Pulsed Laser Cladding Research Articles

Forming mechanism of single-channel multilayer laser cladding Fe60 process under different laser heat source operating mode

Continuous wave (CW) and pulsed wave are the two principal modes of operation used to control the laser heat source. Different laser heat source operating modes have an essential impact on the rapid cooling and heating temperature change rate during the cladding process, which directly determines the cladding layer quality. The laser cladding process is meaningful to quantitatively reveal the mechanism of single-channel multilayer cladding and forming under different laser heat source operating modes. In this article, a multi-field coupled 3D numerical model of the single-channel multilayer cladding process under different laser operating modes was proposed, and the thermal physical parameters of the cladding material were computed on the basis of Calculation of Phase Diagrams method. The mechanism of the impact of distinct operating modes on the multi-field coupled ephemeral evolution process of laser cladding was investigated by using the solid/liquid interface tracking technique, which comprehensively considers the light powder interaction between the powder waist beam and the laser beam under different operating modes. The temperature, flow, and stress fields were computationally solved for a single-channel multilayer cladding process. On the foundation of this study, the impact mechanism of pulse duty cycle and pulse frequency on the cladding behavior of single-channel and multilayers during pulsed laser cladding were dissected. The macroscopic morphology and microstructure of the cladding layer were observed by KEYENCE VH-Z100R ultra-deep field electron microscope, and the feasibility of the model was confirmed. This study provides a significant theoretical rationale for enhancing the cladding quality under different laser operating modes.

Quantitative assessment method of thermal cycle accumulation mechanism during the pulsed laser single-channel multilayer cladding process

Pulsed laser cladding provides a periodical thermal accumulation, enabling a greater temperature gradient and cooling rate inside the substrate, which can efficiently ameliorate the microstructure of the cladding layer. It is crucial to quantitatively investigate the mechanism of the interaction for the cladding process parameters on the transient evolution of the multi-field coupling to improve the cladding quality. In this paper, a 3-D model during the single-channel multilayer pulsed laser cladding process was constructed which is grounded on the temperature-variable physical properties parameters of the material. The integrated consideration in the masking impact of the molten powder waist beam on the pulsed laser beam, the molten pool liquid metal surface tension, the influence of buoyancy on the flow, and the transient evolution of the molten pool edge morphology. The temperature, flow, and stress fields of the single-channel multilayer cladding process were computed and resolved. The mechanism in multi-field coupling impact of laser pulse frequency, laser power, and pulse duty cycle on the single-channel multilayer cladding process was emphasized. The response surface equations between each influencing factor and the cladding temperature, temperature change gradient, and thermal stress were determined according to the response surface method, and the sensitivity of each parameter was attained from the Monte Carlo method. Using SEM to observe the profile and microstructure of the cladding layer, the material hardness distribution was measured experimentally, and the effectiveness of the model was confirmed. This research supplies an essential rationale for upgrading the quality of pulsed laser cladding layers.

Corrosion and oxidation behaviors of CoAlTiWTa RHEA coating on Inconel 718 superalloy prepared by laser cladding

CoAlTiWTa refractory high-entropy alloy (RHEA) coating was prepared on Inconel 718 superalloy by pulsed laser cladding. Corrosion behavior in 3.5 wt% NaCl solution at room temperature and oxidation behavior at 600 ℃ of the coating were systematically investigated. The electrochemical performance, surface morphology, and corrosion and oxidation products were carefully characterized. The results show that the RHEA coating has a higher corrosion potential, smaller corrosion current, higher resistance value, and a more obvious passivation effect. Duplex-layer oxide film composed of an internal Al2O3-TiO2 layer and an external Co oxide layer is formed on the RHEA coating, improving high-temperature oxidation resistance.

Оптимизация параметров импульсной лазерной наплавки стали 30ХГСН2А с использованием генетического алгоритма

The paperpresents the optimization of pulsed laser cladding of structural steel using a genetic algo-rithm. Using the ANSYS Workbench software, finite element modelling of laser cladding on a 30ХГСН2А steel substrate with an additive in the form of wire was conducted, considering the temperature dependence of the material's thermophysical properties. A surrogate model for pulsed laser cladding of 30ХГСН2Аsteel was developed employing a face-centered version of the central composite design experiment. The time inter-vals corresponding to the end time of the three fronts of the laser pulse and the diameter of the filler wire were considered as variable factors. The maximum temperatures in the treatment zone were used as re-sponses. In order to optimize pulsed laser cladding of 30ХГСН2А steel, the maximum temperature limit val-ues in the treatment zone were established for three moments of time that corresponded to the laser pulse fronts at the three points in the finite element model. A comparison was made between the parameters ob-tained from optimization and those derived from finite element modelling. When determining temperatures, the maximum percentage error of the results obtained via the genetic algorithm did not exceed 3.5 %

