Search

In order to refine the microstructure and improve the performance of direct energy deposited (DED) additively manufactured Al–Mg–Sc–Zr alloy, TiC-modified Al–Mg–Sc–Zr composites were prepared by DED and the effect of TiC content on the microstructure and performance was studied. In the absence of TiC particle, the microstructure of Al–Mg–Sc–Zr alloy prepared by DED consisted of fine grains with average size of 8.36 μm, and well-dispersed nano-Al3(Sc,Zr) particles inside the grains and Mg2Si phase along the grain boundaries. With the addition of 1 wt% TiC, the microstructure of TiC/Al–Mg–Sc–Zr prepared by DED became finer apparently compared with that without TiC; while the further increase of TiC content to 3 wt%, the microstructure of TiC/Al–Mg–Sc–Zr prepared by DED became coarser with appearance of a new kind of needle-like (Ti,Zr)5Si3 phase. Also, the addition of TiC decreased the porosity of Al–Mg–Sc–Zr prepared by DED. Simultaneously, after the addition of TiC, the tensile strength increased from 283.25 MPa to 344.98–361.51 MPa, and the elongation increased from 3.61% to 9.58–14.10%. The potential mechanism of the microstructure evolution and strength improvement was discussed. This research will provide new insights into the available metal matrix composites by laser additive manufacturing (LAM).

Selective laser melting (SLM) of aluminium alloys for lightweight application is arousing widespread interest, but the available alloy compositions are limited due to unsatisfactory mechanical performances. The rapid solidification of SLM provides a pathway to design a novel alloy composition with extended solubility. This strategy is demonstrated by an additively manufactured novel Al–2.51Mn–2.71Mg–0.55Sc–0.29Cu–0.31Zn alloy with the supersaturated solid solution in the present study. The microstructure of as-build sample is characterized with multi-modal grains with the fine equiaxed grain (FEG, ~ 800 nm) at molten pool boundaries, coarse equiaxed grain (CEG, ~ 2 μm) and columnar dendrites (CD, ~ 4 μm) inside the molten pool, which relates to the precipitations type and distribution. It is observable that Al3(Sc, Zr) precipitation particles with the size of ~ 50 nm are dispersed in the FEG zone, while the interior of CEG shows no Al3(Sc, Zr) particle which only exists at the CEG boundaries. Regardless of FEG, CEG or CD, the slender Al6Mn precipitation with the length of ~ 500 nm is distributed along the grain boundaries. Meanwhile, a lot of vacancies and thickness fringes are detected in the FEG zone, which confirms the supersaturated solid solution in laser rapid solidification. The ultimate tensile strength and yield strength of the as-printed sample are ~ 380 MPa and ~ 330 MPa, respectively, with elongation ~ 14%, which increase to ~ 440 MPa and ~ 410 MPa with a reduction of elongation to ~ 9% after heat treatment.

In this work, a near-beta Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy was fabricated by selective laser melting (SLM), and the microstructure evolution together with the mechanical properties was studied. The as-fabricated alloy showed columnar β grains spreading over multiple layers and paralleling to the building direction. The distinct microstructure of as-fabricated alloy was composed of near-β (more than 98.1 %) with a submicron cellular structure. Different SLM processing parameters such as hatch spacing could affect the microstructure of as-fabricated alloy, which could thus further significantly affect the mechanical properties of as-fabricated alloy. In addition, the as-fabricated alloy with the distinct microstructure exhibits yield strength of 818 MPa combined with elongation of more than 19 %, which shows that SLM is a potential technology for manufacturing near-beta titanium components.

NiTi shape memory alloy (SMA) with nominal composition of Ni 50.8 at% and Ti 49.2 at% was additively manufactured (AM) by selective laser melting (SLM) and laser directed energy deposition (DED) for a comparison study, with emphasis on its phase composition, microstructure, mechanical property and deformation mechanism. The results show that the yield strength and ductility obtained by SLM are 100 MPa and 8%, respectively, which are remarkably different from DED result with 700 MPa and 2%. The load path of SLM sample presents shape memory effect, corresponding to martensite phase detected by XRD; while the load path of DED presents pseudo-elasticity with austenite phase. In SLM sample, fine grain and hole provide a uniform deformation during tensile test, resulting in a better elongation. Furthermore, the nonequilibrium solidification was studied by a temperature field simulation to understand the difference of the two 3D printing methods. Both temperature gradient G and growth rate R determine the microstructure and phase in the SLM sample and DED sample, which leads to similar grain morphologies because of similar G/R. While higher G×R of SLM leads to a finer grain size in SLM sample, providing enough driving force for martensite transition and subsequently changing texture compared to DED sample.

Al7075 alloy is a typical aviation aluminum with good mechanical properties and anodic oxidation effect. Laser engineered net shaping technology has unique advantages in the integrated forming of high-performance large aircraft structural parts. The manufacturing of 7075 aluminum alloy structural parts by laser engineered net shaping technology has become an important development direction in the future aerospace field. Electrochemical corrosion resistance of aluminum alloys is of vital importance to improve reliability and life-span of lightweight components. A comparative study on microstructure and anti-corrosion performance of Al7075 alloy prepared by laser additive manufacturing and forging technology was conducted. There are hole defects in LENS-fabricated Al7075 alloy with uniformly distributed η phase. No defects are observed in Al7075 forgings. The large S phase particles and small ellipsoidal η phase particles are found in Al matrix. The corrosion mechanisms were revealed according to the analysis of polarization curves and corrosion morphology. It was found that compared with that prepared by forgings, the additive manufactured samples have lower corrosion tendency and higher corrosion rate. Corrosion occurred preferentially at the hole defects. The incomplete passivation film at the defects leads to the formation of a local cell composed of the internal Al, corrosion solution and the surrounding passive film, which further aggravates the corrosion.

