The current design of negative Poisson’s ratio lattice structures is mainly forward-looking and predominantly dependent on several known deformation patterns. To automate the generation of structures ...with programmable Poisson’s ratio, the study utilized the energy homogenization method and the Solid Isotropic Material with Penalization (SIMP) method to establish an optimization model for negative Poisson’s ratio. By proposing a relaxed objective function and eliminating damping in the Optimality Criteria (OC) method, the study achieves the automatic evolution of negative Poisson’s ratio programmable lattice unit cells, with the lowest Poisson’s ratio achieving −0.5367, and an equivalent elastic matrix is derived. The iterative process’s efficiency is comparable to that of commercial software, with a maximum iteration time of 300 s, enabling the prompt identification of fundamental configurations. To validate the method’s effectiveness, finite element analysis was performed on four tubular structures, revealing evident tension–compression deformation patterns. Moreover, the microscale selective laser melting was used to successfully prepare multiple sets of tubular samples made from 316L stainless steel, each with a height of 5 mm. Quasi-static compression experiments showed negative Poisson’s ratio effects and buckling forms that align with finite element analysis results, providing valuable insights for industry applications.
Repairing hot work molds can extend their lifespans and reduce the production costs. This study presents a proposed method for enhancing the red hardness and strength of repaired molds. The method ...involves utilizing PM23 high-speed steel powder to repair H13 steel molds with two distinct surface states through the process of hot isostatic pressing (HIP). The internal microstructure changes, bonding state, fracture morphology, and crack extension behaviors of the repaired molds are characterized using scanning electron microscopy and electron backscatter diffraction technology. Additionally, the mechanical properties, including red hardness and tensile strength, are quantitatively analyzed. The findings indicate that the repaired area in the sandblasted sample exhibits a rough and uneven structure, demonstrating exceptional toughness. The tensile strength of the repaired region is approximately 1195.42 MPa, while the hardness measures around 672.8 HV. These properties effectively enhance the performance of the molds. The experimental findings indicate that HIP can effectively restore molds, resulting in enhanced red hardness and improved toughness, particularly when combined with sandblasting as a pretreatment method.
The effect of tempering temperature on the microstructure and electrochemical behavior of 13wt.% Cr-type martensitic stainless steel (MMS) in 3.5wt.% NaCl aqueous solution has been studied. Based on ...XRD, SEM and TEM-EDS analysis, it has been found that the precipitates in the steels that were tempered at 300°C, 500°C and 650°C, are nano-sized ϵ-M3C carbides, nano-sized Cr-rich M23C6 carbides and micron or submicron-sized Cr-rich M23C6 carbides, respectively. Potentiodynamic polarization curves and electrochemical impedance spectroscopy studies indicate that the pitting potential of the as-quenched steel is higher than those of the tempered steels, and decrease with the increase in tempering temperature. Especially when tempered at 500°C, the corrosion resistance of the steel decreases abruptly. It shows that the precipitation of the massive-amount of nano-sized Cr-rich M23C6 carbides would provide lots of interface of carbides/matrix as the pitting initation and then hinder the formation of protective passive film on the steel surface due to the short interspace between the tempered carbides.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Abstract
Based on the energy uniformization method and topology optimization method, a negative Poisson’s ratio generating model was designed. Using the generated cells, a novel negative Poisson’s ...ratio vascular stent was designed. A finite element model of the expansion process, including the vessel, stent, and balloon, was established. The analysis results showed an obvious tensile deformation pattern. Based on this expansion model, 23 sample points were sampled using the Latin hypercube method. Material parameters were used as variables, and cell equivalent Poisson’s ratio was used as a response. Least squares regression, moving least squares methods, Kriging, and radial basis function response surface models were established, and the fitted surface patterns were consistent with the design. The equivalent Poisson’s ratio measured by the cell was less than 8% different from the theoretical Poisson’s ratio obtained by uniformization.
This study aimed to modulate the magnetic properties of selective laser melting NiFeMo alloy. This was achieved via the controlled addition of Mo elemental in-situ alloying content to change the ...tissue morphology and crystal structure of SLM-formed (NiFeMo)100−xMox alloy (x = 0 wt%, 0.25 wt%, 0.5 wt%, 0.75 wt%, 1.0 wt%, 1.25 wt%, 1.5 wt%, 2.0 wt%). The results of scanning electron microscopy (SEM), X-ray diffraction, electron backscatter diffraction (EBSD), DC B-H hysteresis tester, and transmission electron microscopy (Titan-G2) indicate that all samples are predominantly face-centered-cubic (FCC) γ- (Ni, Fe) solid solutions and typical soft-magnetic hysteresis line features. However, the lattice parameter a of γ- (Ni, Fe) decreased and then increased with increasing Mo content. When the added Mo content is 0–1.25 wt%, the Mo particles inside the (NiFeMo)100−xMox alloy become nucleation sites, creating a diffusive metallurgical behavior with the Ni and Fe elements, and preventing the growth of columnar crystals, leading to the reduction of LAGBs density and the enhancement of the {111} texture orientation in the easy magnetization direction, increasing Bs and the decrease of Hc of the NiFeMo alloy. At the Mo content of 1.25 wt%, the soft magnetic properties were optimal, with Bs and Hc being 0.704 T and 17.31 A/m, respectively. Conversely, when the added Mo content was 1.5–2.0 wt%, the solubility of Mo elements in the γ- (Ni, Fe) solid solution was limited, which resulted in the occurrence of metallurgical defects within the organization such as unfused Mo particles, unfused areas, and porosity. Moreover, when the added Mo content increased to 2.0 wt%, the {111} lattice spacing in the easy magnetization direction increased by 0.2261 nm compared to the NiFeMo alloy, and the average lattice distortion Δε increased to 0.16%, causing a decrease in the soft magnetic performance of the (NiFeMo)98Mo2 alloy, with Bs reducing to 0.6666 T and Hc increasing to 23.44 A/m.
