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The Hall-Petch strengthening coefficient of face-centered cubic alloys has the potential to increase. Herein, we experimentally determined an unconventionally large Hall-Petch coefficient equal to 1100 MPa·µm1/2 and a large lattice friction stress for novel Co0.95Cr0.8Fe0.25Ni1.8Mo0.475 high-entropy alloys (Mo0.475 HEAs). Detailed microstructural characterizations showed Mo segregation at grain boundaries (GBs) and no apparent nano-clustering in the matrix. With the increased Mo content, Mo segregating at GBs is an unexpected outcome. The unconventionally large Hall-Petch coefficient is ascribed to the newly generated effect due to Mo segregation at GBs, besides the factors in the grain interior, e.g. the increased solid-solution strengthening. This study is dedicated to enriching the diversity of Hall-Petch strengthening mechanisms for the development of high-strength materials. [ABSTRACT FROM AUTHOR]

In this study, we investigate the influence of dislocation strengthening in the metastable parent phase on the deformation-induced martensitic transformation behavior of a face-centered cubic (fcc) Co20Cr20Fe34Mn20Ni6 high-entropy alloy. Annealed and hot-swaged specimens were prepared. In-situ neutron diffraction experiments captured an accelerated transformation kinetics in the hot-swaged specimen due to accumulated dislocations. The phase-specific macrostress development showed that the hexagonal close-packed $ \rvarepsilon $ ε -martensite predominantly accommodated the macroscopic plastic deformation of the annealed counterpart. Conversely, the matrix dislocation strengthening promoted cooperative plasticity of the $ \rgamma $ γ -matrix and the $ \rvarepsilon $ ε -martensitic phase, thus enhancing yield stress while preserving ductility. This paper firstly uncovers the role and significance of matrix dislocation strengthening on the mechanical behavior of metastable high-entropy alloys via in-situ neutron diffraction experiments. [ABSTRACT FROM AUTHOR]

Hot compression tests were performed on a cast Ni-based superalloy IN-100 at various temperatures and strain rate ranges. From the flow stress-true strain curves and the microstructure observations, a processing map of the hot deformation was constructed based on the dynamic material model. At 1473 K, flow stresses showed a plateau region resembling the characteristics of a dynamic recovery, although values varied with the strain rate. The crystal orientation rotated from the initial <001> direction parallel to the compression axis to the <101> direction, which is the primary slip direction of the fcc system. Kink band formation was observed perpendicular to the compression axis, and fine discontinuous dynamic recrystallization at the boundary of the kink bands was observed for the slow strain rate. As the strain rate increased, meta-dynamic recrystallization was observed after the compression test. At 1373 K, the flow stress first increased sharply and then decreased gradually with increasing strain over the whole strain rate. Twin deformation was suggested to occur prior to the appearance of dynamic recrystallization under 1373 K for the low strain rate range. The stable region of hot deformation was considered to be located at approximately 1423 K and 0.003 s−1. [ABSTRACT FROM AUTHOR]

Ti–6Al–4V alloys undergo a multiple phase transformation sequence during electron beam powder bed fusion (EB-PBF) additive manufacturing, forming unique dislocation substructures. Thus, determining the dislocation density is crucial for comprehensively understanding the strengthening mechanisms and deformation behavior. This study performed time-of-flight neutron diffraction (TOF-ND) measurements of Ti–6Al–4V alloys prepared via EB-PBF and examined the dislocation density in the as-built and post-processed states using convolutional multiple whole profile (CMWP) fitting. The present TOF-ND/CMWP approach successfully determined the bulk-averaged dislocation density (6.8 × 1013 m−2) in the as-built state for the α-matrix, suggesting a non-negligible contribution of dislocation hardening. The obtained dislocation density values were comparable to those obtained by conventional and synchrotron X-ray diffraction (XRD) measurements, confirming the reliability of the analysis, and indicating that the dislocations in the α-matrix were homogeneously distributed throughout the as-built specimen. However, the negative and positive neutron scattering lengths of Ti and Al, respectively, lowered the diffraction intensity for the Ti–6Al–4V alloys, thereby decreasing the lower limit of the measurable dislocation density and making the analysis difficult. [ABSTRACT FROM AUTHOR]

