Interdendritic Structure Research Articles

Microstructural evaluation and optimization of wear behaviour of vacuum arc melted AlFeCrNiSi high entropy alloy

High-entropy alloys (HEA) are equiatomic, multi-element systems that, while having several elements with various crystal geometries to form a single phase. In this study, a novel equiatomic AlFeCrNiSi HEA is prepared using the vacuum arc melting process. The resulting microstructure featured dendritic and inter-dendritic structures with formations of intermetallic compounds such as Al₃Fe₂Si, NiAl, and AlCrNi phases. EDS analysis confirmed the presence of alloying elements and EBSD analysis revealed refined grains with an average size of 1 ± 0.15 µm size. Pin-on-Disc wear test with varying test parameters is conducted to optimize the wear parameters. Signal-to-noise ratio and analysis of variance identified the most significant wear parameters, with load being the most influential, followed by sliding distance and velocity. The wear rate is minimum at the lowest conditions of applied load, sliding distance, and sliding velocity. The improved microhardness also contributed to the improved wear resistance of the cast alloy. The subsequent worn morphology revealed the formation of grooves, microcracks, and oxide layers on the worn surface.

Joining Behaviour of Thick Plate Using High-Frequency Induction Assisted Arc Welding

Combining a preheating source with conventional arc welding is a promising method to study the weld quality and improvement of strength for high-strength super-alloy materials. The present research used an induction preheating source with plasma arc welding (PAW) to weld Inconel 625 thick plates. The investigation was performed at a constant induction current of 600 A, welding speed of 100 mm/min and a plasma welding current of 135 A. The induction-assisted plasma arc welding (IAPAW) demonstrated that a weld joint was possible with static induction preheating and a high plasma welding current at low welding speed. The microstructural observation showed various dendritic structures in the fusion zone (FZ). The FESEM and EDX analysis confirmed the formation of Laves phase in the interdendritic structure of the FZ. The ultimate tensile strength of the IAPAW joint reached to 658 MPa. The tensile fracture surface of the welded sample revealed a lower number of dimples, indicating the reduction of ductility. The XRD analysis was carried out at various zones and it confirmed the peak shifting towards the higher 2-theta value of the FZ.

Microstructure, mechanical properties and corrosion resistance of direct energy deposited AlCu0.25CoCrFeNi2.1 high entropy alloy: Tailored by annealing heat treatment

In this study, a novel high entropy alloy AlCu0.25CoCrFeNi2.1 is additively manufactured by laser direct energy deposition process. The microstructure, mechanical properties and corrosion resistance of the prepared AlCu0.25CoCrFeNi2.1 high entropy alloy are investigated and tailored by annealing heat treatment. The results indicate the alloy exhibits a dual-phase microstructure with face-centered cubic (FCC) columnar dendrites and body-centered cubic (BCC) interdendritic structures. The annealing heat treatment facilitates the precipitation and coarsening of Cu-rich short rod-like B2 phase within the incipient FCC phase and the dissolution of incipient BCC phase, synergistically varying the proportion of FCC/BCC + B2 contents and tailoring the properties. The hardness of microstructure fluctuates under the coupling effect of precipitation strengthening and lattice distortion reduction and shows an overall downward trend with the increase of annealing time. The tensile properties are noteworthily improved within 6-h annealing and achieve a maximum ultimate tensile strength of 1156.4 MPa. After 8-h annealing, the ductility of the alloy obtains a maximum value of 30.3% with minor loss of ultimate tensile strength. The corrosion resistance is dramatically enhanced and obtains the best value after 2-h annealing, and then gradually deteriorates with the destroying of FCC matrix passive film phase by coarsened B2 phases. These results are of great importance in rapidly designing/manufacturing novel high entropy alloys by laser direct energy deposition process and tailoring microstructure, mechanical properties and corrosion resistance by annealing heat treatment.

