Solid-solution Strengthening Effect Research Articles

Synergistic effects of Monel 400 filler wire in gas metal arc welding of CoCrFeMnNi high entropy alloy

Weldability plays a crucial role in the journey of high entropy alloys towards their engineering applications. In this study, gas metal arc welding was performed to join an as-rolled CoCrFeMnNi high entropy alloy using Monel 400 as the filler wire. The present research findings demonstrate a favorable metallurgical chemical reaction between the Monel 400 filler and the CoCrFeMnNi high entropy alloy, resulting in compositional mixing within the fusion zone that promotes a solid-solution strengthening effect, counteracting the typical low hardness associated to the fusion zone of these alloys. The weld thermal cycle induced multiple microstructure changes across the joint, including variations in the grain size, existing phases and local texture. The grain size was seen to increase from the base material toward the fusion zone. An FCC matrix and finely sparse Cr-Mn-based oxides existed in both base material and heat affected zone, while in the fusion zone new FCC phases and carbides were formed upon the mixing of the Monel 400 filler. The role of the filler material on the fusion zone microstructure evolution was rationalized using thermodynamic calculations. Texture shifted from a γ-fiber (in the base material) to a strong cubic texture in the fusion zone. Digital image correlation during tensile testing to fracture coupled with microhardness mapping revealed that, stemming from the process-induced microstructure changes, the micro and macromechanical response differed significantly from the original base material. This study successfully established a correlation between the impact of the process on the developed microstructural features and the resultant mechanical behavior, effectively assessing the processing-microstructure-properties relationships towards an improved understanding of the physical metallurgy associated to these advanced engineering alloys. In conclusion, this work provides an important theoretical framework and practical guidance for optimizing the engineering applications of high entropy alloys.

Grain growth kinetics, phase evolution during annealing and strain rate sensitivity of TRIP-assisted, dual-phase, non-equiatomic high entropy alloy

Transformation-induced plasticity-assisted dual-phase high-entropy alloys (TRIP-DP-HEAs) belong to a recently developed class of HEAs. TRIP-DP-HEAs have been reported to exhibit superior strength-ductility combination at room temperature as well as at high temperatures. Small amounts of carbon additions to TRIP-DP-HEAs are known to further improve the strength as a result of interstitial solid solution and nanoprecipitate strengthening effects. Current investigation compares the grain growth kinetics in a metastable, dual-phase (FCC and HCP), Fe49.5Mn30Co10Cr10C0.5, carbon-containing high entropy alloy (C-DP-HEA) with that in the corresponding carbon-free variant, Fe50Mn30Co10Cr10 HEA (DP-HEA). The alloys after being subjected to cold rolling, were annealed at 900 °C, 1000 °C and 1100 °C for 3, 30, 60 and 120 min, followed by water quenching. Slower grain growth kinetics was observed in C-DP-HEA due to Zener pinning by carbide particles. The activation energy for grain growth in C-DP-HEA was determined to be 339.71 kJ/mol, which is larger than that of DP-HEA (282.68 kJ/mol). The microstructures of the C-DP-HEA samples, after annealing at 900 °C for different durations of times and quenching, were investigated. The HCP phase fraction in the microstructure initially decreased with increase in annealing time/grain size and later increased with further increase in annealing time/grain size. This is explained based on the counteracting effect of grain boundary density and back stresses acting in samples having increased grain size. Strain rate sensitivity (SRS) parameter, ‘m’, was evaluated for both C-DP-HEA and DP-HEA. The strain rate jump tests were conducted at two quasi-static strain rates, 1 × 10−3 s−1 and 5 × 10−3 s−1, and at room temperature as well as at higher temperatures, 900 °C, 1000 °C and 1100 °C. The ‘m’ value was found to depend on the grain size, test temperature, and the presence of carbon in the alloy.

Effect of Alloying Elements on the High-Temperature Yielding Behavior of Multicomponent γ'-L12 Alloys.