This study demonstrates transformation-induced plasticity (TRIP) in conjunction with twinning-induced plasticity (TWIP) in α + β titanium alloys by introducing metastable retained β-phase. By annealing at 850 °C followed by water quenching, metastable retained β-phase (∼25%) was obtained in Ti–6Al–4V alloy. Stress-induced phase transformation in the retained β-phase produced orthorhombic α′′-martensite associated with (021)α′′ twinning, which significantly increased the work-hardening rate and uniform elongation. The findings reveal that the minor retained β-phase is responsible for macroscopic deformation behavior and could aid in novel alloy design that can increase work hardenability with fewer alloying elements than currently available metastable β-titanium alloys. The minor metastable retained β-phase in an α + β titanium alloy with low alloy content enhanced work hardening because of the combined TRIP/TWIP effect. [ABSTRACT FROM AUTHOR]

The efficiency of power dissipation (η) in a dynamic material model has been conventionally used for qualitative predictions to estimate the hot working conditions at which dynamic recrystallization (DRX) is dominant. However, predicting the quantitative value of the DRX fraction (XDRX) from η remains a challenge. In this paper, a constitutive equation is proposed to quantitatively predict XDRX using η. The proposed equation for describing XDRX is derived from the reaction rate equation using the assumption that the DRX rate depends on η. The proposed equation is verified via hot compression tests of equiaxed Ti–6Al–4V ELI alloys (Ti-64) in the (α + β) region. The predicted and experimental XDRX values are found to be generally consistent with one another, exhibiting an average absolute error of 0.05. Furthermore, the proposed equation provides the same level of prediction accuracy as the conventional Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation. Therefore, the proposed equation can be used to quantitatively predict XDRX following hot compression tests of equiaxed Ti-64. Moreover, compared with the JMAK equation, the proposed equation is expressed in fewer parameters and constant terms. It is, thus, expected to facilitate the quantitative prediction of XDRX. [ABSTRACT FROM AUTHOR]

Ti–26Nb–2Fe–(0, 2, 4, 6, 8)Sn alloys were prepared by arc melting and subjected to homogenization, cold rolling, and solution treatment. The β phase stability of the alloys increased with the addition of Sn. Ti–26Nb–2Fe comprised ω + β phases, whereas a single β phase was detected in Ti–26Nb–2Fe–(2, 4, 6, 8)Sn. With an increase in Sn, the Young's modulus first decreased from 83 GPa in Ti–26Nb–2Fe to 58 GPa in Ti–26Nb–2Fe–4Sn and increased to 63 GPa in Ti–26Nb–2Fe–8Sn. Sn suppressed twinning during tension. Although the work-hardening rate decreased with the decrease of twinning, Sn was beneficial for maintaining a low work-hardening rate and postponed necking. All the alloys exhibited remarkably high plasticity. A strong solid solution strengthening effect of Sn was not observed in the studied Ti–Nb–Fe–Sn alloys. Ti–26Nb–2Fe–4Sn with a good combination of high tensile strength (yield strength of 592 MPa and tensile strength of 622 MPa) and low Young's modulus (58 GPa) exhibited significantly higher cell viability than that of the control group after a 7-day culturing, indicating that it is a suitable candidate for biomaterials. [ABSTRACT FROM AUTHOR]

A novel biomaterial Ti-17Mo (mass%) was designed for orthopedic implant applications. Hot working behavior and deformation characteristics were studied in the β-single structure by hot compression tests in the strain rate range 0.01–10 s−1 and temperature range 1123–1273 K using a Thermec Master-Z simulator. The microstructural evolutions of the deformed alloy were studied by a scanning electron microscope equipped with an electron backscattered diffraction detector. The microstructures of the hot deformed alloy showed that dynamic recovery was more active than dynamic recrystallization (DRX). However, partial discontinuous DRX by grain boundary bulging is activated at high temperatures and low strain rates, e.g., 1273 K and 0.01 s−1. Due to the high stacking fault energy of the β phase with a bcc structure, the Ti-17Mo alloy possessed comparatively low activation energy of hot deformation (283 kJ/mol) compared with the conventional Ti alloys bearing multiple alloying elements. [ABSTRACT FROM AUTHOR]

