Annealed State Research Articles

Corrosion Resistance Enhancement of Selective Laser Melted Cost‐Effective Interstitial Medium‐Entropy Alloy via Deep Cryogenic Treatment

An economically interstitial FeMnCrNiCu medium‐entropy alloy (MEA), which exhibits preferable corrosion resistance in 3.5 wt% NaCl solution, is fabricated by selective laser melting (SLM). Compared with annealing, which is one of the posttreatments for additive manufacturing, deep cryogenic treatment (DCT) also contributes significantly to the alloy properties and is expected to improve corrosion resistance. Herein, the corrosion behavior of SLM‐MEA after DCT in 3.5 wt% NaCl solution is investigated. DCT improves corrosion resistance by promoting the uniform distribution of precipitates in SLM‐MEA and changing the cation ratio in the passive film. After DCT, the corrosion current density of the SLM‐MEA in original and annealed state decreases by 27.07% and 62.69%, respectively. The annealed SLM‐MEA exhibits the worst corrosion resistance as a result of the precipitation of continuous Cr‐rich M23C6 carbides at grain boundaries. The face‐centered cubic structure of MEA does not change after annealing or DCT. Significantly, the number, size, and distribution of the precipitates are greatly affected. DCT after annealing promotes the uniform diffuse distribution of M23C6 carbides and nanoscale Cu‐rich particles while increasing the Cr+Ni/Fe+Mn ratio in the passive film, resulting in a significant improvement in corrosion resistance.

Significant coercivity enhancement of Ga-doped sintered Nd-Fe-B magnet by grain boundary diffusion perpendicular to the c-axis

Grain boundary diffusion (GBD) process is the most effective approach for enhancing coercivity of Nd-Fe-B magnets with minimal consumption of heavy rare earth (HRE). However, understanding of GBD mechanism is still limited, especially on the anisotropic diffusion behavior within sintered magnets. Grain boundary (GB) phase is the key factor in determining the diffusion process, which acts as diffusion channel for HRE atoms. The effects of doping Ga on the grain boundary microstructure and diffusion behavior of Tb in the sintered Nd-Fe-B magnet were investigated. Sintered magnets with different Ga content (0.15 wt%, 0.45 wt%) were prepared. It should be noted that Tb was diffused perpendicular to the easy axis (c-axis) of the magnets. The coercivity increased more significantly to 2.802 T (1.006 T higher than that of the post-sinter annealed state) in magnets with high Ga content than the low Ga content magnets (2.291 T, 0.669 T higher than the post-sintered annealed state). Such a huge coercivity increment almost reached the same value by diffusing Tb along the easy axis reported by other researchers. Chemical compositions and microstructure of the GB phase were found to be key factors in influencing the HRE diffusion process. A considerable amount of Nd6Fe13Ga phase was observed near triple junctions after post-sinter annealing in the high Ga content magnets, which markedly decreased Fe concentration in the intergranular phase. In addition, amorphous intergranular metallic Cu-rich phases provided smooth diffusion channels for HRE atoms. (Nd1-x, Tbx)2Fe14B shell was much more obvious in the high Ga content magnets. Ga dopping induced novel modifications in diffusion behavior of HRE atoms and strongly influenced the magnetic properties of permanent magnets. The present approach provide new path for the manufacture of high performance magnets, which is interesting both for technical applications and fundamental studies.

Magnetostriction of Fe-rich FeSiB(P)NbCu amorphous and nanocrystalline soft-magnetic alloys

