Search

Ni60 alloy is one of the important brands of nickel-based self-fusing alloys. It is widely used in industries such as metallurgy, mining, and other fields for the repair and protection of fragile parts. However, there is little literature on the effect of C content on its properties. In this study, two Ni60 alloy coatings with different C contents prepared by flame spraying and remelting were investigated by means of XRD, SEM, EBSD, friction wear testing, thermodynamic calculation, etc. The results showed that the calculated freezing range (FR) of Ni60 decreased from 983-1165.90 °C to 980-1154.28 °C and the melting range (MR) of Ni60 decreased from 966.27-1089.28 °C to 958.91-1045.41 °C when the C content increased from 0.72 wt.% (S1) to 1.01 wt.% (S2). Besides, the Cr7C3 phase size of the Ni60 layer increased with the increase of C addition. The coating shrinks during the remelting and solidification process, and the inner pores do not have sufficient time to escape, caused by the decreased FR, leading to the generation of holes and the degradation of surface quality in S2. However, the hardness of the S2 was 66 HV higher than that of S1, and the wear resistance of the S2 coating was superior as well because of more precipitated carbides therein. This work would give a hint at balancing the processability and mechanical properties for the development of high-performance coatings. [ABSTRACT FROM AUTHOR]

The industry widely uses WC coatings to protect vital machine parts, including industrial gas turbines, ball valves, and aircraft landing gear shafts. To enhance the comprehensive performance of WC-10Co cemented carbide coatings, this study added VC and Cr 3 C 2 grain inhibitors to refine the WC particles. Two novel powder compositions, S1 (WC-10Co-2Cr 3 C 2 -2VC) and S2 (WC-10Co-2VC-2Cr) were developed using the spray granulation method, alongside a commercial WC-10Co-4Cr powder as a control. These coatings were applied to 316 stainless steel substrates using the HVOF technique and subjected to XRD, SEM, hardness, friction, and electrochemical analysis. The microstructures, phase compositions, and various properties of WC-10Co-2Cr 3 C 2 -2VC and WC-10Co-2VC-2Cr coatings were systematically investigated. The results indicate a significant reduction in decarburization and porosity in S1 and S2 coatings compared to the commercial WC-10Co-4Cr coatings. VC and Cr 3 C 2 suppressed the Ostwald ripening phenomenon, leading to smaller WC particle sizes in S1 and S2 coatings. In terms of performance, WC-10Co-2Cr 3 C 2 -2VC exhibited the highest hardness and superior wear resistance, while the WC-10Co-2VC-2Cr coating displayed the lowest corrosion rate in a 5 wt% H 2 SO 4 solution at 25 °C, all while maintaining excellent mechanical properties. This study opens potential directions for the creation of high-performance WC-based coatings. • VC and Cr 3 C 2 suppressed the Ostwald ripening phenomenon, leading to smaller WC particle sizes. • WC-10Co-2Cr 3 C 2 -2VC exhibited the highest hardness and superior wear resistance. • WC-10Co-2VC-2Cr coating displayed the lowest corrosion rate in a 5 wt% H 2 SO 4 solution at 25 °C. [ABSTRACT FROM AUTHOR]

Here we propose to employ electron beam surface melting (EBSM) to refine microstructural length scale and obtain suited microstructure morphology of Nb-Si based alloys. As characterized by scanning transmission electron microscopy (STEM) and atom probe tomography (APT), nano-lamellar eutectics are created in Nb-20Si (at.%) alloys upon EBSM. Theoretical analysis based on the competitive growth models demonstrates the preferred formation of Nb solid solution (Nbss)/Nb 3 Si eutectics under selected processing parameters. The large cooling rate during EBSM, higher than 8 × 104 K/s, promotes the formation of the nano-scale eutectics. Compared to the initial coarse eutectics by arc melting, simultaneous enhancement of hardness and fracture toughness is enabled owing to the controlled microstructural length scale and morphology. Display Omitted • Nano-lamellar eutectics are created by electron beam surface melting. • Theoretical analysis based on the competitive growth models is performed. • Simultaneous enhancement of hardness and fracture toughness is achieved. [ABSTRACT FROM AUTHOR]