Study on the microstructure and wear resistance of AlCrCuFeNiTix high entropy alloys for surfacing welding

In order to investigate the effect of Ti element content on the microstructure and wear resistance of AlCrCuFeNiTix (x = 0, 0.3, 0.6, 0.9) high entropy surfacing alloy, a melting electrode gas shielded welding technology was used to prepare AlCrCuFeNiTix high entropy surfacing alloy on the surface of carbon steel plates. The microstructure, phase composition, and wear resistance of the alloy were analyzed. The results show that the phase composition of the surfacing alloy becomes a BCC+FCC solid solution phase, with a much higher content of BCC phase than FCC phase. The microstructure consists of disordered BCC phase rich in Fe and Cr, ordered BCC phase rich in Al and Ni, and FCC phase rich in Cu. The microstructure exhibits typical dendritic (DR) and interdendritic (ID) structures. With the increase of Ti element, hard Fe2Ti phase precipitates in the interdendritic zone, and the micro hardness of the alloy shows an increasing trend. The maximum hardness can reach 636 HV, which is 2.4 times that of the base material. With the increase of Ti element, the friction coefficient of the alloy shows a trend of first decreasing and then increasing, and the wear amount first decreases and then increases. When Ti is 0.6, the wear resistance of the high entropy surfacing alloy reaches its best.

Effects of scanning speed on the microstructure, hardness and corrosion properties of high-speed laser cladding Fe-based stainless coatings

Fe-based coatings have been prepared by utilizing laser cladding with the scanning speed ranging from 1.57 to 20.4 m/min. The microstructure and corrosion properties have been further investigated to evaluate the effects of scanning speed. The results show that, both coating's thickness and dilution rate gradually decrease with the increase of scanning speed. However, the deposition efficiency on the surface can be greatly improved by around 4 times. Under high scanning speed, the Fe-based coatings show the similar microstructure feature, comprising with dendrites and inter-dendritic structures. But the coating's microstructure can be significantly refined with the secondary dendritic arm spacing less than 1 μm. Furthermore, the gap of Cr concentration between the two structures can be effectively reduced, which shrinks the difference in corrosion resistance. On the other hand, the Fe-based coating's hardness gradually decreases resulting from the retained austenite and ferrite under high scanning speed. Compared to Q235 steel, the cladded Fe-based coatings show superior corrosion resistance with much higher corrosion potential and lower corrosion current density. Pitting dominates the corrosion forms of high-speed laser Fe-based coatings, which initially takes place on the boundaries of different structures. With the increase of scanning speed, the coating's corrosion resistance increases firstly and then decreases, and the coating cladded with the speed of 15.7 m/min shows the best corrosion resistance. Higher average Cr content and more uniform Cr distribution account for the better corrosion resistance. However, excessive microstructure refinement plays a negative role in the coating's corrosion resistance owing to more grain boundaries.

Effect of the Nb content on the microstructure evolution and properties of the CrFeCoNiNbx layers prepared by laser cladding

Marine engineering components, such as ship stern shafts, are often subject to local overload, wear and seawater erosion. In order to improve the performance and service life of marine engineering components, the CrFeCoNiNb x ( x = 0, 0.25, 0.5, 0.75 and 1) high-entropy alloy (HEA) coating were prepared on the 42CrMo substrate by laser cladding. The microstructure, microhardness, wear behaviour and the corrosion resistance of the prepared HEA coatings with different Nb contents were evaluated. Results show that the cladding layer of CrFeCoNiNb0 is composed of single dendrites with a small amount of short rod-shaped protrusions distributed along the dendrites. The addition of Nb promotes growing of the original dendrite structures into interdendritic structures with internal substructures retained. Apart from the variations in the microstructure, the formation of the Laves phase, which is both hard and corrosion resistant, is also an important factor in the performance of the cladding. This variation leads to the increase of the microhardness of the cladding layer, accompanying with the improvement of wear resistance property. Notably, the improvement of microhardness is ascribed to the combined contribution from the refinement strengthening, the solid-solution strengthening and the dispersion strengthening by Laves phase. The improvement of the corrosion resistance is mainly attributed to dense passivation film formed by the Cr and Nb on the surface of the cladding layer. The above results suggest that the CrFeCoNiNb x cladding layer could achieve synergistic interaction between the mechanical properties and the corrosion resistance on stern shaft surface.