Additive manufacturing of an equimolar CoCrNi medium entropy alloy (MEA) by selective laser melting (SLM) was investigated, emphasizing its microstructure, properties, and metallurgical defects. It was found that SLM sample density exhibited a non-monotonic relation with their volume energy density (VED); the density first increased but then decreased while the input VED was gradually increasing. A maximal relative density of 98.9 pct was accessible at a VED of 83.3 J/mm3. X-ray diffraction indicated that the printed CoCrNi MEA exhibited an FCC single-crystal structure where the lattice constant decreased with the increasing VED owing to the evaporation of the Cr element in the SLM process. The average grain size gradually increased with increasing VED, irrespective of whether viewed from the top or the side of the printed part. Similarly, the residual stress increased with increasing VED, which produced more microcracks and deteriorated the tensile preformation of the printed samples, although the yield strength (630 MPa) showed no apparent difference at different VEDs. Owing to the ultrafine cell structure, the mechanical property of the SLM printed sample was twice that of cast or wrought CoCrNi MEA.

With the rapid development of indium tin oxide (ITO) in the electronic display industry, choosing which raw powders to prepare high-quality ITO targets has always been a controversial topic. In the work, in order to clearly understand the effect of the raw powders on the microstructure and properties of ITO targets and thin films, tin-doped indium oxide (dITO) and In2O3-SnO2 mixed (mITO) powders were chosen to prepare ITO targets for depositing the films and a comparative study on their microstructure and properties was conducted. It is found that, (1) dITO targets possess a higher solid solubility of tin in indium oxide and more uniform elemental distribution, while there are a higher density, a finer grain size and a higher mass ratio of In2O3 to SnO2 for the mITO targets; (2) dITO films with more coarser columnar grains and a rougher surface prefer to grow along the [100] direction in an Ar atmosphere; (3) the conductive property of ITO films only depends on the doping amount of tin and is independent of the raw powders and the preparation process of the target source; (4) dITO films possess the superior optical property and narrower optical band gap; (5) the etching property of mITO films is superior to that of dITO films due to the lower solid solubility of tin in indium oxide.

To develop high-strength Al alloys for selective laser melting (SLM) additive manufacturing, we designed a series of Al-Mg(-Si)-Sc-Zr alloys and additively manufactured them using atomized alloy powders. In the absence of Si, the developed Al-xMg-0.2Sc-0.1Zr (x = 1.5, 3.0 and 6.0 wt%) alloys are all susceptible to hot cracking and the average crack density increases with increasing Mg content. The addition of 1.3 wt% Si into the Al-6Mg-0.2Sc-0.1Zr alloys effectively inhibits hot cracking during SLM and simultaneously refines the microstructure, and thus leading to enhanced mechanical properties in the as-printed samples. By further fine-tuning the alloy compositions, we designed a new alloy Al-8.0Mg-1.3Si-0.5Mn-0.5Sc-0.3Zr. This new alloy demonstrates significantly refined microstructure consisting of submicron cells with coherent Al3(Sc,Zr) nano-particle (2–15 nm) residing in the cell and intergranular Al-Mg2Si eutectic (Mg2Si diameter 10–100 nm). High-density stacking faults and a unique 9R phase are formed in the as-printed sample. The tensile strength and elongation of the as-printed sample are up to 497 MPa and 11%, respectively. After the aging treatment, the tensile strength reaches 550 MPa, while the ductility ranges from 8% to 17%, depending on the aging conditions. In addition to solid solution strengthening, grain boundary strengthening and nanoparticle strengthening, the high-density stacking faults also contributes to strengthening.

The surface of copper-chromium alloy was processed by Al-Si-Ni multi-permeation and friction stir processing, and the microstructure and mechanical properties of the surface layer were tested by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), microhardness tester and friction testing machine. The results show that Al, Si and Ni elements are fully permeated into the surface of copper-chromium alloy after multielement co-infiltration and friction stir processing. In the observation of the microstructures, we found that the reticular structure is fragmented and distributed in the stir zone region. Microstructure becomes finer and grains refinement. The micro hardness of the copper-chromium alloy increased to 129 HV, 44.9% higher than that of the original matrix. The main reasons of microhardness enhancement are solid solution strengthening, fine grains strengthening and dispersion strengthening. The friction test results show that the friction coefficient is basically stable at 0.69 and the wear mass is only 0.0017 g after 10 min of friction test. The improvement of wear resistance was attributed to the increase of microhardness of the alloy surface. Keywords: Copper-chromium alloy, Al-Si-Ni multi-permeation, Friction stir processing, Microstructure, Mechanical properties

Spark plasma sintering (SPS), as a novel powder consolidation method, has great potential in the production of high entropy alloys (HEAs). The heating rate is an important parameter in SPS, and understanding its effect is a critical issue for the purpose to optimize microstructure and promote mechanical properties of HEAs. The AlCoCrFeNi was adopted as a representative HEA in this study. The phase compositions, microstructural textures, and mechanical properties were investigated in this study in detail. It was found that the FCC phase formed at BCC grain boundaries while the σ phase precipitated at the interface of B2/BCC no matter of the heating rate. The texture varied at different heating rates as the texture {110} in B2/BCC was characterized at the heating rate of 150 °C/min while the complex texture {051} in FCC was observed at the heating rate of 200 °C/min. The Vickers hardness and wear resistance decreased with increasing of the heating rate. Furthermore, the compressive strength and corresponding plastic strain reached their highest 2752.0 ± 48 MPa and 26.5 ± 1.3% at the heating rate of 150 °C/min.