Numerical simulation and experimental study on the heat and mass transfer behavior during the pulsed laser cladding process

Compared with continuous wave (CW), pulse wave (PW) perturbation results in a larger temperature change rate inside the cladding layer, which leads to a higher quality cladding layer. In this paper, a three-dimensional numerical model of laser cladding Fe60 powder was established. The multiphysics field coupling transient evolution and solute distribution under PW and CW operating modes were studied. The problem of lack of theoretical support for laser cladding process under different working modes in heat source was solved. Calculations show that at 1970 ms when the temperature is stable, the maximum temperature, flow rate, and stress under the PW mode are 2660 K, 0.34 m/s, and 354 MPa, respectively, which are smaller than those under the CW mode. The four solute distributions at stable temperature are as follows: The minimum mass fractions of Fe and Mn are 87% and 0.49% in the CW mode, and the maximum mass fractions of Cr and Ni are 11% and 5%. In the PW mode, the minimum mass fractions of Fe and Mn are 82% and 0.44%, and the maximum mass fractions of Cr and Ni are 14% and 5%. PW has a smaller heat input than CW, resulting in a smaller molten pool, so the elements in the molten pool are more fully mixed with other alloying elements. Metallographic experiments were performed using a scanning electron microscope to examine the mechanical properties on the fusion cladding layer, and the accuracy of the model was verified by combining numerical simulations with experimental studies for comparative analysis.

Full cycle numerical simulation during the pulsed laser cladding process considering the interaction between laser and powder

Full cycle numerical simulation during the pulsed laser cladding process considering the interaction between laser and powder

Structural and property regulation of double ceramic phase–reinforced AlCoCrFeNiTiZr–based high entropy alloy coatings by pulsed–wave lasers

In-situ synthesis ZrC and TiC reinforced AlCoCrFeNiTiZr–based high entropy alloy (HEA) coatings were successfully synthesized on R60702 using pulsed–laser cladding. The effects of pulse frequency (5, 50, 500, and 5000 Hz) on microstructure evolution, microhardness, wear resistance, and corrosion resistance were investigated. The results demonstrate that the HEA coatings consists of phases including BCC, HCP, and metal carbides (MC). The phase composition and proportion are influenced by changes in pulse frequency. At pulse frequencies of 5 and 50 Hz, the predominant MC phase is ZrC. As the pulse frequency increases, it transitions to a coexistence of ZrC + TiC before ultimately becoming predominantly TiC. Concurrently, the size of the ceramic phase and the proportion of the HCP phase initially decrease, then increase. A pulse frequency of 500 Hz yields optimizations in microhardness, wear resistance, and corrosion resistance. The favorable mechanical properties are attributed to the synergistic effect of solid solution strengthening, fine crystal strengthening, and ceramic phase strengthening. The optimal corrosion resistance is due to the formation of a stable passivation film while local corrosion and galvanic corrosion are weakened.

Pulsed laser cladding on IN718 alloy using pre-coated CrCoNi-TiC/SiC powders for enhancing wear resistance

By employing a pulsed laser, laser cladding was performed on IN718 alloy pre-coated with CrCoNi-TiC/SiC powders and three defect-free coatings were prepared successfully. Microstructures of these coatings were subjected to dedicated characterization and well correlated with their surface performances (hardness/wear resistance). The CrCoNi coating was found to be predominantly composed of coarse grains. The addition of TiC and SiC powders will not only generate fine carbides dispersed in the coatings but also lead to the changes of grain and substructure morphologies through modifying the solidification thermodynamics in the cladding zone. The CrCoNi-TiC and the CrCoNi-SiC coatings have average grain sizes of 8.1 ± 7.9 μm and 6.6 ± 5.6 μm, respectively, much smaller than that of the CrCoNi coating (19.3 ± 19.2 μm), indicating effective grain refinement after incorporating such carbides. The average hardness values of CrCoNi-TiC and the CrCoNi-SiC coatings are measured as 315.9 ± 5.3 HV and 321.8 ± 8.6 HV, respectively, considerably higher than those of the CrCoNi coating (265.3 ± 6.9 HV) and the substrate (255.3 ± 4.5 HV). Both the composite coatings also have lower wear rates (6.6 × 10−4 mm3·N−1·m−1 for the CrCoNi-TiC coating and 2.9 × 10−4 mm3·N−1·m−1 for the CrCoNi-SiC coating) than the CrCoNi coating (9.3 × 10−4 mm3·N−1·m−1) and the IN718 substrate (11.1 × 10−4 mm3·N−1·m−1). Based on dedicated microstructural analyses, the synergistic strengthening effects due to grain refinement, second phase particles, and solid solution of alloying elements are found to have contributed to the superior surface performances of both the composite coatings, with the SiC demonstrated to be a more effective additive.