Primary Austenite Morphology and Tensile Strength in CGI for Different C Contents, Cooling Conditions and Nodularity

Compacted graphite iron (CGI) is a good option for the blocks and cylinder heads in heavy duty engines due to their well-balanced thermal and mechanical properties. In this work, a remelting technique has been utilized for the production of CGI with different nodularity (10 and 20%), C contents (CE=3.5, 3.8, 4.2) and under different solidification and cooling rates. The employed experimental parameters had a sizeable influence on the morphology and fraction of the inter-dendritic structure and resulted in ultimate tensile strength (UTS) that ranged from 335 to 456 MPa and 371 to 521 MPa for the 10 and 20% nodularity, respectively. The results show that the UTS is linearly related to the solidification time and the microstructural parameter that express the scale length of the inter-dendritic region. Different CE and nodularity provide different relationships between UTS, solidification time and microstructure. Finally, an empirical model has been developed for the prediction of the UTS.

3D finite element analysis and experimental correlations of laser synthesized AlCrNiTiNb high entropy alloy coating

A 3D Finite Element Analysis (FEA) model of laser cladding process of AlCrNiTiNb high entropy alloy (HEA) coatings on Titanium alloy (Ti6Al4V) substrate has been developed taking into account heat transfer and free surface movement. The use of Ti6Al4V is highly evident in applications such as aerospace, automobile and marine environments due to their outstanding specific strength to weight ratio. Although they have high strength useful for fabrication of engineering components and movable parts in a mechanical system, Ti6Al4V are restricted to non-friction applications as a result of their low hardness. In this work, AlCrNiTiNb HEA hard-coating with equi-atomic ratio was synthesized on Ti6Al4V alloy substrate by laser cladding technique to mitigate the limitations. Prior to experimental method, a 3D computational model was developed to simulate the physical phenomena based on heat transfers involved during laser surface cladding (LSC) of HEA coating on Ti‐6Al‐4V alloy by a laser-assisted direct energy deposition technique. COMSOL Multiphysics 5.3a was used to create a model using heat transfer in solids module incorporating temperature distribution during the layer-wise build-up of 3 layers. The experimental validation showed that the microstructural analysis by scanning electron microscope (SEM) resulted in coating having dendritic and interdendritic structure which resulted in good metallurgical bonding. X-ray diffraction (XRD) analysis displayed that AlCrNiTiNb alloy coating is composed of ordered and disordered solid solution phases (BCC and FCC) with no intermetallic compounds formed. Energy dispersive spectrometer (EDS) confirmed the presence of elements used. The microhardness of AlCrNiTiNb HEA coating reached maximum value around 892 HV which is more than of the substrate. The microhardness increased significantly due to the combination of BCC and FCC solid solution phases.

AN INVESTIGATION ON MICROSTRUCTURES, MECHANICAL AND WEAR BEHAVIOR OF LASER-CLADDED INCONEL 625 AND NIMONIC 90 OVER NIMONIC 90 SUBSTRATE

The wrought nickel–chromium–cobalt Nimonic 90 alloy is widely used in turbine blades, piston rings and forged tools due to their high stress-rupture strength and creep resistance up to 920∘C. The application components showed unavoidable wear behaviors at high loads due to the reduced resistance of the components. Hence, in order to increase the wear resistance of this alloy, Inconel 625 and Nimonic 90 particle depositions have been carried out on Nimonic 90 substrate through the laser-cladding techniques to study the microstructure, mechanical and tribological behaviors of alloys. The phases, microstructure and microhardness of the claddings were investigated by X-ray diffractometry (XRD), Transmission electron microscopy (TEM), Scanning electron microscope (SEM), Energy-dispersive X-ray spectroscopy (EDS) and hardness test, respectively. Results showed that the mean thickness of the interfacial layer of Inconel 625 and Nimonic 90 was 18.51 ± 4 [Formula: see text]m and 90.68 ± 7 [Formula: see text]m, respectively. The microstructure of the cladding surfaces resulted in dendritic and interdendritic structures. An overall analysis found that the gamma-Ni and hard laves phases were presented in Inconel 625 and Nimonic 90 clad surfaces, respectively. Nimonic 90 clad surface had a high hardness and wear resistance compared with Inconel 625 clad surface and substrate due to the present hard laves phase. Besides, the roughness of the Nimonic 90 clad surface was lower compared with the Inconel 625 clad surface and substrate.