The compositional effect of magneto-elastic and magnetostriction properties of Fe-rich Fe81B15−xPxSi2Nb1Cu1 (ii) Fe82B14−xPxSi2Nb1Cu1 and (iii) Fe83B13−xPxSi2Nb1Cu1 (x = 0, 4, 8) amorphous and annealed nanocrystalline alloy ribbons were investigated. The present study adds knowledge to the limited magnetostriction literature available for Fe-rich nanocrystalline alloys by systematically varying the Fe and P content. A combination of Becker-Kersten and small angle magnetization rotation (SAMR) techniques has been employed for the magnetostriction (λs) evaluation. Both the as-quenched and nanocrystalline ribbons exhibit large positive magnetostriction and show strong compositional dependence to the P content. In the as-quenched condition, 4 at% P addition shows maximum magneto-elastic response and magnetostriction constant, with Fe81B11P4Si2Nb1Cu1 alloy exhibiting a maximum of + 52 ppm and P-free Fe83B13Si2Nb1Cu1 alloy exhibiting a minimum of + 27 ppm. In the nanocrystalline state, a slight reduction of magnetostriction is seen for all alloys, with a maximum of + 32 ppm (4 at% P) and a minimum of + 22 ppm (P-free) in Fe83 at% alloys. The unusual large magnetostriction of optimally annealed samples is attributed to the relatively low crystal volume fraction (30–45%) of nanocrystalline ribbons. The lowest magnetostriction of Fe83B13Si2Nb1Cu1 alloy in both as-quenched and annealed state is explained based on ribbon structural heterogeneity consisting of crystal nuclei and textured α-Fe surface crystallization. The study reveals a contradictory response of magneto-crystal anisotropy (grain size reduction) and magneto-elastic anisotropy to the P addition and ribbon structural heterogeneity. The study discusses the implications of the large magneto-elastic anisotropy associated with Fe-rich nanocrystalline ribbons and the way forward for improving their magnetic softness.

Effect of Non-Isothermal Aging on the Mechanical Properties and Corrosion Resistance of 2A12 Aluminum Alloy.

The effect of linear non-isothermal aging and composite non-isothermal aging on the mechanical properties and corrosion resistance of 2A12 aluminum alloy was investigated. Optical microscopy (OM) and scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS) were used to study the microstructure and intergranular corrosion morphology, and the precipitates were analyzed using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results showed that the mechanical properties of 2A12 aluminum alloy were improved by both non-isothermal aging techniques due to the formation of an S' phase and a point S″ phase in the alloy matrix. Linear non-isothermal aging resulted in better mechanical properties than composite non-isothermal aging. However, the corrosion resistance of the 2A12 aluminum alloy was reduced after non-isothermal aging due to the transformation of matrix precipitates and grain boundary precipitates. The corrosion resistance of the samples followed the order: annealed state > linear non-isothermal aging > composite non-isothermal aging.

Effect of Heat Treatment on the Corrosion Resistance of AlFeCoNiMo0.2 High-Entropy Alloy in NaCl and H2SO4 Solutions

The effects of casting and different heat treatment processes on the corrosion resistance of AlFeCoNiMo0.2 high-entropy alloy in 3.5% NaCl (mass fraction) and 0.5 mol/L H2SO4 solutions were investigated using dynamic potential polarization curves, SEM, XRD, XPS, and other test methods. The results show that in the Cl− environment, the cast alloy has the lowest corrosion current density and higher corrosion resistance compared to the annealed alloy. The elements Al and Mo are severely segregated in the crystal and in the grain boundaries, where galvanic corrosion occurs, and the Al-rich phase produces pitting corrosion in the crystal. The main components of its passive film are oxides of Al, Fe, Co, and Mo, and oxides and hydroxides of Ni. In the SO42− environment, the best corrosion resistance is achieved in the 900 °C annealed state of the alloy. Electrochemical test results show that the alloys all undergo secondary passivation, producing two successive product films to protect the metal matrix. Preferential corrosion areas are concentrated in the molybdenum-rich grain boundaries and nearby dendritic regions, reducing the corrosion resistance of the alloy. The main components of the passive film are oxides of Al and Mo; oxides of Fe, Co, Ni; and hydroxides. The Mo element in the passive film prevents the activated dissolution of Fe and produces the protective component MoO3, which inhibits the dissolution of the alloy and improves the stability of the passive film. The presence of Mo elements increases the selective dissolution of Fe, and the aggregation of Mo elements at grain boundaries after annealing weakens the corrosion resistance of the alloy and leads to the dissolution of the passive film. The main components of the passive film are oxides of Al and Mo; oxides of Fe, Co, Ni; and hydroxides.