Cu-doped martensitic steels (Fe–(13, 16)Cr–3W–2Cu–1C) (mass%) with multiple carbide precipitates were prepared at different quenching temperatures, and their corrosion behaviours were examined by measuring the weight loss during immersion in a 0.5 M H2SO4 solution. Lower weight losses and corrosion rates were obtained for the alloy samples prepared at higher quenching temperatures. Surface Cu enrichment was observed for all specimens with a large fraction of dissolved Cr species. Moreover, quenching from higher temperatures not only reduced the amount of M23C6 carbide but also decreased the local electrochemical potential difference between the carbide phase and the martensitic matrix via enhanced surface Cu accumulation, thus increasing corrosion resistance by suppressing microgalvanic corrosion between the constituent phases. The corrosion behaviour of the studied steels was remarkably different from those of the Cu-doped stainless and low-alloy steels with passive oxide surface films, suggesting the strong effect of multiple carbide precipitates on their corrosion behaviour. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced plastic (CFRP) is a competitive and promising material that is employed in various industries, including the aerospace industry. Metallized CFRPs and multimaterials based on metals are highly attractive for such applications. In this study, we deposited Sn on an epoxy-based CFRP via cold spraying and investigated the effects of gas temperature on Sn deposition behavior. A continuous Sn coating was successfully obtained on the CFRP at gas temperatures ranging from 473 to 523 K. By contrast, severe erosion of the CFRP substrate occurred at 623 K, making the cold spray coating of Sn difficult. The relationships between the processing temperature, surface topology, and erosion state are examined from the perspective of the CFRP surface temperature. The results indicate that a higher gas temperature leads to a greater surface temperature, resulting in an uneven surface topology with more severe erosion accompanied by a gradual decrease in coating thickness. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs) have emerged as a class of structural alloys with various attractive properties, and their application in additive manufacturing, which enables unprecedented thermal history and geometrical complexity, is promising for realising advanced materials. This study investigates the corrosion behaviour and passive film characteristics of an equimolar AlCoCrFeNi HEA additively manufactured by electron beam melting (EBM). Potentiodynamic polarisation in a 3.5 wt% NaCl solution revealed that the bottom part of the EBM specimen shows better corrosion performance than a conventionally prepared cast specimen in terms of both corrosion and passivation current density, while a continuous increase in the current density without any apparent passivity was observed during the anodic polarisation of the top part. The electrochemical impedance spectroscopic study indicated significant differences in the passive film characteristics between the specimens, and revealed an enhanced charge-transfer resistance and the formation of a more protective passive film of the bottom part. The elemental redistribution, in particular, the enrichment of Cr in the B2 phase during the post-melt high-temperature exposure of the alloy during EBM, was responsible for the improved stability of the passive film, retarding the selective dissolution of the B2 phase in the bottom part. These findings indicate that the microstructural evolution caused by 'in situ annealing' during the EBM process significantly influences the corrosion behaviour of the HEA. [ABSTRACT FROM AUTHOR]

