Enhanced mechanical properties and microstructural stability of ultrafine-grained biodegradable Zn–Li–Mn–Mg–Cu alloys produced by rapid solidification and high-pressure torsion

Materials Today Communications

The static recrystallization and grain growth of a hybrid AZ31/Mg-0.6Gd (wt.%) material fabricated by high-pressure torsion (HPT) through 20 turns were explored after isochronal annealing at 150, 250, 350 and 450 °C for 1 h using electron backscatter diffraction, transmission electron microscopy and Vickers microhardness measurements. The results reveal heterogeneity in the grain size distributions of the AZ31 and Mg-0.6Gd regions after annealing at the lower temperatures of 150 and 250 °C leading to a clear AZ31/Mg-0.6Gd interfacial border. At the higher temperatures of 350 and 450 °C the AZ31/Mg-0.6Gd interfaces were not well-defined owing to the occurrence of grain growth. It is shown that grain growth is restricted in the AZ31 and Mg-0.6Gd regions due to the presence of stable nano-size Al8Mn5 particles and the precipitation of Mg17Al12 and Mg12Zn at 250 °C and of Mg5Gd and Mg12Gd phases at …

Surface and Coatings Technology

A supersaturated solid solution nanostructure of an immiscible Cosingle bondCu system is among the promising nanocrystalline (NC) alloys offering enhanced thermal and mechanical stability. In this paper, experiments were conducted to study the phase transformation and tailoring microstructure from a homogeneous/single-phase to a heterogeneous/dual-phase solid solution layered Cosingle bondCu nanostructure via pulsed electrochemical deposition (PED). The increasing concentration of sodium dodecyl sulfate (SDS) in electrolyte played a crucial role in stabilizing a homogeneous solid solution Cosingle bondCu nanostructure. On the other hand, the opposite approach led to the formation of heterogeneous solid solution Cosingle bondCu alloys in the form of multilayered nanostructure consisting of the primary and secondary solid solution Cosingle bondCu differing in 10–15 at.% Cu. The separation of …

The formation of ultrafine grains with nanostructural features in metallic materials by SPD processing can provide superior mechanical and, simultaneously, functional properties of metals and alloys, for example, high strength and electrical conductivity in Cu and Al alloys, enhanced fatigue endurance and high corrosion and erosion resistance in Ti alloys and many other so-called multifunctional properties. This chapter demonstrates that the level of the above properties is determined by small grain size, nonequilibrium grain boundaries with high density of grain boundary dislocations, nanoscale grain boundary segregations and precipitations, etc. Changes in the physical properties of UFG materials are associated with the comparability of grain sizes and characteristics, including the free path length of electrons and the size of magnetic domains.In particular, nanocrystalline magnetic hard materials are …

Journal of Materials Research and Technology

Advanced structural materials are expected to display significantly improved mechanical properties and this may be achieved, at least in part, by refining the grain size to the submicrometer or the nanocrystalline range. This report provides a detailed summary of the role of grain size in the mechanical properties of metals. The effect of grain size on the high temperature behavior and the development of superplasticity is illustrated using deformation mechanism maps and the development of exceptional strength through grain refinement hardening at low temperatures is also discussed. It is shown that the deformation mechanism of grain boundary sliding, as developed theoretically, can be used to effectively predict both the high and low temperature behavior of metals having different grain sizes. This analysis explains the increase in strain rate sensitivity in ultrafine-grained metals with low and moderate melting …

Surface and Coatings Technology

It has recently been proposed to modify conventional WC-Co coatings with nano-sized particles to improve their properties. Modification of the coatings with nano-sized carbides may provide higher wear resistance or phase composition stability. This work characterized the changes in the residual stresses induced by introducing WC nanoparticles into a WC-Co coating and the resulting change in their sliding wear behavior.A powder mixture consisting of agglomerated and sintered WC-17Co feedstock powder and 5 % nano-sized WC was deposited on a carbon steel substrate using the High Velocity Air Fuel (HVAF) process. Microstructural characterization using scanning electron microscopy and EBSD confirmed that nano-sized WC particles were embedded in the coatings after the spraying process, primarily along the boundaries of the WC-Co lamellae. This resulted in an enhancement of microhardness …