Synthesis and characterization of novel high entropy Heusler intermetallics

This study aims at developing novel Full-Heusler high entropy intermetallic compounds (FH-HEICs). To this end, the formation of Heusler-type intermetallic structures and their thermal stability are studied in three systems with (CoFeNiCuV)2MnAl, Co2(FeMnNiCuTi)Al and Co3(FeMnNiCu)Al chemical compositions, where one sublattice composed of multi-component elements. The results indicated that (CoFeNiCuV)2MnAl crystallizes in a pure FH-HEIC type phase consisting of ordered L21 and disordered A2 structures, and it remains stable after 5 h annealing at 900 °C. Annealing could effectively suppress segregation of elements in (CoFeNiCuV)2MnAl, but it did not trigger substantial disorder-to-order phase transition. Co2(FeMnNiCuTi)Al crystallized in a mixture of B2 and FCC phases, in which the ordered B2 structure undergoes a transition to disordered A2 type structure upon annealing at 900 °C. On the other hand, Co3(FeNiMnCu)Al exhibited a A2+FCC two-phase structure in both as-cast and annealed states. (CoFeNiCuV)2MnAl exhibited higher microhardness value (589 HV) compared to Co2(FeMnNiCuTi)Al (474 HV) and Co3(FeMnNiCu)Al (417 HV) FH-HEICs, consisting with its higher degree of ordering. Finally, all the samples exhibited ferromagnetic behavior with relatively high magnetic saturation and coercivity in the range of semi hard magnetic materials.

Influence of initial structure of rolled sections in coils of bearing steel grade on uniformity of obtained structure after spheroidizing annealing.

The article presents the results of the study of the effect of the initial metal microstructure in the surface layer of bunched rolling at the existing technology of rolling in the low-temperature range from bearing steel grades ШХ15 on the formation of decarburized layer after spheroidizing annealing. To meet the customer’s requirements for the metal quality, some studies of the microstructure of the subsurface zone of coiled steel have been carried out. There is a description of the developed process for cooling coiled steel made of bearing steel on an air-cooled roller table for wire rod. The effect of temperature-speed modes of coiled steel cooling on the size of the decarburized layer after spheroidizing annealing has been determined. The microstructure of coiled steel samples with a diameter of 16.5 mm, rolled according to the standard and experimental modes, as well as after spheroidizing annealing, has been studied. The causes of incomplete spheroidization of coiled steel in the subsurface layer have been revealed. The microstructure of hot-rolled samples rolled according to standard conditions has been evaluated and the effect of pearlite dispersion in the subsurface layer, which leads to overestimated values of the depth of the decarburized layer after spheroidizing annealing, has been established. An effective mode of cooling of coiled steel made of a bearing steel grade for subsequent spheroidizing annealing has been determined, which ensures the minimization of the decarburized layer and the uniformity of the microstructure along the entire coil length. The experimental mode, which consists in shifting the initial cooling temperature (in the laying coiler zone) by 30 °C, to the temperature range of 840‒860 °C, with 4 fans involved and the switching-on power of 30%, allowed to obtain a uniform structure in the surface zone (subsurface), both in the hot-rolled state (sorbite-like, fine-lamellar perlite) and in the annealed state (spheroidized), as well as to determine directions of further improvement of the technology

Unraveling structural relaxation induced ductile-to-brittle transition from perspective of shear band nucleation kinetics in metallic glass

Structural relaxation induced ductile to brittle transition seriously hampers the practical applications in metallic glasses. Although there have been many researches focusing on the hidden physical mechanism of ductile to brittle transition, the correlation between ductile to brittle transition and shear band nucleation kinetics is still unclear. In this work, by applying for one new studying strategy based on the nanoindentation, the evolution of the thermodynamic property, the macroscopic mechanical behavior and the corresponding shear band nucleation kinetics including the nucleation site type, the nucleation site density and the nucleation rate with annealing time at one Sub-glass transition temperature, were systematically investigated. We found that there appears one critical annealing state corresponding to the ductile to brittle transition and then the ductile-to-brittle transition induced by structural relaxation is the comprehensive result of the transition of the shear band nucleation mode, the nucleation site density and the nucleation rate. These results provide new enlightenment for the structural relaxation effect on the shear band nucleation and the macroscopic deformation behaviors, and for developing new metallic glasses with improved mechanical properties.

High Temperature Tribological Behavior of Electroless Plating Ni-P-Si3N4-WS2 Composite Coatings