The exceptional mechanical properties of Ni-based high entropy alloys are due to the presence of ordered L12 (γ') precipitates embedded within a disordered matrix phase. While the strengthening contribution of the γ' phase is generally accepted, there is no consensus on the precise contribution of the individual strengthening mechanisms to the overall strength. In addition, changes in alloy composition influence several different mechanisms, making the assessment of alloying conditions complex. Multicomponent L12-ordered single-phase alloys were systematically developed with the aid of CALPHAD thermodynamic calculations. The alloying elements Co, Cr, Ti, and Nb were chosen to complexify the Ni3Al structure. The existence of the γ' single phase was validated by microstructure characterization and phase identification. A high-temperature compression test from 500 °C to 1000 °C revealed a positive temperature dependence of strength before reaching the peak strength in the studied alloys NiCoCrAl, NiCoCrAlTi, and NiCoCrAlNb. Ti and Nb alloying addition significantly enhanced the high-temperature yield strengths before the peak temperature. The yield strength was modeled by summing the individual effects of solid solution strengthening, grain boundary strengthening, order strengthening, and cross-slip-induced strengthening. Cross-slip-induced strengthening was shown to be the key contributor to the high-temperature strength enhancement.

Influence of bismuth addition on the physical and mechanical properties of low silver/lead-free Sn-Ag-Cu solder

The Sn–Ag–Cu (SAC) solders with low Ag content have been identified as promising candidates to replace the traditional Sn–Pb solder for flip-chip interconnects. This study examines the impact of incorporating Bi element on the microstructure, thermal behavior, and mechanical performance of low-silver-content Sn-1.5Ag-0.7Cu (SAC157) solder alloy. Besides using the conventional cross-sectioned microstructure image, X-ray diffraction (XRD), differential scanning calorimetry (DSC) and tensile stress- strain techniques were used to investigate the microstructure, thermal and mechanical properties after the addition of Bi, respectively. The results demonstrate that adding of Bi could refine the microstructure, optimize the thermal properties, and improve the tensile strength. Meanwhile, the ductility of the solder alloys reduced evidently in comparison to the Sn-1.5Ag-0.7Cu solder. From the microstructural analysis, 0.5 wt % Bi addition to SAC157 significantly enhanced the solid solution effect of Bi and refined β-Sn dendrite, as well as extended the eutectic area. Moreover, as the Bi addition increases to 5 wt %, finely dispersed bismuth precipitates within the β-Sn matrix, along with an enlarged eutectic area, lead to a remarkable enhancement in both ultimate tensile strength and yield strength. The electrical resistivity was characterized by the four-point probe technique. The results show that the electrical resistivity of Bi-modified SAC157 solder alloy decrease from 13.9 to 9.8 μΩ cm with the addition of 5 wt % Bi. These improvements can be attributed to the solid-solution and precipitation strengthening effects induced by the presence of bismuth. The results confirmed that the developed material is applicable as a potential high strength solder material in the context of advanced interconnecting applications.

Developing high strength and ductility in cobalt alloy via chromium carbonitride addition

In this study, we present a strategy for the development of cobalt alloy with high performance, by introducing a nitrogen-containing solid solution powder Cr2(C,N). Despite the cobalt accelerates the nitrogen removal from Cr2(C,N) during sintering, interestingly, nitrogen seemingly plays a pivotal role in regulating the microstructure of cobalt alloy. Detailed microstructural analyses indicate that the fcc-Co increase, CrN precipitates and finer grain size are formed within the cobalt matrix with Cr2(C,N) addition. These structural modifications significantly contribute to the strength and toughness. In comparison to the without N-doped cobalt alloy, the compressive strength undergoes a significant 34% increase, rising from 1150 MPa to 1540 MPa. Similarly, the bending strength exhibits an upward trend, ascending from 1605 MPa to 1766 MPa. Concurrently, the introduction of Cr2(C,N) results in an almost 80% enhancement in bending strain compared to the without N-doped one. Additionally, a notable 28% increase in hardness is obtained. The substantial enhancements in strength and toughness are mainly attributed to the combined effects of solid solution and precipitation strengthening. Our findings confirm the capability of Cr2(C,N) to the cobalt alloy reinforcement, providing valuable insights for integrating Cr2(C,N) to enhance the cobalt alloy, and laying a foundation for future investigations into the forms of nitrogen and the strengthening and toughening mechanisms of nitrogen-containing alloy. The insights gained in this study also provide novel strategies for the design of materials characterized by both needed strength and ductility, thereby advancing the development of ultra-strong and ductile materials with superior toughness.

