Remelting Technology Research Articles

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.

Analysis of Thermophysical Properties of Electro Slag Remelting and Evaluation of Metallographic Cleanliness of Steel.

Improving the competitiveness of steel companies is linked to sustainable, quality-compliant steel production. Therefore, new steel production technologies contributing to increased cleanliness of steel are continuously being developed and optimized. One way to achieve a high steel quality is to use electro slag remelting (ESR) technology. In this paper, the principle of ESR technology and the importance of fused slags for optimizing the process are outlined. The aim of this work was to analyze the main thermophysical properties of steel and fused slags used in the ESR process. Determination of the properties of steel and slags was performed using the FactSage calculation software, which involved the calculation of the liquid and solid temperature of steel and slags, the calculation and construction of quaternary diagrams, and the calculation of viscosity. The resulting quaternary diagrams revealed the substantial influence of chemical composition on melting temperatures of slags. In order to validate the acquired results, a CrNiMoV-type steel was subjected to investigation of its metallographic cleanliness and evaluation of its mechanical properties; the ESR process was shown to significantly improve the cleanliness of the steel and improve the mechanical properties of the steel compared to its cleanliness and quality when produced via vacuum degassing (VD) technology. During the ESR process, the average size of non-metallic inclusions was reduced from 20 μm to 10 μm, and the maximum size of non-metallic inclusions was reduced from 50 μm to 28 μm. The mechanical properties of the steel produced using ESR technology were impacted as follows: the ductility increased by 10%, contraction increased by 18%, notched toughness at 20 °C increased by 46%, and at -40 °C (respectively -50 °C) it increased by 30%.

Deformation strengthening mechanism of laser remelted high manganese steel

In order to further improve the deformation hardening ability of high manganese steel (HMnS) under low stress or small deformation, a low speed laser remelting technology was proposed to process the HMnS surface. Through parameters optimization, microstructure characterization, wear testing, and deformation strengthening analysis, the deformation strengthening mechanism of laser remelted HMnS (LR-HMnS) was systematically studied, and excellent wear resistance properties was also achieved. Firstly, by optimizing the parameters of laser remelting, high-quality microstructures with large remelting depth and fewer porosities were obtained. Then, the sliding wear tests showed that although the surface hardness of LR-HMnS (252.83HV0.3) was only 2.56 % higher than that of continuous casting HMnS (CC-HMnS) (246.53HV0.3), its volume wear rate (1.87×10−5 mm3/N·m) was only 10 % of CC-HMnS (18.71×10−5 mm3/N·m), which exhibited excellent wear resistance properties. Finally, for quantitative evaluating its work hardening at high strain rates, Hopkinson compression test of LR-HMnS was conduced according to the operating conditions of HMnS parts. The microstructure after small compression deformation was analyzed using EBSD and TEM. It was found that the larger grain size of LR-HMnS was helpful of reducing the nucleation stress of twins, forming high-density nano-twins, high-density stacking faults, and high-density dislocations. The synergistic effect of stacking faults, dislocations, and twins which segmented the matrix and refined the grains, and achieved the dynamic Hall-Petch effect. The superior deformation strengthening and wear resistance exhibited by larger grain HMnS were called the inverse grain size effect. Additionally, the large number of C-Mn strong bond networks formed by element segregation could enhance the pinning effect of dislocations, promote deformation hardening rate and wear resistance properties under low stress or small deformation. The research results provided a new method for pre-hardening of HMnS, and will also expand the application potential of HMnS in combined conditions of high, medium, and low impact.

New insights into enhancing the mechanical properties of 6061-T6 aluminum alloy MIG welded joints by constructing bionic heterostructure

The trade-off between strength and toughness is a long-term challenge for engineering metal structural materials. However, natural materials overcome the inverse relationship between strength and toughness through their unique structures. Inspired by plant leaves and dragonfly wings, a ‘soft-hard’ alternating bionic heterostructure is prepared on 6061-T6 Al alloy MIG welded joints by laser surface remelting (LSR) technology. After LSR, the grain size of the laser treated zone is significantly refined, dislocation density is increased, and the formation of fine and stable GP zone and β′′ phase is promoted, enhancing microhardness and tensile properties of the LSRed sample. By adjusting the laser stripe spacing and distribution angle, stress transfer and redistribution can be optimized, effectively improving the tensile properties of the welded joint can be. Compared to as-welded sample, the tensile strength, yield strength and elongation of LSRed sample can be increased by 30.6 %, 13.6 % and 102 %, respectively. In addition, the bionic heterostructure composed of grain size gradient, dislocation gradient and precipitated phases gradient can effectively develop heterogeneous deformation induced (HDI) stress strengthening and HDI strain hardening, enabling synergistic strengthening of strength and toughness.