In the study, 0–2.0 wt% cerium oxides (CeO2) were employed to enhance the densification and properties of indium tin oxide (ITO) targets. The effects of CeO2 on the phase composition, microstructure, resistivity and fracture strength of ITO targets and the photoelectric properties of the films were investigated in detail. Experimental results show that the optimum doping amount of CeO2 is 0.5 wt%. The functions of CeO2 doping are: (1) Lowering the sintering temperature by nearly 60 °C, which is attributed to the inhibition of the decomposition of In2O3 and SnO2; (2) Refining the grain size and promoting the formation of In4Sn3O12 phase; (3) As the donor dopant to reduce the resistivity of ITO targets and strengthening the inter-facial bonding force so as to enhance the fracture strength of ITO targets; (4) Intensifying the disorder of film non-crystals, improving the surface morphology and enhancing the transmittance.

Large microstructure gradients in high-power-density welding usually have negative effects on the mechanical properties of weld joints. In this paper, we found that the width of the weld microstructure in transition region was widened (from 65 μm to 140 μm) by applying a static axial magnetic field of 415 mT on the welding process, which efficiently improved the microstructure gradient. Based on our robust comprehensive model, we quantitatively predicted the distributions of thermoelectric currents (TEC) and thermo-electromagnetic force (TEMF) near the liquid-solid (L–S) interface. The three-dimensional annular TEC can reach about 3.0 × 106 A/m2 near the L–S interface. The TEMF vertical to the L–S interface with applying a magnetic field of 415 mT on welding process can reach 1.0 × 106 N/m3 or even larger, which could influence the fluid flow in weld pool and finally the weld microstructure. Furthermore, an intensive parameter of TEMF R T i (a dimensionless ratio) was proposed to estimate the effect of TEMF on the weld microstructure and the estimated results obtained good agreements with experimental data. Using this method, the critical value of the applied magnetic field which can cause the weld microstructure improvement in transition region obviously was predicted to be about 150 mT. Our findings and method can be served as guidance or reference for weld microstructure and joint quality optimization in laser welding process.

Whether selective laser melting (SLM) printed AlMgScZrMn alloy possesses more excellent performances than other processing routes was unknown. In the study, the microstructures and mechanical properties of AlMgScZrMn alloys fabricated by selective laser melting (SLM), spark plasma sintering (SPS) and cast were comparatively investigated. SLM printed sample shows columnar and equiaxed duplex grains with average grain size about 7 μm, which is coarser than SPS consolidated sample with finest equiaxed grain (4 μm) but smaller than casting sample with coarse equiaxed grain (25 μm). SLM printed sample shows the highest tensile strength (394 ± 5 MPa) and elongation (10.5 ± 1.2%) than SPS sample (231 ± 3 MPa, 0.59 ± 0.21%) and cast sample (188 ± 2.3 MPa, 3.7 ± 0.58%), although SPS sample has the finest equiaxed grains. For SPS sample, previous particle boundary (PPB) with oxide inclusion significantly deteriorates ductility. For cast sample, the coarse equiaxed grain with intergranular eutectic leads to inferior strength. In addition, the average dimension of Al3(Sc,Zr) particle in SLM sample is about 1–10 nm, which is much finer than SPS sample (0.5–0.8 μm) and cast sample (1–2 μm). The present study will provide a basis for the future industrial applications of the AlMgScZrMn alloy.

The effect of the volumetric energy density (VED) on the keyhole formation, microstructural evolution and associated mechanical properties of AlSi10Mg fabricated by selective laser melting (SLM) has been systematically investigated. The results indicated that three melting modes could be distinguished during the laser melting process, corresponding to different VED ranges, i.e. conduction mode (65 J mm-3). A high VED not only produced keyhole defects and hydrogen pores, but also generated two types of molten pool, i.e. a general shallow molten pool (GSP) and a keyhole-induced deep molten pool (KDP). The GSP was mainly consisted of an α-Al matrix, with ~30 µm grains size, and enclosed by a ~500 nm eutectic Si cellular network. The grain size of the KDP was less than 15 µm, and it has both a finer Si network (~200 nm) and nano-scale Si particles. No preferential crystallographic orientation could be observed within the KDP, while a strong texture alongorientation was exhibited in the GSP. These were responsible for the different mechanical properties of the SLM parts under different melting modes. The related mechanisms of the GSP and the KDP formation are comprehensively discussed and a correlation between the microstructure and the mechanical properties is also outlined.

Ti-23Nb (at.%) coatings on an NiTi alloy with metallurgical bonding were prepared by laser cladding (LC) technology using Ti-Nb mixture powders. The effects of laser processing parameters on the microstructure and mechanical properties of the coatings were systematically investigated and the corrosion resistance of the coatings was assessed. The coatings were composed of TiNb, (Ti, Nb)2Ni, and β-Nb phases. The coatings increased the hardness of the NiTi alloy by a combined strengthening effect of the eutectics and fine microstructure. The corrosion resistance of the coated part was improved. The coatings with great corrosion resistance could keep the coated parts inert in an aggressive environment, and effectively restrain the release of toxic Ni ions, which means that the Ti-Nb alloy coatings are likely to be used as a biomaterial for medical applications.