Design and characterization of (TiZr)95-xHfxMo5 multi-principal element alloys with excellent properties for biomedical applications

Developing new bio-metallic materials with improved performance has attracted intensive research focus over the last decades. In the present work, a new series of (TiZr)95-xHfxMo5 (x = 0, 10, 15, 20, 25, 31.67) multi-principal elements alloys (MPEAs) have been designed for potential implant materials. The mechanical properties, deformation characteristics, tribological properties, corrosion resistance, and in vitro biocompatibility of the MPEAs were characterized. All the TiZrHfMo alloys possess a high yield strength (913–––1083 MPa) and tensile strength (931–––1118 MPa) and a large microhardness (296–––333 Hv). The addition of Hf into the alloys induced severe lattice distortion, which increased the solid-solution strengthening effect. It also resulted in a finer grain size and led to excellent wear resistance. Meanwhile, the results showed that the dislocation glide mode transformed from planar slip to cross-slip and the transformation became apparent with the decrease of Hf. Also, the MPEAs showed a good corrosion resistance compared to CP-Ti, which was credited to the superior passivation films. The in vitro biocompatibility experiments displayed that the TiZrHfMo alloys exhibited high cell viability ratios, which were close to that of CP-Ti. The present work demonstrates the huge potential of TiZrHfMo MPEAs as implant material for biomedical applications.

The effect of Hafnium on the microstructure and tensile property in a Ni-based superalloy

The effects of Hafnium on the microstructure and tensile property of a Ni-based superalloy after solution heat treatment and long-term thermal exposure were investigated with field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), X-ray diffractometer (XRD). The results revealed reveal that Hf intensified intensifies the element segregation and promoted promotes the precipitation of MC carbide and honeycomb-like Ni5Hf phase in the as-cast alloy. The solid solution strengthening and second phase (MC) strengthening effects are both enhanced in the alloy doping 0.5 wt% Hf after solution heat treatment. Therefore, the tensile yield strength at 700 °C of the alloy with 0.5 wt% Hf is higher than that in the Hf-free alloy. Otherwise, a large amount of the low melting point Ni5Hf phases appear in the alloy with 0.8 wt% Hf. Ni5Hf phase is prone to become the crack initiation, which decreases diminishes the yield strength in the alloy with 0.8 wt% Hf. The addition of 0.5 wt% Hf can inhibit the formation of needle-like δ phase at grain boundary due to the decrease of grain boundary energy and diffusion rate at grain boundary. Therefore, the 700 °C tensile strength and ductility increase simultaneously in the alloy with 0.5 wt% Hf after thermal exposure at 700 °C.

Synergistic strengthening and toughening of eutectic CxCoCr3Fe5Ni high entropy alloy

CxCoCr3Fe5Ni (x=0, 0.1, 0.2 and 0.3, at.%) high entropy alloys (HEAs) were prepared via vacuum induction melting. The effects of carbon content on the microstructures and mechanical properties of the HEAs were intensively investigated. With the increase of the carbon content, the phase structure transforms from a dual-phase (FCC+BCC) to a eutectic mixture (FCC phase + M23C6 carbide). Compared to CoCr3Fe5Ni base alloy, the C0.2CoCr3Fe5Ni eutectic HEA exhibits a significantly improved yield strength (from 307.5 to 378.9 MPa), ultimate tensile strength (from 646.5 to 837.1 MPa), and ductility (from 55.4% to 56.1%). It is shown that these comprehensive enhancements of strength and ductility result from the effect of interstitial solid solution strengthening by carbon alloying and second phase strengthening via the eutectic structure.