Journal of Alloys and Compounds

Aluminium matrix nanocomposites reinforced with carbon nanotubes were fabricated in a new way by direct synthesis using high-pressure torsion (HPT). Aluminium of 99.99 % and 99.5 % purities were used as matrix materials with carbon nanotubes in amounts of 0.5 and 1 wt% as reinforcement. The HPT processing led to extensive grain size refinement which was significantly higher than for pure metals and to a relatively uniform distribution of the fillers. The grain size of the matrix was smaller for Al99.5 compared to Al99.99 while the particle spatial distribution was more homogenous for the Al99.99 matrix. This was attributed to a lower hardness and higher plasticity of Al 99.99 alloy. The addition of carbon nanotubes also improved the thermal stability of the ultrafine-grained structure, especially if homogenously distributed as for the Al99.99 matrix nanocomposites.

UFG metals and alloys attract the materials science community owing to their superior mechanical properties. This chapter considers achieving enhanced mechanical properties in the UFG materials processed by SPD techniques. Special emphasis is laid on the examples and origins of the phenomenon of superstrength as well as the description of the hardening mechanisms in the materials. The chapter views the manifestation of the SPD paradox caused by the formation of equiaxial UFG structure and control of grain boundary type and segregations. The SPD paradox is evident in the simultaneous growth of strength and ductility. Mechanisms for enhancing the ductility of UFG materials are considered. The chapter also focuses on the importance of grain refinement in increasing fatigue strength and endurance, creep resistance of materials, the manifestation of the superplasticity effect at lower temperatures, and …

Journal of Manufacturing Processes

This study focuses on investigating the microstructure and mechanical properties across the interface of a multi-material, Austenitic Stainless Steel 316 L (SS316L) and Inconel 718 (IN718), fabricated using laser powder bed fusion (LPBF) additive manufacturing (AM) technique. Challenges such as distortion, porosity, and intermetallic formation are common in such structures. To address these challenges, high-pressure torsion (HPT), a severe plastic deformation (SPD) process, was employed to eliminate porosity and create a homogeneous microstructure. The samples underwent HPT with varying numbers of turns, namely quarter, half, one, five, and ten turns, at room temperature and under 6 GPa of pressure at a speed of 1 rpm. The process aimed to create ultrafine and nano-grains in the microstructure and reduce the defects. A comprehensive characterization approach was adopted to analyze the interface …

Philosophical Magazine

The Geometrically Necessary Dislocation (GND) density was estimated from Electron Backscatter Diffraction (EBSD) data for an AZ31/Mg-0.6Gd (wt.%) hybrid material fabricated by high-pressure torsion (HPT) at room temperature through an equivalent strain range of ϵeq = 0.3–144 using Kernel Average Misorientation (KAM) and the Nye tensor approaches. The results show that generally the GND densities are significant at the beginning of the deformation (ϵeq = 0.3) and decrease in both alloys when ϵeq increases. The Mg-0.6Gd alloy exhibits a lower GND density due to rapid dynamic recrystallization. These results were compared to the GND densities measured in AZ31 and Mg-0.6Gd mono-materials processed separately by HPT under the same experimental conditions. In these mono-materials the GND densities increase with increasing equivalent strain up to 7 and then decrease with further straining …

Frontiers in Bioengineering and Biotechnology

The currently available treatments for inner ear disorders often involve systemic drug administration, leading to suboptimal drug concentrations and side effects. Cochlear implants offer a potential solution by providing localized and sustained drug delivery to the cochlea. While the mechanical characterization of both the implants and their constituent material is crucial to ensure functional performance and structural integrity during implantation, this aspect has been mostly overlooked. This study proposes a novel methodology for the mechanical characterization of our recently developed cochlear implant design, namely, rectangular and cylindrical, fabricated using two-photon polymerization (2 PP) with a novel photosensitive resin (IP-Q™). We used in silico computational models and ex silico experiments to study the mechanics of our newly designed implants when subjected to torsion mimicking the foreseeable implantation procedure. Torsion testing on the actual-sized implants was not feasible due to their small size (0.6 × 0.6 × 2.4 mm³). Therefore, scaled-up rectangular cochlear implants (5 × 5 × 20 mm³, 10 × 10 × 40 mm³, and 20 × 20 × 80 mm³) were fabricated using stereolithography and subjected to torsion testing. Finite element analysis (FEA) accurately represented the linear behavior observed in the torsion experiments. We then used the validated Finite element analysis models to study the mechanical behavior of real-sized implants fabricated from the IP-Q resin. Mechanical characterization of both implant designs, with different inner porous structures (pore size: 20 μm and 60 μm) and a hollow version, revealed that the cylindrical …