Laser remelting of high-velocity arc-sprayed Fe-based amorphous coating for improving corrosion resistance in 3.5 % NaCl solution with varying Na2S concentrations

In this study, high-velocity arc-spraying (HVAS) was employed to produce Fe-based amorphous coatings, and subsequent to that, laser remelting (LR) technology was applied on the as-sprayed coatings (ASC) to prepare laser remelted coatings (LRC). The corrosion resistance of both coatings was tested in 3.5 wt% NaCl solutions containing varying Na2S concentrations (0, 20, 50, 100, and 200 ppm) to accurately simulate the corrosion environment of offshore components. The corrosion behavior was investigated using electrochemical workstation, scanning electron microscopy, energy dispersive spectroscopy and X-ray photoelectron spectroscopy. The experimental results revealed that LR resulted in the elimination of defects in Fe-based amorphous coatings, a substantial reduction in porosity, the disappearance of the laminar structure, and the achievement of a homogeneous composition. The corrosion tendency of ASC and LRC both exhibited a pattern of initially decreasing, then increasing and finally decreasing with increasing sulfide concentration. This was attributed to the deposition of corrosion products on the surface and the dissolution of the corrosion products. When the sulfide concentration exceeded 50 ppm, the corrosion current density of both coatings slowly and was lower than that at 20 ppm, indicating that both coatings possessed strong corrosion resistance at higher sulfide concentrations. Highly polarized anions in solution (e.g. HS−, S2−) occupied vacancies in the passivation film, destabilizing the coating's passivation film and consequently diminishing its corrosion resistance. From the electrochemical analysis, it was evident that LRC exhibited greater corrosion resistance than ASC at all sulfide-containing solution concentrations, which was attributed to its smoother surface, denser structure and more stable passivation film.

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.

The Effect of Laser Surface Remelting on the Surface Properties of Copper

In order to enhance the wear resistance of copper contacts in high-voltage switches and improve the abnormal discharge phenomenon caused by wear gaps, laser remelting technology was used to strengthen the surface of copper contacts. The surface morphology, microhardness, and wear resistance of the remelted samples were tested and characterized using scanning electron microscopy (SEM), microhardness tester, and friction and wear tester. The test results indicate that laser frequency, pulse width, and energy density parameters can directly affect the surface morphology and wear resistance of the sample, but their influencing processes vary. The laser frequency is achieved by the variation in the superposition relationship between the impact points, while the pulse width and energy density are achieved by the variation in the laser intensity at the impact points. When the pulse frequency is 10 Hz, the pulse width is 10 ms, and the energy density is 132.69 J/mm2, the sample exhibits a more balanced surface morphology, microhardness, and wear resistance.

Study on the Microstructure and Properties of FeCoNiCrAl High-Entropy Alloy Coating Prepared by Laser Cladding-Remelting

Laser remelting technology effectively repairs defects such as pores and cracks in the coating. To investigate the impact of laser remelting on high-entropy alloy coatings, this study used Q235 steel as the substrate and employed laser cladding technology to prepare FeCoNiCrAl high-entropy alloy coatings, followed by laser remelting treatment. The phase composition and microstructure of the coatings were extensively characterized using equipment such as optical microscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Additionally, the wear resistance and corrosion resistance of the coatings were tested using a multifunctional material surface performance tester, an electrochemical workstation, and SVET (Scanning Vibrating Electrode Technique). The results indicate that following laser remelting treatment, the atomic proportion of Fe elements on the coating surface decreased from 33.21% to 26.03%, while the atomic proportion of Al elements increased from 12.56% to 20.31%. The phase composition of the coating underwent a marked transformation, shifting from a structure composed of FCC, A2, and B2 phases to a singular BCC structure characterized by the presence of A2 and B2 phases. Concurrently, the grain morphology on the coating surface transitioned from elongated plate-like grains to equiaxed grains. Laser remelting enhanced the wear resistance of the coating. Laser remelting had no significant impact on the corrosion resistance of the non-cracked regions of the coating.