Mechanical and Structural Characterization of Laser-Cladded Medium-Entropy FeNiCr-B4C Coatings.

Equiatomic medium-entropy alloy (MEA) FeNiCr-B4C (0, 1, and 3 wt.% B4C) coatings were deposited onto an AISI 1040 steel substrate using pulsed laser cladding. Based on an SEM microstructural analysis, it was found that the cross-sections of all the obtained specimens were characterized by an average coating thickness of 400 ± 20 μm, a sufficiently narrow (100 ± 20 μm) "coating-substrate" transition zone, and the presence of a small number of defects, including cracks and pores. An XRD analysis showed that the formed coatings consisted of a single face-centered cubic (FCC) γ-phase and the space group Fm-3m, regardless of the B4C content. However, additional TEM analysis of the FeNiCr coating with 3 wt.% B4C revealed a two-phase FCC structure consisting of grains (FCC-1 phase, Fm-3m) up to 1 µm in size and banded interlayers (FCC-2 phase, Fm-3m) between the grains. The grains were clean with a low density of dislocations. Raman spectroscopy confirmed the presence of B4C carbides inside the FeNiCr (1 and 3 wt.% B4C) coatings, as evidenced by detected peaks corresponding to amorphous carbon and peaks indicating the stretching of C-B-C chains. The mechanical characterization of the FeNiCr-B4C coatings specified that additions of 1 and 3 wt.% B4C resulted in a notable increase in microhardness of 16% and 38%, respectively, with a slight decrease in ductility of 4% and 10%, respectively, compared to the B4C-free FeNiCr coating. Thus, the B4C addition can be considered a promising method for strengthening laser-cladded MEA FeNiCr-B4C coatings.

Surface enlargement of tantalum capacitor foils by pulsed direct current etching and laser cladding

Electrochemical etching for the surface enlargement of tantalum capacitor foils has always been a challenge, due to the ultra-high chemical stability of tantalum foils. Herein, pulsed direct current etching of tantalum capacitor foils assisted by laser cladding was investigated and high surface area enlargement was achieved. The effects of electrolyte composition, power supply parameters and external environment on the etching process of tantalum foil were systematically studied, to screen out the best experimental conditions. Furthermore, iron particles with diameters of 3–5 μm were successfully laser cladded on the surface of tantalum foils. These particles will be easily etched in the electrochemical process to form more previous pores, which can serve as etching sites for further tantalum foil etching. Under the best conditions, high-specific capacitance tantalum foils with a capacitance of 155.1 nF/mm2 were obtained at a high forming voltage of 100 V, which were 8 times larger than the unetched light foils. The surface enlargement of tantalum capacitor foils is expected to realize the development of novel tantalum capacitors with both high operating voltage and high capacitance.

Microstructure, hardness and wear performance of quaternary CrNbTiZr refractory medium-entropy alloy coating fabricated on a commercial Zr alloy by pulsed laser cladding

To attain enhanced surface hardness and wear resistance, a quaternary CrNbTiZr refractory medium-entropy alloy (RMEA) coating was fabricated on a commercial Zr alloy (Zr-702) by a pulsed laser cladding technique. Phase constitution, microstructural feature, hardness and wear performance of the RMEA coating were systematically investigated. The specific influence of Zr diluted from the substrate on the coating was explored. The results reveal that the cladding zone is mainly featured by a BCC solid-solution phase and net-like Cr2Zr intermetallics. Such microstructural features agree with those predicted based on atomic radius difference, Allen electronegativity and valence electron concentration. Allotropic solid phase transformation occurs in the heat-affected zone, resulting in a mixed microstructure of blocky grains (α-Zr) and martensitic laths. The hardness of the RMEA coating (637 ± 46 HV) is ∼3.3 times that of the Zr-702 substrate, which results from joint contribution from solid-solution, low-angle grain boundary and second-phase strengthening. The RMEA coating exhibits a wear rate ∼56% lower than the substrate, demonstrating significantly improved wear resistance. Both oxidation and adhesive wear are determined to be dominant wear mechanisms of the RMEA coating, accounting for its enhanced wear performance.

