Average Microhardness Research Articles

Effects of rare-earth element Y content on the microstructure and properties of quinary Al–Ni–Zr–Co–Y high entropy metallic glasses

A series of quinary (Al1/4Ni1/4Zr1/4Co1/4)100-xYx (x = 16–28 at.%) high entropy metallic glass ribbons were successfully fabricated through the high-speed single roller melt-spinning method. The effects of rare-earth element yttrium content on the microstructure and performances of alloy ribbons were systematically investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), heat treatment, transmission electronic microscopy (TEM), atomic force microscopy (AFM) and electrochemical experiments. The microhardness of metallic ribbons was measured by Vickers hardness tester. Results show that the microstructure of the as-quenched alloy ribbons maintain the glassy state and the average microhardness value of each specimen can reach 488 HV0.1 or above. The surface morphologies of the as-spun ribbon samples exhibit the smooth surface with small roughness value of Ra = 0.115–0.150 nm. In the meantime, with the increase of Y content, the glass transition temperature can be detected in the DSC traces when Y content is over 22 at.%, and the crystallization onset temperature shifts to the lower temperature region, suggesting that the thermal stability of amorphous state in Al–Ni–Zr–Co–Y alloy ribbons has been weakened. The (Al1/4Ni1/4Zr1/4Co1/4)84Y16 alloy ribbons own the highest crystallization onset temperature (∼742 K). Adding appropriate yttrium element can enlarge the super-cooled liquid region and improve the glass-forming ability. In 3.5 wt% NaCl solution, the prepared alloy ribbons can maintain smaller corrosion current densities (∼10−8 A cm−2) than traditional Al-based amorphous alloys, 6061 Al alloy and other common structural steels. The X-ray photoelectron spectrometer results indicate that the passive film of equiatomic alloy ribbons is rich in oxides of Al, Zr, Co, and Y elements, which has excellent resistance to chloride ion attack. On the basis of all experimental results, (Al1/4Ni1/4Zr1/4Co1/4)84Y16 alloy ribbons can optimally combine outstanding corrosion resistance, superior thermal stability, and acceptable microhardness. The above research results lay a solid foundation for the composition development of high-performance high entropy metallic glasses.

Multi-regional microstructure control using ultrasonic-assisted directed energy deposition for Al-Cu alloy

The uneven microstructure and element distribution between the inner-layer zone (INZ) and the inter-layer zone (ITZ) resulting from the thermal cycling effect during the directed energy deposition process with the electric arc energy source (DED-Arc) can lead to inferior mechanical properties. In order to address this problem, the ultrasonic treatment of the 2319 Al-Cu alloy during the DED-Arc process is investigated to control the multi-regional microstructure quantitatively. Therefore, the effect of ultrasonic vibration during the DED-Arc process on grain morphology, distribution of precipitates and mechanical properties in different regions are explored in detail. The formation mechanism of differential microstructure is elucidated by using an ultrasonic-heat-flow coupling simulation model for the DED-Arc process. The results indicate that ultrasonic vibration refines the average grain size, leading to 16% and 40% reductions at the molten pool center (MPC) and boundary (MPB), respectively. However, the grains in the semi-melting zone (SMZ) experience coarsening due to the reduced temperature gradient after ultrasonic treatment. The enhanced melt flow rate is considered responsible for both the homogenization of Cu and the fragmentation of the θ-Al2Cu phase. The higher subgrain boundary density in the ITZ leads to an average microhardness of approximately 60 HV, which is lower than that found in the INZ (72.3 HV). Meanwhile, ultrasonic treatment increases the average strength and elongation by 38.1% and 17.5%, respectively, mainly through precipitation strengthening, which results in a strength increment of 91.6 MPa. The slip directions tend to be consistent after ultrasonic vibration, which is conducive to crystal sliding and displays excellent ductility.

Effect of multiple passes on the properties of Al-5052/SiC surface composites fabricated via friction stir processing

Friction stir processing (FSP) has emerged as a promising technique for producing surface composites with enhanced mechanical, microstructural and tribological properties. This work investigates the influence of multi-pass FSP on various properties of aluminium 5052 alloy reinforced with silicon carbide (Al-5052/SiC). The results indicated that multi-pass FSP effectively dispersed SiC particles within the aluminium matrix, resulting in a refined microstructure and improved mechanical properties. As the number of FSP passes increased, hardness, tensile strength, and wear resistance improved, reaching levels significantly higher than the base Al-5052 alloy. Tensile strength, yield strength, and average microhardness in the five-pass FSPed specimen were improved by about 25 %, 26 %, and 28 % respectively. Wear and corrosion resistance improved with the increase of FSP passes. The quantitative results of the study strongly corroborate with microstructural evolution.

