Effect Of Laser Remelting Research Articles

Effect of laser remelting on the microstructure and properties of an AlCoFeNi eutectic high-entropy alloy fabricated through double-wire arc additive manufacturing

Additive manufacturing (AM) technology is a new method for preparing eutectic high-entropy alloys (EHEAs). The resulting EHEAs have excellent mechanical properties. However, in engineering, material failure, such as wear or fatigue fracture, often occurs on the surfaces of components. There is no report on surface modification and strengthening of additively manufactured EHEAs. Therefore, this study successfully utilized laser remelting (LR) technology to enhance the surface properties of an AlCoFeNi EHEA fabricated by using double-wire arc AM technology. After LR, the distance between adjacent regular eutectic regions and lamellar spacing of the EHEAs significantly decreased, and the proportion of strictly semicoherent face-centered cubic/body-centered cubic interfaces increased. When microhardness increased from 277.7 HV to 302.3 HV, the average friction coefficient and wear rate of the alloys decreased by 32.5% and 51.1%, respectively, and hardness and wear resistance significantly improved. This study has laid a solid foundation for the engineering application of the combination of LR and AM and also provided new ideas for improving the surface performance of additively manufactured EHEAs.

Effect of laser remelting on microstructure evolution and high-temperature fretting wear resistance in a laser-cladding self-lubricating composite coating on titanium alloy substrate

TC21 titanium alloy possesses the advantage including high strength, low density, and great resistance to damage. Combining it with surface modification technology, it is expected to improve the performance of aviation structural components. This work applied laser remelting technology to realize surface modification, and the hardness and fretting wear properties of the coating were investigated. This research has found that laser remelting technology can effectively refine grain size and improve the performance of coatings. By exploring different laser remelting powers (600 W, 900 W, 1200 W) and the different diameters of laser beam (3 mm, 6 mm), the optimal laser process was obtained with laser power and spot diameter of 600 W and 6 mm, respectively. The average grain size is 2.1 μm. The laser remelting coating has an average microhardness about 980 HV0.2, and it is 2.5 times and 1.3 times higher than the substrate and laser cladding hardness, respectively. A minimum coefficient of friction (COF) about 0.5 was obtained by the laser remelting coating, and the wear rate reaches the lowest of 1.87 × 10−6 mm3/(N·m) at fretting temperature with 500 °C. The abrasive wear and adhesive wear were the main wear mechanisms, and accompanied by oxidative wear. This study provides important reference for improving the performance of high-strength titanium alloy to obtain low defect, high-performance coatings with stable quality.

Effect of laser remelting on the microstructures and properties of NiCoCrAlY-based coatings prepared by high-speed air fuel supersonic flame (HVAF)

In order to improve the oxidation resistance of the coating, laser remelting technology was used to remelt the HVAF multi-component modified coating. The influence of laser remelting technology on the phase state, microstructure characteristics, and isothermal oxidation behavior of coatings was studied. The experimental results indicate that a coating with complete morphology and no defects was obtained on the surface. There is a significant amount of metallurgical bonding and partial mechanical interlocking between the remelted layer and the substrate. The remelted layer is mainly composed of β-NiAl phase, accompanied by a small amount of γ′ phase and oxide phase. The microhardness test results show that the average hardness of the remelted layer is 1.1–1.42 times that of the prepared coating, and the bonding strength has increased by 23 %. After 100 h of high-temperature oxidation, the oxidation rate of the 4N3T4H remelted layer is the lowest, at 1.5 × 10−15 cm2/s, which is one order of magnitude lower than that of the as-sprayed coating. This is because after laser remelting, the remelted layer has the inherent hysteresis diffusion effect of HEA, which can improve the high-temperature oxidation resistance of the remelted layer and basically eliminate many pores and cracks contained in the HVAF coating. The coating density is significantly increased, which is conducive to hindering the diffusion of oxygen. Meanwhile, the oxide of HVAF coating mainly accumulates at pores and cracks, and there is no or late formation of uniform and dense oxide film on the surface. The surface of the remelted coating after oxidation forms a relatively uniform and dense oxide film, providing more effective protection for the substrate.