Quantitative evaluation method for the impact parameters during the process of pulsed laser cladding of Fe60

Quantitative evaluation method for the impact parameters during the process of pulsed laser cladding of Fe60

Laser-cladded Al-Cr-Ti ternary alloy coatings on Ti-4Al-2V alloy: Specific microstructure and enhanced surface performance

In this study, two Al-Cr-Ti ternary alloy coatings (denoted as AlCr and AlCrTi0.5) were fabricated on a Ti-4Al-2V alloy substrate by using a pulsed laser cladding method. Specific microstructure characteristics of those coatings were thoroughly revealed by using various characterization methods, with their hardnesses and wear rates measured by a Vickers indenter and a tribological tester. The results reveal that both AlCr and AlCrTi0.5 coatings are comprised of a body-centered cubic phase (β-Ti phase with average grain sizes of 12.6 ± 9.1 μm and 14.6 ± 10.0 μm, respectively), which is related to non-equilibrium solidification and sluggish diffusion of alloying elements during the laser processing. Heat-affected zones of both the laser-cladded specimens are mainly composed of submicron martensitic laths (α′-Ti). Average microhardness values of the AlCr and the AlCrTi0.5 coatings are measured to be 526 ± 37 HV and 510 ± 24 HV, respectively, approximately two times higher than the substrate (270 ± 8 HV). Their wear rates are almost the same, ~2.2 × 10−4 mm3 N−1 m−1, only ~1/3 of that of the substrate. Based on dedicated microstructure analyses, the greatly enhanced performance of the laser-cladded coatings could be attributed to joint strengthening from strong solid solution and lattice distortion, as well as Al/Cr-induced phase structure differences from the substrate.

Laser-clad Al-Ti-Zr and Cr-Ti-Zr coatings on Zr alloy: composition-induced microstructural and hardness differences

In this study, Al-Ti-Zr and Cr-Ti-Zr metallic coatings with thichness of 250-280 μm were fabricated successfully on Zr alloy using pulsed laser cladding. By jointly employing multiple characterization techniques, microstructural characteristics of the coatings were probed with their formation reasons explored. The Al-Ti-Zr coating consists of a single BCC solid-solution phase (average size 8.6 ± 6.3 μm) with hardness of 405.5 ± 16.6 HV that is more than twice that of the substrate (198.7 ± 2.0 HV). Such marked hardening is mainly related to the contribution from the solid-solution strengthening produced by Al and Ti. The Cr-Ti-Zr coating consists of cellular BCC phase (average size 0.9 ± 0.4 μm) and C14-type Cr2(Ti,Zr) Laves phase with nanoscale lamellar structures. Its average hardness is 584.8 ± 33.6 HV, about three times of that of the substrate, which can be ascribed to synergistic effects of solid-solution, grain refinement and second phase strengthening. The formation of the single BCC solid-solution phase in the Al-Ti-Zr coating is mainly due to the relatively small differences in atomic size and electronegativity between Al, Ti and Zr. For the Cr-Ti-Zr coating, however, due to large atomic size and electronegativity differences between Cr and Zr (as well as Cr and Ti), Cr2(Ti,Zr) Laves phase was formed in addition to the BCC phase.

Laser-clad Nb(Ta)TiZr medium-entropy alloy coatings on pure Zr sheet: Microstructural characteristics, hardness and wear resistance

In this work, two Nb(Ta)TiZr medium-entropy alloy (MEA) coatings were fabricated successfully on a commercially pure Zr sheet by pulsed laser cladding. Their phase constitutions, microstructural characteristics, chemical compositions and grain orientations were well characterized and analyzed by using X-ray diffraction (XRD), electron channeling contrast (ECC) imaging, energy dispersive spectrometry (EDS) and electron backscatter diffraction (EBSD) techniques, with hardness and wear resistance measured and correlated with the microstructural characteristics as well. Results show that irregular-shaped bulk grains (BCC solid-solution phase) are formed in the two Nb(Ta)TiZr MEA coatings (cladding zones), both of which have a thickness of ∼800 μm with good metallurgical bonding to the substrate. After adding Ta, grains in the MEA coating are slightly refined. The phase constitutions in both the coatings agree with calculations based on several theoretical parameters. Hardness tests show that the NbTiZr and the NbTaTiZr coatings have hardnesses of 360 ± 18 HV and 430 ± 28 HV, respectively, ∼1.8 times and ∼2.2 times that of the substrate (196 ± 4 HV). This can be ascribed to combined effects of grain refinement strengthening, solid solution strengthening with denser low angle boundaries in the MEA coatings. Specific wear rates of the NbTiZr and the NbTaTiZr coatings are only ∼17% and ∼6% of that of the substrate, respectively, indicating markedly improved wear resistance. This is demonstrated to be closely related to complete oxide films easily formed on the coatings with oxidation and abrasive wear mechanisms.