Electroless nickel composite coatings have the potential for high-temperature tribological applications, and a combination of high wear resistance and low friction factor is one of the desirable solutions but still a tricky problem. The addition of self-lubricating WS2 and hard Si3N4 nanoparticles to the Ni-P coatings is expected to obtain good high-temperature tribological performance. In this work, Ni-P-Si3N4-WS2 composite coatings with various contents of WS2 nanoparticles were prepared using electroless plating and subsequently annealed at 400 °C in an inert atmosphere. The tribological properties of the coatings were evaluated using a ball-on-disc wear instrument at operating temperatures from 25 to 600 °C. The microstructure, chemical composition, and surface morphology of the coatings were characterized by X-ray diffractometry (XRD), energy disperse spectroscopy (EDS), and scanning electron microscopy (SEM). Upon increasing the WS2 dosage in the bath, the WS2 content in the coating increased and the micro-hardness of the as-plated coating increased from 539 to 717 HV. After heat treatment, the coating underwent a crystallization process, and the hardness increased from 878 to 1094 HV. The main wear mechanism of the coating changed from adhesive wear in the as-plated state to abrasive wear in the annealed state. The annealed Ni-P-Si3N4-WS2 coating with a WS2 dosage of 2.5 g/L in the bath exhibited excellent mechanical properties, with a hardness of 10.9 GPa, a friction coefficient of ~0.51, and a wear rate of 8.4 × 10−15 m3N−1⋅m−1 at room temperature, and maintained optimal performance at high temperatures. At operating temperatures of 200, 400, and 600 °C, the form of wear was adhesive wear for coatings with a WS2 dosage <1.5 g/L and abrasive wear for coatings with a WS2 dosage ≥1.5 g/L. The synergism of WS2 and Si3N4 particles refined the grains of the Ni-P matrix in as-plated coatings and obviously reduced the friction coefficient of friction pairs in annealed coatings at all operating temperatures.

Microstructure-Property Correlation and Its Evolution during Aging in an Al4.4Co26Cr19Fe18Ni27Ti5.6 High-Entropy Alloy.

The efficient energy use in multiple sectors of modern industry is partly based on the efficient use of high-strength, high-performance alloys that retain remarkable mechanical properties at elevated and high temperatures. High-entropy alloys (HEAs) represent the most recent class of these materials with a high potential for high-temperature high-strength applications. Aside from their chemical composition and microstructure-property relationship, limited information on the effect of heat treatment as a decisive factor for alloy design is available in the literature. This work intends to contribute to this research topic by investigating the effect of heat treatment on the microstructure and mechanical performance of an Al4.4Co26Cr19Fe18Ni27Ti5.6 HEA. The solution annealed state is compared to aged states obtained at different heat treatment times at 750 °C. The temporal evolution of the matrix and the γ'-precipitates are analyzed in terms of chemical composition, crystallography, size, shape, and volume fraction by means of scanning electron microscopy, transmission electron microscopy, and atom probe tomography. The yield strength evolution and strength contributions are calculated by classical state-of-the-art models as well as by ab-initio-based calculations of the critical resolved shear stress. The findings indicate promising mechanical properties of the investigated alloy and provide insight not only into possible strengthening mechanisms but also into the evolution of main phases during the heat treatment.

300 MPa grade highly ductile biodegradable Zn-2Cu-(0.2-0.8)Li alloys with novel ternary phases

Although a few high-strength biodegradable Zn alloys with yield strengths (YSs) over 300 MPa in rolled state have been developed, their elongations (ELs) are generally less than 30%. This study developed rolled Zn-2Cu-xLi (x = 0.2 wt.%, 0.5 wt.%, 0.8 wt.%) alloys with YSs of 316–335 MPa and ELs of 44%–61%. Three-dimensional atom probe (3DAP) and time of flight secondary ion mass spectrometry (TOF-SIMS) were employed to characterize Li distribution. Three kinds of Zn-Cu-Li ternary phases are identified, which are blocky ε′-(Cu0.5, Li0.5)Zn4, blocky β′-(Li0.9, Cu0.1)Zn4, and small round γ particles with high Li content in the annealed state. Other identified phases are Zn, β-LiZn4, and ε-CuZn4 phases. With the increase of Li content in the alloys, ε′ phase with 6.50 at.% Cu transforms into β′ phase with 2.12 at.% Cu, i.e., the average level in the alloys. Within ε′ phase, there exist nano-scale Li clusters and ε phase, resulting in ε′/ε structure. Dense Zn laths precipitate from β′ phase, resulting in β′/Zn lamellar structure. The lamellar structure is the matrix of Zn-2Cu-0.8Li and leads to near-isotropic plasticity. Electrochemistry tests show that degradation rates fall in the range of 153–196 μm/year, which decrease with Li content. All the alloys exert positive effects on the growth of MC3T3-E1 cells with 10% extract. This research reveals how microstructure evolves in Zn-2Cu-xLi alloys, which lays the foundation for their future applications.