Journal of Alloys and Compounds

The authors regret but we accidentally left out one person who should have been included in this article: Aleksandra Bartkowska from European Organization for Nuclear Research (CERN), 1211 Geneva, Switzerland,[email protected]. If it is possible could you include her to this article with the following order:

Ultrafine-grained (UFG) materials are innovative and quite promising for wide application. The important advantage associated with the use and commercialization of UFG materials includes first of all their advanced properties, also production efficiency is important due to the development of new SPD technique.This chapter discusses the innovative potential and practical applications of UFG materials. Titanium implants made of nanoTi are promising for dentistry and orthopedics. UFG copper alloys can be used for making electrodes for welding. UFG composites based on copper matrix and WС are attractive for manufacturing current carrying cores, electric motors, contact wires. Nanocrystalline alloy Cu–10 at.% Ta is an exciting example illustrating the possibility of increasing thermal stability at elevated temperatures by creating clusters of the alloying element on the grain boundaries, preventing their migration …

Journal of Alloys and Compounds

Ni-Co-Fe-Mn-Ti high entropy alloys (HEA) were fabricated via powder bed fusion using elemental powders. Based on thermodynamic calculations, 3 alloys were designed with medium to high entropy (from 3 to 5 components) and printed. Additive manufacturing (AM) was performed, while varying the laser power and exposure time (point-by-point exposure laser working mode). The obtained samples were characterised by means of macroscopic observations combined with porosity analysis, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), as well as compression and hardness tests. The varied process parameters and the content of individual alloying elements directly impacted alloy processability and sample properties. We proved that it is possible to produce HEAs (Ni-Co-Fe-Mn-Ti) with low porosity and good …

Philosophical Magazine

The influence of high-pressure torsion (HPT) and annealing on microstructure, texture and thermal stability of an immiscible composite Cu43%Cr alloy was studied using electron backscatter diffraction, X-ray diffraction and microhardness measurements. As-received alloy samples were subjected to HPT and subsequent annealing treatment in the range of 210–850°C for 1 h in order to develop ultrafine-grained (UFG) microstructures and highlight their thermal stability. The Cu and Cr grains were refined to ∼0.45 and ∼0.39 µm, respectively and exhibited equiaxed morphology. The crystallographic texture was of shear type in both Cu and Cr with the domination of C and F orientations, respectively. The UFG microstructure and texture were retained in the Cu43%Cr alloy up to 850°C. The global results show that the immiscible composite Cu43%Cr alloy exhibits a high thermal stability up to 850°C. The evolution of …

Journal of Materials Science

This study investigates the correlation between coercivity (Hc), grain size (d), and dislocation density in the Permimphy alloy (Fe–80%Ni–6%Mo). The samples used in this study were subjected to varying levels of applied strain through processing by high-pressure torsion. The microstructure and the magnetic coercivity were analyzed using a scanning electron microscope, electron backscatter diffraction and vibrating sample magnetometry. The grain size of the samples varied from 30 to 190 nm. This study demonstrated a strong correlation between Hc and microhardness when d > 3 µm. The results show that the coercivity of the Permimphy alloy follows an inverse V-shape with respect to grain size. The coercivity of the samples decreased despite increasing the dislocation density and the hardness when d < 3 µm. This phenomenon is attributed to the ferromagnetic exchange interaction across multiple grains …

