A nearly fully dense grade 300 maraging steel was fabricated by selective laser melting (SLM) additive manufacturing with optimum laser parameters. Different heat treatments were elaborately applied ...based on the detected phase transformation temperatures. Microstructures, precipitation characteristics, residual stress and properties of the as-fabricated and heat-treated SLM parts were systematically characterized and analyzed. The observed submicron grain size (0.31 μm on average) suggests an extremely high cooling rate up to 10
7
K/s. Massive needle-shaped nanoprecipitates Ni
3
X (X = Ti, Al, Mo) are clearly present in the martensitic matrix, which accounts for the age hardening. The interfacial relations between the precipitate and matrix are revealed by electron microscopy and illustrated in detail. Strengthening mechanism is explained by Orowan bowing mechanism and coherency strain hardening. Building orientation-based mechanical anisotropy, caused by 'layer-wise effect', is also investigated in as-fabricated and heat-treated specimens. The findings reveal that heat treatments not only induce strengthening, but also significantly relieve the residual stress and slightly eliminate the mechanical anisotropy. In addition, comprehensive performance in terms of Charpy impact test, tribological performance, as well as corrosion resistance of the as-fabricated and heat-treated parts are characterized and systematically investigated in comparison with traditionally produced maraging steels as guidance for industry applications.
High-performance grade 300 maraging steels were fabricated by selective laser melting (SLM) and different heat treatments were applied for improving their mechanical properties. The microstructural ...evolutions, nanoprecipitation behaviors and mechanical properties of the as-fabricated and heat-treated SLM parts were carefully characterized and analysed. The evolutions of the massive submicron sized cellular and elongated acicular microstructures are illustrated and theoretically explained. Nanoprecipitates triggered by intrinsic heat treatment and amorphous phases in as-fabricated specimens are observed by TEM. High-resolution TEM (HRTEM) images of the age hardened specimens clearly exhibit massive nanosized needle-shaped nanoprecipitates Ni3X (X=Ti, Al, Mo) and 50–60nm sized spherical core-shell structural nanoparticles embedded in amorphous matrix. XRD analyses reveal austenite reversion and probable phase transformations during heat treatments. The hardness and tensile strength of the as-fabricated and age-treated SLM specimens absolutely meet the standard wrought requirements. Furthermore, the lost ductility after aging can be compensated by preposed solution treatments. Relationships between massive nanoprecipitates and dramatically improved mechanical performances of age hardened specimens are elaborately analysed and perfectly explained by Orowan mechanism. This study demonstrates that high-performance grade 300 maraging steels, which is comparable to the standard wrought levels, can be produced by SLM additive manufacturing.
Display omitted
•Evolutions of the typical SLMed microstructures are illustrated and theoretically explained.•Precipitation behavior and phase transformation of SLMed maraging steel are characterized by TEM and XRD.•Significant improvement of strength after solution and aging treatment was evaluated and explained.•Relationships between massive nanoprecipitates and improved mechanical performances are elucidated.
•A new approach of processing W-Cu FGM by SLM additive manufacture is explored.•Effects of laser parameter on the performance of W-Cu FGM are investigated.•Intense Marangoni convection contributes to ...interfacial bonding.
A tungsten-copper functionally graded material was processed based on SLM additive manufacture despite encountering some difficulties from materials characters. The effect of laser parameter on the interfacial defects and bonding performance are evaluated. The SLM produced tungsten is in columnar structures with random orientation. Plenty of fine tungsten grains are present at the bonding region, owing to a high cooling rate incited by the underlying copper. A metallurgically bonded interface with a 50–80 μm inter-diffusion region is formed. The interfacial bonding mechanism, which associates with intense Marangoni convection at the interface, is revealed and discussed.
Selective laser melting (SLM) additive manufacturing of pure tungsten encounters nearly all intractable difficulties of SLM metals fields due to its intrinsic properties. The key factors, including ...powder characteristics, layer thickness, and laser parameters of SLM high density tungsten are elucidated and discussed in detail. The main parameters were designed from theoretical calculations prior to the SLM process and experimentally optimized. Pure tungsten products with a density of 19.01 g/cm
3
(98.50% theoretical density) were produced using SLM with the optimized processing parameters. A high density microstructure is formed without significant balling or macrocracks. The formation mechanisms for pores and the densification behaviors are systematically elucidated. Electron backscattered diffraction analysis confirms that the columnar grains stretch across several layers and parallel to the maximum temperature gradient, which can ensure good bonding between the layers. The mechanical properties of the SLM-produced tungsten are comparable to that produced by the conventional fabrication methods, with hardness values exceeding 460 HV
0.05
and an ultimate compressive strength of about 1 GPa. This finding offers new potential applications of refractory metals in additive manufacturing.
Plasma nitriding and plasma-assisted PVD duplex treatment was adopted to improve the load-bearing capacity, fatigue resistance and adhesion of the AlTiN coating. Ion etch-cleaning was applied for ...better adhesion before plasma nitriding. After plasma nitriding Ti interlayer was in-situ deposited by high power impulse magnetron sputtering (HIPIMS), followed by the AlTiN coating through in-situ deposition by advanced plasma-assisted arc (APA-Arc). The microstructure and properties of the duplex-treated coating were carefully characterized and analyzed. The results show that the thicknesses of the nitriding zone, the γ′-Fe4N compound layer, the Ti interlayer and the AlTiN top layer with nanocrystalline microstructures are about 60μm, 2–3μm, 100nm and 6.1μm, respectively. The nitriding rate is about 30μm/h and the AlTiN coating deposition rate reaches 6.1μm/h. The interfacial adhesion of the Ti/AlTiN coating is well enhanced by ion etch-cleaning and a Ti interlayer, and the load-bearing capacity is also improved by duplex treatment. In addition, the instinct hardness of the Ti/AlTiN coating reaches 3368HV0.05 while the wear rate coefficient of 5.394×10−8mm−3/Nm is sufficiently low. The Ti/AlTiN coating, which possesses a high corrosion potential (Ecorr=−104.6mV) and a low corrosion current density (icorr=4.769μA/cm2), shows highly protective efficiency to the substrate.