Microstructure and mechanical properties investigation of carbon/stainless steel composite rod prepared by a special device

On the basis of traditional ESR (electroslag remelting technology) method, a special device is designed in the present study, which combined Electromagnetic induction and Electroslag Remelting technology. The composite rods are successfully made for carbon steel and stainless steel with the device. The microstructure and the mechanical properties of the composites are investigated. The tensile test results indicated that there was high bonding strength between two materials. Aiming to further research about the bonding condition, the microstructure examination is carried. It is discovered that excellent metallurgical bonding between two materials has been achieved, with the thickness of the intermediate layer up to the maximum of 235 μm. It proved that this method is reliable to produce the composite rod, which could obtain high mechanical property, and so far, thicker metallurgical combining layer than any other way.

Picosecond laser remelting of electrodeposited Ni[sbnd]P coating: Parameters optimization and electrochemical corrosion behavior

Excessive P content (≥ 10 wt%) easily leads to cracks on the surface of electrodeposited NiP coatings, causing rapid deterioration of corrosion performance. This study uses picosecond laser remelting (LR) technology to close cracks and improve corrosion performance. The influence of the laser parameters on the quality of laser-remelted (LRed) coatings in ambient air is discussed in detail, and the corrosion performance is evaluated through electrochemical corrosion tests. The results indicated that the scanning rate, laser power, and repetition frequency significantly affect the degree of crack closure and LRed defects. For cracks of similar sizes, both multiple-LR with a lower power (10.4 W, five times) and single-LR with a higher power (19.2 W, once) achieved an excellent crack closure. After single-LR, the surface roughness increased from 3.9 ± 0.3 nm to 33.4 ± 3.2 nm. In addition, the LRed layer crystallized from the initial amorphous state. Although the energy-dispersive spectroscopy results indicated that the oxidation behavior during the LR process was insignificant, X-ray photoelectron spectroscopy showed that the surface composition evolved from Ni/Ni–P compounds to Ni–POx after LR. Electrochemical corrosion tests indicated that the corrosion current density decreased approximately three times from 9.19 × 10−6 to 2.91 × 10−6 A/cm2 after LR. Moreover, the corrosion mechanism shifted from the original stress corrosion to pitting corrosion. Thus, the LR technology can effectively improve the corrosion performance and reduce the issues caused by cracks.

Design and characterization of a novel Cu2.3Al1.3Ni1.7SnCr0.3 multi-principal element alloy coating on magnesium alloy by laser cladding

The evaporation and dilution of substrate seriously limit the performance of laser cladding coatings on magnesium alloys. In order to overcome the above shortcomings, a multi-step ultrasonic assisted laser remelting technology was proposed to improve the performance of the coating. In this work, a novel Cu2.3Al1.3Ni1.7SnCr0.3 multi-principal element alloy coating (MPEAC) was prepared on the surface of magnesium alloy. Characterization techniques such as transmission electron microscopy (TEM), electron back scatter diffraction (EBSD) and scanning electron microscopy (SEM) were employed to characterize the microstructure and phase composition of the coatings. And the phase structure and morphology at the interface between the coating and the substrate were also studied via focus ion beam (FIB) and TEM method. In addition, the corrosion and wear resistance ability of the coatings were monitored by potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS), hardness and friction tests. The results show that Cu2.3Al1.3Ni1.7SnCr0.3 MPEAC with ultrasonic assisted is composed of FCC phase and eutectic phases (Cu10Sn3 and Cu2Ni3Sn3). Due to the forced convection generated by ultrasonic waves, some Cu and Ni phases are precipitated around Cu2Ni3Sn3 phases, which is beneficial to enhance the corrosion resistance. Because of the grain refinement effect caused by ultrasonic, the wear resistance of the coating is also improved. Furthermore, ultrasonic vibration can effectively weaken and eliminate the texture density of the Cu2.3Al1.3Ni1.7SnCr0.3 MPEAC fabricated by laser cladding.

