Journal of Materials Engineering and Performance最新文献

Metastable stainless steels can be used as a load-sensitive sensor. In combination with an eddy current testing system, mechanical overloads of a component can be detected directly during operation. Material sensors were prepared by shot peening fatigue specimen of metastable austenitic steel to obtain a martensitic surface layer and a local heating by a laser beam to obtain an austenitic area in the layer. In order to investigate the response of the material sensor to overload and achieve different trigger thresholds, the thermal energy applied to create the sensor material and the geometry of the material sensors were varied. It is shown that the austenitized volume and the martensite fraction in the material sensor correlate with the phase of the eddy current signals. Starting from the martensitic surface layer, the phase decreases as the austenitized volume increases. If martensite formation takes place due to an overload, the phase increases as a result. To determine the threshold stress needed to trigger the material sensor, cyclic rotating bending tests were carried out on austenitic stainless steel 1.4301 (AISI 304). In step tests, the bending stress was gradually increased and subsequently ex-situ eddy current testing was carried out. The potential for predicting and classifying an overload is significantly greater with a higher applied thermal energy. Three different sensor geometries (rhombus, cross and ring) were employed in tests. In comparison, the rhombus-shaped material sensor provided the greatest potential for load history interpretation due to the significant phase change.

The effect of induction heating temperature on the microstructures and properties of GH4169 nickel-based superalloy was investigated. Both electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were applied to analyze the microstructure. The results showed that the induction heating temperature had a promoting influence on the evolution of static recrystallization (SRX) and the optimization of grain boundary characteristics distribution (GBCD). After induction heating, the coincidence site lattice (CSL) boundaries were mainly Σ3 boundaries, and the main formation mechanism was the growth accident model. With the increasing heating temperature, the SRX behavior was well developed with a gradual increase in the fraction of Σ3 boundaries. This indicates a 'symbiotic relationship' between the SRX grains and Σ3 boundaries. Moreover, it was found that the ductility and corrosion resistance of the alloy were improved with the increasing temperature. This is mainly due to the fact that the SRX behavior can effectively improve the uniformity of the microstructure and eliminate the residual stresses. Meanwhile, the high fraction of Σ3 boundaries disrupts the connectivity of the random grain boundary network, ultimately enhancing the corrosion resistance of the GH4169 alloy.

Microscale tapered hole parts are widely used in various disciplines such as microfluidics, biotechnology, and microelectronics. This paper proposes an in situ laser-assisted micro imprinting (In-LAI) process for machining micro-tapered holes with 10 μm outlet apertures on 300 μm thick Cu-ETP sheets. The laser heats the main deformation area of the workpiece in real time through the diamond indenter, which has the advantages of rapid response and the small heat-affected zone. Hertzian contact theory was used to solve the downward pressure range of the diamond indenter. The optimal machining process parameters targeting the minimum hole diameter at the outlet end are obtained by orthogonal tests. The experimental results show that the technology can controllably process micro conical holes with an outlet diameter of about 5–10 μm. In-LAI technology has provided a new method for manufacturing micro-tapered holes. This technology is also an extension of the in situ laser-assisted processing technology approach.

GH4169 alloy is a representative nickel-based superalloy, which is widely used in the aerospace field. However, GH4169 is prone to phase change during cutting. At the nanoscale, few studies have revealed the formation of phase transition and the relationship between cutting parameters and phase transition formation. Therefore, the phase transformation mechanism of the CBN (cubic boron nitride) cutting tool in nano-cutting nickel-based superalloy GH4169 was studied by the molecular dynamics (MD) method. Dislocation nucleation and dislocation motion in the cutting process were studied. The variation of dislocation density and cutting force and the internal stress distribution of the workpiece are analyzed. The influence of cutting depth on phase change evolution during the cutting process was studied by radial distribution function, coordination number analysis, and common neighbor analysis. The results show that the increase of cutting depth makes the dislocation density increase obviously, the required cutting force is larger, and the stress concentration is more significant. At the same time, the cutting depth will also affect the transformation of the crystal structure. The greater the cutting depth, the more intense the phase change inside the workpiece.

Abstract

Nitinol (NiTi) is an intermetallic compound and a member of the shape memory alloy family. This widely used material has unique properties such as biocompatibility, superelasticity, good corrosion resistance, and abrasion resistance, which distinguish it from the other shape memory materials. The most common applications of this alloy in medical engineering are in the manufacture of orthodontic wires, orthopedic implants, and guide wires in cardiovascular surgery. The production of orthopedic implants requires porous structures and bone-like tissue. In the present study, sodium chloride, polystyrene beads, and sawdust were used as space holder during the combustion synthesis process to produce porous NiTi alloy. The effect of space holder type on the percentage, distribution, and size of porosity of the synthesized samples were investigated. The sample's porosity percentage without the space holder was 30% and increased to 52, 36, and 37% by using sodium chloride, polystyrene beads, and sawdust spacers, respectively. The microstructure and phases of the specimens were examined using scanning electron microscopy (SEM) equipped with x-ray energy diffraction (EDS) spectroscopy and x-ray diffraction (XRD) analysis in samples with NaCl space holders with higher percentages and more controlled porosity. The microstructure of the synthesized sample without the space holder consisted of NiTi, NiTi₂, Ni₃Ti, and Ni₄Ti₃, and the addition of the sodium chloride did not change the phases. The Young's modulus and compressive strength of the synthesized sample without a space holder were 0.4 GPa and 59.7 MPa, respectively, which decreased with the addition of sodium chloride particles to 0.2 GPa and 25.5 MPa.

