The crack behavior of Ni-based WC composite coatings by laser cladding was investigated. The results showed that cracks originated from the interface of the composite coating and the substrate, and ...then passed through the precipitated carbides due to the dissolution of WC particles. To increase the efficiency of laser cladding and eliminate the well-known crack problems in the composite coatings, laser induction hybrid rapid cladding (LIHRC) was carried out experiments to produce Ni-based WC composite coatings on A3 mild steel. The laser scanning speed and the powder flow rate increased with the increasing of the preheated average temperature of the substrate during LIHRC. The dissolution of WC particles decreased due to high laser scanning speed, contributing to reduce the porosities in the composite coatings. Moreover, the temperature gradient decreased with the increasing of the preheated average temperature of the substrate during LIHRC, which was the main reason why Ni-based WC composite coatings were free of cracks.
WC-reinforced Fe matrix composite coatings were prepared by laser induction hybrid rapid cladding (LIHRC). X-ray diffraction (XRD) was used to identify the phases and the growth characteristics of ...the precipitated carbides were observed by environmental scanning electron microscope (ESEM). The results show that WC particles are almost dissolved completely and interact with Fe-based alloy liquid in the molten pool to precipitate M
6C carbides with different shapes during LIHRC. With increasing the weight percent of WC particles, the transition from the fine M
6C carbides, which are precipitated in an intergranular network of the coarse α-Fe, to the coarse herringbone M
6C eutectics and the primary faceted dendritic M
6C occur and the partially dissolved WC particles with an alloyed reaction layer can be occasionally found in the composite coating. Moreover, the eutectic M
6C carbides in herringbone shape grow in terms of the intergrowth mode of layer and slice, while the primary faceted dendritic M
6C in equiaxial branched shape are only precipitated in the crossed region of the coarse eutectic carbides and grow in terms of dissolution and propagation.
In order to investigate the microstructure characteristics and properties of Ni-based WC composite coatings containing a relatively large amount of WC particles by laser induction hybrid rapid ...cladding (LIHRC) and compare to the individual laser cladding without preheating, Ni60A
+
35
wt.% WC composite coatings are deposited on A3 steel plates by LIHRC and the individual laser cladding without preheating. The composite coating produced by the individual laser cladding without preheating exhibits many cracks and pores, while the smooth composite coating without cracks and pores is obtained by LIHRC. Moreover, the cast WC particles take on the similar dissolution characteristics in Ni60A
+
35
wt.% WC composite coatings by LIHRC and the individual laser cladding without preheating. Namely, the completely dissolved WC particles interact with Ni-based alloy solvent to precipitate the blocky and herringbone carbides, while the partially dissolved WC particles still preserve the primary lamellar eutectic structure. A few WC particles are split at the interface of WC and W
2C, and then interact with Ni-based alloy solvent to precipitate the lamellar carbides. Compared with the individual laser cladding without preheating, LIHRC has the relatively lower temperature gradient and the relatively higher laser scanning speed. Therefore, LIHRC can produce the crack-free composite coating with relatively higher microhardness and relatively more homogeneous distribution of WC particles and is successfully applied to strengthen the corrugated roller, showing that LIHRC process has a higher efficiency and good cladding quality.
The influence of Al2O3 addition on the microstructure, mechanical and tribological properties of CoCrAlYTa coating produced by laser-induction hybrid cladding was systematically investigated. The ...results show that the coatings exhibit high metallurgy quality with no obvious defects, and mainly consist of γ, β and TaC phases. In the cladding process, a part of O element exists in the TaC and increases with the increased Al2O3 content, while the other exists in the form of Y2O3 due to low Gibbs free energy. As the Al2O3 content increases, the volume fraction of β phase (Vβ) changes from 23.82 vol% to 67.72 vol%, and leading to the microhardness of coating increased from 515.15 HV to 610.17 HV. Meanwhile, the wear rate of coating increases with the Vβ in a relationship of y = −5.97x+110.65, due to a fact that the wear mechanism changes from adhesive wear to microcutting.