Structural evolutions and tribological properties of laser cladded FeCoNiCrMo high-entropy alloy coating by laser remelting and tempering process: TEM and DFT calculations

A laser cladded FeCoNiCrMo high-entropy alloy (HEA) coating was treated by laser remelting and tempering process in sequence to improve its tribological properties. The morphologies, phases and nanostructures of obtained coatings were analyzed using a scanning electron microscope, X-ray diffraction and transmission electron microscope. The effects of laser remelting and tempering process on the tribological properties were investigated by a ball-on-disc wear tester, and the wear mechanism was revealed with the density functional theory calculation. The results show that the main crystal planes of laser cladded, laser remelted and tempering processed HEA coatings are transformed from (200) and (220) to (111), and the reduced free energy and differential charge density of crystal plane (111) contribute to the improvement of tribological properties on the HEA coatings.

Crack inhibition and mechanical property enhancement of a CM247LC alloy fabricated by laser powder bed fusion through remelting strategy

High cracking susceptibility arising from the high thermal gradients is a critical issue of high γ'-fraction Ni-base superalloys fabricated by laser powder bed fusion (LPBF). Here in, laser remelting was used to inhibit cracking and enhance the strength-ductility synergy of additively manufactured CM247LC alloy by LPBF. The effects of laser remelting with different energy densities and scan strategies on microstructure, cracking behavior and mechanical properties of LPBF-processed CM247LC superalloy were systematically investigated. The crack inhibition mechanisms of laser remelting during the LPBF process were revealed. Low energy density of remelting and scan strategy with a rotation of 90° between remelting and prior melting were promising for decreasing the crack density. The crack inhibition caused by laser remelting could be attributed to the partial elimination of defects (e.g., lack-of-fusion pores), the mitigation of the segregation of elements, the backfilling of the grain boundaries and liquid film, and the reduction of the residual stress and the high-angle grain boundaries (HAGBs). Enhanced mechanical strength and ductility (ultimate tensile strength of 1280 MPa, yield strength of 885 MPa, and elongation of 11.9%) of LPBF-processed CM247LC samples were obtained by optimized-remelting parameters. This work demonstrated the potential of laser remelting in improving the printability of high γ'-fraction Ni-base superalloys fabricated by LPBF.

Effect of Laser Remelting on the Microstructural and Mechanical Properties of High-Velocity Oxy-Fuel (HVOF)-Sprayed WC-NiCr Coating

Effect of Laser Remelting on the Microstructural and Mechanical Properties of High-Velocity Oxy-Fuel (HVOF)-Sprayed WC-NiCr Coating

Effects of in–situ laser remelting on structural evolution and high–temperature tribological properties of plasma sprayed Cu11.85Al3.2Mn0.1Ti coating

A plasma sprayed Cu11.85Al3.2Mn0.1Ti coating on Ti6Al4V alloy was processed with in–situ laser remelting to improve its tribological performance. The effects of laser remelting on the structural evolution and high–temperature tribological properties of plasma sprayed coating were investigated using a wear tester, and the wear mechanism was also discussed in detail. The results show that the pores, layered structures and un–melted particles of plasma sprayed coating are eliminated by laser remelting, and its microstructure and hardness are further improved by in–situ laser remelting. The coefficient of friction of laser remelted coating is reduced by 26% compared with the plasma sprayed coating, and the corresponding wear rate is also decreased by 70%, showing that the superior friction reduction and wear resistance.

The Effect of Laser Remelting during SLM on Microstructure and Mechanical Properties of CoCrFeNiNb0.25.

A sub-eutectic high-entropy alloy composed of CoCrFeNiNb0.25 was prepared using a combination of mechanical powder mixing and selective laser melting (SLM). The mechanical properties of the alloy were enhanced by employing an interlayer laser remelting process. This study demonstrates the feasibility of using mechanical mixing and SLM to form an CoCrFeNiNb0.25 alloy. The interlayer laser remelting process can effectively promote the melting of Nb particles introduced by mechanical mixing, release the stresses near the unfused Nb particles, and reduce their degradation of the specimen properties. The results indicate that the CoCrFeNiNb0.25 alloy, prepared using the interlayer laser remelting process, had an average microhardness of 376 HV, a tensile strength of 974 MPa, and an elongation at break of 10.51%. This process offers a viable approach for rapidly adjusting the composition of high-entropy alloys for SLM forming.

