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The effects of chromium content on microstructure, hardness and wear resistance of as-cast Fe-xCr-1.0B (x = 0, 4, 8, 12, 16, 20) alloys were investigated by means of optical microscope (OM), scanning electron microscope (SEM), x-ray diffractometer (XRD), hardness tester and ring block wear tester. The results showed that the microstructures of chromium-free alloy were mainly composed of pearlite, ferrite, and eutectic borocarbides, and the hardness was very low, only 18.8 HRC. With the increase in chromium content, the matrix of as-cast Fe-Cr-B alloy gradually began to transform from pearlite and ferrite to lath martensite, and the type of borocarbides changed from Fe2(B, C) to M2(B, C), M7(C, B)3 and M23(C, B)6 (M = Fe, Cr). When the chromium content was 12 wt.%, the hardness of alloy reached the highest value of 61.1 HRC, and the wear resistance of alloy was the best. The results of worn surface analysis showed that the wear failure of as-cast Fe-Cr-B alloy was mainly caused by multiple plastic deformation and micro-cutting.

In present study, Fe-based composite layers were fabricated on steel substrate by laser cladding with or without the addition of Nb and B4C in Fe-based alloy powders. The phase composition, microstructure evolution, microhardness and wear properties of Fe-based composite layers were studied. The results showed that the phases in the Fe-based composite layer were mainly α-Fe, Fe2B, Cr7C3 and Cr23C6. The addition of Nb and B4C resulted in the in-situ formation of NbC phase, an increase in the amount of Fe2B phase, and the refinement of the microstructure in the Fe-based composite layer. The microhardness of the Fe-based composite layer was increased by 269.5 HV0.5 and the wear resistance was improved to about 1.5 times the original wear resistance when the 5% Nb and 5% B4C powders were added. The wear mechanisms of both two Fe-based composite layers were abrasive wear and adhesive wear.

This paper presents the microstructure evolution and corrosion resistance of Fe-18wt.%Cr-1wt.%Mo-3.5wt.%B alloy against molten zinc at 520 °C. The objective of this study is to obtain Fe-B alloy with superior corrosion resistance through microstructure regulation and to reveal the underlying corrosion mechanism. The results show that the metal matrix of as-cast Fe-Cr-B alloys have undergone a transition from α-(Fe, Cr, Ni) solid solution into γ-(Fe, Cr, Ni) solid solution, while the eutectic boride is further refined with the increasing of Ni addition in the steels. The corrosion resistance of the Fe-Cr-B alloys has significantly been enhanced, with an optimal Ni addition at 10 wt%. Thermodynamic calculations and EPMA results show that Ni mainly exists in the matrix, leading to the transformation of the matrix structure. The improvement of corrosion performance can be attributed to two factors: the refined boride network in Ni-modified Fe-Cr-B alloy act as a barrier for Fe/Zn reaction, and the formation of face-centered cubic (fcc) structure also contributed to improve corrosion resistance owing to a more densely packed structure compared to body-centered cubic (bcc) structure. In the initial stage of corrosion, the de-alloying of Ni occurs first, which result in the transformation from γ-(Fe, Cr, Ni) to α-(Fe, Cr, Ni). Corrosion mechanism for test alloys in molten zinc may be mainly dominated by the formation and propagation of cracks in the borides. The cracks initiated due to the discrepancy in thermal expansion coefficients between Fe-Zn phases and the borides.