Research on the Microstructure of Laser Remelted As-sprayed TiB2-TiC0.3N0.7 based Composite Coating

Ceramic coatings with excellent properties of wear resistance, corrosion resistance, oxidation resistance, stability in acid and alkaline environments, and good bond strength with a metallic substrate, are widely used in different industries. Air plasma spraying has high energy and efficiency for depositing ceramic materials with a high melting point. Due to intrinsic porosity and mechanical bond strength between coating and substrate, laser remelting technology can be applied to the coating surface for improving coating properties. As-sprayed TiB2-TiC0.3N0.7-based composite coating was surface remelted by laser. The surface roughness of as-sprayed and laser-remelted coatings was measured. The phase composition and the microstructure as well as the Vickers microhardness of coatings were studied by X-ray diffractometer (XRD), scanning electron microscopy (SEM), and Vickers indentation instrument. It is found that the phase composition does not change after laser remelting. However, the surface roughness of laser-remelted coating is smoother than that of as-sprayed coating. And the microhardness on the cross-section is increased after laser remelting. There is a micro-crack in the laser-remelted coating due to the fast heating and cooling of the laser. The microhardness of the laser-remelted coating is increased with bimodal Weibull distribution.

Anti-CMAS corrosion mechanism of Al2O3 pore sealing and laser remelting on thermal barrier coatings

The sol-dip-coating method and surface laser remelting technology are applied to form an Al2O3 layer on a YSZ coating surface to effectively block the environmental sediment CMAS. The behaviour and mechanism for CMAS corrosion of the coating are investigated, and the interfacial reliability of the coating and matrix is calculated by using the Monte Carlo method. The bonding force between the Al2O3 sol and YSZ coating can be effectively improved by laser surface treatment. Samples subjected to a laser pretreatment and posttreatment (YL-AL) of the YSZ coating are found to show the best interfacial bonding strength between Al2O3 and YSZ. Furthermore, the YL-AL sample shows a higher CMAS resistance than the laser posttreatment (Y-AL) samples, which effectively combines the chemical resistance of Al2O3 to CMAS and the physical resistance of the laser re-melted densification layer against CMAS penetration.

A high-corrosion-resistant high-entropy alloys (HEAs) coatings with single BCC solid solution structure by laser remelting

• Preparation of FeCrCoAl x HEA coatings with BCC structure by laser remelting technique. • The FeCrCoAl 1 HEA coatings have high corrosion resistance. • Al played a critical role to improve the stability of the HEAs coatings. A high-corrosion-resistance high-entropy alloys (HEAs) coatings with single BCC solid solution structure was successfully prepared on Cr13 steel by laser remelting technology. The composition, microstructure, and corrosion properties of HEAs coatings with different Al contents were studied in detail. FeCrCoAl x HEAs coatings significantly improve the corrosion resistance of Cr13 steel, and the FeCrCoAl 1 HEAs coatings exhibits the best corrosion resistance, which were attributed to the uniform distribution of various elements in the coatings due to the higher △ S mix of HEAs and the preferentially formed uniform oxide films (mainly AlO x and CrO x ) on the coatings due to the lower △ G .

Research on the mechanical and tribological properties of coating reinforced by a pulsed magnetic field during the remelting process

Remelting technology can effectively reduce the pores and defects, increase the bonding strength and form good metallurgical bonding in coatings. However, coating remelting is a metallurgical process of surface recrystallisation that destroys a large number of nanocrystalline structures in the original coating during quench forming. Therefore, our research group designed a pulsed magnetic field-assisted coating remelting device and prepared coatings by applying a high pulse magnetic intensity during coating remelting. The results show that the tribological properties of the remelted coating are greatly improved by the application a pulsed magnetic field and the friction loss volume of the coating decreases from 0.285× 10−3 mm3 to 0.154 × 10−3 mm3. The distribution of residual stress is more concentrated and residual compressive stress appears. The bonding strength increases from 30 MPa to 51.6 MPa and the hardness increases from 583.0 MPa to 751.0 MPa. Furthermore, when the friction pair is in full contact with the coating, the pore reduction can significantly reduce the interference of pore defects in the coating with the friction pair. The orderly magnetic domain makes the stress distribution in the coating orderly. The residual tensile stress improves the stress mode of the coating. The grain boundaries increase after grain refinement and the crystallinity increases. All these improve the wear resistance of the coating.