The corrosion behavior of the Fe50Mn30Co10Cr10 high-entropy alloy (HEA) manufactured via laser melting deposition (LMD) was investigated using open circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy measurements. The microstructure and morphology of LMD samples before and after the electrochemical tests were compared using X-ray diffraction, optical microscopy, scanning electron microscopy, and electron backscatter diffraction techniques. After the corrosion tests, a striped morphology was observed on the surface of the LMD HEA, which is mainly caused by the interval distribution of high-density and low-density grain-boundary regions. The corrosion performances varied with different planes of the LMD HEA sample, which is mainly controlled by the grain size at each plane. Local corrosion in this HEA is concentrated at the melt pool boundary, which may be due to the abundant metallurgical defects and stress concentration at this location.

Owing to its high specific strength and low density, Al&ndash, Cu alloys have been extensively used in aerospace for lightweight components. Additive manufacturing techniques such as selective laser melting, which offers geometric freedom, is suitable for topology-optimized designs. In this study, the effect of processing parameters on the densification, microstructure, and mechanical properties of additively manufactured Al&ndash, Cu alloy 2124 by selective laser melting was investigated. Parameters such as laser power, scanning speed, hatch spacing, and use of a support were studied. The results revealed that a grille support with a hollow structure played a resistant role in the transfer of heat to the base plate, thus reducing the temperature gradient and lessening cracks in the building part. Smaller hatch spacing was beneficial for the achievement of a higher relative density and strength due to track re-melting and liquid phase backflow, which could fill cracks and pores during the building process. An ultimate tensile strength as high as 300 MPa of the vertically built sample was obtained at optimized processing parameters, while the elongation was relatively limited. Moreover, columnar grains were found to be responsible for the anisotropy of the mechanical properties of the as-printed 2124 alloy.

The poor ductility of the selective laser melting (SLM)-fabricated parts may lead to the limitation of its applications. Therefore, in the present work, four types of post heat treatments of SLM-proceeded Ti-13Nb-13Zr were performed to tailor the microstructure and mechanical performances. In the super-transus heat treatment, the morphologies of grains are transformed from columnar to equiaxed because of the strain-induced grain boundary migration mechanism (SIBM), while in the sub-transus process, the columnar β grains are remained. In the water quenching process, high resolution transmission electron microscopy analysis revealed that the collapse of the partial layers in the (110) planes and [111] direction results in the original stacking sequence from …ABCABC… to a new stacking sequence …AB’AB’… and an w structure is formed, resulting in the highest ultimate (1155 ± 30 MPa), yield strength (874 ± 30 MPa) and unfortunately the lowest ductility (2.3 ± 0.2%). In the air cooling process, as the heat temperature declines from 750 °C to 650 °C, the electron back-scattered diffraction results show that the coarse and irregular α grains with strong {0001} and {2 11 ¯ 0} orientations are gradually transformed into fine acicular α crystals with the dominated {0001} orientation. In this condition, the residual stresses were released and the fine microstructure was largely retained, thus the high yield strength is maintained (799 ± 10 MPa) and the ductility is improved (7.2 ± 0.3%).

Ti-13Nb-13Zr alloy was fabricated by selective laser melting (SLM), and the densification, microstructure evolution, nanohardness, tensile strength and fatigue behavior of the alloy were systematically investigated. A narrow, feasible process window (laser power 325 W, scanning speed 1000 mm/s, scanning distance 0.13 mm, and layer thickness 0.03 mm) was accordingly determined. With the increase of scanning speed, the coarse acicular-shaped α′ grains changed to refined acicular-shaped α′ grains and then defect formed in the microstructure. The optimally prepared Ti-13Nb-13Zr sample had a very high hardness of 519.448 HV and tensile strength of 1106.07 MPa, which are superior higher than that prepared by traditional thermomechanical technique (280 ± 15 HV and 732 MPa). Owing to the change of BCC to HCP structure ([111] β→ [1-21-3] α′), the accumulation of dislocations and the finer grains, the SLM-processed samples exhibited higher fatigue strength than that the alloy processed by cast and was commensurate with the cast Ti-6Al-4 V. Moreover, the influences of phase transition on fatigue behavior have been discussed carefully.

The anisotropic microstructure and mechanical properties of Ti-13Nb-13Zr alloy via selective laser melting (SLM) are investigated for the first time in this study. Owing to the re-melting of the previous layer(s) and the thermal gradient, the prior β columnar grains grow in the building direction while scanning direction are mainly consist of finer equiaxed grains, which result in the higher nanohardness in horizontal section (5.18 ± 0.2 GPa) than in vertical section (4.63 ± 0.2 GPa). The as-fabricated longitudinal samples show slight higher ultimate tensile strength (UTS) (1020 ± 15 MPa) and yield strength (YS) (794.63 ± 15 MPa) than transverse samples (UTS of 996 ± 13 MPa and YS of 794 ± 15 MPa) because of the enhancement of twins in vertical section. The SLM processed samples show no element segregation because of the complete melting and repeatedly re-melting, and the refined microstructure due to the high cooling rate in SLM process, which make the tensile strength superior higher than those obtained by powder metallurgy (750 MPa). Owing to the columnar grain morphology, in building direction, the failure can be postponed, which results in the longitudinal samples (6.5 ± 0.3%) exhibit higher ductility than transverse samples (5 ± 0.3%).

