Simulation Study on Temperature and Stress Fields in Mg-Gd-Y-Zn-Zr Alloy during CMT Additive Manufacturing Process.

A new heat source combination, consisting of a uniform body heat source and a tilted double ellipsoidal heat source, has been developed for cold metal transfer (CMT) wire-arc additive manufacturing of Mg-Gd-Y-Zn-Zr alloy. Simulations were conducted to analyze the temperature field and stress distribution during the process. The optimal combination of feeding speed and welding speed was found to be 8 m/min and 8 mm/s, respectively, resulting in the lowest thermal accumulation and residual stress. Z-axis residual stress was identified as the main component of residual stress. Electron Backscatter Diffraction (EBSD) testing showed weak texture strength, and Kernel Average Misorientation (KAM) analysis revealed that the 1st layer had the highest residual stress, while the 11th layer had higher residual stress than the 6th layer. Microhardness in the 1st, 11th, and 6th layers varies due to residual stress impacts on dislocation density. Higher residual stress increases dislocation density, raising microhardness in components. The experimental results were highly consistent with the simulated results.

The Effect of Silicon Phase Morphology on Microstructure and Properties of AlSi10Mg Alloys Fabricated by Selective Laser Melting.

This paper investigated the effect of silicon phase morphology and size on microstructure, mechanical properties, and corrosion resistance of the AlSi10Mg alloys fabricated by selective laser melting (SLM). Using different heat treatment conditions for SLM-fabricated alloys, the microstructure characteristics and mechanical properties are analyzed. The corrosion behavior analysis is also performed using potentiodynamic polarization, electrochemical and immersion tests. Results show that the AlSi10Mg alloy directly fabricated by SLM has a continuous eutectic silicon network, which has a small driving force for corrosion and facilitates the deposition of corrosion products and generates a dense protective film. On the contrary, the formation of large isolated and uniformly distributed silicon particles produces a greater corrosion driving force after heat treatment, which makes most of the corrosion products transfer to the solution. The corrosion resistance of AlSi10Mg alloy directly fabricated by SLM is better than that of the alloys with heat treatment. Moreover, the heat treatment reduces the hardness of AlSi10Mg alloys due to the decrease in the solid solution strengthening effect.

Effect of irradiation pulses on the microstructure and phase composition of a NiCoCrAlY laser cladding coating under the action of a high-current pulsed electron beam.

To reduce the number of microcracks and pores on the surface of laser cladding layers, we used a novel, to the best of our knowledge, surface alloying method to modify the surface of a NiCoCrAlY laser cladding coating using high-current pulsed electron beam technology. The x-ray diffraction peaks of the irradiated coatings were affected by the residual stress, which caused the peaks to shift and significantly broaden. With an increase in the number of pulses, the cleaning effect of the coating surface became significant. At the same time, the degree of surface alloying increased, and different degrees of slip were formed on the surface of the coating. There were many nanocrystals accumulated at the slip angle, and the grain size of the coating surface increased.

Study on Mechanism of Structure Angle on Microstructure and Properties of SLM-Fabricated 316L Stainless Steel.

In this study, seven 316L stainless steel (316L SS) bulks with different angles (0°, 15°, 30°, 45°, 60°, 75°, and 90°) relative to a build substrate were built via selective laser melting (SLM). The influences of different angles on the metallography, microstructure evolution, tensile properties, and corrosion resistance of 316L SS were studied. The 0° sample showed the morphology of corrugated columnar grains, while the 90° sample exhibited equiaxed grains but with a strong <101> texture. The 60° sample had a good strength and plasticity: the tensile strength with 708 MPa, the yield strength with 588 MPa, and the elongation with 54.51%. The dislocation strengthening and grain refinement play a vital role in the mechanical properties for different anisotropy of the SLM-fabricated 316L SS. The 90° sample had greater toughness and corrosion resistance, owing to the higher volume fraction of low-angle grain boundaries and finer grains.

First Principle Study of TiB2 (0001)/γ-Fe (111) Interfacial Strength and Heterogeneous Nucleation.