A continuous effort has been made in the research field of processing of ultrafine-grained materials (UFG) through the application of severe plastic deformation (SPD) over the last three decades. In particular, a new research focus was developed for the utilization of conventional SPD techniques with some modification in the procedures to synthesize advanced, hybrid nanocrystalline metals and materials demonstrating exceptional mechanical properties and functionalities. Hybrid nanocrystalline materials refer to composites consisting of two or more constituents at the nanometer level or the nano-to-micro level, leading to a gradient or heterogeneous microstructure formation. Accordingly, this chapter describes the recent developments in strategies for the formation of bulk nanostructured metal systems and UFG materials from powders and dissimilar bulk metals. The further sections discuss the uniquely tuned …

Materials Science and Engineering: A

The present study highlights the comparative interplay between microsegregation of alloying elements and structural unit size on the strength and impact toughness properties of a medium carbon low alloy armor grade steel. Interestingly, despite possessing finer substructural unit (Bain width), the sample austenitized at a lower temperature (800° C) exhibits inferior impact toughness. This emanates from centerline fissure cracking assisted by severe segregation-induced tensile residual stress at the mid-thickness region. On the other hand, coarse Bain width reduces toughness at the higher temperature (1200° C). Therefore, austenitization at an intermediate temperature (1000° C) imparts excellent impact toughness (∼ 45 J at–40° C) combined with a commendable yield strength (∼ 1090 MPa). This is attributed to the fine Bain width along with moderate segregation, indicating the significance of austenitization …

Materials Science and Engineering: A

Carbon nanotubes (CNTs) reinforced Al-Li-Cu alloy matrix composite is a promising candidate for the lightweight structural materials demanded in advanced industrial areas such as aerospace. However, how to fully exploit the combined strengthening effects of CNTs and precipitates of the Al-Li-Cu matrix is still an open issue. In the present study, the Cu coating was firstly precoated on CNTs before fabricating CNTs reinforced Al-Li-Cu alloy matrix composite. Benefiting from the Cu coating, the improved CNTs dispersion and Al-CNTs interfacial bonding was achieved, and the precipitation of Al2Cu, Al2CuLi, and Al3Li was enhanced in the AlLiCu alloy matrix, resulting in the enhanced strength-ductility synergy for Cu-coated CNTs reinforced AlLiCu alloy matrix composite. Moreover, strengthening and toughening mechanisms analyzation reveals that the Orowan strengthening of CNTs and precipitates, as well as …

Materials Science and Engineering: A

After scanned laser surface remelting the resultant rapid solidification microstructures of multicomponent alloys exhibit morphological gradients, with scale refinement and non-equilibrium features, including non-equilibrium solute trapping, which are associated with property changes. Combinations of site-specific mechanical property measurements by nano-indentation and microstructural analyses by electron microscopy have been used to determine microstructure-property relationships for the characteristic features of the rapid solidification microstructure of a hypo-eutectic Al–Cu alloy containing 10 atom percent Cu. A microstructure gradient developed as the solidification rate increased monotonically during the re-solidification process. For a laser scan velocity of 3 mm/s most of the rapid solidification microstructure is comprised of micrometer scale refined dendritic cells of α-Al(Cu) and nanometer scale refined …

Materials Science and Engineering: A

This research aimed to investigate the impact of friction stir processing (FSP) as a modifying technique on the microstructure and mechanical properties of Cu–10Al, Cu–10Al–5Ni, and Cu–10Al–5Ni–5Fe nickel-aluminum bronze (NAB) alloys under two different conditions of ambient and underwater submerged conditions concerning the as-cast state of these materials. Adding nickel as an alloying element to the Cu–10Al composition resulted in the formation of NiAl intermetallic compound and a 3% increase in the volume percentage of secondary phases. Furthermore, incorporating iron into the Cu–10Al–5Ni composition prevented the formation of detrimental γ 2 phase and instead created κ intermetallic compounds within the structure, leading to an overall increase of approximately 14% in the volume percentage of secondary phases compared to the Cu–10Al composition. The initial coarse, rough, and …