ITO targets sintered at 1560–1600 °C were selected to deposit ITO films at 25 and 150 °C with a purpose of investigating the relationship between microstructure evolution and grain orientation in ITO targets and the film characteristics. It is found that, with increasing the sintering temperature, the triangle grains of In4Sn3O12 (secondary phase) transform into the dendritic grains of In2SnO5 (secondary phase), following by the increase of the solid solubility of tin oxide in In2O3 phase (main phase). Besides, the sintering temperature has a great influence only on the texture of secondary phase. More solid solubility of tin oxide in In2O3 phase, stronger texture intensity of secondary phase and higher sputtering temperature were found to promote the crystallinity of ITO films resulting in the lower sheet resistance and obtain the films with lower compression stress and strong adhesion. The transmittance of ITO films deposited at 25 °C is closely related to the film surface roughness, while it is mainly associated with the crystal structure for ITO films deposited at 150 °C.

Although laser solid forming (LSF) has a wide range of applications in material manufacturing, the technique has been severely limited due to the solidification cracks during rapid laser melting/solidification. In this paper, an LSF technology assisted by friction stir processing (FSP) is proposed to eliminate the LSF crack through the FSP thermomechanical coupling effect, with the Ni–16Cr–8Fe alloy as a representative material. By FSP-assisted LSF, the cracks at the top surface of the Ni–16Cr–8Fe alloy layer were eliminated. Meanwhile, the severe plastic deformation layers can be observed and gradient grains with tens of nanometers to tens of micrometers from the top surface to the inner. The LSF-printed dendrite microstructure was transformed into nanocrystals or nanotwins in the deformation zone with twining as the main deformation mechanism. The grain refinement results in the increase of hardness about 30%.

The selective laser melting (SLM) of an equiatomic CoCrFeMnNi high-entropy alloy (HEA) powder was studied, with emphasis on its non-equilibrium microstructural evolution and mechanical properties. The printed sample density increases gradually with increasing laser energy density and then decreases at an over-high laser energy density. The microstructure of SLM printed HEA exhibits a large number dislocation pile-ups and lattice distortion. Of particular intrigue are the existence of nanotwins and tetragonal σ phase in SLM printed HEA; such nanotwins and σ phase have never been observed in either cast or deformed HEA with true strain below 3.7%. The grain refinement by rapid solidification and σ phase synergistically improve the mechanical properties, as compared with conventionally solidified HEA. Hot isostatic pressing (HIP) was performed to improve the densification, yielding the increase of tensile strength from 601 MPa of SLM printed sample to 649 MPa after HIP.

The microstructure and mechanical properties of the biomaterial Ti-13Nb-13Zr prepared by selective laser melting (SLM) and hot-forging techniques were studied comparatively. The microstructures were investigated by scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), X-ray diffraction (XRD), Electron probe X-ray microscopy (EPMA) and Transmission electron microscopy (TEM). The results show that the capability of SLM-process to produce parts with tensile strength and yield strength are better than those hot-forging processed samples due to the finer grains, more uniform composition distribution and the accumulation of dislocations in the SLM-processed materials. However, the crystallographic texture in the building direction, porosity, and the presence of α’ phases are responsible for the lower ductility of the SLM-processed samples when compared with the hot-forged samples.

Although laser deposition has found its widespread applications in materials manufacture, this technology has been significantly limited by the associated metallurgical defects, such as pores, brittle phase precipitation along grain boundary during the laser melting/solidification process. In this paper, we used a novel laser deposition technology assisted by friction stir processing (FSP) to eliminate these common metallurgical defects. A Fe–Cr–Si alloy was selected as a representative material. Severe plastic deformation caused by FSP has refined the coarse solidification microstructure into ultrafine grained or even nano-grained microstructure on the top surface of the Fe-Cr-Si samples. Meanwhile, the large and interconnected Fe-Cr intermetallics precipitates were broken down to nanoparticles. The refinement of both primary grains and intermetallic particles results in an increase of microhardness from 640 HV to above 700 HV and a decrease of wear rate from 4.8 × 10−14 to 3.2 × 10−14 mm3/m.

As the typical refractory metal, the W-Ni-Cu alloy faces severe challenge in machining of complex shapes. To deal with the problem, we use selective laser melting (SLM) additive manufacturing to consolidate W-10%Ni-10%Cu composite powder. The effects of laser parameters on densification, microstructural evolution and nano-crystalline formation were studied. With the increase of laser energy density, the absolute density increases apparently and the surface unevenness is slightly alleviated. Except the typical W and Ni-Cu solid solution phases, interestingly, the amorphous W-Ni solid solution was detected in the SLM processed sample. The typical microstructure contains un-melted W region, W dendrite region with the melting of W and Ni-Cu region. The W solidification microstructure adjacent to the un-melt W presents cellular grain and then transforms into columnar dendrite, until it finally becomes equiaxed dendrite. A large number of W-based nanocrystals formed during the solidification process, which was caused by Marangoni migration that the Ni-Cu phase tends to break the liquid W into small ones, yielding the formation nano-crystalline. Better understanding of the corresponding metallurgical mechanisms will help pave the way towards newly refractory metal design for additive manufacturing application.

An Al-5Fe-1Mg-0.8Sc-0.7Zr (wt%) alloy was specifically designed for selective laser melting (SLM) additive manufacturing and atomized powder prepared. The design of this non-equilibrium alloy is based on: first, solid solubility of Fe element in Al alloy can be significantly enlarged during laser rapid solidification; second, Sc and Zr elements are used to refine the microstructure so as to prevent micro-crack and improve strength. At an optimized printing parameters, the SLM printed Al-Fe-Sc-Zr samples exhibited a highest density of 99.2% with rare intergranular cracks. Besides, a bimodal grain structure was observed, consisting of ultrafine equiaxed grain at molten pool boundary and coarse columnar grain inside the molten pool. At the boundary of molten pool, many intermetallic particles (Al6Fe and Al13Fe4) appeared around supersaturated α-Al grains; while the inside of molten pool presented eutectic of α-Al and Al6Fe/Al3(Sc, Zr). Interestingly, a large number of stacking faults were observed around the precipitated particles by HRTEM, which are also conducive to strengthening of SLM printed Al-Fe-Sc-Zr sample. Thus, excellent tensile strength of 489 MPa was obtained at an optimized volumetric energy density (VED) of 70 J/mm3. The current research results have a certain guiding significance for the composition design and microstructure control of additive manufacturing aluminum alloys.