Microstructure and performance of NiCrBSi coatings prepared by modulated arc currents using powder plasma transferred arc welding technology

This study examines the impact of varying plasma arc currents 70 A, 80 A, 90 A, and 100 A on NiCrBSi coatings applied to 15HM steel substrates using powder plasma transferred arc welding (PPTAW). Finite element analysis identifies two thermal cycle zones: the coating middle and coating/substrate transition. Microstructural analysis reveals dendritic structures in all samples, primarily rich in Cr. At the transition zone, various solidification modes are observed, accompanied by a coarse-grained heat-affected zone and minor macrosegregation. Energy-dispersive X-ray spectroscopy (EDS) confirms metallurgical bonding, while electron backscatter diffraction (EBSD) and X-ray diffraction indicate grain refinement as current decreases, with γ-Ni, Cr23C6, and Cr3C2 strengthening phases. PTA current of 70 A emerged as the optimal fabrication current within the tested range of currents, producing coatings exhibiting superior properties over the others. The results show improved corrosion resistance and tribological properties as current drops from 100 A to 70 A. Notably, corrosion current density decreases from 23.6 µA/cm2 to 12.8 µA/cm2, and average microhardness increases from 488 HV to 832 HV, reducing wear rate from 2.9 × 10−2 m3/m to 1.8 × 10−2 m3/m.

Microstructure and mechanical properties of adjustable-ring-mode laser welded and hot-stamped Al–Si coated boron steel joints

The microstructure and mechanical properties of adjustable-ring-mode (ARM) laser-welded, hot-stamped 22MnB5 steel joints were analyzed and compared with those of Al–Si coated 22MnB5. Al segregation into the fusion zone (FZ) was suppressed by a ring beam introduced via ring-beam-mode (RBM) and dual-beam-mode (DBM) laser welding. Dilution of the Al–Si coating in the FZ induced α-ferrite formation during hot stamping. After hot stamping, the α-ferrite fraction in the FZ decreased (from 23 vol% to 4.27 vol%) more than that in the center-beam-mode (CBM) welded joints owing to the ring beam. Electron backscattered diffraction analysis indicated the distribution of high-density and uniform geometrically necessary dislocations, which caused coordinated deformation in the martensite grains, in the RBM and DBM FZs. The average microhardness in the FZ in the tailor-welded blank (TWB) joints was ∼30–40 HV lower than that in the RBM and DBM welded base metal (480 HV) and that in the FZ of the CBM reduced to 295 HV because of the formation of a large amount of ductile α-ferrite. The tensile strength and elongation of the TWB joint in the CBM were ∼989 MPa and 1.1 %, respectively, which were significantly lower than those of the RBM (1245 MPa and 1.96 %, respectively) and DBM (1321 MPa and 2.12 %, respectively). Finally, the 22MnB5 steel sheets were subjected to ARM laser welding without removing the coating layer to evaluate the effect of the ring beam on Al segregation suppression in the FZ and mechanical properties of the TWB joints.

Numerical Simulation and Mechanical Properties of 6063/6082 Dissimilar Joints by Laser Welding

In this paper, the laser welding process of 6082-T6 and 6063-T6 dissimilar aluminum alloys with a thickness of 2.5 mm was numerically simulated by using a rotary surface Gauss heat source and the flow state of the weld pool was analyzed. The microstructure and mechanical properties of the welded joint (WJ) with a laser power of 1.75 kW were also studied. The results show that the recoil pressure in the molten pool tends to be stable with the increase in welding power, and the surface tension was the main driving force affecting the liquid metal flow in the molten pool. Under the action of 1.75 kW of laser power, the macromorphology of the weld was complete, continuous, and clear. The weld metal zone (WMZ) near both sides of the fusion line (FL) was columnar in microstructure, and the center of the WMZ was dominated by equiaxed crystals. The average microhardness of WMZ was 73.46 HV, which was lower than the base material zone (BM) and heat-affected zone (HAZ). The fracture region of the tensile specimen was located in HAZ on the 6063-T6 side of WJ, showing ductile fracture characteristics with a tensile strength of 180.8 MPa and elongation of 4.04%.

