Investigation on the Microstructure and Mechanical Properties of CNTs-AlSi10Mg Composites Fabricated by Selective Laser Melting.

CNT-AlSi10Mg composites fabricated by SLM have drawn a lot attention in structural application due to its excellent strength, elasticity and thermal conductivities. A planetary ball milling method was used to prepare the carbon nanotube (CNT)-AlSi10Mg powders, and the CNT-AlSi10Mg composites were fabricated by selective laser melting (SLM). The density, microstructure and mechanical properties of CNT-AlSi10Mg composites were studied. The density of the test samples increased at first and then decreased with increasing scan speed. When the laser scan speed was 800 mm/s, the test sample exhibited the highest density. The hardness increased by approximately 26%, and the tensile strength increased by approximately 13% compared to those values exhibited by the unreinforced AlSi10Mg. The grains of CNT-AlSi10Mg composite are finer than that in the AlSi10Mg. The CNTs were distributed along the grain boundaries of AlSi10Mg. Some of the CNTs reacted with Al element and transformed into Al4C3 during SLM, while some of the CNTs still maintained their tubular structure. The combination of CNTs and Al4C3 has a significant improvement in mechanical properties of the composites through fine grain strengthening, second phase strengthening, and load transfer strengthening.

Bubble dynamic evolution, material strengthening and chemical effect induced by laser cavitation peening.

The mechanism of laser cavitation peening (LCP) including laser shock wave, bubble collapse shock wave, and water-jet was investigated at various stand-off distances (γ) combined with experiment and simulation. The dynamic characteristics, pressure field, and temperature field of cavitation bubble were investigated. The Q235 steel was impacted by LCP and the strengthening mechanism was analyzed, and the chemical effect in LCP was discussed. The results found that the pressure intensity of shock wave and water-jet decreases with increasing the γ. At γ=0, the laser shock wave, bubble collapse shock wave, and water-jet are 989 Mpa, 763 Mpa, and 369 Mpa respectively. The pressure and temperature of the bubble decrease obviously in the second and third pulsations. The impact of LCP causes plastic deformation on the Q235 steel surface and refines the grains on the surface layer within a depth of 20-30 µm. The enhancement of microhardness and the residual stress increases with the increase of γ, and the optimal value for LCPwc is 0.4. The degradation rate of MB solution in the infinite domain, LCPwc, and LCP is 26.4%, 41.7%, and 34.5%.

Impact of solid particles on cavitation behaviors and laser-induced degradation in aqueous suspension.

A method for degrading organic pollutants in suspension by applying laser-induced cavitation is presented. Cavitation bubbles are produced remotely by laser beams, achieving a purpose of non-contact degradation. In this work, laser-induced bubble dynamics in SiO2 sand suspension were studied by high-speed imaging. Pulsating characteristics of cavitaiton bubbles in the infinite domain and near a solid boundary were investigated among various laser energies and sand concentrations. Furthermore, the extent of degradation after processing in suspension and the mechanism were analyzed. Results indicate that solid particles in the liquid medium reduce the extent of degradation. However, the extent of degradation may rebound at a proper sand concentration. In addition, compared to several small bubbles in a bubble string (in the infinite domain), a single larger bubble (near a solid boundary) has a much higher degradation ability.

Microstructure, Mechanical Properties, and Residual Stress Distribution of AISI 316L Stainless Steel Part Fabricated by Laser Metal Deposition.

In this paper, AISI 316L stainless steel part is obtained by laser metal deposition additive manufacturing method. The microstructure of the part was observed and analyzed by an optical microscope. The tensile mechanical properties and residual stress distribution of the part were tested by tensile test and the contour method. The results show that the bulk structure is mainly columnar crystal and equiaxed crystal, and the latter layer of laser metal deposition will form a remelted zone and heat-affected zone in the former deposition zone. Tensile test results show that the tensile strength of tensile specimens parallel to laser scanning direction and perpendicular to laser scanning direction is basically the same, but the elongation of the specimens perpendicular to the laser scanning direction is relatively better. The main reason is the different distribution characteristics of columnar crystals and equiaxed crystals in the two directions. Relatively large deformation occurs on the cut surface of the specimen after low-speed wire cut. The residual stress test results indicate that tensile stress is formed in the upper part and it reaches 315 MPa at the top surface. And compressive stress is formed at the part/substrate interface and the substrate.

Microstructure and Wear Behavior of Laser Cladded Ni45 + High-Carbon Ferrochrome Composite Coatings.