Cobalt‐chromium‐molybdenum alloys exhibit good mechanical properties (yield strength: ~530 MPa, ultimate tensile strength: ~1114 MPa, elongation‐to‐failure: ~47.3%, and modulus: ~227 GPa) and corrosion resistance. In recent years, from the perspective of osseointegration, they are considered to be lower in rank in comparison to the widely used titanium alloys. We elucidate here the significant and favorable modulation of cellular activity of Zr‐modified Co–Cr–Mo alloys. The average grain size of Co–Cr–Mo alloy samples with and without Zr was 104 ± 27 and ~53 ± 11 μm, respectively. The determining role of small addition of Zr (0.04 wt. %) to the Co–Cr–Mo alloys in favorable modulation of cellular activity was accomplished by combining cellular biology and materials science and engineering. Experiments on the influence of Zr addition to Co–Cr–Mo alloys clearly demonstrated that the cell adhesion, spread and cell–substrate interactions were enhanced in the presence of Zr. The spread/growth rate of cells was ~120% on the Co–Cr–Mo alloy and 190% per day on the Co–Cr–Mo–Zr alloy. While the % area covered by the cells increased from ~5.1 to ~33.6% on Co–Cr–Mo alloy and ~19.2 to ~47.8% on Co–Cr–Mo–Zr alloy after 2 and 24 hr of incubation. Similarly, the cell density increased from ~1354 to ~3424 cells/cm2 on Co–Cr–Mo alloy and ~3583 to ~7804 cells/cm2 on Co–Cr–Mo–Zr alloy after 2 and 24 hr of incubation. Additionally, stronger vinculin focal adhesion contact and signals associated with actin stress fibers together with extracellular matrix protein, fibronectin, were noted. [ABSTRACT FROM AUTHOR]

A series of Ti-29Nb-(4, 7, 10, 13)Zr-2Cr alloys were fabricated to investigate the influence of Zr content on microstructures and mechanical properties. All the four alloys present a single β phase after solution treatment. With the increase in Zr content, the 0.2% proof stress is gradually increased from 388 MPa in Ti-29Nb-4Zr-2Cr to 713 MPa in Ti-29Nb-13Zr-2Cr. The Young's modulus gradually is decreased from 80 GPa in Ti-29Nb-4Zr-2Cr to 63 GPa in Ti-29Nb-13Zr-2Cr. The elongation shows the same trend as that of Young's modulus. The changes of mechanical properties are influenced by the β stability and solid solution strengthening effect, which are both enhanced by Zr addition. The Ti-29Nb-13Zr-2Cr alloy presents a Young's modulus of 63 GPa, tensile strength of 730 MPa and elongation of 18% and is a promising biomedical material. [ABSTRACT FROM AUTHOR]

The effect of manganese content (Mn-content) on the beta phase (β-phase) stability, plastic deformability and mechanical behavior of titanium and (8–18 wt.%) manganese low-cost alloys were investigated. The alloys were produced by electric-arc melting under inert argon atmosphere. Microstructure change during cold rolling was evaluated through x-ray diffraction, scanning electron microscope, transmission electron microscope and electron backscatter diffraction in solution-treated and cold-deformed conditions. The β-phase was predominant in all the alloys under study in addition to very fine ω-phase precipitates, especially in the lower Mn-content alloys. Cold workability of the alloys was initially increased in the low Mn-content alloys and then decreased dramatically in the higher Mn-content alloys. The deformation mechanisms were a combination between dislocation slipping and twinning, with a predominance of twinning in the low Mn-content and slipping in the high Mn-content alloys. Tensile test results showed that an ultra-high-strength alloy of about 1950 MPa was obtained in the high Mn-content alloys after cold deformation. [ABSTRACT FROM AUTHOR]

This work identifies microstructural conversion mechanisms during hot deformation (at temperatures ranging from 750 °C to 1050 °C and strain rates ranging from 10−3 s−1 to 1 s−1) of a Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti-17) alloy with a lamellar starting microstructure and establishes constitutive formulae for predicting the microstructural evolution using finite-element analysis. In the α phase, lamellae kinking is the dominant mode in the higher strain rate region and dynamic globularization frequently occurs at higher temperatures. In the β phase, continuous dynamic recrystallization is the dominant mode below the transition temperature, Tβ (880~890 °C). Dynamic recovery tends to be more active at conditions of lower strain rates and higher temperatures. At temperatures above Tβ, continuous dynamic recrystallization of the β phase frequently occurs, especially in the lower strain rate region. A set of constitutive equations modeling the microstructural evolution and processing map characteristic are established by optimizing the experimental data and were later implemented in the DEFORM-3D software package. There is a satisfactory agreement between the experimental and simulated results, indicating that the established series of constitutive models can be used to reliably predict the properties of a Ti-17 alloy after forging in the (α+β) region. [ABSTRACT FROM AUTHOR]