Elevated temperature tribological performance of non-equiatomic CoCrNiTiWx high entropy alloy coatings developed by mechanical alloying and high-velocity oxy-fuel spray

High entropy alloys (HEA) have applications in multiple fields owing to their exceptional mechanical and physical properties. In the current study, mechanical alloyed CoCrNiTiWx (x; a molar fraction, x = 0.5 and 1.5) HEA feedstock powders were deposited on maraging steel substrate using high-velocity oxy-fuel spray (HVOF). The phase evolution and the microstructure of the milled powders and as-sprayed coatings were analysed by X-ray diffraction (XRD) and scanning electron microscope (SEM). The tribological behaviour of CoCrNiTiW0.5 and CoCrNiTiW1.5 HEA coatings at elevated temperatures was studied extensively using a Pin-on-Disc tribometer. The CoCrNiTiW0.5 and CoCrNiTiW1.5 HEA coatings retained the BCC solid solution phases formed during the milling stage. However, additional oxide and intermetallic phases were formed owing to the in-flight oxidation and high temperatures experienced during the HVOF deposition. The deposited coatings exhibited a lamellar structure and good mechanical bonding with the substrate. The porosities of CoCrNiTiW0.5 and CoCrNiTiW1.5 HEA coatings were found to be 1.69 ± 0.32 % and 1.51 ± 0.37 % respectively.Consequently, the CoCrNiTiW0.5 and CoCrNiTiW1.5 HEA coatings displayed average microhardness values of 863 ± 52 HV0.3 and 1025 ± 39 HV0.3, respectively. Further, the wear rates of coatings exhibited a significant reduction at elevated temperatures, owing to the formation of TiO2, NiCr2O4 oxide tribofilms for CoCrNiTiW0.5, and CoCr2O4, NiWO4, WO3 oxides for CoCrNiTiW1.5. The specific wear rate of CoCrNiTiW0.5 HEA coating dropped by 73.6 % from 22.7 ± 2.6 × 10−6 mm3/N-m to 5.99 ± 1.9 × 10−6 mm3/N-m, while CoCrNiTiW1.5 dropped by 78.8 % from 11.86 ± 3.5 × 10−6 mm3/N-m to 2.51 ± 1.5 × 10−6 mm3/N-m, with a rise in the temperature from RT to 600 °C. Likewise, The frictional coefficients of CoCrNiTiW0.5 HEA dropped from 0.504 ± 0.015 to 0.397 ± 0.005, while CoCrNiTiW1.5 HEA dropped from 0.578 ± 0.025 to 0.471 ± 0.004, with a rise in temperature from RT to 600 °C. At room temperature, the wear mechanisms of the as-sprayed CoCrNiTiWx coatings were dominated by adhesive wear. However, at elevated temperatures, a shift towards oxidative wear was observed.

Дюрометричний аналіз зміцнення приповерхневого шару ADI при терті під впливом TRIP-ефекту

Features of strengthening of the near-surface layer of ADI during friction due to strain-induced martensitic transformation were analyzed by duromeric methods. Indentation under continuous loading (Meyer hardness, HM) and Vickers microhardness Hμ were used. Pop–ins are observed on the ADI continuous load curves, which indicate martensitic transformations during indentation. The effect usually exists at a load of ~0,1 H and an depth of ~1,5 μk. The average microhardness of the initial sample is Hμ ≈ 4,89 GPa. After wear, the average value increases to Hμ ≈ 6,92 GPa. Statistical analysis of the microhardness distribution of the sample after wear revealed that a third of the indentations have abnormally high hardness, which is characteristic of deformation-induced martensite. Probably, these indents are obtained from regions of the structure where deformation-induced martensitic transformation took place. Increasing the indentation load practically does not affect the determination of the microhardness of the initial sample, but reduces the hardness of the sample after wear. This indicates the gradient nature of deformation and phase-structural rearrangements in the near-surface layer during wear. As the friction temperature increases, there is a decrease in microhardness in the wear zone. This is explained by the departure from the temperature range of the martensitic transformation, due to which the TRIP effect is weakened. The maximum degradation of microhardness is observed between room temperature and 50 oC. Keywords: ADI materials, durometric studies, TRIP-effect, wear.