A composite coating with enhanced mechanical properties including high hardness and excellent wear resistance was produced by laser cladding of mixed Ni45 and high-carbon ferrochrome powders on an ASTM 1045 steel substrate. Different quantities, ranging from 10 to 50 wt.% of high-carbon ferrochrome powder were added to the Ni45 powder to investigate the effect of mixture content on the cladding performance. The microstructure of the coatings were examined using scanning electron microscope, and the wear resistance was compared using a wear tester apparatus among the different cases. The results showed that the microstructure of the coating with 30 wt.% high-carbon ferrochrome content was mainly fine solid solution phase. With the increase of high-carbon ferrochrome content to 40 wt.% and above, cracks appeared on the cladding surface due to a large amount of chromium carbides formed during the process. The microhardness was enhanced remarkably by laser cladding the composite coating on the 1045 substrate, with 2.4 times higher than the hardness of the substrate when 30 wt.% high-carbon ferrochrome content was added. The best wear performance was achieved when the high-carbon ferrochrome content was 30 wt.%, demonstrating the smallest surface roughness and depth of wear marks. With further increased high-carbon ferrochrome content, microcracking and delamination were observed on the worn surfaces.

Degradation of Rhodamine B in aqueous solution by laser cavitation.

A novel method of laser cavitation (LC) was proposed for degrading organic dye wastewater. Rhodamine B (RhB) aqueous solution was employed as the simulated organic dye wastewater, and a LC system was designed to conduct the experiments of degrading RhB. The effects of laser energy, initial concentration and cavitation time on the degradation were investigated. Moreover, the degradation kinetics, degradation mechanism and energy efficiency were analyzed. The experimental results indicate that RhB aqueous solution can be degraded effectively by LC and the degradation follows the pseudo-first-order kinetics. The extent of degradation increases by 27.6% with the rise of laser energy (50-100 mJ) while it decreases by 7.8% with increasing the initial concentration from (20-40 mg/L), but RhB can not be degraded when exceeding 100 mg/L. The degradation extent of RhB at 100 mJ and 20 mg/L for 3 h is 81.11%, and the RhB solution is almost completely degraded at 150 mJ (98.4%). The degradation velocity of RhB rises firstly and then decreases as the cavitation time increases. The degradation of RhB by LC can be attributed to the N-de-ethylation and chromophore cleavage caused by oxidation of hydroxyl (OH) radical and thermal decomposition. LC has a higher energy efficiency compared with other methods and is more energy efficient at lower laser energy.

Burial Depth Effect of Crack on the Lcr Wave Acoustoelastic Coefficient for Stress Measurement of Laser Cladding Coating.

In this paper, the influence of burial depth of crack on stress measurement of laser cladding coating with the critical refracted longitudinal wave (Lcr wave) was discussed based on the Lcr wave acoustoelastic effect. The regular rectangular slots with different depths that were used to simulate the burial crack in coating was based on the equivalent theory. The experimental system including an ultrasonic wave generator, digital oscilloscope (2.5 GHz sampling rate), and two Lcr wave transducers (2.5 MHz center frequency) was used to collect the Lcr wave under different tensile loads, and the Lcr wave was denoised by using wavelet analysis technology, then the fracture morphology was observed using SEM. The results show that after the denoising by wavelet analysis technology, the signal-to-noise ratio of Lcr wave becomes bigger and the mean square deviation of Lcr wave becomes smaller. When the tensile load is within the turning point load, the difference in time of flight between Lcr wave increases linearly as the tensile load increases, and the deviation of the experimental results becomes obvious as the tensile load increases. When the tensile load is the same, as the burial depth of the slot increases, the nominal Lcr wave acoustoelastic coefficient decreases and tends to be stable gradually. At last, the experimental results are discussed based on the Lcr wave acoustoelastic effect and deformation theory, and it is analyzed that the uneven deformation caused by the interface in coating, anisotropic microstructure, and the burial crack is considered as the main reason.

Record-high capture of volatile benzene and toluene enabled by activator implant-optimized banana peel-derived engineering carbonaceous adsorbents.

This work developed a super-high performance of engineering carbonaceous adsorbents from waste banana-peel via an optimized KOH-impregnated approach, which affords outstanding structural property (SBET = 3746.5 m2 g-1, Vtotal = 2.50 cm3 g-1), far outperforming KOH-grinding method-induced counterpart and other known banana peel-derived those. Thereby, this triggers a record-high capture value of volatile organic compounds (VOCs) specific to benzene (27.55 mmol g-1) and toluene (23.82 mmol g-1) in the all known results. The structural expression characters were accurately correlated with excellent adsorption efficiency of VOCs by investigating the synthetic factor-controlling comparative samples. Ulteriorly, the adsorption selectivity prediction at different relative humidity was demonstrated through the DIH (difference of the isosteric heats), highlighting the good superiority in selective adsorption of toluene compared to benzene even under humid atmosphere. Our findings provide the possibility for the practical application and fabrication of waste biomass (banana peel)-derived functional biochar adsorbent in the environmental treatment of threatening VOCs pollutants.