Microstructure and Properties of FeCrMnxAlCu High-Entropy Alloys and Coatings

FeCrMnxAlCu (x = 0.5, 1, 1.5, and 2) high-entropy alloys (HEA) and coatings were prepared through vacuum arc melting and cold spray-assisted induction remelting processes. This study investigated the effect of different Mn contents on the microstructure and wear resistance of HEAs and coatings. The results showed that the high-entropy FeCrMnxAlCu alloy prepared through vacuum arc melting and cold spray-assisted induction remelting processes comprised simple body-centered cubic and face-centered cubic phases with dendritic + interdendrite structures. The coating of the prepared alloys exhibited superior performance compared with the cast alloy. In addition, the hardness of the FeCrMnxAlCu HEA coatings synthesized through induction remelting was 1.4 times higher than that of the cast FeCrMnxAlCu HEA. Moreover, the wear rate of induction-remelted produced HEA coating was reduced by 24% compared with that of vacuum arc-melted produced HEA. The hardness of the induction-remelted produced FeCrMnxAlCu HEA coating initially increased and then decreased with increasing Mn contents. At x = 1, the hardness of FeCrMnAlCu HEA coating reached a maximum value of 586 HV, with a wear rate of 2.95 × 10−5 mm3/(N·m). The main wear mechanisms observed in the FeCrMnxAlCu HEA coatings were adhesive, abrasive, and oxidative.

Microstructure and mechanical properties of functional gradient materials of high entropy alloys prepared by direct energy deposition

In this study, FeCrCoNiMo0.5W0.75 HEAs functional gradient materials were prepared by the direct energy deposition (DED) technique, and the phase transition, microstructure and mechanical properties of the materials along the building direction were investigated. The material realizes a transition from a single FCC phase to an FCC + TCP phase from the bottom to the top. The bottom and middle of the material are typical dendritic (DR)-interdendritic (ID) structures, and at the top, due to the precipitation of the eutectic structure σ phase and μ phase, the material transforms into a hypoeutectic structure of FCC + eutectic. According to the EBSD results, the interior of the material is mainly columnar crystals that grow vertically to the molten pool. This unidirectional columnar growth makes the material have a strong texture in the <100> direction. In addition, a large degree of grain refinement is exhibited from the bottom to the top, with the grain size reduced from 19 μm to 6.5 μm. According to the TEM results, the density of dislocations is much higher near the phase and grain boundaries than in other regions, and dislocation entanglement is formed by the continuous accumulation of loose dislocations. The micro-hardness of the material increased along the construction direction up to 892.5HV0.5, and the material has good compressive strength up to 2041 ± 45 MPa. The material has excellent wear resistance and high-temperature wear resistance, forming a continuous oxide layer at 800 °C, which greatly reduces the friction coefficient and wear rate.

Investigation of the Microstructure and Properties of CoCrFeNiMo High-Entropy Alloy Coating Prepared through High-Speed Laser Cladding

High-speed laser cladding was introduced to prepare a CoCrFeNiMo high-entropy alloy (HEA) coating. The microstructure, composition distribution, micromechanical properties, and corrosion resistance of the CoCrFeNiMo coating were characterized. As a result, the coating exhibited a dual FCC- and BCC-phase structure, and the grain size of the coating prepared through high-speed laser cladding was only 2~5 μm. The upper and lower parts of the coating were composed of equiaxed cellular crystals and slender columnar crystals, respectively. The interdendritic structure was a Mo-rich phase that was distributed in a network-like pattern. The nanoindentation tests revealed that the interdendritic BCC phase had high hardness and an elastic modulus as well as excellent resistance to deformation, while the intradendritic FCC phase possessed superior crack propagation resistance. In addition, the two phases could generate cooperative elastic deformation during the elastic deformation stage. The electrochemical performance of the coating was tested in 3.5 wt% NaCl solution, and the corrosion potential Ecorr and corrosion current density Icorr of the coating were −0.362 V and 3.69 × 10−6 A/cm2, respectively. The high-speed laser cladding CoCrFeNiMo HEA coating had excellent corrosion resistance thanks to the presence of the easily passivating element Mo and grain refinement.