Investigation on microstructure and reinforcement mechanism of the TiC-reinforced W-matrix composite prepared by high-energy ball milling and spark plasma sintering

The W–TiC composite with low density and good mechanical properties was prepared by high-energy ball milling and spark plasma sintering. The microstructure morphology and phase composition of the W–TiC composite were investigated. The characteristics of the interface between the second phases and the matrix were calculated and analyzed. The addition of TiC reinforcing phase significantly inhibited the growth of W grains. The reinforcing phase was distributed in long stripes in the W–TiC composite, and a variety of second phases existed in the W–TiC composite such as TiC, Ti, and W2C. First-principles calculations of three heterostructure interfaces (W–TiC, W–Ti, W–W2C) showed that the phases of W2C and Ti play a crucial role in improving interface stability and interfacial strength. The grain refinement effect and the second phase strengthening effect make the average microhardness of the W–TiC composite reach ∼958 HV, and the compressive strength at room temperature and high temperature (600 °C) are ∼2374 MPa and ∼1884 MPa, respectively. Although the compressive strength of the W–TiC composite at high temperature is ∼20.7 % lower than that at room temperature, it still shows certain thermal stability and sufficient mechanical properties.

Effect of electrodeposited Cu interlayer thickness on characterizations and adhesion force of Ni/Cu/Ni coatings on polyetherimide composite substrates

Polyetherimide (PEI) composite is an engineering plastic with excellent performance. After metallization, the metalized PEI composite has some unique properties, such as electromagnetic shielding and high electrical conductivity. In this study, a composite coating of Ni/Cu/Ni was produced on the surface of a PEI composite substrate. Nickel and copper layers were plated by electroless and electrodeposition, respectively. The influences of copper interlayer thickness and heat treatment on the adhesion state of the multilayer coatings on the substrate were studied. The morphology and phase of the composite coatings were determined by optical microscopy, scanning electronic microscopy and X-ray diffraction, respectively. The surface roughness and contact angles of the samples before and after sandblasting were measured by surface profile-meter and goniometer, respectively. The electrical resistivity and adhesion state of the composite coatings were determined by multimeter and the tape test, respectively. The results show that Ni/7.54 μm Cu/Ni and Ni/58.6 μm Cu/Ni multilayer deposits were produced on the substrates. The top surface of the coating with a thin 7.54 μm-Cu interlayer was much rougher than that of a coating with a thick 58.6 μm-Cu interlayer. The initial alkaline electroless nickel layer with 5.8 ± 0.5% phosphorus was composed of a mixture of amorphous and nanocrystalline phases. The Cu interlayer consisted of a face-centered cubic crystalline structure. The phosphorus contents of the top nickel layers for samples #1 and #2 were composed of 6.53 ± 0.4 wt% and 3.52 ± 0.21 wt%, respectively. An increase in Cu interlayer thickness for the composite coating resulted in an increase in electrical resistivity. The average microhardness values of Ni/7.54 μm Cu/Ni PEI composite and the Ni/58.6 μm Cu/Ni PEI composite were about 300 HV0.1 and 244.2 HV0.1, respectively. The adhesion state of the Ni/7.54 μm Cu/Ni and Ni/58.6 μm Cu/Ni PEI composites could be classified as grade 5B and 3B, respectively. The adhesion force of the Ni/58.6 μm Cu/Ni multilayer on the substrate can be improved by heat treatment at 200 °C for 4 h.

Microstructure, mechanical and corrosion properties of FeCrNiCoMnSi0.1 high-entropy alloy coating via TIG arc melting technology and high-frequency ultrasonic impact with welding

With the increase in studies on high-entropy alloys and their impressive structural properties, the preparation processes and applications of high-entropy alloys have become a popular research topic in metallic materials. In this paper, the preparation of FeCrNiCoMnSi0.1 high-entropy alloy coatings was carried out by the follow-welding high-frequency power ultrasonic impact composite TIG arc melting process, the effects of different power ultrasonic impacts on the microstructure and properties of the coatings are investigated. The results showed that the average grain size is reduced by 74 % (from 278 μm to 72 μm), the average microhardness is increased by 41 % from 568 HV1 to 807 HV1, the abrasion resistance is improved by 68 % under the effect of ultrasonic impact. The ultrasonic impact treatment process can effectively refine the microstructure of the coatings and improve the strength of grain boundaries. The corrosion resistance of the coating in 3.5 wt% NaCl solution is enhanced by 65 %, the corrosion type was changed from intergranular corrosion to uniform corrosion. This is mainly caused by the ultrasonic impact treatment which suppresses the elemental segregation of Cr and Mn and improves the grain boundary strength.