L605 (20Cr-15W-10Ni wt pct) and CCM (28Cr-6Mo wt pct) cobalt-based superalloys are candidates for a wide range of applications, from gas turbine components to biomedical implants. Attention is currently focused on the optimization of grain structure as an appropriate approach to increase yield stress without affecting significantly the ductility. In this study, the Laser Ultrasonics for Metallurgy (LUMet) technology is used to examine in situ the evolution of the mean grain size associated with recrystallization and grain growth during heat treatments from the cold-rolled state. The recrystallization process is completed at 1373 K (1100 °C) for L605 and 1273 K (1000 °C) for CCM. The subsequent grain growth rate in L605 is larger compared to CCM. Continuous measurements of the grain size evolution are found to be consistent with grain growth affected by solute drag. Through in situ measurements, the laser ultrasonic technology significantly accelerates the determination of metallurgical parameters allowing for fast optimization of process parameters required to meet specific applications. [ABSTRACT FROM AUTHOR]

This work identifies microstructural conversion mechanisms during hot deformation (at temperatures ranging from 750 °C to 1050 °C and strain rates ranging from 10−3 s−1to 1 s−1) of a Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti-17) alloy with a lamellar starting microstructure and establishes constitutive formulae for predicting the microstructural evolution using finite-element analysis. In the α phase, lamellae kinking is the dominant mode in the higher strain rate region and dynamic globularization frequently occurs at higher temperatures. In theβphase, continuous dynamic recrystallization is the dominant mode below the transition temperature,Tβ(880~890 °C). Dynamic recovery tends to be more active at conditions of lower strain rates and higher temperatures. At temperatures aboveTβ, continuous dynamic recrystallization of theβphase frequently occurs, especially in the lower strain rate region. A set of constitutive equations modeling the microstructural evolution and processing map characteristic are established by optimizing the experimental data and were later implemented in the DEFORM-3D software package. There is a satisfactory agreement between the experimental and simulated results, indicating that the established series of constitutive models can be used to reliably predict the properties of a Ti-17 alloy after forging in the (α+β) region. [ABSTRACT FROM AUTHOR]

Carbide precipitation in biomedical Co–Cr alloys significantly influences the performance in terms of mechanical properties and corrosion resistance. In this study, we examined the carbide precipitation associated with local solute partitioning in as-cast Co–Cr–W-based dental alloys at the micro- and nano-scale. Co–28Cr–9W–1Si (mass%) alloys with carbon concentrations ranging from 0.01 to 0.33 mass% were prepared. It was found that Cr, W, Si, and C segregated at the interdendritic regions of the face-centered cubic (fcc) γ-grain microstructures, resulting in precipitation; the amount of interdendritic precipitates was found to increase with increasing bulk carbon concentration. We identified, for the first time, the nanosized mixed-phase constituents, which were composed of ∼100 nm fine grains of the γ-phase and M23C6-type carbide, at the interdendritic regions of the high-carbon Co–Cr–W alloy. These nanosized M23C6 carbides were produced with a cube-on-cube orientation relationship ([001]γ☋☋[001]M23C6 and (100)γ☋☋(100)M23C6) with the surrounding submicron γ-grains, while the local morphology changed from equiaxed to plate-like morphology. Nanoscale partitioning of the alloying elements was considered to be the origin of the interdendritic nanostructured constituents. As such, the nanoscale elemental partitioning was observed to alter the local mechanical properties and to affect the corrosion resistance of the alloys. The observed results indicate the importance of local chemistry―which has not received sufficient attention to date―along with carbide precipitation in the optimization of alloy design for achieving desirable properties such as high strength, ductility, and corrosion resistance in dental Co–Cr-based cast alloys. [ABSTRACT FROM AUTHOR]