Effects of Laser Remelting on Frictional Properties of Supersonic Flame-Sprayed Coatings

In this study, Cr3C2-Al2O3-NiCr coatings were prepared on INCONEL 600 alloy surfaces using the supersonic flame spraying technique, followed by a laser remelting treatment. In this way, this study further explored what impacts laser remelting has on coating performance. To this end, optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) were employed to carry out microstructural characterization. Energy-dispersive X-ray spectroscopy (EDS) was applied to conduct an analysis of the coatings’ elemental distribution while X-ray diffraction (XRD) was used to determine the coating phases. To measure the microhardness of the coatings, a microhardness tester was applied. In addition, the study investigated the samples’ electrochemical corrosion resistance and friction-wear performance under different surface conditions. According to the results, laser remelting enhanced the coating density, improved metallurgical bonding with the substrate, and optimized the carbide distribution, thereby enhancing corrosion and wear resistance in both air and corrosive media. However, excessive laser power hinders Cr3C2 nucleation, leading to diminished coating hardness and wear resistance in Cr7C3 formation.

Effect of laser remelting on the microstructure and corrosion behavior of high-velocity arc-sprayed FeNiCrBSiNbW amorphous coating

Fe-based amorphous coating was produced using high-velocity arc-spraying (HVAS), and then laser remelting (LR) technology was used to treat the as-sprayed coatings (ASC) to prepare the laser remelted coatings (LRC). The morphology, phase composition, microhardness, porosity, and corrosion property of the Fe-based amorphous coatings before and after LR were investigated. The outcomes demonstrated that the internal defects of the ASC were eliminated and the porosity was significantly reduced after LR, which was significant in dramatically enhancing corrosion resistance. After the LR procedure, the ASC's free corrosion potential (Ecorr) in 3.5 wt% NaCl solution increased, and the corrosion current density (Icorr) almost reduced by a factor of ten. Therefore, LR helped to strengthen the corrosion characteristics of Fe-based amorphous coating and improve its microstructure.

Effect of laser remelting on the microstructure and properties of the aluminum high silicon alloy coating

An aluminum high silicon alloy coating with the composition of AlSi30Cu5 was prepared by the plasma spraying technology, and the coating was remelted by laser remelting process. The microstructure, mechanical properties and wear resistance of the coatings were systematically investigated. After the laser remelting, the defects of the sprayed coating were eliminated, the microstructure was dense and uniform, the porosity decreased from 3.66% to 0.37%, and the phases had not changed. The hardness and elastic modulus increased by 20.7% and 23.3% respectively, the fracture toughness increased by nearly 7 times, and the wear rate decreased by about 37.8%. Therefore, laser remelting can effectively improve the microstructure distribution and enhance the wear resistance of aluminum high silicon alloy coating.

Effects of laser remelting on microstructure and tribological properties of plasma–sprayed Fe45Mn35Co10Cr10 high–entropy alloy coating

To further improve the Fe45Mn35Co10Cr10 high–entropy alloy coating prepared by plasma spraying, laser remelting was used to improve its structures and tribological properties. The effects of laser remelting on the microstructure, element composition, phase and hardness of obtained coating were investigated using a super depth of field microscope, energy dispersive spectrometer, X–ray diffraction and hardness tester, respectively. The tribological properties were measured via a ball–on–disk tester at room temperature and 500 °C, and the wear mechanisms were also discussed. The results show that the laser–remelted HEA coating is still composed of face–centered cubic structure, and its hardness is increased by ~301.4% compared with the plasma–sprayed coating, which is attributed to the grain refinement and solid solution strengthening effects. The average coefficient of friction and wear rate of laser–remelted HEA coating is superior to the plasma–sprayed HEA coating, showing that the laser remelting process plays the roles of friction reduction and wear resistance. The wear mechanism of plasma–sprayed HEA coating at room temperature is fatigue wear, abrasive wear and oxidative wear; while that of laser–remelted coating is abrasive wear and oxidative wear. Moreover, the wear mechanism of plasma–sprayed coating at 500 °C is adhesive wear, abrasive wear and oxidative wear, while that of laser–remelted HEA coating is adhesive wear and oxidative wear, which is attributed to the reduction of plastic deformation by the softening effect at high temperature.