TiB2/316L stainless steel composites were prepared by selective laser melting (SLM), and the adhesion work, interface energy and electronic structure of TiB2/γ-Fe interface in TiB2/316L stainless steel composites were investigated to explore the heterogeneous nucleation potential of γ-Fe grains on TiB2 particles using first principles. Six interface models composed of three different stacking positions and two different terminations were established. The B-terminated-top 2 site interface ("B-top 2") was the most stable because of the largest adhesion work, smallest interfacial distances, and smallest interfacial energy. The difference charge density and partial density of states indicated that a large number of strong Fe-B covalent bonds were formed near the "B-top 2" interface, which increased the stability of interface. Fracture analysis revealed that the bonding strength of the "B-top 2" interface was higher than that of the Fe matrix, and it was difficult to fracture at the interface. The interface energy at the Ti-poor position in the "B-top 2" interface model was smaller than that of the γ-Fe/Fe melt, indicating that TiB2 had strong heterogeneous nucleation potency for γ-Fe.

Failure Analysis of the Tree Column Structures Type AlSi10Mg Alloy Branches Manufactured by Selective Laser Melting.

AlSi10Mg alloy branches were fabricated by selective laser melting (SLM), and the branches were employed to evaluate their effect on the mechanical properties. When the porous branches were compressed along its building direction, the tree column structures-type AlSi10Mg alloy branches collapsed twice, which had typical elastic, shear, collapse, and densification stages. The compressive stress concentration at the interface between the support and the porous body caused the fracture of the tree column structures-type AlSi10Mg alloy branches. The fracture surface indicated that the prepared tree-type branches were distributed with different shapes of dimples, and the Si content inside the dimples was higher than that of the edge. The morphology of the Al-Si eutectic structure formed by SLM and the stress concentration at the Al/Al-Si-eutectic interface affected the fracture morphology and Si content distribution.

The Interfacial Characteristics of Graphene/Al4C3 in Graphene/AlSi10Mg Composites Prepared by Selective Laser Melting: First Principles and Experimental Results.

The Al4C3 phase was precipitated via a reaction of graphene (Gr) with Al during selective laser melting (SLM). The interfacial nature of the Gr (0001)/Al4C3 (0001) interface was determined using the first-principle calculation. The simulation results showed that the influence of the stacking site on the interfacial structure was limited and the Al-termination interface presented a more stable structure than the C-termination interface. The Al-termination-CH site interface had the largest work of adhesion (6.28 J/m2) and the smallest interfacial distance (2.02 Å) among the four interfacial structures. Mulliken bond population analysis showed that the bonding of the Al-termination interface was a mixture of covalent and ionic bonds and there was no chemical bonding in the C-termination interface.

The Relationship between Residual Amount of Sr and Morphology of Eutectic Si Phase in A356 Alloy.

This paper studied the relationship between the residual amount of Sr and the morphology of the eutectic Si phase in A356 obtained through different modification treatment processes; additionally, the cooling rates of molds were studied. The eutectic Si phase revealed a satisfactory modification effect at residual Sr amounts above 0.01 wt % in A356 alloys cast using an iron mould. Complete modification of the eutectic Si phase could be achieved at a Sr additive amount 0.03 wt % in an A356 melt. The addition of higher amounts of Sr (~0.04-0.06 wt %) did not improve the modification effect. With the addition of 0.06 wt % Sr into A356 alloy melt and holding at 750 °C, the anti-fading capacity of Sr modification effect could be sustained for 120 minutes. More Sr is needed to obtain a good modification of eutectic Si for an A356 alloy cast using a sand mold.

Tribological Behavior of TiC Particles Reinforced 316Lss Composite Fabricated Using Selective Laser Melting.