The bifunctional low mismatch nano strengthening phase leads to a high strength-ductility W-Ta-Ni-Fe-Cu alloy

As a typical tungsten-based composite consisting of tungsten (W) particles and matrix phase, tungsten heavy alloys (WHAs) are extensively utilized in the military due to their exceptional strength and high density. However, the large grain size (>30 μm) of powder metallurgy liquid phase sintered (LPS) WHAs and the low strength of the matrix phase limit the further improvement of the alloy. In this work, high-density ultrafine WHAs were fabricated by two-step low-temperature sintering, and the density of the alloy reached 17 g/cm3 with an average W particle size of 7.81 μm. Additionally, the eutectic reaction between Ni and Ta was controlled to generate dispersed nano-Ni3Ta phases in situ in the matrix phase, further improving the strength of the alloy. Under the synergistic strengthening effect of fine-grain strengthening, dispersion strengthening, and solid solution strengthening, the average ultimate tensile strength of the alloy reached 1190.39 MPa. At the same time, the alloy maintained good elongation with a total elongation of 20.8% due to the good co-grid interface orientation between the Ni3Ta phase and the matrix phase. This study provides a new idea for developing high-strength WHAs and has a guiding significance for developing Ni-based alloys.

The microstructure and properties of Mo0.5NbTiZrTax high entropy alloys enhanced by Ta addition

In this study, the Mo0.5NbTiZrTax (x = 0.3, 0.5, 0.7) HEAs obtained by arc melting were controlled by the change of Ta content. The microstructure, the wear properties, and the corrosion resistance of the alloys were studied systematically. The results revealed that the alloys have the BCC (major) phase + BCC (minor) phase structure. At the same time, the increase in Ta content promotes the refinement of grains and the formation of sub-grains with gradually random orientation at grain boundaries but suppresses the randomization of crystal orientation. This also enriched the defect structure inside the alloys, further induced the formation of Zr-rich second phase particles, high-density stacking fault structures, and disordered Zr-rich BCC phases. The increase in Ta content significantly improved the wear properties of the alloys, which is mainly ascribed to the presence of the tough BCC phase and the combined effects of solid solution strengthening, second phase strengthening, fine grain strengthening, lattice distortion effect, and stacking fault strengthening. The electrochemical measurements confirm that the overall corrosion resistance of the alloys shows a trend of first increasing and then decreasing with the increase of Ta content due to the formation of micro batteries between the second phase rich in Zr as the anode and dendrites.

Effect of WC content on microstructure and mechanical properties of (TiZrHfNbTaMo)C‐15 wt.% Co ceramics

AbstractThe (TiZrHfNbTaMo)C‐15 wt.% Co ceramics with excellent comprehensive properties were successfully prepared by vacuum liquid phase sintering. The effects of WC content on the grain size, microstructure, and mechanical properties were investigated. The results showed that WC was dissolved into (TiZrHfNbTaMo)C phase to form a seven‐component solid solution, and the independent WC phase disappeared. The addition of WC improved the wettability between the ceramic phase and the metal phase and promoted the densification of the ceramics. In addition, WC played a role in refining grains and inhibiting the grains growth to a certain extent. The comprehensive properties of ceramics were improved by solid solution strengthening and high entropy effect. When the WC content was 5 wt.%, the toughness reached the maximum of 9.41 ± 0.15 MPa·m1/2, and the hardness of the ceramic with 10 wt.% WC achieved the highest value of 18.18 ± 0.20 GPa.