Based on the Fe Cr B alloy, the Fe 12Cr 1.5B xAl (x = 0, 2, 4, 6 and 8 wt%) alloys were designed by adding Al. The as-cast microstructure and cyclic oxidation behavior have been investigated extensively in this study. The results reveal that the as-cast microstructure of Fe Cr B alloy consists of martensite (bcc), retained austenite (orthorhombic) and M2(B,C)-bct, M7(C,B)3-hcp, M23(C,B)6-complex fcc boron-carbides, gradually changing to α-(Fe,Al,Cr) solid solution (bcc), M2(B,C)-bct, M7(C,B)3-hcp, M23(C,B)6-complex fcc boron-carbides and Fe3Al intermetallic compound with the increasing of Al contents. The oxidation kinetics of all alloy samples follow a parabolic oxidation kinetic law. The oxidation rate constant kp in Al-free Fe Cr B alloy is nearly four times of that in Fe Cr B 8Al alloy. The additions of Al refine the grains and make the distribution of elements more uniform, which results in forming a continuous and dense oxide film containing Al2O3 oxide with excellent fluidity and thermal stability, remarkably enhancing the high temperature oxidation resistance of Fe Cr B Al alloy.

The mechanical behavior of cast nickel-based superalloy Inconel 718 was investigated via hot tensile experiments at 650 °C, 800 °C, and 950 °C to understand the thermal instability of its metallurgic microstructure. Test specimens, which were machined from investment casting, were subjected to a standard heat treatment. Post-tensile testing, microstructure characterization, and fractography observations were conducted with a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The resulting data revealed that the deterioration of toughness and ductility occurred at temperatures above 650 °C. Numerous shear bands and lattice mismatch suggested that plastic deformation through slip movement dominated the ductile fracture mode of the nickel-based superalloy at 650 °C. In contrast, surficial microporosity and grain boundary weakening caused early brittle rupture, before the material yielded, at 800 °C. Significant strain accumulation within grains contributed to plastic flow in the direction of the applied stress load, resulting in intergranular and transgranular fracture at 950 °C. Microstructural evidence displayed the interface debonding between the carbide and the matrix at 950 °C, indicating the temperature limitation of the carbide pileup.

In this study, a high aluminum and chromium Fe-B-C coating was prepared using laser cladding on 2Cr13 steel substrate. The microstructure, microhardness, and wear resistance of the high aluminum and chromium Fe-B-C coating were investigated. The results show that this dense coating possesses good metallurgical bond with the substrate. The microstructure is mainly composed of &alpha, (Fe, Cr, Al) lath martensite, orthorhombic M2B boride, orthogonal M3C2, and orthorhombic M7C3 carbides. The microhardness of the coating can reach 620 HV which is 3.3-times higher than that (190 HV) of the substrate. The coating shows a lower friction coefficient of 0.75 than that of the substrate (1.08). The wear rates of the substrate and the coating are 0.295 mg/min and 0.103 mg/min, respectively, indicating the coating exhibits excellent wear resistance. The wear mechanism transforms severe adhesive wear and abrasive wear of the substrate to slight abrasive wear of the coating. The results can provide technical support to improve the properties of the Fe-based laser cladded coating.

Laser butt welding was carried out for the joining of 5A06 aluminum alloy sheet by using 6 KW fiber laser. The effect of welding speed on the surface morphology, microstructure, micro-hardness, tensile strength and porosity were studied by means of optical microscopy (OM), a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), a Vickers hardness tester and a universal mechanical tensile test. The results show that the weld macro morphology tends to be smooth and the surface defects are reduced with an increase in welding speed. The heat-affected zone was very small due to the large cooling rate. The columnar dendrites grow from the fusion line along the direction of the temperature gradient. The microstructure of the weld zone was in the form of equiaxed grains. The micro-hardness of the weld was lower than that of the base material. The micro-hardness and the tensile strength were gradually increased with an increase in welding speed. When the welding speed is 12 mm × s−1, the micro-hardness and the tensile strength were increased to 96.5 % and 56.2 % of the base mental, respectively. The porosity ratio decreased at first, and then increased with the increase in welding speed. The lowest porosity ratio was 1.99 % when the welding speed was 12 mm × s−1. In summary, the quality of the weld was better when the welding speed was 12 mm × s−1.