Thermal deformation behavior and processing maps of nickel-free high nitrogen austenitic Cr18Mn16Mo2.5N0.83Nb0.15 stainless steel

The nickel-free high nitrogen austenitic Cr18Mn16Mo2.5N0.83Nb0.15 stainless steel was fabricated by electroslag remelting technology. The high-temperature thermal deformation behavior of as-fabricated steel was investigated using Gleeble-1500D type thermal-mechanical simulation testing machine under the condition of the temperature range from 950 °C to 1100 °C and the strain-rate range from 0.01s−1 to 1.0s−1. The constitutive equation containing polynomial of as-fabricated steel was built to describe stress function containing the variable of deformation temperature and strain-rate based on Arrhenius equation. The Q value is 448.915 kJ mol−1 by computing using the experimental data obtained from the thermal deformation tests. The thermal forging temperature should be higher than 1050 °C and the strain-rate below 1s−1 based on the thermal processing maps.

Effect of Scanning Speed on Properties of Laser Surface Remelted 304 Stainless Steel

In order to study the microstructure and properties of stainless steel after laser surface remelting, based on the theory of laser surface remelting, a simulation model of nanosecond-pulsed laser surface remelted stainless steel was established to study the evolution law of the Marangoni force of the molten pool during laser surface remelting. A single-lane laser remelting experiment was performed to study the variation of the scanning speed on the remelting width, roughness, and layer microtopography. The “S” scanning path was used to remelt the stainless steel surface to investigate the bonding force between the remelted layer and the substrate, the hardness, microscopic morphology, and corrosion resistance. The results show that the viscosity of the liquid metal in the molten pool increases with the increase of the scanning speed. Larger liquid viscosity and smaller surface tension temperature gradients promote a weaker flow of liquid metal, which reduces the velocity of the liquid metal flow in the molten pool. With the increase of scanning speed, the remelting width gradually decreases, but the roughness gradually increases. When the element content of Cr increases, the element content of Fe and O decreases. The surface is covered with an oxide film, the main components of which are oxides of Cr and Fe, the remelted layer is greater than that of the substrate, and the corrosion resistance is improved. Laser surface remelting technology can improve the structure and properties of 304 stainless steel.

A preliminary exploration on improving the solidification quality of electroslag ingot based on laboratory scale experiment

ABSTRACT One of the most important characteristics for electroslag remelting technology is that it can improve the solidification structure of metal. However, with the increase of mould diameter, the cooling effect of mould deteriorates, and the solidification quality of the ingot becomes poor, which is more obvious for large and high-alloy electroslag ingots. Therefore, it is necessary to further develop electroslag technologies to excite the potential of electroslag remelting. In this paper, the principle and practical effect of three technologies, i.e. electroslag remelting with mould rotation, electroslag remelting with ultrasonic vibration, electroslag remelting with electromagnetic stirring, are analyzed in detail. The results show that these technologies can effectively improve the solidification structure of electroslag ingot, and have a good application prospect. It is worth noting that the above technologies and its effects are only obtained under experimental conditions. For industrial application, the process parameters must be carefully selected.

Elimination of Primary NbC Carbides in HSLA Steels for Oil Industry Tubular Goods

Two high-strength low-alloyed steels alloyed with various Nb contents were prepared using continuous casting (CC) technology. In the round Steel 30Nb CC billet, it was the segregation of C and Nb in the central equiaxed zone that promoted the precipitation of primary NbC carbides at grain boundaries. After processing into seamless tubes, micron-sized primary NbC carbides were located in the middle of the segregation bands, surrounded by many nano-sized NbC carbides formed during the post-solidification cooling and/or hot-piercing rolling. Even when the Nb content was decreased down to 0.006 wt.%, there were still coarse primary NbC carbides in the segregation bands. However, no primary NbC carbide was found in the round Steel 30Nb billet prepared using the electroslag remelting technology. Therefore, this study revealed that a rapid solidification rate was relatively effective in eliminating primary NbC carbides compared with merely decreasing the Nb content.