Biomedical Co–Cr-based alloys used in dental restorations are usually subjected to high-temperature treatments during manufacturing. Therefore, it is practically essential to characterise and control the oxide films formed on the surfaces of these alloys during heat treatment in terms of material loss, the accuracy of fit, and the aesthetics of dental restorations. In this work, the effects of boron doping on the surface oxide films formed on Ni-free Co–28Cr–9W–1Si (mass%) dental alloys under short-term exposure to high temperatures, which simulate the manufacturing process of porcelain-fused-to-metal (PFM) restorations, were investigated. The surface oxides primarily consisted of Cr2O3 in all prepared alloys. The chemical composition of these surface layers varies with the B concentration in the bulk, with the addition of boron stabilising the dense Cr2O3 phase in the oxide films. Nanoscale boron enrichment is clearly observed at the interface between the oxide films and the metal substrate, with the oxidation of boron atoms leading to the formation of a B2O3 layer. Since B2O3 and Cr2O3 prevent oxygen diffusion, the surface oxide films on the boron-containing alloys are thinner; however, no additional thinning was observed when increasing the boron content from 0.01 to 0.8 mass%. It was also found that a small amount of boron does not degrade the corrosion properties of the alloys in a 0.9% NaCl solution. The results obtained in this study will aid in the improvement of manufacturing processes, and ultimately, the performance of PFM restorations. [ABSTRACT FROM AUTHOR]

A Cu-TiC alloy, with nanoscale TiC particles highly dispersed in the submicron-grained Cu matrix, was manufactured by a self-developed two-step ball-milling process on Cu, Ti and C powders. The thermostability of the composite was evaluated by high-temperature isothermal annealing treatments, with temperatures ranging from 727 to 1273 K. The semicoherent nanoscale TiC particles with Cu matrix, mainly located along the grain boundaries, were found to exhibit the promising trait of blocking grain boundary migrations, which leads to a super-stabilized microstructures up to approximately the melting point of copper (1223 K). Furthermore, the Cu-TiC alloys after annealing at 1323 K showed a slight decrease in Vickers hardness as well as the duplex microstructure due to selective grain growth, which were discussed in terms of hardness contributions from various mechanisms. [ABSTRACT FROM PUBLISHER]

The ultrafine-grained (UFG) microstructures of Ni-free Co-29Cr-6Mo (mass pct) alloys, which are designed for biomedical applications, have been successively fabricated by the conventional hot-forging process. The grain size decreased with increasing hot-forging reduction, and the equiaxed UFG structures with a mean grain size less than 1 μm were obtained in 83 pct (true strain of 1.8) hot-forged specimens. Significant grain refinement drastically enhanced tensile strength; dislocations residual in the grains also play a crucial role for strengthening of the UFG-structured specimen. The elongation decreased with the reduction in grain size. However, we revealed that the addition of nitrogen, which is one of the nontoxic γ phase (face-centered cubic [fcc] structure) stabilizer, improves the ductility of the UFG alloys remarkably with maintaining high strength. It was deduced that the enhanced ductility in the UFG material by N doping was related to constituent phase and strain-induced martensitic transformation behavior: the addition of nitrogen eliminated athermal ε martensite detrimental to tensile elongation, and strain-induced martensitic transformation effectively increased work-hardening rate to avoid the plastic instability at the early stage of deformation. The present method characterized by ultragrain refinement in conjunction with nitrogen addition to stabilize the γ phase can provide a potent strategy to obtain superior combination of high strength and adequate ductility. [ABSTRACT FROM AUTHOR]