Effect of WC content on microstructure and properties of laser-cladded in-situ reactive ZrC/ZrB2 composite coatings on zirconium alloy

ZrC/ZrB2 in-situ reinforced composite coatings were prepared by laser cladding on zirconium alloy. The effect of WC content on microstructure and properties of in-situ reactive ZrC/ZrB2 composite coatings were investigated experimentally. The dilution rate and the inhomogeneity of reinforcements distribution were increased by increasing WC content. The increment of WC content contributed to the refinement of the fishbone dendrites. The microhardness and corrosion resistance of the composite coatings decreased with increasing WC content. When the WC content was 15 wt%, the average microhardness of the coating was the highest as 529 HV0.5. Meanwhile, the corrosion potential was the highest and the corrosion current density was the lowest, which were − 0.660 V and 1.627 × 10−8 A cm−2, respectively.

A multi-objective optimization of laser cladding processing parameters of AlCoCrFeNi2.1 eutectic high-entropy alloy coating

In order to obtain the optimal processing parameters for laser cladding (LC) of AlCoCrFeNi2.1 eutectic high-entropy alloy, a multi-objective optimization method based on response surface methodology (RSM) was proposed. In this paper, a one-way pre-test was conducted by varying the processing parameters using a single control variable method. The results show that the porosity and microhardness of the coating are closely related to the processing parameters. The cross-section microhardness of the coating showed instability under certain process parameters, based on which the optimization window of RSM processing parameters was determined. In the RSM model, a mathematical prediction model was developed according to the laser power, scanning speed, powder feeding rate and microhardness, dilution rate and aspect ratio. Microhardness is inversely correlated with laser power and positively correlated with scanning speed and powder feeding rate. The optimal processing parameters (laser power: 1675 W, scanning speed: 7.8 mm/s and powder feeding rateing rate: 12.91 g/min) were determined. The model showed a good agreement with the experimental validation results. The coatings have good shape with an average microhardness of 322 HV0.2. The maximum average error between model predictions and experimental validation was 5.27 %.

Influences of Ti and Mo alloying on the microstructure and properties of laser cladding for CoCrFeNi high-entropy alloys

The CoCrFeNiTi_(1-x) Mo_x high-entropy-alloy coating was prepared using a powder presetting method. The work investigated the influences of Ti and Mo addition on the microstructure and properties of CoCrFeNi high-entropy alloys. The first-principles calculation showed that CoCrFeNiTi_(1-x) Mo_x was mainly composed of the FCC phase, BCC phase, and IMCs. The coating exhibited high hardness, and the mechanical stability of the high-entropy alloys of FCC and BCC phases was maintained when x = 0.5. The coating primarily consisted of FCC, BCC, σand CoTi2 phases when x ≤ 0.75. The coating primarily consisted of FCC, BCC, σand Co2Mo3 phases when x = 1. It exhibited high microhardness, elastic modulus, elastic stiffness, and wear resistance when x = 0.5. Its average microhardness, local elastic modulus, and elastic stiffness were 873.28 HV0.5, 265.5606 GPa, and 102.8008 GPa, respectively. Besides, COF and the wear mass loss were 0.7026 mm3 and 0.0410 mm3, respectively. The coating exhibited exceptional corrosion resistance with a self-corrosion voltage of −0.700 V and a self-corrosion current of 5.387e-007 A when x = 1. The results offer practical guidance for preparing high-entropy-alloy coatings with various advantages as well as a theoretical foundation for preparing such alloys by laser cladding.