Effect of friction stir processing on microstructural evolution and mechanical properties of nanosized SiC reinforced AA5083 nanocomposites developed by stir casting

AA5xxx alloys are widely used for different parts of marine appliances of low to moderate level of strength. However, these alloys are not suitable for high-strength marine parts because of its low mechanical strength, elastic modulus, and weld yield strength. Hence, with an aim to improve performance of these alloys for various high-strength marine components, the present study efforts to develop fine grained AA5083 alloy-based nanocomposites with uniform dispersion of nanosize SiC particles through stir casting followed by microstructural modification using friction stir processing (FSP). AA5083-SiC nanocomposites (1, 2 & 3 wt%) were produced by an indigenously designed bottom pouring stir casting setup reinforced with nanosize SiC (n-SiC, ∼80 nm) particles. Then, FSP was performed with the optimized parameters (1216 rpm rotational speed and 41 mm/min traverse speed) to modify as-cast interdendritic structures of the nanocomposites. Microstructural investigation through optical and electron microscopy (SEM-EBSD, TEM-EDS) confirmed the evolution of fine recrystallized grains with a uniform distribution of n-SiC within the matrix after the FSP. The FSP is found more advantageous to attain better grain refinement (∼50 % more) for the n-SiC reinforced composites as compared to that of the FSPed pure AA5083 alloy. The mechanical properties were found to improve up to 2 wt% reinforcement significantly as compared to the as-cast counterparts. However, because of huge agglomeration of n-SiC particles in the 3 % reinforced composite, it showed inferior mechanical properties. Tensile yield strength (YS) and average hardness were recorded to be 224 MPa and 84 HV, respectively, for the FSPed AA5083–2 wt% n-SiC nanocomposite as compared to the YS-152 MPa, hardness-75 HV for the FSPed AA5083 alloy without any reinforcement. The enhancement in the mechanical performance is attributed to the breakdown of interdendritic microstructure to evolve dynamically recrystallized fine grains (grain boundary strengthening) with uniform distribution of n-SiC particles (dispersion strengthening) and other secondary precipitate phases. Analysis of strengthening mechanisms’ contribution found to be in good agreement with the experimental YS up to 2 % reinforced nanocomposites. Fractography analysis of the tensile samples is found to correlate well in accordance with the tensile properties.

Microstructure and properties of FexCrMnAlCu high-entropy alloy

FexCrMnAlCu (x = 0, 0.5, 1, 1.5, 2) high-entropy alloys were prepared by vacuum arc melting in this study. The effects of the element Fe on the microstructure evolution, mechanical properties, and wear behaviour of FexCrMnAlCu were evaluated. Results show that all FexCrMnAlCu consisted of dendrites (disordered BCC) and interdendritic (disordered FCC) structures. With an increase in Fe, uniformly distributed rod-like precipitates (Φ50 nm × 300 nm) rich in Al and Cu (ordered BCC) were formed in the dendrites; the volume fraction of the dendrites increased gradually, whereas the content of the interdendritic structures decreased. Through mechanical property testing, it was found that the content of precipitates significantly affected the strength and hardness of the FexCrMnAlCu.

