offers a practical solution to the multi-response optimization problems that can be used in AM and surface treatment of SDSS.

Graphical Abstract

In this study, the changes in the microstructure and mechanical properties associated with the annealing heat treatment (AHT) of Fe–13Mn–5Cr–1Ni–0.4C steel deposited by laser-directed energy deposition (LDED) were investigated. High-manganese steel (HMnS) deposited by LDED exhibited an almost completely dense microstructure, except for a few small pores between the beads, and fully austenitic microstructure. However, the annealing heat treatment (AHT) caused considerable phase transformation from austenite to ε-martensite, leading significant decrease in tensile strength and elongation to under half of as-built state. Scheil solidification simulation method and energy dispersive spectroscopy revealed elemental segregation on cell boundaries, thereby local variation of stacking fault energy (SFE) was caused. Relatively low SFE in the cell interior can cause martensitic transformation during AHT process and it gives rise the premature failure of annealed specimen during uniaxial tensile testing. The results in this study can give new aspect of failure mechanism of additively manufactured metal alloys, especially steels which is likely to be transformed to martensite such as high manganese steel.

Graphical Abstract

This study focused on the fabrication and characterisation of TiO₂/Graphite reinforced Cu-based composite produced by powder metallurgy. The effects of varying amounts of TiO₂ combined with 2% (w/w) graphite on the wear and corrosion behavior of stoichiometric copper (Cu) were investigated using various characterization techniques. The phase analysis revealed that Cu was the main phase. At low doping ratios, graphite peaks were found in trace amounts, while rutile phases of TiO₂ were detected. The microstructure and phase properties of the produced matrix and fracture surfaces were examined by scanning electron microscopy. As a result of the measurements made with the Vickers hardness tester, it was observed that the TiO₂ additive improved the hardness of the composites. Corrosion tests in 3.5 wt% NaCl solution showed that the addition of TiO₂/Graphite to copper shifted the corrosion potential in the anodic (more noble) direction, while graphite alone shifted it in the cathodic (less noble) direction. However, graphite-reinforced Cu composites exhibited a better protective oxide film than those TiO₂/Graphite reinforced Cu-based composite, attributed to the uniform distribution of graphite throughout the material. Although TiO₂ or TiO₂/Graphite with graphite improved the corrosion potential, the corrosion current density was higher than that of unreinforced Cu due to the formation of micro-galvanic cells within the composite. Additionally, the high amount of TiO₂ added positively influenced the corrosion resistance. Using graphite's ability to make the composite self-lubricate when used with metals or ceramics, adding graphite to TiO₂ particles at all volume ratios significantly increased the wear resistance of the composite.

Graphical Abstract

An electroplasticity method for tailoring the flow stress during the thermal deformation of Aermet100 ultra-high strength steel by adjusting the frequency of electropulsing is proposed. This study rigorously controls the electron wind force and Joule heating effect to establish the origin of the electroplastic effect from the perspective of dislocation vibration for the first time. By strictly controlling the electron wind force and Joule heating effect, the origin of the electroplastic effect is verified for the first time from the perspective of dislocation vibration. The results show that the electropulsing frequency of 50 Hz has the lowest flow stress. Moreover, the flow stress of the specimens was nonlinear dependent on the increment in the electropulsing frequency, that it rose first followed by a decline. The electropulsing frequency threshold that can result in the transition in flow stress is 500 Hz. It is attributed to the proximity of the dislocation vibration frequency of Aermet100 steel at high-temperature conditions to the pulsed current frequency, leading to an increase in dislocation amplitude. Furthermore, a pulsed current frequency of 1000 Hz is found to have the highest recrystallization nucleation rate and recrystallized content. It is the threshold for the transformation of grain refinement strengthening. This investigation sheds new insight into the regulation of flow stress and microstructure in Aermet100 ultra-high strength steel using electroplasticity effect.