Plasma sprayed Al2O3–40%TiO2 coating by laser remelting: Structural evolution, tribological properties and DFT calculation

A plasma sprayed Al2O3–40%TiO2 coating was processed by laser remelting to improve its tribological properties. The effect of laser remelting on the tribological properties of obtained coatings was investigated using a ball–on–disc wear tester, and the wear mechanisms were discussed by the density functional theory calculation. The results show that the phase of plasma sprayed Al2O3–40%TiO2 coating is changed from TiAl2O5 to Al2O3/Ti3O5 by laser remelting, and the grains of laser remelted Al2O3–40%TiO2 coating become refined to improve the coating hardness. The average coefficient of friction and wear rate of plasma sprayed Al2O3–40%TiO2 coating is decreased by laser remelting, which is attributed to the higher binding energy of Al–O in laser remelted Al2O3–40%TiO2 coating.

Effect of laser remelting on printability, microstructure and mechanical performance of Al-Mg-Sc-Zr alloy produced by laser powder bed fusion

Laser powder bed fusion (LPBF) is an advanced metal additive manufacturing technology, extensively employed in the aerospace, automotive, biomedical and military sectors. Generally, laser remelting is employed to improve the relative density and surface quality of LPBF fabricated components. Whereas, studies focusing on the influence of remelting on densification, surface roughness, residual stress, crystallographic orientation, microstructure, and mechanical performance of LPBF fabricated Al-Mg-Sc-Zr alloy are still inadequate. The effects of repeated employment of melting on a deposited layer are also not well understood. To address these issues, this work systematically investigated the effects of remelting and layer thickness on the densification, surface roughness, residual stress, crystallographic orientation, microstructure and mechanical performance of LPBF fabricated Al-Mg-Sc-Zr alloy. The experiment results indicated that remelting improved the densification of the specimens, owing to the elimination of large size pores. Meanwhile, laser remelting could significantly improve surface quality compared with single melting condition. The microhardness exhibited remelting dependence, as well as elongation to fracture. In summary, these results provide a fundamentally novel insight into how an integration of layer thickness and remelting can assist in the fabrication of high-performance lightweight Al-Mg-Sc-Zr alloy parts.

Effect of laser remelting on microstructure, salt spray corrosion and electrochemical performance of plasma sprayed CoCrFeNiMo HEA coating

Effect of laser remelting on microstructure, salt spray corrosion and electrochemical performance of plasma sprayed CoCrFeNiMo HEA coating

Effects of Laser Remelting on Microstructure, Wear Resistance, and Impact Resistance of Laser-Clad Inconel625-Ni/WC Composite Coating on Cr12MoV Steel

In this study, an Inconel625-Ni60-Ni60/25%WC (Inconel625-Ni/WC) composite coating was fabricated on Cr12MoV steel by first-stage laser cladding, followed by second-stage laser remelting with various laser powers, and the better laser energy density of 25.0 J/mm2 for laser remelting test was obtained by macroscopic morphology and microhardness analysis. The effects of laser remelting on the microstructure, microhardness, wear resistance, and impact resistance of the composite coating was systematically investigated by combining various characterization methods. The results showed that laser remelting did not cause the composite coating to produce new phases. The microstructure of the Ni/WC layer in the remelted composite coating was denser and finer, and the average grain size of the surface layer was reduced by 11.69%. The impact depth of laser remelting was about 2.0 mm. The average microhardness of the Ni/WC layer in the remelted composite coating increased by 5.9%, and the average wear rate of the surface was reduced by 50.12% compared with that before laser remelting. The wear surface of remelted composite coating exhibited abrasive wear, and the wear resistance was significantly improved. In addition, the impact toughness value of the remelted composite coating reached 5.15 J/cm2, which increased by 87.96% compared with that before laser remelting. The impact resistance of the composite coating was further improved.