The control of solidification microstructure is critical to successful laser processing of single-crystal (SX) nickel-base superalloys and a practical tool for the microstructural control is processing–microstructure maps. However, the maps presented in literature do not consider the effects of powder feeding during laser additive manufacturing (LAM) of SX superalloys. This paper therefore presents a simple and feasible strategy to deal with the effects of powder feeding and to extend the combined numerical model used to calculate processing–microstructure maps. A characteristic ratio of epitaxial SX growth was defined to quantitatively compare the final solidification microstructure. Resulting processing–microstructure maps can estimate the influence of most processing variables, especially powder feeding rate, on the extent of epitaxial SX growth and the position of columnar-to-equiaxed transition. Using the processing parameters selected according to these processing–microstructure maps, a multi-layer SX deposit with fine dendrites was successfully fabricated by LAM. This successful SX LAM indicates that these new processing–microstructure maps involving powder feeding are reliable and useful because they can determine proper processing windows for LAM of SX superalloys and further advance the understanding of the processing–microstructure relationship in powder-feeding LAM process. [ABSTRACT FROM AUTHOR]

Experimental process optimization is essential to obtain reliable processing conditions prior to performing actual laser additive manufacturing (LAM) of single-crystal (SX) nickel-base superalloys. The influence of processing parameters on deposited productivity and epitaxial SX growth in powder-feeding LAM process was systematically investigated by the orthogonal experiment (OE) method, a statistical experiment design method. This method can rapidly and economically estimate the effect of each processing parameter by a small number of experiments. Resulting relationship between the processing variables and each of deposited productivity and microstructure formation contributes to the selection of detailed processing conditions to balance the factors crucial to successful SX LAM, which means that appropriate adjustment of the processing parameters during actual SX LAM is easy to be performed. On the basis of the analyses of the OE results, a combination of relatively high power, low scanning velocity and moderate powder feeding rate is beneficial to both deposited productivity and epitaxial SX growth during powder-feeding LAM, and allows the preparation of good multilayer SX deposits with fine dendrites. [ABSTRACT FROM AUTHOR]

Primary dendritic arm spacing (PDAS) is an important microstructure feature in the nickel-base single-crystal (SX) superalloys by laser rapid directional solidification (LRDS). A combined numerical model was developed in this paper to investigate the influence of laser processing parameters on the PDAS. This model consists of (1) the theoretical PDAS models which relate PDAS to the solidification conditions and (2) the heat-flux calculations of laser processing which provide the solidification conditions as a function of the processing parameters. It is therefore able to immediately relate the PDAS to the processing parameters and obtain corresponding processing–microstructure maps. To verify the predicted accuracy, the PDAS values calculated by different theoretical models were compared with those produced under different processing conditions. Results show that the PDAS firstly decreases and then increases at a lower laser power whereas it decreases with increasing scanning velocity at a higher laser power, leading to nose-shape contour lines. The predicted accuracy depends on appropriate selections of material thermo-physical properties. These processing–microstructure maps can accurately capture the trends of the PDAS variation with the processing parameters and contribute to the control and optimization of dendritic microstructure while determining relevant processing windows for controlled SX laser processing. [ABSTRACT FROM AUTHOR]

Abstract: The compositional variation and the microstructural evolution in laser additive manufactured Ti/Ti–6Al–2Zr–1Mo–1V graded structural material were investigated. An anomalous compositional variation and its good correlation with hardness were found. Although, during the forming process, the ratio of Ti–6Al–2Zr–1Mo–1V in feeded powders abruptly changes from 0% to 100%, all the elements exhibit a gradual variation, which is preferred to a graded material because such gradient change can decrease the discontinuity of its microstructures and properties and can remarkably reduce the costs due to the simplified manufacturing process and the rational distribution of materials. [Copyright &y& Elsevier]