A study of the mechanical properties of AZ61 magnesium composite after equal channel angular processing in conjunction with machine learning

Machine-learning technique was employed in this study to investigate AZ61 magnesium alloy and its composites, in terms of predicting their microstructure and mechanical properties. This study found that, equal channel angular processing (ECAP) deformation decreases grain size and increases phase homogeneity as the number of ECAP passes increases. Microstructure observations revealed that dynamic recovery decreased with the addition of the reinforcement. The hardness values increased from 59.02 Hv at homogenized conditions to 68.9Hv following four passes of ECAP. It was also observed that hardness increased when particle reinforcement was increased. Since hardness is related to the grain size and strength, it was concluded that a decrease in the grain size improves the strength of the alloy. As a result of particle reinforcement, the composites' 0.2% yield strength and elastic modulus improved from 90.206 MPa to 94.285 MPa and from 9.499 GPa to 10.634 GPa, respectively. Using a machine learning model, it was determined that the elastic modulus and yield strength increase as the particle reinforcement ratio increases. • Interdendritic structure is formed along the grain boundaries due to the co-existence of Mg and Mg 17 Al 12. A ternary Mg 32 (Al,Zn) 49 is formed as a minor phase. • Machine learning has been used to predict mechanical properties. • Linear Regression model shows that Yield strength and Elastic moduli increase with increasing particle-reinforcement. • ECAP-deformed samples displays better mechanical properties compared to the composite (non-deformed) • Pure AZ61 Mg undergo ductile fracture while its MMCs fail by brittle-ductile fracture

Development of Ti–Ta–Nb–Mo–Zr high entropy alloy by μ-plasma arc additive manufacturing process for knee implant applications and its biocompatibility evaluation

It describes development of equiatomic Ti–Ta–Nb–Mo–Zr HEA by μ-plasma arc additive manufacturing process for knee implant applications, its microstructure study and in-vitro biocompatibility evaluation using cell viability, released metallic ions, and corrosion behaviour. Cell viability was evaluated by treating HeLa, HEK-293, and BHK cells with 20, 40, 60, and 100 μl concentrations of prepared media for the developed HEA for 24, 48, 72 h incubation durations. Released amounts of Ti, Ta, Nb, Mo, and Zr ions were estimated in 4.4; 5.4; and 7.4 pH value simulated body fluid solution (SBF) for immersion durations of 1, 3, and 7 weeks. Corrosion behaviour was studied in 4.4; 5.4; and 7.4 pH value SBF solution at 37 °C. Ti–Ta–Nb–Mo–Zr HEA consists of BCC major and minor phases having fine dendritic and inter-dendritic structure. Average % cell viability decreased with increase in prepared media concentration. Overall average values of viability for HeLa, HEK-293, and BHK cells treated with prepared media are 90%; 88%; and 92% respectively. BHK cells showed maximum cell viability at each media concentration and for each incubation duration. Ti–Ta–Nb–Mo–Zr HEA did not harm appearance of HeLa, HEK-293, and BHK cells. Overall averaged released amounts of Ti, Ta, Nb, Mo, and Zr ions are 37, 26; 57; 38, and 28 ppb respectively. Ti–Ta–Nb–Mo–Zr HEA has minimum values of all essential corrosion parameters without causing any pitting. It showed excellent biocompatibility hence referred as bio-HEA which is a new class of biomaterials for knee implants that can overcome limitations of the present materials.

Significant evolutions of microstructure and mechanical properties of Al0.3CoCrFeNiTix high-entropy alloys under annealing treatment

The effect of annealing treatment on microstructure and mechanical properties of Al0.3CoCrFeNiTix high entropy alloys were investigated. The results indicated that addition of Ti in as-cast alloys caused the formation of L12, Laves, γ and σ phases to increase the hardness and strength of the alloys. The microstructure remained stable below annealing at 700 °C. However, the (Fe, Cr)-rich phase was found in the interdendritic (ID) structure. Simultaneously, annealing at 700 °C increased the volume fraction of L12, γ and σ phases and decreased the volume fraction of FCC and Laves phases. The (Al, Ni, Ti)-rich rod-shaped precipitated (RSP) phase was found in the FCC matrix after annealing at 800 °C. The hardness and yield strength showed a significant enhancement after annealing at 700–800 °C. The coarsening phenomenon of (Fe, Cr)-rich and RSP phases could be observed after annealing at 900–1000 °C. Simultaneously, annealing at 900–1000 °C caused the further decrease in the volume fraction of FCC and Laves, causing the decrease in yield strength and to improve plasticity of the alloys. The main strengthening mechanisms of as-cast and annealed Tix alloys were discussed, confirming that the precipitation strengthening mechanism was the main strengthening mechanism.