In this paper, the effect of heat treatment (760–1060 °C) on tribological behavior of selective laser melted Ti6Al4V alloy against Si3N4 counter-ball under different applied loads was investigated. Results show the wear rate of as-built Ti6Al4V alloy increased firstly and then gradually decreased with increasing the heat-treatment temperature, which obtained the lowest value when the heat treatment temperature was 1060 °C, exhibiting the best wear resistance. The higher applied load led to larger wear rate and lower coefficient of friction. The wear mechanism was strongly dependent on the microstructure transformation, micro-hardness and applied load, which was discussed in detail.

CoCrFeNi and CoCrFeNiAl0.3 high entropy alloys reinforced with in-situ oxide nanoparticles have been successfully fabricated by mechanical milling in combination with hot pressing and hot extrusion. The as-fabricated CoCrFeNi samples exhibited an ultrafine grained microstructure with in-situ Cr2O3 oxide nanoparticles formed during hot pressing and extrusion process and distributed both on grain boundaries and in grain interiors. Increasing extrusion temperature from 1000 to 1100 °C caused a significantly increase of grain size from 700 nm to 2.5 μm owing to recrystallization and growth of the recrystallized grains, as well as the coarsening of Cr2O3 nanoparticles with their mean size increasing from 57 to 140 nm. When adding Al elements, finer Al2O3 nanoparticles (mean size: 30 nm) formed in the CoCrFeNiAl0.3 high entropy alloy, leading to refinement of the grains (mean size: 504 nm) due to their pinning effect on grain boundary immigration. After T6 heat treatment, the CoCrFeNiAl0.3 high entropy alloy demonstrated improved mechanical properties with yield strength of 1335 MPa, ultimate tensile strength of 1346 MPa and an elongation to fracture of 7.9%. With quantitative analysis based on the current models, it was concluded that grain boundary strengthening and Orowan strengthening acted as the dominant strengthening mechanisms.

In this study, the SiC/Al-Zn-Mg-Cu nanocomposites were fabricated using high energy ball milling combined with spark plasma sintering (SPS) and hot extrusion. The microstructure and mechanical properties were investigated by utilizing X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transition electron microscopy (HRTEM) analysis as well as tensile tests. The results showed that the as-extruded SiC/Al-Zn-Mg-Cu nanocomposite samples demonstrated a microstructure consisting of ultrafine α-Al grains, dispersed SiC nanoparticles and nano-scaled T phases probably formed by dynamic precipitation during extrusion. After T6 heat treatment, the coarsening of α-Al grains, dissolution of T phases and consequently the precipitation of fine η′ phases occurred, leading to a simultaneous increase of the strength and ductility. With increasing the content of SiC nanoparticles from 1 vol% to 3 vol%, the yield strength (YS) and ultimate tensile strength (UTS) increased from 456 and 528 MPa to 580 and 588 MPa (27.2% and 11.4% increase), respectively while the elongation to fracture decreased slightly from 11.8% to 10.2% (13.6% decrease). Various strengthening mechanism calculation results show that Orowan strengthening was mostly contributed to the improved strength of the T6 heat treated SiC/Al-Zn-Mg-Cu nanocomposites.

Nickel-based superalloys have been widely used in manufacturing turbine blades, vanes, and discs of aircrafts and power generators that serve in challenging environment. In order to meet the requirements for rapid manufacturing of these large-scale and high-performance components, the extreme high-speed laser metal deposition (EHLMD) technology have attracted great attention in recent years. The EHLMD technology can significantly improve the efficiency compared with conventional laser metal deposition (LMD). Meanwhile, the solidification condition and the resultant microstructures and mechanical properties can also be dramatically changed. In this study, a high chromium superalloy (K648) has been additively manufacturing by using EHLMD for the first time. The key process parameters and the resulted microstructure and mechanical properties are investigated. The results have shown that the most important factors affecting the height, width, and depth of the single-track deposit of EHLMD K648 superalloy are powder feeding rate, laser power, and scanning speed, respectively. The height and the width of the deposits are the largest when the laser power, scanning speed, and the powder feeding rate are 1400 W, 25 m/min, and 30 g/min. There exist some incomplete fusions in the interlayer region and some pores in the interior region of the multi-track-multi-layer deposits. Columnar grains grow in the build direction within each layer, while equiaxed grains tend to form in the interlayer region. The average value of microhardness of EHLMD K648 superalloy is about 298.1 HV. The ultimate strength of EHLMD K648 superalloy is slightly lower than that of the forging GH648 superalloy but higher than that of the conventional LMD K648 superalloy.