A 3D simulation of grain structure evolution during laser rescanning process of powder bed fusion additive manufacturing

Laser powder bed fusion (LPBF) is an extensively used additive manufacturing process that can build metal parts with complicated geometric designs. However, because of the rapid solidification conditions and the layer-by-layer building, its application is challenged by products having poor surface quality and reduced mechanical properties. The laser rescanning process is often used as a refinement method during LPBF to improve the quality of products. In this study, grain structure formation during the LPBF laser rescanning process is modelled by a 3D cellular automaton based microstructure model coupled with finite element analysis. The coupled model considers different nucleation mechanisms, including epitaxial growth, which are applicable to rapid solidification in melt pool. The model is adapted to reproduce the grain structure and evolution of an Al-Si alloy manufactured by LPBF utilizing a laser rescanning strategy. The effects of laser remelting on the characteristics of the grain structure (i.e., the grain size, aspect ratio and orientation) are evaluated. The mechanisms that enable unique grain structure (i.e., grain refinement) are discussed.

Multilayered WC–Co coatings by Direct Energy Deposition-based cladding: Effect of laser remelting on interface defects

Despite ongoing optimization of WC-Co Direct Energy Deposition-based cladding, the deposition of multilayer coating is currently challenging. Pores and cracks that extended along the deposit thickness have been always observed in medium-large multilayer coatings. The change of substrate from steel to hard metal in multilayer deposition, replaces all of the thermal characteristics and dilution modes. This study looks into ways to improve the deposition quality of WC-Co multilayers for metal cutting application by remelting between subsequent layers. In order to define the key process parameters and to identify the effects of remelting, the characteristics of coatings are first examined in a single-track and single-layer simplified condition. These initial tests demonstrate that remelting reduces porosity and identify a “white layer” microstructural modification. The multilayer configuration was then examined, and a thorough analysis of the microstructure revealed an enrichment in Fe-Co-C elements in the surface that was advantageous for the deposition of a second layer. Remelting's observed effects on porosity and microstructure have been discussed, and the method's advantages and drawbacks have been made clear for potential future application.

Effect of laser remelting on copper‑nickel alloy coating prepared by extreme high-speed laser cladding

Copper‑nickel alloy is an important corrosion resistant material for marine environment. Advanced extreme high-speed laser cladding (EHLA) technology can realize a metallurgical bonding of copper‑nickel alloy and obtain better surface and structural characteristics. However, because of the high heat conductivity and high reflectivity of copper, copper-alloy coatings prepared by EHLA have defects such as segregation, blowhole, and cracks. In this study, EHLA copper‑nickel alloy coating was improved by in-situ laser remelting process. A single pass finite-element-model of the remelting process was built to analyze the effect of remelting speed on the solidification of molten pool. The surface morphology, microstructure, element distribution, and phase composites of coatings at different remelting speeds were characterized, and the anti-corrosion of the coatings was further discussed by constant potential polarization and EIS. The results show that heat input increases the convection strength of liquid in molten pool, promotes the uniformity of the coating microstructure and reduces the defects. Although the columnar crystals to equiaxed crystals transformation of the coatings did not obviously changed at different remelting speed, the high heat input during remelting speed of 5 m/min promoted the alloying of copper‑nickel coating and eliminated the defects, obtaining the best corrosion resistance. The research will provide some technical guidance and theoretical support for the practical application of copper‑nickel alloy coating with EHLA-LR process in marine equipment.

Effect of laser remelting on microstructure and mechanical properties of Ti–6Al–4V alloy prepared by inside-beam powder feeding

Ti–6Al–4V alloys fabricated by inside-beam powder feeding (IBPF) generally exhibit coarse columnar α-lath resulting in slightly poorer mechanical properties than forged parts. In this study, a laser remelting strategy with an annular beam was used to improve the microstructure and refine grain size, thus improving the mechanical properties of IBPF components. This is realized by the formation of ultrafine secondary precipitation αs and more recrystallized nuclei. The formation mechanism of compression twins {10 1‾ 1} and dislocation pinning effect in remelted layer were investigated in detail through TEM analysis. Furthermore, texture evolution and slip systems of the remelted layers were analyzed to determine the deformation patterns. Fine grain strengthening and dislocation strengthening was significant, and the tensile strength of Ti–6Al–4V components after laser remelting is higher than those fabricated by inside-beam powder feeding by about 12.7% and 9.3% in transverse and longitudinal directions, respectively.