Structural and property regulation of double ceramic phase–reinforced AlCoCrFeNiTiZr–based high entropy alloy coatings by pulsed–wave lasers

In-situ synthesis ZrC and TiC reinforced AlCoCrFeNiTiZr–based high entropy alloy (HEA) coatings were successfully synthesized on R60702 using pulsed–laser cladding. The effects of pulse frequency (5, 50, 500, and 5000 Hz) on microstructure evolution, microhardness, wear resistance, and corrosion resistance were investigated. The results demonstrate that the HEA coatings consists of phases including BCC, HCP, and metal carbides (MC). The phase composition and proportion are influenced by changes in pulse frequency. At pulse frequencies of 5 and 50 Hz, the predominant MC phase is ZrC. As the pulse frequency increases, it transitions to a coexistence of ZrC + TiC before ultimately becoming predominantly TiC. Concurrently, the size of the ceramic phase and the proportion of the HCP phase initially decrease, then increase. A pulse frequency of 500 Hz yields optimizations in microhardness, wear resistance, and corrosion resistance. The favorable mechanical properties are attributed to the synergistic effect of solid solution strengthening, fine crystal strengthening, and ceramic phase strengthening. The optimal corrosion resistance is due to the formation of a stable passivation film while local corrosion and galvanic corrosion are weakened.

Achieving high mechanical and corrosion resistance synergy properties of the Mg-11Li-6Al alloy through simple solutionizing treatments

This study aims to investigate the impact of solutionizing treatments on the mechanical and corrosion resistance properties of the Mg-10.93Li-5.45Al-0.08Er (LA116) alloy. The as-cast LA116 alloy is primarily composed of a single β phase along with AlLi and MgLiAl2 phases. Results demonstrate that the mechanical and corrosion resistance properties of the alloy experience considerable improvement after solutionizing treatments due to the synergistic effect of phase compositions and solid solution strengthening. Specifically, at 400 °C, the mechanical properties of the alloy witness a significant improvement due to the coordination of solid solution strengthening and the dissolution of the second phase. In contrast, the best corrosion resistance is observed at 250 °C due to the decomposition and uniform distribution of the AlLi phase.

Effect of the addition of titanium filler on high temperature strength and microstructural characteristics of laser welded tube-end plug socket joints of molybdenum alloy

Three types of Mo alloy socket joints were prepared in this study: a joint without alloying (LW joint), a joint with a trace amount of titanium (Ti) added to the fusion zone (FZ) (LW-Ti-A joint), and a joint with Ti separately added to the FZ and the heat affected zone (HAZ) (LW-Ti-B joint). Tensile tests were carried out on the three types of joints at 360, 900, and 1200 °C. The results showed that the tensile strengths of the base metal (BM) of the Mo tubes were 368.7, 239.9, and 189.6 MPa at 360, 900, and 1200 °C, respectively. At all temperatures, the tensile strengths of the welded joints increased in the order of LW, LW-Ti-A, and LW-Ti-B, which indicates that adding Ti to the FZ and HAZ separately had an obvious strengthening effect. The fracture positions of the joints were primarily affected by the Ti alloying scheme. The LW joints are always fractured at the FZ, showing brittle intergranular fractures; the LW-Ti-A joints fractured at the BM or the HAZ near the FZ; and the LW-Ti-B joints fractured at the BM far from the FZ, exhibiting ductile fracture. Adding Ti to the FZ can induced a solid-solution strengthening effect, which refined the grain size in the FZ by approximately 30–40% and reduced the amount of Mo oxide on the grain boundaries in the FZ, thus improving the joint strength. Presetting a Ti foil on the overlapping interface in the HAZ realized metallurgical bonding between the Mo tube and Mo end plug in the HAZ of the laser-welded joints, enlarge the bearing area, and improve the joint strength. And a new metallurgical bond zone is formed on the overlapping interface in the HAZ during the high-temperature tensile tests of the welded joints, which further improve the joint strength.