Ti–6Al–4V alloys are utilized in various industrial applications. Here, the effect of heat treatment on the microstructural evolution and mechanical properties of the Ti–6Al–4V alloys, which were fabricated by selective laser melting (SLM), was investigated. The as-fabricated-1133 K sample possessed a significantly higher ductility than that of the as-fabricated sample. This was attributed to the precipitation of the micro/nanoscale β and athermal ω phases that was accompanied by the equiaxial transformation of the β columnar grains.

The effects of chromium and vanadium additions on the microstructure, hardness and wear resistance of high-vanadium alloy steel (containing 5–10 wt-% V and 2–10 wt-% Cr) were studied by means of optical microscopy, scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), Vickers hardness and Rockwell-hardness tester & M-200 ring block wear tester. Researching results showed that the solidification structure of high-vanadium wear-resistant alloy steel was mainly consisted α-Fe (martensite), vanadium carbide (VC), M3C and M7C3. Vanadium is mainly distributed over VC, and certain amount of vanadium exists in the matrix and M7C3 type eutectic carbide. Chromium is mainly distributed over the M7C3, and the matrix also contains a small quantity of chromium. It is found that the content of VC increases with the increase of vanadium content when carbon and chromium contents are constant. The change of micro- and macro-hardness was not obvious with the increase of vanadium ...

The Fe-B-Al alloy containing 0 to 10.0 wt.-% Al was melted in a vacuum induction furnace. Effects of the aluminum addition on the microstructure and properties of Fe-B-Al alloys were studied by means of optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), hardness testing and MMG-500 type pin-on-disk high temperature vacuum wear testing. The results showed that the as-casted microstructure of the aluminum-free Fe-B alloy consisted of α-Fe, Fe2(B,C), and Fe23(B,C)6 type borocarbides. However, the as-casted microstructure of the Fe-B-Al alloy consists of a Fe3Al type intermetallic compound when the aluminum content is more than 6.0 wt.-%. Compared with the aluminum-free Fe-B alloy, parts of the borocarbide networks are broken, and the fracture tendency became more obvious with the increase of the aluminum content. Boron is mainly distributed over the borocarbide. Aluminum is mainly distributed over the matrix and Fe3Al type intermetallic compound. Compared with the aluminum-free Fe-B alloy, the addition of a small amount of aluminum reduces slightly the hardness. The hardness gradually increased with the further increasing of the aluminum content. The hardness reached 48.1 HRC when aluminum content was 10.0 wt.-%. The high temperature wear resistance of Fe-B-Al alloy gradually increased with the increase of the aluminum content. When the aluminum content reached 10.0 wt.-%, the high temperature wear resistance of the alloy was the best.

The oxidation behavior of B-bearing high-speed steel was studied at 923[Formula: see text]K. The results showed that the as-cast microstructure of 1.0 wt.%B high-speed steel was composed of pearlite + ferrite + M7(C, B)3+ M2(B, C). When the boron content increased, the microstructure gradually changed into martensite + retained austenite + netlike M2(B, C) + M[Formula: see text](C, B)6+ M7(C, B)3. The cyclic oxidation of B-bearing high-speed steel at K followed parabolic rule. The unit area mass gain of 1 wt.%B high-speed steel was 4.2 g/m2after 923 K/250 h oxidation, and the unit area mass gain of 3 wt.%B high-speed steel was only 3.5 g/m2. The oxidation of boron element formed B2O3, which was mainly enriched at the interface of the oxide film/matrix. B2O3flowed in the oxide film at high temperature and was easy to fill the defect. B2O3was easy to form B2O3-SiO2borosilicate with SiO2. The more boron content was, the more favorable it was to form B2O3-SiO2borosilicate oxide layer rich in B2O3and the more favorable it was to spread in the oxide film, so that the oxidation resistance of B-bearing high-speed steel could be remarkably improved.