We have previously reported that ultrafine-grained (UFG) microstructures can be obtained in a Co-29Cr-6Mo (wt pct) alloy by utilizing dynamic recrystallization (DRX) that occurs during conventional hot deformation (Yamanaka et al.: Metall. Mater. Trans. A, 2009, vol. 40A, pp. 1980−94). The present study investigates the novel DRX mechanism of this alloy in detail. The microstructure evolution during hot deformation under relatively high Zener-Hollomon ( Z) parameter conditions for which ultrafine grains can develop was systematically investigated by electron backscatter diffraction (EBSD) and transmission electron microscopy. This alloy exhibited a different flow stress behavior and microstructural development from conventional DRX mechanisms. The deformation microstructure contained a large number of stacking faults, which implies that planar dislocation slip is the primary deformation mechanism in the hot deformation of the Co-29Cr-6Mo alloy due to its abnormally low stacking fault energy (SFE) at elevated temperatures. Inhomogeneities in local strain distributions induced by planar slip will enhance grain subdivision by geometrically necessary (GN) dislocation boundaries. Deformation twinning may also contribute to grain refinement. The DRX mechanism operating in the Co-29Cr-6Mo alloy is discussed by considering the relationships between anomalous dislocation structures, flow stress behavior, texture development, and nucleation behavior. [ABSTRACT FROM AUTHOR]

The effect of hot rolling on the microstructural evolution and mechanical properties of biomedical Co-29Cr-6Mo-0.14N (mass pct) alloys has been investigated. The alloy strength increases with increasing hot-rolling reduction; the specimen hot rolled to 92.8 pct (equivalent strain of 3.04) exhibits a yield stress as high as 1100 MPa, which is twice that of the conventionally prepared specimens, with no significant loss in ductility. The grain size hardly changed after hot rolling to 60.0 pct, whereas a specimen hot rolled to 92.8 pct has finer grains. The hot-rolled specimens exhibit deformed microstructures with many deformation twins and dislocation boundaries. The accumulated strain increases monotonically with increasing hot-rolling reduction, although short annealing occurs on each hot-rolling pass. The strengthening mechanism in the hot-rolled Co-29Cr-6Mo-0.14N alloys is discussed by considering the dislocation and grain refinement strengthening. [ABSTRACT FROM AUTHOR]

In order to examine the microstructural evolution during hot-compression deformation of the biomedical Co-29Cr-6Mo (weight percent) alloy without the addition of Ni, hot-compression tests have been conducted at deformation temperatures ranging from 1050 °C to 1200 °C at various strain rates of 10−3 to 10 s−1. The grain refinement due to dynamic recrystallization (DRX) was identified under all deformation conditions by means of field-emission scanning electron microscopy/electron backscattered diffraction (FESEM/EBSD) and transmission electron microscopy (TEM) observations. Although the DRX grain size ( d) of the deformed specimens considerably decreased with an increasing Zener–Hollomon ( Z) parameter at strain rates ranging from 10−3 to 0.1 s−1, a grain size coarser than that predicted from the d- Z relation was obtained at strain rates of 1.0 and 10 s−1. An ultrafine-grained microstructure with a grain size of approximately 0.6 μm was obtained under deformation at 1050 °C at 0.1 s−1, from an initial grain size of 40 μm. The grain refinement to a submicron scale of biomedical Co-Cr-Mo alloys has been achieved with hot deformation by ~60 pct due to DRX, in which the bulging mechanism is not operative. The ultrafine grains obtained due to DRX without bulging is closely related to the considerably low stacking-fault energy (SFE) of the Co-Cr-Mo alloy at deformation temperatures. [ABSTRACT FROM AUTHOR]

In powder bed fusion–electron beam melting, the alloy powder can scatter under electron beam irradiation. When this phenomenon—known as smoking—occurs, it makes the PBF-EBM process almost impossible. Therefore, avoiding smoking in EBM is an important research issue. In this study, we aimed to clarify the effects of powder bed preheating and mechanical stimulation on the suppression of smoking in the powder bed fusion–electron beam melting process. Direct current electrical resistivity and alternating current impedance spectroscopy measurements were conducted on Inconel 718 alloy powder at room temperature and elevated temperatures before and after mechanical stimulation (ball milling for 10–60 min) to investigate changes in the electrical properties of the surface oxide film, alongside X-ray photoelectron spectroscopy to identify the surface chemical composition. Smoking tests confirmed that preheating and ball milling both suppressed smoking. Furthermore, smoking did not occur after ball milling, even when the powder bed was not preheated. This is because the oxide film undergoes a dielectric–metallic transition due to the lattice strain introduced by ball milling. Our results are expected to benefit the development of the powder bed fusion–electron beam melting processes from the perspective of materials technology and optimization of the process conditions and powder properties to suppress smoking. [ABSTRACT FROM AUTHOR]