TKD/EBSD and TEM analysis of microstructural changes ongoing in AISI 304L steel exposed to the cyclic loading

The study deals with microstructural evolution of the 304L steel exposed to the low cycle straining. The two states of material were studied, the as-received and solution annealed state. Solution annealing caused grain growth from 29 ± 10 μm to 48 ± 30 μm, reduction of chemical heterogeneity and decrease of overall dislocation density. Cyclic hardening/softening curves were measured and three stages of fatigue life were distinguished. Initial cyclic hardening was followed by cyclic softening. The pronounced secondary hardening was measured in the last stage of fatigue life. Advanced techniques of electron microscopy were used to enlighten origin of the material behavior in particular stages. The material response in individual stages is thoroughly discussed in terms of microstructure evolution. Electron channeling contrast imaging visualized the fine microstructural features and revealed structure evolution, however was not able to identify the features. Transmission electron microscopy is useful for individual structural features characterization, however, it is quite complicated to be performed. Transmission Kikuchi diffraction provided similar results to transmission electron microscopy while characterization of evolved microstructural features revealed the deformation mechanism acting under loading at lower time and relatively smaller effort. Particular damage mechanisms operating in material are linked to the mechanical data.

The native and metastable defects and their joint density of states in hydrogenated amorphous silicon obtained from the improved dual beam photoconductivity method

In this study, undoped hydrogenated amorphous silicon (a-Si:H) thin films deposited under moderate dilution ratios of silane by radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) have been investigated using steady-state photoconductivity and improved dual beam photoconductivity (DBP) methods to identify changes in multiple gap states in annealed and light-soaked states. Four different gap states were identified in annealed state named as A, B, C, and X states. The peak energy positions of these Gaussian distributions are consistent with those recently identified by Fourier transform photocurrent spectroscopy (FTPS). After in situ light soaking, their density increases with different rates as peak energy positions and half-widths remain unaffected. The electron-occupied A and B states located below the dark Fermi level and their density and ratios in the annealed and light-soaked states correlate well with those defects detected by time-domain pulsed electron paramagnetic resonance (EPR) experiments. The A, B, and X states located closer to the middle of the bandgap anneal out at room temperature in dark and define the “fast” states. However, the C states show no sign of room temperature annealing such that they must define the “slow” states in undoped a-Si:H. The results found in this study indicate that the anisotropic disordered network is a more appropriate model than previously proposed defect models based on the continuous random network to define the nanostructure of undoped a-Si:H, where multiple defects, D0 and non-D0 defects, can be identified by using the improved DBP method.

(Fe-Ni)-based glassy alloy containing Nb and Cu with excellent soft magnetic properties

Magnetic properties of amorphous Fe38Ni38B12P5Si3Nb3Cu1 alloy ribbons have been investigated in as-spun and annealed states with the aim of developing an ultrasoft magnetic material which is expected to be used in advanced information data devices. A small amount of simultaneous addition of Cu and Nb to a FeNi-metalloid amorphous alloy system caused the change in crystallization process from eutectic type to the primary one. After annealing at the temperature just below the glass transition temperature (Tg), the glassy alloy ribbon exhibit excellent soft magnetic properties, very low coercive force of 1 A/m and extremely high effective permeability of 7.5·104 at 1 kHz which have not been obtained for any kinds of Fe- and Ni-based amorphous alloys, in spite of relatively low saturation magnetic flux density of 0.86 T. The further increase in annealing temperature causes the precipitation of nanoscale fcc particles with a size of about 7 nm including a high density of planar faults and the resulting nanostructure alloy also exhibits good soft magnetic properties with low Hc below 2 A/m. The formation of nanostructure fcc-(Fe,Ni) + glass soft magnetic alloys is also novel. The syntheses of the new Fe-Ni-based glassy and nanocrystalline [fcc(Fe,Ni) + glass] alloy ribbons with ultrasoft magnetic properties are encouraging as a new type of energy saving-type soft magnetic material.