Additive manufacturing Ti6Al4V alloys have found their potential applications in artificial teeth and hip joints. In this work, the relationships between wear resistance, hardness and microstructure of Ti6Al4V alloys fabricated using various routes were investigated in artificial saliva. The results indicate that comparing with wrought and wrought + heat treated (HT) samples, the as-SLMed samples with hcp-α′ martensite and few bcc-β phase exhibit higher hardness (∼410 HV) and better wear resistance. The as-SLMed samples, however, exhibit the worst wear resistance when wear direction is parallel to the molten pool line on XOZ-plane due to containing the softer fusion zone. Finally, the wear mechanism is discussed in detail, mainly including the abrasive and adhesive wear mechanism. The high hardness of matrix as well as the strong adhesion between the hardened layer, oxide layer and matrix are indispensable conditions for maintaining the optimum wear resistance.

A high chromium (Cr) superalloy, K648, has been additively fabricated by using laser metal deposition (LMD) for the first time, and the microstructure and mechanical properties of the deposits are investigated. The results show that the main phases of the K648 superalloy are γ-Ni, γ′, α-Cr and M23C6. The microstructure from the bottom to the middle region is mainly composed of epitaxially grown columnar dendrites, and the microstructure in the top region is mainly equiaxed grains. Element segregation exists in the LMD K648 superalloy. The average microhardness of the LMD K648 superalloy is about 220.5HV. The tensile strengths of LMD K648 superalloy show obvious anisotropic characteristics and the maximum ultimate tensile strength is about 833 MPa.

The mould foot roller is a key component of a continuous casting machine. In order to investigate the possibility of using laser cladding to repair mould foot roller, Fe-based powders and 42CrMo steel are used in this work. The laser cladding process parameters were optimized by orthogonal experiments. The chemical compositions, microstructure, properties of the cladding layer under the optimum process parameters, and substrate were systematically investigated by using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), microhardness test, wear test, and salt spray corrosion test. The results indicate that the primary factor affecting the width and depth of the cladding layer is laser power. The scanning speed also has a significant effect on the height of the cladding layer. The optimum process parameters for repairing the mould foot roller are 2 kW laser power, 4 mm/s scanning speed, and 15 g/min feeding rate of powder. Along the depth direction of the cladding layer, the microstructure of the coating gradually transforms from plane crystal, cell grains, or dendrites to equiaxed grains. The matrix is mainly martensite with retained austenite, the eutectic phase is composed of netlike M2B, particulate M23(C,B)6, and M7(C,B)3 phase. The hardness of the cladding layer is significantly improved, about three times that of the substrate. The weight loss of the cladding layer is just half that of the substrate. Its wear resistance and corrosion resistance have been significantly improved. The work period of the laser cladding-repaired foot roller is much longer than for the surfacing welding-repaired one. In summary, laser cladding technology can increase the life of mould foot rollers.

With the rapid development of rail transit, the wear problem of track has become a serious challenge. Laser quenching is a new surface modification process, and it is expected to improve the service life of the track. Laser quenching was carried on the surface of rails by using 6[Formula: see text]kW fiber laser. The microstructure, hardness, wear resistance, and contact fatigue resistance (CFR) of the phase transformation hardening layer were studied by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness tester, and wear tester. The results show that the microstructure of the hardened layer is composed of fine martensite and a small fraction of retained austenite. The microstructure of substrate is pearlite and ferrite. The hardness of rails quenched by the laser increased nearly two times than that of the un-treated track materials. When the laser power is 1000[Formula: see text]W, the depth of hardened layer reaches 0.8[Formula: see text]mm, and the wear resistance of hardened layer increases 167% than that of the substrate. The number, length, and depth of fatigue cracks decreased on the cross-section of worn rails after laser quenching, which indicates that laser quenching can improve the CFR of rails.