Effect of Zr on the morphology, microstructure and mechanical properties of NbTa0.5TiZrX refractory high entropy alloy fabricated by selective laser melting

In this paper, the NbTa0.5TiZrX series refractory high entropy alloys(RHEAs) were processed by selective laser melting (SLM). NbTa0.5TiZrX alloy are observed with BCC crystal structures.The effect of Zr content on microstructure and properties of NbTa0.5TiZrX alloys was studied, as the Zr content increases, the main defects of NbTa0.5TiZrX alloy changed from lack of fusion defects to solidification cracks. Due to the different melting points of alloying elements, the elements with high melting point are enriched in the dendrite and the elements with low melting point are enriched in the inter-dendrite. As the Zr content increases, the number of cellular subgrain increases, and the number of columnar subgrain decreases. The fine equiaxed grain at the boundary of the molten pool and the coarse grain in the molten pool make the grain of the NbTa0.5TiZrX alloy with bimodal size distribution. The compressive yield strength increases with the increase of Zr content. Due to the effects of solid solution strengthening, precipitation strengthening and fine crystal strengthening, the alloy has the highest yield strength of 1320 MPa. When Zr content reaches 10 wt%, and the Compressive strain of NbTa0.5TiZrX alloy exceeds 75% at room temperature.

Mechanism of the synergistic effect of solid solution strengthening and fine grain strengthening in an as-cast Cu–9Ni–6Sn alloy induced by Mn

The effects of Mn content on the Sn distributions, grain sizes, second phases, and mechanical properties of Cu–9Ni–6Sn-XMn alloys (wt.%, X = 0, 0.1, 0.5, and 1.0) were studied in this paper. The mechanisms of acting and strengthening through which Mn could promote grain refinement in the alloy were discussed. The results showed that the addition of Mn transforms the as-cast microstructure of the alloy into equiaxed grains, and the grains are obviously refined. When the amount of Mn is approximately 0.1 wt%, the average grain size of this alloy is 91.75 μm, and the grain refinement effect is greatest in the experimental range. In addition, Mn increases the uniformity of the distribution of Sn in the as-cast microstructure. Differential scanning calorimetry (DSC) analysis revealed that the addition of Mn increases the undercooling of the as-cast Cu–9Ni–6Sn alloy and decreases in the critical nucleation radii of the grains. Further microstructure observation showed that Mn is dissolved mainly in the γ-(Cu,Ni)3Sn phase. Consequently, the interfacial relationship between the γ-(Cu,Ni)3Sn phase and the matrix transforms from incoherent to semicoherent. Compared with those of the Cu–9Ni–6Sn alloy, the strength and elongation of the alloy with added Mn are relatively great. When the content of Mn is 0.1 wt%, the strength of the alloy increases from 359.75 MPa to 423.54 MPa, while the elongation remains at 19.14 %. The synergistic effect of solution strengthening and fine grain strengthening of Mn is the main reason for the great improvement in the mechanical properties of the alloy.

Microstructure evolution and ductility improvement mechanism of Fe-containing recycled brass alloy after Mn addition

Excessive Fe precipitates and accumulates during the reusing process of scrap brass, which affects the service performance of recycled brass. Therefore, eliminating the agglomeration of the rich-iron phase in scrap brass is significant research in the preparation of high-performance recycled brass. In this study, 0.4 wt%--0.8 wt%Mn was added in recycled brass containing 0.8 wt% Fe to eliminate the influence of Fe-rich precipitation on the as-cast and extruded brass. The results show that the introduction of Mn inhibits the precipitation of clover-like precipitates in the matrix and reduces the volume fraction of Fe-rich precipitates in as-cast brass. At the same time, the presence of Mn promotes the solid solubility of Fe in the brass matrix, and the solid solubility of Fe and Mn in the α and β phases is significantly different. For extruded brass, its ductility is significantly improved with the introduction of Mn and the strengthening process comes from the synergistic effect of solid solution strengthening and fine crystal strengthening. This study provides insight into the preparation of high-performance regenerated brass alloy with good ductility by eliminating the agglomeration of the rich iron phase in scrap brass.