Materials Science and Engineering: A

In this study the grain size effect on mechanical properties of a body-centered-cubic Ti–30Zr–5Mo alloy was investigated. Double yielding behavior in the stress-strain curves and four-stage behavior in the strain hardening rate curves can be seen in all Ti–30Zr–5Mo materials with different average grain sizes ranging from 6 to 475 μm, which is attributed to the occurrence of the stress-induced α′ transformation. The static Hall-Petch coefficient (k) for phase transformation was calculated to establish the relationship between grain size and trigger stress of the various materials. With the increase of strain, the hindrance of αʹ/β grain boundaries and αʹ/αʹ grain boundaries to dislocations gradually replaced β/β grain boundaries, thus the work hardening ability and k value changed. β grains were segmented by α′ martensite, resulting in a dynamic Hall‒Petch effect. Combined with a large stress field in the fine …

Materials Science and Engineering: A

A commonly used structural steel, namely high-strength low-alloy (HSLA) steel, HSLA-100, was fabricated using the laser powder bed fusion process in this work. Critical processing parameters such as laser power and scanning speed for achieving the least porosity were identified. The designed post-heat treatment differs from the traditionally manufactured HSLA steels. The optimum homogenization time was 80 min at 950 °C with the lowest prior austenite grain size. The peak hardness was achieved after tempering at 550 °C for 5 h, and atom probe tomography showed that the fraction of Cu and M2C (M: Mo, Cr) was the highest along with the co-precipitation of these strengthening phases at this condition. The yield strength (YS) and elongation (%El) of the builds printed with optimized parameters (porosity∼0.5%, YS = 875 MPa, and %El = 23%) were superior to those printed with factory-default …

Materials Science and Engineering: A

Owing to hot cracking, printing aerospace grade AA7050 is challenging via fusion-based additive manufacturing. Using a deformation-based additive process, here we show that forging-like tensile properties are achieved in additively manufactured AA7050 without chemical modification for the first time (excluding lubricant on feed-rod surfaces) — YS: 430 MPa; UTS: 491 MPa; elongation: 11.2% with T74 temper.

Materials Science and Engineering: A

Overcoming the strength-plasticity trade-off in GPa-grade dual-phase steel while simultaneously enhancing both properties poses a significant challenge. In this study, we propose an innovative strategy to break this inherent dilemma by designing an alternately arranged ferrite and martensite lamellar microstructure with appreciable deformation coordination in dual-phase steel. Compared to traditional dual-phase steel (DP steel) with a block microstructure and the same phase components, the newly developed heterogeneous lamellar dual-phase steel (L-DP steel) prepared by a cyclic intercritical quenching process demonstrates a remarkable 90 % increase in uniform elongation (from 9.1 ± 0.4 % in DP steel to 17.3 ± 0.3 % in L-DP steel). The ultimate tensile strength increases slightly from 1002 ± 10 MPa (DP steel) to 1034 ± 11 MPa (L-DP steel). The lamellar martensite and lamellar ferrite with a certain hardness …

Materials Science and Engineering: A

The high design freedom of laser powder bed fusion (LPBF) additive manufacturing enables new integrated structures, which in turn demand advances in the process conditions and material design to exploit the full potential of this process. A computational multi-scale thermal simulation and metallurgical analysis of the aluminium alloy Scalmalloy® were used to develop and present a specific process window to enable an in-situ heat treatment during LPBF. High resolution analysis and synchrotron experiments on specimens manufactured in this process window revealed a major proportion of nano-sized A l 3 (S c x Z r 1− x) solute-clusters were already present in the as-built state, as predicted by simulation. Supported by this experimental research, the new processing concept of in-situ heat treatment yielded the highest recorded strength values combined with high ductility directly after LPBF for Scalmalloy®. This …

Materials Science and Engineering: A

Elucidating the tribological behaviors of CoCrNi-based high-entropy alloys (HEAs) at cryogenic temperatures is crucial for their practical application. This work uncovers the correlation between the wear-induced microstructural evolutions and tribological properties of single-phase CoCrFeNiMn HEA and heterogeneous CoCrFeNiAl HEA upon two contact conditions at 173 K. When CoCrFeNiMn HEA matches with GCr15 rather than Si3N4, low contact stress and high flash temperature suppress the inhomogeneous deformation initiated by martensitic transformation and in turn create a gradient nanograined tribo-layer activated by high-density dislocations and nano-scale deformation twins, which progressively accommodates the frictional strain and reduces wear by an order of magnitude. Instead, the tribological properties of the CoCrFeNiAl HEA sliding against Si3N4 are slightly superior to those sliding against …