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•Amorphous alloy reinforced Cu-based immiscible coatings are produced by laser melting deposition.•Fe-rich particles are embedded within Cu-rich matrix due to liquid phase ...separation.•M12C, M23C6 and CrFe7C0.45 are precipitated inside Fe-rich particles.•Enhanced passive films can be obtained when adopting higher laser energy density.
In order to clarify the effect of Fe-based amorphous alloy on the separation mechanism and corrosion behavior of Cu-based immiscible coatings, 10 wt% Fe-based amorphous powder was designed into 90 wt% pure Cu powder to produce the amorphous alloy reinforced Cu-based immiscible coatings by laser melting deposition. The self-organized microstructure and corrosion behavior of immiscible coatings with different laser energy densities were investigated. When the different laser energy densities are adopted, many carbides (M23C6 and M12C) are dispersed in the lower α-Fe layer and large amounts of α-Fe particles containing carbides are embedded in the upper ε-Cu layer due to liquid phase separation. With increasing laser energy density (LED), the α-Fe dendrites are coarser and the area of carbides decrease. The interface of coating and substrate experiences a transition from “poor bonding (gaps) to “good bonding” and “crack debonding”. Moreover, the corrosion characteristics of immiscible coatings also experience a transformation from “crevice corrosion” to “enhanced protection of passive films” and “reduced protection of passive films”. As a result, the corrosion resistance increases first then decreases and the immiscible coating deposited by the LED of 31.25 J/mm2 exhibits the highest corrosion resistance.
To avoid low cladding rate and cracks of cladding layer, laser induction hybrid rapid cladding (LIHRC) has been put forward in the paper. The microstructure characteristics of Ni-based WC composite ...coatings at the different laser scanning speed were investigated. For low laser scanning speed, the growth of γ-nickel was characterized by coarse columnar dendrites and eutectics, blocky W
2C
+
Fe
3W
3C carbides, and bar-like (W, Cr, Ni)
23C
6 carbides were formed. With increasing laser scanning speed, the growth of γ-nickel presented the fine dendrites and eutectics, the only blocky mixed carbides were precipitated and identified as W
2C
+
FeW
3C
+
W
6C
2.54 carbides. With further increasing laser scanning speed, the growth of γ-nickel was characterized by cellular crystals and eutectics, the only blocky carbides were identified as W
2C
+
W
6C
2.54. Moreover, experimental results showed that the efficiency of LIHRC was increased much four times higher than that of laser cladding without preheating, ceramic–metal composite coatings detected were free of cracks and had a good metallurgical bonding with substrate.
The carck-free Fe-based +20
wt% WC coating with large area was produced by mutli-track overlapping laser induction hybrid rapid cladding. The results showed that the maximum laser scanning speed and ...the maximum feeding rate of powder can be increased to 3500
mm/min and 120
g/min, respectively. The cast WC particles were dissolved almost completely and had a worse wettability with Fe-based metal matrix. The precipitated carbides such as M
12C and M
23C
6 (M=Fe, W, Cr) formed an intergranular network around the primary Fe-based phase enriched with tungsten. The microhardness of coating decreased first, and then increased slightly with an increase in the track. The first track had the highest microhardness (i.e. 870HV
0.2). Moreover, the wear weight of coating approximately had a linear relationship with the sliding distance, and increased with an increase in the sliding speed. The wear rate approximately remained constant with an increase in the sliding distance and was two times lower than that of the hardened steel AISI 1045 with a hardness of 60HRC. The wear mechanism during the dry sliding wear was a combination of oxidation wear and abrasion wear.
► The laser scanning speed can be increased to 3500
mm/min. ► The maximum feeding of powder can be increased to 120
g/min. ► WC had a relatively worse wettability with Fe-based metal matrix. ► The microhardness of coating decreased first, then increased with the track. ► The wear mechanism of coating was a combination of oxidation wear and abrasion wear.