Inhomogeneous deformation substructure and its effect on the recrystallization behavior of yttria dispersion-strengthened tungsten plate

Tungsten materials have been chosen for use in critical parts (i.e., as the armor of plasma-facing material) in fusion reactors. Deformed tungsten will undergo recrystallization at a high-temperature service environment, and recrystallized tungsten exhibits brittleness, which reduces mechanical properties, thermal shock resistance and service lifetime. The deformation heterogeneity may result in an inhomogeneous microstructure, affecting its recrystallization behavior. The main aim of the present work is to qualitatively and quantitatively characterize the heterogeneity in the through-thickness deformed microstructure of an yttria dispersion-strengthened tungsten plate warm-rolled to 50 % thickness reduction ratio and study the effect of heterogeneous microstructure on recrystallization behavior. For this, topological maps of the surface, quarter and center region are measured on the deformed state and annealed state utilizing electron backscatter diffraction (EBSD). Distributions of grain size, geometrically necessary dislocations (GND) energy, potential nuclei density and texture have been analyzed in detail. The results revealed that the deformed microstructure of tungsten plate along full-thickness has no apparent heterogeneity gradient of grain size and texture, but the center layer has a larger subgrain size and more potential recrystallized nuclei compared to the surface layer. The larger subgrain is more conducive to static recrystallization nucleation, while the existing potential recrystallized nuclei can grow rapidly without incubation time during subsequent high-temperature annealing, thereby recrystallization preferentially undergoes in the center layer of the tungsten plate.

Effects of Zr4+-doping on the properties of (Lu, Gd)2O3: Eu transparent ceramics: Insight from the photoluminescent spectra in as-sintered and annealed state

We show the effects of the Zr4+-doping on the microstructural, optical, and luminescent properties of (Lu, Gd)2O3: Eu transparent ceramics in its as-sintered state and annealed state. Zr4+-dopant greatly enhanced the transparency of (Lu, Gd)2O3: Eu ceramic, giving Lu0.42Gd0.5Zr0.03Eu0.05O1.5+δ ceramic with a transmittance of up to 80% at 600 nm. It is found that Zr4+-dopant dominates the luminescent properties of Eu ions in both as-sintered and annealed ceramics. Energy transfer from Eu2+ to Eu3+ was found by photoluminescence spectra, and the ratio of Eu2+/(Eu2++Eu3+) was affected by Zr4+ content in as-sintered ceramics. Moreover, the oxygen vacancy concentration increased with increasing Zr4+ content in as-sintered ceramics. The annealing process enhanced the intensity of all the excitation bands of 4f→4f transitions and the intensity of charge transfer band (CTB) decreased as the Zr4+ content increased in the annealed ceramics. This work highlights that Zr4+ doping is a potential way to improve the transmittance and red emission intensity of 4f→4f transition of Eu3+ in the (Lu, Gd)2O3: Eu ceramic for extended applications.

Properties of medium-manganese steel processed by laser powder bed fusion: The effect of microstructure in as-built and intercritically annealed state on energy absorption during tensile and impact tests

The presented research was aimed at applying laser powder bed fusion (LPBF) technology and TRIP (Transformation Induced Plasticity) steel with medium Mn content to produce thin-walled parts with enhanced crashworthiness. It was expected that the simultaneous use of the excellent combination of strength and ductility of the new type of medium-Mn steel and the advantages of LPBF technology would allow the development of an alternative to the conventional method of manufacturing the energy absorbing components. The energy absorption capability of LPBF-processed Fe-0.15C-7.5Mn-1.8Al steel was evaluated based on its deformation behavior under monotonic and impact loading. Tensile and Charpy V-notch specimens were fabricated by LPBF with layer thicknesses of 30 and 60 μm, using processing windows set established according to the criteria of low porosity (<0.3%) and good surface quality. Specimens were tested in as-built state and after intercritical annealing at a constant temperature (670 °C), but for different holding times and cooling rates to obtain a large fraction (30–50 vol%) of retained austenite capable of strain-induced martensitic transformation. Based on multiscale microstructure examinations (OM, SEM, EBSD, XRD, EDS) the relationships between the morphology of LPBF-specific microstructures before and after intercritical annealing, as well as between their behavior in tensile and impact test, were analyzed and discussed. For both layer thicknesses, the best combination of strength, elongation and impact toughness was obtained after annealing at 670 °C for 6 h followed by argon cooling. LPBF technology has been shown to be suitable for the fabrication of thin-walled energy-absorbing components from medium-manganese TRIP steel with the potential to reduce fabrication time by doubling the layer thickness compared to standard.