Nano-Ni encapsulated h-BN/Ni-based alloy (Ni60) self-lubricating composite coatings on a medium carbon steel were fabricated by laser cladding using two types of lasers: a 5 kW continuous wave (CW) CO2 laser and a 400 W pulsed Nd:YAG laser, respectively. A high-energy ball milling method was adopted to clad nano-Ni onto nano-h-BN with an aim to enhance the compatibility between the h-BN and the metal matrix during laser cladding processing. The microstructure, phase structure and wear properties of the self-lubricating composite coatings were investigated by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD), as well as dry sliding wear testing. The research indicated that laser cladding of the self-lubricating composite coatings demonstrates sound cladding layers free of cracks and porosities. It was found that a reaction between h-BN and Ni-based alloy occurred, which generated hard phase CrB and Ni3B leading to the increasing of the microhardness of the coatings by CO2 laser cladding, while laser molten pool suppressed h-BN floating up to upper regions of coating for lower temperature and rapid solidification by YAG laser cladding. The high energy ball milling of nano-Ni onto nano-h-BN significantly improved the interfacial compatibility between h-BN and Ni60 matrix. The friction coefficient of the laser-clad Ni60/nano-Ni encapsulated h-BN coating was reduced obviously.

In this study, selective laser melting (SLM) of pure tantalum (Ta) was systematically investigated, with emphasis on densification, microstructure and mechanical properties of Ta specimen. The high laser scanning speed resulted in micropores and discontinuous scan tracks, owing to the elevated instability of the liquid induced by Marangoni convection and the balling effect. However, the interlayer thermal microcracks were produced at a low scanning speed, due to the thermal stress and balling effect. The microhardness and tensile strengths of the optimally SLM-processed Ta parts were improved to 445 HV and 739 MPa, respectively, which were considerably higher than specimens processed by cast (110 HV and 205 MPa) or powder metallurgy (120 HV and 310 MPa) method, due to the fine-grain strengthening. The fracture morphology of the tensile-failed SLM-processed specimens showed that the porosities and incompletely melted particles are responsible for the fracture of porous sample. While for dense sample, cleavage fracture and minor ductile fracture both account for the fracture. And the failure mechanisms were discussed. The reduced coefficient of friction of 0.3 and lowest wear rate of 7.1×10 −3 mm 3 N −1 m −1 in dry sliding wear tests were obtained for the optimally prepared Ta parts due to the formed adhesion of hardened tribolayers.

The interest of additive manufacturing (AM) Al-base alloys for lightweight applications, especially the novel scandium modified Al-Mg alloy is growing. In this work, the selective laser melting (SLM) of Al-6.2 Mg-0.36Sc-0.09Zr alloy was systematically investigated, with a particular emphasis on densification, microstructure and properties. An increased laser energy density leads to a higher densification level and a better the surface finish of the SLM samples. The surface exhibits a large number of oxides at the scan track interface and microcracks owing to the high Mg content. The x-ray diffraction reveals a (200) texture due to the preferential solidification in the 〈100〉 direction and the diffraction peaks shift to a higher angle after the laser melting owing to the Mg loss. The horizontal plane presents equiaxed grains while the vertical plane presents columnar ones with the aggregation of 〈001〉 orientation. The microstructure exhibits alternately coarse and fine grain that beneath the weld pool is a fine grained band while the central zone of weld pool shows coarse columnar grains epitaxial above the fine grain band, which is caused by the segregation of Al3(Sc,Zr) particles in weld pool boundary. The microhardness of the densest part is directionally independent, which is much higher than cast alloy but lower than homogenizing annealed alloy. The maximal compression strength of SLM Al-Mg-Sc-Zr alloy reaches 390.25 MPa. The electrochemical corrosion property of SLM alloy is higher than cast one. Better understanding of the metallurgical mechanisms during SLM of the present alloy will help pave the way for designing SLM suitable Al-base alloys.

As the key material of transparent electrodes in various optoelectronic devices, ITO targets with uniform microstructure and homogeneous elemental distributions are vital to obtain high-quality ITO films in industrial production. In this paper, the differences in the crystalline structure, sheet resistance and transmittance of ITO films with 40 nm, 70 nm and 100 nm thickness were studied between two ITO targets that were respectively sintered at 1580 °C for 10 h (target A) and 1600 °C for 5 h (target B). Surface morphology, surface roughness and thickness uniformity of ITO films with 100 nm thickness and etching property of ITO films with 40 nm and 70 nm thickness in mixed acids were further focused in the paper. The results indicate that target A, which owns homogeneous distributions of second-phase particles and elements, could be conductive to obtain the ITO films with low crystallinity that are easy to be etched leaving less and smaller residual particles. Based on the analysis, the change of sintering process has a great influence on the electrical and etching properties, but it has only a little influence on the optical property.