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•The Strengthening effect of refractory element was systematically studied.•Improve the properties of HEAs by precipitation of L12 strengthening phase.•Improve the strength-plasticity ...matching of HEAs by multi-stage strain hardening behavior.
In this study, (Co1.5FeNi)88.5Ti6Al4R1.5 (R = Hf, W, Nb, Ta, Mo, V) high entropy alloys were fabricated by vacuum arc melting, followed by cold rolling and aging treatment. The effects of refractory elements on the phase structure, microstructure and mechanical properties of high entropy alloys (HEAs) were systematically studied by means of XRD, SEM and TEM. The results show that the phase composition of all alloys is the face-centered-cubic (FCC) + L12 dual-phase structure, and the addition of refractory elements has not changed the phase structure of the alloys. The tensile results show that the yield strength and elongation of the matrix HEA are 750 MPa and 18 %, respectively. The strength of HEAs is improved variously by adding refractory elements. The HEAs with Ta element have the best comprehensive mechanical properties, exhibit excellent strength-ductility combination, with the yield strength and elongation of 950 MPa and 20 %, respectively, and the fracture mechanism changes from complete ductile fracture to mixed brittle-ductile fracture mode. In addition, the HEAs have multi-stage strain-hardening behavior, which has higher strength when the strain-hardening curve has larger fluctuations, which indicates that the HEAs can improve the strength-plasticity matching relationship by a multi-stage strain hardening behavior.
In the present research, zinc oxide (ZnO) nanoparticles were added into the alkaline phosphate electrolyte as an additive for grafting the bacteria resistance upon the oxide coatings prepared by ...plasma electrolytic oxidation (PEO) on WE43 magnesium (Mg) alloy. The duration of PEO treatment was determined as one processing parameter for regulating the microstructure, composition, corrosion, and antibacterial properties of PEO coatings. The results showed that ZnO nanoparticles can be incorporated into and relatively uniformly distributed within the PEO coatings. Increasing the duration of PEO treatment not only increases the Zn content in PEO coatings but strengthens their in vitro degradation performance in the SBF solution. Zn ions can be released from ZnO-doped oxide coatings, which caused a negligible impact on the human umbilical vein endothelial cells, but significant antibacterial effects against
Escherichia coli
. This present work elucidated that incorporating ZnO nanoparticles is a feasible and regulable strategy for fabricating antibacterial PEO coatings for biomedical Mg alloys.
Graphical abstract
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•A series of nano-size γʹ-strengthened HEAs have been fabricated successfully.•The effects of doping elements on HEAs were systematically explored.•The strengthening mechanisms of the ...HEAs have been systematically studied.
In this work, a series of novel γ' phase strengthened Ti6Al6-based HEAs with six kinds of alloying elements (including Nb, Hf, Ta, W, Mo, and V) were carefully examined combined with TEM, SEM, XRD, and DSC technologies. The impurities Fe2X (X = Nb, Hf, and Ta) Laves were detected in the Nb-, Hf- and Ta-doping alloys while the other three present a perfect (γ + γ') dual-phase microstructures. And the W-, Mo- and V-doping HEAs possess a much better strength-plasticity combination than the Ti6Al6 alloy at room- and high-temperature. The 1.5 W HEA has a tensile strength of ∼ 1300 MPa and good plasticity (>30 %) at room temperature. In the meantime, it also performs much good at 800 °C (∼11 % elongation and the tensile strength of ∼ 750 MPa). The addition of W, Mo, and V elements causes the main peak of the HEAs to shift to the left to varying degrees, among which the biggest shift is 1.5 V HEA, followed by 1.5Mo HEA, the smaller is the 1.5 W HEA. At the same time, the γ' precipitates phase of the alloy has a highly coherent relationship with the FCC matrix phase, which ensures that the strength of the alloy is increased without sacrificing its plasticity.