The sputtering performance of Ag sputtering targets with different microstructure

Ag thin films are widely used as the key material for electronic industries, and magnetron sputtering has become a general approach for Ag thin films deposition by using Ag targets as source materials. The microstructure of targets could affect the thin films thus sputtered. In our research, the sputtering performance of Ag targets in cold rolling state and annealing state was compared and the relationship between the Ag targets and Ag thin films were discussed. The results showed that annealing at 600 °C after cold rolling deformation of 83.33% can effectively increase the texture density of {110} in Ag. Both cold rolling state and annealing state Ag targets exhibit the similar deposition rate. The resistivity of both kinds of Ag thin films decreases with sputtering time. At the same sputtering time, the Ag thin films sputtered by annealing state Ag targets shows lower resistivity as compare with those sputtered by cold rolling state Ag targets. Due to the uniform microstructure of annealing state Ag target, it shows shallower depth of rack track after sputtering. Annealing treatment after cold rolling is an adaptable method to obtain optimized target microstructure. This knowledge could give some new ideas on the preparing of metal sputtering targets.

Enhancing Titania-Tantala Amorphous Materials as High-Index Layers in Bragg Reflectors of Gravitational-Wave Detectors

Amorphous mixed titania-tantala coatings are key components of Bragg reflectors in gravitational-wave detectors (GWDs). Attaining the lowest possible values of optical absorption and mechanical losses in coatings is of paramount importance for GWDs, and this requires a complex optimization of the coating deposition and postdeposition annealing. We present here a systematic investigation of the optical properties and internal friction of amorphous mixed titania-tantala coatings grown by ion beam sputtering. We consider coatings with six different cation mixing ratios─defined as Ti/(Ti + Ta)─and we study them both in the as-deposited and annealed states. All coatings have been subject to the same annealing of 500 °C for 10 h in air, which is the postdeposition treatment adopted so far for Bragg reflectors in GWD applications. By exploiting spectroscopic ellipsometry data and modeling, along with ancillary techniques, we retrieved the dielectric function of the coatings in a wide spectral range. When varying the mixing ratio and performing the annealing, we find monotonic─in some cases, almost linear─trends for most of the aforementioned properties. Remakably, the postannealing Urbach energy displays a definite minimum for a mixing ratio around 20%, very close to the composition of the coatings showing the lowest optical absorption for GWD applications. We suggest that the observed minimum in the Urbach energy depends not only on the mixing ratio but also on the annealing parameters. On the other hand, the minimum coating loss angle was found to be weakly dependent on the considered measurement frequency and to lie within a rather broad range of Ti content (cation ratios of 21 and 44%), suggesting that the search for an absolute minimum following postdeposition annealing should be rather sought in the study of the best annealing parameters for each specific cation ratio considered. This work constitutes a reference for the optical properties of the amorphous mixed titania-tantala coatings and highlights the relevance of the Urbach energy as an additional parameter to guide the optimization process of materials for high-performing Bragg reflectors.

Order degree and self-accommodation of γ phases in Ni-Mn-Ga alloys

High temperature shape memory alloys Ni-Mn-Ga have high martensitic transformation temperature, good thermal stability and moderate shape memory performance. The second phase γ significantly affects the alloys’ macroscopic performances, but its atomic structure and microstructural feature still remain almost unknown. Microstructure and degree of atomic ordering of γ precipitate are uncovered in Ni54Mn30+xGa16–x (x = 0, 2, 5, 9, 11) and Ni57+yMn25Ga18–y (y = 0, 1, 2, 3, 4) alloys. For as-cast Mn-rich alloys, a hierarchical “nano-lamellae within micro-lamellae” microstructure is found. Nano-lamellae are paired to form a variant, two variants constitute a micro-lamella, a pair of micro-lamellae makes up single group, and there are six groups in a grain. Single nano-lamella is a partially ordered phase with tetragonal crystal structure. All nano-lamellae are of nearly identical crystallographic orientation. This arrangement of the 24 variants is self-accommodated. In annealed state, the lamellae in large γ precipitates still exist due to the constraint from martensites, but in small grains partly or completely disappear and further evolve into nanotwins. For as-cast Ni-rich alloys, the paired nano-lamellae are disordered and another partially ordered phases, respectively. After annealing, they become single crystal with ordered structure. Models describing atomic positions of γ phases with different orderings are built. For Mn-rich alloys, the martensitic transformation temperature reaches about 600 °C, shape memory strain is up to 5%, and compressive stress and strain are higher than 2100 MPa, and 26%, respectively. Relative to Ni-rich samples, Mn-rich alloys have very high martensitic transformation temperature, moderately enhanced ductility and reasonably good shape memory strain. They are closely related to martensite’s electron concentration and γ’s atomic ordering, crystal structure, and lamellar microstructure.