Evolution of recrystallization texture in medium to low stacking fault energy alloys: Experiments and simulations

The present work aims to investigate the evolution of static recrystallization microstructure and texture in medium to low stacking fault energy (SFE) alloys. In these categories of materials, the process of recrystallization becomes complex because of the presence of extensive deformation heterogeneity. Ni-xCo (40 and 60wt.% Co) alloy has been chosen for this purpose, where Ni-40Co belongs to medium SFE, and Ni-60Co belongs to low SFE regimes. The effect of solid solution strengthening and deformed microstructural features on the mechanism of recrystallization are explored. Both the alloys were subjected to 50% cold-rolling reduction followed by isothermal annealing at 600°C. Recrystallization texture of Ni-40Co shows a non-uniform α-fiber having a peak intensity at the Goss component, whereas Ni-60Co shows uniform α-fiber texture. Both the alloys also show rotated cube (Rt C) and rotated Cu (Rt Cu) components after recrystallization. Apart from that Ni-60Co exhibits brass recrystallization (BR) texture component. The differences in the recrystallization texture in both the Ni-Co alloys are attributed to the role of different heterogeneous deformation features in the microstructure and transition from Cu-type to Bs-type as-deformed texture. The recrystallization microstructure is dominated by the formation of substantial annealing twin (Σ3) boundaries, which also produces many new orientations; thereby weaken the recrystallization texture. These experimental findings and the proposed mechanism were used as input to simulate the recrystallization microstructure and texture in the alloy using the parallelized cellular automata (CA) technique. Parallelized CA model has successfully predicted the evolution of recrystallization texture and microstructure through simulation except parallel annealing twin feature.

The role of Cu addition in the metallurgical features, mechanical properties, and cytocompatibility of cardiovascular stents biodegradable Zn-based alloy

Recently, Zn-based alloys have been considered a promising biodegradable material due to their excellent physiological degradable behavior and acceptable biocompatibility. However, poor mechanical performance limits its application, especially for cardiovascular stents. In this work, novel biodegradable Zn-xCu-0.8Mn-0.4Ag (x = 1, 2, 5 %Wt) alloys were prepared. The effects of Cu addition on microstructure, mechanical properties, and cytotoxicity of alloys were investigated. To modify the microstructure and improve the properties of the alloys, the secondary process of hot extrusion was applied. The results of XRD analysis showed that the above alloys have four phases of α-Zn, CuZn5, MnZn13, and Zn3Ag. After hot extrusion, the secondary phase particles were broken and spread throughout the structure. According to the hardness test, due to the presence of CuZn5 hard secondary phase particles, the hardness increased gradually. The tensile test showed that adding copper and performing a hot extrusion process can significantly improve mechanical properties. The as-extruded alloys exhibited suitable mechanical performances mainly due to the combined effects of solid solution strengthening, and second phase precipitation hardening. In particular, yield strength, ultimate tensile strength, and elongation for Zn-xCu-0.8Mn-0.4Ag (x = 5 wt) alloy reached the value of 255.47, 359.82 MPa, and 35.84 %, respectively, which meets the requirements of cardiovascular stent well. Cytotoxicity test also showed that homogenized and as-extruded alloys have acceptable in vitro cytocompatibility. According to the obtained results, Zn-xCu-0.8Mn-0.4Ag extruded alloys can be considered as potential candidates for cardiovascular stents.

Role of Ti on the microstructure and mechanical properties of MoNbTi medium-entropy alloy

Equiatomic MoNb and MoNbTi alloys are synthesized by arc melting. Ti addition resulted in a significant grain refinement (from 115 μm to 34 μm) of MoNb alloy. Exposure to high temperature for considerably longer duration (24 h at 1673 K) did not alter the beneficial effect of grain refinement imparted by Ti addition. Also, addition of Ti (33 at. %) significantly reduces the overall density without effecting the hardness of MoNbTi alloy, which is one of the key findings of the present study (MoNb - 4.06 ± 0.01 GPa, MoNbTi - 4.10 ± 0.01 GPa). MoNbTi also showed an exceptionally high "density-normalized" hardness when compared to various high-entropy alloys of similar family. Finally, from a simple analysis it is found that extraordinarily high "density-normalized" hardness can be obtained in just two/three element equiatomic systems, suggesting that developing new concentrated alloy systems with more than 3 elements in equiatomic proportion may not be offering any benefits with respect to hardness (strength) in single phase material systems where the beneficial effect of solid solution strengthening is exhausted.