This study investigated the microstructure and anisotropic mechanical properties of selective laser melting (SLM) processed Inconel 718 (IN718) component. In as-fabricated alloys, ultrafine columnar grained microstructure with highly dispersed precipitates γ" phases at grains boundary and even-distributed γ' phases inside the grains were observed. It was demonstrated that the as-fabricated longitudinal samples showed lower ultimate tensile strength (UTS) of 1101 MPa but higher elongation of 24.5% compared to the transverse samples which showed UTS of 1167 MPa and elongation of 21.5%. The excellent mechanical properties of both the longitudinal and transverse samples can be ascribed to the refined microstructure of the SLM material resulting from the high cooling rate imposed by laser processing. The anisotropy in strength and ductility was attributed to the {100} fiber texture and columnar grain morphology. The {100} fiber texture of columnar grains leads to high strength in transverse direction, while the columnar grain boundaries also served as a path along which damage can preferentially accumulate, leading to fracture.

Customized porous titanium alloys have become the emerging materials for orthopaedic implant applications. In this work, diamond and rhombic dodecahedron porous Ti-33Nb-4Sn scaffolds were fabricated by selective laser melting (SLM). The phase, microstructure and defects characteristics were investigated systematically and correlated to the effects of pore structure, unit cell size and processing parameter on the mechanical properties of the scaffolds. Fine β phase dendrites were obtained in Ti-33Nb-4Sn scaffolds due to the fast solidification velocity in SLM process. The compressive and bending strength of the scaffolds decrease with the decrease of strut size and diamond structures showed both higher compressive and bending strength than the dodecahedron structures. Diamond Ti-33Nb-4Sn scaffold with compressive strength of 76 MPa, bending strength of 127 MPa and elastic modulus of 2.3 GPa was achieved by SLM, revealing the potential of Ti-33Nb-4Sn scaffolds for applications on orthopaedic implant.

The synthesis of Fe40Mn40Cr10Co10/WC composites by a combination of ball milling and spark plasma sintering is reported and corresponding mechanical and tribological properties of these composites are investigated. Compared with the Fe40Mn40Cr10Co10 MEA (medium entropy alloy), the addition of 10 vol.% WC nanoparticles led to an increase in the compressive strength and hardness from 1.571 GPa and 320 HV to 2.324 GPa and 788 HV, respectively. Meanwhile, tribological tests demonstrated that the friction coefficient, wear depth and width of the composite decreased in comparison with Fe40Mn40Cr10Co10 MEA. Load transfer effect, thermal mismatch mechanism, Orowan strengthening and grain refinement resulting from synergistic effects between ex-situ WC nanoparticles and in-situ M23C6 nanoprecipitates are responsible for the improvement in mechanical properties, especially thermal mismatch mechanism and grain refinement. In addition, the enhancement in tribological properties is also ascribed to these synergistic effects. Keywords: Composites, Medium entropy alloys (MEAs), Microstructure, Mechanical property, Tribological property

The metastable dual-phase non-equiatomic Fe50Mn30Co10Cr10 high entropy alloy (HEA) was successfully prepared via laser melting deposition (LMD) technique. The phase composition, microstructure and mechanical performance were systematically characterized at different sections of LMDed HEA samples. The as-printed HEA specimens were dominated by FCC γ phase, plate and needle-like HCP e phase, and high density stacking faults and dislocations were observed at high magnification. The as-printed samples exhibited anisotropic mechanical properties, together with the maximum ultimate tensile strength of 760 MPa and maximum elongation of 28%. The fracture surface along X and Z directions exhibit smooth curve shape, while the fracture surface along Y direction shows saw tooth shape, indicating the boundary of melt pool is weakly bounded. After deformation, the deformation bands were observed in the FCC matrix, showing that the plastic strain was controlled by FCC γ phase. In addition, stacking faults, dislocation increase significantly owing to the formation of stacking fault is caused by sliding of Shockeley partial dislocation, and the stacking fault is the core of HCP martensite nucleation.

Al0.3CoCrFeNi high-entropy alloy (HEA) was additively manufactured by laser melting deposition (LMD) with emphasis on its microstructure and tensile properties. The LMD as-built HEA features a fiber texture aligned toward the build direction. The dislocation loops are observed with a high density of dislocations neighboring to them in the LMDed samples. The partials dislocation glides induced by thermal stress leading to disordered-ordered transformation during LMD. Besides, the precipitated B2 particles are induced by thermal stress during cooling or thermal exposure during remelting. The cracks easily initiate and propagate along with the phase boundaries between the matrix FCC and precipitated B2 phases. Such cracks damage the tensile properties resulting in poor ductility in the tensile tests. Subsequent annealing facilitate the further precipitation of the B2 and σ phase, which introduces hardening and leading to the increase of the Vickers hardness and wear resistance of the annealed samples. Nevertheless, the annealing induces dislocation recovery, which reduces the required critical shearing stress for plastic deformation. As a consequence, the yield stress decreases from 476.9 ± 6.4–373.5 ± 6.8 MPa after annealing.

The corrosion behaviour of different planes of a selective laser-melted (SLM) equimolar CrCoNi medium-entropy alloy (MEA) was investigated and compared with its counterpart cast alloy in a 3.5 wt% NaCl solution. The microstructures of the SLM products were characterised, and electrochemical corrosion measurements, corrosion surface morphology observations, and X-ray photoelectron spectroscopy analyses were performed. Compared with the cast MEA, the SLM MEA has an inferior corrosion resistance for its more metallurgical defects and smaller grain size. In the SLM MEA samples, The XY-plane of the SLM MEA has a poorer corrosion resistance than the XZ-plane, which is due to more metallurgical defects and lack of fusion pores on the XY-plane and its higher grain boundary density.