Wire and Arc Additive Manufacturing (WAAM) is a cost-effective and efficient technology for producing large-scale metallic parts. It is widely adopted in the automotive, aerospace, and marine industries due to its high deposition rate, material efficiency, reduced production time, and lower costs compared to powder-based additive manufacturing techniques. Titanium alloys are extensively used in the aerospace and astronautics industries due to their exceptional mechanical properties and overall performance. However, manufacturing large titanium components using conventional techniques poses significant challenges, particularly when dealing with intricate geometries and a high Buy-To-Fly (BTF) ratio. As a result, WAAM has gained significant traction for its ability to produce near-net-shape, large-scale titanium alloy components with high efficiency, superior quality, and lower production costs. This study first provides an in-depth analysis of WAAM-deposited titanium alloys, highlighting the key challenges associated with the process, including high heat input, oxidation, residual stress distribution, and grain size control. It then explores hybrid WAAM systems and advanced post-processing techniques, including inter-pass cold rolling, inter-pass cooling, shot peening, and ultrasonic impact treatments to mitigate these challenges and enhance material properties. Additionally, the study evaluates the economic feasibility of WAAM for titanium alloys, highlighting its cost advantages over traditional manufacturing methods. Finally, various industrial applications of WAAM-fabricated titanium components are discussed. These findings underscore the critical role of advanced post-processing techniques in overcoming the inherent limitations of WAAM for titanium alloys, paving the way for further improvements in material properties, process efficiency, and industrial adoption.

Graphical Abstract

Metal three dimensional-printing technology has advanced the fabrication of various metal alloys. One of the most well-known lightweight metal alloys, aluminum alloys, are applied in various fields, including aerospace and automobiles. Aluminum is a special metal with unique chemical and physical properties, including high reactivity to iron that hinders the multi-material additive manufacturing (MMAM) of aluminum and iron-based alloys. The direct deposition of the aluminum alloys onto stainless steel is impossible because the aluminum alloy sides off the base steel. Therefore, a novel anchor design of AISI 316 L stainless steel was developed to prevent this detachment. In this study, laser directed energy deposition (LDED) is proposed for the MMAM of AlSi10Mg and AISI 316 L stainless steel. The hardnesses of the anchor and deposited aluminum alloy were measured. Thereafter, scanning electron microscopy and energy-dispersive X-ray spectroscopy images were observed to determine material solidification and diffusion behavior. Finally, a tensile test was performed to evaluate the bond strength of the aluminum/steel interface. As a result, tensile interface bonding stress of up to 8.4 MPa is produced when the anchor structure was made through rescanning on thin wall with a hatch spacing of the anchor of 1.5 mm. AlSi10Mg was successfully deposited on AISI 316 L stainless steel using LDED. In addition, a macroscopic anchor was designed and manufactured using LDED to overcome the weak bond of the micro-anchor. To demonstrate the Al/Fe MMAM, a multi-material sine wave and QR code were developed.

Graphical Abstract

Significant work has been done on the analysis of microstructure and texture in Ti6Al4V parts with simple geometric shapes like cubes or cylinders manufactured using laser powder bed fusion (LPBF). However, in recent times, there has been considerable interest in the use of triply periodic minimum surfaces (TPMS) in additive manufacturing (AM) in the production of titanium-based lattices for hard tissue applications. The present work utilizes a diamond TPMS lattice-based tensile specimen to explore the geometry-dependent variation in microstructure and preferred crystallographic orientations in relation to the observed tensile behaviour. Three regions within a single tensile specimen namely lattice region (LR), lattice-solid junction region (L-SR) and solid region (SR) were studied. The results indicated a change in the aspect ratio of the martensitic lath from ~ 5 in the LR to 3.8 in the SR within an individual as-built specimen. Moreover, the texture strength was considerably higher in LR as compared to SR. The texture for the as-built LR was noted to be arrested in progression to form a < 0001 >|| build direction (B.D) crystallographic orientation. The underdeveloped texture in the LR was completed to form a < 0001 >||B.D preferred orientation and was further intensified by the heat treatment (HT) done at 750 °C for 4 h and 920 °C for 2 h followed by furnace cooling. An improvement in the ductility was observed for both the HT processes and is mainly attributed to the coarsening of grains and β-phase with negligible impact of the texture within the LR on the ductility of the specimens.

Graphic Abstract