Graphical abstract

The weld metal (WM) and heat-affected zone are often the weak areas of aluminum alloy welded joints, in which poor properties of WM are typically associated with the microstructure formed during the melting and solidification. This paper focuses on the changes in microstructure and properties of aluminum alloy WM. Based on the finite element method, a three-dimensional model for predicting the columnar-to-equiaxed transition (CET) of weld metal during pulsed metal inert gas welding of 6082-T6 aluminum alloy was successfully established.At the same time, this study also analyzed the changes of microstructure and mechanical properties of WM under different heat inputs. The criterion curve for the CET of 6082-T6 aluminum alloy WM was expressed as (G^{n} /R = C_{st}), where (n) is 7.85855, and (C_{st}) is 7.9749 × 10⁴. Additionally, it is found that as the heat input increases, the grain size of WM initially decreases and then increases, and promoting the formation of equiaxed grains. At the same time, the content of Mg₂Si and Al₆ (Mn, Fe) phases in the WM increases, which affects the microhardness of the WM . This method is also applicable to other aluminum alloys joints, and it is of significant importance in predicting microstructure transformation of aluminum alloys WM.

Nanocomposite hydrophobic coatings have garnered substantial interest in recent times due to their remarkable anticorrosion and antifouling attributes. These coatings are designed to repel water and thwart the adherence of contaminants, rendering them valuable for an array of applications, including self-cleaning surfaces, anti-icing coatings, marine protection, and biomedical uses. This study delves into the fabrication of nanocomposite coatings, incorporating mixed oxide nanoparticles of CuO-MgO, MgO-ZnO, and CuO-ZnO at varying weight percentages within a poly (lactic acid) (PLA) matrix. Surface morphology and elemental composition were examined through Field Emission Scanning Electron Microscope (FESEM) and Energy-Dispersive x-ray Analysis (EDAX). The chemical composition of the coatings was assessed using Fourier Transform Infrared Spectroscopy (FTIR), revealing structural changes specific to PLA with Mg-Zn nanocomposite coating. The wettability studies indicate that the PLA/Cu-Mg coated sample exhibits superior hydrophobic properties, with a water contact angle (CA) of 98.2°. This value represents a remarkable 48.7 % increase compared to the bare Galvanised iron (GI) substrate. The coating's mechanical properties were assessed using scratch and adhesion tests. The efficacy of these coatings for anticorrosion and antifouling applications was gauged through comprehensive evaluations, in-vitro corrosion studies, egg white tests, and antibacterial tests. PLA/Mg-Zn nanocomposite coating exhibited exceptional performance in terms of scratch hardness and adhesion strength, whereas PLA/Cu-Zn nanocomposite coating exhibited better anticorrosion and antifouling properties.

Graphical Abstract

Abstract

Material extrusion additive manufacturing was introduced in many industries due to some relevant features such as the capability to process complex geometries and internal microstructures, application of material combinations, low volume production, faster product development cycle and waste reduction. However, this technique also exhibits some drawbacks like highly restricted printable materials and a generally low mechanical performance. The wide variety of processing parameters combined with the influence of complex lattice structure, quality bonding and heating–cooling periods along the building cycle indicates that an extensive mechanical characterization should be performed to warrant the in-service success of 3D printed parts. This study aims to investigate the effect of material extrusion setup, raster pattern and specimen size on the tensile, flexural and fracture behavior. The experimental performance showed that the ductility (strain at break reduction of 50%) was drastically limited with large sample dimensions. Printing setup and raster patterns exhibited a marginal influence on tensile performance. Each test revealed different dependencies with printing parameters, particularly under flexural loading conditions. A coarse printing setup, promoting a reduction of build cycle times, combined with bidirectional patterns looked like a promising way to improve the mechanical performance of 3D printed parts.

Graphical Abstract

Grain refinement and mechanical property enhancement of cast ingot aluminum 6061 alloy were achieved using equal-channel angular pressing (ECAP) at room temperature, employing route A and route R types. Analytical, finite element and experimental methods were utilized to investigate the alloy’s deformation behavior under the ECAP process. The tensile tests conducted at room temperature demonstrated a significant increase in strength with an increasing number of pressings, reaching 44.23, 53.19, and 56.7% for 1-pass, route A, and route R types 2-passes of the ECAP process, respectively. However, ductility, as indicated by elongation, gradually decreased after the first pressing. Electron backscatter diffraction was employed to reveal submicrometer grain sizes resulting from the ECAP process. The grain structure showed substantial improvement under route A and route R types at a 2-passes ECAP process. Wear tests conducted under loads of 10 and 25 N showed an increase in the coefficient of friction within the minimum wear loss intervals. Rockwell hardness also exhibited a significant increase of 119.3, 176.3, and 164.8% at 1-pass and 2-passes using routes R and A, respectively. As part of the evaluation, analytical models were computed using Python, and finite element simulations were performed using ABAQUS software. The results from analytical and finite element simulations demonstrated good agreement with the experimental data.

Electron beam welding of TZM and Ti-6Al-4V was performed with different beam offsets. A comprehensive analysis was undertaken to evaluate the effects of beam offsets on the joint's microstructure, element distribution, phase composition, and mechanical properties. The microstructure of welded joints underwent a transformation from sporadic dendrite to uninterrupted dendrite structure. With the 0.3 mm beam offset, the fusion zone predominantly comprised martensite. Interestingly, as the beam offset increased, the Mo concentration in the fusion zone decreased from 20 to 1.55 at.%. The phase composition of the welded joints also varied with the beam offset. With a minimal offset of 0.1 mm, the phases ranged from (Mo, Ti) to β-Ti and ω-Ti. As the offset increased to 0.3 and 0.4 mm, the α' phase became dominant. The tensile strength of the joints initially increased first and then reduced in the offset range of 0-0.4 mm. The maximum tensile strength of 480 MPa was obtained at the beam offset of 0.2 mm, while fractured at the heat-affected zone of TZM.