Metallic glass composite coatings Ti45Cu41Ni9Zr5 and Ti45Cu41Ni6Zr5Sn3 (at.%) on a Ti-30Nb-5Ta-7Zr (wt.%) (TNTZ) alloy were prepared by laser cladding. The microstructures of the coatings were characterized by means of X-ray diffractometry (XRD), scanning electron microscopy (SEM) equipped with energy dispersive X-ray analyzer (EDXA), and transmission electron microscopy (TEM). Results indicated that the coatings have an amorphous structure embedded with a few nanocrystalline phases and dendrites. A partial substitution of Ni by Sn can improve the glass forming ability of Ti-base metallic glass system, and induce the formation of nano-sized Ni2SnTi phase during the cyclic laser heating. The tribological behavior of both the substrate and the coatings was investigated in detail. A significant improvement in both the hardness and the wear resistance of the coatings was achieved with the addition of Sn. The relationship between the wear resistance and the microstructures of the coatings was discussed.

Selective laser melting (SLM) of Al-3.48Cu-2.03Si-0.48Sc-0.28Zr alloy was systematically investigated in this work, with emphasis on its microstructure evolution, mechanical properties and corresponding metallurgical defects. There is a strong correlation between SLM specimen density and laser parameters; the maximum density of 98.44% was obtained at a volumetric energy density (VED) of 166.67 J/mm3. The formation mechanism of pores is strongly dependent on the laser energy input and the initiation of microcracks is caused by local stress concentration. After SLM, the X-ray diffraction (XRD) peaks of as-printed specimen became broaden compared with powder due to the grain refinement and the shift of diffraction peaks to a higher value due to crystal lattice distortion of the printed specimen. The microstructure exhibits alternately column and fine grain, which is caused by the complex thermal gradient and the existence of Al3(Sc,Zr) particles as nucleating agent. The maximum ultimate tensile strength of 329 MPa and elongation of 9.7% can be obtained at a VED of 166.67 J/mm3. Also, the microhardness increases with the increase of VED owing to the higher cooling rate. This study provides useful guidance for the design of high strength-ductility aluminum alloy without cracking for SLM in the future.

The strong electric current in spark plasma sintering (SPS) often gives sintered materials unique microstructures. In the present study, it is found that the Co3W grains formed at the W/Co bonding interface preferentially grow along [2 1 ¯ 1 ¯0] (or its equivalent orientations) in the current direction during SPS, which is significantly different from that without current. We propose that the resistance anisotropy of grains under electromigration leads to anisotropic atomic diffusion, inducing the preferential growth of grains under current. This work may provide an approach and a theoretical foundation for the preparation of materials exhibiting directional growth.

A series of AlTiCN coatings with different carbon contents (0–0.7 at.%) were deposited on YG10 (WC + 10 wt.% Co) cemented carbide by cathodic arc-evaporation of Ti-Al/Ti-Al-C targets in a mixture of Ar and N2 gases. The influence of carbon doping on microstructure, mechanical properties, wear resistance and cutting performance was systematically investigated by comparing carbon-free coating and coatings with different carbon contents. The microstructure of the coatings has been changed significantly with the addition of C, and the amorphous domains appear when the doping amount of C is among 0.2–0.5 at.%. Instead of forming bonds with other elements in the coating, carbon only acts as a growth inhibitor. When the carbon content is 0.2 at.%, the hardness of the coating significantly decreased, but changes a little with the carbon content continue to rise. The addition of C significantly improves the wear resistance of the coating, which is mainly attributed to the transformation of the crystalline state and the formation of the dense Al2O3 oxide layer. Among them, the coating with a carbon content of 0.2 at.% has both excellent wear resistance and cutting performance.

Selective laser melting (SLM) is a promising technique for manufacturing 2xxx series Al–Cu alloy parts. However, the metallurgical defects in SLM severely limits their applications. In this work, SLM of a Li and Zr modified Al–Cu–Mg alloy (Al–4Cu–1Li-0.4Mg-0.5Zr) was studied with emphasis on its microstructure, metallurgical defects and hardness. The results show that microstructure is composed of fine equiaxed crystals (0.5–1 μm) and columnar dendrites (10–12 μm in length and 1–2 μm in width) with pronounced pore and crack defects. The geometrically irregular micropores distribute at the boundaries of the molten pool while the regularly round micropores distribute randomly. Cracks were observed growing along the grain boundaries with high angle and almost parallel to building direction, which were mainly caused by local stress concentration in the liquid film. The texture of SLM-processed Al–Cu–Mg–Li–Zr alloy was found in {001} and {001} orientation. The microhardness improved as laser energy density increasing due to the higher cooling rate. This research provides useful guidance in the future for designing crack-free and high strength SLM printed 2xxx series Al alloys.

Hot cracking, grains size, crystal orientation and compressive strength of an equimolar CoCrFeMnNi high-entropy alloy (HEA) printed by selective laser melting (SLM) were investigated. The CoCrFeMnNi HEA printed by SLM suffered from hot cracking no matter of the employed printing parameters. The preferred orientation of the printed sample was transformed in the order: 〈2 3 3〉→〈0 0 1〉→〈2 0 3〉→〈1 0 1〉, as the volumetric energy density (VED) rises. Also, the increased VED favors the grain growth and the increase of the grain orientation spread, owing to the presence of high temperature gradient and larger residual stress. The fracture strength increases with the VED, and the maximum compressive strength rises to 2447.7 MPa, but the elongation rate is still 77.6% due to the ultrafine microstructure. The results of this study have reference value for the preparation of HEA materials with controllable grain characteristics, crystalline texture and complex structures by SLM.