Microstructure and Properties of Cold Spraying AlCoCrCuFeNix HEA Coatings Synthesized by Induction Remelting

ABSTRACT Using induction remelting assisted with cold spraying, AlCoCrCuFeNix (x = 0, 0.5, 1, 1.5, 2) HEA coatings with different Ni contents were prepared on the surface of 45# steel. Results show that the AlCoCrCuFeNix HEA coatings structure is mainly composed of dendrites and interdendrites. As the Ni content increase, the BCC phase structure content in the coating first increases and the decreases, and the FCC phase structure content first decreases and then increases; when 0 ≤ x ≤ 0.5, the dendritic structure in the coating is BCC phase and the interdendritic structure is FCC phase; when 0.5 ≤ x ≤ 2, the dendritic structure in the coating is FCC phase and the interdendritic structure is BCC phase. When x=0.5, the performance of the coating is the best, the hardness is 534.7HV, the coefficient of friction is 0.38, and the wear rate is 4.37 × 10−5mm3N−1mm−1 .

Formation and beneficial effects of the amorphous/nanocrystalline phase in laser remelted (FeCoCrNi)75Nb10B8Si7 high-entropy alloy coatings fabricated by plasma cladding

High-entropy amorphous composite coatings have high potential application value in the industrial field due to their excellent performance. (FeCoCrNi)75Nb10B8Si7 high-entropy alloy coatings with amorphous/nanocrystalline phases were prepared by plasma cladding and subsequent laser remelting. The phase, microstructure, mechanical properties, and wear resistance of the coatings were studied. Detailed characterization indicated that the microstructure of the plasma cladding coating consisted of the body-centered cubic (BCC) phase, whereas that of the laser remelting coatings consisted of the Fe and Ni-rich BCC phase in the dendritic area and the Nb, B, and Si-rich nanocrystalline-face-centered cubic (nano-FCC) + amorphous phases in the interdendritic area. Excellent mechanical properties were observed, including high microhardness, high nanohardness (H) to elastic modulus (E) ratio (H/E), high H3/E2, and a high elastic recovery rate (η). Furthermore, the coefficient of friction (COF) was lower in the laser remelting coatings (0.6) than in the plasma cladding coating (0.7), which was attributed to severe adhesive wear of the plasma cladding coating and abrasive and slightly adhesive wear of the laser remelting coatings. The microstructure evolution and strengthening contribution of the interdendritic structure in the laser remelting coatings and the relationship between the microstructure and mechanical properties and wear resistance were analyzed.

Masking Effect of LPSO Structure Phase on Wear Transition in Mg97Zn1Y2 Alloy

Room- and elevated-temperature wear tests were conducted using a pin-on-disk testing machine to study wear behavior of Mg97Zn1Y2 alloy and role of long-period-stacking-ordered (LPSO) structure phase in mild–severe wear transition (SWT). Variation of wear rate exhibited a three-stage characteristic with load at various test temperatures, i.e., a gradual increasing stage, a slightly higher plateau stage, and a rapid rising stage. The wear mechanisms in the three stages were identified using scanning electron microscope (SEM), from which the first stage was confirmed as mild wear, and the other two stages were verified as severe wear. The interdendritic LPSO structure phase was elongated into strips along the sliding direction with Mg matrix deformation in the subsurface, plate-like LPSO structure phase precipitated at elevated temperatures of 150 and 200 °C. The fiber enhancement effect and precipitation effect of LPSO structure phase resulted in a little difference in wear rate between the first and second stages, i.e., a masking effect on SWT. Microstructure and microhardness were examined in the subsurfaces, from which the mechanism for SWT was confirmed to be dynamic recrystallization (DRX) softening. There is an apparently linear correlation between the critical load for SWT and test temperature, indicating that SWT is governed by a common critical DRX temperature.