Preparing large-scale, uniform, and high-performance Cu–Cr–Zr strips by a novel continuous expanding extrusion process

A novel continuous expanding extrusion process for manufacturing Cu–Cr–Zr strips was proposed in the present study. The U-shaped strips with a cross-section of 420 mm × 19 mm were successfully prepared by taking the upward continuous casted Φ 28 mm rods as raw material. Electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were employed to characterize the microstructure and precipitates, respectively, which revealed that the microstructure of the continuous extruded strip is very fine and uniform across the entire cross-section and the Cr precipitates are in a dispersed distribution in the matrix helping to improve the strength of the alloy. The average grain size is approximately 1 μm and much smaller than that of the as-cast state (in millimeters). The average micro-hardness, tensile strength, and electrical conductivity of the extruded strip are 120 HV, 328.8 MPa, and 82.6 % IACS, respectively, increasing approximately by 31.6 %, 29.3 %, and 125.5 % in comparison to these of the as-cast state. In addition, the fracture elongation can maintain a very high level (average value ∼28.9 %). The strengthening mechanisms were then quantitatively calculated, which showed that grain boundary strengthening, precipitation strengthening, and dislocation strengthening take comparable contributions. Thus, our investigations provide new insights into manufacturing high-performance Cu–Cr–Zr strips.

Resistance rivet welding of multilayer dissimilar materials

Resistance rivet welding (RRW) process was applied to join three-sheet of Al/steel/steel. The formation mechanism, microstructure and mechanical performance of three-sheet dissimilar materials joints were studied in detail. The Al/steel/steel mixed nugget is produced by the fusion of Al/steel mixed and steel/steel nuggets. The microstructure of Al/steel/steel mixed nugget varies from mixed martensite and ferrite to full martensite as the increasing heat input. The ferrite contains numerous B2 structure nano-precipitates. The introduced Al element by the rivet cavity plays a significant influence on the microstructure, and the competition between ferrite and austenite stabilized elements in mixed nugget is responsible for the microstructure evolution. The phases performance of ferrite and martensite is determined. The average nano-hardness of ferrite is 2.66 GPa (271.3 HV), while that of martensite is 4.68 GPa (477.4 HV), and the yield strength for ferrite and martensite is calculated to be 475.0 MPa and 771.1 MPa, respectively. The average microhardness of the mixed nugget is 369.1 HV, 454.1 HV and 481.7 HV for welding parameters 7 kA-200 m s, 8 kA-200 m s and 9 kA-200 m s, presenting a trend of increasing with the heat input. Considering the multilayer joining containing both the Al/steel heterogeneous and steel/steel homogeneous interfaces, the comprehensive tensile-shear performance is optimal at welding parameters 8 kA-200 m s, 5334 N for Al/steel interface and 19,531 N for steel/steel interface.

Electron beam welding of Nb-8Hf-2Ti high temperature alloy to Ni dissimilar joint: The microstructural analysis, mechanical properties, and fracture characterization

In this work, the electron-beam welding (EBW) behavior of Ni/C-103 Nb-based refractory alloy was investigated, in terms of fusion-zone characteristics, texture evolution, mechanical properties, and joint efficiency. Compared to Nb, the higher concentration of Ni in weld zone indicated that the Ni side participates more in welding than the C-103 one. A continuous intermetallic layer was formed at the joint/C-103 interface composed of NbNi3, Nb7Ni6 and Hf3Ni7 phases. Continuous curved-shaped layers composed of columnar NbNi3 and eutectic Nb7Ni6+NbNi3 phases were also observed in the central and lower regions of the weld. These have been peeled off from the C-103 upper walls lateral to the weld and directed to the bottom of the weld pool due to the Marangoni flow. Solidification microcracks internal to the continuous intermetallic layers are also initiated and grown at the final stage of eutectic Nb7Ni6+NbNi3 phase formation leading to the brittle cleavage failure within this layer. The average microhardness of the joint was measured as 562 HV, which was higher than the base metals due to the presence of intermetallic compounds. Tensile strength of the joint was measured as 119.5 MPa, which is approximately one third of the value for the bead on plate weld of C-103 plate using EBW method with a tensile strength of 317.5 MPa. Nb7Ni6 and NbNi3 intermetallics were dominant phases in the fracture area.