In order to efficiently utilize the agricultural by-products, apricot kernel skins (AKS) and reduce the resource waste, the AKS was added to partially replace the wheat flour to develop the healthy bread in our preliminary study. In this paper, the effects of AKS addition and ultrasound irradiation on the quality properties of bread were investigated by the texture analyzer, confocal laser scanning microscope, electronic nose, tongue and gas chromatography-ion mobility spectrometry (GC-IMS), respectively. The results indicate that the addition of AKS had the negative effects on the microstructure of dough and the texture of fresh bread, but the ultrasonic treatment on the dough could significantly reduce the negative effects. Furthermore, AKS addition slowed the deterioration of the bread texture during chilled storage, and enriched the varieties of volatile organic compounds (VOCs) of bread. In a word, AKS could be employed in novel bread development so as to reduce the resource waste and environmental pollution. • AKS addition influenced the microstructure of dough and the texture of fresh bread. • The ultrasonic treatment on the dough could reduce the negative effects of AKS. • AKS slowed the deterioration of the bread texture during chilled storage. • AKS enriched the varieties of volatile organic compounds of bread. • Potential applications of AKS and ultrasound were identified. [ABSTRACT FROM AUTHOR]

To optimize the toughness and hardness of laser surface‐hardened high‐carbon–chromium (52100) steel, the effect of preheating on microstructure evolution and impact property is studied, and the impact fracture mechanism is analyzed. The results indicate that preheating deepens the hardened depth, facilitating grain coarsening and cementite dissolution near the surface. Regardless of preheating, the size distribution of cementite follows a typical lognormal distribution. Laser surface hardening leads to a decrease in impact absorbed energy. Preheating at 160 °C increases the impact absorbed energy by ≈25%, at which point the maximum hardness is still as high as 860 HV0.3. The impact absorbed energy of spheroidized microstructure tends to be larger before laser hardening and reduces after laser hardening. The impact toughness is the combined result of the brittleness of the hardened layer, residual stress, and substrate microstructure. Under the impact load, microcracks nucleate near the surface of the hardened layer and propagate in the form of intergranular fracture and then propagate in the form of transgranular fracture toward the inside of the hardening layer and substrate. Herein, a novelty research work on optimizing the impact properties during laser hardening through preheating and adjusting initial microstructure is provided. [ABSTRACT FROM AUTHOR]

A large surface-enhanced Raman scattering (SERS) effect is critically dependent on the gap distance of adjacent nanostructures, i.e., “hot spots”. However, the fabrication of dynamically controllable hot spots still remains a remarkable challenge. In the present study, we employed an external magnetic field to dynamically control the interparticle spacing of a two-dimensional monolayer film of Fe 3 O 4 @Au nanoparticles at a hexane/water interface. SERS measurements were performed to monitor the expansion and shrinkage of the nanoparticles gaps, which produced an obvious effect on SERS activities. The balance between the electrostatic repulsive force, surface tension, and magnetic attractive force allowed observation of the magnetic-field-responsive SERS effect. Upon introduction of an external magnetic field, a very weak SERS signal appeared initially, indicating weak enhancement due to a monolayer film with large interparticle spacing. The SERS intensity reached maximum after 5 s and thereafter remained almost unchanged. The results indicated that the observed variations in SERS intensities were fully reversible after removal of the external magnetic field. The reduction of interparticle spacing in response to a magnetic field resulted in about one order of magnitude of SERS enhancement. The combined use of the monolayer film and external magnetic field could be developed as a strategy to construct hot spots both for practical application of SERS and theoretical simulation of enhancement mechanisms. [ABSTRACT FROM AUTHOR]

High-efficiency gas turbines require high-temperature sealing by use of abradable porous ceramic coatings to increase engine efficiency. In this study, porous AlO coatings were deposited by flame spraying; the coatings were applied in a semi-molten state by controlled melting of the sprayed powder particles. The effects of the degree of melting of the sprayed particles, which depends on spraying conditions, on coating microstructure and porosity were investigated. The degree of melting of the sprayed particles was characterized by use of 3D confocal laser microscopy. The porosity of the coating was estimated by image analysis. The results showed that the degree of melting of alumina particles can be changed from 70 to 30%, and thus coating porosity can be increased from 30% up to over 70%. The standard hardness test yielded no useful data for porous coatings deposited by use of sprayed particles with a degree of melting <60%, and a hardness of 32-75 HR15Y for AlO coatings deposited by use of sprayed particles with a degree of melting >60%. Pin-on-disk abrasion tests, performed at room temperature by use of an Inconel 738 (IN738) nickel-based superalloy pin with a spherical tip 5 mm in diameter, were conducted on the porous alumina coating to evaluate its abrasion behavior. It was found that for coatings of hardness <32 HR15Y and porosity >40% the wear weight loss of the IN738 pin was negligible despite the high rate of wear of the coating. It is evident that flame-sprayed porous alumina coatings of high porosity prepared by this approach have potential for use as abradable coatings for gas turbines operating at high temperatures. [ABSTRACT FROM AUTHOR]