Materials Science and Engineering: A

The aim of this work is to study the mechanical behavior of 6061 aluminum walls produced by Wire Arc Additive Manufacturing at the different scales of the material. The residual stresses of the parts are characterized on the surface and in the bulk thanks to X-ray and neutron diffraction techniques, respectively. Although the residual stress values determined in the close-surface are low (40 MPa for the maximum value), the mechanical state is different in depth with significant maximum residual stress levels ( ± 100 MPa). Tensile tests carried out on samples extracted from a WAAM wall in three orientations reveal that the mechanical properties of the manufactured material are slightly better compared to conventional material in T6 state. In situ X-ray diffraction experiments have also been performed under uniaxial tensile testing in order to determine strain pole figures. An elasto-plastic self-consistent model …

Materials Science and Engineering: A

Heterostructured laminates have attracted significant attention in the materials community owing to their exceptional combination of strength and ductility. However, long-standing questions remain regarding the impact of the strength difference between the soft and hard layers on the synergistic strengthening in hetero-laminates with weak mechanical heterogeneity; the role played by soft/hard layers with various dislocation storage capacities on the strength–ductility synergy is also poorly understood. In this study, a series of typical heterostructured copper–brass laminates were fabricated using the diffusion welding + forging + rolling + annealing technique. The results demonstrated that larger microstructural and mechanical heterogeneities improved the strength–ductility combination of the hetero-laminates. The relatively weak mechanical heterogeneity and superior dislocation storage capacity of the soft copper …

Materials Science and Engineering: A

This study investigated the effect of grain size distribution on the deformation behavior in fine-grained (FG) austenitic stainless steels (γ-SSs). Commercial Cr–Mn–N γ-SS was selected as the coarse-grained (CG) specimen, which was cold rolled and then annealed at 1000 °C for 60 s and 700 °C for 3600 s to obtain FG specimens with similar grain sizes but different grain size distributions. The CG specimens annealed at 1000 °C for 60 s and 700 °C for 3600 s were referred to as unimodal-FG and bimodal-FG specimens, respectively. The tensile properties revealed that the yield strength was enhanced from 383 MPa to 685 MPa when the grain size was refined from CG (10.7 μm) to FG (∼1.8 μm). Moreover, the bimodal-FG specimen exhibited a higher total elongation of 48% than 36.5% for the unimodal-FG specimen. Transmission electron microscopy, electron backscatter diffraction and X-ray diffraction were used …

Materials Science and Engineering: A

Additive manufacturing (AM) is getting significant attention in realizing customizable nitinol (NiTi) devices for biomedical applications. However, due to the change in composition and constituent phases occurring during printing and the microstructural inhomogeneity in the printed parts, obtaining a desired set of phase transformation behaviors and superelastic properties is a major challenge. In this work, laser powder bed fusion (LPBF) was used to fabricate NiTi at a very low laser energy density (35 J/mm3) on a titanium base plate while keeping these behaviors and properties within desirable ranges without any structural defects such as crack and delamination. Our measurements showed that the as-printed NiTi exhibited distinct one-step phase transformation with the austenite finish (Af) temperature of 2.1 °C. To increase the Af temperature to 30.2 °C (within the recommended range of Af temperature for …

Materials Science and Engineering: A

Fine cellular substructures are typical microstructure feature of high entropy alloys (HEAs) produced via selective laser melting (SLM), playing a pivotal role in improving the mechanical properties. Nonetheless, the controlling of cellular substructure and its impact on the mechanical properties remains ambiguous. This study investigates the effect of energy densities on the cellular substructure evolution and mechanical properties of the FeCoCrNiMo 0.2 HEA. It is found the increase in energy density causes a decrease in temperature gradient (G) and solidification rate (R) in molten pool, consequently leading to the increase of cellular substructure size and the intensification of Mo segregation at cellular substructure boundaries. The cellular substructure size (d) can be described by formula, in which G and R can be obtained from discrete element method-computational fluid dynamics (DEM-CFD) simulation. The …