► Copper plate. ► Sodium hydroxide and potassium persulfate solution treatment. ► Crystallized Cu(OH)
2 nanoneedles formed. ► Surface self-assembly with dodecanoic acid. ► Superhydrophobic with water ...contact angle 153̊.
Biomimic superhydrophobic surfaces with contact angle greater than 150° and low sliding angle on copper substrate were fabricated by means of a facile solution immersion and surface self-assembly method. The scanning electron microscopy showed a nanoneedle structure copper surface with sporadic flower-like aggregates after treatment with sodium hydroxide and potassium persulfate solution. X-ray photoelectron spectroscopy and X-ray diffraction results confirmed that the formed nanoneedles were crystallized Cu(OH)
2. And the hydrophilic Cu(OH)
2 surface can be further modified into superhydrophobic through surface self-assembly with dodecanoic acid.
Due to various difficult-to-machine materials and increasingly severe machining conditions, more and more attention has been paid to the physical vapor deposition (PVD) technology in recent decades ...to deposit hard coatings on cutting tools. Combined with the status of industrial application of PVD technology, this paper reviews the main PVD techniques for coated cutting tools from the perspective of the overall PVD coating equipment, including cathodic arc evaporation and magnetron sputtering as well as their hybrid techniques, and the plasma etching which is critical for coating adhesion strength is also involved. With regard to hard coating deposition on cutting tools, the basic principle, cathode configuration, magnetron and power supply are outlined. Issues related to target ionization ratio, coating deposition rate, coating properties and industrial application of numerous PVD techniques are also highlighted. On plasma etching, inert gas ion etching and metal ions etching are discussed. Finally, this paper summarizes and prospects the PVD technology used for coated cutting tools.
Al-based amorphous-nanocrystalline composite coatings were prepared by laser cladding Al95-xCuxZn5 (x = 5, 10, 15, at.%) powders on AZ80 magnesium alloy under a low-temperature water cooling ...condition. The microstructural observations indicate that all the cladding layers exhibit good metallurgical bonding to the substrates while the morphology of the cladding layer varies with the Cu content. The microstructure and properties of the Al85Cu10Zn5 (x = 10, at.%) coating and the substrate were carefully characterized and analyzed. The XRD analysis and TEM observations show that the Al85Cu10Zn5 cladding layer is constituted of amorphous phase, nanocrystallines and ternary intermetallics Mg32Al47Cu7, τ-Mg32(Al,Zn)49, AlMg4Zn11 and S-Al2CuMg. The surface performances of the AZ80 substrate are greatly improved by the Al85Cu10Zn5 cladding layer. The average hardness of the Al85Cu10Zn5 layer is 364 HV0.05, which is about 4 times higher than that of the substrate (∼86 HV0.05), and the relative wear resistance of the Al85Cu10Zn5 cladding layer is 5.5 times better than that of the substrate. Meanwhile, the corrosion potential (Ecorr) is increased by 276.2 mV and the corrosion current density (Icorr) is decreased by two orders of magnitude. In addition, the reasons accounting for the improvements of the mechanical properties and corrosion resistance are elucidated accordingly.
•Novel Al-Cu-Zn amorphous-nanocrystalline composite cladding layers are obtained.•Al85Cu10Zn5 laser cladded specimen has the highest GFA and excellent properties.•Detail microstructural information is determined by XRD, SEM and TEM.•Comprehensive properties of AZ80 Mg alloy are substantially enhanced.•Reasons for improved characteristics are detailedly elucidated.
The relation of microstructure and mechanical property in cathodic arc evaporated (CAE) Cr33Al67N coatings have not yet been fully understood despite their extensive applications. In this work, we ...prepared Cr33Al67N coatings using CAE, a more industrially favored technique. The as-deposited coatings show superhardness (41 GPa), superior fracture resistance, adhesion strength and high compressive stress (6.3 GPa). Phase and bonding analyses show that the coatings comprise single fcc-solid solution structure with (111) orientation. Transmission electron microscope investigation revealed a microstructure evolution of the coatings: columnar grains with a diameter of 20–40 nm ripen from nano-composite structure with grain diameter of about 6 nm. The resulting densification of grain boundary (GB) facilitates growth of compressive stress, confirming the GB adatom pinning mechanism. Compressive stress plays a significant role in the concomitant hardening and toughening of the coatings by impeding grain boundary glide. Hall-Petch effect and low-angle grain boundary also contribute to the hardening-toughening. These findings reveal the relation of structural mechanism between hardening and toughening in PVD nitride coatings, and supplement the measures to tune microstructure towards superhard yet tough coatings.
Display omitted
•Cr33Al67N coatings fabricated by cathodic arc evaporation are solid solutions.•The coatings have high hardness and toughness, as well as compressive stress.•High compressive stress facilitates the formation of low-angle grain boundaries and (111) orientation.•Compressive stress and low-angle grain boundary jointly contribute to the combination of high hardness and toughness.
In this article, we demonstrate that carbon nanostructures could be synthesized on the Ni-plated YG6 (WC-6 wt% Co) hardmetal substrate by a simple ethanol diffusion flame method. The morphologies and ...microstructures of the Ni-plated layer and the carbon nanostructures were examined by various techniques including scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. The growth mechanism of such carbon nanostructures is discussed. This work may provide a strategy to improve the performance of hardmetal products and thus to widen their potential applications.
PDF