•The microstructure evolution of NiFeMo alloy formed by in-situ alloy-SLM was analyzed and described in detail.•The crystallographic relationship of NiFeMo alloy with Mo element was analyzed on an atomic scale by HETEM.•Analyzed the changes in soft magnetic properties of NiFeMo alloy with different Mo additions.•Clarified the influencing mechanism of Mo element in-situ alloying on the magnetic properties of NiFeMo alloy.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
Extreme high-speed laser material deposition (EHLA) technology is a novel approach to surface modification and component repair that offers benefits, including high cladding efficiency, a ...low dilution rate, and environmental friendliness. In this research, numerical modeling was used to analyze how varying substrate preheating temperatures affected the temperature field and residual stress of coatings made of 1Cr17Ni2 stainless steel. It was discovered that the peak melt pool temperature was less affected by the substrate preheating temperature. However, the cooling rate and temperature gradient were greatly reduced. When the preheating temperature was 450 °C, the cladding layer showed the lowest temperature gradient and residual stress. The investigation’s findings can be used as a reference to improve the EHLA of 1Cr17Ni2 stainless steel coatings and lessen the possibility of coating cracking.
Metallurgical defects significantly affect the performance of materials fabricated by selective laser melting (SLM), becoming a bottleneck problem in the application of laser 3D printing technology. ...To investigate the effect of metallurgical defects on the magnetic properties of SLM NiFeMo permalloy. An in-depth characterization of the microstructure and phase composition of SLM-fabricated NiFeMo permalloy samples were carried out. Soft magnetic DC BH hysteresis loop tester was used to assess the magnetic properties. Defect voxel data of as-built samples were obtained using X-ray microcomputed tomography (XCT). The results show that the micro-defects of SLM NiFeMo alloy are mainly composed of lack of fusion, pores, etc., and the phase composition of NiFeMo is mainly γ- (Ni, Fe) solid solution. With the increase of laser volume energy density, the Bs and μm of the material increase, while the Hc and Pu decreases. The equivalent diameter of the defects shows a positive correlation with the coercivity (Hc) and a negative correlation with the saturation magnetic induction (Bs) of NiFeMo permalloy.
•The microstructural features, the evolution of defect size and morphology were analyzed and described in detail.•Defect data information in SLM-fabricated permalloy was extracted and quantified using XCT.•Permalloy samples with relatively good magnetic properties were obtained by adjusting the process conditions.•Constructed and validated an approximate relational model describing the correlation of defects and magnetic properties.
Full text
Available for:
IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The types, dimensions and quantities of inclusions have been examined to quantitatively investigate their influence on the bending strength and impact toughness of HIPed high-speed steel. MgSiO3 ...inclusion was found to be less harmful than Al2O3 inclusion in terms of mechanical properties. Additionally, the inclusion of Al2O3 of 0-20 μm under 0.02 vol.% showed a slight influence on the bending strength of certain HSS.
Abstract
The types, dimensions and quantities of inclusions have been examined to quantitatively investigate their influence on the bending strength and impact toughness of HIPed high-speed steel. ...MgSiO3 inclusion was found to be less harmful than Al
2
O
3
inclusion in terms of mechanical properties. Additionally, the inclusion of Al
2
O
3
of 0-20 μm under 0.02 vol.% showed a slight influence on the bending strength of certain HSS.
With the aim to improve cladding coating quality and prevent cracking, this paper established an extreme high-speed laser cladding thermo-mechanical coupling simulation model to study the evolution ...of the temperature field and the residual stress distribution. Process parameters that impacted the macroscopic morphology of single-pass coatings were investigated. Numerical calculations and temperature field simulations were performed based on the process parameter data to validate the effects of the temperature gradient and cooling rate on the coating structure and the residual stress distribution. The results showed that a good coating quality could be achieved using a laser power of 2400 W, a cladding speed of 20 m/min, and a powder feeding rate of 20.32 g/min. The coatings’ cross-sectional morphology corresponded well with the temperature distribution predicted by the numerical modeling of the melt pool. The microstructure of the molten coatings was affected by the temperature gradient and the cooling rate, which varied greatly from the bottom to the middle to the top. Maximum residual stress appeared between the bonding region of the coatings and the substrate, and the coatings themselves had significant residual stress in the form of tensile strains, that were mostly distributed in the direction of the laser cladding.
PDF