Materials Science and Engineering: A

Inconsistency of equipment and inappropriate design in the laser powder-bed fusion additive manufacturing (LPBF-AM) process are not tightly related to the technology development and are more challenging to avoid. Those processing-related factors can introduce sudden changes in the products' local mechanical properties by internal flaws or microstructure variation. The different property zones and their interfaces will accumulate stress and decrease lifetime. In this work, we applied ultrasound elastography and density profile to evaluate an LPBF Ti6Al4V sample with three property zones induced by different laser speeds to represent equipment errors or inappropriate designs. The elastography clearly distinguished three zones and their corresponding dynamic properties. The ultrasound estimated density profile conforms with profilometer-determined values. The interfaces in the Ti64 sample between the …

Materials Science and Engineering: A

Thermal stability of powder metallurgy (PM) superalloys has a critical impact on their service life. In this study, the microstructure, tensile properties, and fracture mechanism of a novel Ni-based PM superalloy were investigated after thermal exposure at 750–850 °C for 50–2000 h. The coarsening mechanism of γ′ phase transitions from matrix-diffusion controlled to interface-diffusion controlled with an increase in exposure temperature and time. The diffusion activation energy for γ′ phase coarsening was 258.65 kJ/mol, which was primarily controlled by Al, Ti, and W diffusion. Meanwhile, the μ phase precipitated because Cr, Co, and Mo desolvated from the γ′ phase and γ matrix. When the alloy was exposed to a temperature of 800 °C for 50 h, the room temperature yield strength (YS) was 1332 MPa and the elongation was 23.5%, which was significantly better than those of the PM superalloys previously reported …

Materials Science and Engineering: A

To improve the high temperature performance of the titanium matrix composite, solution and aging treatments were carried out on the (TiB + Ti5Si3)/TA15 composite with a two-scale network structure. The microstructure evolution during the heat treatment and high temperature performance at 650 °C were investigated. It is found that a fine matrix with basket-weave structure and nano-scaled Ti5Si3 can be obtained through a proper combination of solution and aging treatment. Optimal high temperature performance is achieved with yield strength and ultimate tensile strength improved by 15 % and 24 % respectively without sacrificing ductility. Matrix refinement is attributed to network-distributed TiB and fine martensite after solution treatment. During subsequent aging, fine secondary α phase and β phase are formed and then grow. The growth mechanisms of the secondary α phase and β phase are phase boundary …

Materials Science and Engineering: A

In the present research, Al7075 matrix composites containing carbon nano-tubes (CNTs) and graphene nano-plates (GNPs) processed through accumulative roll bonding (ARB). Accumulative roll bonding carried out up to 3 passes at 400 °C with 50% thickness reduction per pass. The effect of CNTs and GNPs on the microstructural evolution and strengthening mechanisms were investigated. Microstructural evolutions in processed composites were characterized by using field emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), and electron backscatter diffraction (EBSD).The grain orientation spread (GOS) analysis shows that the volume fraction of recrystallization in deformed grains depends on the level of particle stimulated nucleation (PSN) in the interface between matrix and reinforcement. The occurrence of PSN is affected by the type of reinforcement and the number of …

Materials Science and Engineering: A

This paper presents an in-situ observation, using neutron imaging, of delayed crack propagation in a high-strength martensitic steel specimen. Delayed cracking is believed to be caused by hydrogen embrittlement occurring due to the slow diffusion and accumulation of hydrogen ahead of a crack front, causing decreased ductility and eventual cracking under constant load. The experiment involved mechanical loading of a single-edge-notch bend specimen while submerged in an electrolyte solution (H 2 O+ 3.5% NaCl) under cathodic polarization to facilitate hydrogen ingress. Intermittent crack propagation was observed for 12 h after the environment had been removed. The stress state at each crack configuration was extracted from a three-dimensional elastic–plastic finite element simulation, which was tailored to match the quantitative information acquired from the neutron radiographs of the fracture process. To …