In order to improve the abrasion performance of 316Lss, make full use of its advantages and broaden its application fields, the tribological behavior of the TiC particles reinforced 316Lss composites-which were manufactured by selective laser melting (SLM)-were investigated. In this study, GCr15 bearing steel was selected as the friction material and experiments on the sliding friction and wear under different loads of 15 N, 25 N and 35 N at the sliding speeds of 60, 80 and 100 mm/min were carried out, respectively. The results show that the wear performance of the TiC/316Lss composite is higher than that of the matrix during the friction and wear experiments under all conditions and the wear rate of the TiC/316Lss composite decreases with increasing the friction rate. Similar to the wear mechanism under different loads, it changes from abrasive wear to delamination wear and severe oxidative wear. At the same time, the mechanical mixed layer formed at a high speed has a protective effect on the matrix. The reason for this phenomenon is that the mechanical properties of the TiC/316Lss composites are significantly improved due to the addition of TiC particles, the refinement of cells near the TiC particles and the formation of a large number of dislocations. In addition, due to the presence of the TiC particles, the hardness and strength of the TiC/316Lss composites are greatly improved, thus the processing hardening ability of sub-surface has been improved.

The Reaction Thermodynamics during Plating Al on Graphene Process.

This research explored a novel chemical reduction of organic aluminum for plating Al on a graphene surface. The thermodynamics of the Al plating reaction process were studied. The Al plating process consisted of two stages: the first was to prepare (C2H5)3Al. In this reaction, the ΔH(enthalpy) was 10.64 kcal/mol, the ΔG(Gibbs free energy) was 19.87 kcal/mol and the ΔS(entropy) was 30.9 cal/(mol·K); this was an endothermic reaction. In the second stage, the (C2H5)3Al decomposed into Al atoms, which were gradually deposited on the surface of the graphene and the Al plating formed. At 298.15 K, the ΔH was -20.21 kcal/mol, the ΔG was -54.822 kcal/mol, the ΔS was 116.08 cal/(mol·K) and the enthalpy change was negative, thus indicating an endothermic reaction.

Performance Consistency of AlSi10Mg Alloy Manufactured by Simulating Multi Laser Beam Selective Laser Melting (SLM): Microstructures and Mechanical Properties.

Multi-laser beam selective laser melting (SLM) technology based on a powder bed has been used to manufacture AlSi10Mg samples. The AlSi10Mg alloy was used as research material to systematically study the performance consistency of both the laser overlap areas and the isolated areas of the multi-laser beam SLM manufactured parts. The microstructures and mechanical properties of all isolated and overlap processing areas were compared under optimized process parameters. It was discovered that there is a raised platform at the junction of the overlap areas and the isolated areas of the multi-laser SLM samples. The roughness is significantly reduced after two scans. However, the surface roughness of the samples is highest after four scans. As the number of laser scans increases, the relative density of the overlap areas of the samples improves, and there is no significant change in hardness. The tensile properties of the tensile samples are poor when the overlap area width is 0, 0.1, or 0.2 mm. When the widths of the overlap areas are equal to or greater than 0.3 mm, there is no significant difference in the tensile strength between the overlap and the isolated areas.

The Heat Treatment Influence on the Microstructure and Hardness of TC4 Titanium Alloy Manufactured via Selective Laser Melting.

In this research, the effect of several heat treatments on the microstructure and microhardness of TC4 (Ti6Al4V) titanium alloy processed by selective laser melting (SLM) is studied. The results showed that the original acicular martensite α'-phase in the TC4 alloy formed by SLM is converted into a lamellar mixture of α + ß for heat treatment temperatures below the critical temperature (T0 at approximately 893 °C). With the increase of heat treatment temperature, the size of the lamellar mixture structure inside of the TC4 part gradually grows. When the heat treatment temperature is above T0, because the cooling rate is relatively steep, the ß-phase recrystallization transforms into a compact secondary α-phase, and a basketweave structure can be found because the primary α-phase develop and connect or cross each other with different orientations. The residence time for TC4 SLM parts when the treatment temperature is below the critical temperature has little influence: both the α-phase and the ß-phase will tend to coarsen but hinder each other, thereby limiting grain growth. The microhardness gradually decreases with increasing temperature when the TC4 SLM part is treated below the critical temperature. Conversely, the microhardness increases significantly with increasing temperature when the TC4 SLM part is treated above the critical temperature.

Analysis of Geometrical Characteristics and Properties of Laser Cladding 85 wt.% Ti + 15 wt.% TiBCN Powder on 7075 Aluminum Alloy Substrate.