Temperature and Stress Field Analysis for Pulsed Laser-Cladding of Pure Titanium on Ti-6Al-4V

Temperature and Stress Field Analysis for Pulsed Laser-Cladding of Pure Titanium on Ti-6Al-4V

Investigation of microstructure and wear resistance of laser-clad CoCrNiTi and CrFeNiTi medium-entropy alloy coatings on Ti sheet

Two medium-entropy alloy coatings (MEACs), CoCrNiTi and CrFeNiTi, were successfully prepared on pure Ti sheet by utilizing pulsed laser cladding. Microstructural characterization reveals that both the MEACs are mainly comprised of BCC solid-solution phase along with interdendritic Cr2Ti Laves phase (C14 type) due to element segregation. Hardness and wear tests show that the CoCrNiTi MEAC has a hardness of 762 ± 32 HV and a specific wear rate of 1.7 × 10−5 mm3·N−1·m−1, and those of the CrFeNiTi MEAC are 820 ± 34 HV and 2.8 × 10−5 mm3·N−1·m−1, respectively, both of which are markedly superior to the pure Ti substrate (114 ± 5 HV and 5.4 × 10−4 mm3·N−1·m−1). Comprehensive analyses suggest that the excellent properties of the MEACs can be attributed to combined strengthening effects of solid-solution, short-range order, grain refinement and the Cr2Ti Laves phase.

Microstructure and wear properties of laser-clad NiCo alloy coating on Inconel 718 alloy

A NiCo coating was successfully prepared on the Inconel 718 substrate by pulsed laser cladding. The characteristics and performance of the coating, including microstructure, phase constitution, hardness, friction coefficient, wear volume, wear morphology, and residual stress, were investigated by multiple characterization methods. The hardness of the coating is 427.82 HV, 21.1% higher than that of the Inconel 718 substrate. The coating also shows a higher resistance to wear than the substrate. In addition, the coating's surface residual stress is compressive stress, which prevents crack generation and improves fatigue strength.

Microstructure and properties of pure titanium coating on Ti-6Al-4V alloy by laser cladding

Abstract A coating of pure titanium without defects was successfully prepared on the surface of Ti-6Al-4V substrate by pulsed laser cladding. The characteristics and performance of the coating and the substrate including microstructure, phase constitution and hardness were probed by combined use of multiple characterization methods. Results show that fine lamellar grains are formed in the coating during the ultrafast non-equilibrium solidification process induced by pulsed laser cladding. The average size of these grains is about 0.79 μm. The hardness test shows that the hardness of the coating is 433.82 HV, 30.4% higher than that of the Ti-6Al-4V substrate. Besides, a lower wear volume compared to the substrate is found for the coating which indicates greatly improved wear resistance. In-depth analyses suggest that the improved surface performance can be mainly attributed to grain refinement strengthening in the cladding zone.

Microstructure and hardness of NbTiZr and NbTaTiZr refractory medium-entropy alloy coatings on Zr alloy by laser cladding

Two refractory medium-entropy alloy (RMEA) coatings (NbTiZr and NbTaTiZr) with BCC solid-solution phase as their main constitutional phase were successfully fabricated on Zr702 alloy by utilizing pulsed laser cladding. Phase constitutions, chemical compositions, crystallographic orientations and hardnesses of the coatings were carefully characterized and analyzed. Results show that both the RMEA coatings correspond to cladding zones (CZs) that are composed of irregular-shaped bulk grains (BCC solid-solution phase) with scattered orientations and 370–380 μm in thickness. The addition of Ta is able to promote grain refinement and produce higher micro strains in the coatings. Theoretical analyses show that the phase constitution in the RMEA coatings is consistent with that predicted according to several thermodynamic or structural parameters. Below the CZs, there exist heat-affected zones (HAZs) consisting of a mixture of bulk α-Zr grains and fine martensite plates. Average thicknesses of the HAZs in both the specimens are 180–190 μm. Hardnesses of the NbTiZr and the NbTaTiZr coatings are 510 ± 22 HV and 550 ± 26 HV, respectively, significantly higher than that of the substrate (196 ± 4 HV). Such high hardnesses are attributed to combined effects of solid-solution strengthening, grain refinement strengthening and increased contents of low angle boundaries.