In this study, porous molybdenum (Mo) was prepared by flame spraying of semi-molten particles with low velocity. The influence of spray particle parameters, including velocity and melting degree, on the microstructure and porosity of Mo deposit was investigated to understand the formation mechanism of the pore structure and connection between particles. The results showed that Mo spray particles with low velocity (<20 m/s) and semi-molten state can be generated by flame spraying. The Mo deposits with porosity from 39 to 61% were produced. High porosity in the deposit was achieved through the shielding effect of deposited particles. The surface-molten particles were bonded by the melt which flowed from surface to the particle/particle contact area. Moreover, the porosity decreased with the increase of melting degree of particles before impact. A 2D stacking model of semi-molten particles was proposed to explain the formation of bimodal pores and high porosity. [ABSTRACT FROM AUTHOR]

Laser surface quenching was conducted on the 1.0C-1.5Cr steel with different initial microstructures. The effects of initial microstructure on the cementite dissolution and grain size were studied, and the distributions of temperature and stress were simulated. The results indicated that the thickness of hardened layer was larger when the initial microstructure is martensite, which is mainly because the martensite-to-austenite transformation is displacive transformation during laser heating. Within hardened layer, the volume fraction of cementite (VFC) increases with the increase of depth. For the initial microstructure composed of ferrite matrix and cementite, the refining of cementite will facilitate its dissolution, and within hardened layer, mean diameter of cementite (MDC) decreases first and then increases with the increase of depth. For the initial microstructure composed of martensite matrix and cementite, the MDC changes slightly at deeper position of hardened layer. Tensile stress will form in the heat affect zone, and due to the high sensitivity to tensile stress, the impact resistance and bending properties of spheroidized microstructure are worse after laser surface quenching. Under identical laser parameters, the impact absorbed energy of spheroidized microstructure is about 50% of tempered sorbite and 60% of martensitic microstructure, and its bending strength is about 60% of tempered sorbite, and 40% of martensitic microstructure. The impact absorbed energy can be increased by at least 26% through preheating at 160 °C. In addition, the refining of initial martensitic microstructure will enhance bending resistance. [ABSTRACT FROM AUTHOR]

The 1.0C-1.5Cr steel was subjected to conventional quenching and laser surface quenching treatment. A process combing double quenching and laser surface quenching was proposed for enhancing surface hardness and obtaining finer microstructure. The cementite dissolution and grain growth behavior in the austenitizing process of single quenching, double quenching, and laser surface quenching were studied. The results indicated that compared with single quenching, mean diameter of undissolved cementite particles (UCP) was much finer in double quenching, and the final prior austenite grain size (PAGS) could be decreased by nearly 40% to about 4.5 μm. Both grain and cementite particles near the surface will coarsen after laser surface treatment. Compared with single quenching, the PAGS within hardened layer can be decreased by at least 11% through double quenching, and the mean diameter of UCP at the bottom of hardened layer can be decreased by about 20%. Compared with conventional quenching, surface hardness was enhanced by about 20% through laser surface quenching, contributing to the wear resistance. However, the hard and brittle surface layer tends to be crack source during the impact process, leading to the deterioration of final impact toughness. Under the identical laser parameters, the impact absorbed energy is similar in both single and double quenching, which is about 25% of that before laser surface quenching. The impact absorbed energy can be increased from 22J to 28J by preheating at 160 °C during the laser surface quenching. [ABSTRACT FROM AUTHOR]