Ti/TiBCN composite coatings were prepared on a 7075 aluminum alloy surface by laser cladding. The relation between the main processing parameters (i.e., laser power, scanning speed, and powder feeding rate) and the geometrical characteristics (i.e., height, width, penetration depth, dilution and wetting angle) of single clad tracks is studied by linear regression analysis. The microstructure, micro-hardness and electrochemical corrosion were investigated by scanning electron microscopy, a Vickers micro-hardness machine, and a standard three-electrode cell, respectively. The results showed that all geometrical track characteristics are observed with high values of the correlation coefficient (R > 0.95). In addition, the average hardness value (750 HV0.2) was obtained of the Ti/TiBCN composite coating, and polarization curves indicated that the composite coatings were harder to corrode than the substrate.

Effect of Selective Laser Melting Process Parameters on Microstructure and Properties of Co-Cr Alloy.

Due to the rapid melting and solidification mechanisms involved in selective laser melting (SLM), CoCrMo alloys fabricated by SLM differ from the cast form of the same alloy. In this study, the relationship between process parameters and the morphology and macromechanical properties of cobalt-chromium alloy micro-melting pools is discussed. By measuring the width and depth of the molten pool, a theoretical model of the molten pool is established, and the relationship between the laser power, the scanning speed, the scanning line spacing, and the morphology of the molten pool is determined. At the same time, this study discusses the relationship between laser energy and molding rate. Based on the above research, the optimal process for the laser melting of cobalt-chromium alloy in the selected area is obtained. These results will contribute to the development of biomedical CoCr alloys manufactured by SLM.

Simulation of Stress Field during the Selective Laser Melting Process of the Nickel-Based Superalloy, GH4169.

In this paper, GH4169 alloy's distributions of temperature and stress during the selective laser melting (SLM) process were studied. The SLM process is a dynamic process of rapid melting and solidification, and we found there were larger temperature gradients near the turning of scan direction and at the overlap of the scanning line, which produced thermal strain and stress concentration and gave rise to warping deformations. The stresses increased as the distance became further away from the melt pool. There was tensile stress in the most-forming zones, but compressive stress occurred near the melt pool area. When the parts were cooled to room temperature after the SLM process, tensile stress was concentrated around the parts' boundaries. Residual stress along the z direction caused the warping deformations, and although there was tensile stress in the parts' surfaces, but there was compressive stress near the substrate.

Research on the Thermal Behaviour of a Selectively Laser Melted Aluminium Alloy: Simulation and Experiment.

A 3D Finite Element (FE) model was developed to investigate the thermal behaviour within the melt pool during point exposure to Selective Laser Melting (SLM) processed AlSi10Mg powder. The powder⁻solid transition, temperature-dependent thermal properties, melt pool convection, and recoating phase were taken into account. The effects of Exposure Time (ET) and Point Distance (PD) on SLM thermal behaviour were also investigated and showed that the short liquid phase time and high cooling rate of the melt pool reduced the viscosity of the melt pool at a lower ET or a higher PD. This resulted in poor wettability and the occurrence of balling and micropores. At a higher ET or lower PD the melt pool became unstable and allowed for easy formation of the self-balling phenomenon, as well as further partial remelting in the depth direction resulting in the creation of larger pores. The proper melt pool width (119.8 μm) and depth (48.65 μm) were obtained for a successful SLM process using an ET of 140 μs and a PD of 80 μm. The surface morphologies and microstructures were experimentally obtained using the corresponding processing conditions, and the results aligned with those predicted in the simulation.

Chloridobis(1,10-phenanthroline-κN,N')(2,2,2-trichloro-acetato-κO)cobalt(II).

The title compound, [Co(C(2)Cl(3)O(2))Cl(C(12)H(8)N(2))(2)], was obtained by the reaction of trichloro-acetic acid and CoCl(2) in the presence of 1,10-phenanthroline. The Co(II) ion exhibits a distorted octa-hedral geometry, with three N atoms from two 1,10-phenanthroline ligands and the Cl(-) ion in the equatorial plane and one O atom from the trichloro-acetate ligand and one phenanthroline N atom in axial positions. This compound is isostructural with the analogous Mn(II) complex. The trichloro-methyl group of the trichloro-acetate ligand is disordered over two positions with occupancies of 0.190 (5) and 0.810 (5).