In recent years, spherical powders with no or minimal internal pores fabricated by the plasma rotating electrode process (PREP) have been highly recommended for powder-type additive manufacturing. Most research on PREP is aimed at establishing relationship between PREP parameters and powder size. However, almost no dedicated research on granulation behavior has been conducted so far. In the present study, PREP experiments of Ti64 and SUS316 alloys were carried out. Numerical modeling based on computational thermo-fluid dynamics was developed to analyze the granulation behavior. In particular, the roles of the additionally introduced gas blast and the morphology of the electrode end surface in fluid granulation were preliminarily investigated. The study showed that in addition to the electrode's rotating speed and diameter, manipulating the plasma arc current (i.e., the melting rate) could also be an effective way to control the PREP-powder size. According to the simulation, there were competing actions of the gas blast affecting the powder size. The gas blast created disturbance on the fluid and deepened the depression of the electrode end surface, which facilitated powder refinement. However, the cooling effect enhanced the fluid stability and hindered fluid granulation. The conclusions indicated the possibility of using various methods to manipulate PREP-powder size. [ABSTRACT FROM AUTHOR]

Carbide-reinforced martensitic steels, known as high-speed steels (HSSs), have been used as tool materials in various industries because of their high hardness and wear resistance. Nonetheless, such steels show severe degradation when used in a corrosive environment because typical Cr2O3 films, which generally realise passivity in these alloys, do not often work effectively. Here, we demonstrate that the corrosion resistance of a high-carbon-containing Fe–Cr–W-based alloy in a sulfuric acid solution can be significantly improved by the addition of trace Cu. The enrichment of Cu at the surface of the alloy as corrosion proceeds is key to inhibiting further corrosion. A theoretical model for a micro corrosion cell, which should be applicable to any material employed under the same corrosion conditions in fields such as the chemical and energy industries, was developed to interpret the experimental observations. [ABSTRACT FROM AUTHOR]

In the present study, the hot deformation behavior and microstructural evolution of Ti–5Al–2Sn–2Zr–4Mo–4Cr (Ti‐17) alloy are examined at temperatures above the β‐transus (1153 K). The true stress–true strain curves obtained during hot compression testing (temperature region 1173–1373 K, strain rates from 10−3 to 1 s−1) all exhibited steady‐state flow behavior. The constitutive equations, considering applied strain as the main parameter, revealed that the apparent activation energy of the hot deformation process monotonously decreases with increasing applied strain. Its value obtained at a true strain of 0.6 is equal to 190 ± 52 kJ mol−1, which is close to the activation energy of self‐diffusion in β‐Ti. Processing maps based on the dynamic materials model shows that the power dissipation efficiency generally decreases with increasing strain rate and applied strain. The domain with the peak efficiency of approximately 60% is located at a temperature of 1173 K and strain rate of 10−3 s−1. Furthermore, flow instabilities are observed only at strain rates higher than 0.1 s−1 regardless of temperature. The obtained results can be correlated with the dynamic recovery process, representing a dominant mechanism for the hot deformation of Ti‐17 alloy at β‐stable temperatures. In the present study, the hot deformation behavior and microstructural evolution of Ti‐17 alloy are examined at temperatures above the β‐transus. The constitutive equations and processing maps are constructed as a function of applied strain. The obtained results can be correlated with the dynamic recovery process, representing a dominant mechanism for the hot deformation of Ti‐17 alloy at β‐stable temperatures. [ABSTRACT FROM AUTHOR]