Effect of laser energy density on the microstructure and properties of Tribaloy T-800 coating fabricated by laser cladding on the DZ125 alloy

Tribaloy T-800 coatings are fabricated on the DZ125 alloy by laser cladding, and the effect of laser energy density (η) on the macroscopic morphology, phase composition, microstructure, microhardness and the wear properties of the coatings is investigated. The experimental results indicate that cracks are observed in the coating fabricated with the laser energy density η1 = 33 J/mm2. However, as the laser energy density is raised to η2 = 50 J/mm2 and η3 = 75 J/mm2, the coatings become crack-free. The coatings consist mainly of face-centered cubic Co solid solution and Laves phase (Co3Mo2Si). The microstructure consists mainly of planar crystal, flower-like Laves phase, coarse Laves phase and lamellar eutectic structure. The average microhardness of the coatings is 717 HV0.5, 673 HV0.5 and 572 HV0.5 for laser energy densities of η1 = 33 J/mm2, η2 = 50 J/mm2 and η3 = 75 J/mm2, respectively. The wear mechanism of the coating fabricated with laser energy density η1 = 33 J/mm2 includes abrasive wear, fatigue wear and oxidative wear. However, as the η is increased to 50 J/mm2 and 75 J/mm2, the wear mechanism shifts to abrasive wear and oxidative wear.

Titanium boride coating by high power diode laser alloying of amorphous boron with titanium and its surface property investigations

Present work deals with fabrication of superhard titanium boride coating on titanium surface with preplaced amorphous boron layer using high power diode laser alloying. Amorphous boron instantaneously converts into crystalline boron by the effect of high-power laser interaction, which rapidly drives the boron species into titanium liquid pool and form titanium boride precipitates by its convective flow. Negative Gibbs free energy (ΔG) and enthalpy (ΔH) of amorphous boron crystallization reaction introduces the concept of laser induced self-propagation synthesis. Gibbs free energy (ΔG) for the chemical reactions between Ti and B was calculated to confirm the spontaneous formation of titanium boride compound phases. The diffusion coefficient and activation energy were estimated to understand the phase formation and microstructural evolution. The structural phase, microstructure, microhardness and wear resistance of the laser borided titanium was investigated by XRD, optical and scanning electron microscopy, EDAX, Vickers microhardness analysis and linear reciprocating wear testing. The laser alloyed coating across the cross section shows formation of dendrites and whisker like microstructures. Average microhardness of 800–1600 HV0.2 was measured at different cross-sectional depths and an extreme hardness of about 3800–4700 HV0.2 was obtained in some regions of boron precipitates. The results showed a high negative value of Gibbs free energy of about −250 kJ/mol and −170 kJ/mol at ∼2000 °C respectively which confirms the spontaneity of TiB2 and TiB phase formation. The activation energy of the titanium boride is estimated to be 140 kJ/mol. The laser borided coating with the formation of TiB and TiB2 phases could be useful for surface engineering applications.

Preparation of AlTiVNiCu/Cu–Al gradient functional coating via laser cladding for enhanced wear and corrosion resistance of Mg[sbnd]Li alloy

The poor surface properties of MgLi alloys and the excellent comprehensive performance of high-entropy alloy (HEA) coatings are highly complementary. This study uses laser cladding technology to deposit an AlTiVNiCu/Cu–Al gradient functional coating with favourable wear and corrosion properties on MgLi alloy substrates. Through the design of the gradient coating structure, laser cladding is used to coat HEA layers on low-melting-point MgLi alloys, which effectively reduces further dilution of Mg and Li in the substrate. Notably, the Mg content in the prepared AlTiVNiCu protective layer is only 2.34 %. Furthermore, the microstructure, phase structure, microhardness, tribological and corrosion properties of the gradient coating are systematically studied. The protective layer consists of V-rich BCC1, (Ni, Ti)-rich BCC2, Cu-rich FCC, Mg-rich BCC3 and nanoscale β-Ti phases, with a predominance of body-centered cubic (BCC) structural phases. The average microhardness is 547.46 HV0.3. Under a load of 3 N, the average friction coefficient of the protective layer is 0.54, with a wear volume of only 2.87 % compared with that of the substrate, which is satisfactory wear resistance. In a 3.5 wt% NaCl solution, the protective layer exhibits the highest corrosion potential (−0.49 VSCE, where SEC denotes saturated calomel electrode), and the lowest corrosion current density (1.14 × 10−6 A·cm−2), representing a remarkable enhancement compared with those of the substrate (−1.57 VSCE and 5.41 × 10−4 A·cm−2).